Thermostat Settings

[Grosey]

Now that we’ve moved in I’ve found myself fiddling with the thermostat settings constantly over the first few days. 

 

Never had underfloor heating before before and it is definitely a different beast to living with radiators. Could someone give me a starter for 10 on their settings (times and temperatures) as I seem to be chasing my tail a bit at the moment making too many changes. 

 

Also some idea of how other people time their hot water, I’ve only had a combi boiler before so never really had to think about it. We have a hot water circulation system which does seem to cool the water if the circulation pump is on and the hot water is not. Any advice appreciated. 

[MikeSharp01]

I am sure the @JSHarris discusses the settings for the UFH / room stat in one of his blogs. Hot water circulation is reasonably rare I think so it will be interesting to see how you get on with it.

[ProDave]

The big thing to remember with UFH it takes a lot longer to heat up (and then later to cool down) than radiators.

 

So what I found worked for me was to set the heating to come on 2 hours before you wanted it warm, so in my case that was 5:30AM. Then set it to go off at 9PM

 

If you find as the room warms up, that it overshoots the set temperature, then you probably have the flow temperature at the manifold set too high, so turn that down until it no longer overshoots.

 

Hot water stays hot in the tank a while and does not take as long to heat up, so that was set to come on 1 hour before first expected use in the morning, and to go off at 10pm

[Nickfromwales]

1 hour ago, MikeSharp01 said:

I am sure the @JSHarris discusses the settings for the UFH / room stat in one of his blogs. Hot water circulation is reasonably rare I think so it will be interesting to see how you get on with it.

The link for the stat with 0.1oC hysteresis is here

Very important with UFH to reduce the over / undershoot with such a device

 

[Trw144]

We ve been in a almost a year and I m just starting to look at how I can improve the temperature settings of heating and hot water. Currently for the heating I leave the rooms at the same temperature all day - I m sure I read once that this was just as efficient as having a high/low temp. 

 

The one I am currently logging with a view to improving is the hot water tank - I m currently heating it to 60 degrees (allowing it to drop back to 55 before recharging) all the time so that it can cope with the demands of a shower and bath if used at a similar time. However I can already see how much energy is lost in doing this, so will look to change this to a high/low period whereby the tank temp is allowed to drop further during the day.

[Jeremy Harris]

Our case isn't that typical, as the heating input is so low that I just leave the whole house set to the same temperature, 20.5 deg C.  This week I think the heating has come on once, after that very cold night on Tuesday, the rest of the time the heat from the slab plus incidental gains have kept the house around 21 deg C.

 

Similarly, our hot water system is a low loss, on-demand, system now, as I found the losses from having a big tank of water sat at 60 deg C were too high, no matter what I did to try and reduce them. 

 

When it comes to hot water return loops then the heat loss can be significantly reduced by careful controls.  These things only need to operate for short periods of time before you're actually going to need hot water.  As an example, hot water at a WC basin is only normally going to be needed maybe a minute after entering the room, so a PIR switch to turn on the circulating pump as you enter the room, and turn it off maybe a minute later, or even as soon as the hot tap is operated, will prevent a fair deal of heat loss (and some circulating pump energy).  The same goes for most other areas where there are hot water outlets, most will only need to provide hot water 30 seconds or more after entering the room, more than enough time for the circulating pump to have moved hot water around to the tap.  I can't think of any good reason to leave a recirculating hot water system on for any length of time; all it need to do is make sure that there is hot water at the tap when you need it.  Once it's done that it can turn off, and save heat loss and energy, until the next time you may need to use the hot tap.

[Declan52]

Doesn't matter what way I work the thermostat as soon as my back is turned it some how seems to be increased by persons unknown(wife).

