[BLDG-SIM] HVAC efficiencies in DOE2

[Andy Lau]

I'm working on putting together a document to guide students in defining 
the heating and cooling equipment efficiencies that are input to DOE2.2, 
specifically eQuest v.3.55.  In the process, I've realized that I'm not 
that confident on some of these issues and seek the knowledge of this 
BLDG-SIM group.

First, HIR for furnaces and boilers, derived from AFUE and Et.  Because 
eQuest has built-in HIR=f(PLR) curves, the program accounts for 
part-load effects like cycling and flue losses.  Therefore, I would 
expect that it is Et, thermal efficiency, that should be used to 
determine HIR=1/Et.  The question then is whether there is a documented 
relationship for determining Et from AFUE.  All I have found thus far is 
the California Energy Commission's 2005 "Nonresidential Alternative 
Calculation Method (ACM) Approval Manual" wherein there are 
relationships for HIR for packed and split systems as well as boilers 
(the relationships are in the attached spreadsheet).  Not sure where 
these relations have come from plus I would expect AFUE to be lower than 
Et which is not always the case in these correlations.

Second, EIR for heat pumps in heating mode.  My understanding is that 
the eQuest input should reflect the COP at 47F outdoor temperature, not 
including the supply fan energy use which is modeled separately in 
eQuest.  If a heat pump is rated in terms of HSPF, then this seasonal 
average value must be converted to COP47.  I've found an FSEC/ASHRAE 
publication, "Climate Impacts on Heating Seasonal Performance Factor 
(HSPF) and Seasonal Energy Efficiency Ratio (SEER) for Air Source Heat 
Pumps," that provides a simple correlation, COP47 = 1.718*HSPF/3.413.  
In this correlation, supply fan power is removed from the HSPF using the 
ARI standard blower value of 0.365 W/cfm. 

Third, EIR for packaged cooling equipment in cooling mode.  Here the EIR 
should be based on the COP at 95F outdoor, 80F indoor, which is related 
to the EER, COP95 = EER/3.413.  For smaller units, SEER is often the 
reported measure, which accounts for seasonal variation.  In the same 
FSEC/ASHRAE study, they found this correlation, COP95 = 
1.063*SEER/3.413.  Again, fan power is backed out of the SEER values 
using the ARI standard blower.

On the issue of removing supply fan power when it is included in HSPF, 
SEER, or EER, there is the question of whether it should just be removed 
from the electrical input, or also as a heat gain.

I would appreciate your comments on these relationships and references 
to any other publications that address these issues.

Andy Lau
Associate Professor of Engineering
(814) 863-9075, andylau at psu.edu
www.cede.psu.edu/~andylau

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