Solar Store - heat battery

[Jeremy Harris]

7 minutes ago, PeterStarck said:

We visited Richard Hawkes PH around 2008 while it was being built and he had paraffin wax phase change panels in his walls.

 

 

Interesting.  I've just been looking up the phase transition temperature for paraffin waxes and it seems that they can be very finely tuned, with one form of paraffin wax having a phase transition temperature of 21.7 °C , which looks to be a good match to a room temperature stabilisation system like this.  The effect would be to increase the thermal time constant of the house a fair bit, I would imagine, with the panels absorbing heat when the room temperature is over 21.7 °C  and then releasing it when it drops below that temperature.

[Onoff]

Aren't external "yard" furnaces popular in the States?

 

Can't see the issue of a well insulated, bfo buried tank of oil/wax and well insulated pipes into the house like on an ASHP.

[Dreadnaught]

There has been some limited research into using particles of paraffin wax embedded in sand (even just plain old beach sand) as a latent heat store. Such particles could even be made to flow. Some referred to this being "nano technology".

 

I find it an intriguing idea. Prompted by @JSHarris above, I skim read a few articles in the subject area.

 

Are there any links to that house which had paraffin-wax panels in the walls?

Edited December 7, 2018 by Dreadnaught

[Dreadnaught]

Here's a company commercialising paraffin-wax products for thermal buffering. They mention walls.

 

https://www.microteklabs.com/nextek

 

Who wants to be the first on BuildHub to try this out?  

[Jeremy Harris]

If anyone wants to do some reading, this paper from 2009 reviews many of the available PCMs and is written in a form that seems reasonably easy to read: Review of thermal energy storage with phase change materials - Sharma 2009.pdf

[Ed Davies]

Had a very brief correspondence with http://www.rubitherm.com/ in 2005 regarding the prices their phase-change waxes. They were around €5/kg then. IIRC they did PCM wax micro-capsules embedded in plasterboard then, as well. Don't seem to be on their site now. I think they made the micro-capsules and somebody else put them in the plasterboard.

 

Another intriguing German-speaking phase-change heat store idea is being done by a couple in eastern Austria where they use a tank of water under their house as a store of tepid water (from ambient temperature) which is used as the input to a heat pump. They have a very passive non-insulated thermal collector which picks up ambient heat from the environment (including a bit of sunlight, presumably) to replenish the store over the winter. But, they also deliberately allow the store to freeze as a source of energy. https://elkement.blog/2017/10/12/data-for-the-heat-pump-system-heating-season-2016-2017/ . I'm not entirely sure it's worth the hassle over a standard ASHP but in an environment where your ASHP might well finish up buried in snow it might make sense.

[scottishjohn]

basically its like having a pond in the garden you use for the GSHP?

I asked planning about doing this 20 years ago  ans SEPA said no --cos  i would kill the wildlife in the pond 

[scottishjohn]

how about big water storage under house + 1 or 2 solar thermals to warm it up by thermo syphon 

heat pump to take heat out of it as required--would only need minimum size heat pump as the water will be warm 

while solar heats it back up  as and when it can 

now if doing it while building house it might be viable 

I looked into mega size store tank  using solar thermal ,but costs for tank were too much --guess 10k in concrete forms etc

 

[Ed Davies]

55 minutes ago, scottishjohn said:

basically its like having a pond in the garden you use for the GSHP?

 

No, because they use a tank, hence no wildlife. They actually converted a root store which was already present in their own house but they've done consultancy for others building tanks other ways.

 

44 minutes ago, scottishjohn said:

how about big water storage under house + 1 or 2 solar thermals to warm it up by thermo syphon

Thermosyphon only works downwards when water is between 0 and 4 °C (so gets denser with increasing temperature). If you can put the tank under the house and still have the solar collectors lower, down a hillside perhaps, then thermosyphon could work otherwise you'll need a pump but that's not a show-stopper.

 

I'm doing something a bit like that (big tank charged mostly from solar thermal) and have wondered about the  use of a heat-pump to extract heat from the tank or, as it'll be a segmented tank, pump heat from a cool part to a warm part. However, you have to balance the cost and complexity of the heat pump (and the PV to run it) against the fairly small increase in the efficiency of the solar collector at the lower temperatures. Perhaps it's better to just have a bit more solar thermal and keep the tank at the target temperature you want, though if that's the right temperature for space heating maybe a heat pump would be a good way to get some increased temperature for DHW. But, as always, you need to balance that against just having a bit more PV.

