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

[Sambhav Tiwari]

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 Regards
Sambhav

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 KWH
> Proposed 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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