[bldg-sim] DOE2.1E air source heat pump

Whitehead, Derek dewhitehead at stantec.com
Wed Jul 26 11:44:32 PDT 2006

I am having trouble understanding the behaviour of an air source heat
pump in DOE2.1E and would appreciate any helpful insights. The system
has ample supplementary electric resistance heating capacity, but is
still unable to maintain heating sepoint conditions during cold spells
(typically starting just above the freezing mark) in the early morning
occupied periods (yes, there is a thermostat setback). I have created
hourly reports (all in SYSTEMS), which show:
1. System variable 78 (total heating capacity) is always large - in this
particular case, about 200,000 Btu/h
2. System variable 43 (adjusted capacity of heat pump in this hour)
changes moderately with changes in outdoor air dry bulb - about 40,000
Btu/h when OA temp=32F
3. System variable 166 (output of unit) is the same as variable 43
sometimes, typically when OA temp is about 36 or 37F - if OA temps are
lower, variable 166 values are much lower than variable 43 (down to
about 26,000 Btu/h)
4. System variable 5 (total central coil heating energy input) typically
matches variable 166 in more moderate OA temps, but greatly exceeds this
variable when OA temps are lower than about 38F (reaching a peak of
about 75,000 Btu/h)
5. Zone variable 48 (supplemental heat load for zone's heat pump this
hour) is always zero.
Some questions that come to mind:
1. Does the adjusted capacity of the heat pump (var. 43) not include the
effect of the defrost cycle? Is this why the output of the unit (var.
166) is lower?
2. What does variable 5 represent? Does it include supplemental electric
resistance heating? Defrost energy? (in this case, defrost type is
resistive, the default)
3. Can zone variable 48 be trusted? Is supplemental heat being
delivered? If not, why?
For completeness, some pertinent system inputs are shown below.
 MAX-SUPPLY-T          =  110
 HEATING-CAPACITY      =  -54589
 HEAT-SET-T            =  110
 HEATING-EIR           =  0.2762
 HEAT-CAP-FT           =  SDL-C52
 HEAT-EIR-FT           =  SDL-C57
 HEAT-EIR-FPLR         =  SDL-C62
 MAX-HP-SUPP-T         =  40
 HP-SUPP-HT-CAP        =  -170650
 MIN-HP-T              =  23
 DEFROST-T             =  35

I have tried increasing the airflow, but the number of underheated hours
increased. Increasing supplemental capacity has no effect. My apologies
for the length of this email.
Stantec's North Vancouver office relocates as of May 29, 2006, please
note the new address, telephone and fax. The email address remains the
Derek Whitehead
Sustainable Building Analyst
Stantec Consulting Ltd.
1100 - 111 Dunsmuir Street 
Vancouver, BC, V6B 6A3 
Ph: 604-696-8383
Fx: 604-696-8100 
dewhitehead at stantec.com
www.stantec.com <blocked::http://www.stantec.com>  

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