[Jeremy Harris]

I remember reading about a passive house (may have been in the Passive House magazine) that had a large, central, well-insulated water tank that formed the central column of a helical staircase.  I can't recall the details, unfortunately, but the idea was to be able to buffer heat storage IIRC, rather than try to create a long-duration heat store.  I think that heat was extracted from it for DHW using a small heat pump and heat was pumped back into it from solar thermal, the idea being that the big tank would only ever have a relatively small temperature change from day to day.

 

I can see the logic behind this, as even in winter there are still a fair few days when the output from a reasonable sized collector array will exceed the daily heating and hot water demand by a fair bit. Right now we're exporting around 3 kW, for example (and the damned Sunamp isn't charging....).

[Onoff]

You could use say parrafin wax as the pcm but surround it with a water "jacket". Bit like this fast breeder reactor 

 

 

Parrafin wax goes in the "rods". Thinking this arrangment would maybe prevent localised overheating of the pcm...

 

 

 

 

 

[scottishjohn]

I admit to having a thing about solar thermal,having had 2x20tube thermomax evac tube panels on house for 20 years and seeing how much they contributed to underfloor 

 its all about getting a cheap tank sorted

my thoughts were to use some sort of icf to make make tank  ,and if buidling new house then under it would be fine .

are you going for high temp  and small volume in sections  or just high vol lower temp 

energy stored will be the same ,upside of ging for largevol at lower temp is panels will wor nearly all day --no stagnation at any time 

which was problem with my system 

only 300litre storage 

so if no underfloor requirement it would max out by lunch time 

and as you have no control over solar temp better to get it even at lower temp when ever you can 

 

 

[Onoff]

1 hour ago, scottishjohn said:

I admit to having a thing about solar thermal,having had 2x20tube thermomax evac tube panels on house for 20 years and seeing how much they contributed to underfloor 

 its all about getting a cheap tank sorted

my thoughts were to use some sort of icf to make make tank  ,and if buidling new house then under it would be fine .

are you going for high temp  and small volume in sections  or just high vol lower temp 

energy stored will be the same ,upside of ging for largevol at lower temp is panels will wor nearly all day --no stagnation at any time 

which was problem with my system 

only 300litre storage 

so if no underfloor requirement it would max out by lunch time 

and as you have no control over solar temp better to get it even at lower temp when ever you can 

 

 

 

I wish you'd have been on here a while back! Might have given me the impetus to get my 3x12 panels installed & going before they got broken!

[Big Neil]

Please help clear up some confusion. One of my main aims at understanding these things was to understand where they fit in the scheme of the overall water setup in a dwelling, particularly in the context of wanting to understand POSSIBLE energy efficiencies and the various facilities in a house designed to be energy efficient. All the info above is certainly useful in understanding how they work, but i'm still lost a little on the other point.

 

I guess the closest parallel i can draw is that if you want to have a  electrical appliances working in your house you either need an on site means of generating power or a connection to the grid, but can have both to compliment each other. You can then have a battery backup to sit along side them to allow efficient use of that energy, however much might come from the grid or your on site generation. Ultimately though you could just get away with being connected to the grid. I realise of course that there are other considerations such as load, cost, longevity etc etc, but broadly that doesn't matter in this example.

 

So all questions of energy requirement calculations aside

 

What do i need to provide my hot water, to allow me to run it hot from taps, run it hot through a shower head, run it hot into any appliance i might want to (where they weren't just cold feed) and where i want to provide hot water for the UFH system. CAN i just have an ASHP/several of them, CAN I just have a sunamp unit/several of them, CAN i just have panel collectors such as the ones Think Renewables supply, CAN I just have a massive insulated cylinder with whatever metal coils to keep the water hot (well hot/warm)? (like we used to in our house when i was a kid).

Obviously cost is a factor in a real but lets call it a non-issue at the moment. what do i actually need to i don't freeze and can clean myself if there are a nominally standard 4 adults in the house?

[Jeremy Harris]

If you are OK with hot water at around 55 deg C (which many people find perfectly OK) then an ASHP can deliver that sort of temperature.  You can store that hot water in a hot water tank, but probably not in a Sunamp, as the Sunamp needs charging hot water that is hotter than that; typically around 70 to 75 °C  I believe.  So if you choose to use an ASHP then you probably can't mate that with a Sunamp for hot water storage.

