Hi there,

I've got an underfloor Heating system in my dining room that I've put into the Limecrete screed and am putting wood on top.

The water currently starts at the boiler (Manual, not smart), runs to the mixing valve through the pump round the system with auto actuators on and so on, with a return to the boiler etc...
(this is the pump and Mixing valve I have: https://www.theunderfloorheatingstore.com/manifold-pump-mixing-valve-unit)

anyways I've read that its best to keep it on low constantly and then turn up the temp when you want to warm the room and best on a smart thermostat to do this with so it's warm when you're up. (I currently have it attached to a Nest)

My question is: Is this the most efficent way to run the system?
And if so whats the best way to automatically change the temperature? (would I need to figure out a way to get an actuator to fit on my mixing valve?)

Thanks in advance,
Jon

Thanks very much Tony,

This is super useful information.

So if I was to run like you say: "use a controller that will learn lead times and then set 18 C for breakfast, 16 when out, 21 in the evenings and week ends"

What would be the best way to change the temperatures automatically? Would I need to get an Actuator for my mixing valve or is there a better way to change the temp?

Thanks again,
Jon

Hi Yalch,

I might be misunderstanding your question, but sounds like you think you should be adjusting the set value at the mixing valve at the manifold. That is not how you control UFH.

That TMV should be set at commissioning, may have some slight adjustment over the first few months, say into the first winter, but then left alone. Every system is different with lots of varying parameters, but something around 40oC for that TMV might be about right. That does NOT mean the house will get to 40oC, just that it blends the feed water to the UFH pipes to be up to a max of 40oC.

House temperature should be controlled by "zone" room stats. These should ideally be programmable, so that, as Tony suggests, you set various temperatures over the 24 hour period. The old way was to guess what the room temp would be at a certain time, run the boiler for another guessed time period, switching the boiler off and on. Guessing at room temp based on time wasn't a sensible way to meet required temps.

Programmable stats let you choose the temp target for each zone/room, and the UFH valves will open to allow water to raise the room temp, and close when it has been met. I don't know how you've got the NEST set up, but you ought to have various stats around the house, controlling to set temps for those areas, at different times of the day.

The warmer you keep something, the more heat loss. Now that said, what you don't really want is a lot of cycling, hot/cold. You won't get much more efficient than keeping the room at the temperature you want, which is not the same temp all the time (assuming you are out of the house sometimes, and sleep at a cooler temp than sitting in the lounge.

I never set clients "away from home" temp less than 15oC, and backup frost stat at anything below 12oC. I tend to build very well insulated houses, so that is very little energy consumption in reality. Heating up a cold slab will of course take energy, but less than keeping it unnecessarily warm continuously. Personally, I would tend to vary between 18oC at night, and 20oC or maybe 20.5oC daytime. A 0.5oC can actually make a lot of difference. Focus your energy on getting those programmed correctly.

As with most of these things, take a happy medium of not living like a hermit, nor heating with windows and doors open to keep cool. Don't worry about the slab, it will do it's thing. Just focus on what you can sensibly control, which is room temperatures. Install a sensible number of room stats, to get the room temperatures right for you, and programme them so that the UFH works to only heat it to the temp you require, during the programmed time periods.

By not setting the UFH TMV too high, you won't get so much over shoot in temp, but will take a little longer to respond. Don't over think it.

Posted By: bhommelsIf you are serious about it I would consider a weather compensation controller.

The flaw with these is they usually only take into account temperature and not solar gain. I've certainly not found one that does anyway.

The other thing I have found with UFH is that adjusting by 0.1°C makes a big difference. Most commercial thermostats I have come across work on 0.5°C and that is just too wide a range for UFH. I have a DHT sensor and control the UFH via HomeAssistant.

All of this is incredibly useful guys, thanks very much!
Happy to know not to have to worry about the Slab temp to much and concentrate on the overall room temp via air stats.

Also the load comp sounds great, I'll have a look into that too.

Thanks again all of you, hopefully should have a comfotable effecient system one day :D

I have the the UFH controlled by a weather comp sensor. My Viesmann boiler is reputedly, 'very efficient' but on further investiation, I sound that only applies to the heating side (gas.)

The boiler control input is from a combination of the w/c, set temp and return flow temp. One is fixed (set temp), the w/c does tell the boiler to run or not, depending upon the return flow temp. But this only works if the pumps are more or less running 24/7. No pump, no return flow temp reading.

If there is no requirment for the UFH to kick in, the pumps have to be running for the boiler to process that information. So one way or another, it is not very engery efficient.

So I ignore it all and have the heating switch on twice a day, early morning and late afternoon; it is sufficient to keep my highly insulated house warm without using excessive energy. More specifically, I am not running the pumps needlessly.

Posted By: gyrogear

We have no room thermostat. The internal temperature is not taken into account, it works just on external temp.

gg

Surely the first heating control device you should have is at least one room stat?? Outside temp is irrelevant once the room is up to temp.

