PDA

View Full Version : Air Source Heat Pump x Water-Water Heat Pump (chiller based) - which is better?







anup
27-08-2012, 11:20 PM
Hi Guys,
I need your help and would like you to have your inputs and get the authentic information and clarification on the technical points mentioned below as soon as possible.
We are the Air Source Heat Pump manufacturer in India. For higher capacity systems like 200 kW plus capacity, we are running in to MNC’s regularly. These manufacturers are suggesting the Water-Water Heat Pump using Return Water at 12oC (max) from Centralised Air Conditioning.
We can manufacture the system as desired by the customer, but as a technocrat I am not able to convince myself even to quote such system. I may be wrong that’s why need your guidance to improve my knowledge.
Here the question is not about getting the order but to educate the customer as even today in India, Heat Pump application awareness is not good, rather say, is poor.

Heat Pump Design Parameters

Gas R-134a R-407C
Type Water-Water Air Source
Condensing Temperature oC 55 60
Entering Water Temperature oC 50 50
Leaving Water Temperature oC 55 55
Heat Source Return Water from AC Atmospheric Air
Heat Source Temperature oC 9 - 12 20-35

1. Application
Primary application is to heat water up to 55-60 deg. C for bathing purpose.
2. Heat Source
The average ambient temperature at site location in question is never less than 20 deg. C in the winters when the hot water requirement is most.
In our opinion, Return Water from Centralised AC which is at 12 deg. C maximum based Water-Water Heat Pump is too low efficient than average 20 deg. C ambient air temperature based Air Source Heat Pump.
Where as, Water-Water Heat Pump is efficient when you are using Ground Source water as compared to Air Source Heat Pump even in winters as you get the ground water at steady temperature throughout the day, 365 days a year.
3. Refrigerant
Customer is insisting upon using R-134a for the system (as suggested by any one of these MNC’s) and we are saying to use R-407C.
In our opinion, R-134A is best suited for low temperature application like Chiller where as R-407C is having more efficiency than R-134A and is best suited for Heat Pump for water heating application.
4. Use of By-product
Water-Water Heat Pump – Chilled water is by-product. But since the heating source water is at 12 deg. C (max), the heating COP drops and entire concept of heat pump for water heating is nullifies.
Air Source Heat Pump – Cool Air is by-product. – This cool air can be used in TFA or at any place where cooling is required, reducing the cooling load of Centraslied Air Conditioning but maintaining the Heating COP of heat pump.
5. Cooling Efficiency
Water-Water Heat Pump – as the condensing temperature is 55 deg. C (in case of R-134A) and water entering temperature is 50 deg. C, the effective Cooling Efficiency (COP) will reduce substantially. In other words,
Air Source Heat Pump – Air Cooling efficiency is maintained without affecting heating COP
6. Power Consumption
Water-Water Heat Pump – As the Entering Water Temperature in Condenser is 50 deg. C, the power consumption will increase. Heating Source is 12 deg. C Air Conditioning Return Water, Heating COP reduces and effective Cooling+Heating COP will reduce
Air Source Heat Pump – As it is using fresh air (high temperature ambient air) for heating, total COP (Cooling+Heating) will increase.

In my opinion, either Air Source Heat Pump for tropical conditions like India or Ground Water Source Heat Pump is most efficient Heat Pumps for water heating than the Water-Water Source Heat Pump based on Return Water (12 deg. C) from Centralised Air Conditioner.

Warm regards

Anup

anup
04-09-2012, 09:42 PM
Hi Guys,
I need your inputs. I have a meeting with the client on Sept 6th, 12.

Anup

Josip
04-09-2012, 10:46 PM
Dear anup:)

Sorry about your shortage of time .... here, we all are volunteers - and this is not our primary work (we are struggling for daily bread on some job site), therefore please, be patient ... someone will answer

Another point, it is not good to post the same post all over ... that makes only confusion to members ....

Reading your post/s your own answers sound reasonable to me ... but that doesn't mean automatic acceptance to some other people with maybe particular reason to not accept it.

Please read my sig ...

I wish you a good luck with answers you need.

Best regards, Josip :)

anup
05-09-2012, 09:42 AM
Hi Josip,
Thanks for your reply and sorry for uploading at 2 forums.
There were many views to my post but no reply. I was worried whether my presumptions were wrong. You guys are really masters in technology and I have very high regards to all of you for your knowledge. Validation from RE experts is more important for me.
I am deleting this thread from this forum.

mad fridgie
05-09-2012, 12:41 PM
If you are always utilizing 100% of the cooling and heating side (presume heating will always be similar), then it simply comes down to SST (Te) higher the SST the more efficient.
So keeping it simple water entering 12C, then SST will be around 8C, air on will 20C+, SST will be about 14C.
The unknown is the cost of moving the water or the air, which needs to be calculated into the overall COP.

anup
06-09-2012, 11:13 AM
Thanks Mad Fridge. Cost of moving the water and the air is almost similar.