Carrier 48HG014-028 User Manual download pdf (Page 17)

I Determine cooling and heating requirements

at design conditions.

Given:

Required Gross Cooling

Capacity (TC) . . . . . . . . . . . . . . .229,000 Btuh

Gross Sensible Heat

Capacity (SHC) . . . . . . . . . . . . . .178,000 Btuh

Required Heating Capacity . . . . . . .190,000 Btuh

Condenser Entering Air

Temperature . . . . . . . . . . . . . . . . 95 F Summer

Indoor Air Temperature . . . . . .80 F edb, 67 F ewb

Evaporator Air Quantity. . . . . . . . . . . . 8,000 cfm

External Static Pressure . . . . . . . . . . . .1.30 in. wg

Electrical Characteristics (V-Ph-Hz) . . . . . 460-3-60

Optional economizer required. Vertical supply

required.

II Select unit based on required cooling

capacity.

Enter Cooling Capacities table for 48HG024 at

condenser entering temperature of 95 F, evaporator

air quantity of 8,000 cfm, and indoor air tempera-

ture of 67 F. The 48HG024 unit will provide a total

cooling capacity of 261,000 Btuh and a SHC of

195,000 Btuh. For evaporator air temperatures

other than 80 F, calculate SHC correction using for-

mula in notes under cooling capacity tables.

Unit meets design conditions for TC and SHC.

NOTE: Unit ratings are gross capacities and do not

include the effect of indoor fan motor heat. To cal-

culate net capacities, see Step V.

III Select heating capacity of unit to provide

design condition requirement.

In Heating Capacities and Efficiencies table, note

that 48HGD024 (low heat) unit will provide

205,000 Btuh with an input of 250,000 Btuh.

IV Determine fan speed and power require-

ments at design conditions.

Before entering the Fan Performance tables, calcu-

late the total static pressure required based on unit

components. Tabulated fan performance includes

filters and wet evaporator coil. Refer to Accessory/

FIOP Static Pressure — 48/50HG014-028 table

for added pressure drops.

Calculate pressure drop:

Design External Static Pressure 1.30

Economizer Static Pressure + 0.10

1.40 in. wg (ESP)

Enter Fan Performance tables for 48HGD024 (low

heat units, vertical supply) at 8,000 cfm and

1.40 in. wg. The rpm is 1138 and the Bhp is 6.58.

The factory-installed optional 7.5 hp motor

and alternate drive are sufficient for this operation.

V Determine net cooling capacities.

Cooling capacities are gross capacities and do not

include indoor (evaporator) fan motor (IFM) heat. To

determine input power to the motor, enter the Fan

Performance tables for 48HGD024 (low heat units)

at 8,000 cfm and 1.40 in. wg. Input watts to the

motor are 5719.

Determine net cooling capacity and net sensible

cooling capacity using the following formulas:

IFM Heat = Input Watts x 3.412 Btuh/Watt

= 5719 x 3.412

= 19,513 Btuh

Net Capacity = Gross Capacity – IFM Heat

= 261,000 – 19,513

= 241,487 Btuh

Net Sensible Cap. = Gross Sensible Cap. – IFM Heat

= 195,000 – 19,513

= 175,487 Btuh

The calculations show that a 48HGD024 unit is the

correct selection for the given conditions.

VI Select the unit that corresponds to power

source available.

The electrical data table shows that the 460-3-60

unit is available.

Selection procedure (with 48HG024 example)

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Carrier 48HG014-028 User Manual Page 17

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