A room stat(s)is almost certainly the first control device you need, unless youre running a GG interactive custom system. Pretty sure its a building regs requirement??

If finger trouble is a problem, chose a stat with a limit on it or use a hidden stat with a remote sensor

I might be missing something, but Im struggling to see any circumstances when youd want to start or continue with heat input if the room is at or above desired temperature. Is there something obscure Im missing?

Posted By: djhunless youre running a GG interactive custom system. Pretty sure its a building regs requirement??

If GG means "me", then I can assure you it is not custom !

There is a whold street-load of them up here, all the houses date from the same period (1980 - 1985)

https://www.forumbrico.fr/comment-regler-son-chauffage-au-sol-electrique

sorry it's in French !

gg

Posted By: Yalchanyways I've read that its best to keep it on low constantly and then turn up the temp when you want to warm the room and best on a smart thermostat to do this with so it's warm when you're up. (I currently have it attached to a Nest)

In general the lower the room temperature the less energy is being lost from your house. So you should always aim to have the room temperature as low as possible.

However...

If you set it to be "on low constantly" (say 16C) that doesn't necessarily mean the _heating system_ is using energy. It will only start using energy when the room temperature actually falls below 16C triggering the stat.

So for example suppose you set it to 21C during the day and 16C at night. When night time arrives the room will still be at 21C which is more than 16C so the heating will go off. It will stay off until the room temperature falls below 16C. If your house is well insulated that might not happen. In which case setting it to 16C at night uses no more energy than switching it off totally at night.

Clearly if your house doesn't need heating for longer periods (eg for the 4 weeks every January when you go to the Maldives :-) then setting it to OFF would use less than setting it 16C because temperatures might fall below 16C. If you really do go away in winter then setting it to 10C (or whatever minimum your insurance policy requires) is the way to go.

Posted By: djhIn a well-insulated house, controlling the heat fed into a slab by the air temperature above is not a stable control system. The air temperature increases a noticeable time after the heat is fed into the slab, so the room overheats. Consequently, it's better to measure the slab temperature, which reacts more quickly.

To some extent. But this does depend on the water supply temperature (so max temperature of the slab), how uniform the slab temperature is, how long the loops are (shorter = more reactive), floor covering and whether the control mechanism understands the hyteresis of the system (plus more I've not thought of).

I pretty much know the temperature of the slab by comparing the flow and return temperatures. I also know (by observation), how long the room takes to warm up from x to y temp (external temp seems to only impact how much it has cooled down, not how quickly the room warms up using the UFH). So I can determine that, if the room's temp = target-x, it will take y hours to warm to target.

On this basis I have created a control structure, based on room temp and time to target, that gets the room to where I want it to be and keeps the room at a pretty stable temperature (flow water runs at about 32DegC).

However, most commercial systems don't do that - they simply take the temperature now and if warm enough switch off and switch on when cooler than target.

The control of the input temperature to my UFH is via a TRV with external temp probe. I'd like to be able to control this such that on startup, the flow would be warmer and dimish as it reaches target temp. Then you can, to some extenbt, control the room temp by the flow temp (if you know the rate of loss - for that you'd need some weather compensation). But I have not found a TRV that I can control wirelessly.

I would be interested to see what a Nest would make of the hysteresis of my system, but I'm not forking out on whim. I do have a Heatmiser controller that is supposed to 'learn' but doesn't so is now the fallback if the computer controlled system fails. In addition it only steps and controls in 0.5 degrees so pretty much useless for me. I'm currently set to 20.3!

Personally, I find the biggest issue is overheating when there are lots of folk in the house for a family meal. Almost impossible to mitigate as it needs to be warm enough for when the first folk arrive. Alternatively I could tell them to keep their coats on for an hour or so!

It's only in less well-insulated houses that the heat loss from the room is fast enough to stabilise an air temperature-controlled system.

Ok. I can see from the different systems being talked about here, they are all complex, interactive systems that are far from mainstream. Our room stat seems to work ok with our part UFH/part radiator system, but the UFH cant do the full heat demand so the room stat can hold off the rads and the room cant overheat.... until we light the woodburner!

Posted By: borpinTrouble is, when you only have doors!!!!

Eh? Fire regs require means of escape from rooms? Oh, I suppose you have one of these new-fangled open-plan layouts? I'm afraid I'm an old fogey with a separate kitchen with window (because when my wife fries belacan/balachan I feel I can't breathe the air though I enjoy the result), dining room with a sliding patio door, and living room (because my wife can't stand it when I play the Who at 11). The living room has one opening window (fire regs) and one picture window. (and common sense says have an opening window in every room, just in case of some unforseen circumstance)

Door stops are available for turn-only openings.

We have one outward-opening door in the conservatory that I would really like to be able to 'wedge' open but the suppliers say there are no suitable restrictors (aluminium-faced timber) and I haven't yet found any in the shops. A conventional door stop is impractical because there is a step down outside the door.