 

Using solar thermal for hot water is expensive (high capital cost relative to the power delivered) and won't provide much hot water in the winter months, so you will need something to augment it.   If you don't have mains gas, then electricity is probably the easiest and cheapest (in terms of installation cost) as a way to augment hot water during winter.  You could store heat from solar thermal and electric heating in either a Sunamp or a hot water cylinder, although there may be some challenges in controlling the charging temperature for a Sunamp when connected to a solar thermal system, and there will be a fairly big efficiency hit because the solar thermal system won't be able to start charging until the temperature exceeds 58°C, which means that the solar thermal collectors may sit there doing very little a fair bit of the time.

 

Using PV as the power source will work with either a hot water tank or a Sunamp as the heat store.  It's relatively cheap, maintenance free and has the benefit that it's pretty easy to augment with grid electricity when there's little PV generation.  In terms of efficiency, a Sunamp is a fair bit more efficient than a hot water tank, because of the lower heat losses, but there is the issue at the moment regarding utilisation of all the heat storage capacity of the Sunamp.  I would expect this to be resolved pretty quickly, and if it isn't I should have some figures next Monday that give an indication as to how big an issue this is when the recharge point is configured for 50%, rather than 90%.

 

The solution that is the most complex and maintenance intensive would be solar thermal plus direct electric augmentation.  The storage system that takes up the most space inside the house would be a hot water cylinder, no matter what you use to heat it. 

 

The simplest system in terms of installation may well be a monoblock ASHP coupled with a hot water tank, and this could also run the heating system.  This could be augmented outside the heating season by using either PV running an immersion heater in the tank, or by using solar thermal, but my inclination would be to use PV, as solar thermal is a one trick pony, it will only deliver hot water, and only then when the tank is cool enough to accept it.  You can use PV generated electricity to offset pretty much every other energy using bit of kit in the house, including an ASHP, so you get a fair bit more bang for your buck in terms of the useful energy you get for the investment.

[scottishjohn]

best use of solar thermal I have seen was a house in the swiss alps lots of bright clear days even in winter 

the tank was built on outside of a blank gable end +insulated with 6" of pir foam ,which was then rendered to look like rest of house and very tall  nearly right to peak of very sharp angled roof

fire place and chimney right behind the tank --so some free heat from that when it was on in winter  ,as it had a back boiler type fire set -up  as well

the thermal stratification would be great ,as hot water goes to top  ,where you would have your output coil.

bottom of tank maybe 25ft  below you have the solar coil .

it just keeps pumping up the temp and over time it fills with heat from top downwards .

 On this house it ran all heating and hot water requirements 

dhw coil at top 

UFH coil above half way ,but not near top 

solar and back boiler coils at bottom

my guess would be well over 15000litres

from my close to 20years of running solar thermal  maintaince is very small no more than any other system --you only got a pump,a valve and a controller +a couple of thermo couples 

I used simple analog control system with thermostats to decide when other forms of heating could work ,solar always having priority if the panels were more than 6c hotter than BOTTOM  of tank and unless top half of tank was less than 45c ,then boiler came on till top of tank was 50c 

thats was plenty hot enough for dhw

certainly a modern set of sensors and a laptop would make a much better job of controlling it though

limiting factor was always size of tank -as i used unregulated tubes -did not turn off till solar manifold was 100c ,which was why  I ran it at 3.5bar  and big expansion vessel .

quite common in summer to find tank temps top and bottom were 97c by lunch time

even occasional  boiling and venting of steam,like an old steam engine --so maybe a 500 litre min would have been better--we all learn by mistakes.

analog pipe thermostats are not the most accurate either 

I certainly believe you could get dhw nearly all year if thats all you used it for with 500litre tank and blending the output at tank to say 50c 

 

If you could get a small cheap heat pump then it definately would be a winner. you can get 20c-30c+ hot water from solar  almost everyday of the year 

just not sure you should need that much heat in a near passiv house to be worth the complications -

 

 

Edited December 7, 2018 by scottishjohn

[Big Neil]

I bloody love this forum - Thank you all for the help. 

 

MR Harris, in that last example you mentioned

 

On 07/12/2018 at 16:54, JSHarris said:

The simplest system in terms of installation may well be a monoblock ASHP coupled with a hot water tank, and this could also run the heating system.  This could be augmented outside the heating season by using either PV running an immersion heater in the tank, or by using solar thermal

 

To cement my understanding, it's water in from the mains, through my hypothetical cold water manifold, one of the feeds through the Monoblock ASHP, which will heat the water. ASHP then feeds the tank/cylinder (in which i can have a coil taking excess PV ) where the hot water is stored and then fed back out to my hypothetical Hot water manifold, where it is then fed out to various sources such as taps or the UFH manifolds. That correct?

