Mixer valve on 100% UFH install?

[Myatix]

Hi All,

I have an old gas condensation boiler and have a house with 100% UFH in a 10cm slab with 400mm of insulation under the slab.

Currently my UFH manifold uses a mixer valve to mix flow and return so the temperature isn’t too high flowing in to the floor.

This doesn’t seem to make sense to me as I don’t need high flow temperatures as I don’t have rads.

would it not make sense to have the boiler run at a much lower flow temperature (35-40C) and the remove then switch the mixer vale over so it doesn’t mix?

[jayc89]

1 hour ago, Myatix said:

Hi All,

I have an old gas condensation boiler and have a house with 100% UFH in a 10cm slab with 400mm of insulation under the slab.

Currently my UFH manifold uses a mixer valve to mix flow and return so the temperature isn’t too high flowing in to the floor.

This doesn’t seem to make sense to me as I don’t need high flow temperatures as I don’t have rads.

would it not make sense to have the boiler run at a much lower flow temperature (35-40C) and the remove then switch the mixer vale over so it doesn’t mix?

 

I have a similar set up. My plan is to install weather compensation on the boiler so the flow temp adjusts based on the outside temp and have my UFH mixer valve set to the highest the floor can accommodate (around 45c). So in the coldest depths of winter, the boiler will ramp up, but when you just need to take the chill off it will be running at a much lower temp.

 

You mentioned you're running an older boiler, so this might not be an option for you. Does the boiler also heat your hot water? If so, does that have a different temp setting? This might limit your options too. 

[JohnMo]

My boiler is currently kicking out out about 26 - 29 on weather compensation, but at the end of a firing the supply temperature does rise until the return temperature increase to a max about 5 degrees over the set point.

 

So at an extreme example you have a set temp of 45, you easily be supplying circa 50 deg to the floor.  Secondly you need a over temp protection devise to protect the floor.  The mixer valve supplies both these services, it limits supply temp and provides a layer of protection.  Plus it will cost to remove.

 

With that much insulation in the floor I would be surprised if you need 35-40 flow temps.  I had ours set to 30 for a day and the house got up about 26 degrees.

[ProDave]

I heat with an ASHP that can set a low flow temperature  I still have the mixing valve.  One reason being when the ASHP is heating DHW the water temperature may get up to 55 degrees.  When it changes over from DHW to floor heating, that slug of 55 degree water would go straight into the floor were it not for the mixing valves.

[Myatix]

Thanks for all the comments! 
according to the MCS Heat Loss Calculation the flow temp needs to be around 35-40 degrees but I should point out that I live in Denmark where we calculate the minimum temperature at -12 rather than -3 in the northern parts of the U.K.

 

I don’t think that a 55 degree surge of hot water would effect our floor as the thermal mass of a 100mm concrete slab would need that 55 degrees to run for at least an hour or more to have a significant impact. 
 

I do have a very old weather compensation unit on the boiler but it has been disconnected. My guess is that it didn’t work well or wasn’t commissioned properly.

 

we are planning on installing an ASHP in the near future but until then it would be nice to get the optimum efficiency out of the boiler without spending a huge amount on gas. Current gas prices in Denmark would mean an annual gas bill of £7000. 
 

On the mixer valve shown above I can adjust or completely stop the valve from mixing the flow and return by adjusting it with an Allan key.

 

Any advice or tips would be great fully received.
 

[Nickfromwales]

I'd be more concerned as to why the input group and the pump are completely the wrong way around?!?

The pump is pumping upwards, and the words IVAR are upside down, showing that the water that should be being 'sucked' through the input group is in fact being pushed backwards against it.

 

 

 

Like that.

[Nickfromwales]

Those setups can only be plumbed it as a left handed arrangement, whereas your plumber has gone against this for possible convenience of plumbing it in.....  

 

 

And the isolators ( red and blue valves ) should be between the rails and the mixing set, as per above image, eg so you don't have to drain down the loops to service the mixing valve etc or the pump and then risk getting unwanted trapped air getting into the rails / loops.

Edited November 1, 2022 by Nickfromwales

[Myatix]

Hi NickfromWales,

Thank you very much for that! I had never noticed that, but I think it’s fine! If you look at the flow direction on the pump it’s correct, the front of the pump has been turned 180 degrees but if you look at the image below you will see that the pump direction is correct. (See the arrow showing up the pump direction on the back of the pump).

I can see why the plumber mounted it that way, there is no space in the cupboard to mount it the other way up…

 

I also presume that is why he has moved the automatic bleed valve?

So there is no issue there! But thanks anyway!

 

Edited November 1, 2022 by Myatix
Correct text and add details

[ProDave]

38 minutes ago, Myatix said:

Hi NickfromWales,

Thank you very much for that! I had never noticed that, but I think it’s fine! If you look at the flow direction on the pump it’s correct, the front of the pump has been turned 180 degrees but if you look at the image below you will see that the pump direction is correct. (See the arrow showing up the pump direction on the back of the pump).

I can see why the plumber mounted it that way, there is no space in the cupboard to mount it the other way up…

 

I also presume that is why he has moved the automatic bleed valve?

So there is no issue there! But thanks anyway!

 

Yes your plumber took the assembly as posted by @Nickfromwales a few posts above and rotated the complete assembly 180 degrees, so you now have the flow meters on the bottom and actuators on the top.  That should work okay.

 

What he has done wrong is put the isolating valves in the wrong place, that may make something like a pump change harder as you may get air in the pipe loops making bleeding harder than otherwise necessary.

[Myatix]

11 minutes ago, ProDave said:

Yes your plumber took the assembly as posted by @Nickfromwales a few posts above and rotated the complete assembly 180 degrees, so you now have the flow meters on the bottom and actuators on the top.  That should work okay.

