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HAP FAQ Categories

Installation, Networks and Miscellaneous Program Information
Project Management and Data Entry Tips
gbXML File Transfer
Calculation Methodology
Weather Data
Space and Zone Data
System Modeling
Ventilation Modeling
Chiller, Boilers, Towers and Plant Modeling
Report Interpretation
Energy Modeling

HAP Frequently Asked Questions
Installation, Networks and Miscellaneous Program Information
How much hard disk space does HAP Require?
How can defaults be customized?
Understanding Network Installations
How to Install on a Network without Using the CD
How can I update the Company Name in the software?
Project Management and Data Entry Tips
How do I delete zones from an air system?
Removing Unwanted Project Names from Project List
gbXML File Transfer
What gbXML data will HAP import?
What gbXML tools will HAP be compatible with?
Will HAP export gbXML data?
How do I import the data?
Calculation Methodology
HAP v4.3 vs. V4.20a Calculation Differences
Are the example problem results reliable?
Maximum Quantity Limits for HAP Projects
What is my altitude-adjusted 1.08 or 1.207 factor?
Can HAP calculate lifecycle costs?
Weather Data
How to Install Simulation Weather Data
Space and Zone Data
How do I model more than 1 door per exposure?
Tips for Efficiently Entering Zone Data
Why aren't more day types offered in schedules?
System Modeling
How to Model Closed Loop WSHP Systems
How to Model GSHP Systems
What does the 'Zone T-Stat Check' mean?
Modeling Convective Heating Systems
How can I obtain design water flow data for heating coils?
Pitfalls Interpreting Peak Humidifier Load Data
The heat reclaim device has no effect on my 2-deck Multizone system
What impact does a heat reclaim unit have on terminal unit sizing?
Modeling a unit ventilator (UV) system
How to calculate loads for a decoupled air system
Why does HAP not give me 60% RH when I add a humidifier and specify 60% RH?
How to Specify RTU Performance
How to Specify Unitary Equipment Performance
Ventilation Modeling
Why do I get more ventilation airflow than I asked for?
Why do I get less ventilation airflow than I asked for in a VAV system?
Why do I get less ventilation airflow than I asked for in a CAV system?
How is the ventilation load calculated?
Why did HAP change my ASHRAE 62.1-2004 ventilation rates back to "User-defined" space usage category?
What happened to the public restroom category with ASHRAE Standard 62.1-2004?
Why is the ventilation airflow the same for both ventilation control options, constant and DCV?
Why does HAP not maintain the CO2 differential specified when using the DCV setting?
Chiller, Boilers, Towers and Plant Modeling
Does plant sizing consider diversity among systems?
Report Interpretation
What is the difference between the Zone and Terminal Unit capacities on the Zone Sizing Summary report?
Interpreting Information on File Integrity Reports
What causes my mixed air temperature to be extremely hot?
Why is the off coil temperature greater than the supply temperature for SZCAV?
Energy Modeling
Why doesn't adding an ERV in energy analysis reduce the energy use?
How do high infiltration rates impact energy simulations?
How much hard disk space is required to install HAP?
FAQ: How much hard disk space is required to install HAP?

Answer: Up to 300 MB is required to install HAP and its supporting components. However, the disk space required depends on software components, particularly Microsoft Windows components, already installed on the computer. In most cases many of the required components already exist on the computer. As a result only 80 to 90 megabytes of disk space is typically required when installing HAP.

Finally, each project that is created will also use hard disk space. This space depends on the amount of data entered and calculated. Very small projects require 200-500 kB of disk space. Many projects of moderate size usually require 1 to 10 MB of disk space. Extremely large projects can require 50 MB or more of hard disk space.
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How can I customize the default data in HAP?
FAQ: How can I customize the default data in HAP?

Answer: Currently there is not a direct way to change the standard default data in HAP for things such as weather, walls, roofs, doors, windows, etc. However, one useful approach is to create a "template" project which contains the standard weather data, schedules, and wall, roof, window and door constructions that you use on most of your projects. Here's how to create a template project:
  • A. How to Create and Save the Template
    • Use the Project/New option to create a new project.
    • Enter the standard data you wish to use as the basis for all subsequent projects you create. This might include weather and schedule data, and common wall, roof, window or door constructions.
    • Use the Project/Save option to save the project. When asked for the project name specify "Template" or something similar so you will be able to easily identify this project in the future.
  • B. How to Use the Template
    • When starting a new project, use the Project/New option
    • Then choose the "Import HAP Project Data" option on the Project Menu.
    • When asked to choose a project from which to import data, choose your Template project.
    • Then choose the items in the Template you want to import into your new project.
    • Once finished, begin entering new data into your project.
Note: A Template project is not required to import data. You can import data from any existing HAP project.
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Are the Example Problem Results Reliable?
FAQ: I am learning the program by doing the example problem in the HAP Quick Reference Guide. The results I got don't match those in the manual. Before I check my inputs I need to know whether the example problem results in the manual are reliable.

Answer: Sometimes the example problem results shown in the HAP Quick Reference Guide change after the manual is printed due to modifications to the program. However, current results are always provided on the program CD. Open the Example_Problem_Reports.PDF file found in the \Example folder on the CD.
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Maximum Quantity Limits for HAP Projects
FAQ: What are the maximum quantity limits for data such as spaces, systems and plants in a HAP project?

Answer: Data limits for all data entities offered in HAP are listed below. These limits apply to a single project.
Data EntityLimit per Project
Spaces32000
Systems5500
Plants100
Buildings100
SchedulesUnlimited
WallsUnlimited
RoofsUnlimited
WindowsUnlimited
DoorsUnlimited
External Shading GeometriesUnlimited
ChillersUnlimited
Cooling TowersUnlimited
BoilersUnlimited
Electric RatesUnlimited
Fuel RatesUnlimited
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Interpreting Information on File Integrity Reports
FAQ: What does the information shown on the File Integrity Verification Report mean? How does a person read and interpret this information?

Answer: The File Integrity Verification Report for HAP provides information about all software components involved in the operation of the program. It is used to determine whether there are problems with any components (such as a damaged or missing file) that could cause operational problems in the program.

The report consists of a table in which each row contains data for a different software component and each column contains a different category of information about the component. Working from left to right, the columns are:
  1. File # – This numbers the line items in the report.
  2. Name – The name of the software component.
  3. Status – If listed as "OK" it means the cyclic redundancy check (CRC) value for the software component is exactly the same as the copy of the file shipped with HAP – i.e. it is a valid copy of the component and is not corrupt.

    If the value listed is a series of letters and numbers (example: D1B3B135) this means the copy of the file on the computer is different from the one shipped with HAP. The value listed is the CRC value for the copy of the file found on the computer. A difference does not necessarily indicate a problem. So long as the "Version Found" is later than the "Version Shipped", the difference is legitimate and does not indicate a problem.

    If a message such as "Could not locate file" appears in this column, it indicates a problem with the file and almost certainly will result in program operating problems.
  4. Path – Lists the location where the active copy of this file is found. At the end of the path/file one or more symbols will be found. These symbols are described in the table below.
  5. Version Found – The version of the software component found on the computer. If it is later than the "Version Shipped" this is OK. If it is earlier than the "Version Shipped" this will cause operating problems in the program.
  6. Version Shipped – The version of the software component shipped with HAP. Provided so it can be compared with the "Version Found".
  7. Original Size – The file size for the software component shipped with HAP.
  8. Current Size – The file size for the software component found on the computer. Sometimes comparing original and current file sizes will indicate a problem. For example, if the "Version Shipped" and "Version Found" items are the same, but the file sizes are different this sometimes indicates a corrupted copy of the file.
NotationDescription
®The file requires registration and is properly registered.
!rThe file requires registration but is not properly registered. The registry entry is partial or is corrupt (but the CLSID was found).
!r!The file requires registration but is not properly registered. The file was not found at the location specified in the registry or anywhere on the path.
©The file does not require registration. The CRC file we use to check file status does not provide any registration information for this item, but it was found and properly loaded. This is expected for non-COM objects and certain COM objects also.
1.0 (or other number)An earlier version of the file is registered but not the version specified in the CRC file we use to check file status. Usually this indicates a problem. The number shown is the version number found.
registry subkey not foundThe file is partially registered or the Windows registry is corrupt.
Not registered properlyCould be similar to the "1.0" item above but in addition the file failed to load or could not be found.
Not foundThe file could not be located.
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Can HAP Calculate Lifecycle Costs?
FAQ: I am running energy simulations as the starting point for a lifecycle cost study of HVAC design alternatives. I know HAP can be used for the energy simulations, but can it also be used to calculate lifecycle costs?

Answer: Currently HAP does not include lifecycle cost calculation features. These features are found in Engineering Economic Analysis which is a separate E20-II program. Engineering Economic Analysis provides features for private sector analysis where decisions are typically based on net present worth, internal rate of return or payback, and for public sector analysis where decisions are typically based on the savings-to-investment ratio. Both analyses consider investment costs for purchase and installation of equipment, and annual energy and maintenance costs. The private sector analysis also can consider tax and depreciation issues.

Data can be electronically transferred from HAP to Engineering Economics. This is done using the "Import HAP Data" option in Engineering Economics. Please refer to the Engineering Economics on-line help system for information on how this option works. Note that you need HAP v4.2 or later and Engineering Economics v3.0 or later to make the import feature work.
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How to Install Simulation Weather Data
FAQ: When I try to run an energy simulation with HAP it tells me it cannot because I do not have simulation weather data in my project. What is simulation weather data and how do I get it?

