Solar Store - heat battery

[Big Neil]

So i've been reading with interest a number of the threads relating to various heating setups and pieces of equipment (the bulging case thread is frankly a little confusing but makes sense to me after a fashion). I've got to admit though to not really understanding what a heat battery like the sun-amp is or how it works. So i know that if you have PV on your roof or wherever, you can use it to say charge a home battery backup. I know there are also cylinders which whilst filled with hot water primarily heated by the boiler/heat-pump etc, can have a coil in there which can keep the temp of that water maintained by having power to it diverted from either a PV setup or mains supply.

 

So I guess there are two questions. Given the setup i have (poorly) described above, what is the need for a dedicated heat battery and how do they work? layman's terms please where possible

[Big Neil]

i can't piece together an understanding from the various threads on here, useful though most of them are

[Tennentslager]

Okay I'll try.

PV sends electrons to thermal store heated by an electric element so you have a store of hot water but lots of heat loss from thermal tank.

Alternatively PV sends electrons to a sunamp which stores the heat in a chemical brine by changing its state. Once charged the brine retains the energy and only releases it as required via heating water as it runs through it just like a combi boiler. It has vacuum insulation so negligible heat loss so more efficient but more capital cost.

 

[Dreadnaught]

3 minutes ago, Tennentslager said:

Alternatively PV sends electrons to a sunamp which stores the heat in a chemical brine by changing its state. Once charged the brine retains the energy and only releases it as required via heating water as it runs through it just like a combi boiler. It has vacuum insulation so negligible heat loss so more efficient but more capital cost.

 

 

Yes, and the SunAmp unit is a lot smaller in volume so if space is at a premium then that's another reason why the extra cost might be worth it.

[Jeremy Harris]

A heat battery, or thermal store, is just a way of storing heat until such time as it can be usefully used.  A hot water cylinder is another example, but specifically for providing domestic hot water (DHW) only.  A buffer tank is a lower temperature (usually) hot water store used primarily for allowing low temperature heating to run without the need to constantly run the heat source.  A storage heater is another form of heat battery that stores heat in heavy, electrically heated, bricks.

 

In terms of what's commercially available at a domestic level, there are only really three thermal store technologies:

 

1.  Hot water, held in an insulated tank.

 

2. Storage heater bricks, housed in an insulated case.

 

3. Phase change combined latent heat and sensible heat storage housed within an insulated housing.

 

Dealing just with hot water provision, the choice is between storing heat as hot water in an insulated tank, or storing heat within a phase change material thermal store or heat battery (Sunamp being the only product like this currently available on the domestic market, I believe).

 

There are really three main differences between storing heat in hot water and storing it within a product like the Sunamp:

 

1.  A hot water heat battery needs more volume of water to store a given quantity of heat, so will be significantly larger and heavier than a phase change material heat battery.

 

2. Because of the size difference, and specifically the difference in surface area through which heat will be lost, a phase change heat battery will lose less heat in a given period of time (typically between 1/4 and 1/3 of the heat losses from a water filled heat battery).

 

3.  A phase change material heat battery stores a large proportion of heat as latent heat of phase change.  This energy is "locked up" in the structure of the phase change material when it's in the liquid phase, and is released when it changes to the solid phase,  (hand warmers that use sodium acetate and have a small clicker to activate crystallisation are a good practical example of how this heat can be released on demand).

 

In terms of direct comparison, then a Sunamp UniQ 9 has a total volume (including case and insulation) of about 171 litres and weighs about 155kg.  An equivalent heat capacity hot water tank, including insulation and case, has a total volume of about 350 litres and weighs about 250kg (210 litres water volume).  The Sunamp, being rectangular, may well be easier to fit into a given space, versus a cylindrical hot water tank.

