Under Floor Heating

[woodstalker]

Any under floor heating experts out there?

I've got 3 zones downstairs controlled by 3 obsolete and very simple polypipe thermostats and i would like to upgrade the controls but not sure what direction to go.

Thermostat set for temperature, temperature in room drops, UFH comes on and as soon as air temp matches what the thermostat is set to it shuts off. However there is so much residual heat stored in the concrete floor that the room temp goes right up and can be a bit ridiculous at times.

So basically i am wondering on the best way to control it so it is a nice comfortable temp all the time and not getting the spikes.

Would also consider some smart controls so i can control it if we are away from the house.

Cheers!

 

[RogerS]

I think that your thermostat may be too basic and that you need one that is a bit smarter.

This thread seems to suggest some http://www.greenbuildingforum.co.uk/new ... onID=10320

 

[MJ80]

Is it running through a wiring centre?
Have a look at the heatmister controls, they are pretty cool

 

[RogerS]

Is it running through a wiring centre?
Have a look at the heatmister controls, they are pretty cool

Heatmiser was one of those mentioned in the tread. They look pretty cool.

As an aside I'm a little miffed in that back in the late 70's I was thinking about a heuristic CH controller where basically you told it I want X degrees at this time and date and it measured the outside temperature and worked out how long, for a given outside temperature, you turned the heating on before you needed it...ie to get the room up to temperature. The objective being that for any given outside temperature it would learn and so turn on the heating at the latest time to save fuel.

I see in 1982 that someone in the US patented the idea. I should have kept my mouth shut !

 

[woodstalker]

Thanks Roger and MJ,

The stats are individual wall mounted ones in each zone, battery powered but hard wired to the control unit at the manifold under the stairs. The rest of the CH is radiators run off a traditional time unit by the boiler and that also does the hot water.

Will have a look at heatmiser and see how they compare. Ideally would like a diy install but happy to pay if it means my heating does what its supposed to.

No we have the new stairwell there's two more rads but i think they are overloading the boiler and the rads in the new stairwell and in the basement barely get warm if the ads upstairs and UFH are on. The plumber tried balancing all the rads and they sometimes kick in as they should and other times not; very frustrating.

James

 

[RogerS]

James, read the thread...it explains why you need a PID type thermostat.

 

[woodstalker]

James, read the thread...it explains why you need a PID type thermostat.

Cheers Roger, i think PID is the way to go for the UFH controls at the very least, i am just looking at the website and they have a fair few solutions for different setups. I might email them and tell them what i have and what i would like it to do and see what they suggest as the optimum package.

I did look at honeywell smart controls and tried to get their authorised fitter to come and have a look but he keeps saying he is too busy...

 

[Robert]

If you solve your problem can you post the solution please

I don't have underfloor heating and the reason for not going for it was my brother in laws experience with heat cycling just as you describe resulting in doors open in winter to let excess heat out! Might be able to help him out if you find a solution.

 

[AndyP]

If you solve your problem can you post the solution please

I don't have underfloor heating and the reason for not going for it was my brother in laws experience with heat cycling just as you describe resulting in doors open in winter to let excess heat out! Might be able to help him out if you find a solution.

That is the same problem as we have with the wood burner. The very large chimney breast and the concrete floors above hold a lot of heat. If the sun comes out as well we have to open the windows let alone the doors to cool the place down.

One solution I had, but chickened out on, was to install a small 6" fan in the transom above the living room doors to suck the warm out of the living room an push it towards the hall and stairwell. I was not confident enough to make a hole in the main supporting beam for upstairs.

 

[RogerM]

Woodstalker - this may sound a bit basic, but could the problem be as simple as the flow temperature to the UFH being set too high. The flow temperature from the boiler is usually set for about 65 deg for the radiators, but the Polypipe UFH system I installed in my kitchen has a Zone Regulation Unit (ZRU) which reduces the temperature of the water to the UFH to somewhere in the range 35 - 55 deg. This is done by mixing the return with the flow to reduce the temperature to the selected value.

We find that in practise we have settled on a flow temperature of 40 deg in spring/autumn, and 45 deg in cold snaps. Anything more and the temperature overshoots excessively. We set our room thermostat to a temperature to 17.5 deg, with a night time setback temperature of 15 deg. In practice, the temperature overshoots to about 18.5 deg - maybe 19 deg if the Boss is doing a lot of cooking. This is done with the standard wireless room stat from Polypipe.

 

[Mike G]

The first thing to understand about UFH is that it is slow acting, and relies on high thermal mass. In my last house I ran some very specific tests to 0.1 of a degree, and worked out that the house attained maximum temperature over 7 hours after the heating came on. The effect of the UFH was still evident 10 hours after it went off. So it isn't your thermostat which is the principle control issue, it is your timer (OK, they're generally combined these days).

