UFH balancing and understanding how it works

[peredelkin]

Hello all.

 

I have a relatively new UFH system that runs with a gas-fired boiler. I have two manifolds (one per floor), both fitted with mixing valves that are set to 40C, and Grundfos circulation pumps. Thermostats are heatmisers with UH8-RF wiring centres by the manifolds. When the system was commissioned, the flow rates were set very high (3-4 l/m), which meant that the rooms would heat up very quickly and then cool down as quickly. I have also recently insulated the house with external wall insulation and I am very happy with the way the house feels much warmer now.

 

When the recent cold spell started, I noticed that when a certain zone is "running", the room feels nice and warm, while when it is not running, the room feels colder. This is regardless of the actual room temperature, which makes sense due to the fact that when the zone is not on your skin stops feeling radiant heat.

 

I normally have an overnight set point of 18C in most rooms, which changes to 20C at 6am with the idea to get a comfortable temperature by 8am. Playing around with flow rates, I set them to 1.5 l/m, and lo and behold, at 8.30am the temperature would still be 19.5C but it would feel nice and warm due to radiant heat. Bingo! However, with that setting, at around 11am the room would reach 20C, and the loop would turn off. Fast forward a few hours, at 2-3pm the rooms start "feeling" cold even if the temperature is still 20.1-20.2C.

 

This doesn't seem right to me. In my head, water in the loops should be always circulating, and the temperature should be kept around 20C by some smart controller that should measure flow and return temperatures of each zone, while thermostats would keep the zones "around" 20C all the time. All these components are on/off (thermostats, Grundfos pump, manifold mixer, actuator valves), while ideally they should auto-adjust in a smooth manner depending on measured temperature from the thermostats.

 

Questions:

1. Is there really no such system?
2. If there isn't, what's the best combination of settings with my existing setup to get to a constant "glow" of warmth in my house?
3. Am I doing this wrong by letting overnight temperatures drop to 18C? Should I maybe keep the rooms always at 20C and play around with flow rates so that the thermostat is "on" all the time? Should I aim for a flow rate that's so slow that the water is kept circulating all the time and the thermostats never "reach" their intended temperature?
4. Would perhaps fitting Salus thb23030 actuators help? (Any idea when the thb23031 may come out?)
5. What's the relationship between flow rates and "perceived" temperatures in the house?

 

Thank you!

[Fly100]

Couple of checks to do 1st. you say you have set it a 40c check the temp on the manifolds. My stat adjuster was set a 40c and flowing at 20c, just unscrew the screw in the centre of the knob and move it on the splines so the actual temp matches the displayed temp.

I had multiple issues with flow rates and over temps etc, setting flow rates on one day was great but no good a week later. I bought those Salus auto adjustment acctuators and they solved it.

Just to note , and happy to be corrected here, my understanding is they open fully at the start and only when to flow and return reaches 10c diff do they start to slow the flow rates down to above 7c difference.

[crooksey]

What do you have as a floor screed? Gypsum/Anhydrite based screeds or ones overlaid with wood can warm up quickly, but not retain much heat, giving the feeling you describe above.

 

However sand and cement or thicker cement based liquid screeds retain the heat for much longer, acting as an all day thermal store and can be harder to tell when the UFH is on, unless you stone/tiles/bonded LVT etc.

 

[Lofty718]

This is the issue with poorly controlled UFH, on on/off controls. UFH is best installed open loop and with an electronic mixing valve on weather compensation rather than the old tech mixing valve at the manifold receiving high temperature from the boiler and trying to blend it down.

 

Also what speed is your pump on? some installers leave it on too high. Fiddle around with the flow rates on the manifold start by giving less flow to the smaller loops and see how it reacts

 

 

Edited December 5, 2023 by Lofty718

[peredelkin]

Thank you all for your kind replies.

