arg

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About arg

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  • About Me
    Embarking on major renovation of '80s house - looking to achieve Passivhaus Enerphit level of efficiency while also adding small extension, moving walls around inside, new windows etc.
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    Cambridge

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  1. I thought that, but having spoken to someone local who has had RWH for some years, he claims that in this area (East Anglia) it's not very seasonal. Met Office data seems to bear this out. Usage on the other hand might be - in my case I'm intending RWH primarily for garden use (so very seasonal), but looking at cost/benefit of adding toilet flushing capability.
  2. A couple of thoughts (not based on any experience, yet): If you are doing a microcontroller project, you could potentially detect the pump running dry by sensing the mains current drawn by the pump (with a simple sense coil). As you say, you wouldn't want to leave the pump running dry, but just for a few seconds as the tank empties and then locking it out until it rains again probably wouldn't hurt. Probably more reliable over the long term than trying to sense the water level in the tank. The roof tank with effectively two float valves set at different heights does seem like a neat option, though I'm not sure about the regulatory issues (need to make sure the overflow is such that runaway pumping of the rainwater can't reach the level of the fresh water inlet?). But as a completely different approach,, how about just running the mains water into your underground tank (perhaps manually) when it gets empty? If you think your use vs roof area vs storage volume means you only need the mains water occasionally, the effort of manually topping up when the pump system has alarmed and shut down is offset by the fact that the pump controls etc are now very simple and need little maintenance.
  3. I was afraid of loss-of-pressure issues, and/or other issues I hadn't thought of that people here would pop up to tell me! If running off mains pressure is that easy, why isn't everybody doing it? Or maybe there was a great revelation in the late '90s and everybody now is? This is really why I posted this thread, I want to understand the issues (and every house I've ever lived in has had a tank). Well, we could knock the house down and start again (and occasionally I think that could have been a better idea, assuming we could have got planning permission). But without doing that, there really isn't anywhere suitable. The house was built to be as low height as possible, I am guessing for planning reasons at the time: being an almost triangular plot with the thin end at the street, if the house was built where it "should be" in line with other houses in the street, then it would have been a tiny house. Instead, we have a gratuitously grand-looking garage built where the house should have been, and the house built further back on the plot pretending it's not there (the original planning application describes it as a "Chalet Bungalow", when it's clearly not a bungalow!). Net effect of this is that all the upstairs rooms are built into the roof shape and any corner you partition off will have sloping ceiling and low height. Anyhow, up to now I wasn't feeling particularly compromised - but maybe I didn't know what I was missing.
  4. I'm currently starting on a major refurb/minor extension of our 80's house (upgrade insulation from really poor to Passivhaus Enerfit levels, etc, etc). Current plumbing is traditional for the era - gas boiler feeding vented cylinder, large water tank in attic, only kitchen tap is direct from mains, all other hot/cold are from the tank. Plan is UFH+ASHP replaces heating, 2x sunamps replace hot cylinder. Main reason for particularly favouring sunamps here (over and above the usual trade-offs) is space to put them: the house is an odd shape with low roof height and while there's plenty of odd corners to put stuff they are all low height - existing cylinder cupboard is a triangular space in the eaves with a fairly small cylinder and no height for a bigger one, never mind a meaningful thermal store. Anyhow, the exact detalis of the heating system is a discussion for another day; I'm fairly convinced I want the sunamps and the question is how to plumb them. Obviously the easy thing is to just put them in place of the existing hot cylinder - cold from the attic tank runs through the sunamp(s) and out through the existing pipes to all the taps, cold supplies unchanged, feed in and out of the Sunamp just adapts the existing pipes that go to the cylinder. Nice, quick, easy job..... However, I'm tempted to convert the system at least partly to use mains pressure water to the taps, for the following reasons: As mentioned, the house is an odd shape, and in particular is split into two halves (half single-storey, half 2-storey), with only one possible route from one half to the other for MVHR ducts (low ceiling heights and a structural beam in an awkward place means there's literally no other option). That space is currently filled with a total of 8 pipes running from the tanks in the attic to the cylinder cupboard. Two will disappear (boiler circulation is also vented with a header tank in the attic), but the others - 6 independent cold feeds to various taps/showers etc - will need to be relocated somehow. At minimum, this makes me rip everything out and put it back so keeping the existing arrangement is no longer the "easy option"; also, cold mains comes from the other direction so probably makes it easier to find new routes. Due to the