Patrick

ASHP and unvented Hotwater tank with Underfloor heating . Passivhaus. 170SQM . Who done it.

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Trying it this way:

So this topic has been discussed 1000 times . I was reading a lot about it in 2019 - forgot 90% , re-read a lot in 2020 and forgot another 90% .

Will need to spec up ASHP , unvented Hotwater Tank for Underfloor heating and hot water in a passivhaus . House is 175SQM . 125sqm groundfloor , 50sqm 1st floor

Who has done this on a similar size? Just so i can copy their setup 1:1 ūüėč

Cant find a blog or topic by someone who done this in a similar-sized building . If you could point me in the right direction - search results throw a lot up but nothing quite fits.

 

 

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SIZE does not matter.  Heat requirement is what sizes the heating system. Number of people sizes the HW system.

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Umm... if it's a Passivhaus, shouldn't PHPP give you your sizing numbers directly?

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We are 300m2 PH and have approx 3kW heating load.  Going with:

- Vailant Arotherm Plus 7kW (+ the Vaillant on-wall buffer tank)

- 300L Mixergy Tank.

- MBC installed in-slab UFH operated as 1-zone with Salus auto-balancing actuators for heating + cooling.

- Comfopost on first-floor MVHR supply for supplementary first-floor heating/cooling.

- WWHRS for showers (to save energy, but also to effectively increase the capacity of UVC and make the reheat time less critical)

 

We are going to try to run the Mixergy using the indirect coil which allows for partial "charging", but may revert to using their ASHP approach which is to use an external PHE if needed. 

 

We are only just starting to install elements of this setup though, so won't be able to report back on it for a few of months..

 

ASHP/UVC is about sizing it for you requirements plus any preference in terms of brand and also supply availability, not sure that is a huge amount more to it.  Use of Sunamp, Mixergy, ComfoPost, WWHRS etc. are all alternatives or optional extras that you need to consider if make sense or not for your setup and what you want to do.

 

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29 minutes ago, Dan F said:

We are going to try to run the Mixergy using the indirect coil which allows for partial "charging", but may revert to using their ASHP approach which is to use an external PHE if needed.


So the standard mixergy can’t go direct from the ASHP.?.? So you need the Heat Pump version which adds pumps and controls to the DHW PHR setup which is far more complex than a 300 litre UVC with a standard Heat Pump coil. The tank is ~£1300, tank with circulation pump and PHE and controls adds around £300 as far as I can see, so you’re now £600 more than a standard UVC heat pump cylinder with no moving parts - what’s the benefit of the mixergy..??


The heat loss differentials are negligible (1.9 vs 2.32kW) so what’s the USP apart from a nice app..,?


 

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24 minutes ago, PeterW said:

So the standard mixergy can’t go direct from the ASHP.?.

The standard version has a single (smallish) coil at the top which is in the hottest water. That gives a worse COP compared to standard type coils, which is why they do the external plate heat exchanger which can pull in colder water.

So you can use it direct with an ASHP, but are likely to see a performance hit. Having said that, charging from the top will give much faster recovery so it is probably quite a good match for a big tank/small heat pump.

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Posted (edited)
56 minutes ago, PeterW said:

The heat loss differentials are negligible (1.9 vs 2.32kW) so what’s the USP apart from a nice app..,?

 

I'm sure you'll pick all of these points apart, but in theory at least (and dependent on heat source and requirements):

- If using ASHP, the use of the PHE gets you more effective capacity than a large heat-pump coil would.

- If using top indirect coil and/or immersion, the ability to "partially charge"  if you don't need full tank heated (e.g. low occcupancy) which in turn reduces both energy usage and heat loss.

- Improved inlet difusor and circulation pump both of which improve stratification over a more standard UVC

- Reaheat time much less of an issue because coil/immersion are at top of tank and due to effective stratification.

 

The app can be seen as a toy yes, but if you don't have any home automation set up and it allow you to  i) avoid fully heat the tank when not needed ii) heat tank at specific times based on dynamic tariffs, then IMO this does add significant value, at least for the average user, maybe less so for an advanced users who doesn't need a proprietary app to automate this.   (I won't be using app, and will instead use Modbus interface).

 

I'll be able to report back, hopefully with data, once everything is set up.  The 300L is around £1200 and the PHE is an additional £160, not sure what the additional £300 for controls comes from?

