oranjeboom

Sunamp UniQ HW+i experience? Charge via ASHP?

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Still mulling over my final choice of Sunamp variants...

 

Considering Dual vs HWi+i in combination with an ASHP. In the event that my ASHP goes offline (more likely if I get a cheap import) then the Dual is offline too whilst the HW+i can still be charged electrically.

 

 

Does anyone have the HW+i unit? Am I correct in thinking that the charging of the unit can easily be switched from charging between electric or a heat source? The Sunamp guide states:

"The UniQ HW+i and UniQ HW+iPV heat batteries are designed to be heated primarily by an external heat source (e.g. boiler, heat pump) and for producing mains pressure hot water heating in buildings. Therefore, these heat batteries are equivalent to indirect unvented hot water cylinders or hot water only thermal stores. The UniQ HW+i models are fitted with standby electric heating elements to heat hot water when the main heat source fails."

 

Are these units designed to only be charged electrically for short only durations? Or is it fine to use them primarily via electric heating?

 

I was planning to have a low temp ASHP that will charge my UFH. I am thinking that in those times that there is no call for UFH heating, I could use the ASHP to at least raise the heat in the Sunamp unit to say 50c? Now if I understand, the std units need to be charged to at least 58c, so is it possible then to charge the PCM to 50c (from the ASHP), and then the electrical heating element to take the PCM temp to the required level of 58c?

 

If that's not the case, then no point in considering the HW+i model.

 

 

Other idea is to go for Dual model (does DHW and space heating) and then use a HT ASHP to charge that to the required temps. I can then utilise that to do both DHW and UFH. If the unit is fully depleted in the evening from showers etc and there is a demand for heat, then at least the ASHP can kick in to feed the UFH directly via means of a blending valve. And if I go E10, I can ensure the ASHP is charging the Sunamp units and slab. Just means that I choose to go for a Dual, then I am more inclined to go for a non-cheap import ASHP!

 

 

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In essence, the Sunamp doesn't really start to store much heat at all until it is heated to the phase transition temperature of the PCM, so heating it to, say, 50°C won't do much, it might put around 10% of the heat capacity into the thing, if that.  The major part of the heat stored comes from the phase change, and that won't start until the PCM is heated to about 58°C, and to do that probably needs a flow temperature of over 60°C, perhaps around 65°C, because there will be a small temperature loss across the internal heat exchanger, and through the melted PCM close to the heat exchanger.

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Adding to what @JSHarris says, most of the time a normal (i.e, PCM 58) Sunamp won't be as cool as 50 °C. It'll only get that cool when it's nearly fully discharged. Therefore it won't normally accept any heat at all at that temperature; if you flow 50 °C water through it the heat will flow from the Sunamp to that water, rather than the other way round.

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4 hours ago, JSHarris said:

In essence, the Sunamp doesn't really start to store much heat at all until it is heated to the phase transition temperature of the PCM, so heating it to, say, 50°C won't do much, it might put around 10% of the heat capacity into the thing, if that.  The major part of the heat stored comes from the phase change, and that won't start until the PCM is heated to about 58°C, and to do that probably needs a flow temperature of over 60°C, perhaps around 65°C, because there will be a small temperature loss across the internal heat exchanger, and through the melted PCM close to the heat exchanger.

 

Thanks Jeremy, Ed. I knew that would all have been too simple an approach!  As the literature says "The standard models of the Sunamp heat batteries are supplied with PCM58 and these heat batteries can be used with any heat source which can run at flow temperature greater than 65oC. The discharge temperature from these standard heat battery models will be between 52 and 55oC".

 

I was then thinking of using PCM34 instead as would be able to use a low temp ASHP then as the PCM requires flow temp from heat source at over 45oC. Only downfall then is that the discharge temp is only around 32oC and too cool for our DHW needs.

 

And I'm not aware of where things stand with PCM34 in any case.

 

So I can discount this UNiQ variant then!

