Thermino Thermal Battery

[gmc600]

Hi,

Looking for some advice, an installer came to give me a quote for solar panels and he brought up the subject of a heat pump too. I live in Scotland and apparently the grants only apply if you get both together, which is fine as my boiler is getting old anyway. He said something about the radiator pipes being too small so we would need to install a new hot water system which is essentially one of these thermal batteries containing a phase change material. I asked a few questions and he started sounding like he didn't really know what he was talking about and his claims that this new system would save us so much money became a little too good to be true. I understand how a phase change material works and that it's more compact than a water tank, but why is it superior to my existing HW system in terms of compatibility with heat pumps?

The house was built in 2016 and is fully triple glazed so I was expecting a drop in replacement for our boiler would be possible. We have a large hot water tank which is connected to the boiler and 2 solar thermal panels, I'd like to leave this untouched if possible.

Thanks!

 

[endecotp]

> He said something about the radiator pipes being too small

More likely the radiators themselves being too small. The water temperature (for efficient operation) from a heat pump is lower than for a boiler, so more radiator surface is needed to transfer the heat into the room.

> he didn't really know what he was talking about

Where did you find him?

 

[polesapart]

I asked a few questions and he started sounding like he didn't really know what he was talking about and his claims that this new system would save us so much money became a little too good to be true.

First impressions very likely correct...

 

[gmc600]

> He said something about the radiator pipes being too small

More likely the radiators themselves being too small. The water temperature (for efficient operation) from a heat pump is lower than for a boiler, so more radiator surface is needed to transfer the heat into the room.

> he didn't really know what he was talking about

Where did you find him?

Thanks, I'm aware that radiators might be too small, but he didn't mention that. The pipes were they only thing that he brought up that might be an issue, but what does that (or even the size of the radiators) have to do with how the hot water is stored?

Found him from Home Energy Scotland!

 

[Madrab]

I would recommend you do some background reading about heat pumps and thermal banks etc. These systems aren't quite all they are cracked up to be, especially the further north you come and have to be worked with and managed quite specifically.

Typically with a gas central heating system - a rads output rating is typically taken at a delta of 50deg (70 deg system and 20deg room temp = delta50), so the heat loss calcs to establish how much heat the room needs from the rad is calculated at roughly those delta's. With the lower running temps of a heat pump then the deltas drop to around 30deg (50deg system - 20deg room = 30deg delta) therefore the output rating of the rad drops accordingly, therefore to obtain the same rad heat output to satisfy the heat loss, the rads typically have to be increased in size by 25>30%.
Given a HP runs at around 50Deg - then a standard HW cylinder will only be heated to that temp - it can then become a contamination risk (legionella etc) and it will require an electric top up on a schedule to bring it to a temp (55-60deg) where bacteria will be destroyed. A PCM bank is much more efficient @ usable heat storage (3>4times) than using water etc as a thermal bank, so it makes the system much more energy efficient.

PCM's are relatively new to the domestic heating world so the jury's still out but it does look very promising.

You mention solar thermal - is that and evacuated solar thermal tube setup?

 

[polesapart]

Increased radiator sizes may require larger pipework. Survey and calculation required.

 

[flameport]

We have a large hot water tank which is connected to the boiler and 2 solar thermal panels, I'd like to leave this untouched if possible.

You can.

. I understand how a phase change material works and that it's more compact than a water tank, but why is it superior to my existing HW system in terms of compatibility with heat pumps?

It isn't. Smaller physical size for the same heat storage, but that's only relevant if there is a lack of space.
Any claims about efficiency are hogwash even if true - hot water is a minor part of the operating cost, as most building energy is used for space heating.
Your existing solar hot water provides energy for nothing. If you remove it, then rather obviously you will have to get that energy from somewhere else, which will likely mean paying for it either directly via increased electricity usage, or indirectly via the cost of replacing a working system with something else.

The house was built in 2016 and is fully triple glazed so I was expecting a drop in replacement for our boiler would be possible.

It should be, as an installation from less than a decade ago should have been specified for 55C or lower flow temperatures.

Whether it was or not is another matter.
Even if not, it may be that it will work satisfactorily with low flow temperatures, all depends on the size of the radiators and the heat loss of the building - and if they haven't done that calculation (several hours of work) then they are just guessing at what might be required.

 

[gmc600]

I would recommend you do some background reading about heat pumps and thermal banks etc. These systems aren't quite all they are cracked up to be, especially the further north you come and have to be worked with and managed quite specifically.

