[Equest-users] Excessive Heating Savings

[Eddie Corwin]

My first guess would be to look into the residential systems further.  Read 
the topic on this particular system in the help file.  As far as I can remember, 
this system will automatically, reduce the set point temperatures, and flow 
rates (or something similar) based on the occupancy.  This can provide 
significant savings, especially if you have a low occupancy rate.  So I would 
start from there. If you attach you input file, we (the online community) can 
take a look at it hopefully find the true issue.  


-Eddie



________________________________
From: Robert Stephenson <rstephenson at southface.org>
To: equest-users at lists.onebuilding.org
Sent: Mon, November 8, 2010 2:25:18 PM
Subject: [Equest-users] Excessive Heating Savings

 
Hello All,
 
I am having some issues with modeling the heating and cooling systems in 
mid-rise multifamily buildings. I have a number of these projects and they all 
use similar and fairly simple systems, a single split system heat pump serving 
each dwelling unit. When modeling these projects I have followed the guidelines 
from Appendix G with additional guidance from the ENERGY STAR High Rise 
program’s simulation guidelines. No matter the project location, I am getting 
heating savings that seem very out of whack with the upgrades made in the 
proposed design (higher efficiency HVAC, better windows, upgraded insulation, 
etc.), the particular model I am looking at now has heating savings over 90%.
 
An outline of my system inputs follows. I developed this approach based on the 
guidelines discussed above, past listserv discussions, and the input of other 
local energy modelers.
 
Proposed Model
·         System type set to Residential System 2
·         System capacities based on actual design
·         Electric Input Ratios
o   Cooling
EIR=((1/(SEER*0.778+1.4)-0.012167)/((1/3.413)+0.012167)
SEER 14 yields 0.227 CEIR
o   Heating
EIR= (1/((HSPF*0.28+1.13)*3.412)-0.012167)/((1/3.412)-0.012167)
HSPF 7.7 yields 0.274 HEIR
·         Fan Power set to zero given that fan power is accounted for in SEER 
and HSPF efficiency ratings
 
Baseline Model
·         System type set to PTHP, Packaged Terminal AC with heat pump heating, 
per Appendix G and ENERGY STAR simulation guidelines.
·         System capacities set by equest, 15% oversized for cooling and 25% for 
heating
·         Electric Input Ratios
o   Cooling
EER per 90.1: EER = 12.3-(0.213*Cap/1000)
Capacity set to 15,000 Btu/hr yields 9.1 EER
EIR= (1/EER-0.012167)/((1/3.413)+ 0.012167)
Yields 0.32 CEIR
o   Heating
EIR= 3.2-(0.026*Cap/1000)
Capacity set to 15,000 Btu/hr yields 2.81 COP
EIR=1/COP
Yields 0.356 HEIR
·         Fan Power set to zero given that these are packaged units
 
Outside air rates, infiltration levels, and supplemental heating are set 
identically in both models. The only other issue of note is that the proposed 
design has unit heaters (electric resistance heat) in the stairwells, which I 
have modeled as PTHPs in the baseline design with heating only. I would assume 
this would be a loss for the proposed design, though negligible, given the 
increased efficiency of the PTHPs versus electric resistance, but I’m not seeing 
that reflected in the results.
 
If anyone has advice on what I might be missing I would appreciate it. Tips on 
places to check myself in the .sim file would also be great.
 
Thanks in advance,
 
Robert Stephenson, LEED AP 
Project Manager, Residential Green Building Services
Tel: 404-604-3589
Fax: 404-872-5009
Email: rstephenson at southface.org
Web: www.southface.org
241 Pine Street NE, Atlanta, GA 30308
 
Building know-how for a sustainable future
 
Get involved with Southfacetoday!
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