MarcelHoldinga Posted November 10, 2020 Share Posted November 10, 2020 Hi there, I'm new here. We've just moved in to our selfbuild (contractor built) ICF house. The house has 3 bedrooms, a lounge, a dining kitchen, a utility room, an en-suite and a main bathroom, as well as an entrance lobby/corridor. We've got an air to water heat pump, powering wet underfloor heating powered, and an Airflow MVHR system with radial air distribution. The water temperature for the heating is set to 38 degrees and we have 6 thermostats (Honeywell T6360 analog dials), most of which are set around at 19-19.5 degrees. We were advised by one of the engineers that the heating system should be left running 24 hours, so it's ready to provide heat when/where needed, so I took him on his word and have been leaving it running 24/7. I've noticed that the room temperatures regularly register at 3-4 degrees higher than the temperatures set at the thermostat (on cloudy days - never mind when we get a few hours of sun through the windows on a morning). In particular, the main bedroom has regularly is around 23 degrees C at the time we go to bed - way too hot for a bedroom. There is an MVHR outlet in the ceiling and the thermostat that's set to 18 degrees C, yet the temperature in the room gets jacked up to 23. At those temperatures and settings, I've noticed the floor being warm underfoot, which I wouldn't expect with the temp set as low as it is. I've tried to program the MVHR to dump some heat by lowering the supply air temperature and hoping that the summer bypass will kick, but unless I can adjust my heating temperatures before the bypass comes on, I will just end up running the heating to just have the energy sucked straight outside... Does anyone have any tips for managing the temperature in the house so we don't end up being slow cooked overnight? Thanks in advance for any wisdom you might be able to impart! Link to comment Share on other sites More sharing options...
Bitpipe Posted November 10, 2020 Share Posted November 10, 2020 As mentioned endlessly, MVHR is not very effective at raising or lowering room air temperature as the flows are very low and air is poor at moving heat. It's there to supply you with fresh air that is warmed to near the same temp as the extracted air by recovering the heat. Can act as a trim in a very efficient house. My view is that your house is ICF then it's probably very airtight and well insulated, therefore heating in bedrooms is probably not that necessary - sufficient heat should convect from downstairs, plus solar gain and heat from occupants and powered devices to make the rooms comfortable, especially if you like them cool (as I do). Did you model the house heating requirement before specifying the system? Is there a way to isolate the upstairs UFH circuits and see how that goes? Our passive timber frame only has UFH on ground floor (timber floor) and it's off apart from the winter months. GF air temp stat set to 20, bedrooms comfortable. Link to comment Share on other sites More sharing options...
joe90 Posted November 10, 2020 Share Posted November 10, 2020 I concur with the above, MVHR will not move much heat. My heating (ground floor only) has not come on yet this year ( one zone = ground floor set to 21’ with a room stat in the hallway) so no water is being circulated in the UFH. The ASHP heats the DHW when it’s called for and ready to heat the house when the room stat calls fir heat. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 10, 2020 Share Posted November 10, 2020 45 minutes ago, MarcelHoldinga said: The water temperature for the heating is set to 38 degrees Can you reduce that. Try it at 32°C. Link to comment Share on other sites More sharing options...
joe90 Posted November 10, 2020 Share Posted November 10, 2020 Do you have UFH upstairs? What’s the temp set on your manifold? Link to comment Share on other sites More sharing options...
Bitpipe Posted November 10, 2020 Share Posted November 10, 2020 Forgot my manners to welcome you to the forum Link to comment Share on other sites More sharing options...
joe90 Posted November 10, 2020 Share Posted November 10, 2020 19 minutes ago, Bitpipe said: Forgot my manners to welcome you to the forum sorry, and me Welcome. ? Link to comment Share on other sites More sharing options...
ProDave Posted November 10, 2020 Share Posted November 10, 2020 What I got from reading this was your rooms are too warm, warmer than the room thermostat is set to, and you can still feel the floor warm to walk on. This says to me the UFH loops to the rooms are not turning off when the room thermostat reaches the set temperature. You need to start by looking at the UFH manifolds (post some pictures of them?) there should be a row of flow meters. If you are lucky someone will have labelled them so you know which loop feeds which room. You need to establish if the correct room thermostat controls the correct room. Link to comment Share on other sites More sharing options...