low ceiling heights, there's not enough head for a shower on the 1st floor - existing 1st floor shower room has an electric pump to make it work, which it would be nice to eliminate. Also, given 2x sunamps for total capacity, one option is to split them up - place one of them in that 1st floor shower room right next to the shower and also serving the kitchen immediately below, with the other one in the existing cylinder cupboard over the other side of the house feeding the bathroom and gnd floor shower room there: this would considerably shorten the hot runs and so time/water/energy wasted running the shower/tap waiting for it to warm up. I've never liked having "not really drinking water" at bathroom taps, having been stored in the attic tank. Though maybe this point is moot given I'd probably feed everything from the output of the water softener so that's not ideal for drinking either. Item 1 has suddenly made this urgent, where I'd previously been leaving this stuff until the end of the build . So I could now: Leave as-is, just find alternate routes for all/most of those pipes. Put the 2nd sunamp in the 1st floor shower room, and feed that with mains cold water (easy as it enters the house over that side), mains cold also used for the cold feed to shower and other taps nearby, but leave the other side of the house running off the attic tank. This (I think) eliminates one of my problem pipes, and also frees up what was a hot-out pipe through the (also crowded) floor void that could be used in the reverse direction to replace another one. Scrap the attic tank altogether and run everything off mains pressure. What are the pros and cons here? Current system has dedicated cold feeds to all the main users (though not so much for hot), hence no issue with one tap turned on reducing pressure to others. Is this going to become a big deal if I start using mains cold and at least some of the pipework is shared? Water softener probably makes this worse (it is currently located right next to where the cold enters the building, so no problem for routing, but bound to add to pressure loss). Are there regulatory concerns? Sunamp install guide suggests I need an expansion vessel if the water meter contains a check valve (haven't yet determined if this applies to me). Presumably only a really tiny one given the volume inside the Sunamp - do extra-small ones exist? Note that I've written the above as if I'm doing the work myself, and I might have no option but to get do the first bit DIY since I think plumbers aren't currently working non-emergency jobs, but I'm open to being told that it needs specialist design if that is the case.
  5. You might be in luck - it appears they haven't completely stopped. My planning permission was submitted on Feb13 (so before CV restrictions) but never got validated or appeared on the website - allegedly IT problems. Then suddenly yesterday it appeared - with the "validated date" set as Feb13 and deadline for decision next week! I'm not holding my breath for a decision as they haven't advertised it yet (and maybe can't?), but if you are just looking for discharge of conditions you might find the pipeline is now unblocked.
  6. I was assuming you'd do something like: When PV generation is predicted to be good (summer) and/or your store is fairly full, run the HP only if there's enough excess to cover the whole expected power draw. When generation is predicted to be poor, run the HP as soon as there's any reasonable amount of PV and top up with grid power - on the basis that you are going to have to use grid power when the sun's gone down if there isn't enough hot water in your tank at that point. If you've got something like the Daikin unit (which has 4 configurable power levels controlled by external inputs, corresponding consumption configured in 1A steps), then you can track rather closer, but obviously not as close as something with proportional control. Still, if for example you've set it up for 4 equal steps and you have a COP of at least 2, as soon as you are over the first step to let you turn it on you are then you are automatically winning compared to the resistance heating - the proportional resistance heater could use up the balance between actual generation and the next step of your power control, but the HP is putting out more heat even with that bit "thrown away". As ever with these things, it does depend what you are trying to optimise - overall energy consumption, running cost, initial cost, independence etc. And it also depends what would happen to the excess generation if you can't follow it exactly - the FIT-with-deemed-export, the paid-a-small-amount-for-export, or the store-in-a-battery scenarios give a different level of imperative to closely follow the generation.
  7. Surely you'd still want to divert the PV into the ASHP rather than diverting it to reisistance heating, in order to get more bang for your buck? I suppose there's edge cases like high summer when the ASHP is too busy cooling, or wanting to trickle it in when the PV is generating less than the minimum needed to run the ASHP compressor,. In the latter case using resistance heating is only a win if you have low PV output for hours on end - if it's winter time and you aren't going to have enough anyhow, might as well run the HP on half PV half grid power (if you are getting COP of 2, that ends up using grid power for 1/4 of the total heat input,), and in summer time there are probably enough hours where the PV is generating enough to run the HP to get the job done. Daikin at least has modes for limiting the ASHP consumption for this sort of purpose (only a couple of bands, not fine-grain control). Not sure if Valliant does similar.