Answer: "Simulation" weather data contains actual hour-by-hour measurements of temperature, humidity and solar radiation for your building site. It forms the basis for energy simulations since both building loads and equipment performance are affected by the hour-by-hour and day-by-day change in weather conditions. Simulation weather data is different from "design" weather data. The latter contains one 24-hour profile for each month representing warmer and sunnier than normal weather data used for sizing cooling equipment and one winter design hour for sizing heating equipment.

Both design and simulation weather data are specified by editing your project weather data. Design data is created by choosing a city from the program's design weather database, or by directly entering the design parameters. Both tasks can be performed using options on the General tab of the Weather form. Simulation weather data is added to the project by choosing a file from Carrier's simulation weather library. This is done by pressing the "Select City" button found on the Simulation tab of the Weather form.

The complete simulation weather library is automatically installed with HAP (versions 4.5 and later). If for some reason files are deleted after installation, they can be restored by either reinstalling HAP, or by copying files from the \Weather folder on the program CD-ROM to the \E20-II\Weather folder on your computer.
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How do I model more than 1 door per exposure?
FAQ: I have a space with more than one type of door on a single exposure. Since HAP permits one door type per wall exposure, how can I model more than one door type for each exposure?

Answer: The following procedure can be used:
  1. On the Walls, Windows, Doors tab of the Space input form, define your wall exposure, specifying the quantity for your first door type.
  2. Then add a second wall exposure item with the same orientation. Specify a gross wall area which is equal to the total area for the second door type. Then specify the quantity of door type #2 and specify the appropriate door construction. Therefore, this wall exposure is 100% door since gross wall area equals door area.
  3. Make sure to reduce the gross area for the first wall exposure by an amount equal to the total area of door type #2.
  4. If further door types exist, repeat steps 2 and 3 to define these.
Example: The south exposure of a space has a gross wall area of 800 sqft. On this exposure are two entry doors accounting for 64 sqft of area, and two fire doors accounting for a total of 84 sqft. The entry and fire doors are defined as two different door constructions. This data could be entered in the Walls, Windows, Doors tab of the Space input form as follows:
Exp.Gross Area
(sqft)
Window 1
Qty
Window 2
Qty
Door QuantityDoor Construction
S716002Door Type 1
S84002Door Type 2
where:

"Door Type 1" is the entry door, with 32 sqft each.

"Door Type 2" is the fire door with 42 sqft each.
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Modeling Convective Heating Systems
FAQ: How do I model a baseboard heating system in HAP? This system only includes baseboard heaters, and does not include cooling apparatus or fans.

Answer: To model a baseboard heating system in HAP, we recommend using the following air system inputs:
  • Air System Type = CAV - Single Zone
  • Central Cooling = Not Used.
  • Central Heating = Not Used.
  • Supply Fan Static = 0.00 in wg.
  • Thermostats: Unoccupied Cooling = Not Available.
  • Thermostats: Create a Fan/Thermostat schedule which designates the desired occupied and unoccupied periods for thermostat operation.
  • Zone Heating Units: Choose "Baseboard, Room T-stat Control" zone heating unit for the zone.
With these inputs the program will model a system in which a central fan exists, but this component has no thermal impact on the zone. The zone thermostat will respond to calls for heating and will run the baseboard heating unit to meet zone heating demands.
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Tips for Efficiently Entering Zone Data
FAQ: I have a system in which most, but not all, of the zones have the same data for supply terminals and thermostats. Do I have to say "zones not the same" and then enter data for every zone? Or is there a faster way to set most of the zones the same and then enter only the data for zones that differ?

Answer: There is a simple shortcut approach to make entering zone data in this situation fast and efficient. The shortcut is illustrated with the following example:

Example: A system serves 25 zones. Of these zones, 22 use parallel fan powered mixing boxes having the same sizing criteria while three use simple VAV boxes. To efficiently enter supply terminal data in this situation, use the following steps:
  • In the Supply Terminal data view on the Zone Components tab, mark the "All Zones are the Same" check box. Then enter the common data for the parallel fan powered mixing boxes. This includes terminal type, minimum airflow rate, fan performance and heating supply temperature. As you enter this data, HAP is actually making 25 copies of the data, one copy for each zone in the system.
  • Next, unmark the "All Zones are the Same" check box. This enables zone-by-zone editing of data. But what you are starting with is 25 copies of the same parallel fan powered mixing box data, so you are all set for the 22 zones whose data is identical. All you need to do is locate the three zones having different data and specify the supply terminal data for these zones.
This shortcut approach can also be used when entering thermostat data and zone heating unit data.
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What is My Altitude-Adjusted 1.08 or 1.207 Factor?
FAQ: HAP corrects the density of air for site elevation. When trying to hand check certain program results it would be useful to know the density x heat capacity x correction factor value. Where can I find these correction values?

Answer: The correction factor for the site altitude for your building can be found on the tabular version of the System Psychrometrics report. The factor appears as a footnote beneath Table 1 of the report.

HVAC engineers are well familiar with the density x heat capacity x correction factor for sea level of 1.08 in English units and 1.207 in SI Metric units. Because HAP corrects air density for site elevation, factors other than 1.08 and 1.207 are used in program calculations (unless you are at sea level). The altitude correction equations and factors for common elevations appear below.

English Factor = 1.08 (1 - 6.87535x10^-6 A)^5.2561

Metric Factor = 1.207 (1 - 2.25569x10^-5 A)^5.2561

where:

^ = Exponentiation symbol. 10^-6 is ten raised to the -6 power.
A = site elevation in feet or meters.
English Factor = (BTU/hr-°F)(min/cuft)
Metric Factor = (W/K)(s/L)

The following table lists density x heat capacity x correction factor values for a range of site elevations.
Elevation
(ft)
English Factor
(BTU/hr °F)(min/cuft)
Elevation
(m)
Metric Factor
(W/K)(s/L)
01.08001.207
1001.076251.203
2001.072501.200
3001.068751.196
4001.0641001.193
5001.0611251.189
6001.0571501.186
7001.0531751.182
8001.0492001.179
9001.0452251.175
10001.0422501.172
11001.0382751.168
12001.0343001.165
13001.0303501.158
14001.0264001.151
15001.0234501.144
16001.0195001.137
17001.0155501.130
18001.0126001.124
19001.0086501.117
20001.0047001.110
30000.9688001.097
40000.9339001.084
50000.89910001.071
60000.86512001.045
70000.83314001.020
80000.80216000.995
90000.77218000.971
100000.74320000.947
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How can I obtain design water flow data for heating coils?
FAQ: I am designing an air system that contains hot water heating coils. When I generate the system design reports I don't see a value listed for hot water gpm. Instead there is a dash for this item. How can I obtain design water flow data for heating coils?

Answer: First make sure you have identified the heating source for the heating coils as "hot water". Next, specify the hot water delta-T on the Sizing tab of the Air System input form. Then generate reports. For central and preheat coils you will find hot water gpm (or L/s) data on the Air System Sizing Summary. For terminal reheat or perimeter baseboard coils you will find hot water gpm (or L/s) data on the Zone Sizing Summary.
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Why do I get more ventilation airflow than I asked for?
FAQ: I am designing an air system where the sum of outdoor airflows specified in the space inputs should be 3500 CFM. When I generate the Air System Design Load Summary I see the ventilation airflow for the design cooling hour listed as 9000 CFM. Why do I get more ventilation airflow than I asked for?

Answer: There are three possible reasons for this:

  1. Check your inputs to see if you specified an outdoor air economizer. If so it is possible the economizer is operating for the hour whose data is displayed on the Air System Design Load Summary. To see if this is the case first check the supply airflow rate on the Air System Design Load Summary. If supply is equal to ventilation airflow, its very likely the economizer is operating. Second, check the System Psychrometrics report for the same month and hour. Check temperature and humidity conditions to determine whether the economizer should be operating for this hour. For example, if you are using an integrated dry-bulb economizer, is the return air temperature warmer than the outdoor air temperature? If so, this is an hour when the economizer should operate.
  2. The discrepancy may be due to a mistake specifying "direct exhaust air". Edit the air system and go to the Zone Components tab, Thermostats data view. Check to see if "direct exhaust" air is specified. If it is, check to see if the "All zones the same" box is checked. If so, this quantity of "direct exhaust" air has been specified for all zones, not just one zone. Thus, if you have 500 CFM specified and 18 zones, you'll have a total of 9000 CFM of direct exhaust for the system. Because the system cannot exhaust more air than is entering the building as ventilation air, the program automatically adjusts the ventilation airflow to equal the direct exhaust.

    If you find this problem, there is a simple way to correct it:
    1. First change the direct exhaust value to zero.
    2. Next, uncheck the "all zones the same" box.
    3. Finally, scroll to the zone which has direct exhaust and specify the proper exhaust CFM. This way only that zone will have direct exhaust, not all zones in the system.
  3. The final explanation also involves direct exhaust. If direct exhaust is correctly specified (only for the zones where it exists), but is greater than the outdoor ventilation air, then HAP will automatically increase the outdoor ventilation air to equal the direct exhaust airflow. A system cannot exhaust more air than enters as ventilation, so HAP must equalize these two airflow values.
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Why do I get less ventilation airflow than I asked for in a VAV system?
FAQ: I am designing a VAV air system in which the sum of outdoor airflows specified for spaces in the system is 3500 CFM. When I generate the Air System Design Load Summary report I see in the design heating column that the ventilation airflow is only 1800 CFM. Why do I get less ventilation airflow than I asked for?

