Making underfloor heating control smart
Discussion
Morning all,
The house is heated by Air Source driving UFH. Because the underfloor acts on a very thick concrete slab, it takes time to respond, which is fine, but it always feels like it is behind the curve: when the temperature suddenly drops outside, the house takes a day to get itself back to temperature. The electricity tariff is also based on time-bucketed wholesale prices, so think I could be smarter about using energy when it's cheap rather than when the roomstats call for it.
The controls are HomeKit-enabled, so it should be simple enough to make them internet-enabled and consume electricity cost data and weather forecasts. Does anyone have experience of doing this, and what platform did you use to bring it all together?
Thanks all
TH
The house is heated by Air Source driving UFH. Because the underfloor acts on a very thick concrete slab, it takes time to respond, which is fine, but it always feels like it is behind the curve: when the temperature suddenly drops outside, the house takes a day to get itself back to temperature. The electricity tariff is also based on time-bucketed wholesale prices, so think I could be smarter about using energy when it's cheap rather than when the roomstats call for it.
The controls are HomeKit-enabled, so it should be simple enough to make them internet-enabled and consume electricity cost data and weather forecasts. Does anyone have experience of doing this, and what platform did you use to bring it all together?
Thanks all
TH
As you have discovered an underfloor system with an air sourced heat pump is about energy storage rather than a traditional heating system.
Treat it as a heating system, and you will always be a few hours behind.
Depending on the size and type of heat pump, generally you are best to switch the heat pump on whenever you can - and switch it off with temperature...as long as the thermostat is not in the main living area or where it is affected by the sun too much.
Cheap electricity? run the heat pump. Warm enough, turn it off.
I am, of course, assuming you don't have on/off valves trying to control each run of pipe. These will guarantee you will never solve the problem (reaction times are far too slow).
When an underfloor system (with a heat pump) is running, all runs should be open. If there are areas that tend to get a bit warm (relatively speaking) turn the flow down. The flow valves, generally on the top manifold, can be turned down to reduce the flow.
Does the heat pump have its weather compensation setup up? This is the only smart feature you need.
As caziques mentioned you are better off running it completely open which would mean removing all 'smart control' gadgets and minimising thermostatic zoning. You can then balance the room temperatures to where you want them by adjusting the flow meters on he manifold (asumming each room has its own loop). More flow will give a warmer floor and vice versa.
As caziques mentioned you are better off running it completely open which would mean removing all 'smart control' gadgets and minimising thermostatic zoning. You can then balance the room temperatures to where you want them by adjusting the flow meters on he manifold (asumming each room has its own loop). More flow will give a warmer floor and vice versa.
Thanks both - useful input so far.
I'm hearing clearly that trying to save by switching zones out based on room temperatures is not the way to go, so thank you for that steer.
The heat pump doesn't have weather compensation, and is operating quite dumb at the moment - UFH manifold calls for heat, and the ASHP supplies it at the preset temperature. That's what I would like to improve on.
cazique's point is clear - heat when it's cheap and stop when you're warm enough - but how does that work given the lag? By stopping only when the air temperature is comfortable, you will always overshoot, won't you?
The other question is about the coefficient of performance of the ASHP itself... Is it better to flog the pump when energy is cheap, or have it working more efficiently when it's warm outside? If it's 15deg during the day and 0deg at night, the pump will be significantly more efficient during the day, but the unit price will probably be considerably higher.
Appreciate the inputs guys
TH
I'm hearing clearly that trying to save by switching zones out based on room temperatures is not the way to go, so thank you for that steer.
The heat pump doesn't have weather compensation, and is operating quite dumb at the moment - UFH manifold calls for heat, and the ASHP supplies it at the preset temperature. That's what I would like to improve on.
cazique's point is clear - heat when it's cheap and stop when you're warm enough - but how does that work given the lag? By stopping only when the air temperature is comfortable, you will always overshoot, won't you?