I try to keep the rooms at 20 degrees so if by the of chance we get some sun then it doesn't overheat that much. With winter now starting and the cold mornings and nights I have my stove set to fire up at 5am and this makes sure the house is nice for the kids in the morning. All my kids are cold people so anything under 19 is like the arctic. At night it comes on at 6pm but depending on how much hot water the floors have taken and if some one wants a shower then it might only burn for 90mins before it powers down. If it's been sunny and the PV has heated the water then it might not come on at all.

I have tried heating my thermal store to every temp from 50-80 and my sweet spot is 65 degrees. 

[Trw144]

On 11/16/2017 at 09:37, Declan52 said:

Doesn't matter what way I work the thermostat as soon as my back is turned it some how seems to be increased by persons unknown(wife).

I try to keep the rooms at 20 degrees so if by the of chance we get some sun then it doesn't overheat that much. With winter now starting and the cold mornings and nights I have my stove set to fire up at 5am and this makes sure the house is nice for the kids in the morning. All my kids are cold people so anything under 19 is like the arctic. At night it comes on at 6pm but depending on how much hot water the floors have taken and if some one wants a shower then it might only burn for 90mins before it powers down. If it's been sunny and the PV has heated the water then it might not come on at all.

I have tried heating my thermal store to every temp from 50-80 and my sweet spot is 65 degrees. 

 

What are you heating with Declan?

[ProDave]

On 11/16/2017 at 09:37, Declan52 said:

Doesn't matter what way I work the thermostat as soon as my back is turned it some how seems to be increased by persons unknown(wife).

I try to keep the rooms at 20 degrees so if by the of chance we get some sun then it doesn't overheat that much. With winter now starting and the cold mornings and nights I have my stove set to fire up at 5am and this makes sure the house is nice for the kids in the morning. All my kids are cold people so anything under 19 is like the arctic. At night it comes on at 6pm but depending on how much hot water the floors have taken and if some one wants a shower then it might only burn for 90mins before it powers down. If it's been sunny and the PV has heated the water then it might not come on at all.

I have tried heating my thermal store to every temp from 50-80 and my sweet spot is 65 degrees. 

Ah the old "turn the thermostat up" routine.

 

Some people seem to think, if a room is cold, then turning the thermostat WELL beyond the point at which it goes "click" will heat the room quicker.

 

We regularly found with the B&B people who must have thought "the heating is not working" (it was UFH so took a while to respond) and turned the thermostat all the way. You go in later to clean the room and it was up to 30 degrees!!!!!!!

 

Yes, should  have bought thermostats that would go no higher than 25

[PeterW]

So we have a dummy thermostat in a building I manage - you turn it up and hear the “click” but it does nothing .... and no-one ever says it’s cold..!

[Temp]

It will probably take some bad winter weather to get your set up right.  Ours is set roughly as follows (we have someone home most days)..

 

Night 16C

Getting up 20C

Daytime 18C

Evening 20C
 

We have a stat in most rooms so things like the bathroom are warmer. Unused bedrooms set at 16C constantly. Living room warmer at weekends etc. Transition between two temperature settings can take 1-2 hours so they are set that much earlier depending on the room.

 

Still not quite perfect. Occasionally there is a slight dip in temperature when it transitions from the daytime setting to the evening setting. Could be we loose solar gain rapidly and it can take awhile for the UFH to replace it? Could be the sun shining on the stat itself holding it off without providing solar gain? One day I'll get around to figuring out what causes it but it's not a big problem.

 

[Declan52]

2 hours ago, Trw144 said:

 

What are you heating with Declan?

I have a wood pellet stove that provides all my heat plus dhw.

[ragg987]

2 hours ago, ProDave said:

Some people seem to think, if a room is cold, then turning the thermostat WELL beyond the point at which it goes "click" will heat the room quicker.

With our ASHP's built-in compensation control this is actually how it works - the difference between set and actual temperature is part of the calculation for flow temperature. So raising the stat will boost the flow temp and heat up the room faster.

