UFH mixing valve at low temps

[Benjseb]

I have an ASHP which runs UFH and rads

 

the flow temp from the heat pump is usually 38-45c

 

Wr can run the UFH at a lower temp than this. However, the valve seems a bit... shit. 
 

if I set to 35c I only get flow temp of 25. If I set to 45, it gets to about 30-35. However that 10c difference changes depending upon the heat pump flow temp. 
 

The instructions for the valve state that for it to work correctly the incoming hot flow needs to be approx 15c higher than the desired temp. 
 

is that normal? Or have a just got a cheap mixing valve?

ideally I’d like the UFH to stay at about 35 as it’s only really the rads that need a higher temp when it’s cold. 
 

 

 

[ProDave]

I just set the flow temp I want as the "heat pump water leaving temperature"  and let the HP control it.  the mixing valve is then irellevant.  Not many of them work properly at low temperatures.

[Ed Davies]

But @ProDave, that presumably works fine for you but won't set the right temperature for the OP's radiators.

 

With mixed radiator and UFH systems I wonder if there's ever any sense in running the radiator return water through the UFH?

[Temp]

1 hour ago, Benjseb said:

The instructions for the valve state that for it to work correctly the incoming hot flow needs to be approx 15c higher than the desired temp. 

 

That sounds like the valve might have a limited range. Eg it can't mix 100% flow and 0% return but limits at say 90% flow and 10% return?

[Temp]

Not sure if this link will work but it's to the data sheet for another valve that needs the flow 10C higher than the output. Note 1 suggests this is some sort of safety feature when the valve is used to control the water temperature of a tap or bath. They say its to ensure the valve shuts off if the cold supply fails.

 

https://www.arrowvalves.co.uk/media/wysiwyg/pdfs/tmv5213datasheet.pdf

 

 

Edited October 6, 2019 by Temp

[Jeremy Harris]

One fix is to just bin the mixing valve altogether and use the Salus differential temperature controlled actuators:https://salus-controls.com/uk/product/thb23030/.  I'm using one and find it very good at maintaining a steady temperature across manifolds.  These actuators also open and close a fair bit faster than the hot wax ones, which can be useful.  They maintain a 4°C temperature differential between UFH flow and return if the highest sensed temperature is below 30°C and a 7°C differential if the highest temperature is above 30°C.  I have ours sensing the flow and return temperatures on the UFH loops.

[Benjseb]

1 hour ago, JSHarris said:

One fix is to just bin the mixing valve altogether and use the Salus differential temperature controlled actuators:https://salus-controls.com/uk/product/thb23030/.  I'm using one and find it very good at maintaining a steady temperature across manifolds.  These actuators also open and close a fair bit faster than the hot wax ones, which can be useful.  They maintain a 4°C temperature differential between UFH flow and return if the highest sensed temperature is below 30°C and a 7°C differential if the highest temperature is above 30°C.  I have ours sensing the flow and return temperatures on the UFH loops.

This is interesting!

 

As our current actuators are controlled by the stats what happens if the demand for heat is satisfied, how do you close the zone off?

 

Do they work if it’s not a thick slab? Ours is    A retrofit system under tiles.  The current actuators are very slow though but currently each zone only comes on for a few mins per hour as  it much heat is needed

 

 

[Benjseb]

1 hour ago, Temp said:

Not sure if this link will work but it's to the data sheet for another valve that needs the flow 10C higher than the output. Note 1 suggests this is some sort of safety feature when the valve is used to control the water temperature of a tap or bath. They say its to ensure the valve shuts off if the cold supply fails.

 

https://www.arrowvalves.co.uk/media/wysiwyg/pdfs/tmv5213datasheet.pdf

 

 

I think ours says the same. So not really suitable for heat pumps then!

 

[Jeremy Harris]

1 minute ago, Benjseb said:

This is interesting!

 

As our current actuators are controlled by the stats what happens if the demand for heat is satisfied, how do you close the zone off?

 

Do they work if it’s not a thick slab? Ours is    A retrofit system under tiles.  The current actuators are very slow though but currently each zone only comes on for a few mins per hour as  it much heat is needed

 

 

 

 

They work just like ordinary actuators, and will turn of or off just like wax-filled ones, but a bit quicker.  They just have the added feature of balancing the temperature between flow and return as well, so they do away with the need to control the temperature into the UFH manifold.

 

They should work with any UFH setup, as they make two models, a 230 V one and a 24 V one, so just choose the right ones to replace the actuators you already have.  To save disconnecting the mixer you can just turn it up to maximum, which is what I've done, and then let the auto-balancing valves do their thing.

[Benjseb]

Thanks @JSHarris  did you notice much advantage after doing this?

 

i have noticed that the pump fires up a few minutes before the actuators open which isn’t great so that may help. Does the auto balancing help?

 

Ben

[Jeremy Harris]

10 minutes ago, Benjseb said:

Thanks @JSHarris  did you notice much advantage after doing this?

 

i have noticed that the pump fires up a few minutes before the actuators open which isn’t great so that may help. Does the auto balancing help?

 

Ben

 

 

My personal view is that these actuators are the best thing since sliced bread!  I had problems getting our mixer valve to regulate accurately, and also had the same problem you've described, where the ASHP pump came on with a call for heat, yet the actuators took some time to open.  The Salus valve gets around both these problems and just does its thing, with no need for any setting up.

[Benjseb]

Am I right I’m thinking it’ll just allow the HP flow temp through tho - say 40c - even at a slower rate perhaps, so if we’re not mixing it down it won’t be as efficient?

[Jeremy Harris]

They work in exactly the same way as a two port thermostatic valve, so the mixing happens between the flow and return manifolds, by recirculation, in effect.  The efficiency is identical, as there are no losses anywhere, or not any more losses than there are in the pipework anyway.

