dogman

Controlling underfloor heating in passive house

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My concern would still be obsolescence and emergency repair,  though.  Heating (and ventilation) seem to me to be just a bit too critical to leave to a system that may not be that easy to fix by an ordinary heating engineer.  I accept there are electricians around who have the specialist knowledge to fix this stuff (although not very many, I suspect), but heating engineers tend to be a both plumbers and electricians, having system knowledge that's often specifically applicable to plumbing and heating systems.  How many heating engineers would understand enough about a Loxone control system to fix it on an emergency call out over the Christmas holiday, for example?  You could end up calling out both a Loxone-knowledgable electrician and a heating engineer, so both could check their respective parts of the system to find a fault.

Edited by JSHarris

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HP_SchemWrg.JPG.cc6cb65160cbc7516e03f6e0fa3fbab4.JPG

I agree - if the tech is there then use it, if not then standard time switches on industry standard back boxes make most sense as they will allow you to swap in the future. 

 

For it a single zone slab, timer to run the circ pump and a modified W Plan for heating a DHW tank and Buffer as primary / secondary heat sources I came up with this

 

 

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28 minutes ago, JSHarris said:

My concern would still be obsolescence and emergency repair,  though.  Heating (and ventilation) seem to me to be just a bit too critical to leave to a system that may not be that easy to fix by an ordinary heating engineer.  I accept there are electricians around who have the specialist knowledge to fix this stuff (although not very many, I suspect), but heating engineers tend to be a both plumbers and electricians, having system knowledge that's often specifically applicable to plumbing and heating systems.  How many heating engineers would understand enough about a Loxone control system to fix it on an emergency call out over the Christmas holiday, for example?  You could end up calling out both a Loxone-knowledgable electrician and a heating engineer, so both could check their respective parts of the system to find a fault.

 

I've had friends of mine lose their heating and/or hot water in the depths of winter before.  In some cases they couldn't get a heating engineer out for a couple of days.  In at least two cases, they were then told that the parts would need to be ordered in, so they waited further days before they heat came back.  I can't see that it's any worse for someone with a HA system.

 

95% of the system components - valves, pipework, thermostats, cylinders, manifolds - are completely standard and will be familiar to any heating engineer.

 

All we're talking about here are a couple of relays being controlled by the HA system rather than a timer.  It's a trivial matter for any heating engineer to look at a schematic and figure out where the likely failure is.  If it isn't the HA relays (trivial to test), then it's somewhere in the rest of the system, which is completely standard.  Of course, the HA system itself could fail, but that would manifest itself in many other ways as well.  It's not that expensive to have a standby unit in the cupboard and a backed-up version of the HA software with current settings.


Also, to repeat myself, I'm not suggesting this is general advice for anyone thinking about how to control their heating system.  Alex already has the kit bought and installed.  He's technically knowledgeable and knows how everything's set up.  It just seems crazy to go and buy a whole bunch of other hardware to avoid using an existing system that's optimised for the task at hand.  It's just more things to maintain and more things to fail in my view.

 

Now if he didn't already have a HA system installed and ready to go, I agree completely with what you've said.  There's no point introducing complexity and unfamiliarity for the sake of having it controlled by an HA system, unless it brings other advantages.  Interestingly, I think that low energy houses are less likely to get a benefit from the flexibility offered by HA heating control, because often the system control is very simple (eg, only 1 or 2 zones to control, no need to have several heating periods per day with different turn-on times and temps).   

 

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Bumping my old thread as i am starting the plumbing for the Heating and cooling.

 

I have looked at the examples others have used plus some detail i found on the web

 

Below is my first draft design

5ac90b94f3e9b_systemdesign.thumb.jpg.a5e361182fca89e22f32bd4ee3f1c57f.jpg

 

Its based on a two pipe system for a buffer tank with the two spare bosses used for the pre heat for the sunamp

 

Can anyone see anything that would cause problems?

 

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22 minutes ago, dogman said:

Bumping my old thread as i am starting the plumbing for the Heating and cooling.

 

I have looked at the examples others have used plus some detail i found on the web

 

Below is my first draft design

5ac90b94f3e9b_systemdesign.thumb.jpg.a5e361182fca89e22f32bd4ee3f1c57f.jpg

 

Its based on a two pipe system for a buffer tank with the two spare bosses used for the pre heat for the sunamp

 

Can anyone see anything that would cause problems?