This high-thermal-mass slow-acting thing is brought into sharp relief if you have a house which reacts quickly to changes in ambient temperature. A lot of people think you can stick UFH into a timber framed house......but these warm and cool quickly, and the heating system, as I've just described, acts very slowly indeed. The only (half) answer is to have some sophisticated controls which measure the outside temperature and predict how your internal environment will react. UFH, in my view, is much more suited to high thermal-mass houses, and in those circumstances, it can be the most energy efficient thing to simply have the heating "on" 24 hours a day (if the thermostat calls for heat. Think of the heating of such a building as a massive flywheel, such as on a traction engine. It takes a load of effort to get it going in the first place, but once it is turning it may require less energy to just keep on giving it a little nudge every so often than allowing it to slow right down and having to build it up to speed again.

 

[Mike G]

.......We find that in practise we have settled on a flow temperature of 40 deg in spring/autumn, and 45 deg in cold snaps.....

The normal design temperature is 35C.

 

[Tusses]

as MG said, it's a slow process

I've never used UFH, but always understood it to be a background heat. ?
Not something you turn up when you are cold. more like you set a temp you want the house not to go below within the next week or so. so just above body temp.

35Deg sounds about max. Else I'd imagine it could be like walking on hot coals ! :lol:

I've read a lot about rocket mass heating, stone/brick/bell/ .. same principle .
tiny bit of heat lasting a long time.

 

[Mike G]

...... but always understood it to be a background heat. ?.........

No, no. It can happily maintain the same inside temperature as you would get from radiators. It's just that you don't have hot and cold things in the room as you do with radiators, which creates moving air and thus drafts.

 

[Tusses]

...... but always understood it to be a background heat. ?.........

No, no. It can happily maintain the same inside temperature as you would get from radiators.

yeahbuttt

that just comes back to the OP's post .. if you crank up the heat .. then you have no way of turning it down, if the sun comes out for example.

I still imagine it would be best to have at least 2 heating sources
UFH for a background "Min" temp .. and another for the cool/cold days. ??

it's cold tonight .. I've just put some more coal on the fire ! :lol:

 

[MJ80]

we have got ours running to hit a target temperature of 19 degrees. Its average flow temp is about 25 degrees max is 35. It has two periods when it is running unless the room temperature drops below 16 when it will adjust the manifold to allow more hot through. There is also an external temperature sensor that can also control timing based in the external temperature
Basically its really bloody warm in here. We had it on 24 hours a day but it was just unlivable. Now its set to come on 3:30 am until 7, then again from 3 till 8 in the evenings. Its never chilly in here and is really efficient. Downside is you can't leave a bottle of cool beer on the floor, first world problems. Having it running between quite small temperature variations keeps it really steady.
This is installed over the cellar which is a concrete slab floor with 70mm screed. The rest of the house is on radiators.
I installed it in the last place as well between the joists with 75mm kingspan between and biscuit mix. That had to run hotter i think 50 degrees and didn't get the thermal mass to hold temperature. While it was good, I wouldn't bother doing one again on a suspended floor.
The new pellet boiler does all the control from its fancy programme screen, the thermostats are quite basic dial affairs with programme function. The boiler can also be controlled via the computer of phone, but I haven't connected that in yet. Each of the zones has its own valve and pump in a neat manifold controlled but the boiler. All the functions in the last place were on the thermostats going to a wiring centre for each zone, and a seperate thermostat time for the rads upstairs. I think i did it on S plan with a combi.

 

[woodstalker]

Cheers for all the responses guys, just read through them all but will respond over the weekend rather than now, just feeding my daughter and using my phone to read rather than the laptop so harder to type...

 

[woodstalker]

So my house is 8 (ish) years old and was built by the last owner who was a plumber. The floors on the ground floor are beam & block and screed with the final finish being tiled.

an issue i am finding is that if the room thermostats are set low, then the UFH never comes on because the house is pretty well insulated. This should be a bonus but the cold tiles are not pleasant and there is a slight "edge" in the air if that makes sense?

I would like to have the UFH switched on constantly, as it should be, as Mike says, and that way the floor will be warm to touch and the edge will be gone.

I intend to have a look at the heatmiser controls mentioned which are PID which apparently means they will "learn how long it takes for a room to heat up and shut off accordingly and prevent the overshoot.

I also need to balance the radiators for upstairs and the new bit to make sure the heat is not robbed from the ones in the basement and the stair well. If that doesn't work, I'm not sure what to do; could be that the addition of the extra radiators has pushed my boiler past its capacity (Vaillant ecotec plus 428) which could be an issue too. There's 10 radiators (3 of which are towel rails) and 3 UFH zones.

 

[RogerS]

I think that if your boiler is running constantly then it might be outside its capacity but if it cycles then perhaps it's OK ?

