Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




  1.  
    My first foray into the forum!
    I am seeking some wise advice on a proposed heating, cooling and hot water system.
    I live in the south west of France and have been working on a renovation scheme to what were (and are still in part) very dilapidated farm buildings since 2004!
    I am recently retired and now resident here and seeking to finish the project while I still have a little energy left!
    Holiday time over this 15 yr period has allowed us to restore one 2 bed house in which we currently live. It is served by a 300l Akvaterm Solar sealed thermal store on the first floor, heated by a single solar panel (no room for another) and a wood burning stove in the living room below (with Laddomat), with 2 x 3kw immersion heater back up.
    Whilst down in the south west, it can get very hot here in the Summer and seriously cold in the Winter.
    The system works reasonably well, but is let down in the Spring and Autumn months when it is either too warm for the stove or not quite warm enough for the ST panel particularly when the sun is not shining – causing undesirable and expensive need for electricity back up!
    I am now turning my attention to the proposed adjacent principal residence conversion – a property on 3 levels – planned for 3 bedrooms and two bathrooms on first floor, living rooms and shower room on ground floor (with semi basement below) and kitchen/dining on lower ground floor to the rear.
    The first floor and ground floor are both suspended timber.
    As the other house, the walls are 600mm solid stone, that I am lining with insulated studwork.
    Many years ago I and the wife laid a piped underfloor heating array to the insulated concrete kitchen floor before covering with a screed – the pipes are still sticking up waiting for the manifold that is currently sitting in a box under the bed!
    I want a more flexible, controllable and efficient system here and am scratching my head a little as to the way to go.
    Gas is most effective/instant, but it would have to be LPG and of course it is not green - and its days are arguably limited and LPG is expensive – nevertheless, an option even if only a back up when it is really cold.
    Solar Thermal - plenty of space and good aspect on this roof, so definite potential.
    Solar Voltaic – don’t know much about these or how they connect into/form part of a combined system?
    Air Source Heat Pumps – seem very popular around here for the small square newbuilds, but have picked up on lots of bad press as to (lack of) performance, very high maintenance costs and disappointing running costs, enormous radiator sizing – not convinced that this is the solution on a property of this size and construction?
    Cooling in the summer (40 degrees) is also a consideration - I think these ASHPs can work in reverse?
    Ground Source Heat Pump – too late, external works now sorted!
    Wood Stoves with back boilers – we will have a stove in the living room and down in the kitchen, but loading them with logs for reliance on hot water supply is hard work in the Winter and we are not getting any younger, so I do not see these as being planned as a fundamental part of the CH/HW system. I had also understood that a thermal store had to be physically above such stoves to allow gravity circulation in powercuts – that will not be achievable here as I would ideally like to locate the hot water cylinder in the semi basement.
    So, my initial thoughts are as to a very large pressurised thermal store (TS) or hot water cylinder in the basement, fed by any/all of the above (save the stoves), providing mains pressure hot water, with heating to radiators generally and to the underfloor heating in the kitchen only – whatever the solution, it has to be reasonably simple, cost efficient and low maintenance.
    I’d be very interested and grateful for advice on what combinations the forum members have found to work well or not so well, so here’s hoping!
    I guess that this ground will have been trod before so any pointers to earlier similar discussions would also be appreciated.
    Thanks.
    • CommentAuthorMike1
    • CommentTimeApr 27th 2020 edited
     
    Sounds like an interesting project.

    I'd be looking at an Air Source Heat Pump, despite the negative press you seem to be having. Maybe some of the problems are caused by developers using low specs?

    However ASHP + radiators are normally a bad idea. Heat pumps are most efficient supplying water at lower temperatures - so are ideal for pairing with underfloor heating, and I'd plan on installing that throughout. It is possible to use oversized radiators at a somewhat lower than normal radiator temperature, which may explain the huge ones you've seen, and maybe why the ASHPs you've read about may not have been able to operate as efficiently & economically as expected.

    Most ASHPs can indeed be run in reverse and, from everything I've read, a cooled floor works very well to moderate summer heat, which would be another argument for underfloor heating, though it isn't the same (or as expensive) as aircon. Property age and construction shouldn't matter too much if you're insulating (and sealing against air infiltration).