Typically with a gas central heating system - a rads output rating is typically taken at a delta of 50deg (70 deg system and 20deg room temp = delta50), so the heat loss calcs to establish how much heat the room needs from the rad is calculated at roughly those delta's. With the lower running temps of a heat pump then the deltas drop to around 30deg (50deg system - 20deg room = 30deg delta) therefore the output rating of the rad drops accordingly, therefore to obtain the same rad heat output to satisfy the heat loss, the rads typically have to be increased in size by 25>30%.
Given a HP runs at around 50Deg - then a standard HW cylinder will only be heated to that temp - it can then become a contamination risk (legionella etc) and it will require an electric top up on a schedule to bring it to a temp (55-60deg) where bacteria will be destroyed. A PCM bank is much more efficient @ usable heat storage (3>4times) than using water etc as a thermal bank, so it makes the system much more energy efficient.

PCM's are relatively new to the domestic heating world so the jury's still out but it does look very promising.

You mention solar thermal - is that and evacuated solar thermal tube setup?

Thanks for the info, is there truth to this though:

Not sure I understand how the PCM can be 3-4 more efficient than my existing cylinder which is rated at 2.1 kWh loss per 24h. That would mean worst case I lose about 16% (250 litre cylinder) per day, although I suppose that will add up to quite a lot longer term! What heat loss do they typically have? It does sound promising but I did hear a few complaints about them leaking the PCM and it dripping through ceilings and stuff like that! I'm just not sure if it's really a must to replace it given that these (the Sunamp ones at least) aren't compatible with my existing solar thermal. It's not evacuated tube, just flat panels (something like this: link). They're great in summer, almost no need to run the boiler at all these past few weeks, but useless in winter!

 

[gmc600]

Increased radiator sizes may require larger pipework. Survey and calculation required.

Thanks, but why does that lead on to the need to replace the hot water tank?

 

[gmc600]

You can.


It isn't. Smaller physical size for the same heat storage, but that's only relevant if there is a lack of space.
Any claims about efficiency are hogwash even if true - hot water is a minor part of the operating cost, as most building energy is used for space heating.
Your existing solar hot water provides energy for nothing. If you remove it, then rather obviously you will have to get that energy from somewhere else, which will likely mean paying for it either directly via increased electricity usage, or indirectly via the cost of replacing a working system with something else.


It should be, as an installation from less than a decade ago should have been specified for 55C or lower flow temperatures.

Whether it was or not is another matter.
Even if not, it may be that it will work satisfactorily with low flow temperatures, all depends on the size of the radiators and the heat loss of the building - and if they haven't done that calculation (several hours of work) then they are just guessing at what might be required.

Thanks for the detailed reply, I suppose I can just ask other installers for their opinion as they can all get the same government grants I presume?

 

[Madrab]

Thanks for the info, is there truth to this though:

Yes - the next gen HP's utilising the R290 refrigerant (propane) can get up to higher temps but as suggested the COP can drop dramatically and there are a min output size requirement to effectively reach those temps and as the output rises the % drop in COP increases , which TBH is the whole point. The new regs are pushing the older high GWP refrigerants to be replaced by these newer 'safer' gases. Current R32 systems are due to be phased out by 2026/27. Grants help of course but they are on a sliding scale depending on what's being fitted and these system are still really quite expensive. They new R290 does target the retrofit arena (they are more of a replacement to gas/oil boilers due to the higher temps) rather than the design of a low temp UFH system coupled with solar to augment the HW (which you already have) which I believe was the whole point of of HP. I have a client that uses a HP Vaillant system using R290, fitted last year. He also has a WB gas boiler and uses that more than he uses the HP, noise is one of the issues.

That being said these new units are exactly that - next gen and new - and as with all new tech it usually takes some time to iron out all the bugs, not sure about comparable costs of the hardware too but if grants are available. The hardware is similar though. Again, another inevitable upscale to the tech and R290 is coming online now and it's the next iteration until newer GW regs drive further change.

 

[flameport]

I suppose I can just ask other installers for their opinion as they can all get the same government grants I presume?

You can but the problem with asking people who are signed up to grants schemes is that a lot of them only exist to sell people more stuff.

It's very difficult, but you need to determine whether they are they to provide actual advice which is relevant and will result in you getting an appropriate heating/hot water system,
or if they just want to sell you the latest gadget because they can make loadsamoney by doing so.

The reality is that a hot water system that's barely 10 years old should not need replacing,

 

[Madrab]

Couldn't agree more - these days a lot of 'new and green' companies and installers get on the latest government bandwagon as it's basically a licence to print money, especially where grants are involved - we saw it on the boiler scrappage scheme, then all the green deals and now the newer GW incentives. They will try to lever as much new stuff as they can to maximise their profits.

What the client may have already installed whether viable or not can restrict that.

As suggested, you are obtaining free energy at the moment for your HW, it would be mad to remove that.