Critique my complex(ish) mech plan - 2 floor UFH, 2x ASHP, 2x dedicated ventilation..

[puntloos]

So - it has come to this. As I indicated a long time ago I wanted to be *sure* my house would not overheat, and I don't think I can safely do it with UFH (condensation) so at the end of the day, attached is my heating plan.. Would love to hear some feedback. There are a few things to note:

 

- 2 ASHPs side to side in the garden, one multi-split A2A, one A2W. Both mitsubishi.

- MVHR in loft, 5 FCUs that each can move about 2.5Kwh 

- UFH everywhere too (eh why not)

- Solar is there but not indicated

- 400L standard tank - gledhill heatpump lite (I was debating an OSO but the 40W less loss amounts to like 1p a day.. not worth my while. 

- Service shaft actually turns out not to be too used 

- Both my boxed projector, and boxed network rack have dedicated air lines. Tied into MVHR (heating guy says it will not be a problem to beam 400 resp 1000W (peak) worth of heating into the MVHR

- No hot/cold buffers currently since these inverter-based devices can just run 'as much as needed' rather than alternating on/off but I could be persuaded

 

Looking fwd to hearing any further thoughts

Full plan - all floors, drainage etc here: (sigh, can't upload more pics)

https://drive.google.com/file/d/18N3Pk5uOxdq9G9GJAT6txxETgGfLQw5I/view?usp=sharing

 

[Dan F]

Certainaly very belts and braces! Unless the house is not particuarly well insulated and no shading?  Any summary info on the build relating to heating/cooling load, insulation, shading etc.

Edited January 18, 2022 by Dan F

[joth]

3 hours ago, puntloos said:

- Both my boxed projector, and boxed network rack have dedicated air lines. Tied into MVHR (heating guy says it will not be a problem to beam 400 resp 1000W (peak) worth of heating into the MVHR

 

I don't follow this at all. What does "tied into" and "beam" mean? Additional fans to force air into? That will greatly unbalance the system and you'll probably just have the hot air blowing  back from other extract points.

At normal MVHR air movement rates, extracting an additional 1400W through  and MVHR is not going to happen.

 

3 hours ago, puntloos said:

- No hot/cold buffers currently since these inverter-based devices can just run 'as much as needed' rather than alternating on/off but I could be persuaded

 

 

Depends what size A2W heat pump is specified, and what is the smallest zone that maybe driven?

If you ever  want to use it just for the bathrooms e.g. to make the tiles feel warmer in shoulder season, then yes it will definitely be short cycling.  But then, you'll probably have the A2A running at the same time on cooling mode to compensate so short cycling is the least of the worry ?

 

 

[puntloos]

2 hours ago, Dan F said:

Certainaly very belts and braces! Unless the house is not particuarly well insulated and no shading? 

Yep, well insulated, and every window has either awnings (downstairs) or built-in blinds 

 

2 hours ago, Dan F said:

Any summary info on the build relating to heating/cooling load, insulation, shading etc.

I've anonymised (please let me know if I failed, don't want to expose the unwilling) here:

Heating: https://drive.google.com/drive/folders/1Fe7iriAq7vHQfj5WMB9FdpUKOJFZSO9O?usp=sharing

Their comments:

- Most houses in this country have around 24kW (or 24000W) heat loss, your house only has 3kW heat loss or 12% of an average house. As a rough idea at current prices you should be able to heat your house with an air source heat pump for less than £4 per day even in the worst winter weather.

- Passive house criteria heating load is 10 W/m². Your house is 350m² with a total loss of 3200W which works out at 9.14 W/m² or better than Passive house standard. The EPC may not give you A+ because there are probably a few boxes you didn’t tick, but it is bound to be B+ because you are doing the most important things.

 

SAP: https://drive.google.com/drive/folders/1lKLovkY0_JCoSo4P_6OJEZSbPDAtu1_U?usp=sharing

- SAP rating: 100 A

- Environmental rating: 100A

- CO2 emissions: -0.31/year  

 

All in all, promising sounds, I seem to be hitting what I was hoping for, which is "near passivhaus" but not caring too much about hitting every checkbox just for its own sake.

 

Would love to hear about anything that sticks out, for example if any of the materials can be replaced by anything more substantial. 

 

My main challenge is that I do have a few cold bridges that bug me, I was planning to post the final designs - I'm expecting them soon..

