[Bldg-sim] Difference in chiller energy for VAV and CAV system

Deepak Tewari dipaktwri at yahoo.co.in
Sun Mar 20 23:31:04 PDT 2011

Dear All,

I am comparing the energy performance of a constant volume and variable volume 
system for a composite climate of India (New Delhi) in EnergyPlus. The building 
area is 7500 sq m. The chiller capacity is same for both the cases. The chilled 
water to the cooling coils is supplied by a constant speed pump. 

The savings in the fan energy is evident due to variable speed of the supply fan 
in case of VAV. However i am getting energy saving in cooling energy (chiller 
energy) also, in VAV compared to CAV, which i feel is due to higher delta T 
(chilled water) across cooling coil for CAV compared to VAV, this in turns 
increases the chiller electricity consumption. However while discussions with 
some consultant, it is their feeling that the cooling energy would remain same 
for both type of systems.

I want to ask has someone else tried this simulation and would there be any 
difference in cooling energy or not? 

Thanks in advance.

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