 

EDIT:  Prices are from sometime last year, direct from Mixergy and exclude VAT.   I see midsummer wholesale prices are quite a bit higher!

Edited by Dan F

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14 minutes ago, Dan F said:

The 300L is around £1200 and the PHE is an additional £160, not sure what the additional £300 for controls comes from?

EDIT:  Prices are from sometime last year, direct from Mixergy and exclude VAT.   I see midsummer wholesale prices are quite a bit higher!

https://www.topcylinders.com/mixergy-300-litres-standard-smart-hot-water-cylinder has it at £1150, which includes the control box.

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Thanks - I suppose the only saving then is not heating the whole tank. Still don’t get the point of the PHE - it’s moving parts where none are needed..!

 

In terms of controller I assume the PHE pump has to plug in somehow to the Mixergy controls. 

I’ve seen the 300 litre tank at £1075 ex VAT but the PHE I could only find at £250 ex VAT. That’s still a lot more than £825 ex for a 300 litre Telford and there are going to need to be some substantial savings to make that back. 
 

Will be interesting to see how you get on with it. 

 

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2 minutes ago, PeterW said:

Still don’t get the point of the PHE - it’s moving parts where none are needed..!

 

Agree, most of the benefits are from the partial charging, which is why we are going to try to use the indirect coil even though we are using a ASHP.    I gave up trying to work out how I could possibly use Sunamp with a ASHP when I discovered each ASHP model had to be i) tested ii) have it's own ASHP specific controller!!

 

On the PHE, this is what they say:

- Delivers 10-20% more usable hot water than a similar sized conventional cylinder

- More efficient heat transfer with high surface area PHE minimising heat pump delivery and return temperatures

- More even temperature in tank (due to pump I guess)

- PHE is easier to service/replace than a coil.

 

Of course, the down side is that there is a pump involved I guess.

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2 hours ago, ProDave said:

SIZE does not matter.  Heat requirement is what sizes the heating system. Number of people sizes the HW system.

True. Just by coincidence it might be that somebody on the forum is having a similar setup and also has a similar HW system/amount of people and that I can then copy his/her choice . Like i said, it s only a small chance that this will work. @pdf27
 phpp would probably give me some required figures, if I would use it (not planning to get certified) but that still does not solve the issue of infinity amount  of brands/options.... so I thought I try and get some clever people advise on. And so far seems to work.

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40 minutes ago, Dan F said:

Of course, the down side is that there is a pump involved I guess.

Pump, and flow switch, and a relay between the two. Items which need to be bought, items which consume energy, and items which fail. Every time a component fails, your perceived saving goes into the pocket of the engineer........and you know he will be back again at some stage ;) :( Plus you'll have the extra, significant, associated losses of the external 'gubbings' and the cost of running the secondary pump which needs to run flat out usually. Due to convection, the external stuff turns into a waste radiator when the tank is static ( after being charged and the stat satisfied ) removing the heat to its surroundings.

I get the knee-jerk attraction of part charging via the upper 1/3, but the whole point of providing low cost energy via the ASHP is that you can harvest the max amount of energy in the shortest window, eg the Go! tariff charges the whole larger cylinder once a day at 5p/kWh + the multiplication of the SCoP ( so DHW at ~2.5p/kWh on a good day minimum expected ). With that said, I have zero love for the Mixergy tank, and waaaaaaay less love for the PHE solution and additional costs / losses. Absolutely no sale there AFAIC.

Folk get lost in an seemingly 'miserly' pursuit of maximised costs savings, and it's just a waste of time, effort and money. If you have cheap electricity and an ASHP, or PV and and ASHP,  then you would surely want to maximise the yield and stuff the UVC full to the gunnels at each opportunity. These only lose a degree and hour max, so in 24hrs ( and with an suitably sized UVC aka energy buffer of 300-400L ) the numbers are far better eg that would be the most 'bang for the buck'. Telford stainless cylinder = lifetime warranty too, zero maintenance!!! This solution sells itself.

On top of that would be the default of the immersion being used to convert PV into DHW directly, during the summer with the immersion only, thus not unnecessarily fatiguing the ASHP for the full 12 months of the year. That will promote reduced servicing and maximise longevity of the parts you least want to replace.

 

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7 hours ago, Nickfromwales said:

Folk get lost in an seemingly 'miserly' pursuit of maximised costs savings, and it's just a waste of time, effort and money. If you have cheap electricity and an ASHP, or PV and and ASHP,  then you would surely want to maximise the yield and stuff the UVC full to the gunnels at each opportunity.

