How can I roughly calculate UFH output at given flow temps.

[SimonD]

1 hour ago, jimseng said:

This may be a stupid question but is it then impossible to balance the system so all rooms heat up to similar temperatures without the mixer valve control? Would one not be able to achieve something by having a manual mixing valve to balance between the GF and FF zones.

Like I say, I haven't had/used low flow temp heating before.

I thought the whole point nowadays was to treat the house as a single thermal envelope and not zone. Particularly for me as it is a new build rectangle with high insulation and high performance windows. There may be carpet on the first floor (eventually) but the target temp would be lower than ground floor.

 

Normally what you would do is design the heating system to do this naturally. Each room would have its ufh output designed for the specific heat load - this means you might have different pipe spacing etc.

 

The problem with a manual mixing valve is that it only works reliably with fixed flow temperatures, and many of them only really work well with high flow temperatures. They don't work well when you have modulation from the heat source that you will get with weather compensation.

Using an electronic mixer is not the same as zoning, because you are not cutting flow to the zone, think of it as a heat area instead. What you're doing is controlling the constant flow of heat to that area, appropriate to its heating requirements. So, for example, on a cold day you might need a flow of 45C but on a mild day, it might be as little as 27C, depending on the house heating co-efficient (W/K). Therefore the house is still being treated as a single thermal envelope.

 

The issue with target temperature is down to the floor buildup. If you have a buildup that has a higher TOG value, you need a higher flow temperature - and this may still be the case, even if your target room temperature is lower. None of us can answer this question because we know so little about the house design conditions.

 

The reason we're suggesting a mixed circuit as a possibility is because you already have the existing one in place and we don't know anything about its design other than it's at 150mm spacings. We also don't know about the proposed design for the FF - is it going to be using speader plates, or is it screed too? 

 

There are so many variables you need to consider and then put together your FF design that complements the existing GF, then you'll be able to decide whether you actually need to have a mixed circuit or not. 

 

I think the whole mixer circuit thing was suggested as the alternative to hydraulic separation, not as a dictate about your design. So at the moment, if you're going to attempt the design yourself, spend your time learning about the design and then complete that process, including reverse engineering your existing UFH installation and go from there. Don't spend your time right now worrying about mixers. That will come later.

Edited 17 hours ago by SimonD

[Nickfromwales]

2 hours ago, SimonD said:

The problem with a manual mixing valve is that it only works reliably with fixed flow temperatures, and many of them only really work well with high flow temperatures.

Not so with the Ivar sets. Totally different beasts, have you used these before?

 

2 hours ago, SimonD said:

So, for example, on a cold day you might need a flow of 45C but on a mild day, it might be as little as 27C, depending on the house heating co-efficient (W/K). Therefore the house is still being treated as a single thermal envelope.

How do you achieve disenable segregation of the GF and FF if there not two stats (and therefore 2 zones)? Not a stab btw, I'm still at school every day I'm concious.

 

3 hours ago, SimonD said:

None of us can answer this question because we know so little about the house design conditions.

This...

3 hours ago, SimonD said:

There are so many variables you need to consider and then put together your FF design that complements the existing GF, then you'll be able to decide whether you actually need to have a mixed circuit or not. 

....with this on top.

 

3 hours ago, SimonD said:

Don't spend your time right now worrying about mixers. That will come later.

When we know 'TOG' and anticipated floor coverings, plus the GF situation. Don't worry about it, but don't discount it quite yet, is my 2 cents.

 

It would be a bugger if you design for x floor coverings, and then cannot have anything else, ever, in its place for eg.

[jimseng]

Quote

the whole mixer circuit thing was suggested as the alternative to hydraulic separation, not as a dictate about your design. 

That's the thing with me, I take things quite literally. Anyway. I have time before we get to the FF. And we are approaching a different under floor heating company and this time I have a bit of hindsight and will know how to demand answers so they might be able to get the design right. But so far, I have been met, both by the ASHP supplier and the original UFH supplier with designs that seem over complicated and against the current open loop no zoning philosophy, and I have had to argue the case to simplify everything. 

But still, for me I am trying to work out how to calculate what heat output to expect from the UFH for each room and I haven't (or I have missed in this thread) those basics. The most basic bit I am missing is how to take the known length of the UFH loop, flow temp and flow rate and calculate the heat output. 

So for instance @SimonD's formula: Q (W/m²) = 8.92(Average Floor Surface Temperature - Room Temperature)^1.1  skips over the vital bit of what n m of  pipework at n centres laid on n mm insulation in n mm of screed can transfer at n flow temp and n flow rate. This assumes that 16mm OD plastic pipe is pretty much the same. I was hoping that would be a spreadsheet that would give me a good starting point. Is that a bonkers question? I'm not very good at explaining my own ignorance because my brain was put in upside down as a baby.

[SimonD]

8 hours ago, Nickfromwales said:

Not so with the Ivar sets. Totally different beasts, have you used these before?

 No, I haven't used the Ivar sets. It's good to know about these as a fallback - I'll investigate more!

 

8 hours ago, Nickfromwales said:

How do you achieve disenable segregation of the GF and FF if there not two stats (and therefore 2 zones)? Not a stab btw, I'm still at school every day I'm concious.

