Critique this UFH design, please

[HughF]

I'm casually casting an eye over my builder/friends UFH plans for his barn conversion, he asked me for my input. Just thought I'd ask for some critique from the BH experience, if you could please.

 

The plan is 16mm alpex/alpert stapled down to 150PIR, with 125mm conc covering. Heat generator will be an ASHP (not yet decided which one, but probably one that supports room temperature optimisation/adaption from the manufacturers controls). A buffer will almost certainly be required with this volume of pipe, I doubt the ASHP pump will handle pumping through this length and through two manifolds.

 

My gut feeling is: Too many room stats, the rest looks good...

 

Thoughts?

 

65108-00-P1-redact.pdf

Edited October 18, 2022 by HughF

[Adsibob]

If there are 7 thermostats, one for each room, I think that's okay. We have 12 in my house and I'm really happy with that number. We even have two in one large open plan area, to divide the room into two zones: the kitchen, which has a lot of west facing glazing and the lounge area which has no glazing but is right by a wood burner. Although all one open plan area, zoning those two separately has worked well.

[jayc89]

I really don't get the need for so many stats. We started off with 3 downstairs and I've recently reverted back to a single stat. The entire ground floor now heats up pretty evenly and over the last few days our upstairs radiators haven't come on at all. 

This is all in a 1850's house that currently leaks air like a sieve. 

[JohnMo]

Sorry not really agreeing.

 

Areas referred to as zones are loops not zones.

 

T5A, 6A and 7A, operate as a single zone, from a single thermostat they will be the same temperature even if you don't want them to be.  Do this as a wireless thermostat so you can position where it reflects the temp you want best.

 

But ideally thermostats should be limit stops on temperature, not temperature control.  They are set 1 or 2 degrees higher than your ideal temp.  Flow temp settings balancing is used to achieve the room temp.

 

So basically you operate as a single zone to ensure your min flow requirements of the ASHP always met or exceeded.

 

In a 150mm concrete/ screed room internal optimisation will not work, system inertia will be too slow, heating will chase it's self, temps will be all over the place.  You could do weather compensation as long as works on a 24hr rolling average outside temperature.

 

With that much pipe in the floor I doubt you will need a buffer, if the ASHP is sized correctly.  A buffer is used to mitigate too little flow not too much.

[Adsibob]

17 minutes ago, jayc89 said:

This is all in a 1850's house that currently leaks air like a sieve. 

That explains your query. In a fully airtight and insulated house, Solar gain is much more likely to make a difference to ambient temperature, and so rooms on one side of the house might vary by 1.5C to 2C to rooms on the other side of the house. In the depths of winter, you might just switch everything on and treat the whole floor like one zone, but in the shoulder months, it’s likely you would only want heat in the colder rooms. Hence, multiple stats can save money, but most likely only in an airtight and insulated house.

[jayc89]

7 minutes ago, Adsibob said:

That explains your query. In a fully airtight and insulated house, Solar gain is much more likely to make a difference to ambient temperature, and so rooms on one side of the house might vary by 1.5C to 2C to rooms on the other side of the house. In the depths of winter, you might just switch everything on and treat the whole floor like one zone, but in the shoulder months, it’s likely you would only want heat in the colder rooms. Hence, multiple stats can save money, but most likely only in an airtight and insulated house.

 

I'm fairly sure I've read users on here, in new builds built to PassivHaus standards, or near to it, are also running a single stat. I could be wrong?

[HughF]

18 minutes ago, JohnMo said:

Sorry not really agreeing.

 

Areas referred to as zones are loops not zones.

 

T5A, 6A and 7A, operate as a single zone, from a single thermostat they will be the same temperature even if you don't want them to be.  Do this as a wireless thermostat so you can position where it reflects the temp you want best.

 

But ideally thermostats should be limit stops on temperature, not temperature control.  They are set 1 or 2 degrees higher than your ideal temp.  Flow temp settings balancing is used to achieve the room temp.

 

So basically you operate as a single zone to ensure your min flow requirements of the ASHP always met or exceeded.

 

In a 150mm concrete/ screed room internal optimisation will not work, system inertia will be too slow, heating will chase it's self, temps will be all over the place.  You could do weather compensation as long as works on a 24hr rolling average outside temperature.

