[Er.Pankaj Garg]

Cooling load  calculation using CLTD/CLF Method


CLTD/CLF Method (classical)

1. Cooling load is made up of
   
   
   1. Radiation and conduction heat gain
      
   2. Convection heat gain
      
2. Convective gain is instantaneous
   
   1. No delay
      
   2. Heat gain equals cooling load
      
3. Conductive and radiation heat gains are not instantaneous
   
   1. Thermal delay
      
   2. Heat gain is not equal to cooling load
      
   3. Use CLTD & CLF factors
      

CLTD/CLF Method (ASHRAE 1989)

Cooling load due to solar & internal heat gains

1. Glazing (sensible only)
   
   1. Radiation & conduction
      
   2. Convection (instantaneous)
      
2. Opaque surface ( wall, floor, roof) load (sensible only)
   
   1. Conduction
      
   2. Convection (instantaneous)
      
3. Internal loads (sensible & latent)
   
   1. Radiation & conduction
      
   2. Convection (instantaneous)
      

CLTD/CLF Method
Cooling Load Temperature Difference CLTD
Compare
Q transmission = UA (To – Ti)
Q transmission = UA (CLTD)
• CLTD is theoretical temperature difference defined for each wall/roof to give the same heat load for exposed surfaces to account for the combined effects of radiation, conductive storage, etc
– It is affected by orientation, time , latitude, etc
– Data published by ASHRAE
Cooling Load Factor (CLF)
• This factor applies to radiation heat gain
• If radiation is constant, cooling load = radiative gain
• If radiation heat is periodical, than
Q t = Q daily max (CLF)
CLF accounts for the delay before radiative gains  becomes a cooling load

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