Recent Updates

Saturday, 3 January 2015

HVAC COOLING LOAD CALCULATIONS




We have seen the basic concept of HVAC in our previous post "Heating ventilating and air conditioning (HVAC)". 

Let us consider how we will calculate the cooling load calculation for HVAC system .Before starting the calculation of cooling load, I will suggest looking previous post "Heating ventilating and air conditioning (HVAC)" for better understanding the concept of cooling load calculations, So let us start.

Cooling load calculation

In following table, we will come to know that how we may proceed to calculate the cooling load for our selected site.


Sr. NO.

Load sources

Calculating equation

1

Window & Glass Areas

q= (GLF)A

2

Doors

q=U d A (CLTD)

3

Above grade exterior wall

q=U W A (CLTD)

4

Partitions for unconditioned space

q=U P A  Δ t

5

Infiltration

q = 1.1QΔt
Where, Q = ACH * Room volume / 60

6

Roofs and ceiling

q=U f A (CLTD)

7

Floors those are exposed

q=U f A (CLTD)

8

Internal Loads , such as
   People
Lights
Appliances

Let for one person
230 BTU/Hr

Total Cooling Load
= L F * Summation of sensible cooling load for individual components

Where,

q= Sensible Cooling load (Btu/h)

Δ t = Difference between temperature of air of inside and outside (0F)

Q= Volumetric air flow rate (CFM)

A= Area of surface in ft2

U= U factor for suitable construction (Btu/h. ft2. 0F)

LF = latent load multiplier

ACH = air changes / hour, 1/h

CLTD = Cooling load temperature difference, °F

GLF = glass load factor, Btu/h· ft2

We will determine cooling load room by room in order to calculate the proper air distribution

Living Room

Infiltration-

Q = ACH * Room volume / 60
Q = (0.5 x 3840)/60
Q =32
q = 1.1QΔt
q = 1.1 x 32 x (96-75)
q = 740 Btu/h

Occupant –

As we have mentioned above that one person 230 BTU/Hr
q = 230 x 4 = 920 Btu/h

Appliances-

As we have mentioned above that 50% load of kitchen appliance will be taken in living room, hence
q = 0.5 x 1600
q = 800 Btu/h

Kitchen-

Infiltration-

Q = ACH * Room volume / 60
Q = (0.5 x 1920)/60
Q =16
q = 1.1QΔt
q = 1.1 x 16 x (96-75)
q = 370 Btu/h

Occupant –

As we know that there is no occupant
q = 0

Appliances-

As we have mentioned above that 25% load of utility appliance will be taken in kitchen room, hence
q = 0.5 x 1600 + 1600/4
q = 1200 Btu/h

We will find complete cooling load calculation for living room and kitchen separately with the help of following mentioned table

For Living room

Description
Area (Ft2)
GLF
 (Btu/h· ft2)
Factor-U
(Btu/h. ft2. 0F)
CLTD
(°F)
Cooling Load
 (Btu/h)
West Wall
91

0.06
24
131
Partition
192

0.07
12
161
Roof
480

0.05
48
1152
West door
21

0.32
24
161
West glass
35
44


1540
Shaded glass
13
19


247

For Kitchen

Description
Area
 (Ft2)
GLF
 (Btu/h· ft2)
Factor-U
(Btu/h. ft2. 0F)
CLTD
(°F)
Cooling Load
 (Btu/h)
East Wall
135

0.06
24
194
Roof
240

0.05
48
576
East Glass
14
44


616
Shaded glass
11
19


209

GLF, CLTD are values taken from HVAC design data. These are standard value based on the outdoor design temperature.

Cooling load, we have calculated by using formula that we have mentioned above for each cases.

Complete cooling load calculation

Description
Roof, Door & wall
People
Glass
Appliances
Infiltration
Living room
1605
920
1787
800
740
Kitchen
770

825
1200
370
Storage & utility
1404


1200
443
Bed room#1
559

544

278
Bed room#2
686

548

278
Master Bed room with bath
1682

816

813
Bath room
540

276

295
Final /Total
7246
920
5096
3200
3217


Total cooling load = 7246 + 920 +5096 + 3200 + 3217
Total cooling load = 19679 Btu/h
We have to also consider duct losses which will be 10 % or 1967.9
Duct losses = 1968

Summation of sensible cooling load for individual components = 
19679 + 1968 = 21647 Btu/h
Total Cooling Load = L F * Summation of sensible cooling load for individual components
For a medium construction house L F will be 1.15
Total Cooling Load = 1.15 x 21647 =24894 Btu/h

Total Cooling Load = 24894 Btu/h

This blog is basically based on the process for calculating the cooling load calculations for HVAC system .


I will suggest looking my previous post "Heating ventilating and air conditioning (HVAC)"
for better understanding of calculations as all assumptions have been taken in previous post.

For heating load calculations, please follow my next post

Also Discuss:


Do you have any suggestions, please write in comment box 

No comments:

Post a Comment