Since Florida utilities often experience their
system peak during the state's few cold mornings, understanding
influences on space heat performance is important to controlling demand.
Analysis of heat pump impacts on system load in a large scale monitoring
study have shown large levels of strip heat being used during the winter
morning peak. The implied coefficient of performance of heat pumps
during the system peak hour was only 1.30. Also, analysis of the total
seasonal space heat has shown that the implied Heating Season
Performance Factor (HSPF) of heat pump homes is only 4.4 Btu/W rather
than the 6-8 Btu/W commonly claimed. This paper describes reasons for
the lower than anticipated levels of performance as well as other
significant influences on space heating
A utility load research project by the Florida Power Corporation
(FPC) is monitoring 200 residences in Central Florida. The homes
represent a statistically drawn sample using end-use metering to answer
specific load research questions. A prime objective of the monitoring is
to identify ways in which the winter morning residential peak load might
be reduced within its load management and DSM programs.
As with many utilities, FPC, through rebates, encourages the
selection of heat pumps within its service territory as a means to
reduce the magnitude of the winter morning heating peak. This objective
has largely been realized. Within the statistical sample, 118 homes or
58% possess heat pumps, 32% had electric resistance systems and 9% used
natural gas or oil furnaces. Thus, 64% of electric heating systems in
the service territory are heat pumps. The expectation has been that the
mild conditions of Florida's winter should allow heat pumps to operate
under favorable conditions and provide lower peak demand than electric
Residential Heat Pumps
A residential heat pump takes low-temperature heat from an outdoor
medium (such as air, ground, groundwater or surface water) and
mechanically concentrates it to produce high temperature heat suitable
for heating the interior of homes. Because most of the heat is moved
(pumped) from the outdoor source to the indoor source, the amount of
electricity required to deliver it is theoretically much less than using
electric resistance heat directly.
Heat pumps were introduced to the home heating market in the 1950s,
evolving originally from central air conditioners which featured a
reversing valve and a few other factory components allowing the heat
pumps to provide heat under mild weather conditions. Early models were
plagued with reliability problems related to failed reversing valves,
improperly operating compressors or frost build up on the evaporators.
Performance under colder conditions was often poor due to reduced
heating capacity at low outdoor temperatures. Comfort was another
complaint with early systems due to "cold blow" where the air
temperature delivered by the heat pump was much lower (typically 100 -
105oF) compared with the 125 - 130oF typically
delivered by natural gas furnace systems.
Modern heat pump systems are much more reliable and have become
exceedingly common in Sunbelt states. By far the most common types are
air-to-air heat pumps which use outdoor air as the heat exchange medium.
The problems with inadequate capacity and "cold blow" have been reduced
by the addition of auxiliary resistance strip heat systems with a
two-stage thermostat. As the indoor temperature drops, the first stage
activates the heat pump; the second stage below it activates auxiliary
strip heat. Under this regime, both the heat pump and the resistance
heat operate together until the thermostat is satisfied.
The theoretical Carnot efficiency of heat pumps is greater than
2000%. Thus, the COP, or coefficient of performance, would indicate 20
times as much heat delivered as used. However, the practical efficiency
of the best air-to-air heat pumps produce COPs of 3.0 or less. Because
COP varies with the outdoor temperature, a heating season performance
factor (HSPF) is determined which takes into account operation under
varying outdoor temperatures as well as part load impacts (effects of
running short cycles under mild conditions, coil defrost, etc.). HSPF is
rendered as Btu/Watt so that typical values are on the order of 6.8 - 8
Btu/W.(1) Older systems may have HSPFs of 6 - 7
In the past, utility DSM programs have strongly leaned on heat pumps
to reduce winter peak coincident demands. Reductions in peak demand over
the use of strip heat have often estimated savings of 50 - 70% even when
allowance for supplemental strip heat use was made (AEC 1993).
