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

[puntloos]

2 minutes ago, Bitpipe said:

 

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?

 

Not sure the designer likes asparagus. More of a broccoli guy myself. 

OK that's enough dad jokes for the day. The designer seems fairly sensible and at least came recommended. His entire quote on pressure: "Pumps are only allowed on the water mains if the water passes through a tank first (water regulations). This pump set is called a ‘cold water booster set’ and they can be quite large and expensive. I normally specify ‘Dutypoint’ https://www.dutypoint.com/ because they make compact sets, but even their kit is quite big. I recommend taking a wait and see approach, the water pressure is probably not as bad as you think."

[JohnMo]

Daft question, why do your heat loss calcs have zero for all ventilation losses.  The MVHR is not 100% efficient, so there will be some losses, which will add to the heating kW required?

 

Our ventilation looks to add 11% to the heating loads at 0.5 ACH.

[joth]

2 hours ago, puntloos said:

 

 

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?

 

You don't need to run the water up to the loft and back down again, just use a 2-pipe buffer tank, and install primary sized (22mm IIRC?) pipe from the hydrobox up to the buffer in the loft. Tap the two manifolds off of that pipe as it passes them, with a 2-port zone valve per manifold.

This is *almost* what my installers did, except they reduced the pipe size on the final branch to the loft as it "only" has a single FCU on it, but that makes it tricky for me to upgrade to more loft-hosted FCU or to add the buffer up there. I should have insisted on using full size pipework right the way through.

 

But yes with the buffer tank I can see lots of reasons it might (one day) prove useful to have it, but very little downside to adding it right away. Especially as you have a split system so don't need any glycol in the system.

 

Edited January 19, 2022 by joth

[puntloos]

10 minutes ago, JohnMo said:

Daft question, why do your heat loss calcs have zero for all ventilation losses.  The MVHR is not 100% efficient, so there will be some losses, which will add to the heating kW required?

 

Our ventilation looks to add 11% to the heating loads at 0.5 ACH.

 

Doesn't sound daft at all, seems like it's omitted. Not sure why.

[puntloos]

Btw the reason my heating guy says no 'default hot water return' is that it could ruin the hot water stratification in the water tank. 

Seems .. somewhat logical? 

 

[edit] - looked this up: https://doi.org/10.1080/014576300271040 - the conclusion seems to be that if it's less than 3-tanks-a-day the disturbance should be minimal.

Edited January 19, 2022 by puntloos

[SteamyTea]

45 minutes ago, puntloos said:

Btw the reason my heating guy says no 'default hot water return' is that it could ruin the hot water stratification in the water tank. 

Seems .. somewhat logical? 

Why should that matter.  You can store more energy if the temperature is homogeneous i.e. mechanically stirred.

Here is a picture of what happens in my tank as it is heated, and then settles once the heating is off (settles is a better term than stratifies, stratification implies discrete layers that move up and down).

[puntloos]

4 minutes ago, SteamyTea said:

Why should that matter.  You can store more energy if the temperature is homogeneous i.e. mechanically stirred.

Guessing here but I'd say that since the water gets pulled from the top of the tank, having the hottest water available for use makes calibrating a bit easier?

Isn't this the principle that mixergy tanks claim are a good idea? 

 

4 minutes ago, SteamyTea said:

Here is a picture of what happens in my tank as it is heated, and then settles once the heating is off (settles is a better term than stratifies, stratification implies discrete layers that move up and down).

 

And do you have a full hot water return?

 

 

[SteamyTea]

24 minutes ago, puntloos said:

Guessing here but I'd say that since the water gets pulled from the top of the tank, having the hottest water available for use makes calibrating a bit easier

Hotter water just needs to be mixed with extra colder water. Really makes no difference at all.

 

26 minutes ago, puntloos said:

And do you have a full hot water return

No. My system is as simple as it gets. A cylinder with an immersion heater at bottom, cold water from a tank in loft, and s pipe out the top to the taps.

Works well. Cylinder lasted for about 31 years.

[joth]

2 hours ago, puntloos said:

Btw the reason my heating guy says no 'default hot water return' is that it could ruin the hot water stratification in the water tank. 

Seems .. somewhat logical? 

 

[edit] - looked this up: https://doi.org/10.1080/014576300271040 - the conclusion seems to be that if it's less than 3-tanks-a-day the disturbance should be minimal.

If you drive it from motion detectors and temperature probes in the tank,  it becomes a software problem to chose the correct trade off of stratification vs maximum storage requirement.

