SunAmp : Snog, Marry, Avoid?

[ToughButterCup]

 

For those of us contemplating fitting a SunAmp box, should we   SNOG, MARRY, AVOID?

+++++++++  Last updated 28th Feb, tea time. +++++++++++

THREAD SUMMARY

 

Core issue: given the concerns expressed in this thread , is a SunAmp system a sensible purchase?

• Whats the concern? The issue is that one person (so far) reports that the system he has won't recharge until either 50% or 90% depleted. So you could run 48% out on day 1, it won't charge overnight and then day 2 you try and use 65% and it will go cold. ( @PeterW ) 
• ?  ( @Roz )
• If 'charging' with hot water, then charge management problem disappears : ( @JSHarris  )
• @PeterW suggests  '... simple pump and heater on a dedicated circuit with a small expansion vessel and run at 1 bar ...' 
• The main selling point of the Sun Amp is the much lower standing heat losses than a HW tank.  That is indisputable.  So it comes down to does this advantage outweigh the extra costs and the extra "difficulties"? ( @ProDave )
• So a Sun Amp may have an advantage if you are tucking it down  down in the eaves where a taller tank might not fit, but otherwise I see little advantage. ( @ProDave )
• There are few, if any, significant issues with the non-electrically heated Sunamps, they seem to work very well and provide a reliable, low heat loss, way of storing heat for either hot water or heating.  ( @JSHarris )
• I'd be reluctant to recommend the electrically heated Sunamp versions at the moment, at least until they come up with a more sensible controller. ( @JSHarris below)
• ' ... Why are we debating "work arounds"? The product should just do as advertised! It doesn't!! ...'   ( @Barney12)
• @Nickfromwales joined the discussion; he suggests that errors may well have been made in the specification of some installs -  that error source is likely to be reduced by SA's policy decision to have approved installers involved in the specification process. He points to the distinction between USEFUL capacity and ABSOLUTE capacity.  He also raised an eyebrow at SAs apparently poor communications flow.

• However, there is some evidence that SA may not be (or have recently started)  applying the Installer Only  as Specifier policy in every case. ( @paulmb  and @newhome)

• In respect of Sunamp UniQ units, a clear distinction was drawn by @JSHarris between electrically heated models and those heated by water ( from another source) The former appears to be unreliable, the latter reliable.

• @JSHarris and @Barney12 both argued that the the 'box' should do what it says on the tin.

• @Nickfromwales argument is that we should leave the installer to specify the size of the tin. He presents clear evidence of multiple successful installs. And hints that the problem under discussion might well be unique: so far it has been reported by only one person.

 

I've read and re-read this thread now many times. The thing that worries me is that - as written - the problem statement (one instance of the electric charge version of Uniq doesn't work as advertised) appears to be based on a very small sample size : 1.  

 

So, @Pete, you first? 

[Pete]

Let me know when WE have made a decision pls Ian!! I am with you on this one as we would have gone with a Sunamp but having doubts now.

[Ed Davies]

It'll be a while yet so plans might change but my current thought is to use one without any of their electrics. I.e., charge via hot water through the low-power circuit and extract heat for DHW via the high-power circuit. Maybe also extract some heat for space heating via the low-power circuit.

 

To me the main attraction is to be able to use relatively low temperature heat sources (solar thermal, maybe boosted by diverted PV) to charge to just above DHW temperatures while still getting good capacity. Being purely hydronic is for flexibility of heat sources and sinks beyond anything their controller is ever likely to deal with but @JSHarris 's problems confirm. AIUI, as long as the input water temperatures are kept low enough such a system should be intrinsically safe for the gunk.

[Jeremy Harris]

@Ed Davies, I think your idea makes a lot of sense.  If charging with hot water only then pretty much all the charge management problems go away.  The Sunamp PV only measured the temperature of the hydronic charge circuit in order to determine whether or not to allow the heater to be powered.  This was a pretty fail-safe method, that also allowed the PCM to accept a charge, even when already in the liquid state.  It allowed some additional sensible heat to be stored in the region above the 58°C melting point, up to the hydronic loop maximum temperature, probably around 65°C to 70°C at a guess.

 

I still have the option of doing this with our unit, and just ignoring the electric heating element altogether.  Both heat exchangers are fitted to the eHW models, as they use what seems to be the same heat cell as the water-heated units.  All (!) I'd need to do is put a charging system together, with a heating element (probably a Willis) plus a variable speed pump and some temperature sensors, so that the charge loop could be run at the required temperature.  Pity I don't still have the Sunamp PV, as it would have been relatively easy to just take the whole charging circuit from that and adapt it to charge the UniQ cell instead.