    Economics now tends to mean that solar PV panels are preferred to solar thermal, and can heat water using immersion heaters, as well as feeding any surplus into the grid. You should also get useful electricity in the for hot water heating even if the sun isn't enough for thermal panels, provided skies are reasonably clear and, I'd have thought, potentially enough to power a central heating pump (someone else may well have done the maths on that).

    A thermal store uses mains water pressure for hot water distribution, so you should still get how water if the power goes off. I might well choose one alongside solar PV.

    I'd also be considering installing MVHR (mechanical ventilation with heat recovery) = VMC double flux, in French.
  2.  
    Thanks Mike - really very helpful!

    Can I just pick your brains a little further.

    All floors (except the kitchen) are timber suspended with new floorboards.
    Can underfloor heating pipes be efficiently run below these existing boards with insulation then fixed below it. I can't really interfere with existing floor to ceiling heights due to existing door threshold heights.
    It may be more tricky to fit, but there will be suspended mf ceilings below the existing joists with a c50mm gap that allows general services distribution - that could facilitate continuity of heating pipe circuits between each joist void?
    Would you know if there is any reckoner for sizing an ASHP and any leading manufacturers who have got this technology right?

    I have a couple of boxed ST panels sitting in the workshop for years now that I had planned to make use of.
    The PV route is interesting though. Do you know if there is some gadgetry for directing PV power into the TS immersion heaters when there is availability and call for it; or back into the grid when it doesn't - and how is this control married to the trigger for the ASHP so that pump doesn't run (and use (albeit relatively little) mains power) when its not needed?

    Understanding/designing the overall control/coordination of the heat source inputs and ultimately the heating distribution and temperature control is the most mind-numbing for me!

    Getting there and again thanks for your help.
    • CommentAuthorMike1
    • CommentTimeApr 30th 2020
     
    Yes, it is possible to retrofit UFCH to the underside of an existing timber floor. In the UK Nu-heat produce one such system - https://www.nu-heat.co.uk/blog/underfloor-heating-options-for-first-floors/ - I'm afraid that my knowledge of the French market is more limited, but if stuck & UK shipping is expensive you could maybe get some similar plates made up by a local metal shop. However UFCH in a floor screed would be my preferred option, where possible, as that would provide a more constant temperature profile across the floor (for heating and chilling) - maybe someone else can chip in with some figures on this.

    UFCH manufacturers /installers should be able to provide information on the heat output of their system, and you'd need some calculations to check that this was sufficient to counteract the heat loss though the building fabric and due to ventilation, and that you can reach your required room temperatures. For cooling, particularly for a timber floor, you'd also want to them calculate the temperature at which condensation might form on the pipes / metal plates, and stay above that - though it may not be a problem in practice if you have dry, hot summers.

    For the PV, there are indeed controllers that can switch the power for local use or to the grid as required - for example https://solarimmersion.co.uk/ https://sgwooldridge.co.uk/pvheating/ and https://www.pluginsolar.co.uk/?product=solic-200-solar-pv-immersion-controller

    There are a number of threads on here about UFCH and ASHP which should fill you in on more detail.
  3.  
    Charenteman
    Whether you use (or need) the PV controllers as suggested by Mike1 could depend upon how your grid tie works, - or rather the billing.
    Over here such controllers are not used because the billing for grid use when you have PV is an annual reconciliation. When the PV produces more than you need the surplus goes to the grid and the meter runs backwards. When the PV produces less than needed the grid makes up the difference and the meter runs forwards. At the end of the year the meter is read and a reconciliation is made. The trick here is to get the right amount of PV to match annual usage because what you are paid for over production is very uneconomical against the price of extra PV panels.
    I'm not sure what system for grid tied PV is used in France
  4.  
    Thanks both for your very helpful comments - much appreciated.
    One thing that still puzzles me is the appropriate sizing and set up of a thermal store.
    My simple objective is a controllable warm house and plentiful hot water whenever needed.
    I am thinking of a prolonged cold cloudy winter scenario and how the competing and simultaneous demands of comfortable UFCH and plentiful HW are both reliably and cost effectively satisfied by an ASHP alone?
    Is it simply a matter of the right spec/size store, good house insulation generally and effective draft exclusion - i.e. once the house has been warmed up, the ASHP then principally serves to maintain TS temperature to deliver HW temperatures? Are there simple control systems to manage these priorities? I don’t want or have the budget to go over the top, but should I perhaps consider two dedicated cylinders? Thoughts?
    • CommentAuthorMike1
    • CommentTimeMay 6th 2020 edited
     
    To couple an ASHP with space heating, a small buffer tank is often used so that the heat pump doesn't keep turning on an off with small fluctuations in temperature. It would be possible to add a PV-connected immersion heater to heat the buffer, if you're generating lots surplus electricity.

