Analysis of Electric Energy Usage in Air Force Houses Equipped with Air-to-Air Heat Pumps Page: 6
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during the clothes-drying process. Such a blower,
when in operation, would increase the infiltration
into the house, and create a heating requirement
that would probably more than offset the jacket
heat loss in cold weather. In summer the clothes
dryer would increase the cooling load somewhat.
For the purpose of this analysis, it was assumed
that the clothes dryer contributed nothing toward
heating the sample houses and that all of the
remainder of the energy used by miscellaneous
devices was converted into heat within the house.
The electric energy used by the electric clothes
dryers at Little Rock Air Force Base was not
metered separately from the other miscellaneous
loads. However, the energy used for this purpose
in 15 sample houses at 3 other airbases where
it was metered separately averaged about 100
kw-hr per house per month. Accordingly, the
energy used for miscellaneous devices in the
houses at Little Rock Air Force Base was cor-
rected by subtracting 100 kw-hr from the monthly
totals reported in each case where the monthly
total exceeded 100 kw-hr.
On the basis of the foregoing assumptions, the
monthly contribution of the electric range, water
heater, and miscellaneous devices to house heating
was determined by the following expression:
kw-hrA= kw-hrR +0.15 kw-hrw+ (kw-hrM- 100)
where kw-hrA is the computed contribution of
all appliances, other than the heat pump, to
house heating in kw-hr/month, kw-hrR is the
metered electric energy use of the electric range
in kw-hr/month, kw-hrw is the metered electric
energy use of the electric water heater in kw-hr/
month, kw-hrM is the electric energy used by
miscellaneous devices in kw-hr/month.
This formula has been used later in this report
for deriving one of the three factors for energy
used per degree-day per 1,000 ft2 of floor area for
the sample houses at Little Rock Air Force Base.
It is recognized that this formula could probably
be improved in accuracy by a careful study of
the heat dissipation characteristics of the various
electrical appliances, as used in a house.
3.3 Correlation of Energy Requirements for
Heating and Heating Degree-Days
Heat requirements for residences of similar
construction in different climates and for different
months in the same climate have often been
compared on the basis of the number of degree-
days occurring in each locality or in each time
period. The heat requirements of houses of
similar size and construction are related to the
length of the exterior walls and to the inside floorarea. In an effort to correlate the energy re-
quirements of the 16 sample houses at Little
Rock Air Force Base during the heating season,
3 different energy-usage factors were determined
for the months of October, November, and
December of 1959 and for January and Februaryof 1960. These factors relate the electric energy
used and the inside floor area for each of the
sample houses to the degree-days and have the
units kw-hr/degree-day (1,000 ft2). The data
involved in determining the factors and the factors
themselves are summarized in tables 5 to 9,
inclusive, for the 5 months studied.
The three energy-usage factors shown in tables
5 to 9 each involved the inside floor area of the
house, but employed different values for the
electric energy used for heating the house or
different bases for computing the degree-days.
The first factor was computed from the electric
energy used by the heat pump plus the contribu-
tion to heating made by all other appliances and
the degree-days related to a 65 oF base. The
second factor was computed from the electric
energy used by the heat pump only and the degree-
days related to a 65 'F base. The third factor
was computed from the electric energy used by the
heat pump plus the contribution to heating made
by all other appliances and the degree-days based
on the difference between the monthly average
indoor and outdoor temperatures.
Degree-days based on an indoor temperature
of 65 'F were determined by one or both of
the following two methods. In one method the
maximum and minimum outdoor temperatures
for each day were taken from the temperature
recorder charts and averaged. Each daily aver-
age was subtracted from the value 65 'F, and all
such differences for the month were added to de-
termine the degree-days for the month. In the
other method the degree-days were determined by
evaluating the hourly differences between the
recorded outdoor temperature and the 65 'F base.
Good agreement was found between the two
methods in the several instances when both
methods were used for a given month.
An examination of tables 5 to 9 indicates that
the methods used to obtain the energy-usage
factors provided reasonable consistency among the
average values for the 2-, 3-, and 4-bedroom
houses as subgroups. Considering all the sample
houses as a group, the second factor, obtained
from the energy consumption of the heat pump
only and the degree-days related to a 65 oF base,
did not differ by more than 13 percent in 4 of the
5 months from the third factor, obtained from the
total energy used for heating and degree-days
based on average indoor-outdoor temperature
difference. For the 5 months studied, the second
energy-usage factor averaged 2.14 kw-hr/degree-
day (1,000 ft2) whereas the third factor averaged
2.20 in the same units for all the sample houses.
The near equality of these two factors indicates
that the total energy for heating, including the
quantity kw-hrA, bore the same relationship to
the degree-days based on indoor-outdoor tempera-ture difference as the heat-pump energy did to the
degree-days based on a 65 oF reference value.
Or in other words, it tends to corroborate the
validity of the 65 'F base for computing degree-
days in relation to the energy used by the heat6
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Achenbach, Paul R.; Davis, Joseph C. & Smith, William T. Analysis of Electric Energy Usage in Air Force Houses Equipped with Air-to-Air Heat Pumps, report, July 13, 1962; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc13244/m1/12/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.