 

Back to the Dual and choosing a high temp ASHP then! The mind's beginning to crumble!

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Having read a fair amount about Sunamp's in this forum and having spoken to Sunamp directly we were (are) keen to use Sunamp instead of HWC for i) smaller size ii) reduced maintenance iii) reduced heat loss.  But, our M&E consultant is currently advising us that is best to use a standard HWC. The thinking is:

 

- Heat Pump is preferred over gas for i) colling ability ii) free cooling/HW from PV in the summer ii) gradual decarbonization of the grid.

- But, if we use a heat pump instead of gas for HW, then we'd need to heat to 65C rather than 55C for HWC, meaning most heat pumps wouldn't be suitable.  

- The limited number of suitable heat pumps wouldn't be particularly efficent heating to 65C either.

 

Basically, if there was a PCM55 version, they'd jump on it.. but there isn't.

 

So, in a similair position to @oranjeboom I think, and wondering if we should:

i) Take advice and get standard heat pump and HWC
ii) Insist on HT heat pump and Sunamp and what disadvantages with this might be.

iii) Combine things somehow by using standard heat pump + HWC but also seperatly a Sunamp powered by PV and/or cheap grid import in winter.

 

(heat pump will also be used for UFH downstairs combined with some MVHR post heating/cooling for upstairs)

 

 

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28 minutes ago, Dan Feist said:

M&E consultant

?? Mechanical and electrical boff?

 

HWC = Hot water cylinder?

 

Can't answer all of your questions, however:

 

- If you have gas, that may work out cheaper for you as gas boiler is cheaper install than sunamp and ashp. Yearly gas checks though, standing charges etc. I think in many cases, gas will still win if ASHP has a lower COP than anticipated, house leaks heat like a tent etc.

- A high temp ASHP can modulate down. So once it's done your high temp input into  Sunamp for DHW, it can reduce temp down to your UFH temp.

- Heating costs of DHW using cheap (E10/E7) or 'excess PV via HT ASHP may be cheaper than gas if the ASHP is appropriately sized I think.

 

I am sure others can comment with some facts, figures and science.

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@Dan Feist very similar situation as you, and I've gone for option (i) ASHP + UVC

Sunamp was very alluring but the high temp requirement just put me off too much. I have no doubt it could be made to work, but it puts more constraints on the rest of the ASHP system design and this was already an area of massive scope creep in our project.

In a few years maybe they'll have nailed an elegant ASHP integration, and maybe there'll be some other players offering some competition and choice in PCM heat batteries as it's an idea I really want to widely succeed.

Sorry, that's not very helpful in context of the OP!

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12 hours ago, oranjeboom said:

?? Mechanical and electrical boff?

 

HWC = Hot water cylinder?

@oranjeboom Yes and yes.

 

@JSHarris Do you, or anyone you know use Sunamp with high-temp ASHP?  Or is typical usage of Sunamp's by members of this forum primarily only heating from PV/grid?

 

Thanks,

 

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7 minutes ago, Dan Feist said:

@oranjeboom Yes and yes.

 

@JSHarris Do you, or anyone you know use Sunamp with high-temp ASHP?  Or is typical usage of Sunamp's by members of this forum primarily only heating from PV/grid?

 

Thanks,

 

 

 

I'm afraid I don't.  There aren't many ASHPs that will deliver water at ~65°C efficiently, although the hybrid units, like the Daikin Altherma seem to do a good job, and I believe have been used by Sunamp as a heat source: https://www.daikin.co.uk/en_gb/product-group/hybrid-heat-pump.html

 

Because most of our hot water comes from excess PV generation, overall the energy use from the grid just for hot water is pretty tiny.  Our hot water has been solely provided by solar generation since about March this year, and even in winter maybe 30% to 50% of it probably comes from solar generation.  Because using electricity to heat the thing is so simple and easy, I've not bothered to look at other solutions, in fact I've been thinking about removing our ASHP DHW pre-heat system altogether, as we don't use it and it just seems a bit of unnecessary added complexity. 