 

Get the DHW preheat as an integral coil!!!!! 

PHE and pump / flow switch = PITA.....losses......complexity......grief. 

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8 minutes ago, Nickfromwales said:

Get the DHW preheat as an integral coil!!!!! 

PHE and pump / flow switch = PITA.....losses......complexity......grief. 

 

 

Good point, Nick, but I'd do it the other way around - spec a buffer with a solar/heat pump coil and leave the PHE as is.  The big advantage is that you don't need to fill the buffer tank with very expensive antifreeze/inhibitor, only the relatively low volume heat pump and coil circuit.  The buffer can then be filled with cheap standard inhibitor.

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Regarding the magnetic filter I would leave it in. A few ashp installation kits from manufacturers come with a magnetic filter.

Good point with ashp coil/heat exchanger to cut antifreeze/inhibitor! 

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Thanks for the comments everyone. I am stuck with my buffer tank so it was the best option. 

The design allows isolation of the buffer tank when cooling so it could still be used as a heat dump for excess PV to pre heat the sunamp.

 

Any thoughts on this isolation. i was going for a set of either motorised valves or two manual valves. I  have noticed that i need to add a small expansion to the water heating side to manage expansion when isolated.

 

Other option would be to swap the bottom valve with spring loaded or swing check valve that should allow expansion but prevent the cold and hot mixing.

 

I do have an issue with space so one expansion vessel would be preferable.

 

 

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I used a single motorised ball valve to isolate the buffer tank from the ASHP when it's in cooling mode, just where you have one shown.  I chose a motorised ball valve rather than a conventional motorised valve as I wanted to be 100% sure that it would seal when  closed.  Having looked at the inside of a conventional motorised valve I wasn't 100% convinced that it would be a 100% seal, and as even a small amount of chilled water seeping past into the buffer would cool it down a bit, I opted to use a ball valve that I was confident would be a 100% seal when closed.

 

You could use a manual ball valve, but you'd be operating it a lot in warm weather, when you want to keep the buffer tank warm for preheating hot water but also want to have the floor cooled a bit.

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1 hour ago, JSHarris said:

I chose a motorised ball valve rather than a conventional motorised valve as I wanted to be 100% sure

Thanks for the tip. 

Looking on my normal places that i buy parts they are quite expensive do you know a cheap supplier that may do them

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24 minutes ago, dogman said:

Thanks for the tip. 

Looking on my normal places that i buy parts they are quite expensive do you know a cheap supplier that may do them

 

 

Because I opted to use 12V DC for all the controls (just really a safety preference on my part) I used one of these valves (I bought three, just in case, but they seem really well made): https://www.ebay.co.uk/itm/Motorized-Ball-Valve-Electrical-Valve-DN20-G3-4-12V-2-wire-3-wires/201564641525?hash=item2eee3058f5:m:mpjP6_x5zwaHxqXmPnZZWig

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7 hours ago, dogman said:

I  have noticed that i need to add a small expansion to the water heating side to manage expansion when isolated.

 

I have tried to keep my system as simple as possible.  So for example, my 230V side is isolated from from the low voltage stuff by using some Crydom SSRs. This enables my Sparky to raise his Cert to keep BControl happy.  I haven't added any extra valves in my system since they weren't needed, but I will need at least one extra if I add an ASHP.  As to extra expansion, why not just add a trickle bypass and avoid this.

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20 minutes ago, TerryE said:

why not just add a trickle bypass and avoid this.

good idea thanks

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On 4/7/2018 at 19:55, JSHarris said:

 

 

Good point, Nick, but I'd do it the other way around - spec a buffer with a solar/heat pump coil and leave the PHE as is.  The big advantage is that you don't need to fill the buffer tank with very expensive antifreeze/inhibitor, only the relatively low volume heat pump and coil circuit.  The buffer can then be filled with cheap standard inhibitor.

 

Hi Jeremy,

 

Just to clarify your thoughts on the above,

you would recommend a coil for the circuit from the A2W to the buffer tank but you would leave the PHE in place and feed directly off the tank. in that case you would only need Glycol in the heating loop.

So a tank with a single coil would do the trick?

