AndyT ( Andy Trewin ) formerly of Sunamp

[newhome]

2 hours ago, JSHarris said:

 

The PCM in a Sunamp will hold a thermal charge for days, as it doesn't store heat as heat, as such.

 

So, my TS is heated by my electric boiler. I don’t use all of the hot water with just me there so I lose a fairly significant amount via standing losses. If I’m reading this correctly I could replace the TS with a Sunamp and I then wouldn’t need the boiler to run as often? Correct?

 

So the main question is, if I didn’t change anything else what is the cost of replacing a TS with a Sunamp or 2 (how many are needed to replace a 475l TS)?

 

[PeterW]

I reckon you would need 3 sunamp units - could even bin the boiler however the solar thermal would possibly become redundant unless you had a smaller buffer of say 150 litres acting as a preheat for the DHW. 

 

What say you @Nickfromwales..?

[Nickfromwales]

Leave it alone, and get the ST working for DHW through the summer and use the money saved to buy the first round  ?

 

[newhome]

14 minutes ago, Nickfromwales said:

get the ST working for DHW 

 

???? do you know how many people I’ve asked ????

 

 

[Triassic]

On 09/10/2018 at 20:16, Triassic said:

According to Sunamp a local partner has been appointed, EcoPartners. I’ll have to look them up! I wonder how much experience they have?

When in Duscussions with AndyT I’d wanted a price for a couple of units capable of running both the DHW and the UFH.

 

Having done more research into the various options, I’ve come to the conclusion that I need a system similar to Jeremy’s, with as ASHP supplying a buffer  and the UFH, with a plate heat exchanger providing preheat to the DW supply to the Sunamp. I’ve also thrown into the mix, the fact I’ll have 4kw of PV. Let’s see what EcoPartners come up with!

[Nickfromwales]

With a suitably sized SA unit you won’t need the pre heat tbh. You’ll only need the preheat if you go for a small SA unit. There is merit if you need a buffer anyhow but you could easily get 6kW of space heating from 2x SA units with a 3kW immersion in each. They could be beefed up to do both space heating and DHW with change from the ASHP + buffer etc option tbh but your driving off grid or Eco7/10 then ( unless you’ve got PV ). 

ASHP can be useful for cooling though so needs a lot of thought. ?

[Triassic]

3 minutes ago, Nickfromwales said:

ASHP can be useful for cooling though so needs a lot of thought.

That’s the function I’m interested. The summers are only going to get hotter and a bit of cooling would be nice, especially if I can find an eBay bargain.

[Jeremy Harris]

I'd be inclined to agree with @Nickfromwales about the preheat, in that it's an added complication that was useful when we had the much smaller Sunamp PV, and the old thermal store before that, but it's not really needed for the Sunamp UniQ, with it's much greater storage capacity.  The UniQ 9 eHW we have now is roughly equivalent to a 210 litre hot water cylinder, but with much lower heat losses, just 0.73 kWh/24 hours when it's hot, and I suspect a fair bit less than this when it's just sitting with the PCM charged but not hot.

[MikeSharp01]

2 minutes ago, JSHarris said:

I suspect a fair bit less than this when it's just sitting with the PCM charged but not hot

Does it loose anything if it's just standing waiting to be triggered or is there some background activity that has a price in heat loss?

[Jeremy Harris]

9 minutes ago, MikeSharp01 said:

Does it loose anything if it's just standing waiting to be triggered or is there some background activity that has a price in heat loss?

 

Hard to say.  The thermal camera shows that the thing sits with the case at ambient temperature when it's charged.  There's no background activity, just the ~6 W that the control box draws from the mains.

[Ed Davies]

36 minutes ago, MikeSharp01 said:

Does it loose anything if it's just standing waiting to be triggered

It's still at 58 °C - there's nothing magic about that so heat will flow out of the box, albeit slowly with the vacuum insulation.

[Jeremy Harris]

4 minutes ago, Ed Davies said:

It's still at 58 °C - there's nothing magic about that so heat will flow out of the box, albeit slowly with the vacuum insulation.

