TerryE

I've just done a review of our heating costs over the last calendar year. We only use electricity and have SunAmp PVs heated only by E7 for DHW, and a Willis for UFH heating the slab of our 5 bedroom 3 storey house. Based on my Home Automation logs, our annual (Willis) space heating costs for this last year work out at ~£380 p.a. This would fall to around £115 p.a. if we had used an ASHP so maybe an annual saving of around £265. We use an induction hob and 2 × electric oven/microwave for cooking (with a 2 ring Propane for backup and which we've never used in anger) so we have no other need for gas connection. So there would be maybe a 10-year payback for installing an ASHP if I did this myself, plus some extra benefit if we used one with a cooling mode option for the Jul / Aug temperature peaks. We also saved a lot of money avoiding gas installation, and the annual standing charge for gas connection (~£75 p.a. in our area), and the cost of annual maintenance for a gas appliance (something that is mandatory IMO). And note that if we did have an ASHP, then the avoidance of the gas standing charge represents an offset of some 65% of the ASHP running cost. So in our case the gas vs ASHP argument is a no-brainer.

Read my blog posts in modelling this, plus I've also posted my temp logs. The actual behaviour as shown by the logs is pretty much as characterised by the model. On a full night I put about 21 kWh into IIRC 17 tonne of slab, though it's less than that at the moment. The surface gets maybe 3°C warmer. At peak the return flow temp gets up to maybe 32°C after a 7hr heat. Unlike Jeremy's control regime, I don't use the ∆t to limit the heat input. I can't see the need for this when the 2.88 kW output of the Willis is it's own limit on this same regime.

As an addendum to Jan's comment, we have a lot less glass than JSH and so get no material solar gain in the winter months; we also keep our ground floor at around 22-23°C. Hence we have about 3 months where we need lot of heat input and another 3 months where we need some, though my control system does the heat calcs on a daily basis with all (or the bulk) of heating using the 2.88kW Willis during E7 off-peak, and rarely need heat input beyond this. We also use the UFH slab as the primary thermal battery. I don't really understand twhat is gained by using a SA as an additional heat battery in series with the slab.

Ours didn't have the orientation diagram on it and IIRC minimal fitting instructions. The arrows indicated water flow and there was no "this way up" orientation arrow. The gas accumulation issues are completely different for the standard in unvented cylinder installation where the Wills uses thermal circulation in a potable water environment where the water turnover might be ~1m³ / day, but in our usecase we have about 35 ltr of water in our UFH loops -- the same 35 ltr as 2½ years ago when it was first flushed and bled, so there is no further introduced gas to accumulate. I can't see where this ~100 cm³ gas could come. Whilst the inverted position might avoid a potential gas trap, IMO the device can't have been designed for this because of issues of electrical safety: there is no appropriate IPS protection for the wiring contacts and thermal cut out so any seal failure on the element ring in the inverted position would result in electrical shorting. TBH, I think that there are also pragmatic maintenance advantages in having the heater threaded end up, as the element is pretty much at the highest point in the circuit and being upright it could be replaced with minimal water loss if the element failed, thus simplifying refill, flushing, repressurising the system. Incidentally our thermostat cutout is trimmed to ~50°C and I can't recall logging a peak temperature over ~35°C since the system was commissioned. Notwithstanding this, the next time I do some maintenance to the system (possibly over the summer) I might add "cracking the coil" with a heater element key to see if it bleeds any gas to the todo list.

At the moment we are running at about 70:30 E7 to peak rate, but that 30 % has little to do with direct space heating. It's all the other energy use: cooking, lighting, appliances etc., though except for HW going down the plug hole, this generates waste heat that does eventually heat the environment. Because we are currently limited to 2.88 kW input to our UFH, when the average outside temp falls below about 4°C my heating control will top up using peak rate electricity, but this is a tiny % of our total charges. We run our ground floor at ~22.7 ± ½°C ripple. The upstairs floors are a degree or so cooler.

The Willises should really be vertical. I personally did and would prefer to do the 22mm to/from the manifolds in copper. 3.2m is fine so long as it is unimpeded

BTW totally off topic but this is very sobering viewing for those interested in flight critical SW failures:

IMO, there really needs to a sensible balance of risk here. In practice for contamination to get back into the potable water line we would need 2 ball valves, one lock shield, one PRV and the mains pumps all to fail. By comparison with the 737MAX MCAS implementation, the failure of a single mechanical sensor (which is perhaps at least 4-5 logs more likely) could lead to the deaths of ~200 innocent passengers and without the seeming prospect of criminal prosecution.

This is what we do. The two valves are set to isolate the UFH circuit.

