SELECTION PROCEDURE (With 581B048 Example)

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

Given:

Required Cooling Capacity (TC) . . . . . . . . . . 44,600 Btuh Sensible Heat Capacity (SHC). . . . . . . . . . . . 32,000 Btuh Required Heating Capacity . . . . . . . . . . . . . . 85,000 Btuh Condenser Entering-Air Temperature . . . . . . . . . . . . 95 F Evaporator Entering-Air Temperature . . . . . . . . .82 F edb,

67 F ewb Evaporator Air Quantity . . . . . . . . . . . . . . . . . . . .1600 cfm External Static Pressure (ESP) . . . . . . . . . . . . 0.75 in. wg Electrical Characteristics (V-Ph-Hz). . . . . . . . . . . 230-1-60

IISELECT UNIT BASED ON REQUIRED COOLING CAPACITY.

Enter the Cooling Capacities table (page 18) at condenser entering temperature of 95 F, evaporator-air entering at 1600 cfm and 80 F db and 67 F wb. The 581B--048115 unit will provide cooling capacity of 48,900 Btuh and a sensible heat capacity of 34,700 Btuh. For evaporator-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.

For this example:

Correction factor = 1.10 x (1 – .21) x (82 – 80) = 1.738

Multiply the correction factor of 1.738 by 1600 cfm (a total of 2781). From the Gross Cooling Capacities tables find that the sensible heat capacity at 80 F is 34.7 MBtuh (equivalent to 34,700 Btuh). Add 34,700 and 2781 to get the corrected sensible heat capacity of 37,481.

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.

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 Pressure Drop tables (page 40), find:

External static pressure

.75 in. wg

Durablade economizer

.05 in. wg

Total static pressure

= .80 in. wg

Enter the Fan Performance table for 581B--048115 vertical discharge unit on page 27. At 1600 cfm, the standard motor will deliver 1.1 in. wg static pressure and 1.17 Bhp. This will adequately handle the job requirements.

Using evaporator-fan motor efficiency table and formula on page 40, determine watts.

1.17 (746)

Watts =

.75

Watts = 1164

V DETERMINE NET COOLING CAPACITY.

Cooling capacities are gross and do not include indoor-fan motor (IFM) heat. Determine net capacity using the follow- ing formula:

Net capacity

=

gross capacity

– IFM heat

 

 

=

48,900 Btuh

– 1164 Watts

 

 

 

 

(3.413

Btuh

)

 

 

 

Watts

 

=

48,900 Btuh

– 3972

Btuh

 

Net capacity

=

44,928 Btuh

 

 

 

Net sensible capacity = 37,481 Btuh – 3972 Btuh

= 33,509 Btuh

In the Heating Capacities and Efficiencies table (page 5) note that unit 581B--048115 will provide output capacity of 92,000 Btuh, which is adequate for the given application.

17

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Bryant manual Selection Procedure With 581B048 Example, II Select Unit Based on Required Cooling Capacity
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581B specifications

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