divorcingjack Posted February 25, 2018 Share Posted February 25, 2018 Hi all, We're still on the plumbing/plant room arranging, so the next purchase needs to be the boiler, UVC and buffer tank. So, I'm on the scrounge for advice again I understand from my reading of other threads in this section, that when we're talking about low energy houses, the main requirement for boiler size is ensuring an adequate DHW supply. I've done Jeremy's spreadsheet and the total heat loss power at 20 deg inside and 0 deg outside is coming out at 2.5 Kw. House has a lot of glazing, a non-optimal shape and 240 sqm total area. The current plan is a UVC, buffer tank (for UFH) and a system boiler. 4 occupants, 2 young children, all very keen on baths and excessively long showers. Showers are high flow, rainhead-type. Mains gas, no PV or prospect of any in the future. This is our forever house, so we will at some point have 2 teenagers, with their associated showering habits. So, questions: - Any boiler recommendations. Do I need to think about whether it modulates to a low enough temperature for the UFH if we've got a buffer tank? - What size of boiler do we need? - How do we size the buffer tank and what should it be? Direct, indirect, what tapping points, stainless steel/copper. pressurised? - We were considering a 300-350ltr UVC. Does this seem reasonable? I have a horror of running out of hot water for a bath, having lived with inadequate heating systems in a few houses. Thanks for pointers to any particularly useful threads or direct advice. Cheers, dj Link to comment Share on other sites More sharing options...
le-cerveau Posted February 25, 2018 Share Posted February 25, 2018 It is a simultaneous equation type question! DHW: the bigger the boiler the smaller the UVC, however the bigger the boiler the bigger the buffer for the UFH. You can run a smaller boiler but with a bigger UVC, but recharge will take longer and your buffer won't need to be so large. If the buffer is just for UFH then a simple boiler feed-return and UFH supply-return all in one unified body. Quite a few people here have an ASHP for UFH and use the buffer for DHW pre-heat necessitating a coil/PHE arrangement for the DHW, not an issue for you as there will be little benefit in an all gas install. Have you considered a TS (instead of UVC & Buffer), however heat loss becomes the issue (heating the Low energy house from the TS, especially in summer). With a TS you have one cylinder, UFH tapped from the bottom and DHW from the coil/PHE, with the boiler with variable feed/returns depending on the charging strategy. I know you said no PV, however is there the possibility of an ASHP, for UFH and DHW pre-heat? Link to comment Share on other sites More sharing options...
divorcingjack Posted February 25, 2018 Author Share Posted February 25, 2018 Thanks for your reply @le-cerveau - to answer some questions.. We have the space for a large UVC - presumably this would mitigate the risk of running out of water mid-shower/bath? I understand that the recharge time would be shorter with a smaller one, but we're fairly unlikely to have lots of showers/baths back to back. From my understanding, a buffer tank is recommended for low temp UFH to avoid the boiler short-cycling trying to provide DHW at a higher temp and water for the UFH at a much lower flow temp. My issue with a TS would be the lack of pressure - we have german fittings throughout and would worry that a non-pressurised system would deliver an extremely disappointing shower experience Also - with an ASHP, there would be an additional cost on top of having to buy a boiler, and I'm not sure it's something we can justify. Definitely worth considering though - I'm reading through the threads and making notes as I go along. I have so many notes! Link to comment Share on other sites More sharing options...
PeterW Posted February 25, 2018 Share Posted February 25, 2018 A TS can give full pressure hot water as either it uses a PHE or a heat coil. The downside is the losses as they run considerably hotter and go cold quicker so they overheat a well insulated house and also may not service multiple high flow showers. Link to comment Share on other sites More sharing options...
divorcingjack Posted February 25, 2018 Author Share Posted February 25, 2018 Hmm, that is quite a major issue - we're already trying to mitigate potential over heating problems from our large glazing, so really don't need to add any more potential heat sources. Link to comment Share on other sites More sharing options...
