Afternoon all,
We're trying to obtain the minimum CoP for a Packaged Terminal Heat Pump
in cooling mode for a new construction using table 6.8.1D in ASHRAE
90.1-2004 (SI edition) and the formula is proving to be somewhat
confusing. In the SI edition it is described as
[3.60 - (0.213 x Cap/1000)]
Is this the same equation as listed in the imperial edition of
90.1-2004? If the max. unit capacity of 4.4kW is converted to Btu/hr
(approx 15024 Btu/hr, as per note c) and input to the formula, the
minimum CoP is only 0.4, which seems very low. However, if I use the
value in Watts in the equation, the minimum CoP comes out as a much more
reasonable 2.66.
I can't seem to find any addenda on ASHRAE's website or additional
guidance on this matter and would very much appreciate any guidance you
can provide.
Many thanks for your help.
DAN JESTICO
Hello Dan,
You are correct to use Watts for the SI equation. The counterpart equation for the PTHP (cooling mode, new construction) in the IP version is [12.3 - (0.213 x Cap/1000)], but is expressed as EER (not COP.) COP's are expressed for heating mode as [3.2 - (0.026 x Cap/1000)]. That lower coefficient (0.026) softens the Cap/1000 value, when Cap is in Btu/h.
Larry O. Degelman, P.E.