Specifications

PRO-C Series
5
605040
80
40
30
20
Dry Bulb Temperature (°F)
60
3020100
10
50
Exhaust Air EA2
-5
20.2
-10
1.5
Humidity Ratio
(grains of moisture per pound of dry air)
38
27
70
Return Air RA
1
Return Air RA
2
Outside Air OA
2
Outside
Air OA
1
Example 1:
The return air condition is 70°F and
25% relative humidity (27gr/lb).
Line RA
1
-OA: No frosting occurs at full recovery
Example 2:
The return air condition is 70°F and
35% relative humidity (38 gr/lb).
Line RA -OA: Frosting occurs at full
recovery at exhaust air condition EA .
Therefore, frost preheat is required
to bring the outside air to condition OA .
2
2
2
Figure 3. Using the psychrometric chart to determine the
need for preheat frost control.
Equation 1. Calculating supply, outdoor, and return air
temperatures and moisture contents.
where
X = dry bulb temperature in °F
-or- humidity content in gr/lb.
-or- enthalpy in Btu/lbs.
Indices
SA = supply air
OA = outside air
RA = return air
X
SA
= {X
OA
- (Efficiency
SA
) (X
OA
- X
RA
)}
3. Determine if Frost Protection is Required
Plotted on a psychrometric chart, the performance of
an enthalpy recovery wheel will form a straight line between
the outdoor air and return air conditions. If this line does not
pass through the saturated line on the psychrometric chart,
or if the leaving exhaust air condition of the wheel is not
below freezing, the wheel will not frost. In general, if the
space is not humidifi ed above 30 percent relative humidity
on extreme winter days and the outdoor design is above 0°F,
then frost protection is probably not required.
Should frost protection be required, three different
methods of frost protection are available on the PRO-C
units.
• Preheat is used as the primary method of frost
protection for the energy wheel in PRO-C units. This
employs an electric heater on the outdoor air intake
to raise the incoming air temperature such that the
operating line of the wheel no longer hits saturation.
This is the preferred method since it requires usually
only about 10°F of preheat to avoid frosting and the
wheel continues to operate at full capacity even at the
extreme conditions.
• The stop/jog economizer can be programmed to
stop the wheel rotation below a preset outdoor air
temperature. This has the disadvantage of introducing
untreated, cold outdoor air to the Carrier unit.
• A frost protection thermostat which turns the PRO-
C unit off below a preset outdoor air temperature is
the third available option. This is generally considered
the least attractive solution since it results in the unit
supplying no outdoor air during low temperature
periods.
4. Determine Dimensional & Electrical
Data
The dimensional data for the PRO-C unit is provided
on page 7. The PRO-C unit is mounted adjacent to the
Carrier unit.
The electrical data is determined on page 13, equation 2
and 3. Since the electrical requirements are a function of the
power source, the desired power source (voltage and phase)
must be known before determining this information. If an
electrical preheater is required, the electrical data should be
increased appropriately by the information given in Table
5, page 14.
Example continued:
Assuming that 240V/1Ø power is available, the minimum circuit
ampacity (MCA) for the motors selected in Step 2 is calculated using
equation 2a on page 13.
1.25 * FLA largest fan motor = 8.6 (1.25*6.9)
+ FLA other fan motor = 6.9
+ FLA wheel drive/accessories = 1.1
------------------------------------------------------------
MCA = 16.6
The maximum circuit overcurrent protection is calculated using
Equation 3 on page 13.
2.25 * FLA largest fan motor = 15.53 (2.25*6.9)
+ FLA other fan motor = 6.9
+ FLA wheel drive/accessories = 1.1
------------------------------------------------------------
MOP = 23.53
5. Summarize Selection Information
A selection summary sheet is provided on page 15
which helps organize the performance data when ordering an
PRO-C unit and simplifi es the design schedule preparation
process.
Example continued:
Summer outdoor air design conditions are 90°F, 110 gr/lb with a
return condition of 75°F, 50% relative humidity (65 gr/lb.)
Using Equation 1, the summer supply temperature and humidity
is calculated as follows:
T
SA
= (90°F - .706 (90 - 75)°F) = 79.4°F
w
SA
= (110 gr/lb - .706 (110 - 65)gr/lb) = 78 gr/lb
Winter outdoor air design conditions are 5°F, 4 gr/lb with a
return air condition of 70°F, 32 gr/lb.
The winter supply air temperature and humidity level is calculated
in the same fashion to give a condition of 51°F and 24 gr/lb.