Mixing valve for underfloor heating

[Archmoco]

Hi,

can anyone recommend a good mixing valve for underfloor heating with a good temp range. My UHF is connected to an accumulator tank and water temp could be anything from 30-85+ degrees. I've a Robot Compact Manifold and I don't think it gives me the variation I would like.

regards
Archmoco

 

[Ermintrude]

Myson blending valve

 

[Worcester]

There are lots of ways of controlled temperature of flow depending upon what installation you already have.

You shouldn't need any variation That's controlled by the stats on the manifold, the main mixing valve should be set up to match the design flow temperature of the ufh installtion, and not touched

Flow temperature can easily be controlled by:

Either: temperature controlled 3 port valve
or: a simple TMV (e.g. myson above)
or a combined pump and TRV

1) What controls are fitted to you current system?
2) Why are you concerned they aren't good enough?
2) Why can't your system installer / designer advise you?

If you still need more advice
1) How many rooms / areas are on the underfloor heating system?
2) how many manifolds do you have?
3) how many circuits off each manifold?
4) how many loops on each circuit?

 

[chris watkins]

5) What is the floor construction & finish make-up?

 

[Archmoco]

Chris,

65mm topcem screed 2mm underlay and engineered oak flooring throughout, no problems with heat transfer though.

 

[Ermintrude]

Low stable temp better then. The trv with probes are utter pish! Secondary pump two port and a blending valve

 

[chris watkins]

It's not the heat transfer, it's the max temp for the oak 40-50deg C max

 

[Ermintrude]

It's not the heat transfer, it's the max temp for the oak 40-50deg C max

??????

 

[Archmoco]

Worcester,

I'm trying to ensure the most efficient blending of supply to UFH from the accumulator as possible.

I've 1000ltr akvaterm solar plus accumulator tank
stove with back boiler 16kw( still only getting 8-10kw) Broseley evo 26 to accumulator through laddomat
40 evacuated joule tubes Connect via Laddomat 11-21
house 193m2 all underfloor heating from bottom of acc tank manifold Robot with TRV
high levels of insulation all elements U values 0.12, window triple glazed U value 0.7
'Beam' heat recovery unit, building airtightness around 2
immersion for accumulator still to be fitted.

problem I'm having is I've set the lowest setting on TRV (20 degrees) but supply temp on manifold thermometer is 35-40. Before I set it at 20 the supply temp was off the gauge and worried might damage screed. I could have anything from 40-85 degrees in bottom of tank

Half the house is large open plan dinning, kitchen and living, never needed underfloor on as if cold stove is lit, also utility room has accumulator tank so again no need for heating on. Heat only needed for hall and bedrooms. All rooms controlled by heatmiser stats, all set at 20 degrees, only underfloor heating in hall and bedrooms ever comes on that all I need.

in this good weather the bedroom thermostats would usually drop to 19 degrees in early morning, but I've turned the thermostat on acc tank to 70 so the underfloor will not start, by lunch time the room temps are back up to 20, maybe by passive solar or heat recovery?

I've attached photo of manifold. From manifold to tank, It has it's own pump, TRV, then second pump, myson, then manual 4 way valve joining top, middle and bottom of tank. No idea what it does.

the accumulator tank has 3 manual dial stats, bottom for dumping heat into hall floor screed, middle to set temp for underfloor to come on, and another stat at top of tank to control solar, however I don't know how it is set and neither does guy who designed system.

everything was 'commissioned' back in November, just immersion to fit, all money paid up,plumber his electrician all just very busy, but I'm hoping they will be back on Friday for at least to fit the immersion.

How would you rate the 'Robot' manifold? My only annoyance is they priced and I paid for a manifold with flow meters which I didn't get, but I believe the Robot is self balancing, looks like a robust unit though, do you really need flow meters?

plumber also getting me a price for another 20 SOlar tubes, even in this great weather the panels are pumping at 70-80 degrees, but still a deficit for the next day. if I could only get the system to heat the top section of the tank then the existing set up would be fine, at the moment the whole tanks is being heated and all I need is DHW during this good spell.

 

[chris watkins]

It's not the heat transfer per say , it's the resulting max temp for the oak 40-50deg C max

Sorry does that make a bit more sense ? this after some New Zealand 6.5% stuff that tasted great 2 pints plus a couple of other equally tasteful pints very nice, thank you weather spoon's.

 

[Worcester]

Still comes back to: what was the design flow temperature for the heat loss?

And how come your designer / installer isn't sorting all this for you?

Also

but I've turned the thermostat on acc tank to 70 so the underfloor will not start

The u'floor heating shouldn't be controlled by that, you really shouldn't be altering that on a regular basis, it should be set at it's design temperature.

What do you hope to achieve by altering it?

I'm trying to take as little heat out of the accumulator as possible.

Doesn't make sense.

Your house will take the energy it needs depending upon the heat losses, which is factored by the temperature in the rooms you are heating and the adjacent rooms and the outside air.

I know from your other post you've got problems with you heat source efficiency. However you need to consider all sorts of things, like if you turn the heating down in a room (set back) then it will take more energy to heat up. (it in the order of an additional 22W/m2)

Lets say your accumulator is at 70° and you let it drop to 40°, then a 30° drop on a 1000 ltr accumulator that's only 35kWh of heat storage, and if you're tapping off halfway up then that's even less energy stored. (volume AND temperature gradient)

To answer your original question though, from the photo it looks like a trv with a probe, with all those loops, it would better to swap that for a 3 port mixing valve with a thermostatic head.