 

Hot water circulation causes heat from the DHW to be emitted by the hot water pipes into your house. Which may  be useful in winter, but I would not recommend that as a valid approach. Maybe put the circulator on a simple timer that comes on when you are likely to need hot water - e.g. morning and evening. It should be off 80-90% of the time.

 

I agree with @ProDave, we leave it on all day between 8.30 am to 8.30 pm. The setback for night is 1 or 2C lower - so in case we get a very cold night and the temp falls the heating will come back on. Still experimenting with this - last winter I left it on 24 hrs and let the logic in the controller work it out.

 

Also think aboutin the human response. I find we can get away with a cooler house first thing in the morning compared to in the evening. e.g. 20C morning is fine but would be too cold in evening. I cannot explain this, but maybe we have less "sitting-around" time in the morning or perhaps body core is really warm from sleep under a duvet?

 

In terms of timing of these events, if you have PV or an ASHP then think about these as well. ASHP is going to be more efficient at the warmest time of the day and PV can also lift some (or all) of the load rather than export to grid.

[Jeremy Harris]

It all depends on so many variables, though, that it's hard to compare one system with another.  If I used weather compensation, for example, and increased the flow temp with cold weather (I did try it) then the house room temperature shoots way, way over the set temperature, and takes hours to cool back down again.  The reason is that the house only needs a small amount of heating and the time response of the in-slab UFH is pretty sluggish, maybe an hour or two before the room temperature starts to change noticeably when the UFH kicks in.

 

Half a degree difference in floor surface temperature doubles the heat output at the typical temperature our house sits at, equivalent to around an extra 500 W or so, which is a massive increase when the house only needs around 300 to 400 W to stay warm in winter.  I absolutely have to keep the UFH flow temperature below 26 deg C as a maximum, any more than that and the house temperature starts to swing up and down by over a degree or two, and just doesn't regulate well.

[SteamyTea]

Data, data, data.

 

Apart from that, where is the thermostat.  Does the sun hit it at all and is it in a draught?

 

Apart from that, do some test.  Set it at the desired temperature, say 20°C, note the current internal temperature, the external temperature (maybe an external wall if you have an IR thermostat) and keep checking every 15 minutes and note the internal temperature.  If you can, note the time the ASHP stops too.

 

Do this for a few days and then try again with the thermostat set at 18°C and then at 22°C.

 

Plot it all in excel and it will all make sense.  You need two plots, internal temperature against external temperature and internal temperature against time.  From that you can work out any offset needed for a given external temperature and the time taken to heat the room up to a set temperature.

 

Put some tape over the thermostat when you do the tests, or cut fingers off, both usually work.

 

 

For a change, I have my heating on (I think I am getting older).

Front room is at 17.8°C.  This would usually be a bit cool for me, but as I am decorating the bathroom and running up and down the stairs, I feel a bit warm.  Too warm for a change.

Edited November 16, 2017 by SteamyTea

[Nickfromwales]

23 hours ago, Trw144 said:

We ve been in a almost a year and I m just starting to look at how I can improve the temperature settings of heating and hot water. Currently for the heating I leave the rooms at the same temperature all day - I m sure I read once that this was just as efficient as having a high/low temp. 

 

The one I am currently logging with a view to improving is the hot water tank - I m currently heating it to 60 degrees (allowing it to drop back to 55 before recharging) all the time so that it can cope with the demands of a shower and bath if used at a similar time. However I can already see how much energy is lost in doing this, so will look to change this to a high/low period whereby the tank temp is allowed to drop further during the day.

Do you have any numbers on how the solar thermal is performing ? Iirc, you didn't go with any Pv, no ?

[Trw144]

@Nickfromwales no, I ve only just started logging data. I know hot water tank temperature is nt an issue in the summer as I have oodles of free solar thermal, however I m now logging hot water tank temp, solar collector temp, gas boiler running (and requested flow temp), amongst other things. What I can say is the large waterfall shower can empty the hot water cylinder pretty darn quickly - so i ve been heating the hot water cylinder to 60 degrees (allowing it to drop back to 55 before recharging). However it does lose about 1 degree an hour through heat loss which stacks up a bit, current thoughts are to have it recharge at 55 degrees through likely shower times (early morning and evening) and the rest of the time let the tank drop back to 50 degrees before recharging.

