Solar Underfloor Heating

Redfowler11

Just wondering if anyone has installed a solar system for use of underfloor heating. Looking to heat open plan kitchen/living area. Not convinced that the payback is there for Geo thermal from what I've read. Any help or advice appreciated.

fclauson

you have to look at you overall heating requirments and your current insulation

what is you main heat source?
what is the area to be heated
how will you heath the space at night time/winter

I did publish a chart some time ago showing the geothermal is actually more const effective over a 15 year period that oil + solar

ccsolar

Redfowler11 wrote: »

Just wondering if anyone has installed a solar system for use of underfloor heating. Looking to heat open plan kitchen/living area. Not convinced that the payback is there for Geo thermal from what I've read. Any help or advice appreciated.

Pm sent

JD6910

Can you pm me on this also.thanks

beyondpassive

Redfowler11 wrote: »

Just wondering if anyone has installed a solar system for use of underfloor heating. Looking to heat open plan kitchen/living area. Not convinced that the payback is there for Geo thermal from what I've read. Any help or advice appreciated.

Is this a renovation?

The return on investment is heavily influenced by the return temperature. So you would need to prioritise the following.

1. Perimeter heat loss
2. Fabric heat loss
3. Ventilation heat loss
4. Control

(see the pattern here insulation, insulation, heat recovery and then the knobs and dials.)

Get the demand side right first and the supply side will fall into place. Once you've a radiant slab and building envelope that can hold heat, geothermal or air source will purr away keeping it topped up throughout the heating season.

air

Solar isn't practical for space heating, think about it - you don't have any sunshine at the times when your heat demand is highest - mid winter.
The only possible exception is with the use of an inter-seasonal store but you're looking at huge captial costs there also.
In short anyone selling solar panels will be delighted to facilitate you but you'll be wasting your time and money.

JD6910

beyondpassive wrote: »

Is this a renovation?

The return on investment is heavily influenced by the return temperature. So you would need to prioritise the following.

1. Perimeter heat loss
2. Fabric heat loss
3. Ventilation heat loss
4. Control

(see the pattern here insulation, insulation, heat recovery and then the knobs and dials.)

Get the demand side right first and the supply side will fall into place. Once you've a radiant slab and building envelope that can hold heat, geothermal or air source will purr away keeping it topped up throughout the heating season.

i fully agree here. i am going to town on the insulation and airtightness and i am starting to think do i need the air to water system for such a low energy house.

you said the air to water will work away during teh heating season - what happens in summer ??? - is air to water essentially OFF?????

Do-more

JD6910 wrote: »

i fully agree here. i am going to town on the insulation and airtightness and i am starting to think do i need the air to water system for such a low energy house.

you said the air to water will work away during teh heating season - what happens in summer ??? - is air to water essentially OFF?????

If it's any addition JD6910 all the major elements of my build are around 0.1 or a little less save for the windows which are 0.9, I will install a 5kW air source heat pump and use it for space heating and DHW in the heating season and for DHW for the rest of the year. I have estimated that solar panels will only reduce my running cost by approx. €100-€125 a year at present costs so it is borderline whether I could get a reasonable pay back on solar panels so I don't plan to fit any. I can't remember the figures but I think the heat pump will probably run for less than a hour a day during the summer to satisfy our projected DHW demand.

JD6910

Do-more wrote: »

If it's any addition JD6910 all the major elements of my build are around 0.1 or a little less save for the windows which are 0.9, I will install a 5kW air source heat pump and use it for space heating and DHW in the heating season and for DHW for the rest of the year. I have estimated that solar panels will only reduce my running cost by approx. €100-€125 a year at present costs so it is borderline whether I could get a reasonable pay back on solar panels so I don't plan to fit any. I can't remember the figures but I think the heat pump will probably run for less than a hour a day during the summer to satisfy our projected DHW demand.

Very interesting - can you pm me the details of the make model etc.... My issue with geo , ufh, and air to water in general is the constant temp theory. Why is the ufh on when we all at work!!!!!!