    ASHPs are normally only used for space heating, as they operate most efficiently at lower temperatures - which is why they're good for underfloor heating.

    A thermal store would often be used for hot water, and in your case heated by PV electricity when available, or from the grid when not. If you have plenty of sunshine you could go big enough for a couple of days supply, but it will start to get expensive for more than that. In a smaller property one downside of that would be that the heat given off in summer would contribute to overheating of the property, but if you have a cool basement to put it in that's probably not a problem for you.

    Having said that, you could run everything off a thermal store, heated by the ASHP + PV. Or use the ASHP to pre-heat the hot water in the thermal store. It depends how complex you want to make it / how the financial payback works out.

    BTW, note that really effective airtightness can significantly reduce the space heating requirement - but that involves much more than just draft exclusion at doors and windows - it involves sealing the entire structure.
  5.  
    Posted By: Mike1To couple an ASHP with space heating, a small buffer tank is often used so that the heat pump doesn't keep turning on an off with small fluctuations in temperature. It would be possible to add a PV-connected immersion heater to heat the buffer, if you're generating lots surplus electricity.

    +1 but depending upon the grid tied system that is run in France it might be easier to put the surplus PV output to the grid in the summer to draw on the grid later in the winter


    Posted By: Mike1ASHPs are normally only used for space heating, as they operate most efficiently at lower temperatures - which is why they're good for underfloor heating.

    And not very good at providing hot water

    Posted By: Mike1A thermal store would often be used for hot water, and in your case heated by PV electricity when available, or from the grid when not. If you have plenty of sunshine you could go big enough for a couple of days supply, but it will start to get expensive for more than that.

    +1 but again it depends upon the particular grid tied system you are running under as to how big a hot water store is the most cost effective

    Posted By: Mike1Having said that, youcouldrun everything off a thermal store, heated by the ASHP + PV. Or use the ASHP to pre-heat the hot water in the thermal store. It depends how complex you want to make it / how the financial payback works out.

    +1 The emphasis on the could is correct. It is generally accepted that it is better to separate heating and hot water because the demands (especially with UFCH) between heating and hot water are quite different in timing and temperatures.

    Posted By: Mike1BTW, note that really effective airtightness can significantly reduce the space heating requirement - but that involves much more than just draft exclusion at doors and windows - it involves sealing the entire structure.

    +1 and once it is air tight MVHR then becomes the way to go.
  6.  
    Thanks both, much appreciated!
    • CommentAuthorgoodevans
    • CommentTimeMay 15th 2020
     
    I would dispute the ASHP and hot water statements above - our experience is that If we heat the water once a day (at 2:00pm) and I reckon we get a COP of at least 2 in winter and obviously more in summer.

    For us we have a tank with a 3m2 coil and 250 litres capacity - by 2:00pm the bottom of the tank has got quite cold but the top is still hot enough for the mixer showers to operate correctly up to their maximum.

    The ASHP runs for about 45 minutes each day - during the last 10 minues or so tthe unit has started to modulate down but for most of that time it is drawing approx 2.2kW of electricity. In total most days I uses around 1.5kWh. Because of the large coil and the cold bottom of the tank the return temperature is kept fairly cool allowing the ASHP to run pretty efficiently for the first 15 minutes or so - after that it will not be so good but always better than resistance heating (particularly as it is already on and up to temperature).

    Eventually the return temperature is such that the flow temperature is maxing out at 53 degrees or so - and I let this continue until the mid point of the tank has reached 48 degrees. I estimate that bottom of the tank is at around 43 degrees or so.

    Running in batch mode like this has some advantages.
    It avoids some of the inefficiencies such as leaving a hot ashp and a hot slug of water in the pipes which is simply wasted when the heating isn't on. By choosing a time of the day when showers are unlikely to be used there is little chance the top of the tank gets cooled by the flow temperature being low at the start of the cycle.

