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  • This topic has 21 replies, 11 voices, and was last updated 2 months ago by ajc.
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  • Future proof rad/pipe size for heat pumps?
  • MrSmith
    Free Member

    Hopefully i’ll be moving soon to a new flat and will be internally insulating (60mm insulated plasterboard) and fitting low-E secondary glazing, not allowed to remove the Crittall windows and not sure about cavity wall insulation as it’s on the 6th floor and supposedly the cavity goes all the way up/down so i’ll have to fill the voids below me before i see the benefit!.
    So we are doing as much as we can to improve heat loss, there is some kind of ‘insulating quilt’ under the iroku hardwood floor and a flat above. it’s solid reinforced concrete with brick/blockwork walls built in the 50’s.Boiler is from 2014 and i’ll be fitting new rads and tado TRV’s. my initial thoughts were to over spec the rads and maybe use bigger pipework of 22mm with an eye to the future, is this sensible thing to do?

    At some point i figure the leaseholders (Dulwich Estates) will have to get with the program and decide if heat pumps will be allowed to be fitted to their many buildings from late 50’s early 60’s.
    While it’s not a conservation area they are really strict on maintaining the look of the modernist architecture, ideally they would have communal ground source heat from the grounds around the buildings and use the central flue from the old gas warm air fan heaters that runs up the middle of the blocks to run the pipes for the individual hot water box for each flat. this is probably wishful thinking on my part but you can’t ignore no gas in the future and how do you service an ASHP above ladder height?

    would you bother or just fit what works with the boiler now? far easier to do it while it’s empty and other work going on, maybe we will not be living there come heat pump time but it will help sell if it’s already insulated and the radiators will not need ripping out.

    WWSTW do? can’t be the only one thinking about future-proofing their homes.

    MrSmith
    Free Member

    Bump for the lunchtime crowd of plumbing/heating/heat pump experts.

    ossify
    Full Member

    If it’s a chance that the leaseholder is going to install it at some point for everyone, you’d hope that part of that would also be to upgrade everyone’s rads, seeing as large rads are needed to use heat pumps properly. Which makes it a bit more of a risk you potentially wasting money by doing it yourself now.

    Though whatever happens I suppose you could always just use the large rads at a lower heat setting on your normal boiler, which would be cheaper.

    Not a heating engineer or heat pump expert! Or any expert, come to that.

    MrSmith
    Free Member

    well new rads are going in anyway, double/triple column so i guess more suited to running boiler at lower temp than the existing 2 panel ones that look quite small for the room sizes.
    So whatever gets fitted should make the boiler more efficient assuming i don’t overdo the sizing, online BTU calculator suggests 6000 for the bigger lounge/diner which will also need to raise the temp in adjacent kitchen so i was going to look at 8500-9000 covered by three rads.

    5lab
    Full Member

    I dunno if you need 22mm piping for ASHP or just non-microbore. Why are you putting new rads in? The cost of buying/fitting them is likely to outweigh the marginal benefits from reducing flow temp

    MrSmith
    Free Member

    Fitting new rads because the old ones look horrible plus the pipes are sat in a big ugly box where the skirting is.
    They have to be removed anyway as fitting kingspan k118 insulated palsterboard (62mm) and will run a upvc ‘U’channel cut into the insulation (the stuff used for boxing in pipework) just in the lounge, pipes will be surface in the bedrooms as mostly hidden by furniture. place is going to be repainted/new terrazzo windowsills to cover the insulation depth etc.
    Makes sense to do everything once.

    ButtonMoon
    Full Member

    Ignore the negative comments from people saying that reducing the flow temp will make little difference. I’ve changed my heating design (large rads) and it is running at low temps (weather compensation) with a large reduction in gas consumption. Crucially though, I’ve increased the temperature in the house this year as well.

    Radiator size – If you go to the Stelrad website and look in the download (https://www.stelrad.com/downloads/) section, you’ll see the radiator ranges. If you download say the softline pdf you can see the rated outputs. These outputs are the standard figures printed, but are for a flow temp of 70degC (Delta 50). If you look at the bottom of each section you will see the conversion factor you need (P74) to do in order to size for a 30degC temp which is where you should be looking for low temp. Obviously the size increase should then match your calculated heat loss.