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4 minutes ago, JSHarris said:

our ASHP DHW pre-heat system

 

@JSHarris I'm sure you have detailed this somewhere else in the forum, but can you either summerize briefly or provide a link?

 

Would it make sense to have standard ASHP heat a PCM35 SunAmp which is used for i) UFH buffer ii)) pre-heated HW, and then use a second PCM55 SunAmp which is heated an additional +20C by PV/grid?  (Would this be similair to what you were hoping to achieve with a sungle Sunamp @oranjeboom ?)

 

This approach (if it makes sense) seems like a good idea, the only issue being that if i) you shower a lot ii) don't size PV large enough, then you could end up paying for a lot of grid electricity for your HW, and I doubt it's that easy to model this..

 

 

 

 

 

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The preheat system is just a 70 litre buffer tank that's heated to ~40°C by the ASHP, and this has a flow and return to a plate heat exchanger, with a small Wilo pump as the circulator.  The plate heat exchanger is above the buffer tank, so there's a bit of thermosyphon action that keeps it warm.  I have a flow switch fitted in the cold supply to the hot water system, so when a hot tap is opened the circulator pump turns on, pulling warm water through the primary side of the heat exchanger.  Cold water to the hot water system flows through the other side, and comes out at around 30 to 35°C, before flowing to the Sunamp.  The Sunamp then only needs to boost this by around 20 to 25°C to get the ~55°C hot water to the house, rather than having to boost it by around 47°C if the Sunamp was fed with cold water.

 

In practice there is plenty of capacity in the Sunamp, so the preheating system isn't needed at all.  With the benefit of hindsight it would have been better not to fit the buffer tank downstairs, and to have installed the Sunamp where than sits, as it would have saved a great deal of pain and grief in getting the Sunamp upstairs (it weighs around 150kg or so).

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14 hours ago, Dan Feist said:

Basically, if there was a PCM55 version, they'd jump on it.. but there isn't.

 

PCM55 wouldn't be much of an improvement over PCM58 but, yes, something like PCM45 to 50 sounds about right, the lowest temperature that'll deliver satisfactory washing-up water. I assume it's a matter of what phase transition temperatures are available from chemicals which are otherwise suitable. Waxes do have their problems as PCMs but have the advantage of tunable transition temperatures by picking the right mixtures of chain lengths.

 

There were concerns about PCM38 (resolved yet, anybody know?) and also it has a greater cost but how about one of those with an inline electric heater on the output? Particularly if it could intelligently deliver the right temperature water to the shower, bathroom taps and kitchen taps so wouldn't use a lot of power or energy. Showers and baths use a lot more water than washing up but generally at a lower temperature.

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16 hours ago, oranjeboom said:

was then thinking of using PCM34 instead as would be able to use a low temp ASHP then as the PCM requires flow temp from heat source at over 45oC. Only downfall then is that the discharge temp is only around 32oC and too cool for our DHW needs.

 

And I'm not aware of where things stand with PCM34 in any case.

 

So I can discount this UNiQ variant then!

 

Back to the Dual and choosing a high temp ASHP then! The mind's beginning to crumble!

 

Based on the interesting feedback from others, seems we have four options:

1) High-temp heat pump to drive UFH and PCM58 Sunamp.

2) Standard heat pump to drive UFH and either a buffer tank or PCM35 Sunamp, then use a PCM58 Sunamp powered by PV/grid (not heat pump) to increase temperature.
3) Heat pump for UFH only.  PCM58 powered by PV (+ grid in winter) for HW.

4) Standard heat pump + standard hot water cycliner.

 

 

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I opted for 4)  A lot cheaper and a lot simpler.

 

The main thing is use an unvented cylinder, NOT a thermal store.  And buy one with the high area "heat pump" input coil. 