    Running in the middle of the afternoon will tend to reduce the heat rise required by the ASHP improving the COP fractionally, in addition during the winter it is more likely to operate at this time without requiring defrost cycles.

    Finally, the ASHP is running throughout the summer - any problems with the unit would come to light within 48 hours (you always notice a cold shower) so we have a good chance that any faults will show up when it's not critical. Every 24 hours we can also be sure our zone valves cycle so they won't be seized come the winter. I will heat using the immersion today for comparison.
    • CommentAuthorgoodevans
    • CommentTimeMay 15th 2020
     
    I have Heated the water with the immersion heater this afternoon - it took 4.9 kWh to heat the water up to 46 degC in an hour and 45 minutes.

    Typically the heat pump has used approx 1.5 - 1.6 kwh to do a similar job (in winter nearer 1.8 to 2.0 typically) in 45 minutes.

    That gives a COP of approx 3.0 now and 2.5 in winter - better than I expected. I see no reason why an ASHP should not be used for DHW with a suitably sized cylinder.

    Using the ASHP It costs me the equivalent of less than 5p per KWh to heat the water in summer (7p in winter) - I have to put up with some fan noise for 45 minutes a day - but that is all.
    •  
      CommentAuthordjh
    • CommentTimeMay 15th 2020
     
    Posted By: goodevansUsing the ASHP It costs me the equivalent of less than 5p per KWh to heat the water in summer (7p in winter) - I have to put up with some fan noise for 45 minutes a day - but that is all.

    Which ASHP are you using? (Just interested to know)
  7.  
    GE, thanks for sharing your data!

    You have a good strategy to heat the tank only when it is properly cold (rather than keeping it constantly nearly-warmed) as this is as nearly as possible equivalent to countercurrent heat exchange, which is thermodynamically more efficient (less irreversible). The key point is that the bottom of the tank gets very cold, so it can it accept heat from the ashp when running at low temperature. When the bottom of the tank gets hotter, the ashp efficiency falls off, though if yours never goes above 43degC it's never too bad.

    For it to work as you describe, your daily DHW usage has to be enough to nearly-but-not-quite empty (cool) the tank over a day. You have presumably tweaked the storage temperature to make it so, and you don't consume very much DHW (5kWh/d = ~150litres/day at shower temperature), so you can get by with keeping the tank pretty cool.

    If your tank were/is a standard one, the standing losses would account for a good chunk (>1kWh) of your daily usage. It could be argued that you could have installed a smaller tank, as if you are not using solar or overnight E7/E10 there's no need to store a whole day's worth of hot water. You'd use up the smaller tank and then reheat it several times during a day, eg after each person showers - so perform the same cycle you currently use, but more often. Smaller tank= less standing loss and cheaper to build and quicker to reheat.

    Another strategy is to have two small tanks (or one tank divided up). Use one as the 'tepid' feed tank, and heat it very efficiently with the ashp at low CH/UFH temperature. From there, tepid water goes into the delivery tank, which gets an occasional blast with the ashp or immersion running at high temperature to top it up to usable temperature. I am thinking about using the solar coil region in the bottom of our tank for the 'tepid' heating.

    Sterilise the whole system by heating up weekly if you are bothered about legionella at the temperatures you describe.
  8.  
    Posted By: WillInAberdeenIf your tank were/is a standard one, the standing losses would account for a good chunk (>1kWh) of your daily usage. It could be argued that you could have installed a smaller tank, as if you are not using solar or overnight E7/E10 there's no need to store a whole day's worth of hot water. You'd use up the smaller tank and then reheat it several times during a day, eg after each person showers - so perform the same cycle you currently use, but more often. Smaller tank= less standing loss and cheaper to build and quicker to reheat.

    Given that there is a larger tank installed perhaps running the ASHP more frequently and only heating a partial tank would cut down standing losses. The tank should heat up from the top down and stratify as it does so it might be worth heating say only 1/3 or 1/4 as required leaving the bottom of the tank cold. Perhaps a thermostat suitablely located to control the switching assuming a trial shows it is worth the effort.
  9.  
    That's a good idea! Or perhaps heat the whole tank several times a day, but to a lower temperature (limit the ashp at say 45degC to improve its CoP). Good for a shower but maybe not for washing up.