  8. I happened to be reading the manuals for this thing recently (it's a candidate for my install when I get to that point later in the year). I concluded that it DOES have a seperate hot water mode; there's supposed to be a motorised valve to divert the flow water to either the space heating or the water tank coil. There's separate configuration of the tank target temp(s). There's several documents online, this one "installer reference" seems more detailed than the "installation maual". https://www.daikin.co.uk/content/dam/document-library/Installer-reference-guide/heat/EBLQ05-07CV3-EDLQ04-07CV3_4PEN405544-1D_Installer Reference Guide_English.pdf The exact capabilities of the unit are a bit unclear as it is documenting the whole system including the "optional" backup (resistance) heater, but as I read it the maximum capability of the heatpump alone is 50C (it says you can set it for 55C but won't reach that in low temperature conditions). You can set the tank target temp up to 80C but that will invoke the resistance heater. The bit you quoted earlier about reheat/scheduled setting is to avoid the DHW demand taking away from the space heating since it can't supply both at once: you can have the DHW heated only on a timer (so deliberately chosen times when you don't anticipate using space heating, eg. overnight), or just on demand (so it will take away from space heating), or a compromise that tries to do it on the timer but will top up at other times if it falls below a threshold. There's a huge lot of settings on this thing and it could easily be set up wrongly such that it's only able to deliver less than its full output. Rated maximum input is 15.7A (=3.6kW) - interestingly the 5kW and 7kW versions are almost the same, suggesting that they share the same compressor and the 7kW unit just has a bigger fan/heat exchanger so there's more opportunity for it to run closer to flat out. Stated typical input powers are 1.55kW (at 35C water temperature) to 2.45kW (at 45C water temperature) given 7C ambient. So if it's taking an average of 1.16kW across the day and it's running continuously day and night, then there's quite a lot more capacity there to be turned up (though will of course cost you more money!). If it's only running 12 hours a day (and the resistance heater is disabled), then it's effectively flat out and the only way to get more heat out of it is to run it longer - use the scheduling to get the hot water tank heated in those other 12 hours, leaving the daytime hours to keep the lounge warm. If the 28kWh/day = 1.16kW average included significant amounts of resistance heater usage then there's scope to push the heat pump harder and get more heat for the same money. I think if it was me, I'd start by disabling the resistance heater and see what it's doing by itself. (NB. all the above just based on reading the manuals and analysing the numbers - I don't actually have one of these)
  9. I am doing a major refurb/insulation of my house, and when complete will switch from large hungry gas boiler to a small ASHP, so will have no further need for gas. Currently I have a normal gas meter, in the standard type of white cupboard though mounted on the inside wall of what is now an open front porch, but the porch is about to be enclosed so it will become internal. It's also a prime piece of wall for things like the solar PV inverter. I have read that getting the gas properly disconnected has significant cost (they dig up the street). It appears that having the meter removed but the supply pipe left in place is also an option. Some sources even suggest that it's cheaper to keep the meter due to dual-fuel tariffs being cheaper (though this sounds unlikely). Any views/experience?
  10. I haven't bought any yet, but these people list them (with prices) in their online catalogue (and happen to be local to me): https://midsummerwholesale.co.uk/buy/sunamp-heat-batteries
  11. What was the problem with them?
  12. Initial response from Sunamp to my query about PCM34: "This was not commercialised and only used for a few people by special order." On further conversation, they said that there's now a PCM43 instead (though that is not yet available either). I'm awaiting more info. Given the PCM54 quotes a 65C water temperature to charge it, and an old manual for the PCM34 says 45C, PCM43 will presumably want something like 55C, which is a bit on the warm side for ASHP efficiency.
  13. Thanks. Indeed I am the same @arg as you have encountered elsewhere, but on this forum I fear I'm going to be doing more asking than answering. Having read your trials and tribulations with the PCM54 units I'd concluded they are probably now safe to go with, but was hoping someone had actually had sight of a PCM34. Still, as you say I ought to try talking to Sunamp directly to find out what the official line is. If I learn anything interesting I will report back here.
  14. Is there any sign of the version with the lower transition temperature (ASHP/UFH compatible) becoming available? The standard ones with/without electric element seem to be stocked in several places, but no obvious sign of the other temperatures that were originally promised (the lower temp I am interested in, nor the higher temp one for use with stoves etc). I'm looking at a major refurb of my 80's house (insulation to Passivhaus Enerfit level, MVHR, wet UFH with ASHP, solar PV etc), so I don't have a plant room nor anywhere sensible for large tanks, but I do have a lot of nooks and crannies where Sunamp units would fit. Existing airing cupboard for example has quite a lot of floor area but only quite a small tank for the DHW and no space for a bigger one because the roof slopes down - it could take about 3 Sunamp units if I packed them in! So Sunamp unit(s) heated by solar PV when the sun shines and E7 electricity in the dead of winter seems like a good solution for the hot water, even though the efficiency isn't great. But then I think about the UFH. I know some people here talk about "store it in the slab", but we aren't going to have much of a slab (floors are block-and-beam, with very low ceilings on the ground floor, so it's been a real challenge to insulate the floor and get UFH within the height available), so some storage is desirable and probably needs a buffer tank to stop the ASHP cycling, and it would be nice to have pre-heat for the hot water to get the efficiency of the heat pump. If I had space, a nice big tank with a coil for the hot water to pick up pre-heat on the way to the Sunamp would do nicely, except as above I don't have room for a big tank.... So a combo of the low temp and standard temp Sunamps would be just the ticket if they actually exist.