This is what I went with: install the hardware (pipework at least) during the build, decide when to turn it on (if at all) later

Edited January 19, 2022 by joth

[SteamyTea]

16 minutes ago, joth said:

If you drive it from motion detectors and temperature probes in the tank,  it becomes a software problem to chose the correct trade off of stratification vs maximum storage requirement.

This is what I went with: install the hardware (pipework at least) during the build, decide when to turn it on (if at all) later

Actually, that is more clever than I initially thought.

Turn the pump on and you can store more (OK, you loose a little more though parasitic losses).  May be useful if you have extra guests staying.

[PeterW]

20 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.

Eh..??? Slab can hold it easily. And he’s said earlier you’ve got low losses so something doesn’t add up. 
 

Have you spoken to any of his other customers ..??

[PeterW]

3 hours ago, puntloos said:

Btw the reason my heating guy says no 'default hot water return' is that it could ruin the hot water stratification in the water tank. 

Seems .. somewhat logical? 

again - check his credentials .. if he’s never seen one, on a UVC the HRC goes back about 150mm below the top level so you only really circulating 5-10% of the tank capacity. If it is PIR driven too, then you are about to de-stratify the tank anyway running the taps and putting cold into the bottom of the tank. 
 

Also, check the pricing on the tank as the Gledhill is normally more expensive than the same spec Telford 

[ReedRichards]

I have my DHW on a loop.  My cylinder has the secondary return port quite near the top and it does not seem to adversely affect the stratification.  That's good in winter but in summer I heat my cylinder with spare solar power, the immersion heater is half way up the tank and I could wish for destratification to take place.  If there was such a thing as a three port valve approved for drinking water I would send the return back via the cold feed in summer but such a valve does not seem to exist.   

[joth]

12 minutes ago, ReedRichards said:

.  If there was such a thing as a three port valve approved for drinking water I would send the return back via the cold feed in summer but such a valve does not seem to exist.   

 

You can achieve the same thing with a pair of WRAS approved solenoid valves

https://www.solenoid-valve.world/shako-co-ltd/12-wras-solenoid-valve-0-7-bar-22-nclosed-brass-pu220d-04

 

In fact for this application you'd probably get away with one valve: have it permanently feed back into the 2nd return high level port, and optionally injected via the solenoid valve into the cold water inlet. That will effect the desired tank agitation even if only a small % of the circulated water actually returns via the cold inlet.

You could also do this with a dedicated pump from the top to bottom of tank independent of the secondary return loop.

 

Whichever way, just make it's sure it's all happening downstream of the mains no return value ?

 

 

Edited January 19, 2022 by joth

[PeterW]

15 minutes ago, ReedRichards said:

If there was such a thing as a three port valve approved for drinking water I would send the return back via the cold feed in summer but such a valve does not seem to exist.   

If you’re only using it in the summer then use a manual switch over valve but don’t forget you will need to put a non return valve in to stop the cold feed bypassing the tank and flowing back into the loop. 
 

Something like this will do

 

https://www.vip-ltd.co.uk/Valves/VIP_Brass_Ball_Valves/00_0033/mobile_small.html

[puntloos]

1 hour ago, PeterW said:

Eh..??? Slab can hold it easily. And he’s said earlier you’ve got low losses so something doesn’t add up. 
 

Have you spoken to any of his other customers ..??

 

No - fair callout. 

 

But, to be clear, the work he is doing is quite limited, this is pre-tendering only, so this is a guy that came highly recommended by 2 separate sources and his only job is to do a rough design that provides a good idea to tender off of. 

 

Also, don't forget this is me 'channeling' the guy, and probably doing a poor job. So far his work seems solid if perhaps somewhat conservative.

[puntloos]

Spoke to my heating guy today. We seem to be mostly on the same page.

 

Network and Projector cabinets

On 18/01/2022 at 22:42, 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.

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

You're correct, the idea is not to 'push' air into the MVHR - so no active fans added to the mix, but let it do its work normally - the only difference for it would be it would receive very hot air. I pointed out that perhaps 1000W is a bit much and he agreed it might need some more careful planning, will get back to it. 

 

Hot water buffer (A2W ASHP -> Buf -> UFH)

On 19/01/2022 at 12:42, joth said:

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:

(snip 5 reasons+) 

Indeed, this will now be added, how big is such a buffer? Anyone have a link for the one they are using? (debating putting it above the DHW - since I have a high ceiling)

On 19/01/2022 at 12:42, joth said:

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, we're aiming for the 8kW one as well. It's interesting apart from a minor price difference all of the sizes seem to be about the same cost, am I correct the only downside of having an 'oversized' one (say the 11.2 one) is that in low mode the minimum the inverter can run at is about 20% of max, (so 2-ish kW) which especially in the 'just heat a tiny bathroom tile' case it will turn onoffon? (plus you probably need 3-phase power, butI'll likely have that anyway)? 

