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emmalt
Elm Sapling
Joined: 14 Sep 2007
Posts: 46
Location: UK
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Posted: Thu Oct 01, 2009 3:16 pm Post subject: Opinions on ASHP v. Solar
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I am looking at possibly putting in an ASHP but was wondering which would be better?
ASHP for both hot water and heating
or
ASHP only for heating
Solar panels for hot water
Any opinions?
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martin w
Hazel Seedling
Joined: 01 Sep 2009
Posts: 22
Location: South Wales UK
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Posted: Thu Oct 01, 2009 7:34 pm Post subject:
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Hi, my thoughts would be to use a thermal store and plumb the solar and ASHP (and anything else) into it. The runn the hot water and central heating form the therml store...
the above is a simplified view...mains gas is probably still the cheaest way to heat your home - now if you re using 'green' electricity... thats a different matter...
ASHP works best if using underfloor heating as the supply water temp is around 35°C as opposed to proably 75¯C for radiators (ASHP only go to around 55°C).
just my 2p worth
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DMc
Established Chestnut
Joined: 08 Feb 2009
Posts: 120
Location: Finland
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Posted: Fri Oct 02, 2009 1:17 pm Post subject:
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| martin w wrote: |
| ASHP works best if using underfloor heating as the supply water temp is around 35°C as opposed to proably 75°C for radiators |
True in typical cases, but radiators don't have to run so hot. If you have more rads and/or superior insulation you can run the rads at a lower temperature. For example, mine run between 35C and 55C, not 75C. In the UK it should be possible to heat a house with relatively cool rads.
Edit: I just checked: outside it is 7C and my rads are 28C.
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Billy Rhomboid
Moderator / Ancient Yew
Joined: 17 May 2006
Posts: 13671
Location: The Isle of Avalon
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Posted: Fri Oct 02, 2009 1:28 pm Post subject:
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The way radiators and underfloor heating disperse heat is significantly different though. Underfloor is by far the better idea for low temp ASHP/GSHP.
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DMc
Established Chestnut
Joined: 08 Feb 2009
Posts: 120
Location: Finland
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Posted: Fri Oct 02, 2009 1:36 pm Post subject:
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I think that is true, and in a new build it would be a very relevant factor. The problem is that this view can put people off fitting heat pumps to existing properties when in reality they can work well. Our home was built in the 1890s and our climate makes heating more difficult that in the UK, but our heat pump works well. We didn't change anything else when we installed the heat pump; we are using the old rads that have been here for decades. It is worth pointing this out to avoid anyone dismissing heat pumps just because their home has radiators rather than under-floor heating.
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Andy_WSM
Elm Sapling
Joined: 20 Feb 2009
Posts: 32
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Posted: Fri Oct 02, 2009 3:34 pm Post subject:
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My air-water pump runs at 50C and heats the house perfectly with the rads that were originally fitted. Last Winter we saw lows of -10C out and I was still toastie warm inside, but acknowledge the ASHP did run for considerably longer and had to defrost itself a few times.
Even so, as you will see in my thread here: https://newhousefarm.tv/forum/viewtopic.php?t=17653 I saved a considerable amount of fuel ( & money ) over my previous years consumption.
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Billy Rhomboid
Moderator / Ancient Yew
Joined: 17 May 2006
Posts: 13671
Location: The Isle of Avalon
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Posted: Fri Oct 02, 2009 4:12 pm Post subject:
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Fair point DMc. I do tend to think more from a newbuild perspective, because that is what I do.
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martin w
Hazel Seedling
Joined: 01 Sep 2009
Posts: 22
Location: South Wales UK
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Posted: Fri Oct 02, 2009 6:02 pm Post subject:
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Maybe I should have put a disclaimer with that comment on 'works best with underfloor heating' I was tired and wrote a quick reply (I really should edit all those typos!)
Anyway if you wanted to see if a lower temp was OK on your heating (with rads) you could probably turn the boiler temp down (on the heating) and see if the rads still heat the house OK?.
I think most radiators would have been installed with a room temp of around 20°C in mind (if the plumber did the heat loss calculation right - or could be bothered), so if you are aleady running with room temps at around 18°C you should be ok anyway.
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Billy Rhomboid
Moderator / Ancient Yew
Joined: 17 May 2006
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Location: The Isle of Avalon
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Posted: Fri Oct 02, 2009 6:04 pm Post subject:
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| martin w wrote: |
| (if the plumber did the heat loss calculation right - or could be bothered), |
hohohohohohohohohoho
Yeah right.
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martin w
Hazel Seedling
Joined: 01 Sep 2009
Posts: 22
Location: South Wales UK
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Posted: Fri Oct 02, 2009 6:18 pm Post subject:
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| Billy Rhomboid wrote: |
| martin w wrote: |
| (if the plumber did the heat loss calculation right - or could be bothered), |
hohohohohohohohohoho
Yeah right.