 

On 04/12/2023 at 10:06, Fly100 said:

Couple of checks to do 1st. you say you have set it a 40c check the temp on the manifolds. My stat adjuster was set a 40c and flowing at 20c, just unscrew the screw in the centre of the knob and move it on the splines so the actual temp matches the displayed temp.

I had multiple issues with flow rates and over temps etc, setting flow rates on one day was great but no good a week later. I bought those Salus auto adjustment acctuators and they solved it.

Just to note , and happy to be corrected here, my understanding is they open fully at the start and only when to flow and return reaches 10c diff do they start to slow the flow rates down to above 7c difference.

The temp is actually 40C according to the thermometer that is fitted to the "hot" side of the manifold . But good shout, I thought as much initially.

Agreed, setting flow rates one day doesn't work the next day. I think a lot of it is down to weather compensation issues anyway.

I will check out the Salus actuators... Shame that they're not making it too clear when they're releasing the Ultra THB's. I don't want to be buying 9 new actuators and then in 1 month's time...

I tried emailing Salus sales but 3 weeks have gone and I have not heard back. Does anybody have any idea who I could ask about the Ultra THBs?

 

On 05/12/2023 at 10:46, crooksey said:

What do you have as a floor screed? Gypsum/Anhydrite based screeds or ones overlaid with wood can warm up quickly, but not retain much heat, giving the feeling you describe above.

 

However sand and cement or thicker cement based liquid screeds retain the heat for much longer, acting as an all day thermal store and can be harder to tell when the UFH is on, unless you stone/tiles/bonded LVT etc.

I have an engineered wood floor over foiled polysyrene, on a floating wood floor. Nothing that I could do about that as the house is 1930s.

 

However I also have EPS insulation and since I've had that fitted, I have been VERY happy about heat retention of the house. It makes such a huge difference!

 

On 05/12/2023 at 10:52, Lofty718 said:

This is the issue with poorly controlled UFH, on on/off controls. UFH is best installed open loop and with an electronic mixing valve on weather compensation rather than the old tech mixing valve at the manifold receiving high temperature from the boiler and trying to blend it down.

 

Also what speed is your pump on? some installers leave it on too high. Fiddle around with the flow rates on the manifold start by giving less flow to the smaller loops and see how it reacts

 

The pump is on 2/3 lights. 1/3 lights is too weak when all loops are on.

 

How would I convert my system to open loop? And would that even make sense taking into account that different rooms do require different heat outputs in my house? I am end of terrace, so naturally the rooms that have 2 walls exposed will need more heating output than those that have only 1 wall exposed...

[JohnMo]

WC and a normal manifold mixer is a waste of time, been there spent a year recording and messing with things. The mixer works against you all the time. The only way to get a mixer to work with WC is via an electric mixer.

 

Salus self balancing actuators are pretty good, I have my UFH as a single zone but use the actuators on a few loops. I am also using an electronic mixer, set to 28 deg. The heat pump modulates on/off on low load. So the temp going to the mixer also varies. When the flow temp goes below 28 deg, you notice the Salus actuator starts to open and increase the flow to that loop, once the heat pump starts again, it closes in the flow, back to where you expect it to be. It's basically doing a good job of evening out the energy flowing into the floor by varying dT.

 

To convert to open loop you can do it two ways

1. Set your thermostat to say 24, so loops stay open - good first step while you balance system 

2. Remove all actuators and fit manual valves

3. Install a jumper on wiring centre instead of thermostat.

[JohnMo]

 

10 hours ago, peredelkin said:

Ultra THB'

Just had a look at them, would not bother waiting if you want to buy. Basic benefits are spring action closing mechanism, and don't need to be calibrated. Calibration occurs during the first 40 mins of being powered up for the first time, so no real advantage after that.

[crooksey]

14 hours ago, peredelkin said:

Thank you all for your kind replies.

 

 

I have an engineered wood floor over foiled polysyrene, on a floating wood floor. Nothing that I could do about that as the house is 1930s.

However I also have EPS insulation and since I've had that fitted, I have been VERY happy about heat retention of the house. It makes such a huge difference!