The other question is about the coefficient of performance of the ASHP itself... Is it better to flog the pump when energy is cheap, or have it working more efficiently when it's warm outside? If it's 15deg during the day and 0deg at night, the pump will be significantly more efficient during the day, but the unit price will probably be considerably higher.
Appreciate the inputs guys
TH
Think I'd be looking at getting a wireless smart stat and connecting to your master unit
When you say thick concrete the ufch pipes should ideally be within the (roughly) 65mm screed on top of the insulation, if the pipes are in a significantly thicker slab it will take a good while to heat it up and then start heating the air space above it
Smart stats have the ability to learn so will come on what ever time they need to to get the room at the correct temp at the time you want it, they also learn when to switch off when it gets close to switching off/set back temp
When you say thick concrete the ufch pipes should ideally be within the (roughly) 65mm screed on top of the insulation, if the pipes are in a significantly thicker slab it will take a good while to heat it up and then start heating the air space above it
Smart stats have the ability to learn so will come on what ever time they need to to get the room at the correct temp at the time you want it, they also learn when to switch off when it gets close to switching off/set back temp
Which heatpump do you have and what cheap tariff do you have?
You can try batch charging the floors on the cheap rate (i.e overnight on an EV tariff) and use a thermostat as a timer with a temperature upper limit so it doesn’t overheat. Can add a boost time in the daytime if you need it.
You can adjust the flow temp of the heatpump yourself if you’re inclined to i.e drop it during the shoulder months.
Cheap rate lower efficiency Vs. expensive rate higher efficiency …. I’ve not experimented and probably never will but the way to think about it is in terms of average pence/Kwh – Octopus for example lists this on the bill.
Any Smart stat in my experiance is a waste of time and money with UFH its too slow to respond. Keep it Simple.
You can try batch charging the floors on the cheap rate (i.e overnight on an EV tariff) and use a thermostat as a timer with a temperature upper limit so it doesn’t overheat. Can add a boost time in the daytime if you need it.
You can adjust the flow temp of the heatpump yourself if you’re inclined to i.e drop it during the shoulder months.
Cheap rate lower efficiency Vs. expensive rate higher efficiency …. I’ve not experimented and probably never will but the way to think about it is in terms of average pence/Kwh – Octopus for example lists this on the bill.
Any Smart stat in my experiance is a waste of time and money with UFH its too slow to respond. Keep it Simple.
Edited by jymmm on Monday 29th April 12:31
Thanks both for more food for thought.
Best
TH
jymmm said:
Which heatpump do you have and what cheap tariff do you have?
It's a Daikin Altherma. I'm currently on Octopus Agile, but not wedded to it.jymmm said:
Cheap rate lower efficiency Vs. expensive rate higher efficiency …. I’ve not experimented and probably never will but the way to think about it is in terms of average pence/Kwh – Octopus for example lists this on the bill.
That's true, but it's only half of the equation I was thinking of: when air temperature is higher (or the air is wetter, or both), the CoP of the pump will be higher, so each Kwh of electricity consumed would put more heat into the system - I think it's the difference between Kwh-in and Kwh-out that I was asking about.Best
TH
Look up Heat Geek on YouTube and watch their videos on Tariffs and Zone Valves and Smart Controllers.
Also Skill Builder on YouTube did a series of stuff with a faulty Heat Pump Install and Heat Geek came in a fixed it, the methodology behind it all was interesting and useful for fine tuning your own setup.
As some said earlier, all the loops should be open and rely on the weather compensation to keep it right. You might need to fine tune the weather compensation to get it spot on.
Also Skill Builder on YouTube did a series of stuff with a faulty Heat Pump Install and Heat Geek came in a fixed it, the methodology behind it all was interesting and useful for fine tuning your own setup.
As some said earlier, all the loops should be open and rely on the weather compensation to keep it right. You might need to fine tune the weather compensation to get it spot on.
To answer the question properly, you'd need to know how quickly the slab loses heat to the rooms, and how quick the house loses heat to the outdoors.
