What is the most efficient way to run wet underfloor heating?

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Jenny7026 said:

Thanks very much for everyone's help! I think we will need to think about whether heating zones might save us money. We have put the programmable TRV on and set the timer (currently trying 3h morning, 2h night to see how that goes) so fingers crossed that helps in the meantime.

With programmable stats you should not use timed heating but set the temperature you want at times during the 24hr period
For radiator based rooms.(adjust for use case)
19c 7am-9am(getting up)
10c 9am-5pm(out)
19c 5pm-10pm ( evening)
15c 10pm-7am (overnight)

Let the thermostat do its job.
A good one will be able adjust the time it starts stops the heating to manage the temps for the times you set

For UFH the hysterisis is too long to have big variations in temps

Jenny7026

"Let the thermostat do its job."
As I said in the first post, the house has no programmable thermostat, it has a timeswitch. It literally just switches the heating on and off at set times and cannot set any temperatures. The only radiator which now has a programmable TRV (thermostatic radiator valve) is the main bedroom, most of the rooms just have normal TRVs, and the UFH rooms use analogue, non-programmable thermostats (ie, they are on below x temperature, and off above that).

"Is this ONE prog TRV? And presumably in the main bedroom? Are the other bedrooms being used, or are the TRVs there turned 'off' - ie just to 'background', say '1'?"
Yes, only one prog TRV in the main bedroom, the other bedrooms are all set to 1 - they have standard TRVs. And indeed, the bedroom is only on for 1h in the morning and 2h in the evening, it's the rest of the house that gets the full 4h/2h. The bedroom is slow to heat up though as it's losing heat through sash windows, so we're going to need to look at that.

Bendy_House

Jenny7026 said:

"Let the thermostat do its job."
As I said in the first post, the house has no programmable thermostat, it has a timeswitch. It literally just switches the heating on and off at set times and cannot set any temperatures. The only radiator which now has a programmable TRV (thermostatic radiator valve) is the main bedroom, most of the rooms just have normal TRVs, and the UFH rooms use analogue, non-programmable thermostats (ie, they are on below x temperature, and off above that).

"Is this ONE prog TRV? And presumably in the main bedroom? Are the other bedrooms being used, or are the TRVs there turned 'off' - ie just to 'background', say '1'?"
Yes, only one prog TRV in the main bedroom, the other bedrooms are all set to 1 - they have standard TRVs. And indeed, the bedroom is only on for 1h in the morning and 2h in the evening, it's the rest of the house that gets the full 4h/2h. The bedroom is slow to heat up though as it's losing heat through sash windows, so we're going to need to look at that.

Cool, that's the upstairs taken care of :-) (Until the other bedrooms are required...) It isn't ideal, of course, since the Prog TRV has no control over the boiler to tell it when and when not to 'run'. So, for the bedroom to be warmed, the boiler must already be 'on', so the main timer would need to cover these bedrooms times anyway.

I think you'd need someone in to confirm what your UFH setup is, and whether the room stats in the three downstairs rooms only operate the zone valves, or do they also control the boiler? If the latter - the best scenario - then an obvious and simple improvement would be to replace these basic 'stats with Prog Stats so you can then preset what temps you'd like these rooms to be. Again, you'd need either advice on how rapidly the UFH responds, or else find that info out yourself on t'interweb. But I'd have thought that an hour would surely be enough for it to swing into action and get the room to temp? In which case you set the prog stat to provide the temps you want at the times you want, allowing at least that hour at each end of the timings in order for it to adjust.

Trial and error would then get you closer to the required timings. For example, if bedtime is usually 11pm, I'd try setting the prog stat to drop the room temp to 'overnight' - say 14oC? - at 10pm. Due to its lag, I'd expect it to still be nicely warm near 11pm, but you can adjust that 'overnight' time as required after trialling it. Ditto in t'morn - have it come on to get things moving towards 'comfy' (~20oC?) an hour before you want that warmth, and see how that goes. If folk are away during the day, then have it going back down to 'background-day' warmth - say 17oC - a good while before you actually leave - as before, it should still be warm until you do. Back up to 'comfy' a good hour before folk are due home - you get the idea.

Jenny7026

Yes, I think we're going to have to do a bit of experimenting with temperatures and times! It's a bit tricky to work out "can the ufh demand water from the boiler" as we can never be 100% sure whether it's responding to the UFH or the radiators. If the timeswitch is off but the UFH thermostat(s) are on, the timeswitch will prevent the boiler providing hot water, but the UFH pump will run without any extra hot water coming through. 

