andygo Posted October 7, 2020 Share Posted October 7, 2020 Hi all I've been doing quite a bit of reading up on this forum, but this is my first post (please be gentle). I'm looking for advice on changing the heating source for our UFH from a solid fuel Rayburn to something else (most likely either a ASHP or Willis heater - open to other suggestions). Our house is an old stone 2-bed cottage with no mains gas. The Rayburn has been our main source of heating in winter for the last 12 years (we have an electric shower and cooker for the rest of the year and just boil the kettle to wash dishes). In winter, the Rayburn (a 12kw Supreme model) supplies hot water to a 277 litre Gledhill RE Torrent Thermal store - which in turn heats 30m2 of UFH (concrete slab and flagstones) and 4 radiators upstairs. We've been planning to add solar panels for years and will one day when I get around to it... Anyway... the Rayburn boiler is getting very rusty and I suspect will start leaking any time soon and I'm also sick of schlepping coal in and out on cold winter nights so it's time for it to go, or at least not be the primary source of heat anymore (my wife is still attached to it....) For the last few years the way we've used our heating system is to light the Rayburn in the late afternoon (using about 10kg of coal), and let it burn out by the time we go to bed. That puts enough hot water into the Thermal Store so it heats up the slab overnight and lets us run the radiators for an hour or so before we go to bed (if it's windy we get enough hot water for a bath!). We use on average between one and a half to two tonnes of coal over the winter months which costs £400 - £500. Although the house is drafty, the UFH works well and the house manages to stay reasonably warm (downstairs at least). We also have a wood burning stove. I don't really want to install another type of fossil fuel boiler and would prefer a more sustainable alternative/s. I'm also planning on making the house more airtight. There's lots of insulation in the attic and we've put in double glazing. In an ideal world I'd simply replace the Rayburn with an ASHP... but having exchanged a few messages with Nickfromwales he's advised it wouldn't work and says I'd need to change the thermal store to a UVC - or at least add another buffer cylinder to the system which I'd really rather not do. We don't really have the space for yet another cylinder. I did wonder if it would be possible to connect a smaller ASHP direct to the UFH - maybe with a radiator as a buffer in the kitchen (which would be unheated without the Rayburn). Nick wasn't convinced about this either... Otherwise I'm wondering about using a Willis heater - at least for this winter as a short term fix. But I would like to get some idea of how much that might cost to run. Does anyone have a ball park for how much it would cost to run to heat up 30m2 of UFH...(I'm currently on Igloo variable standard tariff of 13.9p.) Obviously it would be better to heat it overnight. Igloo don't do Economy 7 though I can change to another supplier easily.....but our current electricity usage is already around 3,500kwh per year - so any E7 savings may be negated by daytime use. (We're a family of three so presumably the electric shower and kettle boiling accounts for alot of that). I'm happy to fit a Willis heater (I've a friend who's a qualified electrician to wire it in) but I've also got a few basic install questions - where does it go, how many would I need, does it need its own pump or can I use the UFH pump - as mentioned in the thread below? Out of interest if we did go for a Willis Heater is there a way of plumbing it into the kitchen hot tap too? Appreciate any help or advice and especially any other better ways of heating our home. Many thanks Andy Link to comment Share on other sites More sharing options...
Ferdinand Posted October 7, 2020 Share Posted October 7, 2020 (edited) I am not sure where your requirements on budget vs performance, but if want to consider the Economy 7 route one inexpensive option is secondhand storage heaters. Invite your friends who claim to be home-exercising in Covid to help get them in subject to the Guidance, and you get to see if they have been lying to you or not ?. I think I would suggest building a heat model of your house - that link is to the Jeremy Harris spreadsheet thread, and also to remember that there is a current scheme which may give you part of the cost. If you are going to make it more airtight you may need to think about ventilation too. Ferdinand Edited October 7, 2020 by Ferdinand Link to comment Share on other sites More sharing options...
andygo Posted October 8, 2020 Author Share Posted October 8, 2020 Hi, thanks for reply. I can't edit the last line of my original post, but to be clear... we like the UFH and want to keep it. So what I'm looking for are ways to power the underfloor heating (either at the same time as radiators and DHW or independently). I'll have a look at the heat model link, thanks. Link to comment Share on other sites More sharing options...