Unfortunately, most previous studies examining heat pump performance
have ignored how operation and system related factors can influence
Empirical Tests of Heat Pump
As heat pump technology re-emerged in the early 1970s, a number of
evaluations were performed. Many laboratory studies were conducted under
steady state conditions to evaluate impacts of defrost, crankcase heat
and other influences (eg. Parker et al. 1977; Rettberg 1980).(2) It has been long known that even with
a constant thermostat setting and optimal system operation that as the
building loads exceed the declining capacity of the heat pump with lower
temperatures that the difference must be made up with resistance heat
and this will impact overall efficiency (Reddy and Daniels 1992).
However, few studies have examined how heat pumps operate in real homes
where thermostat settings are altered, indoor coil air flow may be lower
than expected and refrigerant charge may vary from an optimal
Many of the early investigations did show that heat pump performance
was lower than would be expected by the procedures established to
estimate HSPF. In a study for Louisiana Power and Light Company, Orth et
al (1976) performed alternate day resistance heat measurements on two
1967 vintage heat pumps and found seasonal coefficient of performance
(SCOP) measurements of 1.75 and 1.78 for the systems against the
standard seasonal SCOP rating of 2.25 based on manufacturer's data. In
the colder climate of New Jersey, Nicolich (1977) estimated the SCOP of
a single heat pump to be 1.65 based on pre and post measurements. In the
much colder climate of Ontario, Canada, 40 heat pumps were monitored in
detail showing average SCOPs of 1.43 over the heating season from
1975-1977 (Miller and Jaster, 1985). Similarly, a large study by Carrier
Corporation (Groff et al. 1978) showed average seasonal COP values of
1.2 to 1.61 in the Boston and Minneapolis climates.
However, even in moderate climates, performance may be less than
anticipated. Four residences in Albuquerque, New Mexico had heat pump
performance evaluated through alternate day resistance heat operation.
This showed SCOPs averaging only 1.39 as opposed to the HSPF calculation
which indicated a COP of 1.85. The study determined that homeowner
operation of thermostats was largely responsible for the lower than
expected savings. Another study in Knoxville, Tennessee of two heat
pumps (Baxter 1981) yielded measured SCOPs of 1.58 and 1.99 respectively
against calculated SCOPs of 1.99 and 2.61.
In summary, although there is justification for the DOE test
procedures that predict heat pump seasonal performance (Miller and
Jaster 1985), there is reason to suspect that the actual achieved
seasonal COPs are significantly lower than suggested by HSPF
Thermostat Setback and Electrical Heating
A number of studies stretching back to the early 1970s show that
substantial energy savings can be achieved through the use of thermostat
setbacks with heating systems (Nelson 1973; Pilati 1975). Both computer
simulation as well as experimental testing has confirmed the savings of
night setback of heating systems with constant capacity (Quentzel 1976).
Measured seasonal energy savings are on the order of 10-15% - greater in
milder climates. However, the same studies have highlighted the increase
in morning heating pick-up load. Although this is unimportant for
natural gas or oil furnaces, the same is not true for electric
resistance forced air systems where utility peak coincident demand may
be significantly elevated during the morning set-up period.
The impact of thermostat set back on energy savings with heat pump
systems is much less clear. This is due to the fact that the thermal
performance of the heat pump is not independent of the house heating
load. The heating capacity of an air-to-air heat pump drops with lower
outdoor temperature while the house thermal load increases. If the heat
pump capacity drops below the building thermal load, the lower
efficiency supplemental electric resistance heaters must make up the
difference. This issue became evident in early test results from heat
pumps in northern climates. However, an early hourly simulation analysis
with a detailed heat pump model (Ellison 1977) revealed that while peak
morning heating loads were increased by up to 100% (~4 kW for a three
ton heat pump in Atlanta) during the morning pick-up hour, the homeowner
would realize energy savings of 7 - 15% for a 60oF setback
and 10-18% for a 55oF setback.
