View Full Version : Help wanted -very small air-water heatpump advice

27-09-2014, 03:33 PM
Dear all,
Sorry if this has already been raised but I'm new here! I am looking for some pointers of where to look or how to deal with the following problem:

I have a residential Plant Room which has a lot of electronics in it generating about 1.2kW of waste heat. Needless to say it is getting HOT in there! I have redirected the MHVR system to draw from the plant room instead of outside and fitted a blower to suck cold external air in to the plant room. This has helped but it's still too hot.

Now there is an unused solar coil in the large hot water tank so my thought was is there a system that can extract the heat (25-35C) and use it to create hot water (say 60C) via the solar coil? Ideally the system would run continuously. So far any of the systems that I have seen are far too large.

Thoughts please.


monkey spanners
27-09-2014, 05:38 PM
Probably not off the shelf but one could be made. Is the hot water tank heated and if so to what temperature?

27-09-2014, 06:00 PM
The hot water tank's primary heating (internal coil circuit) comes from a ground source heatpump, with a 3kW immersion as a backup. It is heated to 55-60C with regular anti-bacterial superheating cycles. Heatpump runs at night (Economy 7) only.

I'm not surprised that ther's no commercial system, so I was expecting a DIY/custom system.


install monkey
27-09-2014, 07:50 PM
"residential Plant Room which has a lot of electronics in it generating about 1.2kW of waste heat"
add more insulation to the cylinder:o
also if the plantroom is cooler then the cylinder will lose heat quicker, as long as its correctly ventilated for any gas appliances , if there isnt any gas then i wouldnt worry

27-09-2014, 09:18 PM
Good idea but all the heat is coming from the electronics!1.2kW electric in = 1.2 kW heat out. The heat is coming from various inverters and servers rather than the hot water tank.

Yes one option is to move everything but I would rather harvest than dump the heat, hence the question.

Any suggestions?


mad fridgie
28-09-2014, 01:49 AM
Easy enough to do, but I would not use the coil in the cylinder, purchase a vented double wall heat exchanger.
I would choose R134a as the refrigerant for this application. "high suction and discharge pressures"
i would look at small commercial evap, if looks are not important, Size evap and compressor to meet 1.2kw demand (plus humidification is high RH)
Need not cost a fortune.

28-09-2014, 01:55 AM
No way you will get 25-35C heat in the room into a tank that is already 50C+ without the heat pump. Perhaps one of the small Danfoss DC powered beasties could be used. It would be about the right size but the coil in the tank would have to be the right construction and take the pressure (doubtful) unless there was a separate HX.

Too much work......best to just vent it to a bigger area and let its AC system take care of it.

28-09-2014, 01:57 AM
1.2kw, Mad, you think it is worth the hassle?

mad fridgie
28-09-2014, 11:15 AM
Mike, it all depends upon how much hot water they use and pay for.

lets 24Kwhrs of heat per day, at 10p/kwhr thats 800quid plus per year saving, 3-4 year payback then worth doing, and he does want the room cooled as well, so dual benefit.