Using solar (and attached direct) cylinders as heat stores

[chris watkins]

Thermal stores are still available & still have there place but as said before the amount of hot water (heat energy) you would need to store to provide for domestic heating & HW often means they are impractical.

 

[Sharp Point]

Great products, in behemoth sizes. Akvaterm thermal stores.

:: In English

 

[GregKaye]

Long post alert!

Here in Guernsey a local company used make a product called Ecostor. They are no longer available after they never achieved popularity and had some performance issues in day to day use.

It was a large unvented cylinder with a six kilowatt immersion, a coil for connecting either an oil boiler or heat pump and a second coil for solar. There was a heat exchanger mounted on the outside of the unit to provide hot water. The cylinder was heated by the solar coil when conditions were right with the immersion as a backup and also as I mentioned connected to a boiler or heat pump.

The water in the cylinder was not what came out of your taps, but rather a thermal store. This stored water was pumped both through the heat exchanger for on demand hot water and through the rads to do the central heating.

The problem was that you more or less had to choose whether you have a warm house or hot water. If you came home from work and put the heating on, good luck getting enough hot water for a family to use in the evening as the heat was lost too quickly to the room heating. Likewise, long showers or big baths would deplete the heat store and your heating would not perform adequately. If used very carefully and in a specific way with timings it would work. Likewise for very small properties like flats, it worked ok.

There was never enough stored heat to do both jobs and the immersions ended up being used most of the time which kind of defeated the purpose of the system. Sorry for the long post but these things were never liked here and are no longer available as far as I know. I've got one here in the workshop as a demo model but I've just finished ripping it out as our apprentices really don't work on them enough to dedicate the space any longer.

I'd imagine the people developing it thought this will change everything. At this stage I think things like some buffer tank use and use of thermal stores are mainly for people with real ecological commitment.
I'd imagine that a conventional design of system with one of those devices added in would work.
If people actually stopped using energy when renewables were in short supply then the government might think again about all its expensive non renewable investment.
Thanks for th einfo

 

[Welder]

So you’re trying to build an inter-seasonal thermal store?
You’ll see some on that forum, that are behemoth and buried in the ground with differing types of heat exchangers to heat ufh/ rads/ greenhouses

And hot water.

THere are plenty of people who are doing similar things. One thing I would say to you now is that having pressurised solar panels is a nightmare. THere are plenty of examples now of open vented solar systems are they prove far more reliable than closed systems. Google a guy called Eric Hawkins (he's on Twitter I know). He'll be a good resource as he has an open vented heat recovery system for cooling PV panels so they are more effecient.

 

[chris watkins]

Dave, can I ask why they are a problem & are we talking about directly filled or heat pipes?
I teach solar but must confess haven't got a much practical experience, so always interested.

 

[Sharp Point]

Yes, why are they problematic?

 

[Welder]

Dave, can I ask why they are a problem & are we talking about directly filled or heat pipes?
I teach solar but must confess haven't got a much practical experience, so always interested.

My honest answer is I dont know. My experience of solar has only been to ultimately rip em out as they have leaked like sieves. Three instances of calling designers/maintainers back to check, service & refill again and again. Custs all got fed up & ripped em out (including p1ss poorly insulated thermal stores) and instead put in well insulated & controlled UVCs. Last one has halved her gas bill.

From what I know, the pressurisation is a pivotal problem. Ive had vessels fail so they obvs cause leaks as systems go mental. Ive heard vessels don't last too long in such agressive & hostile environs. Thinking about it, no std rubber diaphragm will stand 120c for too long and each was a std htg type vessel.

 

[Welder]

Thermal stores are still available & still have there place but as said before the amount of hot water (heat energy) you would need to store to provide for domestic heating & HW often means they are impractical.

Remember water is actually a rubbish medium for heat transfer as it's shc is so high. We'd be better off using a different medium but it'd be more expensive and less 'simple' to service.

 

[Sharp Point]

Thinking about it, no std rubber diaphragm will stand 120c for too long and each was a std htg type vessel.