In spite of the simulation results, field information gathered by
utilities in the cold winter of 1976-1977 suggested that setting back
heat pump thermostats would lead to elevated consumption and greatly
increased demand (Air Conditioning, Heating and Refrigeration News
1977). Contrasting the earlier ORNL analysis was another done by the
Carrier Corporation (Bullock 1978). This study concluded that the
savings from thermostat setback with heat pumps was modest (2 - 4%) or
even negative, largely depending on the installed capacity of the strip
heaters. Since resistance heat elements are often installed in 5 kW
increments and are typically larger than those assumed in the ORNL
evaluation, this becomes a significant limitation in its conclusions. In
contrast, the Carrier study concluded that a setback more than a couple
of degrees (oF) with a heat pump will lead to only small
seasonal heat energy savings while producing very high morning power
For instance the Carrier evaluation for a mild 44oF day in
Minneapolis, similar to the coldest winter day in Orlando, showed a
daily heating energy consumption for a typical home of 22.8 kWh for no
setback with approximately 2 kW of demand at 7 AM. However, a
10oF setback with morning setup at 7 AM, lead to a daily
reduction in heating energy of 2.4 kWh (10%), but with an increase of
total electric demand of 9 kW!(3) The study concluded that setbacks
should not be used with heat pumps until adaptive thermostat technology
was fully developed.
Florida's Mild Winter
Florida's warm winters would seem ideal for heat pump application.
Florida weather is not commonly thought of as possessing a winter. While
not having a long heating season, it does have short and sporadic space
heating which is very much concentrated during a few cold mornings. The
magnitude of residential space heating in Central Florida is small
relative to more temperate climates. Since Florida's "winter"
temperatures are often very close to the desirable interior thermostat
setting, residential heating loads are very dependent on weather.
The first three winter months of 1999 during which the data were
collected were mild (Table 1). The average temperatures were about
two degrees warmer than the 30 year normals, although the extreme
minimums and maximums were in line with the typical expectation. The
heating degree days, which may approximate energy use, show that while
cooling degree days were similar to the normals (84%), heating degree
days were under 60% of the thirty year normals.
Table 1. Comparison of 1999 Winter Weather with 30 Year
Dry bulb ( +
||63.9 (+ 4.2)
||109 (-125) | 82 (+12)|
||64.0 (+ 2.8)
||92 (-72) | 69 (+11)|
||64.6 (- 2.1)
||61 (-4) | 54 (-63)|
||262 (-201) | 205 (-40)|
|30 Yr Norm
A unique part of the FPC project is that outdoor temperatures are
being collected at each of the 204 sites. This allows analysis of how
temperatures around the homes vary by region and local microclimate. The
temperature data collected in the project mirrored weather data taken at
Orlando International Airport, although there are greater extremes with
respect to individual sites. The 15-minute average air temperature and
space conditioning demand for all sites for January - March of 1999 are
graphically illustrated in Figure 1.
Figure 1. Comparison of average outdoor
temperature with space conditioning loads.
The key evidence seen in Figure 1 is that Florida's winters are
exceedingly mild with very short cold snaps that feature intense
electric demand for very short periods. These loads are very
disadvantageous to serve as they have very short duration with the peak
generation capacity unneeded for much of the year. Evidence of space
cooling is even seen in the data for the warmer period around January
An important influence is seen in Figure 2 which displays a histogram of heating
degree days at a 55oF base when plotted against time for
Central Florida weather over the winter of 1999. Note the concentration
of heating in the morning hours between 5 and 8 AM when nighttime
thermostat set-backs are often setup. For heat pumps, this means that
much of the heating occurs during periods which electric resistance heat
will be required if thermostats are adjusted.
Heating Energy Use
Space heating energy use was recorded for each site and then averaged
into the mean space heat across the residential sample. Since some
cooling occurred at a number of sites during the period, an outdoor air
temperature of 65oF was used as the dividing line between
heating and cooling. As shown in Figure 3, the
outdoor temperature does remarkably well describing when the average
customer ceases to require space heat. However, the same trend shows
that the demand for space heat is non-linear. It is quite steep from 30
to 50 degrees, but becomes flat and nearly asymptotic as 65oF
is approached. A regression based on ambient air temperature
(Tamb) below 65oF adequately predicted average
hourly space heating demand for the overall sample:
The function is superimposed on the plot in Figure 3. Much of the
remaining scatter is explained by systematic differences with time of
day. For instance, much of the data higher than the regression line is
during nighttime hours. Much of data is lower during the afternoon
period. This suggests a non-temperature related component of space heat
- likely solar gains. The function can be used with simple weather data
to predict typical household heating loads.
