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