That's probably the one area that the Mixergy tank makes any sense, and only if you don't use the external plate heat exchanger. With PV your cheap electricity will be during the day in summer and night in winter, and just using an immersion at 5p/kWh (PV export cost) is relatively expensive. Heating from the bottom (or using the plate heat exchanger) means you de-stratify, and if you've got a relatively small heat pump (matched to a well-insulated house) you're going to have lukewarm water for some hours in the middle of the day.

However, for all their "smart" controls and integration with Octopus Agile they have no ability to use PV for anything but an immersion. That's a major failing, and means you've got to be willing to write your own control system to really benefit from the increased cost & complexity (which to be fair is pretty minor in the grand scheme of things).

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9 hours ago, Dan F said:

The app can be seen as a toy yes, but if you don't have any home automation set up and it allow you to  i) avoid fully heat the tank when not needed ii) heat tank at specific times based on dynamic tariffs, then IMO this does add significant value, at least for the average user, maybe less so for an advanced users who doesn't need a proprietary app to automate this.   (I won't be using app, and will instead use Modbus interface).

That would fail in my house.

 

"avoid fully heat the tank when not needed "

 

I can imagine the answer if I asked everyone to give me a weekly schedule of when they want a shower or a bath, so I can program the tank to have a full tank of water for them.

 

For all practical purposes, the tank needs to be full all normal waking hours.

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Posted (edited)

To the OP: we have 100m2 downstairs, 55m2 upstairs, passive House enerphit (so slightly higher heat demands)

PHPP says about 2.6kW max load. We installed a 8.5kW ecodan R32, oversized mostly for the DHW reheat time but also allows us to push more heat (or cold) into the house at the very cheapest times. (8kW of solar to maximize use of too)

 

Ground floor is all UFH, the ecodan drives an electronic mixing valve to run it with very fine control, generally 24¬įC flow temp seems plenty but I set a little weather compensation boost when it's below zero out.

The other zone is a fan coil in the loft which can run at a hotter or colder temperature (thanks to that electronic mixing valve). We'll only use it for cooling. Upstairs bedrooms are generally 1-2¬įC warmer than desired even with no heat sources in them, so glad we didn't! The fan coil will dump cold air in the loft, and hopefully a bunch of that will drop down the service void to each room. If not, we can duct it into specific rooms (bedroom, home office) very easily from up there

 

UVC is an oso geocoil 300L. I looked at all the Mixergy/sunamp but putoff by the complexity. The OSO is fantastic. It stratifies amazingly well: bottom half never once got above 14¬įC when we were using the immersion only. The one downside is it only has one immersion or probe pocket. But in a way it's a blessing: it's forced me to keep the control systems really simple and dumb: heat the whole damn thing up from ASHP and the top up the top half from solar.¬†

 

Mitsubishi have a detailed CAD schematic for this system design, if anyone needs it let me know. I couldn't be happier with how it's performing. (so quiet it took 3 weeks running before we even heard it run, have to be stood outdoors right next to it) 

Edited by joth
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@joth I'd be very interested to see the schematic please, and info on the electronic mixing valve, thanks

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My tank heating strategy is really simple.  Heat the whole tank to 48 degrees with the ASHP.  Then top that up with the bottom immersion heater from solar PV which on a good day will take the tank to over 70 degrees.

 

It's all simple off the shelf stuff nothing too bespoke about it.

 

If the immersion was half way up, there would not be enough capacity to absorb a good days surplus PV generation.

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Just be aware for those looking at UVC for a heat pump, Telford do a 300 litre with twin immersions as a standard product for around £50 more.  
 

Single immersion

 

Twin Immersion

 

Telford are fully configurable to allow placement of the pipework where you require, and will also add additional pockets for around £30 each if you want more monitoring.  

 

 

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As much as we're not using too much hot water yet, I'm definitely glad to have two immersions  in the tank and on the diverter. Top element is halfway up and is satisfied by lunchtime these days, the bottom element destratifying the tank after that.

 

/ but like @ProDave if I was doing it again I'd have another pocket right down at the bottom.

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4 hours ago, trialuser said:

@joth I'd be very interested to see the schematic please, and info on the electronic mixing valve, thanks

PM sent.

 

The mixing valve it the one the Welshman recommended on here a while back.

