Jeremy Harris Posted January 23, 2020 Share Posted January 23, 2020 There seems to be a recurring issue with Willis heaters being installed upside down. The original MI's that were supplied with these back when they were pretty much only used in NI, had a plumbing diagram that was pretty near identical to this one, when they are used for their intended purpose, as a way of providing an immersion heater for a vented hot water system that didn't have one, and didn't have an immersion boss on the cylinder: I've seen a couple of photos posted here of upside down Willis heater installations, like these two (I've added the red crosses to show that they are fitted incorrectly): There is a problem with fitting them upside down, in that it creates an air pocket that cannot be easily bled, which then means that a part of the immersion heater element is running in air, so likely to overheat locally and probably have a shorter life than it should. This is best illustrated by looking at a Willis heater with the insulation removed, where the problem is pretty obvious. This is an upside down photo, annotated to show where the air pocket will be: and this is the same photo, but with the Willis heater correctly oriented, so there can be no air pocket: So far, the only photo I've seen on this forum with Willis heaters correctly oriented is this one (nice job @oranjeboom !): In addition to the risk of premature failure of the element by having an air pocket when these things are fitted upside down, I suspect that the electrical connections may well run hotter than intended (no water just under where they are to keep them cooler) and there may also be an increased risk of corrosion from the air trapped in the pocket. If anyone is using Willis heaters in an unusual configuration, given that they are ideal as a way of providing a simple heat source for low power UFH, then it's probably worth checking to make sure they are installed the correct way up. Willis never intended them to be used for anything other than the configuration shown in the diagram at the top of this post, and so probably didn't think that anyone might consider fitting them upside down. IMHO they could be better labelled, too, but I have a feeling that they are now made by several companies, rather than just Willis, so getting them clearly labelled etc may not be that easy. 2 Link to comment Share on other sites More sharing options...
vivienz Posted January 23, 2020 Share Posted January 23, 2020 Thanks, Jeremy, good to have this on BH. On the other hand, looks like I need a new plumber! Link to comment Share on other sites More sharing options...
ProDave Posted January 23, 2020 Share Posted January 23, 2020 Doesn't "on their side with the side pipe upwards" cure all criticisms of either vertical mounting? 1 Link to comment Share on other sites More sharing options...
dpmiller Posted January 23, 2020 Share Posted January 23, 2020 2 hours ago, ProDave said: Doesn't "on their side with the side pipe upwards" cure all criticisms of either vertical mounting? Yep. Link to comment Share on other sites More sharing options...
Triassic Posted January 31, 2020 Share Posted January 31, 2020 @Jeremy Harris, @ProDave, @vivienz and @dpmiller Does anyone have a photo showing Willis heaters being used for UFH? including a photo of the plumbing to the manifold. Do you need the UFH manifold blending valve in such an installation? Do you need a re circulation loop in the pipework to stop the Willis heater short cycling? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted January 31, 2020 Author Share Posted January 31, 2020 The person here who's been using a Willis heater to run UFH for a fair time now is @TerryE, and he may be able to give some details of his system. I have a feeling that all that's needed is to turn the Willis thermostat right down, but that probably depends on how low it will go. I'm pretty sure most can be set down to around 30°C, maybe lower. Link to comment Share on other sites More sharing options...
Ed Davies Posted January 31, 2020 Share Posted January 31, 2020 13 minutes ago, Triassic said: Do you need a re circulation loop in the pipework to stop the Willis heater short cycling? Why would you need to stop the Willis heater short cycling? Link to comment Share on other sites More sharing options...
Triassic Posted January 31, 2020 Share Posted January 31, 2020 7 minutes ago, Ed Davies said: Why would you need to stop the Willis heater short cycling? I'm not sure, I did read that it was recommend, not sure why? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted January 31, 2020 Author Share Posted January 31, 2020 Shouldn't be a problem. If the thermostat on the Willis is set to run at the desired flow temperature for the UFH then I'm pretty sure it will just turn on and off as required to try and maintain that temperature. Not sure there's any need for a mixing valve, either, as I would guess that just using the thermostat for control should work OK. Link to comment Share on other sites More sharing options...
oranjeboom Posted January 31, 2020 Share Posted January 31, 2020 29 minutes ago, Triassic said: @Jeremy Harris, @ProDave, @vivienz and @dpmiller Does anyone have a photo showing Willis heaters being used for UFH? including a photo of the plumbing to the manifold. There are at least 6 people on here that have done it the 'Willis way' - see users' list here in intro section. Here's my attempt from the other week. Not plumbed into manifold yet, but was going to leave the blending valve in situ. Pipe still to be connected to expansion vessel. As for controls, I may just have it in on/off mode for now and then use the willis thermostat that can heat up to 60c. Not sure how low it goes. 2 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted January 31, 2020 Author Share Posted January 31, 2020 Just looked at a spare immersion stat I've got here (no idea why, we don't have an immersion heater). Rather surprisingly it looks as if the lowest temperature setting goes right down to 10°C. If the ones on the Willis heaters are similar, then it should be easy to set the flow temperature just using the stat. Link to comment Share on other sites More sharing options...
oranjeboom Posted January 31, 2020 Share Posted January 31, 2020 2 minutes ago, Jeremy Harris said: Just looked at a spare immersion stat I've got here (no idea why, we don't have an immersion heater). Rather surprisingly it looks as if the lowest temperature setting goes right down to 10°C. If the ones on the Willis heaters are similar, then it should be easy to set the flow temperature just using the stat. Just checked here too: 25-70°C even though instructions say up to 60°C. Suspect the Willis heaters all vary to some degree (pun not intentional!) 1 Link to comment Share on other sites More sharing options...
dpmiller Posted January 31, 2020 Share Posted January 31, 2020 only niggle is that those stats have a pretty wide hysteresis so a "too-low" setting may let it run for a bit and then just... stop. Link to comment Share on other sites More sharing options...