 

 

You have nothing to retain the heat then. So once you switch it off, the heat just dissipates into the air. Thats why in most specified UFH installs you have a screed to encapsulate the heat and retain it once the UFH is switched off. Would explain exactly why it does not feel warm when the heating goes off as you have no thermal mass to store the generated heated

[peredelkin]

5 hours ago, JohnMo said:

WC and a normal manifold mixer is a waste of time, been there spent a year recording and messing with things. The mixer works against you all the time. The only way to get a mixer to work with WC is via an electric mixer.

What do you mean by "works against you"?

 

5 hours ago, JohnMo said:

Salus self balancing actuators are pretty good, I have my UFH as a single zone but use the actuators on a few loops. I am also using an electronic mixer, set to 28 deg. The heat pump modulates on/off on low load. So the temp going to the mixer also varies. When the flow temp goes below 28 deg, you notice the Salus actuator starts to open and increase the flow to that loop, once the heat pump starts again, it closes in the flow, back to where you expect it to be. It's basically doing a good job of evening out the energy flowing into the floor by varying dT.

Right, but then how are you going to manage the room temperature if you can't control the floor temperature or the flow speed (as the Salus does it for you)?

 

1 hour ago, crooksey said:

You have nothing to retain the heat then. So once you switch it off, the heat just dissipates into the air. Thats why in most specified UFH installs you have a screed to encapsulate the heat and retain it once the UFH is switched off. Would explain exactly why it does not feel warm when the heating goes off as you have no thermal mass to store the generated heated

Is there anything that could have been done with a suspended floor? Because my understanding is that you can't put a screed...

[crooksey]

With a suspended floor you can have overlay systems that use a self levelling compoud to encapsulate the pipes to create some form of thermal mass, but its basic physics. If you dont have anything to store the heat, the room will feel cold quickly, much like a well insulated house with radiators, as soon as they turn off it feels noticeably colder, but not necessarily "cold". 

 

A 1930's house I imagine is nowhere near "air tight" standards, so you are probably losing a lot of generated heat to small draughts.

[JohnMo]

24 minutes ago, peredelkin said:

What do you mean by "works against you"?

A normal UFH mixer will always mix a proportion of the return water in with supply hot water.  So the WC curve never works correctly. An electronic mixer can be operated on WC or if you set to 36 degs and water based on a WC curve is only 30bit will go fully open and flow 30 no more no less.

 

29 minutes ago, peredelkin said:

Right, but then how are you going to manage the room temperature if you can't control the floor temperature or the flow speed (as the Salus does it for you)?

It becomes to degree self balancing.  Salus actuator is trying to manage dT at a set point. If the room gets warmer the dT between floor and room reduces, so less heat is transferred to room, and therefore less energy taken from UFH water within the pipes. This is seemingly working at the moment. As a backstop, have set a second set point on the mixer so if house temp drops to 19.9 degs it then controls at 32 degs.

[peredelkin]

1 hour ago, crooksey said:

A 1930's house I imagine is nowhere near "air tight" standards, so you are probably losing a lot of generated heat to small draughts.

The house is very well insulated. The suspended ground floor has Kingspan between the joists, I have loft insulation and I have 90mm EPS on the external walls. Windows are new and triple-glazed. There aren't any draughts...

 

42 minutes ago, JohnMo said:

A normal UFH mixer will always mix a proportion of the return water in with supply hot water.  So the WC curve never works correctly. An electronic mixer can be operated on WC or if you set to 36 degs and water based on a WC curve is only 30bit will go fully open and flow 30 no more no less.

When you say WC "curve", what do you mean? My Heatmiser wiring centre has three types of outputs to control the manifold: valve, pump, and actuator(s). All of which are on/off. What curve are we talking about?

