14
Air
Selection Procedure
RGED Series
To select an RGEDZ Cooling and Heating unit to meet a job
require ment, follow this procedure, with example, using data
supplied in this specification sheet.
1. DETERMINE COOLING AND HEATING REQUIREMENTS
AND SPECIFIC OPERATING CONDITIONS FROM PLANS
AND SPECS.
Example:
Voltage— 208/240V – 3 Phase
Total cooling capacity— 205,000 BTUH [60.1 kW]
Sensible cooling capacity— 155,000 BTUH [45.4 kW]
Heating capacity— 235,000 BTUH [68.9 kW]
*Condenser Entering Air— 95°F [35°C] DB
*Evaporator Mixed Air Entering—65°F [18°C] WB;
78°F [26°C] DB
*Indoor Air Flow (vertical)— 7200 CFM [3398 L/s]
*External Static Pressure— .70 in. WG
2. SELECT UNIT TO MEET COOLING REQUIREMENTS.
Since total cooling is within the range of a nominal 20 ton
[70.3 kW] unit, enter cooling performance table at 95°F [35°C]
DB condenser inlet air. Interpolate between 63°F [2°C] and
67°F [19°C] to determine total and sensible capacity and
power input for 65°F [18°C] WB evap inlet air at 7725 CFM
[3646 L/s] indoor air flow (table basis):
Total Capacity = 238,300 BTUH [69.78 kW]
Sensible Capacity = 192,500 BTUH [56.37 kW]
Power Input (Compressor and Cond. Fans) = 18,200 watts
Use formula [1.10 x CFM x (1 – DR) x (dbE – 80)] in note ➀ to
determine sensible capacity at 80°F [26.7°C] DB evaporator
entering air:
Sensible Capacity = 177,400 BTUH [51.95 kW]
3. CORRECT CAPACITIES OF STEP 2 FOR ACTUAL
AIR FLOW.
Select factors from airflow correction table at 7200 CFM
[3398 L/s] and apply to data obtained in step 2 to obtain
gross capacity:
Total Capacity, 238,300 x .99 = 235,900 BTUH [69.08 kW]
Sensible Capacity, 177,400 x .96 = 170,300 BTUH [49.87 kW]
Power Input 18,200 x .99 = 18,018 Watts
These are Gross Capacities, not corrected for blower motor
heat or power.
4. DETERMINE BLOWER SPEED AND WATTS TO
MEET SYSTEM DESIGN.
Enter Indoor Blower performance table at 7200 CFM
[3398 L/s]. Total ESP (external static pressure) per the spec of
.70 in. includes the system duct and grilles. Add from the table
“Component Air Resistance,” 0.01 for wet coil, 0.08 for downflow air flow, for a total selection static pressure of .790 (.8)
inches of water, and determine:
RPM = 739
WATTS = 2,862
DRIVE = A (belt drive, low static)
5. CALCULATE INDOOR BLOWER BTUH HEAT EFFECT
FROM MOTOR WATTS, STEP 4.
BTUH = 2,862 x 3.412 = 9,765
6. CALCULATE NET COOLING CAPACITIES, EQUAL TO
GROSS CAPACITY, STEP 3, MINUS INDOOR BLOWER
MOTOR HEAT.
Net Total Capacity = 235,900 – 9,765 =
226,135 BTUH [66.22 kW]
Net Sensible Capacity = 170,300 – 9,765 =
160,535 BTUH [47.01 kW]
7. CALCULATE UNIT INPUT AND JOB EER.
Total Power Input = 18,018 (step 3) + 2,862
(step 4) = 20,880 Watts
EER =
Net Total BTUH [kW] (step 6) = 226,135
= 10.83
Power Input, Watts (above) 20,880
8. SELECT UNIT HEATING CAPACITY.
From Physical Data Table read that gas heating output
(input rating x efficiency) is:
Heating Capacity = 243,000 BTUH [71.2 kW]
Choose Model RGEDZS120ACA222AA
*NOTE: These operating conditions are typical of a commercial applica-
tion in a 95°F/79°F [35°C/26°C] design area with indoor design
of 76°F [24°C] DB and 50% RH and 10% ventilation air, with
the unit roof mounted and centered on the zone it conditions
by ducts.
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