When applied to TMY weather data for Orlando for the "typical"
January - March, the regression predicts 658 kWh. When applied to the
entire year of TMY data including November and December, it predicts the
typical Central Florida residential site would have used 1092 kWh for
space heat under average weather conditions. The regression also
predicts that for an hour when the outside air temperature is
40oF the per site heating demand the utility service
territory will average 2.27 kW, when the outside air temperature is
30oF, it will average 4.41 kW.
Space heat was estimated for each site based on recorded electricity
use on the space heat circuits when the outdoor air temperature was
lower than 65oF. Gas heated sites were not included in the
evaluation. The average measured space heat for all FPC sites from
January through March of 1999 was 616 kWh. However, consumption varied
by two orders of magnitude, ranging from a low of 22 kWh to a high of
2,283 kWh. Figure 4 shows a histogram of the frequency distribution of
measured space heat energy use.
Figure 4. Histogram of Jan-Mar space heating.
The low consumption level was at Site 104 where the occupant allowed
wide indoor temperature swings without space heat. On the coldest
morning of January 6th, the household allowed the interior to
reach 60oF with no space heat. The highest space heat
consumer was Site 138 where strip heat is used and the occupants claim a
desirable winter heating set point of 80oF. Auditors also
observed evidence of significant duct leakage at this site. The summary
statistics on space heating in Table 2 reveal several findings:
- Heat pumps reduce both energy and peak demand, but not by half
- Larger homes and older homes have greater energy use and demand
- Added ceiling and wall insulation show lower use and demand
- Homes with interior air handlers had much lower demand
- Large areas of single pane glass are associated with increased
- Better insulated glass is correlated with lower peak demand
- Installed heating system capacity is strongly associated with peak
Table 2. Impact of Selected Characteristics on Space Heat
Energy Use and Demand.
||< 1600 ft2
||< 9 kW
> 9 kW
|Jan. 5th Interior Temp.:
|Air Handler Location:
|Ceiling Insulation (R-value):
||< 20 hr ?
> 20 hr ? ft2 F/Btu
|Wall Insulation (R-value):
||< 4 hr ? ft2 F/Btu
> 4 hr ? ft2
> 200 Btuh/oF
< 200 Btuh/oF
* Significantly lower at a 90% level
Significantly higher at a 90% level
The increased consumption of larger homes and expanses of single
glass is readily explained by heat transfer theory. In fact, all the
building surface areas divided by the R-values of the audited components
were significant in their impact on measured space heating and demand.
On the other hand, the elevated demand of older homes likely arises from
the confounding influences of greater saturation of electric resistance
heating and lower insulation.
A key finding, however, is the ratio of heating energy use in
electric resistance homes (757 kWh) to that in heat pump homes (589
kWh). The implied seasonal heat pump coefficient of performance is only
1.29 with a high degree of significance. The differences in the peak
demand of the two systems (779 W or 23%) was even less pronounced - and
much less than the 50% or greater reduction that might be expected. The
implied peak performance of heat pumps compared with electric resistance
systems was 1.30.
Heating Thermostat Behavior
One of the most interesting findings was the way in which thermostat
settings influence energy use and demand. Occupant reported thermostat
settings did not well characterize measured space heating consumption,
although the recorded interior temperature showed strong correlation
with space heating demand. For instance, the measured average interior
temperature during a cold snap was significant not only at predicting
the site peak demand the following morning, but also of characterizing
space heating use over the entire winter season.
Also important was the measured "pickup" load on January
4th - 5th. This was estimated as the difference
between the measured interior temperature at 8 AM on
January 5th from the recorded temperature four hours
earlier at 4 AM. The "pickup" load is analogous to the thermostat setup
during early morning hours after allowing it to drop during the
Some 115 project homes had a less than 0.5oF pickup. For
the most part these homes had a relatively constant thermostat setting
with a few allowing the temperature to fall throughout the night and
depart during the morning hours without setting back the thermostat. In
these homes, the average space heat demand between 7 and 8 AM was 2.33
A total of 48 households practiced a 'deep thermostat' setback during
the evening hours with the temperature set up in the early morning
hours. The average temperature recovery or "pickup load" between 4 and 8
AM was 3oF. While these households did reduce their total
space heating energy by about 14% (Figure 5), this practice dramatically increased
space heat demand during the utility coincident period. The average
hourly demand in this group of homes was 3.19 kW during the peak time
frame. The difference in diversified demand (0.86 kW) was significant at
the 99% confidence level. A third of the monitored sample use deep
setback, suggesting that deep thermostat setbacks with a morning setup
may be responsible for up to 300 MW in increased utility peak load.
