Bryant 542J, 549B manual Selection Procedure with 548F048 Example, III Select Electric Heat

SELECTION PROCEDURE (WITH 548F048 EXAMPLE)

I DETERMINE COOLING AND HEATING LOADS AT DESIGN CONDITIONS.

Given:

Required Cooling Capacity (TC) . . . . . . . . . . 38,000 Btuh Sensible Heat Capacity (SHC). . . . . . . . . . . . 24,000 Btuh Required Heating Capacity . . . . . . . . . . . . . . 35,000 Btuh Outdoor Entering-Air Temperature db . . . . . . . . . . . . 95 F Outdoor-Air Winter Design Temperature . . . . . . . . . . .0° F Indoor-Air Winter Design Temperature . . . . . . . . . . . 70 F Indoor-Air

Temperature . . . . . . . . . 80 F edb (entering air, dry bulb) 67 F ewb (entering air, wet bulb)

Indoor-Air Quantity. . . . . . . . . . . . . . . . . . . . . . . .1600 cfm External Static Pressure . . . . . . . . . . . . . . . . . 0.45 in. wg Electrical Characteristics (V-Ph-Hz). . . . . . . . . . . 230-3-60

Enter the Electric Heating Capacities table (page 54) for 548F048 at 208/230, 3 phase. The 6.5-kW heater at 240 v most closely satisfies the heating required. To calcu- late kW at 230 v, use the Multiplication Factors table.

6.5 kW x .92 = 5.98 kW

6.5 kW x .92 x 3413 = 20,410 Btuh

Total unit heating capacity is 38,410 Btuh (18,000 + 20,410).

IV DETERMINE FAN SPEED AND POWER REQUIRE- MENTS AT DESIGN CONDITIONS.

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

External static pressure .45 in. wg

548F036-120

IISELECT UNIT BASED ON REQUIRED COOLING CAPACITY.

Enter Cooling Capacities table at outdoor entering temper- ature of 95 F, indoor air entering at 1600 cfm and 67 F ewb. The 548F048 unit will provide a total cooling capacity of 49,900 Btuh and a sensible heat capacity of 33,900 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 tables.

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

IIISELECT ELECTRIC HEAT.

Enter the Instantaneous and Integrated Heating Ratings table at 1600 cfm. At 70 F return indoor air and 0° F air entering outdoor coil, the integrated heating capacity is 18,000 Btuh. (Select integrated heating capacity value since deductions for outdoor-coil frost and defrosting have already been made. No correction is required.)

The required heating capacity is 35,000 Btuh. Therefore, 17,000 Btuh (35,000 – 18,000) additional electric heat is required.

Determine additional electric heat capacity in kW.

17,000 Btuh

= 5.0 kW of heat required.

3413 Btuh/kW

Durablade economizer	.05 in. wg
Electric heat	.09 in. wg
Total static pressure	.59 in. wg

Enter the Fan Performance table for 548F048 vertical dis- charge. At 1600 cfm and 230-v high speed, the standard motor will deliver 0.76 in. wg static pressure, 723 watts, and 0.64 brake horsepower (bhp). This will adequately handle job requirements.

VDETERMINE 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 = Total capacity – IFM heat

=49,900 Btuh – (723 Watts x 3.413 Btuh/Watts)

=49,900 Btuh – 2468 Btuh

=47,432

Net sensible capacity = 33,900 Btuh – 2468 Btuh

= 31,432 Btuh

Integrated heating capacity is maximum (instantaneous) capacity less the effect of frost on the outdoor coil and the heat required to defrost it. Therefore, net capacity is equal to 38,410 Btuh, the total heating capacity determined in Step III.

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