Heating system for an ICF house with UFH

[ProDave]

Reading this thread is only serving to show that a gas boiler is not the best mate for under floor heating.  I know conventional wisdom says if you have mains gas, use it as it is the cheapest form of heat.

 

For low temperature under floor heating, an ASHP makes a much better companion.  My own system is about as keep it simple as you can get. the ASHP drives the UFH directly, no buffer, and a small 5KW ASHP will happily supply water at 37 degrees and modulate down to very low levels to maintain that, and running at low temperatures like that gives good efficiency from a heat pump.

 

I still think there is merit in individual room thermostats.  We only have 3 heating zones, the big kitchen / diner space, the living room and (not yet fitted) the utility room.  All loops are fed from the same temperature water from the same manifold and pretty much the same flow rates to each loop, but the kitchen / diner is the last room to reach temperature and shut off.  That is simply because so much of that room does not have UFH e.g not under kitchen units or the island, not under the stove, and not under the corner of the room that will eventually be the pantry. So probably 1/4 of that room does not have heating pipes under it, so it is now wonder it takes a little longer than the other room to heat up. 

 

I have used the dry biscuit mix screed as the heat spreader medium under our wooden floors downstairs and am very happy with it.  Upstairs, just in the bathrooms I have UFH with spreader plates and this does not seem as effective to me, but then again the heat has to get through the wooden floor, the wet room tanking membrane then the tiles so it is probably no wonder we get less effective heating there.

 

Lastly with the level of insulation you will have, you WILL need separate control for the bedrooms, much of the time they won't need any heat at all, we don't have bedroom heating, but you can achieve that by just valving off the upstairs manifold as a single zone if you don't want individual room control.

[Nelliekins]

3 minutes ago, ProDave said:

Upstairs, just in the bathrooms I have UFH with spreader plates and this does not seem as effective to me

 

The big difference here is that you don't appear to be keeping everywhere at the same temp 24/7. You are using zoning and there are times when you have rooms that aren't up to temp... 

 

Our desired approach (I think) is to have everywhere at the same temp constantly, which means there are only VERY infrequent times when we are present that anywhere is noticeably having to heat up (maybe twice a year, if we turn the system down - but still not off - whilst on holiday). 

[ProDave]

3 minutes ago, Nelliekins said:

 

The big difference here is that you don't appear to be keeping everywhere at the same temp 24/7. You are using zoning and there are times when you have rooms that aren't up to temp... 

 

Our desired approach (I think) is to have everywhere at the same temp constantly, which means there are only VERY infrequent times when we are present that anywhere is noticeably having to heat up (maybe twice a year, if we turn the system down - but still not off - whilst on holiday). 

I am only "not keeping the same temp 24/7" in so far as I turn the heating off overnight as I want a completely silent house at night (I still have an issue with noise from one of the UFH circulating pumps pending swapping it for a better pump)

 

The house is so well insulated that the overnight temperature does not drop much, certainly not enough for it to feel cold in the morning but most mornings the heating will come on to top up each room back to it's target.

[Jeremy Harris]

6 minutes ago, Nelliekins said:

Our desired approach (I think) is to have everywhere at the same temp constantly, which means there are only VERY infrequent times when we are present that anywhere is noticeably having to heat up (maybe twice a year, if we turn the system down - but still not off - whilst on holiday). 

 

If you are OK with having bedrooms at the same temperature as the living rooms, then that's fine, but we have found we prefer the bedrooms to be a few degrees cooler.  We have no heating at all in the bedrooms, so they end up at a temperature of around 18 to 19 deg C, when the living rooms beneath may be at 21.5 to 22 deg C.  Our bathrooms have heated towel rails and that seems fine for us. 

[Nelliekins]

36 minutes ago, PeterW said:

 

As a complete random thought, the other trick could to be to use a 3 port diverter valve on each manifold, when it was activated it would open the flow to the buffer, closed would be a “closed loop” so the pump can recirculate and even out the slab etc.... Hmm... ?.. that removes the need to try and balance a bypass valve, and these do have a habit of squealing under low pressure. 

 

Now see that's the kind of thinking I like. ?