Esbe ARA662 actuator 230v 50hz 120 sec

 

https://www.wolseley.co.uk/product/esbe-ara662-actuator--230v-50hz-120-sec-(1)/

 

Happily the heatpump will drive up to 60¬ļC (using a separate "smart grid" input to boost it +10¬ļC when the sun it out), so I can get the whole tank fairly¬†hot on a sunny day. Definitely if we were more than two people, maximising the whole tank temperature via multiple / lower immersion pockets would have been a higher priority. As it was I focused on¬†minimizing losses:¬†just 2 people here, and foolishly designing for a long forgotten world where we only spend a few waking hours at home each day, and away a lot at weekends

 

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1 hour ago, joth said:

 

What is a " 3-point signal"?  Do you are also have a temperature sensor on output of this and are using something like https://www.loxone.com/enen/kb/mixing-valve-controller/ ?

 

Was just talking about this with out installer this morning, he was suggesting a mixing value with 0-10v input for UFH/Comfopost, not sure which one though...

 

 

 

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Posted (edited)
24 minutes ago, Dan F said:

 

What is a " 3-point signal"?  Do you are also have a temperature sensor on output of this and are using something like https://www.loxone.com/enen/kb/mixing-valve-controller/ ?

 

Was just talking about this with out installer this morning, he was suggesting a mixing value with 0-10v input for UFH/Comfopost, not sure which one though...

 

 

 


Not sure the 3 point bit - appears to be a powered open, powered closed actuator.
 

I have used the Loxone mixing valve control for my heating circuits, using a temperature sensor on the forward flow pipe.

Edited by Trw144

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26 minutes ago, Dan F said:

 

What is a " 3-point signal"?  Do you are also have a temperature sensor on output of this and are using something like https://www.loxone.com/enen/kb/mixing-valve-controller/ ?

 

Was just talking about this with out installer this morning, he was suggesting a mixing value with 0-10v input for UFH/Comfopost, not sure which one though...

 

 

 

 

I think 3 point means it supports three commands: "Turn CW,  Turn CCW, Stop"

 

It's driven from the FTC6 controller: see OUT5, page 20.

Our FTC6 has 7 thermistors, a pair for flow & return on each of zone 1, zone2, and primary loop, plus one in the UVC, so has full visibility of everything it needs.

 

I really wouldn't enjoy driving this from loxone, it's too stateful and too much risk of oscillations. ¬†For example, before turning on zone 2 only, it preloads the valve to be fully open and then uses the primary flow temp to set the UFH temp, but before opening the other zone, it first closes down the UFH mixing valve completely, then cranks up the primary temp to the one requested for the fan coil¬†(e.g. 40¬ļC) then slowly opens back up the mixing valve a little at a time, sensing the UFH flow temp and adjusting as needed. Programming 5+ minute sequences like that would be a PITA in the loxone flowchart editor. (The valve has a 2min rotation time. I'm finding it tedious enough to programme and fine-tune 10sec sequences for my blinds in loxone)

 

FTC6 also seems to have a nice failsafe, if the mixing valve fails to close down sufficiently (or it sees temp overrun for any other reasons) it shuts off the UFH circulation pump to avoid overheating the loop.

 

My one gripe is there's no real documentation, let alone feedback, about all the error states  &  diagnostics it must know about internally.

 

 

 

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Posted (edited)
1 hour ago, joth said:

I really wouldn't enjoy driving this from loxone, it's too stateful and too much risk of oscillations. ¬†For example, before turning on zone 2 only, it preloads the valve to be fully open and then uses the primary flow temp to set the UFH temp, but before opening the other zone, it first closes down the UFH mixing valve completely, then cranks up the primary temp to the one requested for the fan coil¬†(e.g. 40¬ļC) then slowly opens back up the mixing valve a little at a time, sensing the UFH flow temp and adjusting as needed.


In Loxone the mixing valve with PID control does the trick and solves the issue of overshooting/undershooting - I ve had it in 4 years and whenever I watch it, it keeps a stable temperature with very little movement on the valve. Mine starts off fully closed (no heat going into the circuit) and works it's way up from this position. As a fail safe I have gone old school mechanical (in case of programmer or controller error) so a pipe stat on the flow that the pump is wired through. Admittedly, if the heat pump controller has all this built I would probably leave what I can say within it (I'm on a gas boiler).

Edited by Trw144

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