[Equest-users] Air cooled chillers versus water cooled chillers

[Rathna Shree]

Dear All,
A project has 14 floors and 3.5 lakhs sq.ft. of conditioned area. The project is going for LEED certification. The baseline HVAC system will be Variable air volume system with water cooled centrifugal chiller of COP 6.1. LPD is maintained at 0.7W/sft. Building envelope is more or less equal to baseline case. In this scenario, the proposed HVAC system is air cooled screw chillers with variable primary pumping system. Even though the project is getting negative results in cooling category, there is a huge savings from pumps which is compensating for the negative in cooling energy consumption. Ultimately, the overall plant energy consumption (Cooling, heat rejection, pumps) is lesser in proposed case than base case. I am surprised with the result as i believe for such a building, water cooled chillers work more efficiently. For more clarity, the results are given as below:
Base case: Cooling: 14,26,659 KWH, Heat rejection: 1,23,357 KWH, Pumps: 426,506 KWHProposed case: Cooling: 17,89,814 KWH, Heat rejection: 0 KWH, Pumps: 62,264 KWH
These are results are for default chiller curves in both the cases. If air cooled part load values are used, then cooling energy consumption further reduces in proposed case. Then can it be concluded that air cooled with primary variable pumping system is a good alternative to use. 
Is this conclusion appropriate? Are the results correct? Please help.
Regards,Rathnashree
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