SELECTION PROCEDURE (with example)
I DETERMINE COOLING AND HEATING REQUIRE-
MENTS AT DESIGN CONDITIONS:
Given:
Required Cooling Capacity (TC) . . . . . . . . . 172,000 Btuh
Sensible Heat Capacity (SHC) . . . . . . . . . . 133,000 Btuh
Required Heating Capacity . . . . . . . . . . . . . 170,000 Btuh
Outdoor Entering-Air Temperature . . . . . . . . . . . . . . 95 F
Indoor Entering-Air Temperature
(Cooling) . . . . . . . . . . . . . 80 F entering dry bulb (edb)
67 F entering wet bulb (ewb)
Outdoor Coil Entering Air Temperature (Heating) . . . 0° F
Indoor-Air Winter Design Temperature . . . . . . . . . . . 70 F
Evaporator Air Quantity . . . . . . . . . . . . . . . . . . . 6000 cfm
External Static Pressure (ESP) . . . . . . . . . . . 0.75 in. wg
Electrical Characteristics (V-Ph-Hz) . . . . . . . . . . 230-3-60
II SELECT UNIT BASED ON REQUIRED COOLING
CAPACITY:
Enter Gross Cooling Capacities table on page 9 at outdoor
entering-air temperature of 95 F, indoor air entering at
6000 cfm and 67 F ewb. The 542F unit will provide a total
cooling capacity of 185,400 Btuh and a sensible heat ca-
pacity of 146,700 Btuh.
For indoor-air temperature other than 80 F edb, calculate
sensible heat capacity correction, as required, using the
formula found in Note 3 following the cooling capacities
table.
NOTE: Unit ratings are gross capacities and do not include
the effect of indoor-fan motor heat. To calculate net capaci-
ties, see Step V.
III SELECT ELECTRIC HEAT:
Enter the Integrated Heating Capacities table on page 9 at
6000 cfm. At 70 F return air and 0° F air entering outdoor
coil, the integrated heating capacity is 67,000 Btuh. (De-
ductions for outdoor-coil frost and defrosting have already
been made. No correction is required.)
The required heating capacity is 170,000 Btuh. Therefore,
103,000 Btuh (170,000 – 67,000 Btuh) additional electric
heat is required.
Determine additional electric heat capacity in kW.
103,000 Btuh
= 30.2 kW of heat required.
3413 Btuh/kW
Enter the Electric Resistance Heater Data table on page 11
for 542F at 230-3-60. The 31.0-kW heater at 230 v most
closely satisfies the heating required.
31.0 kW x 3413 Btuh/kW = 105,800 Btuh
Total unit heating capacity at 0° F is 172,800 Btuh
(105,800 + 67,000).
IV DETERMINE FAN SPEED AND POWER REQUIRE-
MENTS AT DESIGN CONDITIONS:
Before entering the Air Delivery table calculate the total
static pressure required based on unit components. From
the given and the Pressure Drop tables, find:
External static pressure
0.75 in. wg
Economizer
0.07 in. wg
Electric heat
0.09 in. wg
Total static pressure
0.91 in. wg
Enter the Air Delivery table on page 10. At 6000 cfm, the
standard motor with alternate drive will deliver up to
1.40 in. wg static pressure and 3.82 brake horsepower
(bhp). This will adequately handle job requirements.
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:
Convert bhp to Watts using the formula found in the note
following the Air Delivery table on page 10.
For example:
746 x Bhp
Watts =
Motor Efficiency
746 x 3.82
Watts =
.81
Watts = 3518
Net capacity = Gross capacity – IFM heat
= 185,400 Btuh – (3518 Watts
x 3.413 Btuh/Watts)
= 185,400 Btuh – 12,007 Btuh
= 173,393 Btuh
Net sensible capacity = 146,700 Btuh – 12,007 Btuh
= 134,693 Btuh
Determine net heating capacity as follows:
Net capacity = Gross ca IFM heat
+ Electric heat capacity
= 67,000 Btuh + 12,007 Btuh
+ 105,800 Btuh
= 184,807 Btuh
8
Содержание 542F
Страница 14: ...TYPICAL FIELD WIRING 14 ...