Any ducting between the MVHR unit and the plenums running through cold spaces should be lagged or under the insulation. Air exchanged through the MVHR has a 90% heat recovery; air exchanged through other leaks has a 0% heat recovery. Also look up the concept of latent heat of evaporation. Air condensed out by the MVHR heat exchanger and vented as water through the condensate drain recovers additional heat is also lost in non-MVHR systems. Yes, the efficiency will drop considerably in a leaky house if there are external winds which cause pressure differentials and increase the % of non-MVHR exchange, but IMO even so the overall benefits to the freshness of the living environment and removal of damp / mould remain.

You definitely need the PRV, but not the BV. The Wunda manifold has a manual bleed which you can use to release any gas, but the system is closed so you won't get any gas build up. You need to do you UFH routing but ~160 m2 of slab should work out at around 7-8 x 100m loops. You want to balance you loops for even flow and keep the loops to just under 100m each or alternatively 75m if you are using 300m coils. You must avoid any joins in the slab: each loop has to be one continuous length of pipe. I note that given a wall U-value of 0.33 and your calcs seem off to me: I can't understand why your floor and wall losses are of a similar order when you have 50% more wall and the U value is 3x worse. You also seem to be planning far below a PH class house, so your house as a system is quite a bit different from mine in its operating nature. I use the thermal capacity of the slab to advantage so pretty much all of our heating is done using E7 low tariff rates and we operate the house as a single zone. You seem to be designing your 2 x Willis as a pretty much always on (during peak heating months) heat source. Have you costed the running costs? IMO, you've moved well into the zone where a more cost efficient heating method such as an ASHP or even gas should be considered as an option. Something doesn't hang together here.

We have a passive-class house with MVHR which ensures that we have an airy damp-free environment. The HR element roughly halves the overall heat losses for the house. We only have ground floor UFH in the slab and this heats our entire 3 storey house effectively. Without the HR we would have had to design and install some form of secondary CH for the upper two floors. As it we don't so no rads, no boiler, no wet CH piping, and unencumbered walls. So for us, MVHR was a cost-effective self-install and far cheaper / simpler than the alternatives. And I strongly suggest MVHR is a no-brainer for anyone wanting a passive-class home.

Yup these comply with current English BRegs. I've got some pics on my blog.

+1 to Russell's point. The chromed surface is harder then the teeth on the steel grip ring in a standard pushfit connector. However standard compression fittings will work fine, so you can do as @Alexphd1 has done, or have a copper - HEP2O compression straight coupling dropped under the boards. I personally would be a bit uneasy about mechanical risks from vacuum cleaners, kids toys etc. crashing into plastic pipe as it rises out of the floor. I am of the camp that a few wraps of PTFE are best used on compression fittings, but in this case only only on the chromed copper side. You also need to make sure that the olive has properly bitten into the chromed surface, but don't over-tighten. @Nickfromwales , any words from the guru?

Another way to phrase this might be "enough to be competent in his profession, but also young enough for his knowledge to be current", and if you are attempting to build a passive-class house then this is highly relevant. 99p sounds a steal to me.

If you've played around with NodeRED, you can get NodeRED for Android.

Ian, I think this is almost certainly one for being a little sanguine. The failure case here is that the front 220mm is an airgap. If these are occasional and isolated, then the overall impact on U-values should be small. I though that the 175×185×250mm PIR inserts were factory installed. Is this not the case? Or were you relying on your contractor to insert these during erection? If this is an occasional issue, then the voids will be isolated so you won't be experiencing significant convection elevators in the void columns. If we do a back-of-the fag packet calc of the U-values of (i) the proper profile and (ii) the voided profile, hen we can come up with a realistic guess to the failure %. The net U-value is roughly the prorated value, e.g. if you reckon 10% then its 0.9×U1+0.1×U2. And you will see that this is extremely annoying but isn't that material. Cast you mind back to erection. You were hovering during this. You also had a wall blow over. Surely you would have noticed an excess of PIR inserts floating around the site if they weren't being installed? One possible scenario comes to mind is that there were a number of blocks that had the PIR missing or dropped out and one good place to use them up is on an internal wall where the insulation isn't needed. If you are still concerned and want to get a better view on whether this is a significant issue, then one option would be to try some pilot holes to get a statistical sample. OK, this involves drilling into the wall from the outside with a 60cm×15mm drill (or whatever you use to pilot holes through the wall fabric) to probe the void / PIR, and you will only want to try this where you can repair / make good the holes afterwards. But if you do 10 holes, say, and 10 go into PIR then I'd forget the issue. If you get one void then your might want to survey a little more, 2 or more then I'd be concerned.

Our ensuites are all wet-rooms. No UFH upstairs. The floor temp is typically around 22°C so they aren't really cold. The pan area gets hotish after a few secs of shower stream. We do use a mat in front of our ensuite toilet to keep the old tootsies warm when sitting contemplating. ? I personally don't see the need for UFH in the ensuites but this is a personal preference. We also have a 30cm window blade in each of our 3 ensuites. The main reason is that we decided not to bother with any shower screening so we do end up with some water splash on the flat area of floor outside the area of the tray area. It's a 30sec job to run the blade over the floor and shower walls after a shower, and (with the help of the MVHR extract) the room is pretty dry 5 mins later -- and absolutely no mould anywhere.

