DamonHD Posted September 9, 2022 Share Posted September 9, 2022 Hi, Our old gas combi may be on its way out. Our house is due to be bulldozed in 5Y, so ASHP upgrade extra punitive. We are already a low user (<3MWh DHW and space heat per year). Winter heat demand typically 3kW, peak ~6kW. Already have a heat battery installed (Thermino). Other gas appliances long since gone. Electricity is single-phase. What would the learned mob here advise: a condensing gas combi, an electric combi, something else? Obvs, I want to minimise carbon, including embedded/upfront carbon. I'm prepared to be a bit spendy to do that. Rgds Damon Link to comment Share on other sites More sharing options...
Temp Posted September 9, 2022 Share Posted September 9, 2022 Just replace with similar gas combi. 1 Link to comment Share on other sites More sharing options...
Marvin Posted September 9, 2022 Share Posted September 9, 2022 23 minutes ago, Temp said: Just replace with similar gas combi. +1 Link to comment Share on other sites More sharing options...
ProDave Posted September 9, 2022 Share Posted September 9, 2022 Or find a better plumber to patch up the old one so it will last? 2 Link to comment Share on other sites More sharing options...
DamonHD Posted September 9, 2022 Author Share Posted September 9, 2022 It has already had a number of repairs, and I will repair it if I reasonably can. Part of the problem is the way that this device is put together which makes the fix at the very least slow, but then also regs have changed since the last big repair was done... Rgds Damon Link to comment Share on other sites More sharing options...
DamonHD Posted September 9, 2022 Author Share Posted September 9, 2022 (Thanks for comments so far!) Link to comment Share on other sites More sharing options...
Iceverge Posted September 9, 2022 Share Posted September 9, 2022 That is exceptionally low usage. About half of ours in our passive house (2 adults + 2 kids) DHW about 3.5MWh and space heating somewhere about 3MWh. Just keep the boiler going for now. If it packs in completely direct electric might be best considering the very limited payback window. Alternatively if an ASHP would plug into your rads as is, with a new cylinder there's nothing to stop you taking it with you in 5 years time when you move out. Link to comment Share on other sites More sharing options...
JohnMo Posted September 9, 2022 Share Posted September 9, 2022 Wow that only an average of less than 9kWh per day. Are you bulldozing a passivhaus? 1 Link to comment Share on other sites More sharing options...
JohnMo Posted September 9, 2022 Share Posted September 9, 2022 9 hours ago, DamonHD said: We are already a low user (<3MWh DHW and space heat per year). How do you do it? Link to comment Share on other sites More sharing options...
DamonHD Posted September 9, 2022 Author Share Posted September 9, 2022 (edited) Magic! Good heating controls, good IWI, always eg looking to buy the most efficient appliance when one needs replacing, some behaviour change, etc, etc. http://www.earth.org.uk/towards-a-LZC-home.html#todo Rgds Damon Edited September 9, 2022 by DamonHD Link to comment Share on other sites More sharing options...
JohnMo Posted September 9, 2022 Share Posted September 9, 2022 You've been busy. Link to comment Share on other sites More sharing options...
SteamyTea Posted September 9, 2022 Share Posted September 9, 2022 (edited) Have you considered A2AHPs for space heating. The layout of your house means you could get away with one in the living room, your kitchen is probably fine with nothing. Maybe another on in the loft but piped to each of the rooms upstairs. Or night storage heaters, though the CO2 penalty may be too high for your liking. Edited September 9, 2022 by SteamyTea Link to comment Share on other sites More sharing options...
markocosic Posted September 9, 2022 Share Posted September 9, 2022 You're in a similar pickle to me in when it comes on wanting to play but being mindful of moving on. The fabric is done for. There's no 5 year paybacks available. Everything you put into it will get wrecked. The gubbins are (trans)portable. Your PV, for example, will be coming with you. With that in mind... A £500 combi will probably outperform whatever you have now. Will that pay for itself in 5 years at £0.15/kWh and 3,000kWh/year? Probably not. Hot water? Hot water from a gas combi at 80% efficiency beats hot water from PV environmentally. How so? Every kWh of electricity exported will save about 2.5 kWh of marginal gas being burned at a power station. It is a fallacy to consider the mean grid carbon intensity when evaluating what difference your immediate behaviour makes. As such use of PV diversion and the Sunamp is interesting but environmentally irresponsible. Both are (trans)portable and (re)saleable durable assets though so can make it to a new house or somebody else's house should you wish. Only the install/uninstall costs are dead money. To do better than the combi heat you could: - preheat the feed to the combi with drainwater heat recovery (unlikely to be viable do to payback time, retrofit difficulty) - preheat the feed to the combi with solar thermal (in the event that your connection capacity is maxxed out and you've still got space for more sun, unlikely on any modest house) Else you're into heat pumps. I think this is possibly your scene. They spank running the combi. Relatively easy to bring with or resell after you're done experimenting. https://www.tesy.co.uk/heat-pump https://www.electricpoint.com/dimplex-edel-hot-water-cylinder-heat-pump-200l-edl200uk-630rf.html https://www.ariston.com/en-me/products/heat-pump-water-heaters/domestic/ https://gathering.tweakers.net/forum/list_messages/1941248 https://www.auer.fr/en/products/heat-pump-water-heaters/edel-water-heat-pump-water-heater/ The Sunamp is useless for heat pumps because it requires that all heat is delivered at the maximum possible temperature rather than ramping up as the cylinder heats. You couldn't do anything