Does anybody know why the baseline COP's for Packaged Terminal HVAC equipment (HVAC systems 1-2 for residential) are less for larger capacities and lower for smaller capacities i.e. Using the formulas......
PTHP Cooling Mode (new construction)
Anything in between 2.1 – 4.4 kW will have a COP generated by the following formula........3.6 – (0.213 x Cap/1000) COP.
≤2.1Kw unit = 3.153 COP
≥4.4Kw unit = 2.663 COP
I would have thought that units with higher capacity should have better efficiency as it is easier to achieve than with a smaller unit size. But this is the reverse of that. Or am I missing something here?
Also, does the baseline capacity of the unit include the space loads as well as the fresh air load i.e. is the PTHP for the baeline model essentially like a wall mounted heat pump which brings in a contant fresh air rate and also recirculates indoor air through the cooling coil to deal with the space loads?
Any help is much appreciated
Michael Tillou
Director of Energy ServicesCannon Design
52 thumbs up
September 27, 2010 - 10:28 pm
I don't know the exact answer to the first part of your question. The answer to the second part is "yes" when using the PTAC or PTHP baseline system type in residential building/space types the capacity is based on both internal loads and outdoor air loads. The assumption is that the unit brings in outside air directly to the unit.