 

I presume this would work using the original design of the buffer tank leeching heat via the coil from the DHW system, too. 

 

A question then - would this still facilitate distribution of solar gain heat from the kitchen to the entire house, or only the ground floor? I guess the answer is actually down to how well the valves are controlled in this situation. 

[Nelliekins]

Just now, JSHarris said:

 

If you are OK with having bedrooms at the same temperature as the living rooms, then that's fine, but we have found we prefer the bedrooms to be a few degrees cooler.  We have no heating at all in the bedrooms, so they end up at a temperature of around 18 to 19 deg C, when the living rooms beneath may be at 21.5 to 22 deg C.  Our bathrooms have heated towel rails and that seems fine for us. 

 

TBH we won't know until we are in the house with it heated. 

 

If that proves to be the case, @PeterW's idea of 3 port diverter valves on each manifold would allow us to achieve a lower upstairs temp too. 

 

As mentioned previously, my wife appears to be one of the alien characters from the TV show "V", so bedrooms at same temp might be the minimum I get away with! ?

 

[PeterW]

41 minutes ago, Nelliekins said:

 

Now see that's the kind of thinking I like. ?

 

I presume this would work using the original design of the buffer tank leeching heat via the coil from the DHW system, too. 

 

A question then - would this still facilitate distribution of solar gain heat from the kitchen to the entire house, or only the ground floor? I guess the answer is actually down to how well the valves are controlled in this situation. 

 

I think I / you need to draw this out as I’m still not sure where the connections are going. Can you get the KW rating for that coil ..?

 

I am just concerned that even on full chat, that 30kw boiler won’t kick enough high grade heat into the tank for a pair of showers plus the UFH but could be wrong ... 

 

Edited to add : the answer is no on the recirc of heat to other floors as the three way would be stopping recirc other than of the manifold it was supporting. 

 

Edited December 30, 2018 by PeterW

[Nelliekins]

13 minutes ago, PeterW said:

 

I think I / you need to draw this out as I’m still not sure where the connections are going. Can you get the KW rating for that coil ..?

  

I am just concerned that even on full chat, that 30kw boiler won’t kick enough high grade heat into the tank for a pair of showers plus the UFH but could be wrong ... 

 

Hi Peter.

 

I did most of this in the PDF included in the OP. Here's a better labeled PNG version... Please excuse the lack of correct symbol for the bypass valve! ?

 

 

FYI, the "DHW Cylinder" shown on both parts of the drawing are the same cylinder - the drawing was simply drawn as 2 separate diagrams to explain it to a mate!

 

I'll have to check re the coil capacity, but that coil only has to cope with (part of) the UFH load anyway. Regarding the boiler capacity, I would assume that since we are heating the DHW cylinder directly (ie not using the coil), we can get the full beans out of the boiler, i.e. 30kW give or take. I would expect 30kW to be more than enough to drive 2 showers, would you agree?

 

If the DHW cylinder only copes with with the DHW demand at peak but not the leeched UFH demand as well, it doesn't matter one jot. This is because a 15 minute hiatus for the UFH will have near-zero impact on the house or floor temperature anyway. It's no different than a combi boiler that can only do DHW or CH, but not both... but the fabric of the house and the "constant running" of the UFH heating system makes the effects of the switch from UFH to DHW undetectable to the occupants (I think!), because of the inherent/latent heat capacity of the fabric.

 

Remember also that if we used the same style of (el cheapo) cylinder for the UFH buffer tank, that too would have an immersion port if it were needed, which would be able to supplement / replace the leeching of heat from the DHW tank (and completely separate the 2 systems if that were desirable). That would also free up the DHW coil for uplift of the DHW incoming mains water, potentially (although I suspect there is then the risk that the cold mains gets heated well above 50C if left standing in the coil - so maybe that's a stupid idea, cos the TMV won't work!)

[PeterW]

You’re basically turning your boiler and tank into the same sort of setup that you get on an oil boiler here - a stored water combi. 

 

Putting aside the issue of filling loops and venting for a minute, I’m trying to come up with any downsides to not even bothering with the UFH buffer as the DHW tank is working as that anyway. 