 

With that much pipe in the floor I doubt you will need a buffer, if the ASHP is sized correctly.  A buffer is used to mitigate too little flow not too much.

You’d need some sort of hydraulic separation I would have thought, given that there are two manifolds in this job, each with pumps. Can’t have pumps in series with the ashp pump so you need some sort of separation, either a buffer or an llh.

 

What I mean by internal optimisation was a controller that has some idea of the internal room temp, if one were to use the wall stats as hi-limit stats only and rely on the WC (which is the best way, obvs). Internal optimisation could/should figure the curves out for you.

 

If it was me I’d just have hi-limit stats in the bedrooms and leave the rest of the system on an on/off switch 🤣 Let the WC sort the temps out.

 

Any issue with the pipe spacing or loop lengths?

[Adsibob]

8 minutes ago, jayc89 said:

 

I'm fairly sure I've read users on here, in new builds built to PassivHaus standards, or near to it, are also running a single stat. I could be wrong?

Well my house is not passive, or anywhere close, but it is airtight and fairly well insulated for a building that is almost 100 years old. The multiple stats work well for us. We have hardly put the heat on this year, but when we have it is usually only in one or two of our multiple zones. I spent over £1000 on 12 smart thermostats and I don’t regret it. But each to their own.

[JohnMo]

I found with a thick concrete floor screed, 100mm plus thick, that my heating runs with around 6 hour delay. So much so that nighttime setback starts at 1730 and finishes at 0130.

 

I am running with a flow temp at the moment of about 23 to 26 and have 300mm UFH pipe spacing.

 

Could you operate the two manifolds as a single manifold with a suitable sized single pump.  Have a temperature mixing valve upstream (more as an insurance policy, to limit max temp) 

26 minutes ago, HughF said:

If it was me I’d just have hi-limit stats in the bedrooms and leave the rest of the system on an on/off switch 🤣 Let the WC sort the temps out.

This basically how mine is running.

 

For me there is way to much pipe in the floor, but seems to what people like to do.  (I did 300mm centres, so have 400m in 192m2 on 7 loops), have no dedicated loops in halls, but all room loops go through the hall so I just spread them out throughout the floor. But this will depend on heat load required, to some extent.

 

Don't like pipes under walls , to easy for a numpty to put a drill through a pipe.

[PeterW]

Bed 1 should be it’s own zone / loop 

ES should be it’s own zone / loop

Zone 6 needs to be hallway only not 10% of the kitchen

The big open plan needs sorting once the others are done - but it’s a single zone for TS purposes. I would even push them to 120m loops

Pipework needs coming out from under the baths and the WCs

Manifold is in an odd place -  is it possible to move ..?

 

[dpmiller]

I've been doing a bit of monitoring of recent days and find that our system (65mm of hemihydrate, pipes on roughly 200mm centres, 8.5kW ASHP vs worst-case loss of between 2.6 and 4kW) gives a useable floor temp rise in about 90 mins that takes about 4hrs to dissipate

eg

/testo 184 logger sitting on the screed surface. Ignoring the first drop as I'd been holding it in my hand, the small peak was to satisfy the hall to 19.5C in the evening, the larger one bringing it again to 19C in the morning after a frosty overnight.

 

[JohnMo]

I take it your flow temps are quite high, looks like you could reduce and get a gain in CoP?

[dpmiller]

7 minutes ago, JohnMo said:

I take it your flow temps are quite high, looks like you could reduce and get a gain in CoP?

I could, other than I'm currently controlling on the return temperature to give meaningful heat to a second manifold with oversized rads and towel rails on it. The system is currently running at a DeltaT of 7C and a return of 38C so there's 45C or so available to each manifold, but that drops a fair bit once the manifolds warm plus the flow runs through the TS coil continuously to buffer it. This is our first winter in the house so I'll be trying to bring things down a touch, yes.

[HughF]

2 minutes ago, dpmiller said:

I could, other than I'm currently controlling on the return temperature to give meaningful heat to a second manifold with oversized rads and towel rails on it. The system is currently running at a DeltaT of 7C and a return of 38C so there's 45C or so available to each manifold, but that drops a fair bit once the manifolds warm plus the flow runs through the TS coil continuously to buffer it. This is our first winter in the house so I'll be trying to bring things down a touch, yes.