 

Also fit a larger volume that you may think necessary, because you will be storing hot water at a lower temperature, so will need more hot water as it is diluted less with cold water than a normal boiler setup.

 

Ours is a Telford Tempest 300 litre version and we heat water to 48 degrees with the heat pump.  This was found by experiment to be just about as hot as you can possibly bear to hold your hands in when you have filled the washing up bowl with just hot water.  I see no point in heating DHW any hotter than that with the heat pump.  This results in the flow temperature from the ASHP reaching about 55 degrees as the cylinder nears it's target temperature.

 

That also leaves plenty of capacity for excess solar PV to heat it further, at the moment my immersion heater thermostat will open at about 75 degrees.

 

The 2 issues with this are it needs G3 unvented cylinder signoff and annual service, and the heat loss to the room will be higher than a SunAmp.  But I find the Telford cylinders pretty well insulated, and of course take care to lag all the connecting pipework well.

 

Also, I don't use a buffer tank.  When space heating, the ASHP directly feeds the under floor heating, and I rely on the heat pump setting the UFH flow temperature (because that is lower than the blending valve on the UFH manifold can be set to)

 

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this whole thread reminds me of why I love buildhub.

I have followed threads on sunamps for a while seeing the upsides, then the downsides regarding ones with electrical input and other issues.

A recent thread about dangers of overheating from hot water cylinders made me reconsider my options and thinking maybe sunamp could be the way to go as but thanks to this thread it seems clear that sunamp and just ASHP isn't going to be that efficient as I hadn't realised the temperature at which the sunamp works best.

 

so back to ASHP and cylinder I will go!

 

 

21 hours ago, ProDave said:

Also fit a larger volume that you may think necessary, because you will be storing hot water at a lower temperature, so will need more hot water as it is diluted less with cold water than a normal boiler setup.

 

Ours is a Telford Tempest 300 litre version and we heat water to 48 degrees with the heat pump.  This was found by experiment to be just about as hot as you can possibly bear to hold your hands in when you have filled the washing up bowl with just hot water.  I see no point in heating DHW any hotter than that with the heat pump.  This results in the flow temperature from the ASHP reaching about 55 degrees as the cylinder nears it's target temperature.

 

dave this is very interesting reading. Is your 300l cylinder for 2 people, 4 people? I had been looking at 170l for what will be 2 people in a small barn conversion. Maybe I should go bigger to account for the lower water heat as you suggest.

I had been looking at a pre plumbed cylinder due to worries about ease of getting it all working together (no plumbing expert myself) but they are expensive. Did you have any problems getting the Telford cylinder plumbed in to the ASHP and everything else? Is it just finding a plumber who has some experience with this sort of configuration?

 

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My set up is similar to @ProDave and I plumbed my cylinder to ASHP with no probs (after advise on this forum), I did however have a few glitches with wiring it all up and setting up the ASHP to do what I wanted but that is all done now (after some more advise on here 👍).

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18 minutes ago, jfb said:

dave this is very interesting reading. Is your 300l cylinder for 2 people, 4 people? I had been looking at 170l for what will be 2 people in a small barn conversion. Maybe I should go bigger to account for the lower water heat as you suggest.

 

We're also planning ASHP + 300L for 2 people, but a 4 bed house and wanted enough for having guests over etc too.

Also we're having 8kW of PV so want the capacity to use the UVC to store heat across days of intermittent solar generation. 

 

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2 hours ago, jfb said:

dave this is very interesting reading. Is your 300l cylinder for 2 people, 4 people? I had been looking at 170l for what will be 2 people in a small barn conversion. Maybe I should go bigger to account for the lower water heat as you suggest.

I had been looking at a pre plumbed cylinder due to worries about ease of getting it all working together (no plumbing expert myself) but they are expensive. Did you have any problems getting the Telford cylinder plumbed in to the ASHP and everything else? Is it just finding a plumber who has some experience with this sort of configuration?

 

This is for 3 people.

