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How to Estimate heat Load of the room?

The total heat load of the room is contributed by various sources. The total heat load can generally be divided into two broad headings.

 1. Sensible heat load,

 2. Latent heat load. 



1. Room Sensible heat Load ( RSH ) :

a) Solar gain - glass ( Q1 ) :

 Radiation from sun can enter the conditioned space through glass and heat is absorbed by materials and air in the conditioned space. 

Heat gain = A* R * MF 

A    - Area of  Glass, 

MF - Multiplying factor for type of glass/shading,

R    - Solar gain.

b) Solar transmission through walls and roof (Q2) :

 As a result of  direct absorption of  the radiation of the sun , temperature of  walls and roof rises. This causes larger difference in temperature with respect to the conditioned space.

c) Transmission through partitions and glass (Q3) :

 In addition to the above , heat gain is possible through partitions and glass due to temperature difference. 

d) Heat gain from occupants (Q4) :

 Heat energy released by the occupants add to the heat load of the system.

e) Heat gain from appliances and lights (Q5) :

 Appliances and lights, because of energy release add to the heat load of  the a/c system. 

f) Safety Factor and Duct Leakage (Q6) :

 This is employed in designing the a/c with a little overload capacity and to consider the heat gained   through the duct when it comes through the unconditioned air. 

 RSH = Q1 + Q2 + Q3 + Q4 + Q5 + Q6 

2.) Effective Room Sensible Heat Load (ERSH) :

 With RSH, if the effect of  bypass factor is also considered and added, it will give the ERSH. 

 i.e.,  ERSH = RSH + Effect of  BF

3.) Room Latent Heat Load ( RLH ) :

 I) i) Infiltration,

    ii) Internal heat gain from people, appliances,

   iii) Vapor Transmission,

   iv) Safety factor and Duct leakage.

     RLH = B1 + B2 + B3 + B4   

II) Effective Room Latent Heat Load ( ERLH) 

   ERLH = RLH + (Effect of BF)


Grand Total Load on A/c apparatus :

a) Total Sensible Heat ( TSH ) :

TSH is the sum of : 

i) ERSH, 

ii) Sensible heat of outside air that is not bypassed,

iii) Dehumidifier pump horse power, return duct leakage gain. 

b) Total Latent Heat (TLH) : 

 This is the sum of :

 i) ERLH 

ii) Latent heat of outside air which is not bypassed,

iii) Return duct Leakage gain.

Total Latent Heat = ERLH + ii + iii 

c) Grand Total heat Load (GTH) : 

This is the total heat Load the a/c system is to operate at. It is the sum of Total sensible heat and Total latent heat. i.e., 

GTH = TSH + TLH 

Thus the grand total heat load of the a/c system is determined and thus the system is designed.  


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