Selection Procedure Example - Rheem RKKB SERIES Owner's Manual

SELECTION PROCEDURE EXAMPLE—RKKB/RKMB/RKNB- SERIES
To select an RKKB- Cooling and Heating unit to meet a job
requirement, 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:
Total cooling capacity—
Sensible cooling capacity—
Heating capacity—
*Condenser Entering Air—
*Evaporator Mixed Air Entering—65°F [18°C] WB;
*Indoor Air Flow (vertical)—
*External Static Pressure—
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 7400 CFM
[1888 L/s] indoor air flow (table basis):
Total Capacity = 232,700 BTUH [68.2 kW]
Sensible Capacity = 186,500 BTUH [54.66 kW]
Power Input (Compressor and Cond. Fans) = 21,600 watts
Use formula in note ➀ to determine sensible capacity at 78°F
[26°C] DB evaporator entering air:
Sensible Capacity = 172,500 BTUH [50.55 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, 232,700 x .995 = 231,540 BTUH [67.86 kW]
Sensible Capacity, 172,500 x .987 = 170,260 BTUH [49.90 kW]
Power Input 21,600 x .999 = 21,578 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," .15 for wet coil, .05 for downflow
air flow, for a total selection static pressure of .900 (.9) inches
of water, and determine:
RPM = 942
WATTS = 4,717
DRIVE = M (standard 7.5 H.P. motor)
205,000 BTUH [60.1 kW]
155,000 BTUH [45.4 kW]
235,000 BTUH [68.9 kW]
95°F [35°C] DB
78°F [26°C] DB
7200 CFM [3398 L/s]
.70 in. WG
5. CALCULATE INDOOR BLOWER BTUH HEAT EFFECT
FROM MOTOR WATTS, STEP 4.
BTUH = 4,717 x 3.412 = 16,094
6. CALCULATE NET COOLING CAPACITIES, EQUAL TO
GROSS CAPACITY, STEP 3, MINUS INDOOR BLOWER
MOTOR HEAT.
Net Total Capacity = 231,540 – 16,094 =
215,446 BTUH [63.14 kW]
Net Sensible Capacity = 170,260 – 16,094 =
154,166 BTUH [45.18 kW]
7. CALCULATE UNIT INPUT AND JOB EER.
Total Power Input = 21,578 (step 3) + 4,717
(step 4) = 26,295 Watts
Net Total BTUH [kW] (step 6)
EER =
Power Input, Watts (above)
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]
*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.
[ ] Designates Metric Conversions
7
215,446
= = 8.19
26,295