Are you using rads or ufh??????? I would imagine the 5kw pump is handy money????? From what I see the the oil,solar, solid fuel option is almost same price as air to water system but the big difference is the solar won't send you a bill every two months and you can turn on and off the oil and solid fuel as you want!!!!!! Still don't agree with the heat pump coming on at 2pm on a weekday because the temp has dropped and we all at work, school etc!!!!!

BryanF

JD6910 wrote: »

Very interesting - can you pm me the details of the make model etc.... My issue with geo , ufh, and air to water in general is the constant temp theory. Why is the ufh on when we all at work!!!!!!

Are you using rads or ufh??????? I would imagine the 5kw pump is handy money????? From what I see the the oil,solar, solid fuel option is almost same price as air to water system but the big difference is the solar won't send you a bill every two months and you can turn on and off the oil and solid fuel as you want!!!!!! Still don't agree with the heat pump coming on at 2pm on a weekday because the temp has dropped and we all at work, school etc!!!!!

the old rational with regards to heating cycles is not revelant in this discussion. If you go air-tight, Hrv, solar gain and so on, you will be planning for a constant temp. Savings are made by reduced heat load and only have the addational heat requirement ticking over at its absolute min. The days of blasting a 200+ m2 house when you come in from work are gone unless you've a forest out back..

Do-more

JD6910 wrote: »

Very interesting - can you pm me the details of the make model etc.... My issue with geo , ufh, and air to water in general is the constant temp theory. Why is the ufh on when we all at work!!!!!!

PM sent, wot Bryan said...

beyondpassive

If its any use, there's a guy down in north Wicklow who has a Solar heated Passivhaus (I had no involvement in the project) completed in 2011. He is offering site visits for a modest fee and is highly recommended to see solar with accumulator and conventional boiler in-situ. The MHRV and treble glazed windows are also interesting.

I can send on details by PM.

air

Why does he have a conventional boiler at all if the house is truly "solar heated"?
Using solar for space heating makes no economic sense.

quentingargan

air wrote: »

Why does he have a conventional boiler at all if the house is truly "solar heated"?
Using solar for space heating makes no economic sense.

Couldn't agree more. Also, the more passive a house is, the shorter its heating season. There is a short window in spring and autumn when a solar panel may provide some useful space heating. As you improve insulation, this window narrows to the few sunny winter days that you might get.

I really think this is a waste of money. Solar panels are great for providing hot water in the summer, at a time when the heating is off, and your hot water is more expensive as a result. So it displaces an expensive immersion heater. Using them to generate a fraction of the heat displacing much cheaper space heating fuel just doesn't stack.

If you need to use more solar to meet the renewable element of Part L, then use solar PVs to do that.

PeteHeat

I agree with Quentin, a passive house should not really need a constant heating system my understanding is they may require the occasional boost.

What would you do with all the heat the solar system will generate in summer?

One system we did has an over sized solar system that dumps all excess heat into a buffer tank when the cylinder for hot water is satisfied, this works for the customer because the house has a high heat demand, the house was built circa 1955 and added to over the years so good quality insulation is not a practical option.

.

fclauson

PeteHeat wrote: »

...., a passive house should not really need a constant heating system my understanding is they may require the occasional boost.


.

Unfortunatly not true - a Passive house has a constant heat loss dependant on temperature (much like any other house) all be it very low - if you have a sustained period of low or no solar gain into the building then you will need to replace this heat loss.

Now some say you can do this with your MHRV which can be possible (if the PHPP sheet suggest its possible) but it will never heat up a large thermal mass which has lost temp. The volumes are low (0.3 x your SqM approx) l/s. This will carry very little heat into the building.

So take the following example - a typical dark cold wet winter period of say 5 or 6 days - where there is very little sun. Your solar thermal will get no effective heat and you glazing will get no solar gain (they will be heat emmitters not collectors). Your superstructure starts to cool - its solid block or ICF - say it drops 1deg. Think of the energy required to raise all of your superstructure back to 20deg (because that's what a passive house is - all at one temp not just having one room at 20 and the rest at 15). It will take a lot of energy.

