Bryant manual SELECTION PROCEDURE WITH 549B048 EXAMPLE, Iiiselect Electric Heat, 549B, 549C

SELECTION PROCEDURE (WITH 549B048 EXAMPLE)

I DETERMINE COOLING AND HEATING REQUIRE- MENTS 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. . . . . . . . . . . . . . . 95 F Outdoor-Air Winter Design Temperature . . . . . . . . . . . 0° F Indoor-Air Winter Design Temperature . . . . . . . . . . . 70 F

Indoor Entering-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

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 549B048 unit will provide a total cooling capacity of 46,300 Btuh and a sensible heat capacity of 35,600 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 22,400 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, 12,600 Btuh (35,000 – 22,400) additional electric heat is required.

Determine additional electric heat capacity in kW.

Enter the Electric Heating Capacities table for 549B048 at 208/230, 3 phase. The 6.5-kW heater at 240 v most closely satisfies the heating required. To calculate 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 42,810 Btuh (22,400 + 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
EconoMi$erIV	.07 in. wg
Electric heat	.09 in. wg
Total static pressure	.61 in. wg

Enter the Fan Performance table for 549B048 vertical dis- charge at 1600 cfm and .61 in. wg static pressure. The bhp is 0.79 and the watts are 781. The rpm is 997. The standard motor 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

=46,300 Btuh – (781 Watts x 3.413 Btuh/Watts)

=46,300 Btuh – 2665 Btuh

=43,635

Net sensible capacity = 35,600	Btuh – 2665 Btuh
= 32,935	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 42,810 Btuh, the total heating capacity determined in Step III.

549B, 549C

12,600 Btuh	= 3.7 kW of heat required.
3413 Btuh/kW

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