Dave, that last figure that you referenced is really misleading for a passive house: surface temperatures of 15°C are just silly, IMO. All of the internal surfaces, ceilings, etc will be at equilibrium with the air temperature and even the external walls will be reasonably close: the rough guide is 7W/°C radiant transfer to a surface, so with a U-value of 0.12, say and a delta T of 17°C (and few places in the UK have greater than this as daily average for more than perhaps 30 days a year), then the net heat flow through the external wall will be maybe ~2 W/M² which will make the external walls less than ½°C cooler. In our case the only surface that is materially different is the slab which might get a couple of degrees warmer when the UFH is on. I've gone around our house with an IR thermometer and its readings are consistent. The external corners are perhaps ½°C cooler. The big delta is in the window reveals where the 10cm closest to the outside might be 2-3°C cooler, but everything else is basically at the same temperature ±¼°C. We only have heating on the ground-floor slab, so the 1st floor is heated parasitically and the similar distribution exists but maybe a degree cooler. So my advice to any new builder is not to over-engineer the heating solution and just concentrate on getting the walls (as built) to a maximum U-value of 0.14, say, get it decently airtight and invest in an MVHR and decent triple-glazed fenestration. If you do this, then you will have a warm house in winter and (so long as your architect hasn't persuaded you to have acres of south facing glass) a cool house in the summer.

I understand that the current SAP has improved, but we still got a pretty acceptable SAP rating. Wasn't an issue, but then again we didn't have one of these self-build mortgage requirements; we just needed to meet min Breg requirements. I didn't care about the SAP rating (so long as our BInsp was happy), just real-life performance.

See and as I said you can get zero-volt input SSRs in both panel mount and DIN rail mount configurations. Dumping the 30+W can be a PITA to manage.

As I have on previous posts, based on our current year-round heating costs, I estimate that using an ASHP instead of a Willis would save me about £400-500 / year in electricity bills because we don't have PV, so that's a 5-7 year break-even for a decent ASHP if I do the fitting myself. There's no way we could make an economic case if we had to use an approved installer. We don't anticipate any change in our occupancy experience as we have absolutely no issues with our current Wills/SunAmp configuration. So very marginal in terms of heating. The one win would be the ability to run the ASHP in cooling mode in hot spells in July/Aug, and that could tip the balance for me.

This would be better as a boffins topic and I apologise @Robert Clark for the digression on your thread, but such is the Buildhub way ?. For others, the main point is that you need the correct device for switching power circuits. You can buy remote switches and cheap relay from eBay and various suppliers and there are three points that you need to ask: Is the device correctly rated for 240V? What is the maximum peak power rating? What is the maximum sustained power rating? If you want to drive a Willis or a SunAmp then you need a switching device that will support a 240V 12A load for multiple hours on a duty cycle of up to 1,000 cycles per year minimum, and as @ProDave suggested in one post it makes sense to have a little safety margin so having device rated at 240V (not 220) 16A and 50Hz and supplied by a reputable OEM is sensible. As @dpmillercorrectly points out you can get these with "zero V" inputs as well. Typical prices are in the £45 ballpark for the SSRs which have a decent heat sink and DIN mount or £35 for the ones designed to be directly attached to the steel plate of the cabinet and use it as the heatsink. (SSRs are only about 99% efficient, so they typically give off perhaps 20-30W when switching a 3kW load. That's enough to hatch chicken eggs. Though another option for zero volt input is to use a decent contactor which only give off maybe 5W from the energised coil.

@Nickfromwales I used the Crydom CKR range which is supplied here by RS Components with other options. These have an in-built heat sink and are Din mount so go well into a simple steel enclosure. The nice thing about these is that they include an opto-isolated input that you can drive directly with a 5V 15mA [TTL] input. Some of the Arduino GPIOs can drive this, but devices like the RPi and ESPs use 3.3V logic. I use a MCP2008A 3.3V I2C to 8-port 5V driver IC to drive the Crydom iputs,, but another option is to use something like a SparkFun Logic Level Converter which surface mounts the MOSFET drivers to do this magic and costs a few £. The advantage of using an RPi directly is that you can use something like NodeRED or one of the HA products to do all of the nasty S/W stuff. Either contact me offline or raise a Boffin's topic and poke me if you want to go into more detail.

@PeterW be careful that you don't repeat what JSH did once - - which was to crank up the heating to try to get back to setpoint quickly. If you do that then you'll get there reasonably quickly; and the temperature will the over shoot, and then oscillate as the slab vs the rest of the fabric get back to equilibrium. IIRC Jeremy overshot to something like 26°C.