 

[puntloos]

2 hours ago, joth said:

I don't follow this at all. What does "tied into" and "beam" mean? Additional fans to force air into? That will greatly unbalance the system and you'll probably just have the hot air blowing  back from other extract points.

Yeah I was wondering about this, but the guy said he accounted for it but I forget the detail. Let me ask.

 

2 hours ago, joth said:

At normal MVHR air movement rates, extracting an additional 1400W through  and MVHR is not going to happen.

Well, on the other hand e.g. cooking on a powerful hob would also generate an additional heat for a longish time. But yeah I will ask.

 

2 hours ago, joth said:

Depends what size A2W heat pump is specified, and what is the smallest zone that maybe driven?

I think for A2W the ecodan 6.0 kwh is planned - PUZ-WM60VAA - very similar to yours I seem to recall?

2 hours ago, joth said:

If you ever  want to use it just for the bathrooms e.g. to make the tiles feel warmer in shoulder season, then yes it will definitely be short cycling.  But then, you'll probably have the A2A running at the same time on cooling mode to compensate so short cycling is the least of the worry ?

 

 

Yeah it's a bit of an exception to have the only thing that's needed in the house is slightly heating the UFH and nothing else.. eh.. dunno..I'll ask but the guy said that It isn’t wise to only run the heat pump overnight, it wouldn’t produce enough heat even if you could store it all. As you said, maybe electric UFH is a solution but eh, it's a bit iffy for various reasons, efficiency, reliability etc.

[SteamyTea]

3 hours ago, puntloos said:

.I'll ask but the guy said that It isn’t wise to only run the heat pump overnight, it wouldn’t produce enough heat even if you could store it all

Not sure I understand that.  Is your plumber/designer saying an ASHP don't produce much at night?

 

And, just to be pedantic.  Your chosen heat pumps/MVHR will have a power output in kW, not kWh (or Kwh, kwh, kW/h, KWH).

 

If you have an A2WHP and UFH, just get a buffer plumbed in, it will save grief.

[Dan F]

10 hours ago, puntloos said:

Yep, well insulated, and every window has either awnings (downstairs) or built-in blinds 

 

Your house is 350m² with a total loss of 3200W which works out at 9.14 W/m² or better than Passive house standard.

 

Your house is therefore very similair to ours, which also has 10W/m2 heating load, blinds on the majority of windows/sliders and a very low cooling load (given insulation + blinds).

 

It all seems a bit overkill to be honest given the specification of the house. With such high levels of insulation and comprehensive shading, you should only need minimal heating/cooling, not UFH and fancoils on all floors.

 

We have:

- 305m2 (two floors)

- Single 7kW ASHP

- UFH on ground floor.

- MVHR heat-battery for supplementary heatng/cooling on the first floor (fancoils not justified given all first-floor windows have blinds).

 

This was based on PHPP and an M&E consultant who calculated UFH cooling power (considering dew-point) as well as heating/cooling output of heat-battery vs. required based on PHPP which gave me confidence this was enough.

 

As an example: our cooling load was just 335W. Given UFH is able to supply 3.6kW of cooling (considering dew point) and heat-battery able to supply 1.1kW cooling to first floor I was happy no additional cooling was required.  Also, given minimal heating/cooling it was clear that a single A2W ASHP was enough for everything.

Edited January 19, 2022 by Dan F

[joth]

11 hours ago, puntloos said:

 

Quote

At normal MVHR air movement rates, extracting an additional 1400W through  and MVHR is not going to happen.

Well, on the other hand e.g. cooking on a powerful hob would also generate an additional heat for a longish time. But yeah I will ask.

Yes but I don't put the hob in a small insulated box, and it is designed to deal with heat in a way that a rack of network equipment or a projector might struggle with, nor does it run for hours and hours at a time at full whack.

 

So long as there's a way to ventilate these electronics aside from the MVHR you'll be fine: worst case the respective rooms start to overheat and the FCU kicks in.

 

11 hours ago, puntloos said:

Quote

Depends what size A2W heat pump is specified, and what is the smallest zone that maybe driven?

I think for A2W the ecodan 6.0 kwh is planned - PUZ-WM60VAA - very similar to yours I seem to recall?

Similar, ours is 8 kW for about half the floor area. We could have got away with 5kW but oversized it for DHW tank reheat speed. With a 400L tank, you should check what happens there too.

