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lenny

Good evening,

a question for the experts!

What air and water temperatures should be used when calculating heat pump sizes?

Thanks in advance

len
 
Good evening Len. First I am not an expert but I have installed my system that works well for me.
I think your question will be one for Worcester and would depend on so many factors. Need to know more about building fabric, heat losses, insulation, rooms, window sizes & DG /TGlazing heat losses. etc. Can under floor heating be installed ? Will HP be used as a hybrid ? ASHP or GSHP ? How big s your budget We need to know alot more about what you want to do ? etc. It is not a simple answer to HP sizing which is possibly why so many plumbers run away from the challenge when faced with anything unfamiliar.
A simple answer to your question, my HP is 15 KW output for 4 bed semi 10 oversized rads, some under floor and Koi Pond. In my case Circ temp of 39 to 48 degs C auto optomised by various sensors. You will not achieve good COP factors if outside temps drop below about 5 degs C or if aiming for output temps above 49 degs C depending partly on the Make / model of the HP you install.
Hope this is a helpful start to a viable system, will need to be hybrid in UK. Whats your location ?
 
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Air temp will be dependant on location, flow temp will be 50 degrees or lower for RHI eligibility, but as low as possible ideally to improve COP and SPF. It all depends on how much work/expense is required to increase emitters sizes in order for them to still be able to heat the rooms with lower flow temp at the design temp. You could be talking 50% + bigger. This all depends on heat loss calculations.
 
Your flow temperature will depend upon your emitter design, your air temperature will depend upon your location, your sizing will depend upon your load.

So to answer your question
1) You need to do a full room by room heat loss calculation to BS EN 12831
2) You need to design your emitters to cope with your desired flow temperature (the lower the more efficient the heat pump)
3) you need to know your location so that you know the air temperature to design to
4) you need to know the CoP's of the different heat pumps.
5) don't believe the labels on the tin :) a 15kW heat pump is more usually a 10kW Heat pump at 0/35

Hence a simple design will take a professional around a day to do properly

You can find out how to do it here: Microgeneration Certification Scheme - Installer Standards if you follow all the guidance there it will take you about 120 hours to work through it (just for heat pumps) you'll then have half an idea of how to get it very wrong :) like about 95% of the installations done pre february 2012, and about 75% of the ones done since that haven't been done by MCS certified installers.
 
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Thanks Worcester good answer as usual.
Your comment 5;- Good point, that`s one of the reasons I use mine Hybrid as the COP is not so good at low temps. This is when my optomiser is set to bring on my GCH & to inhibit the low COPs.
I did not go down the MCS route, would have been too much trouble & cost for me, to make it worth while, as it would have extended pay back time & short term costs. I wanted my system working 15 months ago after a few mods it`s working well, & I am pleased I did go hybrid !
 
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