    Why would the ‘UK Industry Standard’ be 70degC flow when it has been mandatory to fit condensing boilers since 2006? Because that’s the how much the UK care about environmental issues and efficiency….. 🙁

    Pipe type should be copper, avoid pushfit as the inserts reduce the pipe diameter. The sizes would depend on the radiators, but for a flat I would be surprised if 22/15mm wasn’t big enough.

    Have you considered low profile wet UFH? Maybe a better solution if you are gutting the place?

    ButtonMoon
    Full Member

    Sounds like a great project! Have you considered MVHR?

    If you get all that PIR sealed, you may get a big benefit from it.

    MrSmith
    Free Member

    ButtonMoon, thanks for the info, i’ll investigate the stelrad calculator.
    15mm will obviously be easier to fit, definitely no plastic or micropore though.
    Can’t do underfloor as there is an original Iroku strip floor in every room apart form bathroom and kitchen, the bathroom tiles are coming up but it’s such a small room i’m not sure if there will be enough surface once toilet and sink take away the space plus that might complicate the tado system?

    the MVHR is interesting and something the Mrs would probably like as she hates dust and some system of filtering air would appeal. there is even a central cupboard where the unit could go based round a flue that runs up the whole building that was for warm air gas boilers, there were ducts that went into each room from this middle cupboard so wouldn’t be a tricky install apart from where you pull air in and where you exhaust (no roof space) can’t go into the central flue as that’s having fire stopping work done on it and they will only allow those with original warm air boilers to vent into this.

    Believe me i would love to go the full monty on this place but are limited by what’s allowed, what there is room for and costs. was quoted 25k for aluminium windows and then i couldn’t get anyone to fit them 6 floors up as there was so little gap for the Crittall windows they would have to chase out an inch of concrete round the reveals which the Dulwich Estate would have had a fit over.

    I’m hoping the secondary glazing helps with any condensation as the temp differential from inner surface (say 20º) will be more gradual from glass/air gap/glass to the outside surface (0º) so less moisture in the gap and no dew point on the interior pane. if not we will buy one of those karcher window vacs…

    dovebiker
    Full Member

    I have an ASHP with wet UFH downstairs and 3 radiators upstairs – they are plumbed with 15mm pipes. 110m2 property.

    jimsmith
    Free Member

    Ive fitted a few heating systems like this… gas boiler, rads and pipework ‘heat pump ready’.
    seems to work well but makes it an expensive install compared to plastic/cheap combi boiler, The place will heat up quick smart though!
    Ive used 22mm copper main loop with rads teeing off in 15mm… standard stuff really. K3 rads usually but on one job K2s with pipework that could be moved to fit K3 depth easily.

    One thing to remember in a flat is that heat pump systems need quite a bit of space inside as they mostly need an unvented cylinder, a buffer vessel, 2 expansion vessels as well as valves, heating pump, controls etcetc. its a lot and getting it in a small space with clearances for service/repair can be fun and games. the heat pump primary will likely be in 28mm copper which isnt easy to tuck away. Drilling through the external wall and making good can be a big chunk of the job. Not easy in a flat Id think…

    thats my 2p anyway
    Jim

    MrSmith
    Free Member

    Think i’ll go with the same (15mm off 22) there is a large cupboard that would take an unvented cylinder if needed but no heat pump can be considered yet until the thinking changes on conservation areas/older ‘heritage’ buildings and sticking boxes on the side of them, that will likely come in the next decade.

    I’m hoping we end up with ground source for the whole block and a ‘shoebox’ in each flat

    Shoebox Ground Source Heat Pump

    Bear
    Free Member

    Mr Smith – see if you can go and look at Bell House see hitch must be near you in Dulwich. There is a ground source heating that building.
    As for pipe size with a Delta T of 10 rough guide is 5500 watts through 22.
    Heat pump primaries are usually 22 for 3.5kw unit, 28 on the 5&7, then 35mm for 10 and 12.

    MrSmith
    Free Member

    Every time i walk past i seem to have just missed the open day they have every month.at least the estate are amenable to ground source heating on ‘their land’.

    dovebiker
    Full Member

    The internal gubbins for my heating system apart from the ASHP – cylinder, 6ft expansion tank, controller etc was installed into an 800 wide, 600 deep floor-to-ceiling cupboard in my kitchen. Builder wasn’t sure it would all fit, but the installer enjoyed the challenge and was pleased with the result. I only need to access the cupboard occasionally to tweak the controller.

    cynic-al
    Full Member

    Apols if I’ve missed something but where will an ASHP go for a 6th floor?