As you're using a split system, it's a shame the A2A and A2W can't share a single 4-pipe external unit. That way you'd have the full power of it available for DHW reheat, and it would be more effective in moving excess heat between areas (cooling and heating different rooms simultaneously).

 

11 hours ago, puntloos said:

Yeah it's a bit of an exception to have the only thing that's needed in the house is slightly heating the UFH and nothing else.. eh.. dunno..I'll ask but the guy said that It isn’t wise to only run the heat pump overnight, it wouldn’t produce enough heat even if you could store it all. As you said, maybe electric UFH is a solution but eh, it's a bit iffy for various reasons, efficiency, reliability etc.

 

It's actually more the norm than the exception: for 9 months the year you need next to no heating, but it's still pleasant to walk on not-freezing tiles in the morning.

 

The buffer has many purposes, and only if you're sure you'll never (for the lifetime of the system) want any of them would I be confident to forgo it. Off top of my head:

 

1/ Load shifting. Both for overnight cheap rate and for times of excess solar generation. This is not so much about "storing more energy" as allowing the heat pump to operate for a longer period at a significantly higher flow rate, as the UFH manifold then mixes it down to the desired temperature.

The ecodan FTC6 has a "smart grid" input to make use of cheap electricity (inc from solar) but this only works if you have a buffer tank with thermistor.

 

2/ Faster DHW to heating transition. Maybe ecodan specific, but I find it takes 20-30 mins to cool down after doing DHW before enabling heating. Buffer tank should remove that delay. (Having a split system might also resolve this one)

 

3/ Deal with very low heat demand. The "one bathroom calling to heat up tiles" scenario is the one I can easily see, but there maybe others. (Guest staying that likes a bedroom extra hot?) - the smaller 6kW size will help a bit with this at least.

 

4/ Backup heating, if it has an immersion. (Moot as you have an independent A2A system anyway)

 

5/ provides a heat source for defrost cycles, but probably moot with split system and everything else going on.

 

Couple other comments:

- be interested how you get on with tendering. My contractor quoted £12,000 to install  a single H20 FCU! (Hence why I DIYed it, with variable level of success)

- do you have a plan for control systems for it all? It would be easy for the A2A and A2W, and even MVHR and stack venting (if you automate it?)  all to end up in a battle royale unless something is coordinate the lot.

 

 

 

 

[joth]

On the rooms with MVHR supply and FCU, will the MCHR "Fresh air spigot" be supply fresh air into the ceiling void (the -ve pressure supply plenum for the FCU) or into the room? If the former, you'll only get the fresh air supplied when the FCU is operating, which seems less than idea, but if the latter then I'd expect it to be nearer the "Return air grille" plenum inlets if the intention is to use the FCU to disperse fresh air (which appears to be the intent)

EDIT: looking at the first floor, it does indeed seem you only get fresh air supply when the FCU is running. I'm not sure how wise that is. The MVHR fresh air supplies are directly tied into the FCU supply plenum which might make balancing the whole system a lot more complex, and if you run any FCU at high speed it might suck air out of the MVHR network, pulling air back up out of other supply-side rooms. What I've read suggests it's easier to commission and operate if the two systems air kept independent, and I've generally seen the FCU acting as an optional agitator of the fresh air supply once it's already made it into a room (e.g. by positioning the supply vent somewhere near the FCU intake)

 

How will downstairs FCU be accessed for maintenance, filter changes?

If the ceiling void is being used as an open negative pressure plenum (which I think is the intent, as there's not pipework shown from the Return air grille to the FCU) then is any special allowance made to avoid trades leaving a lot of dust and plaster and general sh*te in the void that it will blow around? Is there no rockwool for sound insulation between ceiling and floor above,  to impede air movement in that channel?

 

 

Edited January 19, 2022 by joth

[puntloos]

9 hours ago, SteamyTea said:

Not sure I understand that.  Is your plumber/designer saying an ASHP don't produce much at night?

 

I think that's the point, yes. Producing heat at night is somewhat less efficient, which might not outweigh doing it on-demand?

 

9 hours ago, SteamyTea said:

And, just to be pedantic.  Your chosen heat pumps/MVHR will have a power output in kW, not kWh (or Kwh, kwh, kW/h, KWH).

 

Ah fair.

