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anup
02-12-2011, 08:11 PM
We have received an enquiry where in a customer needs water cooled chiller for centalised air conditioning and hot water as by-product. The desired parameters:
Cooling Side: Water at 7 C
Heating Side - Water at 60 C (Delta T desired is 45 C from 15C inlet water to 60 C outlet water)
My queries:
1. Whether it is possible to design system with 60C water as by-product?
2. How it will affect the system performance in terms of cooling and the life of the compressor?

As the heating load (heat from return cold water line) will vary, we may not get 45 C temp rise in condenser. In that case, we might have to re-circulate the water. While re-circulating, inlet condensing water temp could be 45 C.
In this situation, whether
3. How much cooling efficiency will vary?
4. How it will affect the life of the compressor?

Planned compressor to use: Danfoss, Scroll, SZ300, 25 tr.

james10
02-12-2011, 08:14 PM
Carrier do a 30HXC that will do exactly that why not look them up

Magoo
02-12-2011, 10:24 PM
Hi , I agree with jame10, basically they have a desuperheater that recovers 15 odd % total heat of rejection with out effecting system performance.

NoNickName
03-12-2011, 09:48 AM
Yes, it may be possible, but it's better to exchange heat into a DHW buffer. It doesn't make sense to produce DHW instantanously, as you may not have heat load on the cold side, just when you need hot water on the DHW side.

anup
04-12-2011, 07:46 PM
It doesn't make sense to produce DHW instantanously, as you may not have heat load on the cold side, just when you need hot water on the DHW side.

Thanks NoNickName.
I agree with you and we have planned to use buffer tank. As I said earlier, due to lower heat load on cold side, we may not get 45 C temp rise hot water side. To raise the temp up to 60 C, we were planning to recirculate hot water from buffer tank, just like we do in our Air Source Heat Pump.
I have further queries:
1. In case of lower heat load at cold side, can we regulate the water flow in condenser side to get 45C temp rise in single cycle i.e. from 15 to 60 C, irrespective of the heat load in cold side? How it could affect the cooling performance or any other problem you may foresee.
2. Assuming
a. There is 100% heat load at cold side
b. We are using 25 Tr Scroll compressor in chiller
c. Condenser side water inlet temp i.e. from buffer tank is 45C instead of normal 25 C
How, it will affect the cooling efficiency?
Is there any chart/standards which will show the variation in cooling efficiency of chiller w.r.t. inlet water temp at condenser side?

NoNickName
04-12-2011, 07:53 PM
1) No, you can't because the lower heat load, the lower heat rejection, the lower delta T. As a bad side effect I would expect an excessive subcooling, with possible liquid slugging.
2) I don't understand the question.

No, there is no chart. Good luck with your homework.

mad fridgie
04-12-2011, 09:27 PM
You need to do an energy mass balance (s).
How much cooling and when (include temps)
How much Hot water and when.(include temps)
This then determines the approach to the solution.
Understand your application first! Then the engineering becomes easy!
It would be very rare where heating and cooling demands are the same!

Magoo
04-12-2011, 11:40 PM
Wise words and advise from MF and NNN.

mad fridgie
04-12-2011, 11:56 PM
Thanks magoo!
$$$$$$$$$$$$$$$$$$$$ put this in your back pocket!