 

[Jeremy Harris]

8 minutes ago, Big Neil said:

I bloody love this forum - Thank you all for the help. 

 

MR Harris, in that last example you mentioned

 

 

To cement my understanding, it's water in from the mains, through my hypothetical cold water manifold, one of the feeds through the Monoblock ASHP, which will heat the water. ASHP then feeds the tank/cylinder (in which i can have a coil taking excess PV ) where the hot water is stored and then fed back out to my hypothetical Hot water manifold, where it is then fed out to various sources such as taps or the UFH manifolds. That correct?

 

 

Not quite.  The ASHP heats a sealed circuit, that may include the UFH loop, and that also includes the indirect coil in the hot water tank.  This circuit is filled with antifreeze/inhibitor.  You will probably have a three port valve as well to switch between heating hot water and running the UFH.

 

The mains cold water fills the hot water tank, and that tank gets heated by the coil, and also by an immersion run from excess PV generation when it's available.  The result is mains pressure hot water at around the maximum temperature that the ASHP can operate, typically 50 to 55 deg C, which is generally fine.

 

@Stones has a set up like this, and has found it works well; it's worth having a read of his blog on here.

[Dreadnaught]

7 minutes ago, JSHarris said:

typically 50 to 55 deg C, which is generally fine

 

I know that this has been covered before, but is there a legionella risk? I think the consensus from last time this was discussed was that the risk was overblown. I thought it worth mentioning for new people who may not have read the old threads.

[Big Neil]

If the same as the last time i managed the compliance team at Carillion, temps are a pass at above 50 degrees for the hot and below 20 degrees for the cold. Could be a bit out of date though.

[Jeremy Harris]

27 minutes ago, Dreadnaught said:

 

I know that this has been covered before, but is there a legionella risk? I think the consensus from last time this was discussed was that the risk was overblown. I thought it worth mentioning for new people who may not have read the old threads.

 

Possibly, but given that the hot water system (assuming an unvented cylinder) is sealed, then it's very hard to see how any bacteria could get into the system in the first place, let alone multiply.  As a safety precaution, wiring the immersion up with a timer to heat the tank to 65 deg C every couple of weeks would eliminate any risk.  Personally I'm not convinced it's worth the hassle if you're on mains water, as the residual disinfection that the water companies leave in the water should deal with anything.

[Big Neil]

I will look at @Stones blog during the day if I get a moment. Thanks

[Dreadnaught]

6 minutes ago, JSHarris said:

As a safety precaution, wiring the immersion up with a timer to heat the tank to 65 deg C every couple of weeks would eliminate any risk.

 

On the subject of cylinder temperature, while the ASHP could only heat to 55 or 55ºC in practice, I assume there is no reason why the immersion heater powered by PV could not, if plentiful sunshine allowed, heat the water to a higher temperature. A TMV would blend the temperature down as required for output. That would also do for any sneaky legionella bacteria too if the chlorine in the mains water hadn't done so already.

 

I wonder, is there any upper limit for the temperature of the cylinder water heated by PV? Would the immersion heater have a cut off?

 

 

[Jeremy Harris]

28 minutes ago, Dreadnaught said:

 

On the subject of cylinder temperature, while the ASHP could only heat to 55 or 55ºC in practice, I assume there is no reason why the immersion heater powered by PV could not, if plentiful sunshine allowed, heat the water to a higher temperature. A TMV would blend the temperature down as required for output. That would also do for any sneaky legionella bacteria too if the chlorine in the mains water hadn't done so already.

 

I wonder, is there any upper limit for the temperature of the cylinder water heated by PV? Would the immersion heater have a cut off?

 

 

 

 

Yes, the immersion can heat up to a much higher temperature, as set by the thermostat in the immersion heater itself.  Typically this would be set to around 65 to 70 deg C, I think.  For further over-temperature protection, immersion heaters also now have a second, resettable, over-temperature cut out, to stop the tank from boiling.

[PeterW]

8 hours ago, JSHarris said:

For further over-temperature protection, immersion heaters also now have a second, resettable, over-temperature cut out, to stop the tank from boiling.

 

This is how they are allowed to fit immersions into UVCs as it provides the secondary link required on all Part G UVC  installs.