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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    Friends of ours live in a Victorian terrace and their gas boiler has just given out. Given the season they're looking to replace it soon, but want to do that in a low-carbon way if possible.

    I'm aware of all the things I could say about reducing air leaks to get demand down etc. which they'll likely get onto as they continue to renovate, but in the short term what water heating options are out there in 2020?

    Given current progress on grid decarbonisation, I had hoped to find an electric alternative but I'm aware that all of these will be competing with a boiler on cost terms.

    From what I've read on here they could possibly use an Air to Water heat pump to supply DHW - indeed their current boiler is upstairs on an external rear-facing wall so to swap it out for a unit with pipes to a wall mounted external unit would probably be possible.

    Ultimately though, they just want something that can plug into their existing 'wet' heating system of radiators etc. Is it still the best bet to just stick with a replacement gas boiler, even given everything we know about where the home heating market is going?
    • CommentAuthorSimonD
    • CommentTimeOct 28th 2020
     
    I'm by no means an expert rather an educated buyer of these things and I was unquestionably an alternative technologies nerd for quite some time before deciding to take some time out to build my house myself (I almost did a Msc in the stuff a while back) :wink: To put it midly, I believe the real-world value of Air source heat pumps as a direct replacement to a gas boiler right now is highly debatable. The required capital investment is also significant. What I am aware of through some of my professional work is the amount of resource being put into the use of hydrogen distributed through the gas network. It's even possible right now to buy gas boilers suitable for conversation to hydrogen and indeed hydrogen boilers. None of this is an immediate solution and various structurural issues need to be overcome, but if you're interested you can look at Drax's proposed development in north Humber which is not just about carbon capture but about hydrogen production as an example of some things going on.

    Meanwhile, concentrate on reducing consumption through those sensible measures.

    For what it's worth, just my humble opinion :smile:
    •  
      CommentAuthordjh
    • CommentTimeOct 28th 2020
     
    Posted By: Doubting_Thomasin the short term what water heating options are out there in 2020?

    Cheapest to buy and quickest, easiest to fit is an immersion heater or inline electric heater. Yes, it will be more expensive to run but as a short-term fix it can't be beat IMHO at maybe £30.
    • CommentAuthorrevor
    • CommentTimeOct 28th 2020
     
    When I came to do my build/renovation I debated for some time as to what heating to go for. I was in a better situation than your friends as I had a clean slate apart from the issues with building around and incorporating a1750's stone farmhouse. I was able to concentrate on fabric first approach so insulation air tightness and elimination of cold bridges was easier to do. These are the areas one should start with which will reduce the heating demand which is key. I discounted heat pumps, pellet boilers etc as I had got the heat demand down to a level that the cost even with RHI was disproportionate to the benefit. I ended up with a gas boiler (LPG) and a thermal store fed by solar thermal panels. I spent £400 on the gas last year and about 25% of that was used to condition the floors before tiling, heating 340 sq M supplemented by a wood burning stove. If you can rationalise the green bit in that one is doing other things to keep ones carbon footprint down I would not get too hung up about replacing gas with gas, natural gas is the cheapest option both capital and running cost and recently the gas wholesale price has dropped.
  2.  
    I'd definitely go for air-to-water heat pump (in fact I did that in our last Victorian house) - can't see there's any future in fossil-burning boilers. There's great stuff out on the horizon like hydrogen gas grids, but your friends can't wait for it.

    There are grants available in England. They'll probably need to replace some radiators with doubles, but that's ok. If they don't have a hot water cylinder they may need to add one.

    Absolutely right they should insulate and draught proof _as well_, and then they'll run the heating for less of the time, but from experience that will take some time to complete (a decade in our case...) So swapping to an ashp is by far the quickest way for most people to make a really significant reduction in carbon, even with the present grid.

    As always with old houses, it would be nice to do all the upgrades in the 'right' order, but circumstances and events conspire against you! In our new old house I hope we get through the plan as far as replacing the boiler in a considered thoughtful way, fingers crossed it doesn't pack up in winter and force a rush-job replacement... sympathy to your friends!

    (From your last para I understand they need to replace their home heating boiler - others have understood that they just need to replace their source of hot tap water)
  3.  
    Posted By: Doubting_ThomasFriends of ours live in a Victorian terrace and their gas boiler has just given out. Given the season they're looking to replace it soon, but want to do that in a low-carbon way if possible..........but in the short term what water heating options are out there in 2020?.....................Ultimately though, they just want something that can plug into their existing 'wet' heating system of radiators etc. Is it still the best bet to just stick with a replacement gas boiler, even given everything we know about where the home heating market is going?