Answer: Make sure you specified "constant" control for the ventilation air. Without special controls outdoor ventilation airflow varies as a constant percentage of supply fan airflow. If ventilation air is 20% of supply airflow at the design cooling condition, it will be roughly 20% of design airflow at all other conditions as the VAV boxes close and the fan throttles. This is modeled by the "proportional" control option, which essentially means that ventilation air is not controlled. With this option you would have your specified 3500 CFM ventilation airflow when the VAV fan is at full airflow. If the VAV boxes close to 10% of design flow, you would have only 350 CFM of outdoor air when all VAV boxes were at their minimum position.
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Why do I get less ventilation airflow than I asked for in a CAV system?
FAQ: I am designing a Single Zone CAV air system in which the sum of outdoor airflows specified for spaces in the system is 3500 CFM. When I generate the Air System Design Load Summary report I see the correct ventilation airflow in the cooling column. However in the design heating column the ventilation airflow is only 1800 CFM. Why do I get less ventilation airflow than I asked for?

Answer: Check the following possibilities:

  1. First, check the System Components tab, Central Heating Coil data view to see if the "capacity control" is specified as "constant temperature., fan cycled." If so, that is the culprit. For cycled fan operation The Air System Design Load Summary lists the average airflow during the hour. Therefore, if the fan operates at full airflow for 31 minutes during the hour, it will bring in 3500 CFM of outdoor air for those 31 minutes and 0 CFM of outdoor air for the remaining 29 minutes of the hour. The average flow for the hour is 31/60 x 3500 or approximately 1800 CFM.


  2. Why would the fan only be cycled on for 31 minutes? Generally cooling operation creates a greater demand for supply airflow. In a cooling/heating system the supply fan is typically sized for the cooling duty. Since this airflow is more than is needed to meet the design heating demand the supply fan will wind up cycling off for part of the design heating hour, sometimes for a significant portion of that hour.

    Note: If local codes require a continual supply of fresh ventilation air, cycled fan operation may not be appropriate because there will be portions of each hour where the fan is cycled off and no fresh air is being provided.

  3. Second, check the System Components tab, Ventilation data view to see what kind of control is specified. If "Scheduled" or "Demand Controlled Ventilation" control is specified that could explain the result. Both of these control methods vary the outdoor ventilation airflow continually. If you need a constant ventilation airflow to be maintained, the "constant" control option should be used.
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How do I delete zones from an air system?
FAQ: I am designing an air system which serves 100 zones. Each zone is a single space. Midway through this design work, the system layout was changed so I only need to serve 98 zones. The two zones that are being removed are zones #51 and #52. How to I delete these two zones from the air system?

Answer: Use the following procedure:
  1. First, make sure you know which spaces are assigned to zones 99 and 100. You'll need this information in step #3.
  2. Next, go to the General tab in the Air System input form and change the number of zones input from 100 to 98. This will delete zones 99 and 100 (HAP always deletes zones from the end of the zone list when the number of zones is decreased).
  3. Because it was zones 51 and 52 we wanted to get rid of, go to the Zone Components tab and edit the space assignments for these two zones. Insert the space assignments from the original zones 99 and 100. This way you have 98 zones and the original assignments for zones 51 and 52 have been eliminated.

    An alternate approach is to respecify space assignments for all zones from 51 through 98 but this takes much, much longer.
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What causes my mixed air temperature to be extremely hot?
FAQ: I am designing an air system. When I generate the Air System Sizing Summary report I find that the entering air temperature for my draw-through cooling coil is 138°F. This is in a climate where the design outdoor dry-bulb temperature is 95°F and the indoor temperature is 75°F. What causes this mixed air temperature to be so hot?

Answer: There are several situations that could cause the mixed air temperature to be such a high value:

  1. If the system includes a return air plenum, and the heat gains assigned to the plenum are very large relative to the airflow through the plenum, extremely large plenum delta-T values can result.


  2. Example: Suppose 10000 CFM flows through the return plenum. 100% of roof heat gain, 90% of lighting heat gain and 20% of wall heat gain have been assigned to the plenum. This total heat gain is 756,000 BTU/hr. Assuming sea level conditions, this results in a temperature rise of 70°F (39 K) across the plenum.

    In such as situation, the plenum heat gain values must be adjusted. Long before a 70°F temperature rise occurred, heat would begin flowing through the ceiling tiles to the room below until an equilibrium was reached. Much less than the 100% roof, 90% lighting and 20% wall heat gains would be transferred to plenum air.

    One common mistake is to specify 100% of roof heat gain to plenum thinking that all the heat must travel through the plenum before it reaches the zone. While its true the heat must flow through the plenum, not all of it is transferred to the plenum air. As the plenum air warms, heat is transferred to through the ceiling tiles to the zone. So the effective percentage of roof heat gain to plenum may only be 70% or 80%.

  3. If the system includes a return fan, check the fan static and efficiency for this fan. We have seen instances where extremely large statics or extremely low efficiencies (1% to 10%) have been specified by accident. The result is an enormous return fan heat gain, on the order of 70°F to 100°F (39 K to 56 K). The solution is to adjust the inputs for the return fan.
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Why doesn't adding an ERV in energy analysis reduce the energy use?
FAQ: I am running an energy analysis and am studying the energy use of a base case system versus a system which includes an energy recovery ventilator (ERV) unit. When I compare the final energy use and operating cost results I find there is no difference. Why doesn't adding an ERV reduce the energy use and cost?

Answer: Check the system inputs to see if 100% of outdoor ventilation air is being directly exhausted from zones in the system. If all ventilation air is being directly exhausted this is the culprit.

An Energy Recovery Ventilator (aka Ventilation Reclaim device) transfers heat and moisture between the outdoor ventilation and exhaust air streams. These devices can be heat wheels, heat pipes, pump-around systems, air-to-air heat exchangers or similar equipment. In order to function, a flow of outdoor ventilation air and exhaust air is required at the air handler. If all outdoor ventilation air is directly exhausted from zones (via toilet exhausts, lab hoods, kitchen exhaust, thru-the-wall exhaust or similar means) then no ventilation air returns to the air handler to be exhausted. Because there is no exhaust at the air handler, the ventilation reclaim device cannot function and no energy savings will be seen.

If you remove direct exhaust from the system you should see the reduction in energy use and energy cost that you expect.
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Pitfalls Interpreting Peak Humidifier Load Data
FAQ: I am designing an air system which includes a steam humidifier. When I compare the peak humidifier load shown on the Air System Sizing Summary with the humidifier load data shown for the design heating hour on the Air System Design Load Summary and the System Psychrometrics reports, the values are different. The load for the design heating hour is smaller than the one shown on the Air System Sizing Summary. How can this be?

Answer: In unusual cases the peak humidifier load occurs for one of the hours in a design cooling day rather than the design heating hour. This was the explanation in your case. HAP searches all hours on design cooling days and the design heating hour to identify the peak humidifier load. Because the humidifier peak load typically occurs at the design heating condition, it is natural to assume that the peak load always occurs at design heating. But this is not always the case. Note the peak month and hour shown on the Air System Sizing Summary (in the "Max Steam Flow" item – it is easy to overlook). This tells when the maximum humidification load occurs.

Typically this unusual situation happens for VAV systems. The combination of a moderate airflow during a cooling design day in one of the winter months coupled with a moderate inlet humidity generates a larger humidifier load than the combination of a smaller airflow coupled with a lower humidity value at the design heating hour. At the design heating condition, all VAV boxes will be at minimum flow position so the system airflow will be small. During design cooling days, even in winter months, VAV boxes may be above their minimum position leading to larger system airflows. While this can happen with VAV systems, it is still an unusual occurrence.
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What does the 'Zone T-Stat Check' Mean?
FAQ: I am designing a 6-zone VAV reheat system. On the Air System Sizing Summary report under the section titled "Central Cooling Coil Sizing Data" there is an item "Zone T-stat Check: 4 of 6 OK". What does this mean?

Answer: The "Zone T-stat Check" item describes the status of zone air temperatures for the month and hour when the maximum cooling coil load occurs. This item is only provided for the central cooling coil. The first value listed is the number of zones whose air temperature lies below the upper limit of the cooling thermostat throttling range. The second number is the total number of zones in the system.

Example: A VAV Reheat system serves six zones. The cooling thermostat setpoint is 75°F with a throttling range of 3°F. Therefore, the upper limit for the cooling throttling range is 75 + 3 or 78°F. For July 1500 when the maximum cooling coil load occurs, the air temperature in all six zones is at or below 78°F. Therefore the output states that "6 of 6 OK". However, if two of the six zones were warmer than 78°F, the output would instead state "4 of 6 OK". Therefore 2 are not OK. The "Max Zone Temperature Deviation" item listed just below "Zone Tstat Check" lists the worst case temperature difference between the zone temperature and the upper limit for the cooling throttling range. For example, if "Max Zone Temperature Deviation" is 0.3°F in this case, we know the worst case zone is at 78.3°F.

Diagnosing Thermostat Problems: The "Zone Tstat Check" item is a useful check figure for confirming that the system is maintaining desired comfort conditions in the zone for the hour when the maximum coil load occurs. If one or more zones are warmer than the upper limit of the thermostat throttling range, you can find further information about operating conditions on the System Psychrometrics report. This report will show the air temperatures for all zones in the system. Make sure to generate this report for the same hour as the peak cooling coil load occurs.

When examining this report, you may find that zone air temperatures only exceed the upper limit of the throttling range by a few tenths of a degree. In such a case this may not be cause for concern. In other cases zone temperatures may exceed the upper cooling limit by several degrees. These kinds of problems are often due to operational problems dealing with unusually large pulldown loads. Or if user-defined sizing was used, the airflow or supply air temperature may not be sufficient to meet a zone's peak loads.

Further useful information may be found on the Hourly Zone Design Day Loads report. This report shows zone air temperatures and loads for complete 24-hour periods. These 24-hour profiles will help you understand the daily cycle of operation and whether problems with pulldown loads are the culprit.