 

[9fingers]

If you have good insulation and yet a 28kW boiler is running continuously there must be some other source of loss? Your gas bill must be horrendous!
If you just want the ufh to take the edge off chilly tiles then maybe consider controlling the floor temperature. This works well in my bathroom with home made electric ufh and four sensors in the floor and a radiator system looking after maintaining the air temperature. The tiles are always pleasant to walk on but not expensive to run as the rad and towel rail do the space heating.
In your case a PID controller set the maintain floor surface temperature should make a reasonable job of keeping the air temperature comfortable too. There could be disparity in the numerical floor temp but you can learn which setting give air temp you want.

Bob

 

[Robert]

My boiler is a vailant ecotec 428 as well.

Mine was not commissioned properly and it took me a few years to work out why it didn't work as well as it should. It sounds like yours is set up properly but needs adjusting for your additional load.

It was all down to the maximum output setting of the boiler. out of the box it is set at 30kW (even though it is a 28kW boiler). At 30kW it heats up too fast. The boiler senses that as a problem and goes into limp mode for 20 minutes then tries full power again with the same result. Increasing the flow eased the problem and confused me as to what was wrong.

I eventually found a post on a plumbing forum describing the problem and detailing the fix - lower the maximum power setting. How to do it can be found in the install manual and online. I added up all my radiators and hot water load then added 2kW and came up with 18kW. My boiler now has a maximum output of 18kW and runs continuously at max flow temperature with no cycling until the thermostat turns it off.

You can view the max power setting with a couple of button presses. Might be worth checking..

 

[woodstalker]

My boiler is a vailant ecotec 428 as well.

Mine was not commissioned properly and it took me a few years to work out why it didn't work as well as it should. It sounds like yours is set up properly but needs adjusting for your additional load.

It was all down to the maximum output setting of the boiler. out of the box it is set at 30kW (even though it is a 28kW boiler). At 30kW it heats up too fast. The boiler senses that as a problem and goes into limp mode for 20 minutes then tries full power again with the same result. Increasing the flow eased the problem and confused me as to what was wrong.

I eventually found a post on a plumbing forum describing the problem and detailing the fix - lower the maximum power setting. How to do it can be found in the install manual and online. I added up all my radiators and hot water load then added 2kW and came up with 18kW. My boiler now has a maximum output of 18kW and runs continuously at max flow temperature with no cycling until the thermostat turns it off.

You can view the max power setting with a couple of button presses. Might be worth checking..

Hi Robert, thanks for the tip, it was installed by the previous owner (a plumber) and just after we moved in we got him back because the boiler kept tripping out and needing resetting. When we moved in it was part of the handover from the wife "when the boiler trips just press these buttons and it will start again..." not really what you want to hear from the plumbers wife! Anyway he came back and apparently fixed it by adjusting a valve in the loft which was the flow back to the boiler from the HW tank. He said it was being caused by the return temp being too high and the boiler detected this and thought it had been plumbed in back to front and so shut off.

Do you have a means of calculating the load from the rads and UFH so i can see what my boiler is trying to deal with?

Cheers

James

Edit: Just found on a forum how to check if it is set to max output (30Kw) which apparently can cause problems. Its actually set to 21Kw, but not sure if my need matches that. Also the same site suggested that the pump (a 15-60 type) should apparently be set to 3 (max) for this range of boilers (?), mine was on 1 so i've switched it to 3.

 

[Robert]

I was misled by thinking poor flow was the problem for ages - hence saying it took years to work out what was happening. my pump is on 3 but is not a super high flow type.

Anywhere that sells radiators will list the heat output in kW so working out the radiator load should be easy enough - just find similar sizes listed. As for the UFH no idea but you can probably find a guesstimate if you google search long enough!

My boiler was installed by a plumber too. Don't think programming boiler parameters was in his skill set though.

When you say 'trip out' do you mean it goes into limp mode? It runs at something like 40 - 50C flow temperature and has little heating effect while in that tick over state. Turning the flow temperature knob right down then up again will reset it to try heating again but if it heats too rapidly it will be back to the same state.

Mine was not cured at 20kW. it took a few tries to decide 18 was right but now it is faultless after annoying me for years. I had vailant service it during its problem time and they said it was mechanically fine. they obviously have no interest in the settings.

oh and I have a midpoint valve for heating/hot water and have an automatic bypass valve which is usually closed (it would only open if all the thermostatic rad valves closed and the thermostat still called for heat). There is no flow control other than the midpoint valve shutting off the water heating. Consequently when heating water there is a very high flow possible and no problem at all... so some of what you were told sounds nonsense. All I have read says is is the rate of heating that upsets the boiler not the return temperature.

 

[woodstalker]

Robert, thanks for all the info.. Vaillant came out and looked at it under warranty and simply said there was nothing wrong with it, the problem was the installation but didn't elaborate what was wrong with the installation. I'll see how it behaves tonight.

When I say trip it stopped working and showed error code F23 and had to be restarted.