more inappropriate for heat pumps. Space heat? You've done what's reasonable for reducing consumption. Heat pump is next. I might try an air to air unit in a central location given your minimal heat loads and tolerance for minor discomfort. What's the COP on the Panasonic CU-VZ12SKE / CS-VZ12SKE combination that's sat on my wall? 3.7 kW output at -7C with a COP of 3.8 or 14 pence per kWh 2.25 kW output at +2C with a COP of 5.7 or 9.1 pence per kWh 1.45 kW output at +7C with a COP of 7.8 or 6.7 pence per kWh 0.9 kW output at +12C with a COP of 10 or 5.2 pence per kWh Those COPs spank the gas combi. So does the cost. Note I've used the previous price cap figures for a more accurate reflection of what energy actually costs rather than the "deposit" that we'll be paying today and ignoring the interest and repayment charges that come later courtesy of the government's latest insane plans to avoid the demand reduction that is required in the light of reduced supplies this winter. Comfort is not as good though. There will be some draughts. There will be some noise. The efficiency is up there though. Easy to unplug and bring with when the building is demolished. Close one valve, pump the gas back into the outdoor unit, shut the other valve and knock the power to the outdoor unit off, crimp the copper pipework then snip and reinstall with new copper pipework in the new location. Planners are unlikely to know the difference between a monobloc for space heat / hot water and an air to air unit that can heat/cool. Functionally they're identically obtrusive / noisy too so it doesn't make any odds. I wouldn't ask for consent. I have a vacuum pump and gauges that you're welcome to borrow if doing a naughty DIY install. Alternative? Single outdoor heat pump and a cylinder to suit. Possibly higher performance for hot water but will be lower performance for space hating unless you get very involved with radiator swaps. More disruptive to install. Fewer draughts. Less noise. -- M 1 Link to comment Share on other sites More sharing options...
JohnMo Posted September 10, 2022 Share Posted September 10, 2022 Another alternative is a cylinder incorporating a heat pump as linked to above, for hot water only. And a small heat pump for heating/cooling. Link to comment Share on other sites More sharing options...
DamonHD Posted September 10, 2022 Author Share Posted September 10, 2022 (Did I remember to say that our house is very small, including the kitchen where the current boiler lives!) Thanks for the comments above: I am thinking hard about them! Rgds Damon Link to comment Share on other sites More sharing options...
markocosic Posted September 10, 2022 Share Posted September 10, 2022 Floorplan? Link to comment Share on other sites More sharing options...
DamonHD Posted September 10, 2022 Author Share Posted September 10, 2022 That might be a good idea... Maybe you can infer what you're after from these: https://www.earth.org.uk/note-on-data.html#Unstructured Link to comment Share on other sites More sharing options...
DamonHD Posted September 11, 2022 Author Share Posted September 11, 2022 Thanks all for thoughts and suggestions so far. I have started writing it up here... https://www.earth.org.uk/note-on-combi-replacement-dilemma.html Rgds Damon Link to comment Share on other sites More sharing options...
JohnMo Posted September 11, 2022 Share Posted September 11, 2022 If your boilers is just loosing pressure sounds like the diaphragm or Schrader valve has gone, either is an easy enough fix. Way more eco to fix instead of replace, with some something manufactured in China on coal generated electric then shipped half way around the world. Link to comment Share on other sites More sharing options...
DamonHD Posted September 11, 2022 Author Share Posted September 11, 2022 That is what I would like to do. However the last gas engineer to replace the expansion vessel cursed about how the Potterton Performa 24 was laid out. It may not be possible to replace without removing the boiler from the wall, and thus disconnecting from the gas supply. At which point it may not be legal to reconnect it (non-condensing, non-boilerplus, etc) under new regs. (Also the old expansion vessel is a bit expensive and will take hours of expensive engineer time to swap out, likely.) Rgds Damon Link to comment Share on other sites More sharing options...
dpmiller Posted September 11, 2022 Share Posted September 11, 2022 If it's not actually leaking, could you not just add another expansion vessel elsewhere in the system? 1 Link to comment Share on other sites More sharing options...
JohnMo Posted September 11, 2022 Share Posted September 11, 2022 Assuming it's the same boiler as this looks easy enough. Maybe a different plumper, seem to be plenty of expansion vessels in the £45 to 80 price range. https://www.google.co.uk/url?sa=t&source=web&rct=j&url=https://m.youtube.com/watch%3Fv%3DhpcAJ5b7UDg&ved=2ahUKEwj2w7qaxoz6AhVSnFwKHeNjBGUQjjh6BAgtEAI&usg=AOvVaw3kyI-ON7JT_0dc7fUuYnij Link to comment Share on other sites More sharing options...
DamonHD Posted September 11, 2022 Author Share Posted September 11, 2022 Also a possibility, but that takes space that we don't have and/or will be ugly. But it may be the best worst option... Rgds Damon Link to comment Share on other sites More sharing options...
DamonHD Posted September 12, 2022 Author Share Posted September 12, 2022 Thank you so far. I've added another layer of sub-options / questions to my thinking! https://www.earth.org.uk/note-on-combi-replacement-dilemma.html#sub I can copy them in here if anyone thinks that that would be a good idea! Rgds Damon Link to comment Share on other sites More sharing options...
JohnMo Posted September 12, 2022 Share Posted September 12, 2022 Just make a decision and get on with it. Asking for opinions and public blogs doesn't get anything done. Just goes round in circles. 2 Link to comment Share on other sites More sharing options...
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