Its a myth to say a PH needs no heating - it just needs very little.

One other thing to bear in mind is that a PH need even heating. You would not cook a sausage by sticking just one end in the grill and hoping the other would get cooked via convection/conduction. MHRV is very ineffective at differentially distributing heat (your back bedroom will get colder than your sitting room with large glazed patio doors) So you need to think of your stratergy for heat distribution.

JD6910

PeteHeat wrote: »

I agree with Quentin, a passive house should not really need a constant heating system my understanding is they may require the occasional boost.

What would you do with all the heat the solar system will generate in summer?

One system we did has an over sized solar system that dumps all excess heat into a buffer tank when the cylinder for hot water is satisfied, this works for the customer because the house has a high heat demand, the house was built circa 1955 and added to over the years so good quality insulation is not a practical option.

.

i am thinking of putting in a buffer tank (not sure what size yet) which will be contributed to by large solar array (this will do some of the hard work for free), solid fuel stove with back boiler which we plan to light every winter evening and most saturdays and sundays and have a gas OR oil boiler to "top up" the buffer tank as required.
the house will be well built, no thermal bridges, 200mm cavity etc... full airtightness and MHVR system. also all the living spaces are south facing with super solar gain - any thoughts???

air

Have you read any of the previous posts above? Active solar space heating makes no sense & even less so when you already have passive solar gain as you say.
Adding panels may yield some negligible additional heat on a few select days in Autumn & Spring but due to the capital costs involved in buying the panels this will be the most expensive heating source imaginable.
I would suggest that you engage a competent indepent professional to advise you as you don't appear to have a great grasp of the fundamentals here.
If you're set on installing a huge thermal array, work away but don't fool yourself into thinking its going to do anything worthwhile.
The one exception would be if you had a use for large amounts of heat in summer time, such as a swimming pool.

PeteHeat

JD6910 wrote: »

i am thinking of putting in a buffer tank (not sure what size yet) which will be contributed to by large solar array (this will do some of the hard work for free), solid fuel stove with back boiler which we plan to light every winter evening and most saturdays and sundays and have a gas OR oil boiler to "top up" the buffer tank as required.
the house will be well built, no thermal bridges, 200mm cavity etc... full airtightness and MHVR system. also all the living spaces are south facing with super solar gain - any thoughts???

If you intend installing solar for hot water then it may be practical to oversize it by an extra panel using the buffer as a heat dump, better again fit the panels in the garden where you can easily add to the system, it would allow you to add an extra panel and measure exactly what the contribution is to the buffer in winter.

I would not be recommending a 150 tube system to anyone who is expecting a sustained heat contribution all year simply because we can't control the weather or the fact that we have much shorter days in winter which means less solar time for the system to harvest heat.

The stove is really only a good idea if you have a good source of fuel that comes almost free, even trees on your own land need to be cut, blocked, dried and stored, anything above 12 > 14 Kw output and I would go for a an outside wood boiler because the the bigger stoves need so much fuel to work properly you may as well make provision for the wheel barrow to transport the fuel through the house.

A stove as a room heater might be more practical, you get the fire / flame in the living room and any excess heat distributed by the MHVR.

Solid fuel is not cheap and the customer must be prepared to work to get it to produce heat, the theory can be good however it is a different story when everyone returns home on a cold evening knowing the fire must be lit to heat the house.

Maybe if you are looking on the excess heat from the solar and the stove as secondary contributors to a primary heat source which can be called on by the thermostats to prevent the temperatures dropping to a point where the house is only comfortable just when you are ready to go to bed, you could have a good system.

For comfort in your home with UFH it is important to recognise that your primary heating may have to be called on when nobody is home to maintain the minimum temperature or you are looking at long drawn out recovery times.

.

JD6910

PeteHeat wrote: »

If you intend installing solar for hot water then it may be practical to oversize it by an extra panel using the buffer as a heat dump, better again fit the panels in the garden where you can easily add to the system, it would allow you to add an extra panel and measure exactly what the contribution is to the buffer in winter.