Further Information: HAP uses a system-based design procedure which utilizes the transfer function load method to determine loads. This approach requires that calculations be performed in two stages. In the first stage zone loads are calculated assuming 24-hour cooling and a constant room temperature. In the second stage, zone loads are corrected for actual operating conditions (such as a thermostat throttling range, and a setup, setback or shutdown period at night) at the same time as system operation is simulated. Stage 2 yields not only the coil loads but also data about air temperatures in all zones.
In order to correct the loads and simulate operation in Stage 2, the sizing of zone and fan airflow rates must already be determined. Therefore, the airflow rates must be based on Stage 1 load calculation results. Ideally zone and fan airflows would be based on the corrected loads from Stage 2 since the corrections can change the zone peak loads. However, the corrections cannot be made without knowing the zone and fan airflow rates first which is what forces airflow sizing to be done using Stage 1 results. Usually these airflow rates are sufficient and yield system operation that keeps zone air temperatures within the cooling range. But there are unusual situations where air temperatures stray outside this range.

As mentioned earlier, zone air temperature problems are usually the result of large pulldown loads. If the system and zone airflow rates are not sufficiently large, the system may struggle to extract this pulldown heat and deal with the hourly loads throughout a large portion of the day. There are several strategies that can be used to correct these problems:
  1. If the cooling equipment is turned off during the "unoccupied" period (cooling is specified as not available during the unoccupied period), you could allow unoccupied cooling at a setup temperature to reduce the heat that accumulates during the unoccupied period. This makes the pulldown load smaller and easier to manage.
  2. The thermostat schedule could be modified to start one or two hours earlier. This allows the system one or two hours to deal with the pulldown load before lighting and people loads are present.
  3. Internal load schedules should be checked. Sometimes heat gains such as lighting, occupants and electrical equipment are scheduled at 100% for 24 hours a day when the building is actually unoccupied and lights and equipment are off for a period of the day. Excessive heat gains, especially during a shutdown period or a setup period can result in unusually large pulldown loads.
  4. If user-defined sizing was used, airflow rates to the zones having trouble maintaining air temperature should be checked. They may need to be increased to provide greater cooling capacity to the zone.
  5. If none of the above solve the problem, the user-defined sizing option in system inputs can be used to increase fan and zone airflow rates to provide greater amounts of cooling to address shortfalls in those zones having trouble maintaining proper air temperatures.
An Alternate Viewpoint: There are two schools of thought about the system design procedures used in HAP. One group of users wish to consider all the aspects of system operation and control in the design calculation, and accepts that considering all these aspects sometimes introduces complications, including the problems with maintaining zone air temperature.

A second group of users feels that design calculations should be more idealized and should not consider as many details of control and operation. For these users we recommend using a thermostat schedule with all 24 hours in the occupied period and a thermostat throttling range of 0.1°F (or 0.1°C). This will eliminate many of the dynamic factors (such as pulldown loads) which lead to the zone thermostat check problems. Results are more straightforward to interpret with this approach but may neglect important aspects of operation such as the pulldown load.
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How is the Ventilation Load Calculated?
FAQ: I am designing a constant volume rooftop system. The load calculation results are much lower than I expected and it appears to me the culprit is the ventilation load. The outside air quantity is 2000 CFM and the total supply air is 5000 CFM. I specified a supply temperature of 55°F, a zone thermostat setpoint of 72°F and the outdoor air dry-bulb for my site is 93°F. Using the sensible heat equation: SHC = 1.1 x CFM x delta-T or 1.1 x 2000 x (93 - 55) = 83,600 BTU/hr. HAP reported a sensible ventilation load of only 39,986 BTU/hr. Why is HAP undercalculating the ventilation air load by 50%?

Answer: Due to two common misconceptions your equation for calculating the ventilation load is incorrect.

First, the ventilation load is the net heat transfer to the system due to fresh outdoor air entering the system and exhaust air leaving the system. Therefore the delta-T used in the equation must be based on the outdoor air temperature and the exhaust temperature. 93°F is the correct outdoor air temperature, but 55°F is a supply temperature, not an exhaust temperature. Use the System Psychrometrics report to determine the exhaust air temperature. In your case it was 74.4°F. This is because the zone air temperature was 74.4°F and there were no plenum heat gains or return fan heat gains. Therefore the delta-T was (93-74.4) = 18.6°F, not 38°F.

Second, the 1.1 factor is the product of air density, heat capacity and a conversion factor. Air density varies with altitude so it is not always safe to use 1.1 for this calculation. For sea level conditions this factor is 0.075 lb/cuft x 0.24 BTU/lb-°F x 60 min/hr = 1.08. Your site elevation happened to be 100 feet so this factor only changed slightly when corrected to become 1.076. For further information on the density correction see the footnotes beneath table 1 on the System Psychrometrics Report or click here to review on altitude-adjustments to the correction factor.

Therefore, in this case the ventilation load calculation is 1.076 x 2000 x (93 - 74.4) = 39,986 BTU/hr and this matches the HAP report.

Further Information: Note that the exhaust air temperature can sometimes be several degrees warmer than the zone setpoint and this reduces the delta-T and therefore the ventilation load. Reasons for differences between the exhaust air temperatures and the zone setpoint include the following:
  1. The thermostat setpoint and the thermostat throttling range together determine the operating range for the thermostat. If the setpoint is 72°F and the throttling range is 3°F, then the cooling range is between 72°F and 75°F. For peak cooling hours, the zone temperature is often in the upper end of this range near 75°F as we saw in the example.
  2. If a return air plenum is present, air flowing through the plenum picks up a portion of roof, lighting and wall heat gains and its temperature increases.
  3. If a return air fan is present, heat gain from the fan will increase the return air temperature further.
  4. If a ventilation reclaim device is present, the heat transfer to the exhaust air stream will elevate its temperature even further.
  5. When leakage in the supply duct is specified the program assumes air is leaked from the supply duct into the return plenum, or if a return duct is used, it is assumed the leaked air indirectly reaches the return air stream. In either case, this mixes cold supply air with the return air and this is a reason the temperature of the return air can decrease.
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Why is the off coil temperature greater than the supply temperature for SZCAV?
FAQ: I am designing a constant volume rooftop system. I specified the design supply air temperature as 55°F. On the Air System Sizing Summary report, in the Central Cooling Coil Sizing Data section I see the leaving dry-bulb temperature is 57.4°F. Why isn't the leaving temperature 55°F?

Answer: The "design supply temperature" you specified defines the temperature of air at the supply grille. The air temperature leaving the cooling coil can differ from this design value for two principal reasons which are explained below.
  1. The "design supply temperature" is only required for times when the zone is at its peak load. If the zone load is not at its peak when the peak coil load occurs, then a warmer supply temperature will be sufficient to meet the zone load. The peak zone load may not coincide with the peak cooling coil load for two reasons:
    1. While the coil load is strongly affected by the zone load, it is also affected by other load components the ventilation load, supply fan heat gain and plenum heat gain. If these loads peak at a different hour than the zone load, then the overall coil peak may be at a different time. Therefore, when the coil load peaks, the zone load may be at less than 100% of its peak load. Consequently a warmer supply temperature is sufficient.
    2. Effects of the thermostat throttling range and zone dynamics can affect the zone load. The supply airflow rate is determined based on a load estimate assuming the equipment runs 24 hours a day and maintains the zone exactly at the cooling setpoint. These loads are then corrected for actual operating conditions (thermostat throttling range, nighttime shutdown or setup period) to simulate system operation and determine the coil loads. These adjustments alter the zone loads and can cause the load to be less than 100% of peak when the peak cooling coil load occurs. For example, if operating at 77°F zone temperature due to the thermostat throttling range instead of 75°F, the zone load will be slightly less (see discussion below for more details).
  2. If you have a draw-thru coil/fan configuration or duct heat gain, the off coil temperature must be slightly colder than that required at the grille to overcome these heat gains. However that explains why the off coil temperature might be colder than design.
Typically both factors above are at work at the same time. The temperature required at the supply grille rises as the zone load drops below 100% of peak. At the same time, duct heat gain and fan heat (for a draw-thru unit) require a lower temperature. Often the net of these two factors results in the off coil temperature being higher than the design supply air temperature you specified.

It is also important to remember that the principle of constant volume system operation is that a constant volume of air is provided and the supply temperature is varied to meet the load. Because we are calculating loads according to 1-hour time steps, we are talking about the average supply temperature over one hour. With a DX unit the compressor is cycled or staged. The average hourly supply temperature varies according to the number of minutes the compressor is cycled on or off during the hour, or due to the compressor staging. For the minutes the compressor is on, air close to or below the design temperature is provided, and for the minutes the compressor is off neutral air is provided (for example at 75°F). In a chilled water unit, the water flow or water temperature to the coil is regulated to control the off coil temperature.

Further Information: Earlier it was mentioned that one reason the zone load was less than 100% of peak was the thermostat throttling range and zone dynamics. HAP uses a system-based design procedure utilizing the transfer function load calculation method. This approach requires that loads be calculated in two stages. In the first stage, loads are calculated assuming the equipment provides cooling 24 hours a day and maintains the zone at the cooling setpoint all the time. In the second stage, system operation is simulated to determine coil loads and in doing so the original loads are corrected for actual operating conditions. These conditions include the fact that the thermostat controls zone temperature within a throttling range rather than to a precise temperature, and that the equipment may not operate 24 hours a day, instead using a shutdown period or a setup period during unoccupied times. The corrections to the loads change the shape of the load profile. So where Stage 1 results yield a peak zone load at one time, the adjusted loads from Stage 2 can yield either a higher or lower zone load at the same time. To understand these corrections, review the Hourly Zone Design Day Loads report. It shows the "Zone Load" which is Stage 1 results and the "Zone Conditioning" which is Stage 2 results.