 

9 hours ago, SteamyTea said:

If you have an A2WHP and UFH, just get a buffer plumbed in, it will save grief.

 

Yeah a buffer doesn't seem too expensive, the concern is mainly location.. 

[puntloos]

1 hour ago, joth said:

Yes but I don't put the hob in a small insulated box, and it is designed to deal with heat in a way that a rack of network equipment or a projector might struggle with, nor does it run for hours and hours at a time at full whack.

To be fair though, the network closet doesn't either. (nor the projector). 

But I take your point.

 

1 hour ago, joth said:

So long as there's a way to ventilate these electronics aside from the MVHR you'll be fine: worst case the respective rooms start to overheat and the FCU kicks in.

 

Similar, ours is 8 kW for about half the floor area. We could have got away with 5kW but oversized it for DHW tank reheat speed. With a 400L tank, you should check what happens there too.

Yes, not too expensive to oversize somewhat.

1 hour ago, joth said:

As you're using a split system, it's a shame the A2A and A2W can't share a single 4-pipe external unit. That way you'd have the full power of it available for DHW reheat, and it would be more effective in moving excess heat between areas (cooling and heating different rooms simultaneously).

 

I tried quite hard to find one of those devices but of the 4-pipe units that I could find, 90% were too big (20+ kW) and 10% were R410 only. 

 

1 hour ago, joth said:

 

It's actually more the norm than the exception: for 9 months the year you need next to no heating, but it's still pleasant to walk on not-freezing tiles in the morning.

 

The buffer has many purposes, and only if you're sure you'll never (for the lifetime of the system) want any of them would I be confident to forgo it. Off top of my head:

 

1/ Load shifting. Both for overnight cheap rate and for times of excess solar generation. This is not so much about "storing more energy" as allowing the heat pump to operate for a longer period at a significantly higher flow rate, as the UFH manifold then mixes it down to the desired temperature.

The ecodan FTC6 has a "smart grid" input to make use of cheap electricity (inc from solar) but this only works if you have a buffer tank with thermistor.

 

2/ Faster DHW to heating transition. Maybe ecodan specific, but I find it takes 20-30 mins to cool down after doing DHW before enabling heating. Buffer tank should remove that delay. (Having a split system might also resolve this one)

Huh, I didn't realise ecodan does 'different things' for heating as it does for .. heating.. ?

 

1 hour ago, joth said:

 

3/ Deal with very low heat demand. The "one bathroom calling to heat up tiles" scenario is the one I can easily see, but there maybe others. (Guest staying that likes a bedroom extra hot?) - the smaller 6kW size will help a bit with this at least.

 

4/ Backup heating, if it has an immersion. (Moot as you have an independent A2A system anyway)

 

5/ provides a heat source for defrost cycles, but probably moot with split system and everything else going on.

 

Yeah the guy mentioned defrost cycles.

 

1 hour ago, joth said:

Couple other comments:

- be interested how you get on with tendering. My contractor quoted £12,000 to install  a single H20 FCU! (Hence why I DIYed it, with variable level of success)

 

Yeah that's .. shocking really. I don't quite understand why? Did you ever find that out? The devices themselves are in the area of 1000 quid.. and while of course there are subtleties it's not that much more than bolting the thing to your ceiling or whatnot? I guess it sounds like the old adage in building: 'if you dont want to do it, charge an outrageous price'? 

 

1 hour ago, joth said:

- do you have a plan for control systems for it all? It would be easy for the A2A and A2W, and even MVHR and stack venting (if you automate it?)  all to end up in a battle royale unless something is coordinate the lot.

 

It's a fair shout. Clearly we can't have both systems going in 'dumb mode' where they just turn on when temp below the setpoint (or for a2a, turn on cooling when temp above x). 

Short answer: no plan yet. Longer: I've spoken to a few installers that said they wanted to do it in KNX. I don't think I have the willpower to teach myself KNX or loxone beyond beginner level, but the idea is that this mech plan is really mostly a "draft for tendering" where I have 3 M&E teams who can ask a price for the pair, where I'd expect them to supply M, E and the programming of 'E'. 