To better understand this problem, it is useful to examine a heat
pump case with strip heat demand. Figure 6 shows the heating demand profile at
Site 2 on the coldest day of the year (January 5th).
The programmable thermostat at this site raises its setting at 7 AM
by 2oF. This activates the strip heat for a single 15 minute
cycle after which the strip drops off and the heat pump properly returns
to compressor operation (~4 kW with air handler). Many sites showed
similar behavior. With thermostat set-up with heat pumps, strip heat
will be used on cold mornings.
Winter Peak Demand
The utility winter peak for 1999 occurred between 7 and 8 AM on
January 6th. The minimum temperature at the Orlando
International Airport was 31oF at 7 AM. Figure 7 shows
that the total electric demand for a one hour period averaged 5.74 kW in
the 114 all-electric non-load control sites with valid data (22 sites
had missing data or were not yet on-line). The importance of the heating
load to total peak demand is seen in the end-use component summary in Figure 7.
Figure 8 shows a frequency distribution of
hourly space heat demand for all sites on the morning of January
5th, 1999. This was the coldest non-load controlled day.
Although space heat demand averaged 3 kW between 7 and 8 AM, 20% of
customers used no space heat at all, while some sites had demand as
great as 12 kW.
The significance of heating system type on peak demand is seen from a
segmentation of the data. Within the sample of 204 homes, 60% were heat
pumps (the most common type), 33% were strip heat with the balance using
natural gas, fuel oil or propane. Several homes (Sites 077, 161,166,
172, 175) had window units with either strip heat or a reversible heat
pump. Sites 16, 19, and 201 have fuel oil heat. A number of houses (8%)
also reported using either portable space heaters of either the electric
or kerosene type.
Heat Pump Performance
On January 6th, non-load controlled homes with heat pumps
experienced an average total household electric demand of 5.11 kW during
the peak hour as opposed to 6.63 kW in homes with electric resistance
heating. As expected, homes using strip heat showed almost all of the
activity on the air handler circuit (4.66 kW; n = 43). Surprisingly,
however, the 68 homes with heat pumps showed a large amount of back-up
strip heat on the air handler circuit (1.70 kW), averaging more
than that recorded on the compressor side (1.61 kW). A significant
number of homes with heat pumps showed coincident demand on the air
handler side greater than 7 kW indicating that a large capacity of
back-up strip heat is installed.
Three sites showed evidence of improper operation with emergency heat
being commonly activated during morning heating. This may be due to
misunderstanding about proper heat pump operation and/or choice of this
mode due to insufficient recovery time or discomfort. Figure 9 illustrates improper heat pump
operation at Site 99. There were other physical problems in several
sites which led to strip heat operation. Site 88 had a non-functional
compressor and sites 55, 68, 102, and 117 had an improper thermostat
installed so they operate as if they were a strip heat system.
More problematic, however, is the impact of thermostat setup on heat
pump performance. When these are reset and cannot meet load, internal
control logic on adaptive control type thermostats often activate
emergency strip heat.(4) Heat pumps controlled by conventional
analog-type mercury-bulb bi-metal thermostats will be triggered into
strip heat if the thermostat is adjusted more than 2oF away
from the current temperature. Since most set-backs and set-ups are more
than 2oF, strip heat will be required during the period
subsequent to thermostat set-up. Also, some heat pumps feature a time
delay which allows strip heat and the air handler fan to operate for
some time after the thermostat has stopped calling for heat. Finally,
misinformed or frustrated customers may activate "Emergency Heat" on the
thermostat which moves the heat pump into directly strip heat mode.