There are two schools of thought regarding this procedure. One group of users endorses this approach because it considers the real aspects of system control and building dynamics. Another group feels that design loads should be more idealized. For this second group we recommend using a thermostat schedule with all 24 hours in the occupied period and a throttling range of 0.1°F (or 0.1°C). These inputs will minimize the load corrections and dynamic effects so Stage 2 results will be nearly identical to Stage 1 results. Note that this still may result in differences between off-coil and design supply temperatures if the coil load and zone load peak at different times, or duct heat gain or a draw-thru unit configuration are used.
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How to Model Closed Loop WSHP Systems
FAQ: I am doing an energy analysis in which one of the alternatives is a conventional closed loop WSHP system. How do I model this type of equipment?

Answer: This system consists of WSHP units connected in parallel to a common water loop. Both a cooling tower and an auxiliary boiler are also connected to the loop. When the majority of WSHP units are in cooling mode, heat rejection to the water loop will cause the water temperature to rise. When the water temperature reaches the maximum loop setpoint, the cooling tower turns on to maintain the loop at the maximum temperature. When the majority of WSHP units are in heating mode, heat extraction from the loop will cause the water temperature to fall. When the water temperature reaches the minimum loop setpoint, the auxiliary boiler turns on to maintain the loop at the minimum temperature. To model this system:
  1. Create a new air system. Use Equipment Type = Terminal Units and System Type = Water Source Heat Pumps.
  2. In this system each zone represents a separate WSHP unit. Therefore, define a number of zones equal to the number of heat pumps in the system.
  3. Enter data for the WSHP system on the General, Vent System Components, Zone Components and Sizing tabs.
  4. On the Equipment Tab, press the "Terminal Cooling Units" button to enter cooling mode performance data for the heat pumps.
  5. On the Equipment Tab, press the "Terminal Heating Units" button to enter heating mode performance data for the heat pumps.
  6. On the Equipment Tab, press the "Miscellaneous Components" to describe the system configuration. Enter the maximum and minimum water setpoints for the loop. Link a cooling tower or auxiliary boiler to the system, if these already exist, or create and link them on the fly.
  7. Finally save the system.
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How to Model GSHP Systems
FAQ: I am conducting an energy study in which one of the alternatives is a Ground Source Heat Pump system. How do I model this type of equipment?

Answer: This system consists of WSHP units connected in parallel to a buried heat exchanger or to vertical borehole ground heat exchangers. To model this system:
  1. Create a new air system. Use Equipment Type = Terminal Units and System Type = Ground Source Heat Pumps.
  2. In this system each zone represents a separate GSHP unit. Therefore, define a number of zones equal to the number of heat pumps in the system.
  3. Enter data for the GSHP system on the General, Vent System Components, Zone Components and Sizing tabs.
  4. On the Equipment Tab, press the "Terminal Cooling Units" button to enter cooling mode performance data for the heat pumps.
  5. On the Equipment Tab, press the "Terminal Heating Units" button to enter heating mode performance data for the heat pumps.
  6. On the Equipment Tab, press the "Miscellaneous Components" to describe the system configuration. Create a cooling tower whose type is 'Geo, well or surface water'. Note that the program assumes electric auxiliary heaters, if auxiliary heating is needed. No inputs are required to define these auxiliary heaters.
  7. Finally save the system.
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Does plant sizing consider diversity among systems?
FAQ: I am designing a central chiller plant which serves twelve air handling units. Looking at the Cooling Plant Sizing Summary I am wondering whether the peak chiller load is based on the sum of the peak loads for the 12 air systems or whether diversity is considered.

Answer: The peak chiller load is determined from the coincident peak load, not the sum of the peaks. Consider the following example:

Example: Suppose we are designing a chiller plant which serves two air handlers. AHU-1 has a peak load of 100 Tons at July 1300 while AHU-2 has a peak load of 150 tons at July 1800. Loads for these two air handlers are shown in the table below. Rather than size the chiller for the sum of the peaks (250 tons), the program finds the coincident peak load (212 tons at 1500). This is the correct value to use because it is the maximum load imposed on the chiller.
HourAHU-1 Cooling Coil
Load (Tons)
AHU-2 Cooling Coil
Load (Tons)
Total Cooling Load
Imposed On Chiller (Tons)
0600433174
0700484391
08005551106
09006457121
10007864142
11009071161
12009682178
130010097197
140098110208
150089123212
160072138210
170061146207
180056150206
190049128177
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Why Aren't More Day Types Offered in Schedules?
FAQ: While using HAP, I noticed that you can only assign profiles in a schedule to a single "design day". This is very limiting. I also need to assign profiles to various other day types like weekdays, weekends and holidays. Will this feature be improved in future versions?

Answer: It sounds like you are either running HAP System Design Loads, or are running the HAP in System Design mode. In either case the program will only provide features for designing air systems. Therefore it is only concerned with building operation on one design cooling day per month. Thus, the only schedule information that is relevant for system design is "design day" data. This is the reason "design day" is the only day type currently offered.

When running HAP with energy analysis features enabled, the table on the Assignments tab of the Schedule form expands to permit scheduling for the following nine day types:
  • Design Day
  • Monday
  • Tuesday
  • Wednesday
  • Thursday
  • Friday
  • Saturday
  • Sunday
  • Holiday
In this way a high degree of flexibility is available for scheduling building operation for energy simulation studies.
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How to Install on a Network Without Using the CD
FAQ: I am a network administrator installing HAP on a network serving 20 workstations. I do not want to have to carry the CD-ROM to each workstation to install the software. Is there a way to install the software onto each workstation using the network server instead of the CD-ROM?

Answer: Yes. Please use the following procedure:
  1. Create a temporary folder on the server, and a subfolder named FILES
  2. Copy the SETUP.EXE file from the root of the CD-ROM and paste it in the temporary folder from step #1. Copy the files from the \FILES folder on the CD-ROM and paste into the FILES subfolder from step #1.
  3. Then, from each workstation running HAP, double-click the SETUP.EXE file in the temporary folder on the server drive to launch the installation.
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Understanding Network Installations
FAQ A: I want to install HAP on a computer network so our engineers can share project data. I notice in the instructions I have to install HAP from each workstation that will run the program. If I am installing one copy of the program to the network, why do I have to install from each workstation?

FAQ B: While installing HAP on a computer network I noticed that it is installing files on the C: drive of the workstation computer. When I ask it to do a "network" install, is it really installing files on the network or on the local workstation?

Answer: The short answers to these questions are:

A. HAP must be installed from each workstation to install software components in the C:\Windows\System32 folder on each workstation.

B. HAP installs software both on the local workstation and the network server drive. The bulk of its software is installed on the network server drive you specify during installation, but it also must install supporting components in the C:\Windows\System32 folder (or equivalent) on the local workstation.

The reason for this installation behavior is that HAP is a 32-bit Windows software program that is "network aware", but is not "client-server" type of software. Therefore it has the same requirements for software configuration as any 32-bit Windows program, whether installed for network use or operation on a standalone computer. This requires certain software components (DLLs and OCXs) to be installed in the \Windows\System or \Winnt\System32 folder on the C: drive of the workstation. The remaining software components (the program itself and supporting read-only data files) are installed on the drive you designate.

Because HAP cannot run without the DLL and OCX software components, HAP must be installed to the network drive from each workstation that needs to run HAP. This is the only way to install the DLL and OCX components on the C: drive of that workstation. As you install from each workstation, the common files on the network server are being overwritten each time, but this does no harm.
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Removing Unwanted Project Names from Project List
FAQ: I have a significant number of projects listed in my list of available projects, however some of these are old projects that are no longer present or needed. When I attempt to remove them using the "Project > Delete" option I get an error indicating "The project you selected cannot be opened because its project folder no longer exists". How do I clean-up this list of old projects and remove the names of old projects from the project list that are no longer needed?

Answer: If you are running HAP v4.1, v4.2 or v4.3 in conjunction with ECAT/E20-II Configuration Services v2.14 or later, the following procedure can be used:
  1. Run HAP.
  2. Attempt to open the project.
  3. If the project folder no longer exists, the following message window will appear.
  4. To remove the project from the project index list, press the Remove button. The project will then no longer appear in the Project Open list.
HAP Project Not Found Dialog
 
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HAP v4.3 vs. V4.20a Calculation Differences
FAQ: I recently loaded the new HAP 4.3 version on my computer. What, if anything, changed from the previous version 4.2a that might affect the calculation results?

Answer: The new version 4.3 contains the new ASHRAE Std. 62-2004 calculation method in addition to the 2001 method that was contained in version 4.2a. The new Standard 62-2004 significantly changed the values used for space level ventilation rates to include two components of ventilation air: one for the people and one for the building. Consult ASHRAE for specific differences between the two methods.

The only other change made to the HAP program, affecting the calculation results, was for VAV systems minimum allowable airflow quantity. There is a new override for minimum primary airflow in VAV systems in v. 4.3. If you use either of the ASHRAE 62 methods and if the calculated ventilation requirement for a zone is larger than the specified minimum zone airflow, the ventilation requirement is used to set VAV minimum flow. For example, if you specified 20 CFM/person as the minimum and that resulted in 400 CFM minimum, but the 62-2001 calculation required 450 CFM for the zone, then we now set the box minimum to 450 CFM. Previously we did not override the min box setting, rather used it as specified by the user to arrive at the minimum airflow quantity for each zone.

Using the new override, as a result, you will see on the Zone Sizing Summary that many of the zone minimum (not design) CFMs have increased. This will lead to small changes in RH coil capacity, very small changes in peak cooling system behavior, and changes in the design heating preheat and reheat coil loads.