(You'll need a bypass on the main circulation pump)

Don't see any flow gauges on the u'floor heating loops though so how have the flow rates been set up?

View attachment 18334

I've set the lowest setting on TRV (20 degrees) but supply temp on manifold thermometer is 35-40. Before I set it at 20 the supply temp was off the gauge and worried might damage screed. I could have anything from 40-85 degrees in bottom of tank

That's the purpose of the mixing valve, it should quite happily cope with a supply temperature of 85°, and blend it down to the DESIGN flow temperature.
If you've set the TRV to 20° then the rooms will never heat up and the u'floor heating will be pumping all day to no avail, you need a flow temperature greater than the room temperature, once again it comes back to: What is the design flow temeprature of the u'floor heating - go back to the original design documents and set the trv at that and let it do its job.

Also if you're having all these issues then:
1) it clearly wasn't fully commissioned in November
and
2) You really need to get the designer and installer back to properly commission and configure the whole system..

Or were you the designer, and the "plumber" is just doing what you told him to do?

- Note not all plumbers are heating engineers.... and as an aside we always leave the customer with a 'retainer' until we've finished, commissioned and certified ALL the work.

 

[Archmoco]

Worcester,

Again many thanks, I'm sure the guys will get it sorted, :21: the project was a self build, I designed the house but my input to the heating was limited to I want an accumulator tank, wood burning stove and solar panels.

 

[Gray0689]

This is in Northern or Southern Ireland I presume
The manifolds are not very good imho ok but I prefer I better method of controlling heat with a proper mixing valve

Why is solar on a laddomat valve where it's own pumping station
Joule are not the best solar tubes 40 tubes is same as about 25 kingspan thermomax

Air tightness 2 is not good

 

[Dotty]

And it's a buffer vessel you've got. Not an accumulator.

Two entirely different things. You had me confused for a moment.

 

[Gray0689]

Why is your underfloor being fed from the bottom of the buffer tank ?

 

[Worcester]

I presumed it was one of these :: AKVA SOLAR

So 'bottom' is a relative term - ie below the baffle, top used for DHW, though I may be wrong.

 

[Dotty]

I presumed it was one of these :: AKVA SOLAR

So 'bottom' is a relative term - ie below the baffle, top used for DHW, though I may be wrong.

I stand corrected re buffer/accumulator........

 

[Gray0689]

Basically a thermal store

 

[Dotty]

Aye, I was referring to the naming thing.

I accept the paddle of rebuke.....

 

[Archmoco]

Yes, but it's the 'plus' version so it has two coils for the solar thermal

 

[Archmoco]

As Worcester says top 400 ltr above baffle does DHW, tank stratifies really well so top can be 70 while below baffle 30 degrees

 

[Invisible Heat]

Hi,

can anyone recommend a good mixing valve for underfloor heating with a good temp range. My UHF is connected to an accumulator tank and water temp could be anything from 30-85+ degrees. I've a Robot Compact Manifold and I don't think it gives me the variation I would like.

regards
Archmoco

Hi

The robot manifold, using a trv bleeding , which has a probe in the bottom of the manifold, which is the flow into the floor.

You do not need an additional mixing valve, as the one on the manifold will maintain the temperature on the flow side as long as the thermal tank is supplying the water at the right temperature or higher.The manifold pump pumps the water from the bottom of the manifold through the ufh pies to the return side of the manifold(top) and what ever water is injected into the manifold from the thermal store, the same amount of water returns to the thermal store. Who supplied the manifold ? email the pictures to invisibleheat

 

[Invisible Heat]

I can not see a by pass across the flow and return pipework to the manifold.How far away is the manifold from the thermal store, as it maybe possible to use the manifold pump and re plumb the manifold.

 

[Worcester]

Hi

The robot manifold, using a trv bleeding , which has a probe in the bottom of the manifold, which is the flow into the floor.

You do not need an additional mixing valve, as the one on the manifold will maintain the temperature on the flow side as long as the thermal tank is supplying the water at the right temperature or higher.The manifold pump pumps the water from the bottom of the manifold through the ufh pies to the return side of the manifold(top) and what ever water is injected into the manifold from the thermal store, the same amount of water returns to the thermal store. Who supplied the manifold ? email the pictures to invisibleheat

I can not see a by pass across the flow and return pipework to the manifold.How far away is the manifold from the thermal store, as it maybe possible to use the manifold pump and re plumb the manifold.

And therein lies many a problem, we've seen many a diy systems assume that because they only have a single manifold, the manifold pump will act as the circulation pump for the ufh.

Hence sometimes better to run a tbv and a blended down supply to the manifold from the circulation pump and sometimes you can then do away with the manifold pump (or re-use it as per your comment).

For boiler read thermal store in the picture below. i.e you need three circulation pumps, Heat source to Thermal store / buffer tank, Circulation Pump, Manifold pump.

 

[Ermintrude]

Worcester yo da man ! I concur that only a gibbon would rely on primary circulation in ufh. I always use a blending set and a PUMP!