 

A2A cost, value for money

On 19/01/2022 at 12:42, joth said:

- 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)

In my heating guy's view, it should be "about 2500 per device- supplied and installed" - so indeed the extra-over for my 6 devices (5 FCU, 1 A2A SHP) is 15,000 (and a bit for the planning approval..) - will see for tendering if this estimate holds up but in my mind if the extra cost of A2A is - say - 25,000 I would need to have a think but it still feels somewhat ok given the amount of extra flexibility, reaction speed, precision of heating location and overall redundancy.

 

Fresh Air

On 19/01/2022 at 12:51, 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 ideal, 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)

 

 

MVHR everywhere

On 19/01/2022 at 12:51, joth said:

EDIT: looking at the first floor, it does indeed seem you only get fresh air supply when the FCU is running.

I don't think this is entirely true, in Bed 3 there is a supply, and I think there are often only one supply room and the other rooms are only extract rooms - only bed4 has no extract at all. (and the garage, arguably too..)

 

My current understanding is that you would want to be able to draw a line from the supply through 'most places' and then into an extract, and with the exception of bed4 and garage that's the case?

 

Hot water return

We'll go the 'Joth' approach and put it in, but perhaps not open it up (and/or experiment) to see the pros and cons.

 

 

[joth]

2 hours ago, puntloos said:

the only difference for it would be it would receive very hot air. I pointed out that perhaps 1000W is a bit much and he agreed it might need some more careful planning, will get back to it. 

 

Remember there's a range of ways to move 1000W through air, from a small amount of superheated  air though to a lot  of slightly warmer air. Your electronics will thank you the cooler you can keep them, thus toward the higher volume, lower temperature end of that spectrum. I think that's my main point: to move 1000W at acceptable temps you need very considerable air speed.

 

21 hours ago, puntloos said:

Yes, we're aiming for the 8kW one as well. It's interesting apart from a minor price difference all of the sizes seem to be about the same cost, am I correct the only downside of having an 'oversized' one (say the 11.2 one) is that in low mode the minimum the inverter can run at is about 20% of max, (so 2-ish kW) which especially in the 'just heat a tiny bathroom tile' case it will turn onoffon? (plus you probably need 3-phase power, butI'll likely have that anyway)? 

 

yeah higher chance of short cycling, but your buffer should solve that. at some point it becomes a lot large twin fan beast and eyesore, and around then it also demands 3ph, but 8 kW seems a sweet spot.

You'll probably want 3ph down the bottom of the garden anyway, given the amount of plant you're hiding down there.

 

21 hours ago, puntloos said:

Yes, we're aiming for the 8kW one as well. It's interesting apart from a minor price difference all of the sizes seem to be about the same cost, am I correct the only downside of having an 'oversized' one (say the 11.2 one) is that in low mode the minimum the inverter can run at is about 20% of max, (so 2-ish kW) which especially in the 'just heat a tiny bathroom tile' case it will turn onoffon? (plus you probably need 3-phase power, butI'll likely have that anyway)? 

 

/sub I'm interested in this too, mostly looking at 100L as that fits in the space I have.

There is some rule of thumb about 10-15L per kW of ASHP (IIRC?) but the real answer is calculate smallest emitter size (UFH of your smallest zone) and then either look at the water volume or kW mismatch to the ASHP spec when just that is in use. I'll see if I find the links again

Anyway for now, for tender I'd say put in 150L and you can reduce it if needed when you get into the detailed layout planning before ordering.

 

21 hours ago, puntloos said:

I don't think this is entirely true, in Bed 3 there is a supply, and I think there are often only one supply room and the other rooms are only extract rooms - only bed4 has no extract at all. (and the garage, arguably too..)

 

Maybe I wasn't very clear. Then normal idea is bedrooms (and living rooms) only have MVHR supply vents, never extract. My point is Bed 1, 2 and 4 don't have a supply valve at all - it's in the loft at the FCU intake, so may not make it to the room if the FCU is not running. (or if hard tied to the FCU plenum, risks unbalancing the MVHR if the FCU is put on full)

 

My preconception said it would normally be done like this:

 

 

 

 

[puntloos]

3 hours ago, joth said:

Remember there's a range of ways to move 1000W through air, from a small amount of superheated  air though to a lot  of slightly warmer air. Your electronics will thank you the cooler you can keep them, thus toward the higher volume, lower temperature end of that spectrum. I think that's my main point: to move 1000W at acceptable temps you need very considerable air speed.