[puntloos]

1 hour ago, joth said:

On the rooms with MVHR supply and FCU, will the MCHR "Fresh air spigot" be supply fresh air into the ceiling void (the -ve pressure supply plenum for the FCU) or into the room? If the former, you'll only get the fresh air supplied when the FCU is operating, which seems less than idea, but if the latter then I'd expect it to be nearer the "Return air grille" plenum inlets if the intention is to use the FCU to disperse fresh air (which appears to be the intent)

Interesting point. Yes I think it is the former (into void only). I will ask to clarify. Perhaps the FCUs are intended to run permanently but even with the heat/cool off that sounds less than ideal.

 

1 hour ago, joth said:

EDIT: looking at the first floor, it does indeed seem you only get fresh air supply when the FCU is running. I'm not sure how wise that is. The MVHR fresh air supplies are directly tied into the FCU supply plenum which might make balancing the whole system a lot more complex, and if you run any FCU at high speed it might suck air out of the MVHR network, pulling air back up out of other supply-side rooms. What I've read suggests it's easier to commission and operate if the two systems air kept independent, and I've generally seen the FCU acting as an optional agitator of the fresh air supply once it's already made it into a room (e.g. by positioning the supply vent somewhere near the FCU intake)

Indeed, I'll inquire.

1 hour ago, joth said:

How will downstairs FCU be accessed for maintenance, filter changes?

The assumption is the ceiling void can be opened. But it will need to be designed to allow this of course. (and as.. I think you pointed out elsewhere) - I also need to make sure the downlilghters are designed around the FCU sections. will need some careful planning.

1 hour ago, joth said:

If the ceiling void is being used as an open negative pressure plenum (which I think is the intent, as there's not pipework shown from the Return air grille to the FCU) then is any special allowance made to avoid trades leaving a lot of dust and plaster and general sh*te in the void that it will blow around? Is there no rockwool for sound insulation between ceiling and floor above,  to impede air movement in that channel?

My understanding is that yes there is rockwool, and we need to understand how much air it will let through, and work out those details.

 

1 hour ago, joth said:

 

 

 

 

Thank you for your comments, these are all very worth figuring out today rather than later... 

[puntloos]

3 hours ago, Dan F said:

 

Your house is therefore very similair to ours, which also has 10W/m2 heating load, blinds on the majority of windows/sliders and a very low cooling load (given insulation + blinds).

 

Remind me - does your house already stand? Either way would love to see some designs if you're willing to share.

 

3 hours ago, Dan F said:

It all seems a bit overkill to be honest given the specification of the house. With such high levels of insulation and comprehensive shading, you should only need minimal heating/cooling, not UFH and fancoils on all floors.

 

You'd think! (below more)

 

3 hours ago, Dan F said:

We have:

- 305m2 (two floors)

- Single 7kW ASHP

- UFH on ground floor.

- MVHR heat-battery for supplementary heatng/cooling on the first floor (fancoils not justified given all first-floor windows have blinds).

 

That is indeed similar in many ways

 

3 hours ago, Dan F said:

This was based on PHPP and an M&E consultant who calculated UFH cooling power (considering dew-point) as well as heating/cooling output of heat-battery vs. required based on PHPP which gave me confidence this was enough.

 

As an example: our cooling load was just 335W. Given UFH is able to supply 3.6kW of cooling (considering dew point) and heat-battery able to supply 1.1kW cooling to first floor I was happy no additional cooling was required.  Also, given minimal heating/cooling it was clear that a single A2W ASHP was enough for everything.

 

It's an interesting point. The cost of installing (or at the very least provisioning for..) a secondary system is certainly non-zero. I guess I am expecting an extra-over of 30,000 when all is said and done, for the A2A. But doing it "now" is certainly cheaper than retrofitting, and on this forum and elsewhere I've heard many stories of overheating houses. Perhaps those were 'passivhaus teething problems' but I think part of these design choices are me making absolutely sure that particular situation won't happen. 

 

Am I right about that 30,000? the actual devices perhaps make a grand total of 10,000, so 20,000 to add the pipes, add the extra programming to the 'smart home'.

 

[SteamyTea]

1 hour ago, puntloos said:

Producing heat at night is somewhat less efficient, which might not outweigh doing it on-demand?

It takes quite a long time after sunset for air temperature to reduce. Humans tend to feel the difference as we take advantage of solar radiation. Take today, air temp about 8⁰C, but when I sat in the sun I felt very comfortable.

[puntloos]

 

34 minutes ago, SteamyTea said:

It takes quite a long time after sunset for air temperature to reduce. Humans tend to feel the difference as we take advantage of solar radiation. Take today, air temp about 8⁰C, but when I sat in the sun I felt very comfortable.