Triassic Posted February 1, 2020 Share Posted February 1, 2020 First may I start by thanking everyone for their contributions to this thread, for me a photo paints a thousand words. KISS UFH here we come! Second, thanks for the photo of the KISS approach to the electrics, could someone post a photo of their approach to wiring up their Willis heating system and describe how it works. Link to comment Share on other sites More sharing options...
ProDave Posted February 1, 2020 Share Posted February 1, 2020 Just a thought. Everyone seems to be using 2 willis heaters. Our worst case heat load when -10 outside and +20 inside is just a little over 2kW so if I were doing this, I am sure just one heater would be plenty. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted February 1, 2020 Author Share Posted February 1, 2020 1 minute ago, ProDave said: Just a thought. Everyone seems to be using 2 willis heaters. Our worst case heat load when -10 outside and +20 inside is just a little over 2kW so if I were doing this, I am sure just one heater would be plenty. Good point. I'm pretty sure that @TerryE is only using a single Willis heater. It depends on the heated floor area, but if you had, say, 100m² of heated floor and ran it at a maximum output of about 25 W/m² (which is a fair bit higher than we run our UFH) then you only need 2.5 kW. Link to comment Share on other sites More sharing options...
Dreadnaught Posted February 1, 2020 Share Posted February 1, 2020 (edited) How fast I wonder can the concrete raft heat up, in its role as a thermal store? One thought about having a single Willis, double or even triple Willises, is that these new electricity tariffs restrict the lowest cost to 4-hours, 7-hours or 10-hours each day (and the 4-hour one is particularly attractive at 5p per kWh), it might be advantageous to heat up the raft quickly. Three Willises could impart the raft with 9kW, if it could only take it. Edited February 1, 2020 by Dreadnaught Link to comment Share on other sites More sharing options...
Dreadnaught Posted February 1, 2020 Share Posted February 1, 2020 (edited) For example, in @ProDave's case of a 2kW heating-requirement to maintain a temperature difference of 20º, he would need to impart 48kWh in a 24-hour period. But could he use four Willises for 4-hours at cheap rates and be done for the day, costing him £2.40? (A gross simplification I know.) Edited February 1, 2020 by Dreadnaught Link to comment Share on other sites More sharing options...
Jeremy Harris Posted February 1, 2020 Author Share Posted February 1, 2020 There's a finite limit set by the water flow rate, the ∆T between flow and return and the heat capacity of water. For a total flow rate of 12l/m and a ∆T between flow and return of 4°C, the maximum power that you can deliver to the floor is about 3,345 W. Our UFH runs at a total flow rate of about 9l/m and a ∆T between flow and return of 4°C, so the maximum heat we can deliver to the floor is less, about 2,508 W. We could increase the heat delivery rate by trying to increase the ∆T between flow and return, but that gets harder to do as the slab warms up, or if the slab is close to the desired temperature. Link to comment Share on other sites More sharing options...
ProDave Posted February 1, 2020 Share Posted February 1, 2020 17 minutes ago, Dreadnaught said: For example, in @ProDave's case of a 2kW heating-requirement to maintain a temperature difference of 20º, he would need to impart 48kWh in a 24-hour period. But could he use four Willises for 4-hours at cheap rates and be done for the day, costing him £2.40? (A gross simplification I know.) Instead I get that 48kWh from an ASHP which on my single rate tariff of 14.183p per kWh and assuming a COP of 3, costs me £2.36 There is indeed a good case for direct electricity on an off peak tariff, but you do need a floor capable of storing that much. I doubt my timber floor / biscuit mix would. You really do need a decent concrete slab. 1 Link to comment Share on other sites More sharing options...
Dreadnaught Posted February 1, 2020 Share Posted February 1, 2020 Just now, ProDave said: but you do need a floor capable of storing that much Yes. Or use a SunAmp to store the cheap heat, which can then be imparted in to the raft at leisure. This has been suggested to me by my M&E adviser. Link to comment Share on other sites More sharing options...
Ed Davies Posted February 1, 2020 Share Posted February 1, 2020 Big Sunamp to store 30 or 40 kWh. Link to comment Share on other sites More sharing options...
TerryE Posted February 2, 2020 Share Posted February 2, 2020 (edited) 18 hours ago, Dreadnaught said: How fast I wonder can the concrete raft heat up, in its role as a thermal store? 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. Edited February 2, 2020 by TerryE Link to comment Share on other sites More sharing options...
ZacP Posted December 10, 2020 Share Posted December 10, 2020 Sorry to drag up an old thread. would/could you use one of these as a backup for ASHP UFH? For example install it just in case it gets too cold for the ASHP to work either to take over or sublimely the heating or if there were any other issues? trying to build in solutions at source rather then scrabbling round when something does go wrong! Link to comment Share on other sites More sharing options...
LA3222 Posted December 10, 2020 Share Posted December 10, 2020 49 minutes ago, ZacP said: Sorry to drag up an old thread. would/could you use one of these as a backup for ASHP UFH? For example install it just in case it gets too cold for the ASHP to work either to take over or sublimely the heating or if there were any other issues? trying to build in solutions at source rather then scrabbling round when something does go wrong! If you have your UFH running via a buffer tank then you can have an immersion in that tank. If your UFH is running direct from the ASHP then its something those with more know how on here should be able to answer for you. Link to comment Share on other sites More sharing options...
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