I would not be recommending a 150 tube system to anyone who is expecting a sustained heat contribution all year simply because we can't control the weather or the fact that we have much shorter days in winter which means less solar time for the system to harvest heat.

The stove is really only a good idea if you have a good source of fuel that comes almost free, even trees on your own land need to be cut, blocked, dried and stored, anything above 12 > 14 Kw output and I would go for a an outside wood boiler because the the bigger stoves need so much fuel to work properly you may as well make provision for the wheel barrow to transport the fuel through the house.

A stove as a room heater might be more practical, you get the fire / flame in the living room and any excess heat distributed by the MHVR.

Solid fuel is not cheap and the customer must be prepared to work to get it to produce heat, the theory can be good however it is a different story when everyone returns home on a cold evening knowing the fire must be lit to heat the house.

Maybe if you are looking on the excess heat from the solar and the stove as secondary contributors to a primary heat source which can be called on by the thermostats to prevent the temperatures dropping to a point where the house is only comfortable just when you are ready to go to bed, you could have a good system.

For comfort in your home with UFH it is important to recognise that your primary heating may have to be called on when nobody is home to maintain the minimum temperature or you are looking at long drawn out recovery times.

.

peteheat - we are thinking 90 tubes of solar and a suitable large buffer tank.

please note we are thinking of high efficency rads throughout the house and not UFH. again the UFH works on the constant temperature theory and we feel that we dont want that - we want a system that we control as we feel cold. we also feel because of house orienation, build spec and design that we will need relatively little heat.
thinking of a gas boiler which is more efficent that oil??
gas companies will give a bulk storgae tank for underground which is a nice touch also. any thoughts??

PeteHeat

JD6910 wrote: »

peteheat - we are thinking 90 tubes of solar and a suitable large buffer tank.

please note we are thinking of high efficency rads throughout the house and not UFH. again the UFH works on the constant temperature theory and we feel that we dont want that - we want a system that we control as we feel cold. we also feel because of house orienation, build spec and design that we will need relatively little heat.
thinking of a gas boiler which is more efficent that oil??
gas companies will give a bulk storgae tank for underground which is a nice touch also. any thoughts??

The number of tubes is not really important, the quality is where the real difference in performance and of course initial outlay come into play.

Regardless of the system be it rads or underfloor the more the temperature drops the more expensive it is to bring it back up again, there is also the comfort factor, nobody wants to spend a lot of money and come home to a cold house.

With rads zone it properly, fit TRV's good thermostats and programmer will pay off very quickly.

By high performance rads are you thinking of a low temperature system or modern rads all of which claim to be high efficiency and you are looking at high temperature flow rates.

Unless they have had radical changes in there pricing LPG was always more expensive than oil, especially with the underground tank you are married to one supplier so no competition.

.

JD6910

LPG is circa 72C a litre and apparently burns on a blue flame which is more efficent - also the gas boiler is modulating and oil boiler is not.

the tubes will be by the "kings that span" - can mention company names do hope this is OK with the powers that be!!!!

delighted to see that you reckon this system will work but the key is the insualtion and airtightness to reduce the heat load to the absolute minimum!!!

PeteHeat

JD6910 wrote: »

LPG is circa 72C a litre and apparently burns on a blue flame which is more efficent - also the gas boiler is modulating and oil boiler is not.

the tubes will be by the "kings that span" - can mention company names do hope this is OK with the powers that be!!!!

delighted to see that you reckon this system will work but the key is the insualtion and airtightness to reduce the heat load to the absolute minimum!!!

I would double check the contract as it appears to be the only fuel to have a significant drop in price for the last 12 twelve months, LPG tracks oil but if you can lock in at around 72c it looks a very good deal, keep in mind that unless you are in Northern Ireland you can only buy from one supplier as they own the tank not you.

Modulating oil boilers are available.

Tubes are good quality so no problem there.

As we are talking about the heating system "The Key" is fitting a low temperature system that can call on heat when it is needed, a standard high temperature system needs a flow temperature of 70c with a return of 55c.