I take it you clipped the 'buffer temp' sensor onto the return line? Still not sure where to put mine, as I'm trying to run without a buffer or a LLH

Edited October 18, 2022 by HughF

[dpmiller]

5 minutes ago, HughF said:

I take it you clipped the 'buffer temp' sensor onto the return line? Still not sure where to put mine, as I'm trying to run without a buffer or a LLH

Yes

 

then you can choose to control on the unit's internal flow sensor or the buffer "return" one

[HughF]

1 minute ago, dpmiller said:

Yes

 

then you can choose to control on the unit's internal flow sensor or the buffer "return" one

The more I read up about the iVT-9, the more I'm impressed by that Carel pCO controller that's inside, seems like a very adaptable unit.

[dpmiller]

2 minutes ago, HughF said:

The more I read up about the iVT-9, the more I'm impressed by that Carel pCO controller that's inside, seems like a very adaptable unit.

Yes, if you can get past some dodgy chenglish terminology, it's a very competent controller. You don't find this kinda kit inside every supermarket freezer for no reaason...

 

What amazes me is just how tuned the whole system is to the compressor and gas combo.

[HughF]

10 minutes ago, dpmiller said:

Yes, if you can get past some dodgy chenglish terminology, it's a very competent controller. You don't find this kinda kit inside every supermarket freezer for no reaason...

 

What amazes me is just how tuned the whole system is to the compressor and gas combo.

I've been trying to get my head around the Carel cSuite software for programming these controllers, and it's a mighty clever beast of a development environment. It's built on full-fat visual studio with a graphical core for building refrigeration control applications. Quite a powerful bit of software.

 

I believe they have pre-defined and tested 'applications' that you can drop into the controller and these are tuned to gas and compressor combinations. They've clearly spent a long time working on it.

 

[Olf]

4 hours ago, HughF said:

Thoughts?

Another autogenerated layout that makes little practical sense, but takes the company no time to make (and increases bill of materials, extra win)

They did not even bother to mask out under toilets/bath!

If that was my barn:

- hall/utility and corridor warmed by this bunch of pipes going elsewhere, especially ends of return legs. Does plant room really need heating? If yes, just skimp on pipes insulation there.

- living area - one concentric loop: maybe closer to 200m length, but due to lack of U turns less flow resistance than current 3 loops . Way easier to lay and more uniform heat delivery

- the same with kitchen/diner - lov(th)e the dendrites surrounding the kitchen island on the 'project'. I hope the fridge/freezer is built in, otherwise will be cooked from underneath.

- bedrooms - I'd run serpentine across the room, so the most heat is delivered in never obstructed traffic areas. Possibly even U shaped circit, with nothing under the bed (at the windows)- as little heat will travel up anyway as shielded by the bed. But that is a bit personal, dependant on comfort night tempreature (though U shaped circuit with reduced pipe spacing will match output of what's on that sketch and will be more efficient - less losses downwards)

[JohnMo]

My layout, for comparison, managed to find a photo, similar layout of house (single storey) and floor area from the looks of it.  But 200mm PIR in floor instead of 150mm.

 

Bathroom, hall by front door and kitchen diner on a single loop around 100m long.

Lounge 2 loops each 100m long ish.

Bedrooms single loop each.

Master bedroom ensuite single loop, pretty short.  Circa 12 l/min flow rate.

 

[Adsibob]

2 hours ago, JohnMo said:

Master bedroom ensuite single loop

My only issue would be with this. But that's personal preference; i like my bedroom to be cool whereas I like my bathroom to be warm.

[JohnMo]

15 minutes ago, Adsibob said:

My only issue would be with this. But that's personal preference; i like my bedroom to be cool whereas I like my bathroom to be warm.

I totally agree.

 

Sorry obviously I wasn't clear - the Master bedroom is on its own loop.  Master bedroom ES on a separate loop.  For the reason you state.

[HughF]

Thanks everyone for your valuable input. It is appreciated.

[HughF]

Well, the pipe is down and we blew it up to 5bar with the compressor... I was mistaken, single manifold was used.

 

They removed the loops from under the stairs, under the baths/toilets. 16mm pex stapled down, 100mm concrete going over the top on Saturday. 19m3 pour.