As a test, the Example Problem contained on the HAP installation CD was run first in version 4.2a then converted to the new 4.3 version and the results compared using the ASHRAE Std. 62-2001 method. A very slight difference in results occurs as follows:

Total Cooling Coil Peak : changed from 404.6 MBH to 405.0 MBH.
Preheat Peak : changed from 199.6 MBH to 234.6 MBH - because of increase in minimum airflow from 3265 to 3884 CFM.
Supply Fan CFM : unchanged.
OA ventilation CFM : unchanged.
Zone Minimum CFM : changed for all zones (some by a tiny bit, some be a large amount) due to the new ventilation airflow override.
Reheat Coil capacities changed by small amounts - due to larger minimum airflow.
Component loads (top part of Air System Design Load Summary): unchanged.
Component loads (bottom part of Air System Design Load Summary): changed by small amounts due to the changes noted above (min airflow changes).
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The heat reclaim device has no effect on my 2-deck Multizone system
FAQ: I ran a 2-deck Multizone (2DMZ) system and specified an energy recovery device. My system load peaks at August at 1400 hrs. The heat reclaim device has no effect and appears to not be working, why? Here is my system psychrometric report:
System Psychrometrics Report - Table 1: System Data
ComponentLocationDry-Bulb
Temp
(°F)
Specific
Humidity
(lb/lb)
Airflow
(CFM)
CO2 Level
(ppm)
Sensible
Heat
(BTU/hr)
Latent
Heat
(BTU/hr)
Ventilation AirInlet94.40.01460435400757511287
Ventilation ReclaimOutlet94.40.0146043540000
Vent - Return MixingOutlet79.60.009603942939--
Supply FanOutlet79.90.0096039429391169-
Central Cooling CoilOutlet55.00.0086437049399683516412
Central Heating CoilOutlet110.00.009602389397510-
Cold Supply DuctOutlet55.000.08643704939--
Hot Supply DuctOutlet110.00.008642389390-
Zone Air-77.50.0089839421006794125125
Return PlenumOutlet77.50.00898394210060-
Return FanOutlet77.80.00898394210061169-
Answer: HAP disables the vent reclaim unit when there is simultaneous operation of both hot and cold decks because vent reclaim will adversely affect one or the other depending on the relative flows thru each deck. It is not possible to determine which deck (hot or cold) takes priority. During hours when there is flow thru the cold deck only (hot deck inoperative) or hot deck only (cold deck inoperative) the ventilation reclaim unit will operate.

In a 2DMZ system the hot and cold deck operate at the same time for many hours of the year; the hot deck air is used to temper cold air to each zone to maintain the precise temperature needed.

Referring to the psychrometrics report, there is hot deck airflow (238 cfm) even at the summer design condition of 94.4°F ambient. Any energy reclaimed by the heat reclaim device would impose an additional load on the hot deck. In other words, the hot deck tries to make 110°F air and the outdoor ambient air is 94.4°F. However, after flowing through the vent reclaim device it would be cooled to around 85°F entering the hot deck instead of 94.4°F if the reclaim unit was off.
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What impact does a heat reclaim unit have on terminal unit sizing? and/or
What is the difference between the Zone and Terminal Unit capacities on the Zone Sizing Summary report?
FAQ: I ran a terminal system with a common ventilation unit and a heat reclaim unit (ERV). I am trying to understand the difference between the MAXIMUM COOLING SENSIBLE shown on the Zone Sizing Summary report and the SENS COIL LOAD indicated on the Terminal Unit Sizing Data table (see below). What is the difference between the terminal unit sizing data and the zone sizing data? Here is an example:
Zone Sizing Data
Zone NameMaximum Cooling Sensible(MBH)Design Air Flow (CFM)Minimum Air Flow (CFM)Time of Peak LoadMaximum Heating Load (MBH)Zone Floor Area (ft²)Zone CFM/ft²
Zone 131.217251725Jun 170012.81000.01.72
Zone 238.421232123Aug 170019.81000.02.12
Zone 311.51200635Jul 16004.9275.04.36
Terminal Unit Sizing Data - Cooling
Zone NameTotal Coil Load (MBH)Sens Coil Load (MBH)Coil Entering DB /WB (°F)Coil Leaving DB / WB (°F)Water Flow @ 10.0 °F (gpm)Time of Peak Load
Zone 140.133.278.7 / 66.960.6 / 59.5-Aug 1700
Zone 248.741.578.2 / 66.159.8 / 58.7-Aug 1700
Zone 333.224.384.4 / 72.165.3 / 64.2-Aug 1700
Answer: First, it is important to understand two basic principles about the content of this report:

  1. The "Zone Sizing Data" table contains peak room loads. These loads are used to determine the required supply airflow rate for the zones. Both the peak room loads and the required airflow rates are shown in this table.


  2. The "Terminal Unit Sizing Data - Cooling" table contains equipment loads and related data such as coil inlet and outlet temperatures.
Therefore:

  1. Since the "Maximum Cooling Sensible" item is in the "Zone Sizing Data" table, it represents the peak room sensible cooling load. As such it only considers load components from the room.


  2. Since the "Sens Coil Load" item in the "Terminal Unit Sizing Data" table, it is an equipment load — specifically the sensible component of the cooling coil load for the fan coil units. The load on the coil is affected by the room load and other factors and therefore will differ from the room load.
The coil load could be different from the room load for a number of reasons. The following two reasons are the most common:

  1. The coil load is affected by the room load and other factors such as fan heat gain, ventilation load and/or plenum heat gains. Commonly it will be larger than the room load because of the added cooling requirement to overcome fan heat gain and ventilation load. If a common ventilation unit is used, that unit might pretreat the air to a neutral temperature. In this case ventilation load would be negligible. However, the common ventilation unit could also pretreat the air to a non-neutral temperature. If that temperature is above the room temperature, the fan coil unit would have to handle the remainder of the ventilation load not handled by the ventilation AHU. If that temperature is below the room temperature, the fan coil unit would see a credit and the coil sensible load might be less than the room sensible load. In this case the ventilation AHU is picking up part of the room demand.


  2. The coil load shown in the table might occur at a different time than the peak room load. In the example above, the peak total cooling coil load occurs at August 1700 while the peak room load occurs at June 1700. That suggests the room load is at an off-peak condition at August 1700. Therefore comparing the two numbers is misleading because the loads occur at different times. To determine the room load and coil load occurring during the same hour, use the tabular version of the System Psychrometric Report.
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Why did HAP change my ASHRAE 62.1-2004 ventilation rates back to "User-defined" space usage category?
FAQ: I recently changed an existing HAP 4.3 project from the ASHRAE Standard 62-2001 ventilation sizing method to the newer Standard 62.1-2004 method. In doing so, I noticed the default space ventilation rates were changed to "User-Defined" but the ventilation values did not change. Why is this?

Answer: You are correct, switching an existing 62-2001 project to a 62.1-2004 project resets all the ventilation rates to user-defined but retains the previous values. This is done because a number of the space usage tables and categories changed from 2001 to 2004. These changes could not be handled automatically by HAP. As a result, the program could not make decisions as to which new category to use. If a new project is created using the 2004 method, the space usage category can be selected as before. Keep in mind, the user-defined values can be manually overridden and set back to 2001 levels if desired.

When a HAP project is changed from one ventilation sizing method to another the following dialog box appears:
HAP Ventilation Defaults Changed Dialog
 
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What happened to the public restroom category with ASHRAE Standard 62.1-2004?
FAQ: I am running a new HAP project using the newer ASHRAE 62.1-2004 ventilation sizing method and I noticed in the space usage drop-down there is no category for restrooms. In the old 2001 method there was a space usage called, "PUBLIC: Public Restrooms". In the 2004 method I do not see restrooms listed. How do I enter a restroom and how do I account for the exhaust air?

Answer: Restrooms are no longer on the space usage drop-down list for the 2004 method, nor are there a number of other categories. ASHRAE modified the category list and ventilation requirements when they updated the standard and restrooms do not appear on the 2004 tables. There is a new table for exhaust rates called Table 6-4. Restrooms do not need outdoor air ventilation. So, any combination of outdoor air, transfer air or recirculated air can be exhausted for these areas. According to Table 6-4 of the 2004 standard:

Toilets (public): 50/70 (cfm/per w.c. or urinal)
Toilets (private): 25/50 (cfm/per w.c. or urinal)

The two numbers are for normal usage and high usage. High usage is for applications such as movie theatres, auditoriums, etc. Otherwise, the lower value can be used.

The exhaust rate is set under Air System Properties > Zone Components > Thermostats for the zone that includes the restrooms.
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Modeling a unit ventilator (UV) system
FAQ: I am trying to model a self-contained Unit Ventilator (UV) system for a school project where a dedicated UV is used for each classroom. I cannot find a UV listed as one of the system types in HAP. How do I model a UV system?

Answer: A Unit Ventilator is very similar to a hotel/motel unit often referred to as a PTAC (packaged terminal air conditioner). This is what HAP calls a "Terminal System". Under Air System type select a "Packaged DX Fan Coil". For the input field "Number of Zones" enter the quantity of individual UV units you plan to use. Each zone will represent a dedicated UV.

You did not state how you were supplying ventilation to these terminal units. Most unit ventilators are equipped to handle ventilation air introduced directly through the back of the UV cabinet. For this situation , select "Direct Ventilation" for the Ventilation type on the General tab on the system input screen. It is also possible to pre-condition the ventilation air by using a make-up air unit (MAU) to condition air directly to the mixed air point of the UVs. In this case, you should select "Common Ventilation System" for the Ventilation type. This enables the Vent System Components tab allowing ventilation unit parameters to be defined.

