SELECTION PROCEDURE (with 558F240 Example)

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

Given:

Required Cooling Capacity . . . . . . . . . . . . . 230,000 Btuh Sensible Heat Capacity . . . . . . . . . . . . . . . . 170,000 Btuh Required Heating Capacity . . . . . . . . . . . . . . . . . . . 75 kW Condenser Entering Air Temp . . . . . . . . . . 95 F (Summer) Evaporator Entering Air Temp . . . . . . . . . . . . . . .80 F edb,

67 F ewb Evaporator Air Quantity . . . . . . . . . . . . . . . . . . . 8,000 cfm External Static Pressure . . . . . . . . . . . . . . . . . . 0.4 in. wg Electrical Characteristics (V-Ph-Hz). . . . . . . . . . . 460-3-60

Vertical discharge unit with optional economizer required.

edb — Entering dry-bulb ewb — Entering wet-bulb

IISELECT UNIT BASED ON REQUIRED COOLING CAPACITY.

Enter Cooling Capacities table for 558F240 (page 140 at condenser entering temperature 95 F, evaporator air enter- ing at 8,000 cfm and 67 F wb. The 558F240 unit will pro- vide a total cooling capacity of 249,000 Btuh and a sensible heating capacity of 188,000 Btuh. For air entering evaporator at temperatures other than 80 F edb, calculate sensible heat capacity correction as required using the for- mula in the notes following the Cooling 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 HEATING CAPACITY OF UNIT TO PROVIDE DESIGN CONDITION REQUIREMENTS.

In the Electric Resistance Heater table (page 130) select the 75 kW output heater.

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

Before entering the Fan Performance tables, calculate the total static pressure required based on unit components. From the given and the Accessory/FIOP Static Pressure table on page 145 find:

External static pressure

0.40 in. wg

Electric heater static pressure

0.22 in. wg

Total static pressure

0.62 in. wg

Enter the Fan Performance table 558F240 (page 144) at 8,000 cfm and 0.62 in. wg external static pressure. By interpolation, find that the rpm is 1061 and the watts are 4552.

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 = 4552

Determine net cooling capacity using the following formula:

Net capacity = Gross capacity – IFM heat

 

 

= 249,000 Btuh – 4552 Watts

 

 

 

 

 

Btuh

 

 

(3.412

 

)

 

 

Watts

= 249,000

Btuh – 15,531 Btuh

 

 

= 233,469

Btuh

 

 

 

Net sensible capacity = 188,000

Btuh – 15,531 Btuh

= 172,469

Btuh

 

 

The calculations show that a 558F240 unit with the standard motor and standard low-medium static drive is the correct selection for the given conditions.

558F180-300

139

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Bryant 551B, 551A SELECTION PROCEDURE with 558F240 Example, 558F180-300, Ii Select Unit Based On Required Cooling Capacity
Page 138 Page 140

551A, 551B, 558F specifications

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