 

Fair shout. I think i'll just try for a buffer, as @joth pointed out a bunch of other smallish(?) reasons I think the small benefits are starting to add up whereas the downsides seem to be managable. I wonder if I can somehow have that buffer in my loft rather than try to crowd it in the under-stairs. Would it be a problem to have water go up 2 floors, then down again? Or would something more elegant be doable?

[puntloos]

One further thing to point out, I wonder if people had opinions on:

 

Rather than have a full hot water return - which, as I understand it, is really a loop of hot water circulating around 'your entire house' - the heating eng figures that 90% of my taps are local to the hot water cylinder, so instead he put a PIR sensor tied to a pump in the only remote ensuite to make sure that one starts pulling hot water the moment I enter that bathroom..  

 

It does sound like a useful simplification of the design?

[Bitpipe]

10 minutes ago, puntloos said:

One further thing to point out, I wonder if people had opinions on:

 

Rather than have a full hot water return - which, as I understand it, is really a loop of hot water circulating around 'your entire house' - the heating eng figures that 90% of my taps are local to the hot water cylinder, so instead he put a PIR sensor tied to a pump in the only remote ensuite to make sure that one starts pulling hot water the moment I enter that bathroom..  

 

It does sound like a useful simplification of the design?

 

if the tap is not open and on a single leg, how will it 'pull water'?

 

Our return loop goes from the furthest end of the dhw run back to the UVC - it's actually not that far really as the supply plumbing itself is 80% of the 'loop'.

 

Some use a manifold system and have that stay hot so you minimise length of dead legs. 

 

For baths and showers, it's of limited value as they are high flow and are usually on for a while. It's just when you need 30s of hot water to wash your hands and don't want to wait 2 mins for it to arrive.

 

WRT the rest of your design, it's belt and braces but a lot feels unnecessary (UFH everywhere etc) but if you have the money to spend then up to you I suppose.

 

We only have UFH on ground floor, rarely comes on outside of dec-feb. Low power electric UFH in first floor bathrooms to avoid chilly tiles in morning plus towel rads for warm towels. That's it.

[puntloos]

4 minutes ago, Bitpipe said:

 

if the tap is not open and on a single leg, how will it 'pull water'?

I assume it's a loop too really, just that it will be only turned on by that movement detector, so to avoid the losses of a continuous running loop? 

 

4 minutes ago, Bitpipe said:

Our return loop goes from the furthest end of the dhw run back to the UVC - it's actually not that far really as the supply plumbing itself is 80% of the 'loop'.

But does your loop pass past some, most, or even all of your taps?

 

4 minutes ago, Bitpipe said:

Some use a manifold system and have that stay hot so you minimise length of dead legs. 

Do you have any design example for that?

 

4 minutes ago, Bitpipe said:

For baths and showers, it's of limited value as they are high flow and are usually on for a while. It's just when you need 30s of hot water to wash your hands and don't want to wait 2 mins for it to arrive.

Agree

4 minutes ago, Bitpipe said:

WRT the rest of your design, it's belt and braces but a lot feels unnecessary (UFH everywhere etc) but if you have the money to spend then up to you I suppose.

 

Yeah, it's tough to strike that balance. I'm perhaps over-steering on getting things done "while it is cheap" (e.g. during build time) rather than having to possibly retrofit things. One thought I've been having is to make sure the house could do without the A2A and do everything except actually put it in. 

 

But as above, I think the amount of benefits of A2A are fairly substantial, even if everything goes well and I could do without it theoretically. I'd love to have a price tag to the "A2A option" so during tendering I can forego it if I have to. 

 

4 minutes ago, Bitpipe said:

We only have UFH on ground floor, rarely comes on outside of dec-feb. Low power electric UFH in first floor bathrooms to avoid chilly tiles in morning plus towel rads for warm towels. That's it.

 

[Bitpipe]

20 minutes ago, puntloos said:

I assume it's a loop too really, just that it will be only turned on by that movement detector, so to avoid the losses of a continuous running loop? 

 

The losses are minimal really, the return (and all the DHW) are also well insulated runs.

 

Without a loop, if you were to run a distant tap then you'd still have losses once the tap was closed and the hot water in the leg cooled.

 

20 minutes ago, puntloos said:

But does your loop pass past some, most, or even all of your taps?

