smart51
|
| posted on 9/8/15 at 01:06 PM |
|
|
Electric underfloor heating and solar PV
We're planning to buy a house that needs total renovation. Rather than install conventional gas central heating, we're thinking about
electric under floor heating and a large solar PV array on the 64m2 flat roof. Do any of the locost builders know anything about this sort of thing?
I'm always willing to consider the unconventional, like building your own car. But masses of solar PV and underfloor heating is a lot of money
to experiment with. Does electric underfloor heating work as a building's sole source of heat? Would an 8 or 10 kWp solar panel arrays
generate usable quantities of power in the winter? Because we will insulate the building well, the house would lose between 80 and 100 W of heat per
°C temperature difference. So 1kW of heat would be needed on a mild winter's day and 2kW on a fairly cold day.
[Edited on 9-8-2015 by smart51]
|
|
|
|
|
BenB
|
| posted on 9/8/15 at 01:35 PM |
|
|
I think as you've guessed it's not an ideal situation. PV production in the winter is pathetic in the UK. We covered our roof with it at
work. Great in the summer (powers the AC nicely) but in winter we're lucky if we can run 3 computers off it. Also unless you're prepared
to get cold at night you'ld need a massive slab to heat it up during the day to stay warm. Returns off a PV system in the height of summer are
marginal, designing a system for it's winter returns? Don't think it would be feasible. Kudos if you manage it but you'ld have to
massively over-compensate for the reduced winter output and I can't help but feel the costs would be massive and pay for quite a lot of more
conventional heating.
|
|
|
smart51
|
| posted on 9/8/15 at 03:12 PM |
|
|
We'd have a feed in tariff, so we'll get a big cheque every month in the summer. It's just that you get paid less than you pay for
a unit of electricity. So long as you get paid more in the summer than you are charged in the winter, I guess you're OK.
|
|
|
cliftyhanger
|
| posted on 9/8/15 at 04:05 PM |
|
|
In which case why not use the PV's to generate cash, and then gas (much cheaper) to heat the house?
And 2KW to heat a house in a cold spell?? sounds mighty low to me, unless a new build code 5 (or is it 6 now) house.
|
|
|
smart51
|
| posted on 9/8/15 at 05:38 PM |
|
|
Gas (water) under floor heating takes up about 100mm of space above the floors. Electric underfloor heating needs 12mm of latex under carpet or can
be tiled directly over. Its electric or traditional radiators, which just take up wall space. We're planning to insulate and make airtight to
modern standards and fit mechanical heat recovery ventilation. It won't go as far as being a passive house (no heating at all) but should need
very little heating.
|
|
|
macc man
|
| posted on 9/8/15 at 06:13 PM |
|
|
I worked on a house that had been totally rebuilt. It had water underfloor heating and solar water heating panels on the roof.
It felt very warm with just the underfloor heating on and the boiler runs at a much lower temp saving fuel.
The heating panels work very well warming the water even on a dull day. All in all a much better solution than electric heating.
I don't think the feed in tariff is going to be around for too long either. I would do some more research before diving in.
|
|
|
tegwin
|
| posted on 9/8/15 at 06:55 PM |
|
|
As above, the more sensible option is to install a large thermal store tank and use solar vacuum tubes to heat the water in the tank. Supplement the
heat with a log burning stove and back boiler or a dedicated gas boiler...
You then draw off the heat from the thermal store as and when you need it for underfloor heating and direct mains pressure hot water...
Without the feed in tarrrif pv makes little sense..... Solar water however makes perfect sense if you had the right roof for it...
Other options are ground source or air source heat pumps all fed into the same thermal store.
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
coozer
|
| posted on 9/8/15 at 07:02 PM |
|
|
Go on the BBC iPlayer and watch The House That £100k built. Series 2:4, Jo-ann and Andy.
That will give you the ideas.
Their idea was for a house that cost nothing to run.
Also I would go for a ground source pump with a deep shaft drill for the floor heating.
[Edited on 9/8/15 by coozer]
1972 V8 Jago
1980 Z750
|
|
|
40inches
|
| posted on 9/8/15 at 08:30 PM |
|
|
quote:
Originally posted by macc man
I don't think the feed in tariff is going to be around for too long either.
This is true. The tariff is being reduced every year, but it is locked at the price in place when you have the installation, for 20 years but
increases by the amount of inflation within the 20 year period.
We had a 3 Kw system installed 6 weeks ago, we have generated 4 times more than we used, so building up a reserve for the winter 
|
|
|
big-vee-twin
|
| posted on 9/8/15 at 09:51 PM |
|
|
The well insulated standard house need about 45 watts\meter to heat at 21inside -5 outside
With walls at 0.25 uvalue.
So needs aound 10-15kw to heat correctly.
Your 1-2 kW is extremley ambitious how did you come to this figure?
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
|
|
|
daniel mason
|
| posted on 9/8/15 at 10:43 PM |
|
|
1-2 kW is simply not enough!
|
|
|
russbost
|
| posted on 10/8/15 at 08:21 AM |
|
|
First of all I'm assuming you are going to be staying there for the next 10 years minimum, if not you might want to recalculate some of the
investment strategies.