So my heating guy says that it will require the MVHR to move 8L/sec to take away 1000W worth of heating whilst keeping the closet about 10C above living temp (aka say 32C), and on the other end it will supply 8L/s. 

 

Quote

yeah higher chance of short cycling, but your buffer should solve that. at some point it becomes a lot large twin fan beast and eyesore, and around then it also demands 3ph, but 8 kW seems a sweet spot.

You'll probably want 3ph down the bottom of the garden anyway, given the amount of plant you're hiding down there.

Yeah, I've been aiming for 3ph

 

Quote

 

/sub I'm interested in this too, mostly looking at 100L as that fits in the space I have.

There is some rule of thumb about 10-15L per kW of ASHP (IIRC?) but the real answer is calculate smallest emitter size (UFH of your smallest zone) and then either look at the water volume or kW mismatch to the ASHP spec when just that is in use. I'll see if I find the links again

Anyway for now, for tender I'd say put in 150L and you can reduce it if needed when you get into the detailed layout planning before ordering.

I'm a bit confused, liter, as in total contents of the UFH pipes?

 

Quote

 

Maybe I wasn't very clear. Then normal idea is bedrooms (and living rooms) only have MVHR supply vents, never extract. My point is Bed 1, 2 and 4 don't have a supply valve at all - it's in the loft at the FCU intake, so may not make it to the room if the FCU is not running. (or if hard tied to the FCU plenum, risks unbalancing the MVHR if the FCU is put on full)

Yeah I needed to be taught this (yesterday) that indeed doors are not airtight (I assumed so because of fire regs..) and you extract in wet rooms and put air into dry rooms. 

 

Quote

My preconception said it would normally be done like this:

 

 

I was thinking the same but when I asked the guy said it was already done, perhaps in a more subtle way. He's been trying hard to hide most pipework in unobtrusive locations - under eaves etc, so I'm pretty happy with his designs for now.

 

My suspicion is that the loft FCUs might actually be used as supply (an unpowered FCU, I assume, is basically a pipe, and there's one located in every spot where you drew your spigots..)

 

 

 

Edited January 21, 2022 by puntloos

[puntloos]

Small addition, the heatguy proposes https://library.mitsubishielectric.co.uk/pdf/book/VL-CZPVU-RL-E_PI_Sheet?model_query=VL-500CZPVU-R%2FL-E#page-3 (the 350 seems sufficient.. 500 probably better for buffer..)

 

"Lossnay" - sounds like the real name is NLoss. Pig latin?

 

People here seem more fond of Zehnder, but (so far) I'm an all-Mitsubishi farm. Not sure if there are huge benefits to sticking to one brand but as @joth noted, having all heat equipment talk the same language might prevent some battle royale while one thing is heating what the other is cooling etc.

 

 

[joth]

3 hours ago, puntloos said:

So my heating guy says that it will require the MVHR to move 8L/sec to take away 1000W worth of heating whilst keeping the closet about 10C above living temp (aka say 32C), and on the other end it will supply 8L/s. 

 

 

Close? My Google calculator says 80 l/s but I'd love to know if there was a bug I made it that - I can't see it.

 

My MVHR on normal setting moves about 4 l/s per vent.

 

3 hours ago, puntloos said:

My suspicion is that the loft FCUs might actually be used as supply (an unpowered FCU, I assume, is basically a pipe, and there's one located in every spot where you drew your spigots..)

 

Right, that is exactly what I was saying was my suspicion too. You asked for feedback on the design, and that was my feedback: this is a more complex design and likely more complex (=expensive) to balance and commission and maintain, and could still unbalance the MVHR if the FCU is on full.

If you couple the systems like this, you'll definitely want a single installer commissioning MVHR and FCU (and so presumably doing both ASHPs too) else you'll get never ending buck passing between the trades.

 

 

Edited January 21, 2022 by joth

[puntloos]

2 hours ago, joth said:

 

Close? My Google calculator says 80 l/s but I'd love to know if there was a bug I made it that - I can't see it.

 

My MVHR on normal setting moves about 4 l/s per vent.

 

Ah! Interesting, yes, very much worth checking then. The math seems straightforward enough in theory (but completely haven't wrapped my head around it yet) - let me peruse your thread there.

 

2 hours ago, joth said:

Right, that is exactly what I was saying was my suspicion too.

 

Oh sorry I guess I misread that part, I thought you figured the FCUs had to permanently be on, but either way, yes it's somewhat complicated but I currently feel there's a certain elegance in that both systems can work together or separately.

 

2 hours ago, joth said:

You asked for feedback on the design, and that was my feedback: this is a more complex design and likely more complex (=expensive) to balance and commission and maintain, and could still unbalance the MVHR if the FCU is on full.