 

Not sure it is, TBH.  When the sodium acetate has changed phase from solid to liquid, the energy is locked up within it, so the PCM can cool down, yet still store sensible heat as a liquid. 

 

When we were clearing the old house to move I found a sodium acetate phase change hand warmer in a drawer.  It was liquid, so I clicked the nucleator and it immediately started to crystallise and get hot.  I've no idea how long it had sat "charged" in that drawer, but it was certainly more than 3 years.

 

The PCM 58 used in the hot water Sunamps is sodium acetate, too, so I'd expect the same sort of behaviour.

[MikeSharp01]

39 minutes ago, JSHarris said:

 

When we were clearing the old house to move I found a sodium acetate phase change hand warmer in a drawer. 

Yes we have loads of these at home the kids took skiing and I suspect they all still work as I used one last year to great effect. I have not really looked at the underlying technology but heat loss once it is charged feels counterintuitive although the vac panels must have some function.

[Ed Davies]

37 minutes ago, JSHarris said:

yet still store sensible heat

 

Latent heat.

 

You've obviously had much more to do with this than I have. Still, I'd be surprised if there's anything more than the temperature controlling the phase transition. With those clicky things in hand warmers once you've clicked it the whole lot transitions (over a period of half an hour or so). (BTW, just clicked one which had been in the draw since last winter - seems to run at 46 °C.) There's no way to stop it other than heating it up again. Doesn't the water come out at 50 something degrees immediately? That means it must be stored at that temperature, doesn't it?

[jack]

4 minutes ago, Ed Davies said:

Doesn't the water come out at 50 something degrees immediately? That means it must be stored at that temperature, doesn't it?

 

Yes, I believe that's right. It will stay at the transition temperature as heat is extracted until it's completely melted, and will then start cooling again.

 

Presumably the material can also be heated above 58 deg C, in which case it will cool like any other material until it reaches the transition temperature. 

[Onoff]

Off to find the vinegar, bicarb and an old flask...

Edited October 11, 2018 by Onoff

[Jeremy Harris]

One of the key things that isn't in the public domain (AFAIK) is the way that Sunamp control nucleation and stop and start it.  I think this was the key to getting the system to work as well as it does.  Others had tried to use sodium acetate as a phase change heat store and not been able to crack the nucleation problem.

 

The additional 1.5 kWh that's stored (over the 9 kWh rating of the UniQ 9) comes from the heat capacity of the sodium acetate when it's hot and liquid, I believe, whereas the 9 kWh base heat storage is from the latent heat from phase change.

[MikeSharp01]

This is more interesting than I had thought as there must be heat loss if the first water out is at 50 deg C plus although it could be tiny if it can then heat water quickly which I guess must be a function of the internal arrangements of water pipework and the cells. If you think about it the nucleation will perhaps need to be controlled backwards down the pipework as the water starts to move through the lattice  (if there is one) the early cells at the output end of the line will exhaust and start to be a drain on the heat from cells further back down the chain. So control becomes everything and there might, one supposes, be some internal gubbins that directs the flow across several pathways to reduce this effect which may also use flow rate to control. Will the patents not be viewable? Might give us a hint!

[Jeremy Harris]

16 minutes ago, MikeSharp01 said:

This is more interesting than I had thought as there must be heat loss if the first water out is at 50 deg C plus although it could be tiny if it can then heat water quickly which I guess must be a function of the internal arrangements of water pipework and the cells. If you think about it the nucleation will perhaps need to be controlled backwards down the pipework as the water starts to move through the lattice  (if there is one) the early cells at the output end of the line will exhaust and start to be a drain on the heat from cells further back down the chain. So control becomes everything and there might, one supposes, be some internal gubbins that directs the flow across several pathways to reduce this effect which may also use flow rate to control. Will the patents not be viewable? Might give us a hint!

 

 

There's no switching of water pathways, just two embedded heat exchangers and a heating element, and there is now just a single big heat cell.  There's nothing mechanical that moves at all in the heat cell, the key is in the formulation of the PCM compound I believe.  Although it's sodium acetate based, it has been modified, presumably to make it self-nucleating, and that knowledge is being kept pretty secret by Sunamp.  All I know is that when I've pointed a thermal imaging camera at a charged Sunamp PV, it's at room temperature, but when you turn on a hot tap, the outlet pipe gets hot almost immediately.  How they control nucleation seems to be key, and not something we're likely to find out easily, I think.