    A bit of confusion here, are we talking about a DHW solution or heating as well? however
    Above mentioned an immersion heater - a good fix if there is a DHW tank and a cold tank in the loft to feed it otherwise a mains pressure tank gets expensive (unless they have one already. If it is a combi boiler then an immersion heater starts to get expensive.

    If heating also comes into the mix then I would go for a new gas boiler, probably a combi and do away with the DHW tank if they have one.

    It would be nice to go green but IMO that is going to cost more than a replacement gas boiler and will take longer to install. Given that it is a terraced house I guess the neighbours will be fairly close so ASHP will need thought about placement and some power upgrade may be needed depending on the available capacity on their consumer board.

    IMO the quick cheap fix has to be a replacement gas boiler with the choice between combi or not and a cheapie to last until a (planned?) green alternative in a few years or a better up market one to last until it doesn't and then go for the green alternative.

    (Oh and if they are planning to move within the next 7 years I would go for a gas boiler just because that is what the house buying public expect).
  4.  
    Posted By: WillInAberdeen(From your last para I understand they need to replace their home heating boiler - others have understood that they just need to replace their source of hot tap water)


    Will, correct the whole boiler has gone. I think they have a hot water cylinder already.

    Thanks everyone for the responses so far. Any makes/models to consider?

    Also, other than slightly cooler-to-touch radiators are there any 'surprises' for a household that's used to a conventional boiler?
  5.  
    Posted By: Doubting_ThomasAlso, other than slightly cooler-to-touch radiators are there any 'surprises' for a household that's used to a conventional boiler?

    If you are talking about ASHP then the surprise could be the electric bill if the rads are not big enough to cope with the heating demands with cooler rads so the temp. is cranked up which destroys the ASHP COP.
    And if you are changing the rads to cope then that can be an expensive bill.
    • CommentAuthorbhommels
    • CommentTimeOct 28th 2020
     

    Thanks everyone for the responses so far. Any makes/models to consider?

    Also, other than slightly cooler-to-touch radiators are there any 'surprises' for a household that's used to a conventional boiler?

    Viessmann make very good boilers, as I think a few more on this forum can testify

    Irrespective of the make, try to get a weather compensating controller.
    • CommentAuthorrevor
    • CommentTimeOct 28th 2020
     
    Worcester Bosch, have a look at their website they have a very good guide to choosing the correct boiler for a particular situation. As a HW cylinder exists then a system / conventional boiler may be appropriate if a lot of hot water is required as a combi may not keep up particularly if there is more than 1 bathroom. Going combi route means taking out or leaving in situ the cylinder. Plumbers like combi quick to fix much less plumbing involved and may push them when a conventional or system boiler would be more appropriate. However Worcester Bosch guide lines help one to choose the correct solution. Modern boilers because they are compact come with 22mm tails which regardless of what the system may require in water flows plumbers will plumb in 22 mm where going up to 28 mm may be required to get good flow out of the boiler. You can get a 40 kw boiler with 22 mm tails and if the property requires this size of boiler then it needs connecting to 28 or even possibly 35 mm pipework. A lot depends on the heat load which will depend on u values of walls roof etc as to the pipework required. A proper heat demand calculation is required to properly size the boiler coupled by good design of the pipework to distribute the heat properly. This is the key to an efficient system more important IMHO than weather compensating.
    • CommentAuthorphiledge
    • CommentTimeOct 28th 2020
     
    This time of year and with risk of unkown lockdown(s), just replace like for like with whatever branded modern no frills boiler their plumber is comfortable installing. Then start planning a longer term solution.
  6.  
    interesting thing popped up recently
    looks like a heat battery similar perhaps using Sunamp kit
    https://tepeo.com/technology
    • CommentAuthorjms452
    • CommentTimeOct 28th 2020
     
    See if they can fix the boiler so they can evaluate without the rush and reduce energy usage in advance of a change.
    • CommentAuthorMike1
    • CommentTimeOct 28th 2020 edited
     
    I'd be looking at an ASHP for heating, with maybe some bigger radiators as suggested by WillInAberdeen. Plus an immersion heater for the hot water, though with a little additional complexity you could use the heat pump to pre-heat the water to radiator temperature, which won't squash the heat pump's performance as much as heating it to tap temperature.

    For greenness, avoid gas if possible. See http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16654
    • CommentAuthorCWatters
    • CommentTimeOct 28th 2020
     
    Scroll down this page to the table..

    https://nottenergy.com/resources/energy-cost-comparison/

    Compare the figures in the column "Pence per kWh (after boiler efficiency)".
  7.  
    Err, this is the GBF forum not MSE, shouldn't we also be comparing the column 'KgCO2e per kWh' ?

    Gas: 0.208. ASHP 0.107. *

    There's not many other changes they could make that would halve their carbon emissions in one go... :-)

    We saved money switching from oil to an ashp, but since then the price of kerosene has crashed because of Covid. It's hard to say whether it will stay that way.

