SELECTION PROCEDURE (with 558F048 example)

I DETERMINE COOLING AND HEATING REQUIRE- MENTS AT DESIGN CONDITIONS:

Given:

Cooling Capacity Required . . . . . . . . . . . . . . 44,000 Btuh Sensible Heat Capacity . . . . . . . . . . . . . . . . . 32,000 Btuh Required Heating Load . . . . . . . . . . . . . . . . . 50,000 Btuh Condenser Entering-Air

Temperature . . . . . . . . . . . . . . . . . . .95 F Edb/78 F Ewb Evaporator Entering-Air

Temperature . . . . . . . . . . . . . . . . . . .80 F Edb/67 F Ewb Evaporator Air Quantity . . . . . . . . . . . . . . . . . . . .1600 cfm External Static Pressure . . . . . . . . . . . . . . . . . 0.75 in. wg Heating Capacity . . . . . . . . . . . . . . . . . . . . . . 50,000 Btuh Power Supply (V-Ph-Hz) . . . . . . . . . . . . . . . . . . . 230-3-60

Edb — Entering dry bulb

Ewb — Entering wet bulb

IISELECT UNIT BASED ON REQUIRED COOLING CAPACITY.

Enter cooling capacity table for 558F048 on page 36 at condenser entering dry bulb temperature 95 F, air entering evaporator at 1600 cfm, 80 F edb and 67 F ewb. The

558F048 unit will provide a total cooling capacity of 50,500 Btuh, and a sensible heating capacity of 35,600 Btuh. For evaporator-air temperatures other than 80 F edb, calculate sensible heat capacity correction as required using the formula in the notes following the Cool- ing Capacities tables.

NOTE: Unit ratings are gross capacities and do not include the effect of evaporator-fan motor heat. To calcu- late net capacities, see Step V.

IIISELECT ELECTRIC HEAT.

Heating load required is 50,000 Btuh.

50,000 Btuh

= 14,654 Watts of heat required

3.412 Btu/W

= 14.7 kW

Enter the Electric Heating Capacities table on page 64 for the 558F048 at 230-3-60. The 16.0 kW electric heater most closely satisfies the heat required.

To calculate kW at 230 v, use the multiplication factors table on page 64.

16.0 x .918 = 14.7 kW

16.0 x .918 x 3.413 = 50,115 Btuh gross capacity

IV DETERMINE FAN SPEED AND MOTOR HORSEPOWER REQUIREMENTS AT DESIGN CONDITIONS.

Enter Accessory/FIOP Static Pressure table on page 61 at selected unit size and heater kW.

Find that at given air quantity (1600 cfm), pressure loss is 0.09 in. wg.

Before entering the Fan Performance tables, calculate the total static pressure required based on unit components. From the given find:

External static pressure

0.75 in. wg

16 kW Heater static pressure

0.09 in. wg

Total static pressure

0.84 in. wg

Enter Fan Performance table for the alternate motor verti- cal discharge unit 558F048 on page 41. At 1600 cfm and

0.84in. wg external static pressure, the fan speed is

1038 rpm and the watts are 877. (Interpolation is neces- sary.) The alternate motor and drive is suitable.

VDETERMINE NET COOLING CAPACITY.

Cooling capacities are gross capacities and do not include indoor (evaporator) fan motor (IFM) heat. Use the watts input power to the motor calculated in “Section IV” above.

IFM watts = 877

Determine net cooling capacity using the following formula:

Net capacity = Gross capacity – IFM heat

=50,500 Btuh – 877 Watts (3.413 WattBtuh )

=50,500 Btuh – 2992 Btuh

=47,508 Btuh

Net sensible capacity = 35,600 Btuh – 2992 Btuh = 32,608 Btuh

As demonstrated above, the 558F048 with the 16.0 kW electric heater and an alternate motor meets the cooling capacity, sensible heating capacity, and heating capacity requirements.

558F036-150

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Bryant 551A SELECTION PROCEDURE with 558F048 example, I Determine Cooling And Heating Require- Ments At Design Conditions

551A, 551B, 558F specifications

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