Although homes with heat pumps used less
heating energy during the monitoring period, the demand characteristics
of these systems were disappointing when compared against electric
resistance types. Figure 10 shows the average performance of
these systems. To further examine the issue, we segmented the
performance of heat pump systems on the coldest non-load control day
(January 5, 1999) by their relative strip heat use. Examining the
performance plot for each individual system we found that 62 of 99
systems (63%) showed fair to good performance with large levels of
compressor operation (27.1 kWh) and relatively little strip heat the air
handler circuit (7.3 kWh).
By comparison, some 33 systems (33%) showed very high levels of strip
heat consumption (36.4 kWh) compared with compressor (20.4 kWh). The
averages for these systems are shown in Figure 11. Total space heating energy for the
day varies significantly: 57 kWh for the group using considerable strip
heat against 34 kWh for the group using mainly the heat pump
Even more revealing are the recorded average interior air
temperatures in the two groups. Whereas the group with superior heat
pump operation maintained more constant temperatures on average, the
group with large levels of strip heat allowed large fluctuations from
the evening to morning temperature, suggesting a greater degree of
nighttime setback. In general the group practicing more even temperature
control also achieved better comfort with lower total consumption. For
instance, between 7 and 8 AM, the group with good heat pump operation
showed a demand of 2.24 kW against 3.53 kW for the group with excessive
strip heat use. At the same time, the households with better heat pump
operation maintained 70.3oF inside against the
69.0oF in the homes using considerable strip heat. Although
thermostat setback (strip heat) is a large factor explaining poor
performance, there are other reasons. Examination of data from
individual sites suggested resistive coil defrosting was responsible for
a portion of the shortfall.
Also, previous assessments have shown that low air handler airflow
can significantly reduce heat pump capacity with all of 27 audited
forced air installations exhibiting this problem (Parker, et al., 1997).
Improper refrigerant charge has also been identified as a large issue in
many heat pump installations which adversely impacts performance
(Proctor, 1997; Blasnik et al., 1996). Finally, there are the issues of
installation of non-heat pump thermostats on heat pump systems as well
as inappropriate use of "emergency heat." Such factors reduce the
efficiency of heat pumps relative to electric resistance systems. Our
findings suggest several opportunities for improving heat pump
- Load control could concentrate on interrupting strip heat on homes
with heat pumps so that they may not be operated during the control
- Adaptive recovery thermostats to reduce the frequency of strip
heat through slowly staged thermostat set-ups.
- New construction and heat pump installation programs could limit
the installed capacity of back-up strip heat to no greater than that
suggested by Manual J.
- Heat pump tune-up programs which correct low indoor unit airflow
and incorrect refrigerant charge should improve heat pump capacity and
reduce strip heat use.
A utility load research project is monitoring 200 residences in
Central Florida. Since the utility experiences its annual system peak
during Florida's few cold mornings, the performance of heat pump systems
is important to controlling demand. Similarly, the mild conditions of
Florida's winter should allow heat pumps to operate under favorable
Compressor and air handler/strip heat energy demand was measured
separately in each home along with interior temperature. Data analysis
revealed a pronounced impact of auxiliary electric resistance strip heat
on site-achieved heat pump efficiency. Households practicing a
temperature setback followed by a morning setup (approximately a third
of the sample) showed large levels of strip heat during morning
operation, significantly reducing overall coefficient of performance
(COP). Further, approximately 5% of audited households had a non-heat
pump thermostat so that such systems operated exclusively in strip heat
mode. Other customers operated the thermostat into "emergency heat" mode
which exclusively uses strip heat.
Based on comparative analysis of the large samples, the implied
coefficient of performance of heat pump to electric forced air furnace
homes during the system peak hour was only 1.30. Also, analysis of the
total seasonal space heat has shown that the implied Heating Season
Performance Factor (HSPF) of heat pump homes is only 4.4 Btu/W rather
than the 6-8 Btu/W commonly claimed. Suggestions are made on methods to
improve the performance of heat pumps under peak
AEC. 1993. Engineering Methods for Estimating the Impacts of
Demand Side Management Programs, Vol. II, TR-100984, Palo Alto, CA:
Electric Power Research Institute.
Air Conditioning, Heating and Refrigeration News. 1977.