 

Both the hot water tank and the Sunamp will perform similarly in practice, so the difference really comes down to the lower size, weight and heat losses of the Sunamp.  Quantifying these isn't as easy as it should be, as the standard heat loss test for hot water tanks assumes that they get cycled and left cool for a time every 24 hours, but based on my tests of adding insulation to a thermal store, and measuring the rate of heat loss over 24 hours, I would guess that a very well insulated 210 litre hot water tank would lose around 2kWh over 24 hours and an equivalent Sunamp UniQ, run at the same temperature, would lose around 0.7 kWh over 24 hours.

[Dreadnaught]

10 minutes ago, JSHarris said:

The Sunamp, being rectangular

 

If an ablate sphere is one that bulges in the middle like the Earth, what describes a rectilinear volume that does the same? 

Edited December 6, 2018 by Dreadnaught

[Jeremy Harris]

10 minutes ago, Dreadnaught said:

 

If an ablate sphere is one that bulges in the middle like the Earth, what describes a rectilinear volume that does the same? 

 

In the UK we use the ellipsoid defined by the Airy oblate spheroid for our OS grid, but the USA (and much of the rest of the world tends to use WGS84, I believe.  Not sure how you describe a rectilinear volume with bulges...

[Big Neil]

41 minutes ago, Tennentslager said:

Okay I'll try.

PV sends electrons to thermal store heated by an electric element so you have a store of hot water but lots of heat loss from thermal tank.

Alternatively PV sends electrons to a sunamp which stores the heat in a chemical brine by changing its state. Once charged the brine retains the energy and only releases it as required via heating water as it runs through it just like a combi boiler. It has vacuum insulation so negligible heat loss so more efficient but more capital cost.

 

Probably kick myself for not reading the rest of the comments first but i think this answers it. So in the element in a tank example, there is an efficiency leak by heat loss, whereas in the sunamp case, chemical magic stuff happens  which can then be magicked around again later to heat the water just like a boiler/heat pump does? This about right?

[Ed Davies]

4 minutes ago, JSHarris said:

In the UK we use the ellipsoid defined by the Airy oblate spheroid for our OS grid

At the risk of going way off-topic, we don't any more. The Ordnance Survey grid is now defined in terms of the European Terrestrial Reference System which is, in turn, defined in terms of the International Terrestrial Reference System (via a transform which takes account of the drift of the European continent north eastwards at about 2cm/year). The ITRF is basically the coordinate system which forms the axes of the WGS84 ellipsoid.

[Ed Davies]

8 minutes ago, Big Neil said:

So in the element in a tank example, there is an efficiency leak by heat loss, whereas in the sunamp case, chemical magic stuff happens  which can then be magicked around again later to heat the water just like a boiler/heat pump does? This about right?

Yep, that's about right.

 

To add to @JSHarris's reply, one of the key things about a phase-change-material store  is that most of the heat is stored at the same temperature (58 °C in the case of the Sunamp). This means that rather than have a very hot store (say 80 °C) in the case of a DHW cylinder with the resulting extra heat loss and need to mix the water down to a usable temperature the leakage from the Sunamp is less and the output water is already at a safe temperature for distribution. At the other end of the scale, the temperature of the water cylinder as it discharges heat will drop to the point (around 40 °C) when it's no longer much use but still losing more heat if it's not recharged. A Sunamp will continue to give nearly 58 °C water all the time until it's nearly completely discharged.

[Onoff]

12 minutes ago, Big Neil said:

 

Probably kick myself for not reading the rest of the comments first but i think this answers it. So in the element in a tank example, there is an efficiency leak by heat loss, whereas in the sunamp case, chemical magic stuff happens  which can then be magicked around again later to heat the water just like a boiler/heat pump does? This about right?

 

Yep. The Sunamps impart their heat to the water more efficiently too I believe.  It's a space thing also. The Sunamps are a fair bit smaller than a "water tank" type heat store. That being said I've often wondered as in my case (space rich, cash light ), whether I could just have a MASSIVE heat store and just treat the heat loss as space heating?

