7. Nonresidential Mechanical
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, starting with the 2013 modeling rules, the Standard (Budget) building will typically have a Variable Air Volume (VAV) system anytime the building being modeled is greater than 10,000 sqft or more than one story. 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 Natural Ventilation (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 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.