PeterW Posted February 25, 2018 Share Posted February 25, 2018 Right so a 400 litre UVC sounds like a plan ... What is your heat requirement as that will also dictate the buffer size...? You may get away with a 12kw or 15kw boiler but @Nickfromwales can comment further... Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 25, 2018 Share Posted February 25, 2018 This is where i cause murders, because I would put a much bigger boiler in, a 300L TS and do away with the buffer tank. Your enemies here are your expected DHW needs, eg it'll likely be all in the morning, a bit thorough the day, and another load in the evenings. If theres 4 of you then I would suggest the bathing may well be back-to-back and even simultaneously at the peak Having no PV in a "for life" property seems a bit counter productive to me, have you had that as a planning condition or just discounted it because of the cost ? Sunshine will remain free, gas will rise continuously. Id seriously rethink that approach as a zero-renewable solution isn't ideal imo. You dont want the boiler to modulate down as far as the ufh would need as you'd then be outside of the condensing range and your efficiencies would plummet. The TS would be set to sit at around 65-70oC, return set to sit around 50-55oC and thats achieved by pulsing heat in in chunks rather than trickle charing as its consumed. 1 Link to comment Share on other sites More sharing options...
ragg987 Posted February 25, 2018 Share Posted February 25, 2018 As you have mains gas then boiler seems the right approach. ASHP can, in theory, be cheaper to run but you get into the issues of low COP when your supply temp is high (DHW at 50C becomes a problem). The good thing about gas is that, provided return is below the condensing temp of 55C, you do not hit the same efficiency issues as ASHP. Factor in current and likely bathing habits, so if you expect to run 2 large baths in the evening then you need more than 4 short showers in the morning. With my kids, I found "more means more" - we had a 120l DHW in the old house and it ran out, we have 300l now and it still runs out! There is a tendency (esp my younger boy) to stay in the shower until water gets cold. So maybe a 200l UVC with at least 20kW (or higher, depending on the spec of the coils in the UVC to transfer heat) to reduce recovery time to about 30mins or less. 100l of hot water at 60C will easily fill a large bath. Or a 15-20 min shower at 10l/min. (Both assume blending with cold at 33%). For UFH, a buffer + blending valve would give you what you need. The boiler will modulate based on energy transferred from coil to cylinder, gas boilers can modulate quite low, I think down to 10-15% of peak. Once your UFH load gets too low then the boiler will cycle. Inevitable at some point. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted February 25, 2018 Share Posted February 25, 2018 4 minutes ago, ragg987 said: There is a tendency (esp my younger boy) to stay in the shower until water gets cold. I think I suggested this before, but submarines used to have a timed shower valve that would sort this problem out. You pressed a button and got just enough water to get wet before it shut off. You then lathered up with a flannel, then pressed the button again and rinsed as fast as you could to get all the soap off before the shower shut off again. Pressing the button again did nothing, you only got two shots of water for each shower....................... 2 1 Link to comment Share on other sites More sharing options...
le-cerveau Posted February 25, 2018 Share Posted February 25, 2018 2 minutes ago, Nickfromwales said: This is where i cause murders, because I would put a much bigger boiler in, a 300L TS and do away with the buffer tank. Personally I agree with Nick, this is what I have effectively done though with bespoke (high cost) SunAmp modules (low heat loss). GO with a TS but super insulate it, get the most insulate one possible, over insulate all the pipework completely, and put the TS in an insulated box, to mitigate unintentional heat gain. You will have some similar problems with an UVC and buffer, unintentional heat gains and getting super insulated buffers is not that standard. Link to comment Share on other sites More sharing options...
divorcingjack Posted February 25, 2018 Author Share Posted February 25, 2018 @Nickfromwales The PV issue has a few aspects: - conservation area and notoriously nightmarish planning - flat roof -surrounded by 3/4 storey blocks of flats which cast extensive shadows on our roof, there is very little of the roof which is not overcast at some point in the day. Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 25, 2018 Share Posted February 25, 2018 Have you done a survey / estimate on the potential yield anyway? If its a flat roof and you smother it, plus use micro inverters, you'll get some yield surely ? Someone posted an online doo-dah to work this out....anyone? Link to comment Share on other sites More sharing options...