If you have a buffer with a store of water at say 50c you will not be getting full value as your boiler will have to fire to top up the temperature in which ever zone is calling.

If your system is low temperature the buffer at 50c can answer the call without calling on the boiler.

If you use timers or manual switch on and all the zones in the house call for heat at the same time the buffer will not get any chance to recover so you are guaranteed there will always be a call on the boiler.

Allow each zone to call for heat when the thermostat senses the need and you can have a lot of small demands instead of a series of big calls everyday, the small calls (separate zones) will give your buffer a chance to recover using the stove and solar.

You can use Weather compensating control as described by Soundness in the other thread and get the best of both worlds in system controls and efficiency.
.

fclauson

PeteHeat wrote: »

....

Modulating oil boilers are available.

.

really - which brands - all the research I did 6 months ago failed to turn up anything for the domestic market

JD6910

any thoughts on the gas modulating boilers!!!!

air

I'm not sure modulation makes as much sense when you're dealing with a slow response system such as underfloor where even a small increase in air temperature requires heating quite a large thermal mass to be heated.

Also it's possible the efficiency of a modulating boiler at low output is going to be lower than at full capacity as boiler heat losses and running overheads are going to stay relatively constant.

It's all very well comparing name plate statistics on new equipment and making projections based on this, however the reality is that real world performance is dependent on such a number of factors as to make simple comparisons irrelevant.
For example - I have an old gas boiler that is labelled as circa 65% efficient. In simple theory if I replaced it with a 95% efficient boiler I'd save 30% per year on my heating cost (about 160 euro / year savings).
However, the reality is that a large portion of this 30% efficiency loss is lost through the boiler casing. My boiler is in my utility room (within the house's thermal envelope) so only a small portion of that 30% is actually lost (out the exhaust).

You need to get an independent professional to evaluate any offerings from any solar/geo/boiler supplier in the context of your own house if you're going to have any hope of getting honest projections on running costs and payback.

JD6910

air wrote: »

I'm not sure modulation makes as much sense when you're dealing with a slow response system such as underfloor where even a small increase in air temperature requires heating quite a large thermal mass to be heated.

Also it's possible the efficiency of a modulating boiler at low output is going to be lower than at full capacity as boiler heat losses and running overheads are going to stay relatively constant.

It's all very well comparing name plate statistics on new equipment and making projections based on this, however the reality is that real world performance is dependent on such a number of factors as to make simple comparisons irrelevant.
For example - I have an old gas boiler that is labelled as circa 65% efficient. In simple theory if I replaced it with a 95% efficient boiler I'd save 30% per year on my heating cost (about 160 euro / year savings).
However, the reality is that a large portion of this 30% efficiency loss is lost through the boiler casing. My boiler is in my utility room (within the house's thermal envelope) so only a small portion of that 30% is actually lost (out the exhaust).

You need to get an independent professional to evaluate any offerings from any solar/geo/boiler supplier in the context of your own house if you're going to have any hope of getting honest projections on running costs and payback.

thanks air - i am thinking of going with RADS throughout the house with the solar, stove gas buffer tank system.

take your point on every house and person is different but was chatting with a few people in relation to gas and the quantities used are small because of the solar and stove and also because of the south facing glazed areas and serious insulation and airtightness construction.

PeteHeat

fclauson wrote: »

really - which brands - all the research I did 6 months ago failed to turn up anything for the domestic market

The answer to a range of different manufacturers and models was Here

I was thinking of the Wolfe Comfort line.

.

ccsolar

Hi JD6910
If you intend to us your solar for central heating then your best bet is to install a 60-80 tube solar collector onto a 300 litre tank then dump the excess heat into an 800-1000litre buffer tank, you could also go with option 2.
Fit a 60 tube collector onto a 500-800 litre multi-fuel stratification tank with a solar coil, get a second coil if you are pressurising the UFH as the solid fuel will be vented and you cannot mix both heating sources with out some kind of heat exchanger.
If you are going with rads check out the HR40 radiator stats from honeywell, they have a built in timer and thermostat in 1 unit, a bit expensive but worth the money.
PM me for further details.

CC