Installation guide

Example: A PDX442080 is installed in a residence where
the electrical utility cost is 9 cents per kilowatt-hour and the
gas cost is 90 cents per therm. Proceed as follows:
1. $.09/$.90 = .1
2. Using Figure 10, a PDX342080 with a .1 cost ratio =>
Economic Balance Point Temperature = 20°F
Some utilities have asliding cost based on consumption. In
this case, take the total bill and divide by the total
consumption to determine the average utility cost.
Some natural gas suppliers sell gas by every 100 cubic feet
(CCF) of gas. For an approximate gas cost per therm,
multiply CCF by 97. Example: A price of $.01 per CCF is
approximately equivalent to $.97 per therm.
Note: The 97 multiplier is based on a typical heating
value of 1030 Btu per cubic foot of natural gas. For a
more accurate cost, contact your gas supplier to obtain
the Btu content of natural gas in your area. Divide
100,000 by the actual Btu content per cubic foot to obtain
the correct multiplier.
If the economic balance point is chosen, keep in mind that
utility rates fluctuate substantially over time. Review
monthly utility bills and re-calculate economic balance
)oints as necessary.
11 I Load Balance Point
m
Figure Temperature
I
Load Balance Point Temperature
The load balance point temperature is the outdoor
temperature at which the load may be met using either heat
pump mode or gas heat mode. Ifthe outdoor temperature is
above the load balance point temperature, the demand for
heat may be met using the heat pump mode. If the outdoor
temperature is below the load balance point temperature,
the gas heat mode is required to meet the building load.
To find the load balance point temperature, a load
calculation must be performed on the building. The load
calculation must be performed at 3 different outdoor
temperatures and graphed on Figure 11. Plot the three
load calculations at their appropriate outdoor temperatures
and draw a smooth line through the 3 points. NOTE: The
line connecting the 3 points may not be a straight line.
Locate where the building load line intersects the
appropriate model capacity line. This is the load balance
point temperature.
No matter what the balance point temperature is set at, the
unit will automatically switch to gas heat if the heat pump is
not able to meet the demand of the house. Calculating the
load balance point temperature and programming it into the
thermostat will minimize temperature fluctuations in the
house.
Load Balance Point Temperature
10 20 30 40 50 60
Outdoor Air Temperature (F)
7. DUCTWORK
Ductwork Sizing
The maximum recommended velocity in trunk ducts is 1000
feet per minute. The maximum recommended velocity in
branch ducts is 800 feet per minute.
Ductwork sizing affects the discharge temperature, airflow
velocity, and efficiency of the system. Be sure to properly
size ductwork to the capacity of the unit and to the airflow
requirements of the conditioned space. Failure to properly
size ductwork can result in inadequate airflow and poor
efficiency. Undersized ductwork may result in tripped limit
controls and premature failure of compressors, motors and
other components.
Ductwork Insulation
Ductwork installed outdoors must have a minimum 2" thick
fiberglass "wrap" insulation and a weatherproof vapor
barrier installed around it. The insulation and vapor barrier
must be protected against potential damage. Caulking,
flashing, and other means of providing a permanent
weather seal must be used.
Ductwork Connections
The use of flexible, non-combustible connectors between
main trunk ducts and supply and return air plenums is
permitted. If flexible connectors are used, they should be
protected from potential mechanical damage such as
punctures and tears.
NOTE: When connecting the supply and return plenums to
the unit, make sure that the plenums are sealed against the