Bryant 549C manual SELECTION PROCEDURE WITH 542J180 EXAMPLE, Vdetermine Net Capacities

SELECTION PROCEDURE (WITH 542J180 EXAMPLE)

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

Given:

Required Cooling Capacity (TC) . . . . . . . . . 164,000 Btuh Sensible Heat Capacity (SHC). . . . . . . . . . . 120,000 Btuh Required Heating Capacity . . . . . . . . . . . . . 170,000 Btuh Outdoor-Air Temperature (Cooling) . . . . . . . . . . . . . . 95 F

Indoor Entering-Air Temperature

(Cooling). . . . . . . . . . . . . . . . . . . . . .80 F Edb/67 F Ewb

Outdoor Coil Entering-Air Temperature

(Heating) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0° F Indoor Winter Design Temperature . . . . . . . . . . . . . . 70 F Indoor-Air Quantity. . . . . . . . . . . . . . . . . . . . . . . 6000 Cfm External Static Pressure (ESP) . . . . . . . . . . . . 1.30 in. wg Electrical Characteristics (V-Ph-Hz). . . . . . . . . . . 230-3-60 Economizer is specified.

Edb — Entering dry bulb Ewb — Entering wet bulb

IISELECT UNIT BASED ON REQUIRED COOLING CAPACITY.

Enter Cooling Capacity table on page 146 at outdoor- entering temperature of 95 F, indoor air entering at 6000 cfm and 67 F ewb. The 542J180 will provide a total capacity (TC) of 180,800 Btuh, a sensible heat capacity (SHC) of 136,400 Btuh and a total unit kW of 15.88.

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 table on page 146.

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

Determine additional electric heat capacity in kW.

111,500 Btuh	= 32.7 kW
3412 Btuh/kW

Enter the Electric Resistance Heater Data table at 230-3-60. The 34-kW heater satisfies the electric heater requirements.

IV DETERMINE FAN SPEED AND MOTOR HORSE- POWER REQUIREMENTS AT DESIGN CONDITIONS.

Before entering Fan Performance table, calculate the total static pressure required based on unit components. From the given and the Accessory/FIOP Static Pressure table on page 151, find:

External static pressure	1.30 in. wg
Economizer static pressure	0.07 in. wg
Electric heat static pressure	0.09 in. wg
Total static pressure
	1.46 in. wg

Enter the Fan Performance table on page 149. At 6000 cfm and 1.46 in. wg external static pressure, the fan speed is 1214 and the bhp is 3.95 (interpolation required). The standard motor and alternate high static drive and suitable.

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= Gross capacity – IFM heat

2545 Btuh

= 180,800 – 3.95 bhp x		hp
	.85
= 180,800 – 11,827
= 168,973 Btuh

IIISELECT ELECTRIC HEAT.

Enter the Integrated Heating Capacities table on page 147 at 6000 cfm (interpolation required). At 70 F return indoor air and 0° F air entering the outdoor coil, the integrated heating capacity is 58,500 Btuh with a unit input kW of 11.71.

The required heating capacity is 170,000 Btuh; therefore, 111,500 Btuh (170,000 – 58,500) additional electric heat is necessary.

Net sensible capacity = 136,400 – 11,827 = 124,573 Btuh

Determine net heating capacity as follows: Net capacity =

Gross capacity + IFM heat + Electric heat capacity

=56,800 + (IFM kW x 3412) + (Elec. kW x 3412)

=56,800 + 11,827 + (34 x 3412)

=56,800 + 11,827 + 116,008

=184,635 Btuh

542J

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