Carrier 50HQ User Manual download pdf (Page 11)

I Determine the actual cooling and heating

loads at the desired dry bulb and wet bulb

conditions.

Assume cooling load at desired dry bulb 80 F and

wet bulb 65 F conditions are as follows:

Given:

Total Cooling (TC). . . . . . . . . . . . . . .65,500 Btuh

Sensible Cooling (SC) . . . . . . . . . . . .54,700 Btuh

Entering-Air Temperature db . . . . . . . . . . . . .80 F

Entering-Air Temperature wb . . . . . . . . . . . . .65 F

II Determine the following design parameters.

Entering water temperature, water flow rate (gpm),

airflow (cfm), water flow pressure drop and design

wet and dry bulb temperatures. Airflow cfm should

be between 300 and 450 cfm per ton. Unit water

pressure drop should be kept as close as possible

to each other to make water balancing easier. Enter

the appropriate Performance Data tables and

find the proper indicated water flow and water

temperature.

For example:

Entering Water Temp (Cooling) . . . . . . . . . . .90 F

Entering Water Temp (Heating) . . . . . . . . . . .60 F

Water Flow . . . . . . . . . . . . . . . . . . . . 15.0 GPM

Airflow Cfm . . . . . . . . . 2100 Cfm (350 Cfm/Ton)

III Select a unit based on total cooling and total

sensible cooling conditions. Unit selected

should be closest to but not larger than the

actual cooling load.

Enter tables at the design water flow and water

temperature. Read the total and sensible cooling

capacities.

NOTE: Interpolation is permissible, extrapolation is

not.

Example equipment selection for cooling:

Enter the 50HQP072 Performance Table at design

water flow and water temperature. Read Total

Cooling, Sensible Cooling and Heat of Rejection

capacities:

Total Cooling . . . . . . . . . . . . . . . . . .67,500 Btuh

Sensible Cooling . . . . . . . . . . . . . . . .52,300 Btuh

Heat of Rejection . . . . . . . . . . . . . . .87,900 Btuh

Airflow Cfm . . . . . . . . . . . . . . . . . . . . 2400 Cfm

NOTE: It is normal for water source heat pumps to

be selected on cooling capacity only since the heat-

ing output is usually greater than the cooling capac-

ity.

IV Determine the correction factors associated

with the variable factors of dry bulb and wet

bulb using the Corrections Factor tables

found in this book.

Using the following formulas to determine the cor-

rection factors of dry bulb and wet bulb:

a) Corrected Total Cooling = tabulated total cooling

x wet bulb correction x airflow correction.

b) Corrected Sensible Cooling = tabulated sensible

cooling x wet/dry bulb correction x airflow

correction.

V Determine entering air and airflow correction

using the Corrections Factor tables found in

this book.

The nominal airflow for the 50HQP072 is 2400

cfm. The design parameter is 2100 cfm.

2100/2400 = 88% of nominal airflow. Use the

88% row in the Airflow Correction table.

The nominal EAT (wb) is 67 F. The design parame-

ter is 65 F. Use the 65 F correction factor row from

the Entering Air Correction Factors table. Use

design temperature 80 F (db) column for sensible

cooling correction.

Using the following formulas to determine the cor-

rection factors of entering air and airflow correction:

Compare the corrected capacities to the load

requirements established in Step I. If the capacities

are within 10% of the load requirements, the equip-

ment is acceptable. It is better to undersize than

oversize as undersizing improves humidity control,

reduces sound levels and extends the life of the

equipment.

VI Determine the correction factor associated

with antifreeze in system loop.

If heating EWT is 50 F or below, antifreeze may

need to be used. Calculate leaving water tempera-

ture per performance data selection notes (opera-

tion is shaded areas). If antifreeze is required, use

Anti-Freeze Correction table for correcting total and

sensible capacities.

If the EWT for heating is 40 F, then the system

requires antifreeze. If a solution of 15% propylene

glycol is required, then:

Corrected Total Cooling =64,365 x 0.986

Corrected Total Cooling =63,464

Corrected Sensible Cooling =53,139 x 0.986

Corrected Sensible Cooling =52,395

VII Water temperature rise calculation and

assessment.

Calculate the water temperature rise and assess the

selection using the following calculation:

Table Ent Air Airflow Corrected

Corrected Total

Cooling

= 67,500 x 0.977 x 0.976 = 64,365

Corrected Sensi-

ble Cooling

= 52,300 x 1.089 x 0.933 = 53,139

Corrected Heat

of Rejection

= 87,900 x 0.998 x 0.976 = 85,619

Actual Temperature

Rise =

Correction of

Heat of Rejection

GPM x 500

Selection procedure

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Carrier 50HQ User Manual Page 11

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