ProDave Posted October 8, 2020 Share Posted October 8, 2020 So you burn 1.5 - 2 tons of coal per year to heat the house. Now if someone could look up how much heat you get from burning 2 tons of coal and convert it to kWh, you would have a pretty good measure of how much heat you need from another source. @SteamyTea Link to comment Share on other sites More sharing options...
SteamyTea Posted October 8, 2020 Share Posted October 8, 2020 (edited) Coal varies in energy density, so does depend on what you are burning. Anthracite is between 7.2 and 9.2 kWh/kg Bituminous is between 6.7 and 9.7 kWh/kg Lignite is between 2.7 and 5.6 Ranking them in order and taking the median value gives 7 kWh/kg. So a tonne gives 7 MWh. The hard part is the efficiency of the Rayburn. Rayburn claim that their ranges can give an efficiency of between 86% and 87% for the oil and gas versions, so safe to assume that the coal one is lower, let us say 75%. So that will be 5.25 MWh/tonne. A tonne of coal will produce, in ideal combustion conditions, 3.667 tonnes of CO2. Edited October 8, 2020 by SteamyTea Link to comment Share on other sites More sharing options...
ProDave Posted October 8, 2020 Share Posted October 8, 2020 13 minutes ago, SteamyTea said: So that will be 5.25 MWh/tonne. Lets do some rough sums. For the sake of easy numbers, 10MWh per year total for heating An ASHP with a COP of 3 will reduce that to 3.33MWh of electricity used. At typically 14p per kWh that will be typically £462 per year, so similar cost to burning coal. Assuming the heating is on for 180 days per year, that will be an average of 55kWh of heat per day. Lets say the coldest day is twice the average, so 110kWh per day and the heating is on for 10 hours per day, that will be an average heating power of 11kW So I would be thinking of something like an 18kW Air Source Heat pump. All VERY rough estimates. Link to comment Share on other sites More sharing options...
SteamyTea Posted October 8, 2020 Share Posted October 8, 2020 Just have re-read the original question, how about putting in a Willis and seeing how it goes. It will not do the DHW, but you could do that with a simple immersion heater. It will give you a better idea of what is actually needed, then you can design a heat pump system better. May be worth calculating how much DHW you actually use, and at what temperature it is both stored at and used at. Link to comment Share on other sites More sharing options...
andygo Posted October 8, 2020 Author Share Posted October 8, 2020 (edited) Thanks for the replies so far. We normally use anthracite nuts (smokeless fuel). There's a table here https://www.coals2u.co.uk/faqs/smoke-emissions-from-residential-buildings---a-summary-from-cpl/ giving details of their energy content (I can't pretend to understand it though.) In the real world we normally run the Rayburn at I would guess medium for around 4 hours. The max output is 16kw (not 12kw as I first thought) according to this where we bought it https://www.countrystylecookers.com/rayburn-ranges/supreme but it's nowhere near maximum when we use it (unless it's really windy outside) so I would guess there is around 8-10kw of heat going into the store for 4 hours (I know very little about all this though). The figure of 55kwh probably isn't too far out. After 4 hours the temperature at the top of the Thermal Store will reach around 80c and the return pipe at the bottom will be too hot to touch. If we put the central heating on for the radiators there's only enough hot water to keep them hot for an hour or so. Obviously on colder days we keep topping up the Rayburn to put more hot water into the thermal store. Another good reason for separating the UFH from the Thermal Store is that it's fed directly (not via a loop in the store), so the UFH gets blocked with silt fairly regularly. Having a clean loop for the UFH would make it more efficient no doubt. Experimenting with a Willis Heater seems the most sensible way forward (it's cheap to buy and I can use it as a back up if I get something else later on). What concerns me is how much it might cost to keep it running. I can work out how much it will cost to heat the thermal store - https://www.thegreenage.co.uk/much-electricity-immersion-heater-use/ But is there a formula to work out the cost of running 30m of UFH to a given temperature for a certain amount of time? Does anyone have any real world figures or can give a ball park idea...? I read on here about people heating a much larger area of UFH on 5 or 7kw ASHPs for pennies, albeit in a more favourable house than mine. The whole Rayburn/thermal store combo has proved to be a bit of a mistake (in hindsight I should have gone for the solar option from the outset) but you live and learn. What I don't want to do is make another expensive mistake.... Thoughts appreciated Andy Edited October 8, 2020 by andygo Link to comment Share on other sites More sharing options...