    Electricity for heat pumps is much cheaper than that list at most times of day, especially if they heat their cylinder overnight.

    If they get RHI, it pays 10.85p/kWh which might swing the cost balance....

    Edit to add: No personal experience, but someone linked to a Vailant arotherm ashp that seems aimed at gas boiler replacements. It uses R290 so can run at high flow temperature, they claim SCOP of 3.4 at 55degC which should be hot enough to run radiators and heat DHW.

    * Further edit to acknowledge that marginal intensity is more complicated, Notts Energy is a great simplified resource
    • CommentAuthordereke
    • CommentTimeOct 29th 2020
     
    A boiler breaking down is the worst time to switch energy sources!

    You really need to have heat loss calculations to figure out what sort of state the house is in before recommending a solution. Of course the solution is ultimately an ASHP (don't be distracted by hydrogen) and probably some amount of insulation and possibly upgraded rads or higher running costs until those things are rectified.

    Personally I'm very happy with my ASHP as a direct replacement for an oil boiler with no rad upgrades. I've still got some improvements to make but until I've done those I've been happy to eat the cost difference.

    That table with the costs is a bit crazy. Who is paying 19p/kWh? If they can buffer some heat then they should also look at an agile tarrif where you can get very low rates and in some cases be paid for using energy. If you are purely interested in cost then that is something to consider and I don't think gas can compete with that!
  8.  
    I run my ASHP how water at 50c and my UFH and rads at 35c

    Haven't even bothered checking the COP but a stone wall mid terrace with 50mm IWI to the front and 90mm EWI to the rear our running costs are minimal
  9.  
    I'm by no means an expert and will be looking at similar kinds of questions next year when we address our home's heating. However, I'm on oil and my boiler is currently working, so there are a few differences... ;)

    I'm glad people have mentioned the potential need for a rad upgrade, as that is something we weren't aware of when we first looked at ASHP as an option. The other thing I think is worth bearing in mind is what your friends consider a comfortable temperature - IE where's their thermostat set? And how much hot water do they use? We like a cool house as it is what we are used to. If it hits 18C+ we start to feel the need to turn things down. We hardly use any hot water. And for these reasons we are starting to think ASHP isn't suitable for us. Because the efficiency drops as the outside temperature lowers, we figured that when we need the heating the most we'll be paying a lot, and when it runs more efficiently (because it's warmer outdoors) we'll either not be running it at all, or will only have it on for short periods.

    People with more knowledge and experience, please correct me if I'm wrong in any of the above. But if it rings true at all, then I think desired temperature is definitely something to bring into the decision making equation.
  10.  
    Greenfinger, things have moved on and ASHPs run fine at UK winter temperatures.

    This corner of Scotland is known for chilly weather in Winter* and ASHPs work efficiently here. They are popular in Scandinavia and Germany too.

    Eg the popular mitsu ecodan monobloc has a COP of ~3 at outside air temperature of -3degC (so 300% efficiency) , compared with its all-year-round-average SCOP of ~4. So slightly less efficient in the coldest weather, but still much better than electric heaters, and if you get RHI then the ASHP will be cheaper to run than gas, and greener than both.

    * =anytime other than August 🙄
    • CommentAuthorrevor
    • CommentTimeOct 29th 2020
     
    When I looked at ASHP about 5/6 years ago they were not at all efficient if you needed to heat DHW to 60deg as one needed extra input to raise the temperature which off course led to a decrease in COP. What is the current situation?
    Worcester Bosch did develop a combined ASHP with a gas boiler and it would work by using the most efficient combination of the two. Not sure what happened to it and have not gone looking.
    It is very well factoring RHI to help the economics but probably millions of households many on prepayment meters who cannot afford the capital to go green are paying a levy towards subsidising those who can afford the outlay.
  11.  
    Agree with the principles. RHI does come from government (general taxes), it doesn't come from peoples energy bills like FIT/ET/CfD do, so it is a little bit more progressive, but certainly an important point.

    I mentioned an ASHP a few posts up the thread that apparently would do DHW efficiently, and there was a thread recently (by Goodevans I think) who had good results with his heating a DHW cylinder. The 2-stage ASHP I had previously was designed to be efficient at DHW temperatures, I posted about it a bit.
    •  
      CommentAuthordjh
    • CommentTimeOct 29th 2020
     
    Posted By: revorWorcester Bosch did develop a combined ASHP with a gas boiler and it would work by using the most efficient combination of the two

    Are you sure it was Bosch? There is a 'unique' Daikin product: https://www.cityplumbing.co.uk/Daikin-Altherma-Hybrid-Heat-Pump-Pack-8kW/p/100180
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