Fair, thank you for taking a very close look.. 

2 hours ago, joth said:

If you couple the systems like this, you'll definitely want a single installer commissioning MVHR and FCU (and so presumably doing both ASHPs too) else you'll get never ending buck passing between the trades.

Absolutely, that was the idea, in fact I would only tender for teams of "M" and "E" so also the programming of the 'smarts' is done by effectively the same team.

 

[Dan F]

If you are geting one installer to do UFH, fancoils and MVHR then have them calculate heating/cooling power available from each system and compare this to your heating/cooling demand.  You can then, based on data, decide if the dual ASHP's and UFH + fancoils on both floors are really justified.  Remember, with fewer systems, not only do you save on capital costs, but also avoid issues with:

- Different bits of the system competing/conflcting (or would UFH only do heating and fancoils only do cooling?)
- The need for, ideally, an uber-controller that controls all heating/cooling systems.

- Additional potential maintance costs.

- How easy will it be for anyone else to understand/operatre the system if for some reason you aren't around.

 

Don't get by wrong,  your proposal is fantastic and very comprehensive and I can already imagine how much fun it would be be to implement the uber-controller portion of this using Loxone!  It's just that there are some downsides to putting so much kit in, and given the spec of your build, you are almost certainly going to find you only ever use a small percentage of installed capacity.

Edited January 22, 2022 by Dan F

[puntloos]

1 hour ago, Dan F said:

If you are geting one installer to do UFH, fancoils and MVHR then have them calculate heating/cooling power available from each system and compare this to your heating/cooling demand.  You can then, based on data, decide if the dual ASHP's and UFH + fancoils on both floors are really justified.  Remember, with fewer systems, not only do you save on capital costs, but also avoid issues with:

- Different bits of the system competing/conflcting (or would UFH only do heating and fancoils only do cooling?)

 

That was certainly my base plan, yes. That can still conflict of course.

1 hour ago, Dan F said:

- The need for, ideally, an uber-controller that controls all heating/cooling systems.

Hence the idea to have it 'all mitsubishi' so their single 'MEPcloud' app could control it. To be clear I'd probably go for loxone or KNX as the true brains (since I'd also have awnings etc) but the basic idea is there.

1 hour ago, Dan F said:

- Additional potential maintance costs.

Fair, but well, I think *normally* only one or the other device would work so the total running time of either would be split in half. I know that doesn't fully mitigate extra maintenance cost, complexity itself also means more stuff can fail. 

 

1 hour ago, Dan F said:

- How easy will it be for anyone else to understand/operatre the system if for some reason you aren't around.

Good shout, hoping that the mitsu melcloud app would handle the 'simple situation'.. 

 

1 hour ago, Dan F said:

Don't get by wrong,  your proposal is fantastic and very comprehensive and I can already imagine how much fun it would be be to implement the uber-controller portion of this using Loxone!  It's just that there are some downsides to putting so much kit in, and given the spec of your build, you are almost certainly going to find you only ever use a small percentage of installed capacity.

 

Yeah, it's a fair shout. It's funny how you end up in a place sometimes.

 

- Start with standard boiler. Want AC for those hot days.

- Learn about ASHP. OK, ASHP+AC

- Learn ASHPs can cool. Nice. ASHP in reverse and done

- Probably need a split ASHP since I was planning to put the device in the far garden, and water-based coolant runs are more lossy over distance

- Hear tons and tons of people overheating in their cleverly designed passivhauses. (also- learn about 'global warming')

- Hear cooling ASHP has a bunch of theoretical issues with condensation if not handled very carefully.

- Hear joth and others have Fan Coil Units. Maybe that's an approach.

- Learn that coolant-based FCUs are much more efficient than water. 

- OK so then I need a split ASHP that can handle a few FCUs too.

- Nope, doesn't exist in UK market since I want R32 or better coolant (there is a R410 setup). Guess I need a separate device. So A2W ASHP and A2A ASHP. I guess?

 

 

And here I am. Not saying I am in the right place necessarily but it's a logical path, no? ?

 

[puntloos]

Quick update: heating guy said he did indeed miscalculate and 80 is correct, will need to get different provisions than the MVHR for that cooling.

 

@joth regarding the absence of supply spigots, apparently it stems from my wish to put the 1st floor FCUs in the loft (since 1st floor has no proper void).  This meant the fresh air connections are connected directly into a return air plenum fixed to the FCU. The return air plenums are also connected to the two return air grilles by ductwork.

 

If the FCU is off, the fresh air travels along the return air ducts into the bedroom below.