If you heat the slab, then turn off the heat, does the room temperature overshoot in 15 minutes, because you've got hard tiled floors, or does it hold asteady temperature for the next 12 hours, because heat loss is low and your thick carpets mean the slab warms the room slowly?
If you kept your rooms at a steady temp through varying weather, how much would the slab temp need to vary to achieve that?
The other question is how happy are you about the house being warmer in the morning after heating the slab cheaply overnight and cooler in the evening? Personally it's the reverse of what I'd prefer, but how many degrees change would it take to annoy me?
And if the OP has a woodburner, now would be a good time to say so...
A bloke I know was looking into UFH, with a view to using solar PV to heat the slab in the afternoons.
The thing to bear in mind is that your annual bills are driven by the 30 ordinary weeks your heating is on, more than the 2 or 3 really cold weeks.
If you heat the slab, then turn off the heat, does the room temperature overshoot in 15 minutes, because you've got hard tiled floors, or does it hold asteady temperature for the next 12 hours, because heat loss is low and your thick carpets mean the slab warms the room slowly?
If you kept your rooms at a steady temp through varying weather, how much would the slab temp need to vary to achieve that?
The other question is how happy are you about the house being warmer in the morning after heating the slab cheaply overnight and cooler in the evening? Personally it's the reverse of what I'd prefer, but how many degrees change would it take to annoy me?
And if the OP has a woodburner, now would be a good time to say so...
A bloke I know was looking into UFH, with a view to using solar PV to heat the slab in the afternoons.
The thing to bear in mind is that your annual bills are driven by the 30 ordinary weeks your heating is on, more than the 2 or 3 really cold weeks.
I dont think a smart controller is mutually exclusive with UFH, but i suspect what you are hoping to do with the smart controller / tarriff is, or at least is going to mean your UFH wont work as well as it could, even more so with an ASHP.
Your UFH really needs to be on 24x7 in with colder months, with the except of two or three 30-45min windows when you heat up your hot water at that time. ie Dont have the ufh on at the same time as the hot water.
For me the benefit of a smart controller are being able to simply flex the heating up a degree or two, and do things like set it as on holiday on the way to the airport because you forgot on the way out!
Trying to use it to only heat the floors on an off peak tarriff is always going to make your UFH struggle. Ours takes 24-48hrs to warm up or cool down, so any tinkering on an hourly basis is at best a waste of time, and at worse actually making it less effective.
Id suggest what you need is a battery solution. Charge it up off peak and then use it thru the peak periods to allow your UFH to run 24x7 as above. Then use a smart controller really for the ease of use and app on your phone to monitor actual consumption, rather than trying to flex an off peak rate.
Your UFH really needs to be on 24x7 in with colder months, with the except of two or three 30-45min windows when you heat up your hot water at that time. ie Dont have the ufh on at the same time as the hot water.
For me the benefit of a smart controller are being able to simply flex the heating up a degree or two, and do things like set it as on holiday on the way to the airport because you forgot on the way out!
Trying to use it to only heat the floors on an off peak tarriff is always going to make your UFH struggle. Ours takes 24-48hrs to warm up or cool down, so any tinkering on an hourly basis is at best a waste of time, and at worse actually making it less effective.
Id suggest what you need is a battery solution. Charge it up off peak and then use it thru the peak periods to allow your UFH to run 24x7 as above. Then use a smart controller really for the ease of use and app on your phone to monitor actual consumption, rather than trying to flex an off peak rate.
Edited by AdamV12V on Wednesday 1st May 12:16
thr32 said:
That's true, but it's only half of the equation I was thinking of: when air temperature is higher (or the air is wetter, or both), the CoP of the pump will be higher, so each Kwh of electricity consumed would put more heat into the system - I think it's the difference between Kwh-in and Kwh-out that I was asking about.
Best
TH
You could try then Octopus cosy - their heatpump specific tarrif. It has a cheaper rate 13:00 - 16:00 which would also be the point with the warmest outside air temperature so good for efficiency. Best
TH
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