[PeterW]

I’m with @Ed Davies and @JSHarris on this - Willis based simple pump and heater on a dedicated circuit with a small expansion vessel and run at 1 bar which would be outside of the G3 regs. 

[Dreadnaught]

2 hours ago, Ed Davies said:

It'll be a while yet so plans might change but my current thought is to use one without any of their electrics. I.e., charge via hot water through the low-power circuit and extract heat for DHW via the high-power circuit. Maybe also extract some heat for space heating via the low-power circuit.

 

To me the main attraction is to be able to use relatively low temperature heat sources (solar thermal, maybe boosted by diverted PV) tocharge to just above DHW temperatures while still getting good capacity. 

 

Would you be using the PCM 34 of 58? 

 

58 I assume. But, I wonder, is there a role for a PCM 34 cell too, @le-cerveau-style? Presumably not. Which makes me wonder why @le-cerveau went for both types of cell, especially when PCM 34 has had some issues, although I think those issues are now resolved.

 

The mantra I thought I had learnt early on in my research about PCMs was that the input (not output) temperature defines the PCM to be chosen.

Edited February 27, 2019 by Dreadnaught

[PeterW]

@recoveringacademic if you start to introduce volumes of pressurised hot water above a certain size then it gets into the realms of G3 and other regulations and needs various pressure relief systems and subsequent sign off / servicing. 

[epsilonGreedy]

So pleased I can only afford Jurassic PV and as a result I will not have to understand this debate.

[Jeremy Harris]

48 minutes ago, Dreadnaught said:

The mantra I thought I had learnt early on in my research about PCMs was that the input (not output) temperature defines the PCM to be chosen.

 

 

This is true, as if you heat the PCM to a temperature below the phase change temperature then it can only store heat in line with the heat capacity of the solid PCM.  Once you heat it to the phase change temperature it can store a lot more heat, over a very small change in temperature around the melting point of the PCM.  Heating the PCM above the melting point goes back to just relying on the heat capacity of the liquid PCM for additional heat storage, rather than the latent heat of fusion, but it adds some useful extra capacity, around 1.5 kWh for a 15 K ∆ T (with a guess that there is around 130kg of PCM in a UniQ 9).

 

. 

 

 

[ToughButterCup]

So, is any SunAmp product worth considering to provide any form of heating - water or space in a house?

(Trying hard to boil this down to a fairly understandable answer to a very simple question)

[Jeremy Harris]

10 minutes ago, recoveringacademic said:

So, is any SunAmp product worth considering to provide any form of heating - water or space in a house?

(Trying hard to boil this down to a fairly understandable answer to a very simple question)

 

There are few, if any, significant issues with the non-electrically heated Sunamps, they seem to work very well and provide a reliable, low heat loss, way of storing heat for either hot water or heating.  

 

The advantages over a hot water cylinder are primarily the smaller physical footprint and the much lower heat losses.

 

The disadvantages are the price premium and the weight of the units (not heavier than a hot water cylinder when full, but a lot heavier to install initially).

 

I'd be reluctant to recommend the electrically heated Sunamp versions at the moment, at least until they come up with a more sensible controller.

[ToughButterCup]

24 minutes ago, JSHarris said:

[...]

I'd be reluctant to recommend the electrically heated Sunamp versions at the moment, at least until they come up with a more sensible controller.

 

Thats @JSHarris key point.

I bet there are others. 

 

Anyone?

[ProDave]

As I see it:

 

Yes the sun amp is "smaller" but it takes up just about the same amount of floor space as a hot water cylinder, it's just that the HW cylinder is taller.  So a Sun Amp may have an advantage if you are tucking it down  down in the eaves where a taller tank might not fit, but otherwise I see little advantage.

 

The main selling point of the Sun Amp is the much lower standing heat losses than a HW tank.  That is indisputable.  So it comes down to does this advantage outweigh the extra costs and the extra "difficulties"?

 

The big question is how are you going to heat the tank?  And the fly in the ointment there is the PCM temperature is too high for heating with an ASHP.  Now you might only get a COP of say 2 from your ASHP when heating hot water temperatures but that is still better than a resistance heating element.

 

If you have a lot of PV (and I am not sure 4KW is really "a lot") and can be sure that a lot of the time you have excess PV to heat the water then that swings it in favour of a SA, but don't forget your HW tank also has an immersion heater, so it can do that as well.

 

Oddly enough, to me a Sun Amp makes a lot more sense as a companion to a gas system boiler instead of a HW tank, where you can reliably heat it from the boiler, or (when it is playing ball) from surplus PV.   For a "heat pump house" I saw too many disadvantages.