If the vessel was installed in a non stagnation area, the vessel would see no more heat than a standard vessel. Poor installers screwing it up for the customer

 

[Welder]

If the vessel was installed in a non stagnation area, the vessel would see no more heat than a standard vessel. Poor installers screwing it up for the customer

What's a non stagnation area? #IgnoranceIsBliss

 

[Sharp Point]

What's a non stagnation area? #IgnoranceIsBliss

Lol, I’m sure I don’t need to tell you😉

 

[chris watkins]

Or use intermediate vessel, but it is more likely no maintenance on the vessel caused problems.

 

[Welder]

Lol, I’m sure I don’t need to tell you😉

Oh yes you do - please.

 

[Welder]

Or use intermediate vessel, but it is more likely no maintenance on the vessel caused problems.

Thing is, with an open vented system there are no vessels to cause those problems! Regardless, even for systems just ten years old the energy they consumed via their thermal store aspect was simply huge as they were all so poorly controlled.

I do see the benefit of solar but I'd never entertain a thermal store neither would I entertain a sealed/pressurised system. Of course what I do not understand is how one would 'lose' the heat if it wasn't a thermal store. Perhaps it needs to be, is a bigger metalic thermal mass heated using solar but designed more like nuclear fuel rods calculated to absorb huge amounts which can then be lowered into a medium to heat our water. Then we go back full circle to the shc of water and it being a b1tch to heat up...

I need a beer!

 

[chris watkins]

I need a beer!

Your overheating Dave😀

 

[GregKaye]

Thermal stores are still available & still have there place but as said before the amount of hot water (heat energy) you would need to store to provide for domestic heating & HW often means they are impractical.

thanks.
its appreciated to get advice from an actual pro 🙂

 

[GregKaye]

Looks similar to a wet (heating only) system I installed years ago at an outdoor centre. Place was off-grid and previously relied on a generator which had been replaced by a wind turbine and solar PV feeding battery storage & inverters with the genny as backup. Existing turbine controls dumped excess energy into a large resistor heating up the locality once the batteries were charged. We fitted a 1000L buffer tank with 4kW immersion heaters (8x500W) switched by the existing controls so instead of wasting energy it was used to preheat the tank. Heating was weather compensated with 3-way valve. According to the site manager the boiler hardly ran at times in spring and autumn.
Water might not be the best material for thermal storage but it's the easiest to install without getting expensive.

Thanks, its also easy to get the heat out of water which, at times when people might not want to use much energy, has its own value.

 

[GregKaye]

Remember water is actually a rubbish medium for heat transfer as it's shc is so high. We'd be better off using a different medium but it'd be more expensive and less 'simple' to service.

That's new to me. I thought that a high specific heat capacity was a good thing. I thought it meant that more heat could be contained.

 

[Welder]

That's new to me. I thought that a high specific heat capacity was a good thing. I thought it meant that more heat could be contained.

It's that double edged sword Greg. Reasonable retention but hard as hell to heat.

 

[Brambles]

We design and instal, one off renewable energy solutions, generally for larger properties or small commercial premises. In essence your scheme is viable, but would require a fairly complex control system to optimise the performance - the inclusion of the intermittent heat pump (gym powered) significantly adds to the complexity of the system. Heat pumps ideally need to be operational 24/7

In general, if you can design around standard components a neater more economic solution would be achieved.

Three or four coil tanks are only viable with tank capacities greater than 500 litres.

If you are looking for the system to be granted RHI status, then it would need to be designed strictly in accordance to the RHI scheme rules

Hope this helps

 

[Chrisjones.7976]

To store enough water for heating isn't on. You would need a massive amount of storage, just think how much water is contained in a central heating system & multiply it by the number of changes you need to keep the house warm. Yes you can get 3 coil cylinders, I have one, the intermediate coil above the solar one is heated by a wood stove, the boiler heats the top one. I also have an immersion heater which is fed by PV solar panels to stop the surplus electricity going back into the grid.

Regards

Chris

 

[Stigster]

To store enough water for heating isn't on. You would need a massive amount of storage, just think how much water is contained in a central heating system & multiply it by the number of changes you need to keep the house warm.
Chris

This was exactly the problem with our local brand Ecostor heatstores. You put the heating on in the morning and your thermal store was full of luke warm water in about an hour, no good for bathing in conjunction with that. Ecostor were usually 300 litres volume I believe and even that would only work with very careful timed use of the system or in a bedsit with 2 rads and one shower, usually electric!