    GE, have you tried running the same cycle but at 2am instead of 2pm? This might reduce the CoP, but you could use a cheap smart-meter tariff and lower-carbon nighttime electricity. Interesting if that would work out better/worse overall.

    Full disclosure: like Charenteman we have an old stone house and am planning how to improve the heating while not starting from the ideal ingredients. I'm certainly not looking to pick holes in GE's setup, sorry if sounded like that, instead I'm mulling out loud what to do with ours.

    Charenteman, I am thinking along the same lines as Mike1, using low temperature ashp for heating. Hot water pretty much decoupled from space heating, so no thermal store, but interested in GE's experience. Log stove, but not coupled into heating system. This setup worked very well in our previous old stone house renovation!

    Big decision is whether to: add underfloor heating (big job but we might lift some floors anyway to insulate); or just fit bigger radiators; or go for air-to-air heat pumps (aka Aircon units) and no piped system.

    Where I live, I can't make the numbers work for adding domestic solar (thermal or PV) - its much more effective to buy energy from utility-scale solar farms.

    We are planning to insulate the stone walls first before fixing the heating system, so will be a few years before we commit. (We have lived in the house for one winter and used much less energy than expected, there's a body of opinion that stone rubble walls are more insulating than we used to think, when made airtight.)

    The previous owner fitted a 250l hot water cylinder with two coils. We are only using the upper coil, leaving the lower half of the cylinder unheated, we heat the cylinder twice a day for family of 5.
    • CommentAuthorMike1
    • CommentTimeMay 16th 2020
     
    Interesting additional thoughts.

    These are the sorts of issues that I was referring to when I mentioned that going beyond separate systems depends how complex you want to make it / how the financial payback works out...
    • CommentAuthorGreenPaddy
    • CommentTimeMay 17th 2020
     
    Since a thermal store (providing DHW and heating) warms the cold feed water for DHW starting at the base, and gradually getting hotter as the coils winds up through the TS, the low grade water at the base is used as part of the DHW production. If you split cylinders into a DHW cyl and effectively a buffer tank, you lose that benefit.

    It also fixes the potential usage of that heated water, with no flexibility over the DHW to heating ratio.

    PiH, it would be good to see the figures that show it is generally accepted that you should not combine DHW and heating in a TS. I think the range of possible scenarios for energy inputs and outputs make that statement too general. Probably true if you have a big old energy guzzling building. Not true if you have a well insulated set up.
  10.  
    Horses/courses?!

    As I understand it:

    The distinction between a DHW cylinder vs a thermal store is a bit artificial, conceptually they both store heated water, just the construction practicalities are different. You choose one that suits your needs for storing heat. (Or both, or neither).

    The cylinder we have inherited has two coils and stratifies just like a TS, but at 250l it is twice as big as we need.

    Thermal stores are great if you want to store lots of heat in the form of hot water. However we don't have solar, don't heat water by burning wood, and our house has plenty of thermal mass, and we can heat DHW nearly as fast as we consume it, so we don't need to store lots of warm water.

    Particularly when we change heat source to an ashp which can work anytime of day or night, but prefers to deliver water at 30-40deg, which is too bulky to store many kWh of.

    We don't want to heat a CH store up to DHW temperature, as that hits the ashp CoP, hence the advice to separate them.

    We want a good amount of the joules of heat in each litre of DHW to be come from a coil at 40degC, to max the ashp CoP, not by putting raw cold feed into a coil of 60+degC.

    As GP mentioned, you get the same effect in a TS, but only when it is evenly stratified from cold at the bottom to hot at the top, not if it is nearly 'full’ or 'empty' (so its temperature profile is ’mostly hot’ or ’mostly cold’).


    >>" If you split cylinders into a DHW cyl and effectively a buffer tank... no flexibility over the DHW to heating ratio”

    Disagree with that comment - the flexibility comes by the duration of heating the two stores. If you need more DHW, then heat the DHW store for longer, or heat it more times a day, and v.v.
  11.  
    Posted By: GreenPaddyPiH, it would be good to see the figures that show it is generally accepted that you should not combine DHW and heating in a TS. I think the range of possible scenarios for energy inputs and outputs make that statement too general. Probably true if you have a big old energy guzzling building. Not true if you have a well insulated set up.