 

Is your thinking on this that the PHE would be more efficient at exchanging the heat than an internal coil or is it just 

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On 07/04/2018 at 19:55, JSHarris said:

Good point, Nick, but I'd do it the other way around - spec a buffer with a solar/heat pump coil and leave the PHE as is.  The big advantage is that you don't need to fill the buffer tank with very expensive antifreeze/inhibitor, only the relatively low volume heat pump and coil circuit.  The buffer can then be filled with cheap standard inhibitor.

Just flicking through this again, and agree on the coil if wanting to reduce the A/F volume, but it would still be better, IMO, to have DHW via a ( second ) internal coil rather than a PHE. Accepting that @dogman has already got his buffer, this can now simply be for reference for other readers.

 

The next issue would be down to the size of there vessel and just how much coil can be physically fitted inside it, so at that point you'd probably be into a 300L buffer. Not a problem afaic as its low temp storage so lower losses, and id want as much DHW preheat volume as possible ( to get as much of the bathing temp DHW from the HP as possible eg at the lower cost of producing it ).

Current one I'm speccing will be getting a 250L buffer heated primarily by an ASHP, which will be providing DHW preheat for a Sunamp PCM58. Just finalising a decision on the best option for isolating the A/F and primary water bodies. 2 more paracetamol and ill crack it :S 

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On 15/03/2017 at 17:11, PeterW said:

Or use a standard tank with a normal coil and a solar coil to do the DHW uplift. 

Just reading back through this top resource as the SA issue has caused a major re-think :/ 

 

The solar coil would be too low IMO, particularly at the low temp the buffer will operate at, to be fully extracting the heat out at the rate it would be consumed, assuming max ( typical ) flow of 15-20 l/p/m. I'm getting on the phone this morning to Telford to have a yap with the cylinder gods there and I'l update here with any juicy bits of info I extract. Cant help thinking the arrangement in a standard UVC would be best suited, eg heat via the coil and extract DHW preheat by putting the cold in at the bottom and removing the heated ( 40oC ) water out of the absolute top of the cylinder. 

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2 minutes ago, Nickfromwales said:

The solar coil would be too low IMO, particularly at the low temp the buffer will operate at, to be fully extracting the heat out at the rate it would be consumed, assuming max ( typical ) flow of 15-20 l/p/m.

 

So use them the other way up... ST coil to put heat in at the bottom from ASHP, std coil to draw it off for preheat...

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On 16/03/2017 at 16:50, Nickfromwales said:

Yes. That way you keep the potable ( drinking quality ) water completely separate. I would not use a coil on the ashp, but would instead feed the buffer 'volume' direct as that'll have the quickest recovery / transfer rates of heat from the HP to the buffer / TS. 

 

Edit to add : that brine ( HP water ) needs antifreeze so I'd recommend a stainless coil for DHW uplift. You don't want those two bodies of water ever mixing ☠️

hashtag : eating my own words :D 

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To summarize (I think as the SunAmp PCM34 cells aren't available, even though I have 2), you want a cylinder with 2/3 coils:

image.png.c5e2cfc495529b9eae7742ba7c880c14.png     image.png.b308039d673415a3e1589a8f019feb69.png  

Then it depends how you plumb it together.  (I would consider 3 coils as at the temperatures this will operate at you need maximum surface area so run the two coils (upper and lower) in sequence.  At a ΔT of 5oC (ASHP normal) you will only get about 5kW from these sort of coils so use two and/or increase the ΔT to 10oC.

 

Option 1: (Minimises Antifreeze in a Monoblock install)

  • DHW from the DHW coil.
  • ASHP from the other coil(s).
  • UFH from the tank.

Option 2: (Maximises recovery rate)

  • DHW from the DHW coil.
  • UFH from the other coil(s).
  • ASHP to the tank.

Option 3: (Maximises DHW pre-heat flow)

  • DHW from the tank.
  • ASHP to the DHW coil.
  • UFH from the other coil(s).

Option 4: (Install a Split ASHP, professional installer required) only DHW coil required as ASHP and UFH can share inhibitor, no antifreeze required.

  • DHW from coil.
  • ASHP and UFH to tank.

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@le-cerveau  Thanks for your helpful post, as of last night I thought I’d got this whole heating / hot water thing cracked, now I’m not sure! Thinking cap back on !!

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4 hours ago, le-cerveau said:

Option 4: (Install a Split ASHP, professional installer required) only DHW coil required as ASHP and UFH can share inhibitor, no antifreeze required.

