DInwood

Choice of ASHP for near-passivehouse

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Does anyone have any experience of Alpha Innotec ASHP? (model LWD 50A/SX + HMD1 SE)?  I've seen this on the spec from the heating engineer working on our house but have been unable to find out much about it, apart from some quite sparse documentation on Omnie's (the UK agent's) website.  The house is 150sqm, designed to be carbon neutral, so well insulated with MVHR & UFH & 6kWp of PV (enough over full year to meet energy needs).  Are there other small ASHPs that should be considered?

Also, can anyone help me understand how an ASHP provides both low temperature output for the UFH and yet hot enough water for the DHW?  I'm not doubting that it does, I just dont understand how it works despite studying the various plumbing diagrams on this forum.  Plus what happens in the summer when in theory the ASHP could be cooling the "UFH" pipes yet heating the DHW?  I'm feeling rather stupid despite my science degree (or is that because of...).  I'll bet this has been well explained somewhere I haven't found yet.

Thanks to all for a brilliant forum.

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Hello and welcome,

 

6 minutes ago, DInwood said:

Also, can anyone help me understand how an ASHP provides both low temperature output for the UFH and yet hot enough water for the DHW?

 

Space heating, domestic hot water and cooling are all separated in time, i.e. only one function at a time. The hot water may come on for 0.5hr then it returns to space heating then back to hot water etc.

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I have a 5kW LG ASHP heating a similar sized house.

 

Mitsubishi Ecodan is a popular choice and they do a 6kW size.

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2 hours ago, DInwood said:

Also, can anyone help me understand how an ASHP provides both low temperature output for the UFH and yet hot enough water for the DHW? 


my 5 kW ASHP only delivers one temp water, and I have set it to 48’, that is quite hot enough fir DHW as long as you store enough as you don’t blend down as much as you do with 60’ DHW. When in heating mode it heats a buffer tank with a stat set to 35’, this then feeds a UFH manifold with a blender set to 24’. It all works very well.

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@DInwood Alpha is part of the Nibe group so been around a while. The Innotec units are all new - use propane as a refrigerant and pretty sure they call come with a buffer as standard which is a plus. 
 

Downsides are they have a single U.K. distributor so don’t expect pricing to be in line with LG/Panasonic/Mitsubishi. Also means support is limited and technical documents are thin on the ground. 
 

Make sure your plumber isn’t specifying just because his favourite supplier has an offer on .. 

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19 hours ago, DInwood said:

I'm feeling rather stupid despite my science degree (or is that because of...)

Picked the wrong area of science then.  Thermodynamics is the Royalty of Science.

 

Basically you have a cold side and a hot side, just like any heat engine.  What goes on in the middle is irrelevant, but in the case of heat pumps it is the expansion (cooling) and compression (heating), that does the work.

Where it differs from a combustion engine is that the cold side is below ambient temperature and the hot side is is above ambient temperature, though not as much as a combustion engine.  Though the overall temperature differences may well be similar i.e. 70°C to 80°C.  It just starts at a lower temperature say -30°C.

So when you need to cool, it is really just a bit of plumbing change, pump the cold side around the house, cool the hot side with external ambient air.

When heating DHW, it ramps up temperature (compresses harder) and diverts this to the cylinder (lots of debate about cylinders, they are only a bucket of water that starts at a low temperature and gets heated, ready for use), while disconnecting the rest of the system.

 

The thing to remember with a heat pump is that as they approach their maximum output, the CoP (efficiency multiplier) drops towards parity i.e. 1 kWh in, 1 kWh out.  This is why they need to be oversized, usually around 30% above the power (the kW, not the kWh) of the DHW requirement heating times i.e. a sensible reheat time, say 2 hours.

 

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On 20/12/2020 at 14:01, joe90 said:


my 5 kW ASHP only delivers one temp water, and I have set it to 48’, that is quite hot enough fir DHW as long as you store enough as you don’t blend down as much as you do with 60’ DHW. When in heating mode it heats a buffer tank with a stat set to 35’, this then feeds a UFH manifold with a blender set to 24’. It all works very well.

 

Useful guidance - thanks.

 

Just out of interest, if you are cooling in the summer, then I assume you have a bypass round the buffer tank and blender? Or are you not cooling the slab in the summer?

 

Simon

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3 minutes ago, Bramco said:

are you not cooling the slab in the summer?


No, I don’t find it necessary, for the few weeks a year that are hot enough, I enjoy it 🤣, saves paying fir a holiday to the south of Italy where the temps are that high anyway!

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The climate up here does not really warrant cooling.  There was one hot spell the year before last, I briefly tried cooling the floor, but being a timber floor I was concerned at (possibly unseen) condensation, and in any event that only helped to cool downstairs.  To properly cool the house I concluded it would need two fan coil units one in each of the main bedrooms to introduce cooled air at a high level.  Something I may implement one day.

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36 minutes ago, joe90 said:
41 minutes ago, Bramco said:

are you not cooling the slab in the summer?


No, I don’t find it necessary, for the few weeks a year that are hot enough, I enjoy it 🤣, saves paying fir a holiday to the south of Italy where the temps are that high anyway!

We don't get exceptionally high summer temperatures, or exceptionally cold winter ones.

We just get wind and rain.

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2 minutes ago, SteamyTea said:

We just get wind and rain.


yes, down in the South West. Jeremy ended up cooling his house more than heating but he had a micro climate, something very difficult/impossible to model.

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Just now, joe90 said:

he had a micro climate, something very difficult/impossible to model.

Very easy to measure though.

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Just now, SteamyTea said:

Very easy to measure though.

Yes, after it’s built. As I have said before I did no modelling whatesoever for my build but followed very easy to work out basic insulation and airtightness measures and it’s worked well (phew).

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38 minutes ago, joe90 said:

Yes, after it’s built. As I have said before I did no modelling whatesoever for my build but followed very easy to work out basic insulation and airtightness measures and it’s worked well (phew).

All it has every been really, just more fun to make it complicated.

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