Frequently Asked Questions

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7. Nonresidential Mechanical

Start by looking at Table C on the form.  You will find individual columns that indicate Yes and No for specific aspects of the HVAC design.  Identify which column shows No.  You will find a Table Reference indicated in the Column header.  Find the table further back on the form and you should be able to identify what aspects of the design is out of compliance. Often times this will be Table F that is the problem.  If you review the data in this table, it provides for the HVAC system sizes as proposed (column 8), as well as the Maximum allowed system sizes (column 11).  Confirm that the HVAC system is not oversized.  More information on this limitation can be obtained in Section 140.3 of the Standards, as referenced in this table, also note that you can identify if this is the Smallest Size Available at the System level of the Building Tree, MCH tab.

Note that this section applies to EnergyPro V8 or above, and non-Title 24 applications of VRF systems.  For Title 24 applications, see this FAQ.

The VRF models are located in the sample files, located in the example files section of this site.  You will need to export the systems from the sample file into the file you are working with.  Begin by opening your project, and then open one of the sample files with the Manufacturer name of the models you wish.  Navigate into the Central System library in the sample file by clicking on the bottom left button “Libraries” and then in the pane above, select “Central”.  A list of models will appear on the right for you to select.  You can select multiple systems by clicking on one system, then holding down the shift key and selecting another system.  Once you have selected all of the systems you want to export, select the export button on the top of the window.  Select your project from the window that appears (you may need to scroll to the bottom of the window) and hit ‘OK’.  The systems you had highlighted will now be available in your project.

Repeat this procedure by selecting the “Zonal” library and exporting all of the indoor units.

Included with EnergyPro is a flexible heating input tab in the Central System Library.  The system selection choices give you the ability to specify any source of heating, when dealing with most systems.  The inputs allow you to specify a hot water coil, for instance, combined with a Packaged DX system.  This type of input would allow the user to model a radiant floor heating system fed by a boiler, with a conventional packaged system providing air conditioning.

In the Plant element, under the Heating Hot Water tab, create a boiler or select one from the Boiler Library.  Enter the Boiler pump size and flow rate.

In the System element, create a HVAC system with the appropriate system type and ‘Hot Water’ as the heating type.

The hydronic system may also have a cooling component, in which case, you would also model the cooling information (see the topic on No Cooling if none exists).

For Nonresidential buildings, the Standard (Budget) building will typically have a Variable Air Volume (VAV) system anytime the building being modeled is greater than 25,000 sqft, more than two stories, or has a cooling capacity > 65,000 Btuh. Your proposed design is likely a Constant Volume system, and thus is going to have significantly higher fan power usage than the Standard building. We have been recommending you choose prescriptive compliance when you have high fan power.

For High-rise Residential buildings, the Standard building will have fans that run intermittently instead of a continuous running fan for the guest rooms.  Check your input at the Central System, Controls tab to see what setting you have for the fan operation, and consider if using Zone Ventilation fans (Zone level of the tree, Mechanical Tab) will be possible.

In both cases, review your inputs for the fan BHP to be sure this number is not excessive.  Please also understand that the fan power used in the Performance modeling for the budget does not necessarily align with what is required for Prescriptive, so many times your fan will comply under Prescriptive and not Performance.  If so, take that route.  For VAV systems, review the airflows you have input at the Zone level of the tree, Mechanical tab as well as the VAV turndown ratio indicated on the VAV terminal boxes.

In the Central System Library, create a new system. Set the System Type to SplitDX. Now, set the heating type to Electric, and input the HSPF as 3.413

In the Central System Library, in the Outdoor Air Tab, select 100% OA in the Economizer Type dropdown list.

The Supply CFM is input in the Central System library, Fan Tab.

The Outside Air CFM is input at the Room Level of the Building Tree, Occupant Tab.

When modeling this type of system with the DOE-2 calculation (used in the 90.1 calculations), you would  put in a dummy zone. That is not needed, nor should you do that with the new CBECC Com calculation running under the Nonresidential T24 Performance calculation. Note that currently, this calculation only permits a DOAS systems feeding Zonal Type Systems (Four Pipe Fan Coil, Packaged Terminal Air Conditioners and Heat Pumps, Hydronic Heat Pumps, SplitDX , PackagedDX, Single Packaged Vertical Units and VRF). Simply create that system as you have per prior instructions, and select the “Outside Air From” setting at the system level of the tree. See the DOAS.bld example we include in the sample files section.

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