 

The weather compensation deals with it. The 'mixed' circuit just has different flow temperature parameters by setting min and maximum temperature in the controller and then this is adjusted as the whole house weather compensation does its magic. This has the advantage that the whole system remains open. But you can also set these things up to work based upon a set flow temperature with circuit always open, or with a room stat, or even have the circuit activated/deactivated based on the weather compensation curve or water temperature sensor.

[SimonD]

10 minutes ago, jimseng said:

So for instance @SimonD's formula: Q (W/m²) = 8.92(Average Floor Surface Temperature - Room Temperature)^1.1  skips over the vital bit of what n m of  pipework at n centres laid on n mm insulation in n mm of screed can transfer at n flow temp and n flow rate. This assumes that 16mm OD plastic pipe is pretty much the same. I was hoping that would be a spreadsheet that would give me a good starting point. Is that a bonkers question? I'm not very good at explaining my own ignorance because my brain was put in upside down as a baby.

 

No it doesn't skip over those bits of information, it provides you with the foundations for your design. Without it, you can't do any of the rest. The length of your pipework is actually irrelevant right now, that is just selected on the basis of pressure drop, not heat output. The heat output is given by the formula I provided. But in your design, you also need to know things like down losses, which is more involved than just knowing the thickness of your floor insulation because it depends on the proportion of external edges to floor area and the shape of the room. But it's not just down losses to the outside, it's also downloss in intermediate flooring because otherwise you can provide excess heat to the room downstair. And it's not just your floor downloss but the heat load of the room, which means you need your heat loss calculations. These will give you a required W/m2. Then you take the formula I gave you and you can calculated the average floor temperature and work back from there to determine mean water temperature and pipe spacing.

 

What I gave you was a suggestion of book that provides you with a very easy way to determine what you need with simple nomographs - all you need to know is your pipe spacing, which you have on GF and the heat load in W/m2 and then you can find your mean water temperature for that system - it includes a standard screed and a spreaderplate. Or you can do it the other way round by selecting your mean water temperature and knowing your W/m2 requirement, you can find the pipe spacing. All you need to do is spent 25-30 pounds on the book and use a ruler. However, this just gives you a basic guide.

 

You need to know your floor coverings why?

 

Take a screed floor fairly standard covered with ceramic tiles a mean water temperature of 30C and target room temperature of 20C. With 150mm spacings the output of that floor will be about 55.5W/m2 and average floor surface temperature will be about 25.3C. If you instead had hardwood flooring you're looking at an output of 33 W/m2 and an average floor surface temp of 23.3C. As mentioned above, in some instances a resistant floor cover may give rise to greate down losses in intermediate floors.

 

I work in the business and even though I have the industry guides to do the design so I can pull out the figures above, I still wouldn't sit down a do it myself because the UFH suppliers do the design for me and they have the software packages to do it. 

 

This is why you're not getting or finding a spreadsheet. 

 

[JohnMo]

1 hour ago, jimseng said:

But still, for me I am trying to work out how to calculate what heat output to expect from the UFH for each room and I haven't (or I have missed in this thread) those basics.

I posted the information you need, last night so you missed it.

 

1 hour ago, SimonD said:

No, I haven't used the Ivar sets. It's good to know about these as a fallback - I'll investigate more!

I used one, it's same in many respects to most mechanical UFH mixers it requires a minimum (always on) mixing, so there is always temperature distortion through the mixer. You try to regulate this with various internal adjustments but it's always there. 

 

1 hour ago, SimonD said:

weather compensation deals with it. The 'mixed' circuit just has different flow temperature parameters by setting min and maximum temperature in the controller and then this is adjusted as the whole house weather compensation does its magic

You're sounding like me.

[Nickfromwales]

4 minutes ago, JohnMo said:

I used one, it's same in many respects to most mechanical UFH mixers it requires a minimum (always on) mixing, so there is always temperature distortion through the mixer. You try to regulate this with various internal adjustments but it's always there. 

Not afaic. It works silently, and completely reliably down at 20 degrees C. No regular mechanical TMV can do this. Most shit the bed at 30 degrees, and whine or make noise, and really struggle to blend down.

[JohnMo]

46 minutes ago, Nickfromwales said:

Not afaic. It works silently, and completely reliably down at 20 degrees C. No regular mechanical TMV can do this. Most shit the bed at 30 degrees, and whine or make noise, and really struggle to blend down.

Didn't say it couldn't control well with silence - it can, but you still have flow temperature distortion. That's ok in a mixed system with a reasonable flow temp difference but not in one with only a couple of degrees. Electronic offer zero distortion if you want it, so radiator demand goes, electric mixer become an open piece of pipe.

[SimonD]

3 hours ago, JohnMo said:

I used one, it's same in many respects to most mechanical UFH mixers it requires a minimum (always on) mixing, so there is always temperature distortion through the mixer. You try to regulate this with various internal adjustments but it's always there. 

 

Ah, okay, I'll keep that in mind. Thanks.

 

3 hours ago, JohnMo said:

You're sounding like me.

 

🤣 What is the world coming to. I wonder if BH can cope...

[JohnMo]

21 minutes ago, SimonD said:

What is the world coming to. I wonder if BH can cope

We my break it - lets hope not