 

We have on about 3 occasions run out of hot water.  Never under estimate how much water a woman with long hair can use in the shower. Our shower will run at about 11 litres per minute at full tilt (and of course it is only ever full on, or off) so that's as little as 30 minutes in the shower, a bit longer as it will be adding some cold water so say 45 minutes.  With 3 back to back showers the third one went cold with hair full of shampoo.

 

Remember an ASHP will re heat the tank a lot slower than a high power gas boiler, so don't bank on the HP making up lost heat in real time.  Regard it as purely a stored heat device.

 

I "solved" the run out of hot water issue by fitting as well a Stiebel Eltron  modulating instant water heater,

 

So if the tank does go cold, real time electric heating will make it up the shortfall.  This also enables me to delay the hot water on period until late morning when there is a fair chance the solar PV will be generating something useful, safe in the knowledge that if there is some unexpected early hot water demand, it will be met.

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22 minutes ago, ProDave said:

I "solved" the run out of hot water issue by fitting as well a Stiebel Eltron  modulating instant water heater,

 

Dave, it was mentioned on here some time ago that the Stiebel may cause flow restrictions as it’s only 15mm pipework, did you find this was the case? (I still have mine as a plan “B”).

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12 minutes ago, joe90 said:

 

Dave, it was mentioned on here some time ago that the Stiebel may cause flow restrictions as it’s only 15mm pipework, did you find this was the case? (I still have mine as a plan “B”).

No.  The showers will still flow "too quick" even with all HW piped in 15mm and the Stiebel in line.

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4 minutes ago, dpmiller said:

stealthy flow restrictor time @ProDave?

 

 

Funny you should say that, but back when we were having problems with the Sunamp controller misbehaving (now fixed, they changed the design to eradicate the problem) I fitted an 8 litre/minute flow restrictor to the shower.  It just replaces the normal rubber washer where the shower head connects, and after several months the slight reduction in flow rate, from around 10 to 11l/m to 8l/m, hasn't been commented on, so I've not bothered to remove it.

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3 hours ago, jfb said:

Is your 300l cylinder for 2 people, 4 people? I had been looking at 170l for what will be 2 people in a small barn conversion. Maybe I should go bigger to account for the lower water heat as you suggest.

We have a 180l cylinder heated to 45C which has been fine for the two of us over the last eighteen months. It's heated by an EASHP which runs when needed.

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3 hours ago, jfb said:

 

I had been looking at a pre plumbed cylinder due to worries about ease of getting it all working together (no plumbing expert myself) but they are expensive. Did you have any problems getting the Telford cylinder plumbed in to the ASHP and everything else? Is it just finding a plumber who has some experience with this sort of configuration

 

This is standard S Plan pipework and wiring, or W Plan if you want to prioritise hot water over heating. 

 

An ASHP has two pipes, a cylinder has two, and a UFH manifold has two. Assuming you are not wanting floor cooling, combine the returns from tank and floor, and pipe the feed into a 3 way diverter valve that is open to DHW and closed to UFH. That’s the pipework done. It’s that simple. 

 

Demand comes on with the tank stat and the ASHP fires up. Heating stat comes on, 3 way switches over and you’ve got heat to your UFH. 

 

Not much more to it to be honest ..??

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4 minutes ago, PeterW said:

 

This is standard S Plan pipework and wiring, or W Plan if you want to prioritise hot water over heating. 

 

An ASHP has two pipes, a cylinder has two, and a UFH manifold has two. Assuming you are not wanting floor cooling, combine the returns from tank and floor, and pipe the feed into a 3 way diverter valve that is open to DHW and closed to UFH. That’s the pipework done. It’s that simple. 

 

Demand comes on with the tank stat and the ASHP fires up. Heating stat comes on, 3 way switches over and you’ve got heat to your UFH. 

 

Not much more to it to be honest ..??

All I would add, is my preference is separate 2 port valves rather than a 3 port.

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