    I don't have figures, - and yes it's a general statement predicated by the notion that DHW and CH have different heat requirements and temperatures and those heat demands occur at different times. Given the options for obtaining heat - wood fired, ST, PV, ASHP, GSHP and electricity with all its various billing options IMO it will generally be better to separate the demands of DHW and CH. If you are storing your heat and you generally need more stored heat for CH than DHW there will usually be a loss of efficiency during the non-heating periods due to increased standing losses if you only have one heat store for both DHW and CH.
    A few of us have big old energy guzzling building, a few of us have a well insulated set ups, most of us have something between the two either because of architectural, planning or cash limitations and each building will have its own 'best fit' options but as a general rule I would argue that separating DHW and CH is better.
    •  
      CommentAuthordjh
    • CommentTimeMay 17th 2020
     
    Posted By: WillInAberdeenThe distinction between a DHW cylinder vs a thermal store is a bit artificial

    It doesn't seem artificial to me at all. A DHW cylinder contains potable water that is fed out of the tank into basins, baths and whatever else you choose. A thermal store does not contain potable water. The water in the thermal store never goes near a tap. Instead the potable water is heated as needed by passing it through a coil in the tank or through an external heat exchanger (usually a PHE).

    So the legionella risk assessment is completely different for the two situations, and the hot water from a thermal store is most definitely drinkable, since it is exactly as fresh as the cold water.
  12.  
    Thats right, and the pressure ratings are usually different, and the number of nozzles, and the materials, size, weight, design regs and the price. But for the purpose of GP's question
    conceptually they both store heated water.
    so
    You choose one that suits your needs for storing heat. (Or both, or neither).
    • CommentAuthorMike1
    • CommentTimeMay 18th 2020
     
    Worth knowing that a pressurised hot water cylinder relies on working pressure relief devices to keep it safe, including an expansion vessel which will eventually need replacement. Annual inspections are therefore strongly recommended, and are probably required by your insurance policy, if not actually legally required in the UK (not sure about France).

    Thermal stores and unvented hot water cylinders don't store hot water under pressure, so they don't require inspection (technically the small quantity of water in a thermal store heat exchanger is above atmospheric pressure, but is insignificant).
    • CommentAuthorEd Davies
    • CommentTimeMay 18th 2020
     
    Posted By: Mike1Thermal stores and unvented hot water cylinders don't store hot water under pressure


    I'm sure it's just a typo but, to avoid any confusion, it's vented hot water cylinders (i.e., usually ones fed from a tank in the loft with an expansion pipe going back up to that tank) which don't store hot water under pressure. Unvented cylinders store the water under pressure.
    • CommentAuthorgoodevans
    • CommentTimeMay 18th 2020
     
    To answer some of the questions and thoughts above...

    My ASHP is a Samsung Mono 9KW Gen5 and the Cylinder is a Gledhill StainlessLite HP 250L.

    The Samsung unit appears to run at the advertised efficiencies/cop - but some of its logic is screwy - so I have taken away it's ability to control the zone valves (the thermostats alone do that - I will post separately on getting the best out of a Samsung gen5).

    I use no buffer tank/low loss header or heat exchanger. The cylinder coil and UFH are directly connected to the ASHP and one pump does the lot (with 2 zone valves). I use inhibitor but no glycol - I am using the inbuilt mandatory freeze protection of the ASHP (It runs whether you like it or not when it's cold and In case of a prolonged power cut in freezing conditions I will be able to run the pump with a 12 volt battery and a leisure inverter to prevent freezing - I just hope I'm at home if that happens).

    It would be difficult to partially heat the top of the cylinder to say 50 deg C without the bottom of the tank being heated to at least 40 deg c as the flow rates required of the ASHP ensures a maximum delta T of 10 deg C if the flow rate is cranked right down. So its all or nothing - set the cylinder size for 24 hours storage for 90% of the time and run on demand (instead of daily batch) if guests or family show up.

    I have looked at different tarrifs - E7/E10, Smart and flat rate and our energy usage profile seems to be that flat rate is probably cheapest for us. We are lazy and use our dishwasher for everything - including pots pans, teapots occasionally - it runs once a day and uses 0.98kWh. We have used 2190kWh of electricity this year so far - 18th May. That's all the energy - no solar, no gas, no oil. (insulation is the reason however not an ASHP). If we should ever need very hot water in the washing up bowl we would have to use a bit of kettle water but so far in 6 months SWAMBO has not had to do that.