Bendy_House

Jenny7026 said:

Yes, I think we're going to have to do a bit of experimenting with temperatures and times! It's a bit tricky to work out "can the ufh demand water from the boiler" as we can never be 100% sure whether it's responding to the UFH or the radiators. If the timeswitch is off but the UFH thermostat(s) are on, the timeswitch will prevent the boiler providing hot water, but the UFH pump will run without any extra hot water coming through. 

Although I understand the principles of UFH - as you also do - I am not familiar with the details of how it's controlled.

I think that the UFH itself has a dedicated pump which circulates the water around the UFH pipework, and the thermostats on each zone control the amount of hot water that's added to this from the boiler in order to keep it at the required temp - ie the boiler output doesn't just head straight into the UFH pipework, but gets blended in order to keep it at the required, lower, operating temp.

So, yes, when you turn on an UFH 'stat, its pump will come on.

Then there's the boiler. This is a combi type. This will have its own circulating pump inside it, and this will be the pump that supplies the rads upstairs.

As it's currently set up, unless the boiler's timer is 'on', then the UFH just won't work - ie it'll be cold, even if its own pump is running. So, for you to be able to turn the rads and UFH on and off at will, via their respective 'stats (the rad one being the TRV jobbie), then the boiler timer will always have to be 'on'. Ie, the boiler is always running, or trying to run. (It will shut itself off when it simply cannot disperse hot water, ie when neither the rads or the UFH is calling, but that's a pants way to operate.)

If this is the case, then an immediate improvement would be to properly 'zone' off the upstairs by having a zone valve installed where the boiler flow tees off to head upstairs. This would be controlled by a Prog Stat - 'Smart' or not - which would be wall-mounted either in the master bedroom, or else in the upstairs hallway (I'd recommend the former).

The UFH could then theoretically also be wired so that it controls the boiler directly, to come on as and when required. With the main room's wall 'stat also swapped for a Prog type (Smart, ideally), the new upstairs and downstairs PStats would take over the job of the old timer.

That is my best understanding... You need an UFH specialist to come out and check what you have, or else carry out lots of investigation yourself :-)

Rosa_Damascena

What is the most efficient way to run wet underfloor heating?

This is my first winter with wet UFH and in December it had a life of its own. It's a big home but I can only ever be in one room at a time, and last month the gas alone came to £96, the highest it's ever been. So I did something radical and turned off the heating at the start of the month and used it very sparingly in the evenings only (plus HW), and submitted a reading just today. The gas bill went down by all of 1/3 and I have been freezing all month. 

Compared to petrol costs it's still small, so the heating has gone back on now.

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I think that the UFH itself has a dedicated pump which circulates the water around the UFH pipework, and the thermostats on each zone control the amount of hot water that's added to this from the boiler in order to keep it at the required temp - ie the boiler output doesn't just head straight into the UFH pipework, but gets blended in order to keep it at the required, lower, operating temp.

the house we have with UFH is a single manifold mixing valve.

any room stat can call for heat and activate the circuit actuators on the manifold.

Bendy_House

That just shows how little I know about these systems, gm4l :-(

How are room temps controlled? What does the room stat actually do - how does it adjust the temp?! By turning a circuit actuator on and off?

And is it common or typical for an UFH pump to be running pretty much constantly?

Rodders53

Bendy_House said:

That just shows how little I know about these systems, gm4l :-(

How are room temps controlled? What does the room stat actually do - how does it adjust the temp?! By turning a circuit actuator on and off?

And is it common or typical for an UFH pump to be running pretty much constantly?

Google?

https://www.johnguest.com/speedfit/underfloor-heating/underfloor-heating-explained/what-is-ufh/

There's a few You Tube videos there, too.

To give proper advice to the OP we need more accurate info about the installation... with picture of parts.

My home has 8 loops to a manifold. Each loop has a flow meter and thermal actuator to open/close flow to the loop.  There are two rooms with two loops and both loop actuators are controlled by the one wall mounted thermostat for each room.  The other two rooms have individual wall stats.

Whenever one of the stats calls for heat the controller wiring unit operates a pump relay (for the manifold) and a boiler call for heat relay --- in my case that operates a zone valve causing my oil boiler to start its circulating pump and oil pump to heat up the water fed to a thermostatic mixer valve.

My UFH pump runs as long as there is demand for heat from a room on the ground floor.

The water tank is another zone, as is the upstairs radiators.

But every install can / will be different.

getmore4less

Bendy_House said:

That just shows how little I know about these systems, gm4l :-(

How are room temps controlled? What does the room stat actually do - how does it adjust the temp?! By turning a circuit actuator on and off?

And is it common or typical for an UFH pump to be running pretty much constantly?

Not in the house we have that has UFH the pump shuts down a lot of the time even in the winter.

In a well insulated property the hysterisis will be a decent long cycle where no call for heat is needed.

The same pump heats the HW storage tank not a separate pump.