 

Is the UFH pipe 16mm PEX..?? And it’s 2.2km long ...??! How many manifolds and loops ..?

[Nickfromwales]

So, to clarify, your cylinder has the 4 individual tappings as shown, plus the 2 for the coil ? 

[Nelliekins]

1 hour ago, PeterW said:

You’re basically turning your boiler and tank into the same sort of setup that you get on an oil boiler here - a stored water combi. 

 

Putting aside the issue of filling loops and venting for a minute, I’m trying to come up with any downsides to not even bothering with the UFH buffer as the DHW tank is working as that anyway. 

 

The biggest one I can see is that the flow into the manifolds would be too warm unless we get really lucky on a combination of flow rate and coil efficiency. By separating the two into their own cylinders i can have whatever temp I like in both at all times. 

 

1 hour ago, PeterW said:

Is the UFH pipe 16mm PEX..?? And it’s 2.2km long ...??! How many manifolds and loops ..?

 

It's 16mm PEX-Al-PEX, 2.2km over 3 manifolds and 28 loops. Basement manifold has 6 loops set in concrete. Ground floor manifold has 12 loops set in concrete. First floor has 10 loops set in EPS70 (sat in top of router'd 50mm panels) with 18mm chipboard going over. 

 

[PeterW]

Just now, Nelliekins said:

The biggest one I can see is that the flow into the manifolds would be too warm unless we get really lucky on a combination of flow rate and coil efficiency. By separating the two into their own cylinders i can have whatever temp I like in both at all times. 

 

Irrelevant - just set a blending valve to 38c and leave it alone. Just one off the coil will be fine. 

[Nelliekins]

48 minutes ago, Nickfromwales said:

So, to clarify, your cylinder has the 4 individual tappings as shown, plus the 2 for the coil ? 

 

No, it has 2 for coil, 2 for top/bottom heat/return and 1 for overflow. I would have to tee the bottom fitting (not the coil, obviously) or fit a new flanged fitting. 

[ProDave]

7 minutes ago, Nelliekins said:

It's 16mm PEX-Al-PEX, 2.2km over 3 manifolds and 28 loops. Basement manifold has 6 loops set in concrete. Ground floor manifold has 12 loops set in concrete. First floor has 10 loops set in EPS70 (sat in top of router'd 50mm panels) with 18mm chipboard going over. 

 

What's the size of this house?

 

That's an average of 78 metres per loop and a lot of loops.

 

My modest 147 square metre house has a total of 7 loops longest 70 metres but several MUCH shorter. A total of about 400M of pipe

 

I have "left out" heating loops from unwanted places like the hallway. My previous house I had a system designed by a "professional" that had 19 heating loops.  Some were just completely bonkers, like a heating loop for the landing that I don't think EVER turned on, it was a complete waste of pipe and effort.

[PeterW]

Ok - so you’ve got around 350 litres of water in that system, and would need an expansion vessel of ~40 litres to cope with the loops, but you could drop the pressure to 1 bar and it would be fine. 

 

If you are still planning on using that PHE setup then you’re going to need to be careful with the pump positions and also double check the boiler doesn’t have an internal pump also. 

 

Do you already have the flow switch ..?? BIG TIP - fit a non return valve before the switch and after you have tee’d off for any cold supplies - assume you’re also fitting a PRV..??

[Ed Davies]

Part of why I was so confused by earlier bits of this conversation is that the “DHW Cylinder” doesn't actually contain DHW; it just happens to be used to heat DHW (via the PHE) amongst other things. Much better to call it a (small) thermal store, I think.

[Nelliekins]

48 minutes ago, ProDave said:

What's the size of this house

It's a little under 300m2 across the 3 floors.

 

50 minutes ago, ProDave said:

 "left out" heating loops from unwanted places like the hallway. My previous house I had a system designed by a "professional" that had 19 heating loops.  Some were just completely bonkers, like a heating loop for the landing that I don't think EVER turned on, it was a complete waste of pipe and effort.

Yeah me too. There are 3 left out here:

 

- 1 kitchen loop because I ran 3 loops with longest being 103m length, instead of 4 with longest being 80m.

