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Following is an example using the heat load form:
A space to be conditioned is part of a house geographically
located in an area where the lowest outdoor ambient winter
temperature is 40°F. The calculated heat loss is 184 BTU/
Hr./°F.
Subtract 40°F (lowest outdoor ambient temperature for the
geographical location) from 70°F (inside design temperature
of the unit) for a difference of 30°F. Multiply 184 by 30 for a
5500 BTU/Hr. total heat loss for the calculated space.
On the graph, plot the base point (70°) and a point on the
40°F line where it intersects with the 5500 BTU/Hr. line on
the left scale. Draw a straight line from the base point 70
through the point plotted at 40°F. This is the total heat loss
line.
Knowing that we have a 5500 BTU/Hr. heat loss, and
we expect that our heat pump will maintain a 70°F inside
temperature at 40°F outdoor ambient, we plot the selected
unit capacity BTU/Hr. of the unit between 35° and 60° on the
graph and draw a straight line between these points. Where
the total heat loss line and the unit capacity line intersect,
read down to the outdoor ambient temperature scale and
fi nd that this unit will deliver the required BTU/Hr. capacity
to approximately 30°F.
The heat load form on the following page may be used by
servicing personnel to determine the heat loss of a conditioned
space and the ambient winter design temperatures in which
the unit will heat the calculated space.
The upper half of the form is for computing the heat loss of
the space to be conditioned. It is necessary only to insert
the proper measurements on the lines provided and multiply
by the given factors, then add this result for the total heat
loss in BTU/Hr./°F.
The BTU/Hr. per °F temperature difference is the 70°F
inside winter designed temperature minus the lowest outdoor
ambient winter temperature of the area where the unit is
installed. This temperature difference is used as the multiplier
when calculating the heat loss.
The graph shows the following:
Left Hand Scale Unit capacity BTU/Hr. or heat loss
BTU/Hr.
Bottom Scale Outdoor ambient temperature, base
point.
Heat Pump Model BTU/Hr. capacity heat pump will
deliver at outdoor temperatures.
Balance Point Maximum BTU/Hr. heat pump
will deliver at indicated ambient
temperature.
HEAT LOAD FORM