    Also how do larger rads use less gas? Sounds like free energy.

    didnthurt
    Full Member

    Where’s the mechanical engineers when you need one…..

    ajc
    Free Member

    Retrofit like this requires good attention to detail. Your insulation should be fully bonded to walls and carefully sealed to prevent air leakage behind or it will turn into a mould sandwich. Personally I’m not a fan of foam insulation but it will be the thinnest option. Insulate into window reveals, head and window board to prevent thermal bridging. It is also essential to have a robust ventilation strategy. Constant extract humidity controlled fans in kitchen bathroom at least and mvhr at best. Graham from abc heat pumps will give you good advice regarding rad and pipe sizing for a small fee. Buy a data logger temp humidity meter to keep track on air once you’re living there. You can get them from Amazon for under £15. Retrofit done wrong will create thermal bridges and an underventilated home and be a cause of mould problems.

    5lab
    Full Member

    Also how do larger rads use less gas? Sounds like free energy.

    larger rads let you run a lower flow temperature, letting your boiler heat the water to a lower absolute temperature, letting your boiler work in a marginally more efficient manner – maybe 3 or 4% more efficiently for most people, maybe 8% in extreme scenarios.

    molgrips
    Full Member

    I think large rads work better anyway with normal CH as you can run lower temps which improves efficiency. As 5lab has just said.

    Fit the biggest rads you can I’d say. I replaced the tiny one in our hallway years ago because the hallway was always cold. However now I have been properly tinkering with the system it actually works much better than the ones in the rest of the house. It can be warm at the top and relatively cool at the bottom which means lots of heat is being emitted into the room nicely, and the return flow is cool as it should be. The smaller rads are warm at the top and warm at the bottom. In order for them to get much heat out the inlet needs to be hotter. This means if you are near a rad you might be uncomfortably hot whilst the rest of the room is still relatively cool.

    MrSmith
    Free Member

    Retrofit like this requires good attention to detail. Your insulation should be fully bonded to walls and carefully sealed to prevent air leakage behind or it will turn into a mould sandwich. Personally I’m not a fan of foam insulation but it will be the thinnest option. Insulate into window reveals, head and window board to prevent thermal bridging.

    I’m aware of interstitial moisture so will be fully sealing each board edge rather than just dabs of adhesive. plus any fixings that go right through to blockwork i’ll probably squirt some sealer in before fixing, less heavy stuff i’ll use an undercutting tool for some grip-it’s that will not penetrate into the void.
    window reveals are tricky as there is simply not enough room to insulate due to the thin crittall frames so i plan to cut back the insulation edge to fit a strip of 12mm foil backed PB which will but up against the existing reveal corner then when the secondary glazing is fitted this will have a 10cm gap meaning most of the ‘cold’ reveal is inside the air gap. i’m hoping by not having a 20º/0º cold bridge interface (the existing crittall window) the air in the gap will be somewhere between the inside/outside temp and dry meaning less condensation. we will be buying one of those karcher window vacs as a precaution. the tado TRV’s have humidity sensor (i think).
    In the 50’s when built they fitted a drying cabinet with a small gas heater in the base and when you closed the door a lever opened a flap directly into the central communal flue, surprised nobody got poisoned by CO2, it was quite a nifty system for the times, along with a little hatch in the corridor where bread and milk could be delivered directly to your larder cupboard these were blocked off as kids were nicking stuff.

    the flats are not prone to damp transmission from outside just human made inside but having viewed a few before putting an offer in including one that had been insulated i haven’t seen any major condensation issues apart from in the corners of the window frames where people haven’t cleaned or painted them properly and without secondary glazing.

    I don’t expect it to be passive house perfect but i’m doing what i can without going OTT.

    ajc
    Free Member

    Full bonded boards with notched trowel rather than strip of adhesive round the edge. You ideally want no air gaps not just no flow of air. You can use aerogel backed plasterboard in reveals but it does cost an arm and a leg. You are obviously aware of potential issues so that is a very good start. Important to monitor humidity as closed up insulated buildings isn’t a good thing.obviously extract moisture in kitchen and bathrooms and don’t dry washing inside. I used to own a 50’s flat in Battersea that sounds very similar. Crittal windows always leaked but mostly a very solid build.

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