Note you only need a professional installer for the refrigerant connection between the internal and external unit. A local refrigerant engineer did this part for me, relatively low cost. The rest is no different than a monobloc install from a "special skills" perspective.

 

I feel this is a better solution than monobloc. No need to add glycol (which is not a trivial or cheap option if the volume is large), no need to check or top-up glycol, no need to replace glycol every x years.

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1 hour ago, le-cerveau said:

To summarize (I think as the SunAmp PCM34 cells aren't available, even though I have 2), you want a cylinder with 2/3 coils:

image.png.c5e2cfc495529b9eae7742ba7c880c14.png     image.png.b308039d673415a3e1589a8f019feb69.png  

Then it depends how you plumb it together.  (I would consider 3 coils as at the temperatures this will operate at you need maximum surface area so run the two coils (upper and lower) in sequence.  At a ΔT of 5oC (ASHP normal) you will only get about 5kW from these sort of coils so use two and/or increase the ΔT to 10oC.

 

Option 1: (Minimises Antifreeze in a Monoblock install)

  • DHW from the DHW coil.
  • ASHP from the other coil(s).
  • UFH from the tank.

Option 2: (Maximises recovery rate)

  • DHW from the DHW coil.
  • UFH from the other coil(s).
  • ASHP to the tank.

Option 3: (Maximises DHW pre-heat flow)

  • DHW from the tank.
  • ASHP to the DHW coil.
  • UFH from the other coil(s).

Option 4: (Install a Split ASHP, professional installer required) only DHW coil required as ASHP and UFH can share inhibitor, no antifreeze required.

  • DHW from coil.
  • ASHP and UFH to tank.

Ive spoken to Telford to address this and I think there is some middle ground. 

Where we are all looking at the buffer tank as, for eg, a 200L buffer then the assumption is that there will be 200L of A/F ( antifreeze solution ) to factor in. Not always the case ;).

 

If we are to accept that the buffer, in a particular instance, is primarily for cold mains uplift aka DHW preheat, then there will be a whopper of a coil inside the cylinder consuming a large amount of the total cylinder volume. In the case of my current enquiry, around or just over ( TBC ) 50% of the cylinder volume will be occupied by the coil. So, for a 250L buffer, <125L will be A/F. The benefit of having the ASHP to the cylinder ( aka tank ) is it can get all its heat into the cylinder as quickly as possible. Going through a coil isn't as efficient so as this is not just a buffer to prevent short cycling ( eg a much smaller cylinder ) I've looked at maximising heat transfer from ASHP to DHW pre-heat. To get that, somethings gotta give. 

My thoughts then turn to the UFH and how to glean heat without having to have A/F in that system too. "Stick another coil in the buffer" I hear you cry, but alas, no room exists inside the buffer now as to get any meaningful uplift from a 250L vessel stored at ~40oC you need a bloody huge coil. It just about leaves room for 1 immersion heater ( 3kW or 6kW ), so where does that leave us? Before anyone asks, a smaller cylinder or smaller coil is a waste of time as the uplift wouldn't make it worth the bother, so 250L is the starting point IF you want to lean heavily on the ASHP at high CoP for DHW production, and also remember that part of this remit is to avoid G3.

 

From the ASHP I am looking into the pros and cons of fitting an oversized PHE inline with the flow. As its oversized ( to get a top through-flow rate on the primary side ) it should not impede upon the flow velocity of the ASHP pump and not impede upon water circulation to the buffer. So that gets us an A/F rich primary flow that goes from the ASHP to the PHE primary side ( PHE flow ), then it comes out of the PHE primary side ( return ) and then on to the body of the buffer to heat that. Im not bothered about recover / reheat times as this will purposely be set to come on and stay on during occupancy. The benefit of this setup will be no need for an additional pump / flow switch as the UFH manifold pump will simply draw heated water from the PHE as its required. 

The other option is Teeing the UFH PHE across the ASHP flow and return.

@JSHarris any thoughts?

 

Theory only at the moment.

 

 

 

 

 

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Oh, and that image in the last but one post shows a TS which I recon will be at least 450 / 500 L to get all those coils inside it and for them to be of any meaningful capacity. 

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As an alternative you could charge the TS via a PHE from the ASHP (no AF in the TS) , UFH from TS, it however requires an extra pump but you get the rapid recovery due to the PHE!

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