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I did my heat loss calcs and have fitted rads around 200% the size I needed so I can use a ASHP if I want....
do you mean that plumbers don't do heat losses and calc the rads anymore? (my father in law always has) - I know that in my ex council house (1952 vintage) the existing rads are ... ahemm 'just a pack of rads that we had and fitted' type none of which were anywhere near the correct specs.
(mind u I am over spec by a way so maybe i should not comment
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Billy Rhomboid
Moderator / Ancient Yew
Joined: 17 May 2006
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Location: The Isle of Avalon
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Posted: Fri Oct 02, 2009 7:01 pm Post subject:
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My opinion of the average plumber these days is perhaps marginally lower than my opinion of the average architect.
Don't get me wrong - a proper pukka old-school plumber is worth his wait in copper piping, but they are very few and far between nowadays. The huge explosion in 'you can make £££ as a plumber' courses a few years back has meant that most of the plumbers in the Yellow Pages these days are are complete numpties who wouldn't know a Stilson from Stilton.
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farrpau
Elm Sapling
Joined: 23 Jun 2009
Posts: 52
Location: South Wales
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Posted: Fri Oct 02, 2009 7:37 pm Post subject:
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| Billy Rhomboid wrote: |
My opinion of the average plumber these days is perhaps marginally lower than my opinion of the average architect.
Don't get me wrong - a proper pukka old-school plumber is worth his wait in copper piping, but they are very few and far between nowadays. The huge explosion in 'you can make £££ as a plumber' courses a few years back has meant that most of the plumbers in the Yellow Pages these days are are complete numpties who wouldn't know a Stilson from Stilton. |
This is why i keep two copies of the yellow pages ones about 7 years old now and the other is current if their not listed in both with the exact same details i won't use them. protects against the here today gone tomorow companies. course recomendations will be used first.
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DMc
Established Chestnut
Joined: 08 Feb 2009
Posts: 120
Location: Finland
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Posted: Sat Oct 03, 2009 6:36 am Post subject:
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| martin w wrote: |
| Anyway if you wanted to see if a lower temp was OK on your heating (with rads) you could probably turn the boiler temp down (on the heating) and see if the rads still heat the house OK?. |
Yes. Also check what temperature the rads are at normally. If they are way over 55C a heat pump may not just be a drop-in replacement.
| Quote: |
| I think most radiators would have been installed with a room temp of around 20°C in mind (if the plumber did the heat loss calculation right - or could be bothered), so if you are aleady running with room temps at around 18°C you should be ok anyway. |
That's where I struggle. I'm not a professional but I can do heat loss calculations - in the UK. I don't know how to adjust them for the very different construction methods we have here. I want to make some changes to my rads but I'm just going to have to go by guesswork.
We usually keep our house at 21C. We would not be comfortable at 18C, but each to his own. Certainly if you are happy with a cooler house you can run your rads at a lower temperature.
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Andy_WSM
Elm Sapling
Joined: 20 Feb 2009
Posts: 32
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Posted: Sat Oct 03, 2009 9:55 am Post subject:
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| DMc wrote: |
We usually keep our house at 21C. We would not be comfortable at 18C, but each to his own. Certainly if you are happy with a cooler house you can run your rads at a lower temperature. |
I am the same as you actually. I read all the advice about keeping the house at a lower temperature, but I do find it uncomfortable. I don't work 60 hours a week to spend my evening & weekends feeling uncomfortable.
I think too much emphasis is being put on radiator size here. If the radiators are marginally undersized then the system will need to run for longer to obtain the desired temperature, that's all. The amount of energy you are releasing into a room will be the same, it will just take longer to release it. Likewise, if the radiators are over sized, you will heat the room quicker. The single most important thing is insulation. If everything is insulated as best as you can, that will make the biggest difference to the performance of any system. You will struggle to heat any room where the heat is leaking out quicker than you are putting it in! Increasing the size of the radiators means you would have the potential to leak more heat to the outside!
The advice on turning the boiler down to test if the house still reaches the desired temperature is probably the best actual test that you can do as it proves whether everything will work for you given the level of insulation you have and the size of your existing rads.
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DMc
Established Chestnut
Joined: 08 Feb 2009
Posts: 120
Location: Finland
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Posted: Sat Oct 03, 2009 10:09 am Post subject:
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| Andy_WSM wrote: |
| I think too much emphasis is being put on radiator size here. If the radiators are marginally undersized then the system will need to run for longer to obtain the desired temperature, that's all. .... The single most important thing is insulation. |
I agree. In most houses the radiators won't be so small as to be a problem and improving poor insulation is always going to be a better solution than installing even the best heat source.
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