I have a 4kW PV array, it generates a little over 2000 kW hours per year on average, but hardly any of this is generated in Dec, Jan, Feb when you
would most need it, typical output at that time of year would be just a few hundred watts a day (none if the panels are covered in snow!). I'm
in the S.E. of England, but my panels are partially shaded for probably 1/3 to 1/2 a day which makes a significant difference, I have a mate in
Newcastle with an East/West installation (far from ideal) & he actually generates a little more than I do. I got in on the first stage of tarifs
& it pays me around £1000 a year plus saves around £200 - £300 on the electricity bill, it's been in 4 years this Nov & has already paid
back around half my initial investment, I believe current tarif is about 1/4 of the original, but installation costs are probably only around 1/2 what
they were then. There is no way you could possibly use it to heat anything in winter. I would expect an installation to cost around £6k (assuming you
don't have anything awkward to push cost up) & if you get direct sunlight particularly from a southerly direction then expect payback in
around 10 - 12 years - income of around £250 pa increasing year on year & saving on electric bill of similar, probably a little more if you
intentionally use electric at around the right times
I also have gas, wet underfloor heating for part of the downstairs of our house & have to say I would not particularly recommend it, it's
expensive (time consuming) to install & now in, although it works ok, you have to have the heating switch on around an hour b4 you actually need
the heat for it to do anything effective, once working properly it is a very pleasant heat, as you don't get any obvious hot & cold spots.
If you have someone at home most of the time it might be a worthwhile investment, but I think there are better ways
If I were starting from scratch with a place I think I'd be looking at heat pumps & possibly even a heat pump type boiler, although electric
because they take heat from the outside you can get 3 - 4 kW out for only 1kW in, so even tho' electricity costs around twice what gas does per
therm, you're getting more than twice the efficiency - plus you'd be using all your solar power to run it, so none is going back to the
grid (you still get paid the same either way). I'm not saying do it, I'm saying look at costs vs returns. Depending on your position &
how windy it is I would also look at wind turbine generators
One place you can make a massive saving is on heating hot water, don't get a commercial firm in as they will charge anything between around £5k
- 15k!!! But it is something you can do yourself very cheaply either with home made panels or shop bought solar tubes & installation is a fairly
simple DIY job, remember you only need to heat the house thro' winter, but you need hot water all year round & you only need a sunny day to
generate it, doesn't need to be a warm day, just sunny - there's loads of stuff about this around on the web. I'm contemplating a
DIY reflecting trough arrangement, perhaps using fresnel lenses to increase sun concentration, just toying with ideas at the moment. I'm sure
there are a few people on here who've already done a DIY hot water install
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
|
NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
|
jmad
|
| posted on 10/8/15 at 09:44 AM |
|
|
As others have said I think you will struggle to get the numbers to add up during the winter. We had a 4kW system installed in Nov 2011 so got in
under the original tariff. The roof faces south and has no shade, but we would still struggle to generate more than 150 KW hours a month in the
winter, but this will increase 500 KW hours a month in the summer. We recently renovated the downstairs of the house and looked at adding electric
underfloor heating (due to the height issue) and I couldn't get it to add up even at 50p per unit. I look at it as a money making exercise in
the summer that funds the costs in the winter. As others have said I would look at heat pumps.
Our figures:
14/02/2012 500
15/05/2012 1699 121%
14/08/2012 3086
14/11/2012 4153 123%
01/05/2013 5417
06/08/2013 7258 126%
29/10/2013 8263
6/11/2013 8336 115%
30/01/2014 8783
30/04/2014 9905 133%
23/07/2014 11445 124%
23/10/2014 12737 124%
27/01/2015 13315 137%
06/05/2015 14610
04/08/2015 16185 119%
|
|
|
smart51
|
| posted on 10/8/15 at 06:24 PM |
|
|
I've had another look at wet underfloor heating and have found two good solutions. The first uses 10mm pipe and latex screed and raises the
floor by just 15mm. It can be carpeted directly over too. The second, and potentially better option starts with fitting foam board insulation
between the joists, which we are planning to do. But you fit the foam boards lower and put the hot water pipes below the floor boards. A bit of
cement or latex screed to build up to the top of the joists and you get underfloor heating without raising the floor level at all. This is probably
the system we'll go for.
|
|
|
smart51
|
| posted on 10/8/15 at 07:49 PM |
|
|
quote:
Originally posted by daniel mason
1-2 kW is simply not enough!
The calcs for the house as it stands are a 5 kW heat loss for a 10 degree temperature differential and 10kW for 20 degrees. I'm planning to get
the u values down by a factor of 5. Like I said, it won't become a passive house but it will be pretty good.
|
|
|
cliftyhanger
|
| posted on 10/8/15 at 09:38 PM |
|
|
5kw at the moment?
Just as a comparison, our house is a 1950's jobbie. It has 270mm of loft insulation, double glazed, solid floors (only some have insulation,
about 1/3) and cavity wall insulation. Part built from solar lightweight blocks, mostly 1950's concrete internal skin. But that takes a 30kw
boiler gently chugging away in the winter, probably on 50% of the time. so about 15kw when it is sub zero out.
I am amazed that the place is already 3x better, that would take a lot of extra insulation (or a tiny house) to start with.
To reduce it significantly would require triple or more glazing plus lose loads of space to extra wall insulation. That is before the roof and
floors.
I still believe your calcs are out somewhere, buy a significant factor.
|
|
|
russbost
|
| posted on 10/8/15 at 09:38 PM |
|
|
"The second, and potentially better option starts with fitting foam board insulation between the joists, which we are planning to do. But you
fit the foam boards lower and put the hot water pipes below the floor boards. A bit of cement or latex screed to build up to the top of the joists
and you get underfloor heating without raising the floor level at all. This is probably the system we'll go for"
That is the same system we have, as said, expensive & time consuming to install, uses a second pump to run the system & takes a good hour at
least to start generating any real warmth in the room, that said it also takes an hour plus to cool back down so can be reasonably well controlled by
a timer, but doesn't fit with the timing needed by the rest of the system
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
|
NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
|