"Utility says don't set back heat pump thermostats in winter,"August,
Baxter, V.D. 1981. ACES: Final Performance Report December 1, 1978
through September 15, 1980, ORNL/CON-64, Oak Ridge, TN: Oak Ridge
Blasnik, M. , Downey, T., Proctor, J. and Peterson, G. 1996.
Assessment of HVAC installation in New Homes in Arizona Public
Service Company Territory, Final Report, San Rafael, CA: Proctor
Bullock, C. 1978. "Energy Savings Through Thermostat Setback with
Residential Heat Pumps," ASHRAE Transactions, Vol. 84, 2:
352-363, Atlanta, GA: American Society of Heating, Refrigeration and Air
Ellison, R.D. 1977. "The Effects of Reduced
Indoor Temperature and Night Setback on Energy Consumption of
Residential Heat Pumps," ASHRAE Journal, Atlanta, GA:
American Society of Heating, Refrigeration and Air Conditioning
Groff, G.C., Bullock, C.E. and Reedy, W.R.
1978. "Heat Pump Performance Improvements for Northern Climate
Applications," 13th Proceedings of the Intersociety
Engineering Conversion Conference, San Diego, CA.
Miller, R.S. and Jaster, H. 1985. Performance of Air Source Heat
Pumps, General Electric Company EM-4226, Palo Alto, CA: Electric Power
Nelson, L.W. 1973. "Reducing Fuel Consumption with Night Setback,"
ASHRAE Journal, Feb., Atlanta, GA: American Society of Heating,
Refrigeration and Air Conditioning Engineers..
Nicolich, M.J. 1977. "Residential Heat Pump
Use: Saving Electrical Energy," ASHRAE Journal, Vol. 19, No. 12,
Atlanta, GA: American Society of Heating, Refrigeration and Air
Orth, Jr., L.M., and Hamilton, D.C. 1976.
Thermodynamic and Economic Analysis of Improved Residential Climate
Control Systems, Louisiana Power and Light Co., Dept. of Mechanical
Engineering, Tulane University, Aug. 1976.
Parker, D.S., Sherwin, J.R., Raustad, R.A. and Shirey, III, D.B.
1997. "Impact of Evaporator Coil Airflow in Residential Air-Conditioning
Systems, ASHRAE Transactions, Vol. 103, Part 2, Atlanta, GA:
American Society of Heating, Refrigeration and Air Conditioning
Pilati, D.A. 1975. The Energy Conservation Potential of Winter
Thermostat Setback and Energy Savings, ORNL-NSF-EP-80, Oak Ridge,
TN: Oak Ridge National Laboratory.
Proctor, J., Downey, T., Blasnik, M., and Peterson, G. 1997.
Residential New Construction Project in Nevada Power Company Service
Territory, EPRI TR-108445, Palo Alto, CA: Electric Power Research
Quentzel, D., 1976. "Night-time Thermostat Setback: Fuel Savings in
Residential Heating," ASHRAE Journal, March, Atlanta, GA:
American Society of Heating, Refrigeration and Air Conditioning.
Reedy, C.S. and Daniels, S.A., 1992. "Analysis of Heat Pump
Performance in the Northeastern U.S.A.," Proceedings of the
27th Intersociety Energy Conversion Engineering
Conference, Vol. 3, Society of Automotive Engineers, IECEC-92, San
Diego, CA, 1992.
Rettberg, R.J. 1980. "Cooling and Heat Pump Heating Season
Performance Effects Evaluation Models," ASHRAE Transactions, Vol.
86, Pt. 1, Atlanta, GA: American Society of Heating, Refrigeration and
Air Conditioning Engineers.
1. Since a Watt contains 3.413 Btu by
definition, an HSPF of 6.8 - 8 implies a seasonal COP of 2.0 to 2.3.
2. Percentage increases to measured seasonal
heat pump energy consumption associated with evaporator defrost vary
from a low of 2% (Orth et al. 1976) to a high of 15% (Cattell 1976).
3. The assumed strip heat capacity was 10 kW
for a three ton heat pump system.
4. Adaptive control thermostats (programmable
or digital) recursively determine if the heating system can recover 1
oF every six minutes. If not, strip heat is
2000 ACEEE Summer Study on
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