This has been covered in a few posts here before, but I'm not sure the prototype approach or the 90.1 budget system formulas will give me what I'm looking for (representing generic systems based on default PDs, fan efficiencies, autosized capacities and airflows)
To calculate COP-nf for a generic system, does the following approach (basically removing calculated fan power from the denominator of the COP) work?
- total power input [BTU/hr.] = capacity / COP
- fan power input [BHP] = cfm x PD / (fan-eff x 6356)
- compressor power input = total power in - fan power in
- COP-nf = capacity / compressor power input
(obviously there are some conversions in there)
and, if this is a valid approach, for VRF/multi-split systems, is the supply fan power merely the sum of each connected indoor unit's fan power?
lastly, what about other elements of systems that consume energy, could/should these also be removed from the COP denominator? Including those that are defined within the object where COP-nf is an input, such as:
for various coil types
- Crankcase Heater Capacity
- Resistive Defrost Heater Capacity
or other objects necessary to define a system (but don't take COP-nf as an input) such as
ZoneHVAC:TerminalUnit:VariableRefrigerantFlow
- Parasitic Electric Energy Use
For some background if someone comes across this post and would like to know about the standard approaches:
DOE Prototype approach:
cop = (eer / 3.413 + R) / (1 - R)
where R is "the ratio of supply fan power to total equipment power at the rating condition." and 0.12 is typically used
and here are the various formulas from 90.1 (12.5.2.c in 2022):
- cop = -0.0076 * seer * seer + 0.3796 * seer
- cop = 1.48E-7 * coph47 * Q+ 1.062 * coph47 (system 6 and 9 heating)
- cop = -0.0296 * hspf * hspf + 0.7134 * hspf
- cop = 7.84E-8 * eer * Q+ 0.338 * eer
- cop = 0.3322 * eer - 0.2145 (system 8 and 10 cooling)
- cop = 1.1329 * cop - 0.214 (system 8 heating)