PeterW Posted November 10, 2020 Share Posted November 10, 2020 I think this is due to the IFH pipes being fairly deep in the slab and a 38c flow will settle out and the slab is probably coming up to surface temperature an hour or two after the pumps have gone off. Running 24x7 is unusual - and expensive - and I would look at load shifting across to E7 and doing the heating overnight and only boosting when necessary during the day. Bear in mind the UFH will lag a bit, I would start with lowering the flow to 32/33c and then running overnight with a 2 hour boost about 4pm. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 10, 2020 Share Posted November 10, 2020 9 minutes ago, PeterW said: Running 24x7 is unusual - and expensive Not necessarily. It really comes down to how variable the weather is. It could work out cheaper if you do not have to 'overheat' to get the temperature you want later. An ASHP works best when it is doing the least work. Link to comment Share on other sites More sharing options...
joe90 Posted November 10, 2020 Share Posted November 10, 2020 13 minutes ago, PeterW said: Running 24x7 is unusual yes but surely only when the stats are calling fir heat?. Mine is on 24/7 but room stat has not called fir heat since last winter ?. Link to comment Share on other sites More sharing options...
Hobbiniho Posted November 10, 2020 Share Posted November 10, 2020 i think the short term solution would be to try setting the thermostats down by 3-4 degrees and see if it still overshoots which would be the correct temp for you, as has been said the slab will still emit heat for long after the heating has clicked off, and as you have a well insulated house the temperature just keeps increasing not sure if a "smart" control system would be able to compensate for this better as your control system is incredibly simple, also 38 degrees is relatively high for UFH that is the temperature i run my radiators at there could also be problems with your mixing valve/actuators etc as prodave has elluded to Link to comment Share on other sites More sharing options...
MarcelHoldinga Posted November 10, 2020 Author Share Posted November 10, 2020 6 hours ago, Bitpipe said: Forgot my manners to welcome you to the forum Thank you Bitpipe, for a moment there I was worried I was just getting told off on my first day! ? Link to comment Share on other sites More sharing options...
MarcelHoldinga Posted November 10, 2020 Author Share Posted November 10, 2020 Thanks everyone for your responses... too many to keep up with, so I'll do a load of @ replies in this post... ? @Bitpipe The house is a bungalow, and the heating system (afaik) was designed to match the heating requirement of the house. The heating was on when we moved in - not entirely sure why, unless the intention was to dry out the slab/tiles, and we were advised to keep it running for some reason. We're in Orkney, so we're quite far north, so that could be a reason, I suspect - it doesn't tend to get that cold here, but we do get winds that take anything that isn't securely bolted down away @SteamyTea I spoke to the company that installed the system and when I mentioned reducing the UFH water temp, they said "oh, but if you turn your water temp down, your heat pump will hardly be on..." - funny that, because I thought the whole point of an energy efficient building method like ICF is to minimise running time of your heating system! I've turned the temperature down to 36, but I will have a look whether it gets better with 32. @PeterW We have an E7 (or possibly E10) meter, though at the moment we're with Bulb, who all of a sudden can't supply E7 electricity, so it's all the same rate at the moment - oddly, they could supply us E7 in our previous house... probably due a switch to a supplier that can provide 100% green energy on dual rates... @joe90 The temperature on the heat pump was set to 38 (though I turned it down to 36 this morning), the manifold gauge read 32 at one point yesterday, shortly after, I heard the ASHP kick in and made a point of checking again some time after, and it had increased to 38. @ProDave What you said sounds about right, the room temperature is overshooting the set temperature. I suspect it might be the high water temperature and the fact the actuator motors take about 5 minutes to close once they're open. The pipes on the manifold are marked, so I'll have to take a day or so to figure out which stat controls which loop, and see if there's a couple that have been swapped over. They should be fairl straightforward to swap around if needed, shouldn't they? I've also just noticed that the design specification states that the heating system needs to be "fully programmable with intelligent thermostatic control" - I don't think a timer at the manifold and 6 on/off dial stats counts as intelligent (unless that part was intended to be the owner, in which case, fat chance!). I suspect we need to have a word with our builder to see what's going on here. We should really have noticed, but the build took twice as long as it should, and we've been ground down by the whole process and ended up just pleased we had somewhere to move into! Link to comment Share on other sites More sharing options...
Fly100 Posted November 10, 2020 Share Posted November 10, 2020 Those dial stats are terribly inaccurate. They are potentially have a 3 degree spread over your target temperature.I would suggest switching to a decent Digital Stat. FLY Link to comment Share on other sites More sharing options...
joe90 Posted November 11, 2020 Share Posted November 11, 2020 10 hours ago, MarcelHoldinga said: @joe90 The temperature on the heat pump was set to 38 (though I turned it down to 36 this morning), the manifold gauge read 32 at one point yesterday, shortly after, I heard the ASHP kick in and made a point of checking again some time after, and it had increased to 38. with my ASHP system the hot water from the heating buffer tank is set to 35’ but at the manifold it’s blended down to 24’, this stops heating over shooting , does yours have a blending valve? Link to comment Share on other sites More sharing options...
