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

[Rathna Shree]

Hi Sambhav,
Does that mean, air cooled chillers with variable primary pumping system performance is almost equivalent or better than the ASHRAE 90.1 2007 defined water cooled centrifugal chiller system?
Regards,Rathnashree 


     On Saturday, 17 October 2015 12:57 PM, Sambhav Tiwari <tiwari.sambhav at gmail.com> wrote:
   

 Hi Rathanashree,
For me the results seems to be alright
1 Being a air cooled chiller with less COP than baseline water cooled your compressor energy consumption is increasing which is clear from the results .
2 Now there is a debate going these day to replace ( constant primary & variable secondary pumps) with variable primary pump system although many HVAC experts  advocate against it that it can have negative impacts on chiller too.But definitely it will save energy consumption under pumps which is clear from your results your proposed case is left only with VFD based primary pump compared with baseline of ( constant primary+variable secondary+constant condenser water pumps) therefore pumps energy is too less and justified to me.
3 Your cooling tower energy consumption will be nil in proposed case being a air cooled system that is also fine.
But the main driver or  you can say main ECM in your analysis is variable primary and no secondary chiller which is contributing siginifant savings in pumps along with no cooling tower present hence your over all energy saving are positive.
Hope this may help.
Warm RegardsSambhav
On Fri, Oct 16, 2015 at 11:50 PM, Rathna Shree <rathnashreep at yahoo.in> wrote:

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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