[ProDave]

9 minutes ago, JSHarris said:

They work in exactly the same way as a two port thermostatic valve, so the mixing happens between the flow and return manifolds, by recirculation, in effect.  The efficiency is identical, as there are no losses anywhere, or not any more losses than there are in the pipework anyway.

Sorry I am struggling to understand that.

 

It is an on / off valve (probably proportional)  As such it can allow water to flow or not flow or flow slowly.

 

I cannot see how it can do any blending, it can just adjust the flow rate to get the desired difference between flow and return. But that might be at a high or low temperature depending on the feed temperature.

[Jeremy Harris]

Just now, ProDave said:

Sorry I am struggling to understand that.

 

It is an on / off valve (probably proportional)  As such it can allow water to flow or not flow or flow slowly.

 

I cannot see how it can do any blending, it can just adjust the flow rate to get the desired difference between flow and return. But that might be at a high or low temperature depending on the feed temperature.

 

The blending happens through the mixing between the return and flow manifolds via the pump.  Return water gets mixed with flow water, and the result is a pretty tightly controlled differential across the UFH pipes.  Seems to work very well indeed - ours has been running like this for a couple of years or so now, and the temperature control is far better than we had with the two port mixing valve (which works in exactly the same way - it just throttles the incoming hot flow, exactly like a thermostatic radiator valve).

[ProDave]

Ah so is this connected to a spare port with a direct short link from flow manifold to return manifold?

[PeterW]

1 hour ago, ProDave said:

Ah so is this connected to a spare port with a direct short link from flow manifold to return manifold?

 

No they work the same way as the wax cap based TMVs - allowing more hot into the blender when the return is below the target temperature and closing more as the return temperatures increase 

[Temp]

I'm also confused...

 

So they are intended to be used like normal actuators but (with auto balancing via loop temperature sensors) but @JSHarris has an extra one configured to replace the mixer so it controls the flow temperature to the floor?

 

Any chance of a diagram?

[Ed Davies]

8 hours ago, Temp said:

Any chance of a diagram?

 

+1

 

I thought I understood but now I'm not so sure.

[Jeremy Harris]

9 hours ago, Temp said:

I'm also confused...

 

So they are intended to be used like normal actuators but (with auto balancing via loop temperature sensors) but @JSHarris has an extra one configured to replace the mixer so it controls the flow temperature to the floor?

 

Any chance of a diagram?

 

 

In practice, all that matters in terms of heat output, is the differential temperature.  The higher this is, the more heat is emitted to the room.  In our case, because the mixer tends to be a bit variable at very low flow temperatures, I turned it up to a bit over 30°C when fitting the Salus units (it seems to be stable at around this setting).  This results in a flow manifold temperature that's a bit under 30°C in practice (due to mixing from the return), so the actuators work with a 4°C differential.  This seems to work very well, with good room temperature control and very little overshoot.  The problem we had before was that if the flow temperature got too high (because of poor regulation by the thermostatic valve) the room temperature would overshoot the set temperature by up to about 1°C or so, then slowly come back down over the next day.  Now the overshoot is much smaller, maybe 0.2°C at most.

 

On our manifold the UFH circulating pump draws from both the return side and the incoming hot water side (via an inline thermostatic valve), as there is just a tee where the pump connects, with the left arm being the flow in, the right arm going to the return manifold and the upper arm going to the pump.  This means that there is always a bit of mixing taking place in the pump and the flow manifold , as the pump tends to draw in some of the cooler return water, as well as some of the hotter flow supply.  The main return back to the ASHP and buffer connects to the right hand side of the return manifold.

 

Another advantage of these actuators is that you can open up all the flow controls to maximum, and let each loop just control itself, as the actuators will automatically balance to maintain the right heat output from each loop.

[Benjseb]

Yes I’m unclear. 
 

surely the only part of the system that can blend down the temp is the mixing valve as it has both flow and return inputs. 
 

the actuators are simply flow rate of the return feed. Sealed loop so can only co tell flow, not temp?

 

i guess it controls delta T by adjusting the flow rate 

[Benjseb]

Thanks @JSHarristhats clearer now

 

i will give this a go with 2 of our 4 actuators and see how they compare

 

it certainly appeals that they do t take 10 mins to react, and the balancing is a bonus on top. 

[ProDave]

9 hours ago, PeterW said:

 

No they work the same way as the wax cap based TMVs - allowing more hot into the blender when the return is below the target temperature and closing more as the return temperatures increase 

Nope totally confused. Diagram needed.

 

Every blender I have seen has 4 ports and does not have a removable actuator with an M30 thread.  So I am now at a complete loss to know where you would put one of these Salus proportional actuators.

[Jeremy Harris]

17 minutes ago, ProDave said:

Nope totally confused. Diagram needed.

 

Every blender I have seen has 4 ports and does not have a removable actuator with an M30 thread.  So I am now at a complete loss to know where you would put one of these Salus proportional actuators.

 

 

This is the thermostatic valve and hot feed into the UFH manifold:

 

 

Hot water from the ASHP/buffer comes in at the bottom of that valve.  Temperature controlled water comes out of the right hand arm.  The tee where the pump connects is key, as that causes the pump to be able to recirculate return water (coming from the return manifold at the lower right).  The output from the pump is at the top, and only feeds the flow manifold.  The temperature sensor for the thermostatic valve is in a  pocket inside the end of the flow manifold.

 

The Salus actuators just fit where normal actuators fit, each with a flow and return sensor clipped to the UFH pipes.

 

[ProDave]

Ah, so this will only work on some manifolds.

 

Here is mine (before being piped and wired)

 

 

The blending valve does not have a removable head, so I could not replace it with the Salus unit.