divorcingjack Posted February 25, 2018 Author Share Posted February 25, 2018 I thought I had this all sorted out!! I am so confused now Do I really need to read up about Thermal stores again? Nooooooo 1 Link to comment Share on other sites More sharing options...
divorcingjack Posted February 25, 2018 Author Share Posted February 25, 2018 2 minutes ago, Nickfromwales said: Have you done a survey / estimate on the potential yield anyway? If its a flat roof and you smother it, plus use micro inverters, you'll get some yield surely ? Someone posted an online doo-dah to work this out....anyone? It's highly unlikely that we would get planning for them tbh - it's taken us 5 years to battle through planning for the house. Even if we did - surely the payback time just wouldn't be worth it? Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 25, 2018 Share Posted February 25, 2018 9 minutes ago, ragg987 said: As you have mains gas then boiler seems the right approach. ASHP can, in theory, be cheaper to run but you get into the issues of low COP when your supply temp is high (DHW at 50C becomes a problem). The good thing about gas is that, provided return is below the condensing temp of 55C, you do not hit the same efficiency issues as ASHP. Factor in current and likely bathing habits, so if you expect to run 2 large baths in the evening then you need more than 4 short showers in the morning. With my kids, I found "more means more" - we had a 120l DHW in the old house and it ran out, we have 300l now and it still runs out! There is a tendency (esp my younger boy) to stay in the shower until water gets cold. So maybe a 200l UVC with at least 20kW (or higher, depending on the spec of the coils in the UVC to transfer heat) to reduce recovery time to about 30mins or less. 100l of hot water at 60C will easily fill a large bath. Or a 15-20 min shower at 10l/min. (Both assume blending with cold at 33%). For UFH, a buffer + blending valve would give you what you need. The boiler will modulate based on energy transferred from coil to cylinder, gas boilers can modulate quite low, I think down to 10-15% of peak. Once your UFH load gets too low then the boiler will cycle. Inevitable at some point. Intersting, but that would clearly just leave the OP short, or out of DHW..... plus as per my last, you do NOT want the boiler modulating all winter to follow the ufh demand as you'll be way out of condensing range. Just now, divorcingjack said: It's highly unlikely that we would get planning for them tbh - it's taken us 5 years to battle through planning for the house. Even if we did - surely the payback time just wouldn't be worth it? You need to do the maths. Guessing isn't as good as finding out it IS worth doing. Remember you said this is a life property so thats hopefully a long time and a lot of grid gas and electricity to buy, possibly into retirement. Could you not just ring the planners and ask them outright? 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 25, 2018 Share Posted February 25, 2018 18 minutes ago, JSHarris said: I think I suggested this before, but submarines used to have a timed shower valve that would sort this problem out. You pressed a button and got just enough water to get wet before it shut off. You then lathered up with a flannel, then pressed the button again and rinsed as fast as you could to get all the soap off before the shower shut off again. Pressing the button again did nothing, you only got two shots of water for each shower....................... "During the war, Rodney" @JSHarris Would a flat roof not have a reasonable yield as its facing the sky at the end of the day. Partial shading of differing areas of the roof, and panels with micro-inverters would still see a return from the incidental / indirect sunshine as well as the limited direct imo. DIY job with loads of it and consume what you generate? Link to comment Share on other sites More sharing options...
divorcingjack Posted February 25, 2018 Author Share Posted February 25, 2018 3 minutes ago, Nickfromwales said: Could you not just ring the planners and ask them outright? Ha! Our planners do not lower themselves to talk to members of the public who have questions about planning. How utterly ridiculous. I can try and get hold of someone, but it's just another task on the so-long list. I was hoping this would be straightforward. Or at least not as nightmarishly complex as every other sodding thing has been. Can you explain why @ragg987 suggestion of a UVC + buffer + blending valve would leave me out of DHW? Could I just upgrade the size of the cylinder? Link to comment Share on other sites More sharing options...