SteamyTea Posted November 11, 2020 Share Posted November 11, 2020 1 minute ago, joe90 said: with my ASHP system the hot water from the heating buffer tank is set to 35’ but at the manifold it’s blended down to 24’, this stops heating over shooting , does yours have a blending valve? And a buffer tank. Could this be a case of a traditional plumber treating a heat pump system wrongly and turning up the temperature as high as they dare because 'heat pumps are not hot enough' 1 Link to comment Share on other sites More sharing options...
joe90 Posted November 11, 2020 Share Posted November 11, 2020 33 minutes ago, SteamyTea said: And a buffer tank. Could this be a case of a traditional plumber treating a heat pump system wrongly and turning up the temperature as high as they dare because 'heat pumps are not hot enough' Yes, my ASHP will only deliver one temp and that’s set to 48’ to satisfy DHW therefore I have a buffer tank (indirect) which is heated to 35’ and then UFH manifold blends this down to 24’ to heat the slab. Link to comment Share on other sites More sharing options...
ProDave Posted November 11, 2020 Share Posted November 11, 2020 10 hours ago, Fly100 said: Those dial stats are terribly inaccurate. They are potentially have a 3 degree spread over your target temperature.I would suggest switching to a decent Digital Stat. FLY Not if they are wired properly with a neutral connection so the inbuilt little accellerator heater operates to remove the otherwise large temperature hysterisis. Mine are working just fine to keep the rooms very close to their target temperature. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 11, 2020 Share Posted November 11, 2020 5 minutes ago, ProDave said: wired properly with a neutral connection so the inbuilt little accellerator heater operates to remove the otherwise large temperature hysterisis. Can you explain more, with some pictures please. Link to comment Share on other sites More sharing options...
dpmiller Posted November 11, 2020 Share Posted November 11, 2020 when the stat is "on" a tiny heating element heats the bimetal strip, so that it accelerates ahead of the ambient temp slightly. Link to comment Share on other sites More sharing options...
Stones Posted November 11, 2020 Share Posted November 11, 2020 @MarcelHoldinga Our house is ICF, and has an ASHP and UFH set in a 155 sqm slab. Our ASHP has 3 options in terms of control, weather compensation (where flow temp varies), heating curve control (where you can set the flow temp for any given outdoor temperature) or fixed flow temp (which is what you seem to have). I use the weather compensation setting and it works flawlessly, calls and gets heat when required, and keeps the house 24/7 to our desired set temp of 21C (21.5C in reality). Our flow temps rarely go above 30C, and more often than not sit in the mid 20's. More info on our system here: From everything you have said, the flow temp setting is too high. Our neighbour (another new house) had exactly this issue, 3-4C temp overshoot, and this was all down to the flow temp (offset) which had been set by the installer +9C above the heating curve, which effectively meant the flow temp was boosted 9C higher than required for the given outdoor ambient temp. We removed the offset and problem solved. As suggested by others, reduce the set flow temp down. If you are not convinced about reducing it in one go, do it in small steps, 2C every three or four days and see what the difference is. If you have the option of weather compensation control, you could try that instead. Link to comment Share on other sites More sharing options...
ProDave Posted November 11, 2020 Share Posted November 11, 2020 40 minutes ago, SteamyTea said: Can you explain more, with some pictures please. Try this, not a perfect description but it might help https://inspectapedia.com/heat/Heat-Anticipator-Operation.php Basically, when the thermostat is on and calling for heat, the little accellerator heater is on so it locally warms the inside of the thermostat just enough to overcome the hysterises of a mechanical thermostat. When the thermostat turns off, the accellearator heater turns off so the inside of the thermostat cools down and will click back on again much sooner rather than having to wait for the room to cool down by the otherwise large hysterisis temperature. the key to it working is the manufacturer has sized and positioned the accellerator heater correctly so it's heating effect exactly cancels the hysterises temperature. You need the neutral connection as the heater is connected between switched L and N . for an electronic thermostat you don't usually need a N connection. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 11, 2020 Share Posted November 11, 2020 10 minutes ago, ProDave said: Try this, not a perfect description but it might help https://inspectapedia.com/heat/Heat-Anticipator-Operation.php Thanks Link to comment Share on other sites More sharing options...
Bitpipe Posted November 11, 2020 Share Posted November 11, 2020 12 hours ago, MarcelHoldinga said: Thank you Bitpipe, for a moment there I was worried I was just getting told off on my first day! ? Sorry, we can be very quick to jump in with questions and answers and sometimes forget to say hello! Link to comment Share on other sites More sharing options...
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