 

 

[joe90]

 

 

Well being a Luddite I went with a hot water cylinder (recommended and purchased thro our friendly welsh plumber) probably because the sun amp was very new and I did not want to be a guienny pig!. I know @JSHarris had over heating probs from his cylinder but my missus is complaining our airing cupboard is not warm enough and frankly storing DHW at 47’ I can feel very little heat loss from it at all. 

 

P.S. we don’t have PV.

Edited February 27, 2019 by joe90

[Jeremy Harris]

In reality the floor space is a fair bit smaller, too, as being rectangular the Sunamp will fit closer to walls:

 

[ProDave]

7 hours ago, joe90 said:

. I know @JSHarris had over heating probs from his cylinder but my missus is complaining our airing cupboard is not warm enough and frankly storing DHW at 47’ I can feel very little heat loss from it at all. 

I think, like me, you have a Telford unvented cylinder?  I have to say I am impressed with the as supplied thermal insulation, and I have take care to well lag all the connecting pipework.  I don't "feel" any heat loss and certainly not enough to cause problems.  I am pretty sure the foam lagged copper tanks on common sale are a lot worse from an insulation point of view, and a thermal store more so because of the higher temperature of the stored water.

 

 

[ToughButterCup]

1 hour ago, epsilonGreedy said:

So pleased I can only afford Jurassic PV [...]

 

Been going long before the Jurassic son.......

[Roz]

I'm confused, what is the problem with electrically charged sunamps? I thought the love was across the board. We had planned to use one charged on cheaper overnight electricity for our DHW as we cant afford PV right now. Then space heating directly from ASHP...

[PeterW]

3 minutes ago, Roz said:

I'm confused, what is the problem with electrically charged sunamps? I thought the love was across the board. We had planned to use one charged on cheaper overnight electricity for our DHW as we cant afford PV right now. Then space heating directly from ASHP...

 

The issue is that they won't recharge until either 50% or 90% depleted. So you could run 48% out on day 1, it won't charge overnight and then day 2 you try and use 65% and it will go cold.

 

The water heated ones don't have this issue.

[Jeremy Harris]

1 minute ago, Roz said:

I'm confused, what is the problem with electrically charged sunamps? I thought the love was across the board. We had planned to use one charged on cheaper overnight electricity for our DHW as we cant afford PV right now. Then space heating directly from ASHP...

 

 

There's a long running issue with trying to reliably get an electrically charged Sunamp UniQ to work from either excess PV generated power or from timed off-peak power, like E7.  It's all buried in these two other (long) threads about Sunamp issues:

 

 

 

[Roz]

@PeterW @JSHarris    ?

[PeterW]

Just a mad thought....

 

If you put a Steibel Eltron in line water heater into the flow from an ASHP to the Sunamp, would it not then take the output from the ASHP up to recharge temperature..? They are thermostatically controlled and the heat would only be the delta between the ASHP and 58c..?

 

Or should I stop smoking tea bags..?

 

 

[Jeremy Harris]

Just now, PeterW said:

Just a mad thought....

 

If you put a Steibel Eltron in line water heater into the flow from an ASHP to the Sunamp, would it not then take the output from the ASHP up to recharge temperature..? They are thermostatically controlled and the heat would only be the delta between the ASHP and 58c..?

 

Or should I stop smoking tea bags..?

 

 

 

 

Yes, it might work, but probably only with a PV diverter that pulses full voltage, rather than one that modulates voltage (I think the newer Immersun modulates the supply voltage, as does at least one other unit I've heard of). 

 

Not sure how A steibel Eltron type control circuit would cope with being pulsed on and off every second or so, but it might tolerate it.  It might be possible to alter the internal wiring to maintain power to the control side and modulate power to the heating element power control part.  That might then allow the temperature control bit to try and do it's thing, free from being pulsed on and off, yet modulate the power available to the heating element.

 

It only needs a low power one, though, so I wonder if they do a 3 kW version? 

[PeterW]

@JSHarris I'm thinking for those that want to run an ASHP and a Hot Water Sunamp, so it is only being used as a booster to allow you to use just a SunAmp DHW on E7 alone but use the ASHP

[Dreadnaught]

1 minute ago, PeterW said:

@JSHarris I'm thinking for those that want to run an ASHP and a Hot Water Sunamp, so it is only being used as a booster to allow you to use just a SunAmp DHW on E7 alone but use the ASHP

 

Wouldn't it be better to have a PCM 34 Sunamp and the Steibel Eltron in line water heater between the Sunamp and the shower head?