 

45 minutes ago, JohnMo said:

It becomes to degree self balancing.  Salus actuator is trying to manage dT at a set point. If the room gets warmer the dT between floor and room reduces, so less heat is transferred to room, and therefore less energy taken from UFH water within the pipes. This is seemingly working at the moment. As a backstop, have set a second set point on the mixer so if house temp drops to 19.9 degs it then controls at 32 degs.

Right, but what's the set point in question? I see no way to control the set point on the Saluses.

[JohnMo]

16 minutes ago, peredelkin said:

When you say WC "curve", what do you mean?

Weather compensation is when a boiler modulates its flow temp based on outside temp. You are obviously running a set flow temperature so ignore my ramblings about weather compensation (WC)

 

18 minutes ago, peredelkin said:

Right, but what's the set point in question? I see no way to control the set point on the Saluses.

Salus self balancing actuators function by reading flow and return temperature from the floor loops. They have a temperature detector on either end of each pipe loop by the manifold. Below a flow temperature of 30 deg, they (Salus actuators) manage the flow to achieve a set point point 4 deg dT (Delta between flow and return), and over 30 degs they manage this as a 7 deg dT.

 

As more or less energy is taken from the floor (room temp change, solar gain etc) the dT will naturally fluctuate, the actuator will open and close to maintain it's internal dT set point.

[peredelkin]

Thank you all. I bought a Salus and will put it in place to see how that works out.

 

I do run a fixed flow temp, but that's just because the boiler doesn't have a heat store and is way too powerful to run this system (don't ask, I'm very annoyed about this). Question: can the manifold mixing valve be replaced easily with an electronic one? If so, have you got any recommendation for an electronic one that works well and can be controlled via an app?

[JohnMo]

ESBE do a range of controllers that go with their 3 port valves and actuators, not cheap, I bought all mine for peanuts off eBay. Mine is set up to run on pipe flow temp mode. It has two set points (T and T2) I trigger the two different temperatures via thermostat. On a call for heat (T2) I allow it flow up to 36 degs, once thermostat senses house up to temp (T) is set to 22, it moves the 3 port to full recycle and switches off the pump.

 

Early image without insulation.

 

 

With underfloor heating there is zero advantage having an App controlling anything, run time are too long. If you want to switch your heating on before you leave work, your going to cold all night.  

[peredelkin]

4 hours ago, JohnMo said:

ESBE do a range of controllers that go with their 3 port valves and actuators, not cheap, I bought all mine for peanuts off eBay. Mine is set up to run on pipe flow temp mode. It has two set points (T and T2) I trigger the two different temperatures via thermostat. On a call for heat (T2) I allow it flow up to 36 degs, once thermostat senses house up to temp (T) is set to 22, it moves the 3 port to full recycle and switches off the pump.

Interesting. So when the house is up to temp, you keep the pump running but switch off the mixer valve...? Is that something allowed by your ESBE controller or did you wire something custom to get this particular setup to work?

 

4 hours ago, JohnMo said:

With underfloor heating there is zero advantage having an App controlling anything, run time are too long. If you want to switch your heating on before you leave work, your going to cold all night.  

I want to control the mixer temp via an app because the mixer and manifold are in my loft and I don't want to go up and down my very steep loft ladder every time I want to change something. Nothing to do with switching the whole heating on/off.

[JohnMo]

27 minutes ago, peredelkin said:

Interesting. So when the house is up to temp, you keep the pump running but switch off the mixer valve...? Is that something allowed by your ESBE controller or did you wire something custom to get this particular setup to work?

Basically what happens the mixer closes (goes in to full recycle mode) and a microswitch in the actuator switches the pump off. All wired as ESBE recommend. If there is a heating demand the mixer moves to allow hot water into the system, the microswitch switches on the pump.

 

This is the remote controller, they either come as wired or wireless. You can change settings and see what the water temp is downstream of the mixer.

 

 

ESBE do lots of variation, with subtle differences.

[Lofty718]

Nice setup John, I also have an esbe mixer wired directly into my Vaillant wiring centre working on weather compensation. Best way to control UFH