[Ed Davies]

Anybody know if I'm right in thinking that a UniQ HW could be used without any electricity at all? E.g., in an Amish house (?) charge it via thermosyphon from a back boiler or solar thermal through the low-power circuit, with some sort of thermostatic valve to stop it overheating, and take heat out by flowing cold water through the high-power circuit.

[Jeremy Harris]

Sounds feasible, as long as the charge temperature is controlled. 

 

I've noticed that the UniQ eHW pulses the heating element on and off when charging from cold, when the PCM is solid.  I'm guessing it does this to make sure the PCM doesn't locally overheat.  Once the PCM has started to melt it seems that convection in the liquid works to prevent local overheating.

[mvincentd]

On 11/10/2018 at 15:27, Triassic said:

Let’s see what EcoPartners come up with!

Well on Wednesday they tried to tell me SA couldn't do heating AND dhw....then said they'd check with technical, and i've heard nothing since.  I don't see these guys solving any time soon the difficulties we're all having with the communication of good information on Sunamps.

[Nickfromwales]

11 hours ago, mvincentd said:

Well on Wednesday they tried to tell me SA couldn't do heating AND dhw....then said they'd check with technical, and i've heard nothing since.  I don't see these guys solving any time soon the difficulties we're all having with the communication of good information on Sunamps.

Most of it can be solved here TBH.

I'm having a training day up in Scotland on the 25th, so the last of the fog should lift then ( hopefully ).

To be fair, I think the various companies now bragging up their ability to provide and install SA's will all be just ringing SA technical until their phone melts. Thats a bottleneck at the moment but that should soon be resolved. I've been told they ( SA ) have recruited more staff for various key positions to get some oil onto the cogs. .

SA's will indeed service heating and hot water, but its a huge calculation on sizing and unit type selection.

 

On 11/10/2018 at 19:20, Ed Davies said:

Anybody know if I'm right in thinking that a UniQ HW could be used without any electricity at all? E.g., in an Amish house (?) charge it via thermosyphon from a back boiler or solar thermal through the low-power circuit, with some sort of thermostatic valve to stop it overheating, and take heat out by flowing cold water through the high-power circuit.

It would indeed be heated by a wet external heat source. The criteria would be that the heat of the input water never exceeded 80^oC, with an absolute of 85^oC. Im not exactly sure how controllable or reliable that would be with such a coarse means of heat delivery as typically I am specifying a pumped, thermostatically blended input to maintain flow and temperature control as accurately as possible. If you overheat one of these its in the bin with no warranty claim.

This is where the 'issue' lays, eg you need to have someone sense check your ideas, ( by knowing what there talking about or cross referencing your idea with SA directly ), or you fly solo and take your chances by yourself ( if your a tinkerer ).   

[Ed Davies]

Thanks @Nickfromwales, yes, I realise that you need to be sure of not going over the temperature limit. My doodles have this all controlled in software but I've just sketched in a normally-closed pipe thermostat in series with the valve motor controlling the heat input to the Sunamp as a backup.

 

My main point, though, was that there's no electrical input needed to control the PCM's phase-change behaviour; as I understand it; that's purely a thermodynamic/chemical/mechanical thing, however it actually works?

[Nickfromwales]

It is, but I’m not sure hydraulically how thermosyphon would work in a SA with the connections at the top and the HEx downward orientated. In theory it shouldn’t be a problem as that’s how some of the early top loaded immersion coils were configured, but I’d make sure there was sufficient pipe work between the two to properly promote circulation. 

I do zero with thermosyphon tbh and I’ve not done a gravity DHW install for over 15 years now so I’m a bit rusty on that, and the exact / relevant criteria. 

I very much fear any single means of controlling that heat and would imagine it’s not a setup that SA would endorse or warranty. You could, I suppose, jump that hoop by fitting a pipe stat and a zone valve, eg one that’s normally closed / energise to open.