Each classroom space must be assigned to one of the zones under the Zone Components tab. The "Zone 1", "Zone 2", etc. zone name can be renamed to something more relevant such as "Classroom 101", "Classroom 102". This makes it easier to associate the spaces with the zones they are connected to.

Finally, if an energy analysis is necessary, enter the appropriate performance information under the "Equipment" tab since this will affect energy consumption results.
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How to calculate loads for a decoupled air system
FAQ: I have a make-up air unit that provides conditioned ventilation air to the return side of a group of VAV systems. How do I model the cooling and heating loads for the make-up air unit and the VAV systems? I will not be performing an energy analysis.

Answer: If you have a ventilation system which feeds the returns in a group of VAV air systems, it could be approached as follows. This approach assumes the objective is system design rather than energy analysis.
  1. VAV Systems
    1. Set up each VAV system with the proper amount of ventilation air assigned to the system.
    2. Place a precool coil and preheat coil upstream of the mixing point with the proper setpoint temperatures. The setpoints must be the same as those specified for the Ventilation System described below.
    3. This will allow you to properly account for the thermal effect of the tempered ventilation air on the VAV unit central cooling coil inlet conditions.
    4. Since a separate fan can not be inserted upstream of the mixing point, and the ventilation cooling/heating coils are controlled off a duct thermostat downstream of the supply fan, the thermal effect on the VAV system loads will not be affected.
  2. Ventilation System
    1. Create a tempering ventilation system with cooling and heating coil.
    2. Specify the cooling coil setpoint to the same temperature as the zone thermostat cooling setpoint.
    3. Specify the heating coil setpoint to the same temperature as the zone thermostat heating setpoint.
    4. This will yield peak cooling and heating coil loads as well as fan data.
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How do high infiltration rates impact energy simulations?
FAQ: Why is my fan energy in winter so much higher than in summer when I add infiltration to my space properties?

I have modeled a SZCAV system with gas heat in Michigan. Occupancy is from 8AM to 5PM on weekdays with cycled or staged compressor and “Fan On” control. Fractional schedules were applied to lights, people and misc. electric at 100% during occupied hours then at 10% during unoccupied hours. There is NO economizer on the system. On the Air System Sizing Summary the cooling season fan energy is much less than the heating season fan energy. As a matter of fact, the fan energy is twice as much in December as in July. Also, the load profiles look reasonable. Cooling loads exist only in the summer months and peak in July and the heating loads exist only during winter, peaking in January. Also, there are no unmet loads or zones out of range.

Why might this occur? With “Fan On” control, shouldn’t the fan energy be about the same for each month? If this is due to the internal heat gains being on at 10% during the evening, wouldn't the cooling energy be higher? The heat gains from lights and other internal loads should make the winter heating and corresponding fan energy less since the internal heat gains offset the building heating requirements.

The Air System Sizing Summary report follows:
Air System Simulation Results (Table 1):
MonthCentral Cooling
Coil Load
(kBTU)
Central Cooling
Eqpt Load
(kBTU)
Central Unit Clg
Input
(kWh)
Central Heating
Coil Load
(kBTU)
Central Heating
Eqpt Load
(kBTU)
Central Heating
Coil Input
(kBTU)
Central Heating
Misc. Electric
(kWh)
January00092579257115710
February0007923792399030
March515144891489161140
April207207181964196424550
May147614761506646648300
June336133613501110
July462346234950000
August341834183630000
September207920792122322322900
October280280251637163720470
November333334157415751960
December11083508350104380
Total155291552916193907639076488460
Air System Simulation (Table 2):
MonthSupply Fan
(kWh)
Lighting
(kWh)
Electric
Equipment
(kWh)
January198402183
February174350159
March144367167
April113385175
May98385175
June92367167
July103402183
August91367167
September92385175
October113402183
November132350159
December188402183
Total153845662075
Answer: The problem is a result of a large amount of infiltration air entering the building during “unoccupied” hours in the heating season. The building is located in Michigan so in the summer, infiltration of relatively cool air during unoccupied times tends to reduce the cooling load and minimize the need for the fan to run during unoccupied hours. In the winter, infiltration of cold air during unoccupied times increases heat loss and tends to increase the need to run the fan to hold the set-back thermostat setting in unoccupied hours. While the number of fan ON hours in occupied times is relatively constant each month (varying only for days of the month), the number of fan ON hours in unoccupied periods is much greater in the winter than in the summer. That results in larger fan kWh for winter months.
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Why is the ventilation airflow the same for both ventilation control options, constant and DCV?
FAQ: I modeled a system in HAP with two different ventilation control options: Constant and Demand Controlled Ventilation (DCV). I notice on the System Sizing Summary reports the ventilation quantity remains the same for both options. Why is this? I thought that DCV controls reduce the amount of ventilation air required.

Answer: This is a common misunderstanding. DCV is a controls (energy savings) strategy not a design strategy. A DCV control system modulates the quantity of ventilation air introduced into the building using CO2 sensors that measure zone or a combination of zone and outdoor air CO2 levels. According to ASHRAE Standard 62 (all versions) there are minimum required ventilation rates for each usage area in the building. These ventilation rates are required minimum values.

Consider the following example: An air handler serves one office space having 1,000 sqft floor area and 10 people. According to ASHRAE Std. 62-2004, Table 6-1, the design ventilation rates for an office are:
    Rp = 5 CFM/person
    Ra = 0.06 CFM/sq. ft.

    where:
      Rp = people outdoor air rate
      Ra = area (space) outdoor air rate
So for 10 people, the total ventilation required is: 10 people(5 CFM/p) + 0.06CFM/sq. ft. (1,000 sq. ft.) = 50 + 60 = 110 CFM.

This is the design ventilation rate when the space is fully occupied. Of this 110 CFM, 50 CFM is meant to remove occupant-generated contaminants like CO2 and odors, and 60 CFM is meant to remove space-generated contaminants such as outgassing from carpets and furnishings. The 60 CFM component is sometimes called the Base Ventilation Rate. So a DCV strategy allows you to reduce the people component (Rp) of total ventilation in response to varying space CO2 levels. If the space is fully occupied the space requires 110 CFM of ventilation. If half (5) of the people leave the people component of the ventilation rate might be reduced to half (25 CFM) for a total of 85 CFM (25 + 60).

Regardless of whether you use "DCV" or "Constant" ventilation control the system must still be sized to deliver 110 CFM of ventilation at the design condition. However, DCV can be used to reduce the people component of the ventilation rate at off-design conditions. If you are performing an energy simulation this is where you will see the benefits of using a DCV control strategy.

Carrier has a number of design guides and white papers discussing DCV controls, strategies and products. Please Click here for more information on DCV, or search for "DCV" under the Carrier Commercial HVAC Systems web page for additional information: http://www.commercial.carrier.com
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What gbXML data will HAP import?
FAQ: What gbXML data will HAP import?

Answer: HAP v4.3 will import all of the data listed below.

gbXML files can contain a wide range of information. Depending on the tool that generated the gbXML file and how much effort the user invested in adding content to the original CAD drawing, the gbXML file could contain alot or a little of this data. Item 1 tends to be the minimum data present in a gbXML file. Some tools are capable of adding information about items 2-11 if the user chooses to do so.

  1. Surface data: dimensions (HxW, LxW), gross areas, and orientations for
    • Exterior walls
    • Horizontal roofs
    • Sloped roofs
    • Windows
    • Doors
    • Skylights
    • Basement floors
    • Basement walls
    • Slab-on-Grade floors
    • Raised floors
  2. Exterior wall construction information.
  3. Roof construction information.
  4. Window and skylight thermal performance data.
  5. Door thermal performance data.
  6. Construction and thermal performance data for basement floors, basement walls and slab-on-grade floors.
  7. Software automatically calculates building weight for the space if items 1, 2, 3, and 6 are supplied.
  8. Internal heat gain data for the following:
    • Occupant density, sensible and latent heat gains.
    • Overhead lighting W/sqft
    • Electric equipment W/sqft
  9. Schedules for internal heat gains.
  10. Infiltration airflow data.
  11. Outdoor ventilation airflow requirements
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What gbXML tools will HAP be compatible with?
FAQ: What gbXML tools will HAP be compatible with?

Answer: Any tool that generates gbXML conforming to the gbXML schema rules.

gbXML is a standardized, neutral format for defining building information. It uses an “XML schema” to define the rules and conventions for formatting the information. As long as the tool which generates the gbXML file conforms to the gbXML schema rules, HAP should be able to import data from the file. We have tested the HAP feature with gbXML files generated by today’s most popular CAD and BIM tools.
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Will HAP export gbXML data?
FAQ: Will HAP export gbXML data?

Answer: Currently, HAP only imports gbXML data.
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How do I import the data?
FAQ: How do I import the data?

Answer: The procedure works like this:
  1. Use your building information modeling (BIM) or CAD tool to generate gbXML for the project.
  2. Run HAP.
  3. Open your project or create a new one.
  4. Choose the "Import gbXML" option on the Project Menu.
  5. Select the gbXML file created in step #1.
  6. gbXML file data is read, translated and stored in the HAP project.
  7. A "Translation Report" can be displayed. It summarizes the data that was imported and lists any problems or issues that arose during the translation.
  8. Work with the imported data in your HAP project. Depending on the quantity of data in the gbXML, users may need to add content to the project or adjust data that was defaulted. For example, if the gbXML only contained surface data, the user will need to add construction data, internal loads, schedules, infiltration, ventilation requirements, etc...
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How can I update the Company Name in the software?
FAQ: Our company recently had a name change and I notice on all my reports it still lists our old company name. How do I edit this name in the software? I see no settings inside the program to do so.