ragg987 Posted February 25, 2018 Share Posted February 25, 2018 7 minutes ago, Nickfromwales said: plus as per my last, you do NOT want the boiler modulating all winter to follow the ufh demand as you'll be way out of condensing range Fair point, might be my ignorance but would a TS be more beneficial in this respect, assuming you are only running UFH? Link to comment Share on other sites More sharing options...
ragg987 Posted February 25, 2018 Share Posted February 25, 2018 Not trying to convince you re PV (in my view, the case is diminished if you cannot use the generated power effectively, and an ASHP is a part of that usage), however PV is permitted development even in conservation areas provided panels are not fronting a highway. https://www.planningportal.co.uk/info/200130/common_projects/51/solar_panels/2 1 Link to comment Share on other sites More sharing options...
divorcingjack Posted February 25, 2018 Author Share Posted February 25, 2018 1 minute ago, ragg987 said: Not trying to convince you re PV (in my view, the case is diminished if you cannot use the generated power effectively, and an ASHP is a part of that usage), however PV is permitted development even in conservation areas provided panels are not fronting a highway. https://www.planningportal.co.uk/info/200130/common_projects/51/solar_panels/2 Does that apply in Scotland too? OK OK, so say we did go for PV eventually, as we have no cash for the foreseeable - could we mount the panels flat? Or would they have to be at an angle? Having them at an angle would pretty much ruin the look of the house (I know, I know) as you would see them on approach to the single storey section. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted February 25, 2018 Share Posted February 25, 2018 21 minutes ago, Nickfromwales said: @JSHarris Would a flat roof not have a reasonable yield as its facing the sky at the end of the day. Partial shading of differing areas of the roof, and panels with micro-inverters would still see a return from the incidental / indirect sunshine as well as the limited direct imo. DIY job with loads of it and consume what you generate? It's easy enough to work out using PVGIS: http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php?lang=en&map=europe As an example, our 6.25 kWp array that is angled at 45 deg and faces 206 deg (26 deg W of S) has a PVGIS predicted annual output of 5720 kWh The same array at the same location, but horizontal, with no shading, gives a PVGIS predicted annual output of 5070 kWh. Not a massive difference really, but the flat orientation has a lower output in the winter months and a slightly higher output in the summer months: 1 Link to comment Share on other sites More sharing options...
ragg987 Posted February 25, 2018 Share Posted February 25, 2018 Sorry quoted the England regs. Missed you are in Scotland. It seems that a short and free conversation with your local PV installer on options / costs / returns might be worth it, at least you will know. As per @JSHarris, PVGIS is a great tool. 1 Link to comment Share on other sites More sharing options...
divorcingjack Posted February 25, 2018 Author Share Posted February 25, 2018 I had a quick google and it looks like the same regs for scotland tbh. So, if we were to install the panels flat, how do mitigate the partial shading? I thought that any shading on any of the panels basically took out the whole array? Is that wrong? Link to comment Share on other sites More sharing options...
le-cerveau Posted February 25, 2018 Share Posted February 25, 2018 Just now, divorcingjack said: how do mitigate the partial shading? I thought that any shading on any of the panels basically took out the whole array? That is what a micro inverter is for, each panel produces it's maximum through it's micro inverter. With a traditional string inverter any reduction on any panel impacts the whole array connected to that inverter. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted February 25, 2018 Share Posted February 25, 2018 (edited) 4 minutes ago, divorcingjack said: I had a quick google and it looks like the same regs for scotland tbh. So, if we were to install the panels flat, how do mitigate the partial shading? I thought that any shading on any of the panels basically took out the whole array? Is that wrong? Fitting microinverters under each panel mitigates the partial shading problem and gives you a direct 230 VAC feed from the array. Edited February 25, 2018 by JSHarris Cross posted! Link to comment Share on other sites More sharing options...
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