 

- 1 landing loop, because it already has 12 loops in the floor for the other parts of upstairs

 

- 1 laundry loop, ditto

 

53 minutes ago, PeterW said:

Ok - so you’ve got around 350 litres of water in that system, and would need an expansion vessel of ~40 litres to cope with the loops, but you could drop the pressure to 1 bar and it would be fine. 

 

Sounds good. 

 

53 minutes ago, PeterW said:

If you are still planning on using that PHE setup then you’re going to need to be careful with the pump positions and also double check the boiler doesn’t have an internal pump also. 

 

Will grab the manual when I go to site next and look at the servicing drawings to check about the boiler pump (or lack thereof) 

 

53 minutes ago, PeterW said:

Do you already have the flow switch ..?? BIG TIP - fit a non return valve before the switch and after you have tee’d off for any cold supplies - assume you’re also fitting a PRV..??

 

I don't have the flow switch yet - that's next on my list of purchases once I identify the correct model. 

 

I would indeed be fitting a PRV as mentioned way back near the top of the thread - it's not on the drawing yet though! 

 

13 minutes ago, Ed Davies said:

Part of why I was so confused by earlier bits of this conversation is that the “DHW Cylinder” doesn't actually contain DHW; it just happens to be used to heat DHW (via the PHE) amongst other things. Much better to call it a (small) thermal store, I think.

 

Yeah that's my bad. The plan was always to use the cylinder like a heat bank, and a PHE to provide mains pressure hot water. 

 

[PeterW]

14 minutes ago, Nelliekins said:

don't have the flow switch yet - that's next on my list of purchases once I identify the correct model. 

 

CPC sell them and if you ask @newhome nicely, she will probably drive 7 hours to get you the right one..... ?

[Nelliekins]

1 hour ago, PeterW said:

 

CPC sell them and if you ask @newhome nicely, she will probably drive 7 hours to get you the right one..... ?

 

Private joke? 

 

So something like this? 

[newhome]

14 minutes ago, Nelliekins said:

 

Private joke? 

 

So something like this? 

 

Not very private, it was on here lol. ?. @PeterW had me drive 7 hours in a round trip from Edinburgh to Preston to collect one! That’s the one I got from there anyway! 

 

 

[Nickfromwales]

5 hours ago, Nelliekins said:

and 1 for overflow

Do you mean it has an auxiliary tapping 2/3 of the way up on one side ( which is a hot return tapping ) ?

A regular cylinder has cold in, side mounted at the very bottom x1, combined hot and vent out of the very top x1, and nowt else other than the coil tapping's which are hydraulically separate. 

[PeterW]

They are very sensitive switches and I would suggest you look carefully and find one with a low flow rate of 2+ l/m. 

[Nelliekins]

2 hours ago, Nickfromwales said:

Do you mean it has an auxiliary tapping 2/3 of the way up on one side ( which is a hot return tapping ) ?

A regular cylinder has cold in, side mounted at the very bottom x1, combined hot and vent out of the very top x1, and nowt else other than the coil tapping's which are hydraulically separate. 

 

Hmmm you have got me wondering now! There is definitely 2 for coil, 2 on opposite side (top and bottom) and vent out at top. 

 

2 hours ago, PeterW said:

They are very sensitive switches and I would suggest you look carefully and find one with a low flow rate of 2+ l/m. 

 

Roger wilko. I have CPC account(s) and frequently pop into the sales counter to grab bits and pieces. I get 3 sets of mailshots every weekend ?

 

There are a couple of brass models sold by CPC - one is AC and one DC. Failing that, BES sell brass ones as well. 

 

[PeterW]

You cannot wire the pump direct to the switch ..! Have to put a relay in as otherwise you will fry the contacts, irrespective of what the MIs say about current rating ..!

Edited December 31, 2018 by Nickfromwales
fry

[Nickfromwales]

7 hours ago, newhome said:

@PeterW had me drive 7 hours in a round trip from Edinburgh to Preston to collect one

Just enough time to try all your frocks on

Images I cannot un-see