 

The DHW supply goes from UVC to utility above then to kitchen then to front bathrooms and finally to rear ensuite (all in 22mm) before it returns in 15mm to UVC. Hot taps tee off this loop.

 

As I said above, the return loop in 15mm is only about 20% of the run length.

 

[puntloos]

20 minutes ago, Bitpipe said:

The DHW supply goes from UVC to utility above then to kitchen then to front bathrooms and finally to rear ensuite (all in 22mm) before it returns in 15mm to UVC. Hot taps tee off this loop.

To be clear, this includes your shower and bath taps?

 

Do you get enough water pressure? My designer figures the added complexity and noise of pumps might not be worth trying to add pressure mechanically vs letting the mains do the work. Do you all have pumps to increase tap pressure?

 

 

[SteamyTea]

1 hour ago, puntloos said:

only remote ensuite

How often would that be used?

If it is the master one i.e. yours, could you not just live with it.

 

Not sure about a buffer in loft. As long as everything is well insulated, can't see why not.

[puntloos]

2 minutes ago, SteamyTea said:

How often would that be used?

If it is the master one i.e. yours, could you not just live with it.

 

Most water runs in this house are below 6m. The master ensuite has a loop at 12ish. 

 

2 minutes ago, SteamyTea said:

Not sure about a buffer in loft. As long as everything is well insulated, can't see why not.

 

I suppose it adds complexity. One silly question I have but the hot buffer is only for UFH I assume? Or will the buffer also buffer DHW?

[Dan F]

2 hours ago, puntloos said:

Remind me - does your house already stand? Either way would love to see some designs if you're willing to share.

 

Yes. Only just moved in though, all heating is working fanastically, but haven't tested cooling yet.  Anything specific you are interested in?

 

 

Quote

It's an interesting point. The cost of installing (or at the very least provisioning for..) a secondary system is certainly non-zero. I guess I am expecting an extra-over of 30,000 when all is said and done, for the A2A. But doing it "now" is certainly cheaper than retrofitting, and on this forum and elsewhere I've heard many stories of overheating houses. Perhaps those were 'passivhaus teething problems' but I think part of these design choices are me making absolutely sure that particular situation won't happen. 

 

Am I right about that 30,000? the actual devices perhaps make a grand total of 10,000, so 20,000 to add the pipes, add the extra programming to the 'smart home'.

 

Why not run some calcs (or get someone to run them for you) and  get some real confidence on what you can/can't do without doubling up systems and spending 30k?  You are right it's cheaper than retrofitting, but still lot more expensive that installing systems you don't need!   You have already made a number of design choices (fabric/shading) that really limit how much heating/cooling you'll need, which is great, so do you really need a 30K insurance policy?

 

People with overheating problems typically haven't considered shading/overheating at the design phase or haven't allowed for any active cooling.  Others have allowed for active cooling on the ground floor, but find the first floor gets a bit to warm as they have minimal shading and/or no active cooling on the first floor.  But if you design to avoid overheating (idealy calculate your cooling load based on design) and have one form of active cooling on each floor, then I think you can be confident you aren't going to have issues. If in doubt get someone else to run calcs too.

 

If you still want an insurance policy, then run some pipes in ceiling voids for potential future water-based fancoils, and remember where they are, but don't put anything else in until you find you need it.

Edited January 19, 2022 by Dan F

[Bitpipe]

11 minutes ago, puntloos said:

To be clear, this includes your shower and bath taps?

 

Do you get enough water pressure? My designer figures the added complexity and noise of pumps might not be worth trying to add pressure mechanically vs letting the mains do the work. Do you all have pumps to increase tap pressure?

 

 

 

Yes, as the whole DHW feed is driven by the return loop.

 

We have a pressure reducing valve on the way in, 32mm feed from main. Pressure is not an issue.

 

There is a small brass pump that drives the return - water pressure is same whether it is on or off.

 

Pump is silent even when you're next to it.

 

Not wanting to cast aspersions on your designer, but have they any actual real world experience of this?

[SteamyTea]

5 minutes ago, puntloos said:

One silly question I have but the hot buffer is only for UFH

Usually. 

It gives the system enough fluid to work with. If there is not enough the HP will keep turning on and off.

There is no real harm in the buffer going a little hotter than needs be, just mean you have stored a bit for later.