    The Gledhill specs indicate heat losses of 1.78 kWh per day (at 55 degC I think). Anecdotally I don't loose that much (as the bottom of the tank is can only average around 30 deg C and the top is not that hot - ever) - I suspect real losses are at around the 1.2kWh mark per day or less (approx 0.4 kWh of electricity). Even with these losses it is still better to heat the water with the ASHP than use electric resistance heating - however a cylinder has to be bought and takes space so it isn't a slam dunk no brainer.
  13.  
    Hi Goodevans, thanks again for sharing your info, very helpful! Impressive electricity consumption. Thanks for the pointer on the gen5.

    Hi Mike1, good point but I would advise that the safety devices on both vented and unvented systems should be regularly maintained, including the thermal cutouts as well the safety valves. This very tragic accident involved the F&E tank of a vented system where the immersion did not cut out.
    http://www.dailymail.co.uk/news/article-506604/Water-tank-fault-scalded-baby-girl-death-known-unreliable.html
  14.  
    Incidentally, our unvented CH and DHW systems had their annual service today, by a chappie with excellent qualifications, local reputation and (by the look of him) many decades of experience.

    He didn't feel the need to go up in the loft, where the pressure safety valves, expansion vessels and immersion heater are :-(

    In discussion, he thought they'd be of more interest to a plumber, whereas he considered himself to be a 'heating engineer' so he doesn't concern himself with inspecting those bits.

    Possibly, we'd all be safer without wet heating...
    •  
      CommentAuthordjh
    • CommentTimeMay 28th 2020
     
    Posted By: WillInAberdeenIn discussion, he thought they'd be of more interest to a plumber, whereas he considered himself to be a 'heating engineer' so he doesn't concern himself with inspecting those bits.

    I wonder if there are standards that are supposed to be followed for describing and executing such services? And whether those standards are optional or mandatory, and whether as a 'heating engineer' he's a member of any professional association that subscribes to those standards?

    I confess I'm fairly pleased that all the water storage in our house is in a single cupboard downstairs, apart from WC cisterns, for I expect we'll get some plumbing problems eventually. We have had two floods in the garage - once when it was all new and the plumber hadn't tightened up one connection fully and again recently when I turned the outside tap back on without closing the drain valve fully. The first time there was a couple of inches over the whole floor by the time we noticed; this time just a six foot diameter puddle.
    • CommentAuthorMike1
    • CommentTimeMay 29th 2020 edited
     
    Posted By: djhI wonder if there are standards that are supposed to be followed for describing and executing such services?

    Possibly BS 8558:2015 'Guide to the design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages.'

    The old standard (BS 6700) - at least the 1997 version, included periodic inspection for buildings 'other than single dwellings'. I don't have a copy of the latest.
  15.  
    There are no requirements for any testing / inspection of mains pressure DHW tanks in domestic installations here - and I can't recall hearing of any problems either. The only problem I have had with mine (at one time I had 4) is that about every 5 years I had to take out the base plate (containing the immersion heater, thermostat socket, safety thermostat socket and sacrificial anode) and dump the whole lot in the bin and replace with new due to limescale build up, done on a fix when broke schedule.

    Given the millions (literally) of mains pressure DHW tanks there are here and the total lack of issues (other than limescale) IMO the UK requirement for annual inspection is a bit OTT
  16.  
    The building standard (building regs) have lots of requirements for safety of vented and unvented DHW systems, including temperature cutouts and pressure safety valves. But I can't find anywhere they have equivalent requirements for vented and unvented CH systems.

    Seems odd, as quarter of a tonne of scalding water in an DHW cylinder above the stairs, would seem to be as hazardous as quarter of a tonne of scalding water in a thermal store, location and pressure being equal...?

    Building Stds/regs apply when constructing or modifying, so can't impose requirements for maintenance.

    Has anyone checked this year that the thermal cutouts are working on their immersion heater? It's easy to withdraw the thermostat so I might try putting it in a flask of boiling water.

    I discovered from the 'heating engineer' that heating oil now contains biofuel and some polymer components of our boiler are not compatible, including the fire valve and the burner hose.

    Gas Safe and Oftec regulate the competence of maintenance technicians.
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press