SteamyTea Posted October 8, 2020 Share Posted October 8, 2020 23 minutes ago, andygo said: What concerns me is how much it might cost to keep it running. According to this 24 minutes ago, andygo said: https://www.coals2u.co.uk/faqs/smoke-emissions-from-residential-buildings---a-summary-from-cpl/ About the same. 25 minutes ago, andygo said: But is there a formula to work out the cost of running 30m of UFH to a given temperature for a certain amount of time? Yes there is, but you need a whole load of information. Do you now how much insulation there is under the UFH pipes, and the overall heat losses from the area you are heating. It is not that hard to work out, just a lot of repetition and very dull. It is the same formula that you use to work out heat loss though a wall, just have to jiggle things about i.e. treat the surface area of the pipe as the hot side, and the floor as the cold side. Link to comment Share on other sites More sharing options...
Temp Posted October 8, 2020 Share Posted October 8, 2020 I think it might help to know what sort of temper you run the existing store at and the UFH flow temperatures needed to keep those rooms warm? Link to comment Share on other sites More sharing options...
andygo Posted October 13, 2020 Author Share Posted October 13, 2020 Hi, the problem with having a solid fuel appliance as a primary source is there's no constant to measure and compare (especially the way we used it) so I can't answer any of the questions above unfortunately. The only info I've got is what I've posted above. From memory I think there was around 6 inches of insulation below the UFH pipes - but I'm not even sure about that. Presumably installing a Willis heater will at least be able to give me a benchmark.... Since I last posted I've managed to obtain some used solar panels. I need to fix the odd leak, but once I've done that I was wondering about incorporating them to pre-heat water going into the Willis heater. Has anyone done something like this? Wondering about how many pumps I may need and anything else required...expansion vessel? As always any advice appreciated Andy Link to comment Share on other sites More sharing options...
PeterW Posted October 13, 2020 Share Posted October 13, 2020 Do not include a thermal solar panel in a heating circuit containing UFH pipes !! They are not rated to the correct temperatures and you can get significant system temperatures with solar. Link to comment Share on other sites More sharing options...
SteamyTea Posted October 13, 2020 Share Posted October 13, 2020 12 minutes ago, andygo said: Since I last posted I've managed to obtain some used solar panels. I assume these are solar thermal, not photovoltaic. Can you send then back or resell them. Failing that, you could plumb them in to supply some energy to your domestic hot water. You will probably need a new hot water cylinder, an expansion tank, lots of compression fittings, some flexible stainless pipe, a controller, antifreeze, service schedule and other things I have forgotten about. But the efficiency is tip top while heating the water, assuming the water is only luke warm to start with. PV is so much better. Link to comment Share on other sites More sharing options...
andygo Posted October 13, 2020 Author Share Posted October 13, 2020 They are solar thermal and were free (because of leaks), no reason to sell on or send back. Since they won't contribute much over the winter in a 277l tank I figured they'd be better of making a more significant contribution to UFH using the little winter sun we get. In summer I'd hook them up to the thermal store and use them as designed. There's also a blending valve between thermal store and UFH....suppose I could incorporate that...but do you really think solar panels get that hot over winter? As mentioned earlier I'd really not have to go to the hassle and expense of getting yet another hot water cylinder when we've got a thermal store. Link to comment Share on other sites More sharing options...
Gav_P Posted October 13, 2020 Share Posted October 13, 2020 Could they be used to heat a thermal store, then take the heat for the UFH from there? Much as @joe90 has for his UFH (but heated by ASHP) Link to comment Share on other sites More sharing options...