Answer: The company name is entered the first time the Carrier E20-II software is installed on the computer and is only required to be entered one time only, then all Carrier software uses this same name. To change your company name please contact Software Systems at 800-253-1794 or software.systems@carrier.utc.com. In order to correct the name, Software Systems will need the following file along with the new company name exactly as you would like for it to appear.

File Name: E20xycfg.mdb

This file is located inside the E20-ii folder (C:\E20-II\E20xycfg.mdb), where "C" is the hard drive letter where your Carrier software is installed.

This is a Microsoft Access database file which contains the company name and other configuration information. It is not recommended that the user edit this file themselves because the file is written in a Microsoft Access '97 compatible format. Opening the file and editing or saving the database file with a newer version of MS Access will cause the file to be unreadable by the Carrier software.

Please contact Software Systems to determine the best method to transfer this file.

We will edit it and send it back to you. You should then overwrite the old file with the new edited file.
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Why does HAP not maintain the CO2 differential specified when using the DCV setting?
FAQ: I am using a CO2 Demand Control Ventilation (DCV) setting in HAP with 400 ppm outdoor air and 700 ppm CO2 differential. From the system psychrometrics report I notice for some hours the CO2 levels are going up to 1152 ppm. With 700 ppm differential shouldn't the HAP DCV control maintain my CO2 levels at or below 1100 ppm (= 400 + 700 ppm)?

Answer: When the CO2 in the zone is 1152 ppm it is likely that your system is operating at the design outdoor ventilation CFM. If so then this is just a case of the design ventilation CFM specified not being sufficient to achieve the 700 ppm differential. This is an issue of "tuning" the ventilation CFM and the ppm differentials so they are in synch (i.e. that at design ventilation CFM you can maintain the desired CO2 ppm differential).

Design ventilation CFM is calculated based on CFM/person and CFM/sqft requirements set for the space. However, these CFM/person and CFM/sqft requirements don't guarantee anything about the CO2 levels in the space (indirectly the CFM/person and CFM/sqft numbers may intend to get you to certain CO2 differentials, but there are enough independent factors at work that the ASHRAE Std 62.1 requirements can't guarantee a CO2 differential). It is important to understand that HAP will not override the user-specified ventilation quantities to automatically maintain the desired zone CO2 levels. If 700 ppm is the maximum differential desired, but if using the design ventilation CFM isn't sufficient to flush the CO2 out of the building, then you will see CO2 differentials going above 700 ppm.

A couple of the factors that are outside the control of Std 62 are:

  • Activity level of the occupants - User is free to define these as whatever he or she feels are appropriate and they might not be perfectly in synch with what Std 62.1 assumed in setting the CFM/person value. The higher the activity level (higher heat gains), the higher the MET rate for occupants and therefore the higher the CO2 generation.
  • Infiltration or lack thereof. The more infiltration you have the more flushing with low-CO2 outdoor air. When none is present, you have no flushing.
If you are finding that CO2 differentials are going above 700 ppm (or your particular setting) a solution might be to tune the system by increasing the design ventilation CFM slightly to provide the ability to flush the building with more low-CO2 outdoor air.
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Why does HAP not give me 60% RH when I add a humidifier and specify 60% RH?
FAQ: I am modeling a system with a steam humidifier set to maintain a minimum of 60% RH. I have entered 60% under System Components, Humidification using a steam injection humidifier w/ setpoint of 60%. After calculating and viewing the Air System Sizing Summary, it shows Resulting RH = 50%. Why can I not get the 60% RH that I asked for?

Answer: To figure these types of problems out you need to look at the system psychrometric graph. Most systems that control the cooling coil leaving air temperature (LAT) to something like 55F with a bypass factor of say, 0.10 will result in an off-coil condition very close to the saturation line (point 3 below). On a typical draw-thru fan the supply air then passes through the fan where it picks up some sensible heat (line 3-4) before entering the humidifier at (point 4), as shown below.
Psych Chart 1 for HAP FAQ
 
Since the humidification process is 100% latent the process is a vertical line from point 4 to point 5, where it hits the saturation curve, meaning the air cannot hold any additional moisture at that temperature. From point 5 to point 6 defines the room process line with point 6 being the final room condition, in this case corresponding to a 50% RH.

The solution is to increase the required LAT off the coil such that the humidification process can add additional moisture to the air. In other words the 55F LAT you have specified is dehumidifying the air too much. Go back to the cooling coil setting in the air system, system components and raise the cooling coil LAT to say 61F. Now re-run the calculations. As you can see from the figure below the warmer air is now capable of holding more moisture, therefore the Point 5 (humidifier outlet) now results in a condition whereby the room process (line 5-6) results in a zone RH=60% as indicated.
Psych Chart 2 for HAP FAQ
 
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How to Specify RTU Performance
FAQ: I am trying to model a packaged rooftop unit (RTU) in HAP for a LEED simulation. My design outdoor ambient temperature (OAT) is 110 F and I am using "Auto-Sizing" for the Equipment Sizing. The default values in HAP for the Design OAT is 95 F and the EER is 9.50. Should I use the default values or if not what values do I enter for the Design OAT and the EER?

Answer: The inputs that should be used for your situation are shown below in Figure 1.

Explanation:
  1. Design OAT = 110 F specifies that you want the autosized gross cooling capacity to correspond to an OADB of 110 F. If you set Design OAT = 95 F, then you're telling the program autosized gross capacity corresponds to 95 F OADB. In this case when you are at 110 F OADB you will have less capacity - and hence unmet loads.
  2. ARI Performance Rating = 9.5 EER -- Regardless of what other inputs you make in this window, when you choose the "ARI Performance Rating" option the EER you input automatically corresponds to the ARI condition which is 95 F OADB in this case. Since this is for a LEED simulation you must look-up the required minimally-compliant EER from ASHRAE 90.1-2004, Table 6.8.1A based on the type of equipment and the capacity. For your convenience this information is also included in the HAP Help system by pressing F1 on the input field for EER.
  3. HAP then sorts everything out for you as explained below, and also in section 31.12 of the HAP on-line help system. For a packaged RTU:
    1. HAP calculates the net cooling capacity at 110 F OADB by subtracting fan heat.
    2. HAP calculates the net cooling capacity at 95 F by correcting the result from 3-1 to the lower OADB.
    3. HAP derives total input kW at 95 F using EER (which is at 95 F) and the adjusted net cooling capacity at 95 F from step 3-2.
    4. HAP derives compressor + OD fan input kW at 95 F by subtracting indoor fan kW from the total input kW from 3-3.
    5. HAP calculates the compressor + OD fan input kW at 110 F by correcting the result from 3-4 to the higher OADB.
The gross capacity at 110 F and the compressor + Outdoor (OD) fan input kW at 110 F derived in this way are then used as the two anchor points for the RTU simulation.
Air Cooled DX Equipment Data Inputs
 
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How to Specify Unitary Equipment Performance
FAQ: I am modeling unitary equipment in HAP. The equipment input screen has a number of different inputs. Can you advise me on the correct approach to these inputs? I want to make sure all the capacity and efficiency inputs are correctly specified.

Answer: When modeling unitary cooling equipment such as RTUs, VPACs, PTACs and WSHPs, the following basic principles apply:
  1. Design OAT or Design EWT - Specify the entering condenser temperature at the equipment design condition. For example, if the peak cooling load occurs at an outdoor air temperature of 100 F for air-cooled DX equipment, Design OAT must be 100 F.
  2. Equipment Sizing - Select "Auto-Size Capacity" if you want the program to automatically determine gross cooling capacity and also enter a "Capacity Oversizing Factor" to specify how much additional capacity above the peak load is required.
    On the other hand if you want to directly specify capacity, choose "User-Defined Capacity" and then enter the gross cooling capacity. In both cases, the design capacity will be assumed to occur at the Design OAT or Design EWT entered on this screen.
  3. Performance Rating - Choose "ARI Performance Rating" or "ISO/ARI Performance Rating" to enter a standard EER rating for the equipment. Regardless of what you have specified for Design OAT or Design EWT, this EER corresponds to standard ARI or ISO/ARI rating conditions. For air-cooled units HAP will use the EER to automatically derive the compressor plus OD fan kW at your specified Design OAT. For water-cooled units HAP will use the EER to automatically derive the compressor kW at your specified Design EWT.
    On the other hand, if you want to directly specify input power, choose the "Compressor + OD Fan Power" or "Compressor Power" options. In this case, the kW value you define must correspond to the Design OAT or Design EWT you specified.
  4. Low Ambient Control - For air-cooled equipment specify the low temperature cutoff temperature. If the unit has head pressure control, specify that low ambient controls are present and specify the cutoff for conventional operation and the cutoff temperature for low ambient operation.
When modeling unitary heating equipment such as RTU heat pumps, PTHPs or WSHPs, the same general principles apply:
  1. Design OAT or Design EWT - Specify the entering air or water temperature corresponding to the heating design condition. For example if the design EWT for a WSHP loop application will be 60 F, specify that value.
  2. Equipment Sizing - Choose "Auto-Size Capacity" if you want the program to determine capacity. Choose "User-Defined Capacity" if you want to enter the gross heating capacity yourself. In both cases, the capacity corresponds to the design entering temperature entered above.
  3. Performance Rating - Choose "ARI Performance Rating" or "ISO/ARI Performance Rating" to enter a standard COP for the equipment. This performance value corresponds to the standard ARI or ISO/ARI rating conditions. HAP will automatically derive the compressor + OD fan kW or the compressor kW from the value you enter, corrected for your specified design entering temperature.
    On the other hand, if you want to directly specify input power, choose the "Compressor + OD Fan Power" or "Compressor Power" options. In this case, the kW value you define must correspond to the Design OAT or Design EWT you specified.
 
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