Edited November 17, 2017 by Trw144

[SteamyTea]

Sounds like the cylinder is loosing a fair bit of heat, how much insulation does it have?

[Trw144]

Here's a graph from the last few days to show that steady heat loss from the cylinder....

 

 

Edit. Can anyone spot when I have a bath and read buildhub on my phone?!

Edited November 17, 2017 by Trw144

[Nickfromwales]

@JSHarris

Do You know if there is a similar room thermostat to your wireless one, but hard wired? I'm thinking of recommending them to the customer I did the manifold and auto-balancing actuators for as they have the basic Honeywell rotary manual stats with a horrible 1.5oC hysteresis . The house has pretty poor floor insulation ( ~70mm pir over a ventilated block and beam ) and a thin liquid screed, so the overshoot is difficult to manage, plus, as the rooms are quite big, the undershoot takes some time to recover. The manifold temp is set a bit higher than would be ideal ( so further exaggerating the overshoot ) so I think an upgrade to the stats would pay dividends. 

[Trw144]

It's a valliant solar cylinder (aurostore or something like that) so whatever standard insulation is. However it is in my garage - which whilst insulated, isn't heated so the ambient temp is lower. To an extent I don't mind a bit of heat loss in there as I store quite a bit in there and it can help keep the moisture out. I just think I can reduce the unnecessary waste. Whilst not the point,  reality is the heat loss probably doesnt cost much - I'll do the calcs at some point.

[Nickfromwales]

10 minutes ago, Trw144 said:

@Nickfromwales no, I ve only just started logging data. I know hot water tank temperature is nt an issue in the summer as I have oodles of free solar thermal, however I m now logging hot water tank temp, solar collector temp, gas boiler running (and requested flow temp), amongst other things. What I can say is the large waterfall shower can empty the hot water cylinder pretty darn quickly - so i ve been heating the hot water cylinder to 60 degrees (allowing it to drop back to 55 before recharging). However it does lose about 1 degree an hour through heat loss which stacks up a bit, current thoughts are to have it recharge at 55 degrees through likely shower times (early morning and evening) and the rest of the time let the tank drop back to 50 degrees before recharging.

Your tank is an UVC is it not?

1oC per hour is typical, even for an well insulated cylinder,  I think, and not disastrous tbh. Your backed up by gas though iirc, so with the boiler kicking in to replace lost heat do you find the heat exchange rate isn't enough to cope with demand ( linear )? Eg heat capacity of the UVC + gas boiler input doesn't give much sustain ?

 

Oh, and what kW boiler did you go for?

[Trw144]

@Nickfromwales no, I don't think it's too bad - but I can improve it. Boiler is a 15kw, so either this or most likely the heat exchanger rate (will need to check what it is on my tank) is nt big enough to keep up with an 650 x 650 Bossini shower - it literally destroys the how water tank! To be honest I think I ll try and throttle the flow to it a bit by closing the isolator valve on the manifold to it - my wife won't notice flow rate but she does notice cold water.

[PeterW]

25 minutes ago, Trw144 said:

Here's a graph from the last few days to show that steady heat loss from the cylinder....

 

 

Edit. Can anyone spot when I have a bath and read buildhub on my phone?!

 

What are you using to log the temperatures @Trw144 ..?

[Trw144]

@PeterWHi Peter, I m on a Loxone home automation system. They are nt cheap but it is great for integrating things like boiler, hot water, heating, shading etc. and, if you understand basic logic, very easy to programme.

 

@Nickfromwales a quick check and it looks like it takes about 30 mins to increase the tank 5 degrees.

Edited November 17, 2017 by Trw144