 

What he has done wrong is put the isolating valves in the wrong place, that may make something like a pump change harder as you may get air in the pipe loops making bleeding harder than otherwise necessary.

Thanks for confirming its okay! 
Back to the original subject of the thread!

Should I change my mixer valve settings so it doesn’t mix and have the boiler run at a lower temperature to save money?

should I be using the weather compensation on the boiler? If so any tips on setting it up?

[JohnMo]

Leave the valve and pump, just do what I did to set mixer valve.

 

Use this spreadsheet to calculate your heat loss

 

 

Use sheet to calculate +20 and -20 heat loss, this will give you the heating curve, convert to W/m2 at the extreme ends.

 

Use this this sheet to calculate the flow temps at the the different outside temps from the W/m2.

 

[Myatix]

1 hour ago, JohnMo said:

Leave the valve and pump, just do what I did to set mixer valve.

 

Use this spreadsheet to calculate your heat loss

 

 

Use sheet to calculate +20 and -20 heat loss, this will give you the heating curve, convert to W/m2 at the extreme ends.

 

Use this this sheet to calculate the flow temps at the the different outside temps from the W/m2.

 

this looks very cool! I have already done my Heat Loss Calculation using the MSC Heat Loss calculation spreadsheet and the w/m2 came out at 38w/m2. This is on the generous side. The issue is it’s very difficult and in accurate to calculate the flow temperatures if the mixer valve is mixing the return cold water with the calculated Flow temperature. This means that the actual flow temperature going through the ufh loops is lower than the boiler flow temperature as it gets mixed before flowing through the floor circuits???

 

This was the main reason for me asking about the mixer valve as it seems to be a waste of energy to mix cold return water with hotter flow temperature than you need because the mixer valve is cooling it down prior to flowing around the floor???

[JohnMo]

Just get an infrared temperature gun, and adjust the mixer so inlet flow and the supply header temperature are the same.  Seemed to work ok for me.

[Myatix]

Also at what point does it make sense to measure the DT? Is it when the heating has been on for 20 hours or when you just turn on the heating? Presumably this depends on the thermal mass of the floor and how long it takes to get up to temperature? 
 

[Myatix]

2 minutes ago, JohnMo said:

Just get an infrared temperature gun, and adjust the mixer so inlet flow and the supply header temperature are the same.  Seemed to work ok for me.

Okay I actually tried with an infrared thermostat and it gave stupid readings. I then purchased a testo pipe thermostat and the flow temperature was about 10 degrees different to the infrared gun stat I initially used. Great if it worked for you but my infrared stat was miles out and I think I am much more likely to trust a calibrated Testo pipe thermostat.

 

[Myatix]

Here are the details from my MCS Heat Loss Calc and the UFH Design details. I have also included in the flow rates (l/m) to set the flow rates

 

Now I need to optimise the manifold and flow temperatures at the boiler but this is were it gets tricky. Because I can set a flow temperature of 35 degrees from the boiler but the actual flow temperature at the actuator is about 24 degrees and 23 degrees on the return. My guess is that this is because of the mixer valve. 

[dpmiller]

what were you pointing the IR gun at? the shiny manifold would give false readings

[Myatix]

8 hours ago, dpmiller said:

what were you pointing the IR gun at? the shiny manifold would give false readings

Exactly! You can’t use an IR gun to get an accurate flow and return on a heating system 

[dpmiller]

19 minutes ago, Myatix said:

Exactly! You can’t use an IR gun to get an accurate flow and return on a heating system 

certainly you can, just don't point it at shiny things. A bit of duct tape or such  stuck on as a target is all that is required.

[Myatix]

6 hours ago, dpmiller said:

certainly you can, just don't point it at shiny things. A bit of duct tape or such  stuck on as a target is all that is required.

it depends on the IR gun! Most ir guns take an average reading from a set area depending on the distance from the pipe and the ir guns I have used tend to take an average reading from a minimum of a 40mm area which means that they also include the temperature of the surface of the area behind the pipe. It’s not just the red dot that is the point of measurement.

anyway this is not what this thread is about!

[JohnMo]

The nearer you get the smaller the cone gets.  I used white masking tape also.  But if you have a calibrated thermometer even better.

[Nickfromwales]

45 minutes ago, Myatix said:

anyway this is not what this thread is about!

Indeed. 
So, do NOT remove the mixing set, as that is there for failsafe at the very least and it is a bad idea to remove this and then rely solely on the heat source to deliver safe and reliable flow into the floor.

 

Also, your pump being upside down is not great. Look at the manufactures installation guide and that setup has a big ❌ against it as it will cause the pump to wear out prematurely.

The plumber detached the pump head and rotated it 180° to make it look right, clearly demonstrating that they knew it wasn’t done properly. 

[Nickfromwales]

@PeterW

 

I used the ° symbol 😇. “I’m a real boy now!”  

[PeterW]

@Nickfromwales are you now …..? 
 

[Myatix]

5 hours ago, Nickfromwales said:

Indeed. 
So, do NOT remove the mixing set, as that is there for failsafe at the very least and it is a bad idea to remove this and then rely solely on the heat source to deliver safe and reliable flow into the floor.

 

Also, your pump being upside down is not great. Look at the manufactures installation guide and that setup has a big ❌ against it as it will cause the pump to wear out prematurely.

The plumber detached the pump head and rotated it 180° to make it look right, clearly demonstrating that they knew it wasn’t done properly. 

@NickfromwalesCan you please share the installation guide you are referring to with the big ❌. Thanks for the input!