PeterW Posted October 13, 2020 Share Posted October 13, 2020 If you have a TS then the solar can go into that but not directly into the floor. Why is the UFH not fed from the TS..? That is their primary purpose to provide an equalising store for multiple heat sources and heat loads. Link to comment Share on other sites More sharing options...
andygo Posted October 13, 2020 Author Share Posted October 13, 2020 The underfloor heating is currently fed from the Thermal Store...which is what is causing the problem and the reason for the original post.... I want to separate the UFH from the Thermal Store for two reasons: 1 Currently the only heat source into the Thermal Store is a solid fuel Rayburn which is coming to the end of its days and a pain to keep running. If I can find another heat source for the UFH then we can possibly live without the Rayburn - or just fire it up on really cold days to power the radiators upstairs. 2 The water which goes into the Thermal Store gets black and sludgy because it's fed from the Rayburn. This same black, sludgy water goes direct from the TH to the UFH - so the UFH gets blocked up and I guess pretty inefficient. It was a poorly designed system from a plumber who has since disappeared... The long term goal is to replace the Rayburn with a better heat source. But in the short term (and fairly urgently as its getting colder) I need a way of ONLY heating the UFH. A Willis Heater heating ONLY the UFH would be cheap to install (and hopefully relatively easy to do) and would give me some solid figures to work with (though I am concerned about how much it might cost to run). Obviously in the long-term I'll add the thermal solar panels I've obtained to the Thermal Store....which will give us DWH in summer - but they're not going to do much to a 277l store in Winter. I'm wondering however if there is a way of taking advantage of the weak winter sun and use a panel or two to pre-warm the relatively small amount of water needed to run the UFH. (It might save us a few quid on electricity.) The question I have is does anyone know a way of doing that? And if so how many pumps would I need. Thanks again Andy Link to comment Share on other sites More sharing options...
Gav_P Posted October 13, 2020 Share Posted October 13, 2020 Weird set up that the Rayburn can contaminate the UFH system. I would have assumed they were separated, by the Rayburn heating the store via a coil? Link to comment Share on other sites More sharing options...
Gav_P Posted October 13, 2020 Share Posted October 13, 2020 13 minutes ago, andygo said: I'm wondering however if there is a way of taking advantage of the weak winter sun and use a panel or two to pre-warm the relatively small amount of water needed to run the UFH. (It might save us a few quid on electricity.) The question I have is does anyone know a way of doing that? I’m not sure anyone would recommend a way of doing this as you could end up with some very high temps on a sunny day without even knowing it. Unless you used it to heat the thermal store, then top up the temp if required by electric? Link to comment Share on other sites More sharing options...
Gav_P Posted October 13, 2020 Share Posted October 13, 2020 Link to comment Share on other sites More sharing options...
andygo Posted October 13, 2020 Author Share Posted October 13, 2020 14 minutes ago, Gav_P said: Weird set up that the Rayburn can contaminate the UFH system. I would have assumed they were separated, by the Rayburn heating the store via a coil? Sadly, that's the way mine is set up. Life would be easier if there was a coil for the Rayburn and/or the UFH....but there isn't...they're both direct. 11 minutes ago, Gav_P said: I’m not sure anyone would recommend a way of doing this as you could end up with some very high temps on a sunny day without even knowing it. Unless you used it to heat the thermal store, then top up the temp if required by electric? How about if the panels were connected to both the UFH and Thermal Store via some sort of valve. If the water temp got too hot for UFH it would just be directed into TS instead. We're talking about winter sunlight, how hot do you think they're likely to get? Don't want to overcomplicate it though.... I can live without the panels for now...but I do want to find a way of heating up the UFH independently... Link to comment Share on other sites More sharing options...
SteamyTea Posted October 13, 2020 Share Posted October 13, 2020 You could connect the ST via a plate heat exchange. But start off with getting the UFH fitted with a Willis and see how it goes. Link to comment Share on other sites More sharing options...
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