Product data

129
I Determine heating and cooling requirements
at design conditions.
Given:
Required Cooling Capacity (TC) . . . .164,000 Btuh
Sensible Heat Capacity (SHC) . . . . .120,000 Btuh
Required Heating Capacity . . . . . . .170,000 Btuh
Outdoor-Air Temperature (Cooling). . . . . . . . .95 F
Indoor Entering-Air Temperature
(Cooling) . . . . . . . . . . . . . . 80 F Edb/67 F Ewb
Outdoor Coil Entering-Air Temperature
(Heating) . . . . . . . . . . . . . . . . . . . . . . . . . . 0° F
Indoor Winter Design Temperature . . . . . . . . .70 F
Indoor-Air Quantity . . . . . . . . . . . . . . . 6000 Cfm
External Static Pressure (ESP . . . . . . . .1.30 in. wg
Electrical Characteristics (V-Ph-Hz) . . . . . 230-3-60
Economizer is specified.
Edb — Entering dry bulb
Ewb — Entering wet bulb
II Select unit based on required cooling capacity.
Enter Cooling Capacity table on page 130 at out-
door-entering temperature of 95 F, indoor air enter-
ing at 6000 cfm and 67 F ewb. The 50HJQ016 will
provide a total capacity (TC) of 180,800 Btuh, a
sensible heat capacity (SHC) of 136,400 Btuh and a
total unit kW of 15.88.
For indoor-air temperature other than 80 F edb, cal-
culate sensible heat capacity correction, as required,
using the formula found in Note 3 following the
Cooling Capacities table on page 130.
NOTE: Unit ratings are gross capacities and do not
include the effect of indoor-fan motor heat. To cal-
culate net capacities, see Step V.
III Select electric heat.
Enter the Integrated Heating Capacities table on
page 131 at 6000 cfm. At 70 F return indoor air
and 0° F air entering the outdoor coil, the integrated
heating capacity is 56,800 Btuh with a unit input
kW of 11.36.
The required heating capacity is 170,000 Btuh;
therefore, 113,200 Btuh (170,000 – 56,800) addi-
tional electric heat is necessary.
Determine the additional electric heat capacity in kW.
Enter the Electric Resistance Heater Data table at
230-3-60. The 34-kW heater satisfies the electric
heater requirements.
IV Determine fan speed and motor horsepower
requirements at design conditions.
Before entering Fan Performance table, calculate
the total static pressure required based on unit com-
ponents. From the given and the Accessory/FIOP
Static Pressure table on page 134, find:
Enter the Fan Performance table on page 133. At
6000 cfm and 1.46 in. wg external static pressure,
the fan speed is 1214 and the bhp is 3.95 (interpola-
tion required). The standard motor and alternate
high static drive are suitable.
V Determine net capacities.
Capacities are gross and do not include the effect of
indoor-fan motor (IFM) heat.
Determine net cooling capacity as follows:
Net capacity = Gross capacity – IFM heat
Net sensible capacity = 136,400 – 11,827
= 124,573 Btuh
Determine net heating capacity as follows:
Net capacity =
Gross capacity + IFM heat + Electric heat capacity
= 56,800 + (IFM kW x 3412) + (Elec. kW x 3412)
= 56,800 + 11,827 + (34 x 3412)
= 56,800 + 11,827 + 116,008
= 184,635 Btuh
113,200 Btuh
= 33.2 kW
3412 Btuh/kW
External static pressure 1.30 in. wg
Economizer static pressure 0.07 in. wg
Electric heat static pressure 0.09 in. wg
Total static pressure 1.46 in. wg
2545 Btuh
= 180,800 – 3.95 bhp x
hp
.85
= 180,800 – 11,827
= 168,973 Btuh
Selection procedure (with 50HJQ016 example)
50TFQ004-01250HJQ014,016