 

 

[Big Neil]

9 minutes ago, Onoff said:

whether I could just have a MASSIVE heat store and just treat the heat loss as space heating?

sort of like the range in 'The Good LIfe' you mean?

 

and Sunamp hot water is for all hot water required other than heating yes? so showers, drinking water etc etc

[Jeremy Harris]

Not at all sure there's any inherent efficiency advantage between the way the heat exchange system works in a Sunamp relative to the way it works in a water-filled thermal store. 

 

The only efficiency gain I can see comes from the lower losses from the outer surfaces of a PCM heat battery, as despite the different mechanism for storing heat energy, there's nothing else that I can see that would impact on efficiency to any noticeable degree.  There may be a very slight decrease in efficiency for a PCM based heat battery resulting from the need to overcharge it slightly to ensure that all the PCM has changed from solid to liquid, but this is probably tiny.

 

 

[Big Neil]

So practically speaking, with current systems, not that much difference relatively speaking in terms of efficiency assuming correct design for the intended purpose. To use you as an example Mr Harris, given what you knew at the time you got your current SunAmp unit, was space the primary reason for going to a PCM (Phase Change Material??) system as opposed to an insulated tank? Could one actually use both systems in tandem to effectively minimise any losses further, particularly in a case where one has PV but no battery storage?

 

Actually, with the mammoth bulging case thread in mind, could you use a tank system to dump some of the capacity from the sunamp given the 50/90% issue, in order to them utlise the excess PV better? 

 

Also to clarify, is system not for heating, but just all water outlets?

[Jeremy Harris]

29 minutes ago, Big Neil said:

So practically speaking, with current systems, not that much difference relatively speaking in terms of efficiency assuming correct design for the intended purpose. To use you as an example Mr Harris, given what you knew at the time you got your current SunAmp unit, was space the primary reason for going to a PCM (Phase Change Material??) system as opposed to an insulated tank? Could one actually use both systems in tandem to effectively minimise any losses further, particularly in a case where one has PV but no battery storage?

 

Actually, with the mammoth bulging case thread in mind, could you use a tank system to dump some of the capacity from the sunamp given the 50/90% issue, in order to them utlise the excess PV better? 

 

Also to clarify, is system not for heating, but just all water outlets?

 

There were two reasons I opted to remove our old thermal store and replace it with a Sunamp.  The first was heat loss.  Despite adding an extra layer of 50mm PIR foam around the store, foaming it in place and sealing the edges with tape, we were still losing around 2.5 kWh/day from it, and that was making the services room very hot (over 40 deg C in summer) and damaged the oak door between it and the adjacent bedroom.  It also made the adjacent bedroom too hot. 

 

The secondary reason was to free up space in the services room, as the thermal store took up a lot of room.  This is a size comparison between our old thermal store (after I'd removed it), complete with added layer of insulation, and the original Sunamp PV to give an idea of the difference between the two:

 

 

Using a hot water tank in conjunction with a Sunamp doesn't really make that much sense to me, as you may as well just choose to use a bigger water tank to do the whole job.  Although a water filled store will not suffer from the inability to accept excess generated power when it cools below the thermostat set temperature, it will lose a lot more heat than a Sunamp, so over a few days of sporadic excess PV generation I doubt  there would a difference between the two in practice.  Adding a lot more insulation to a hot water tank, and reducing any heat lost from attached pipes, etc, would, perhaps, even things up, albeit at the expense of a much greater volume taken up.

[Onoff]

1 hour ago, Big Neil said:

sort of like the range in 'The Good LIfe' you mean?

 

and Sunamp hot water is for all hot water required other than heating yes? so showers, drinking water etc etc

 

Dunno, thinking about Felicity Kendall now...

[Big Neil]

52 minutes ago, JSHarris said:

Using a hot water tank in conjunction with a Sunamp doesn't really make that much sense to me

 

IN that particular instance I was actually thinking of getting around your charge issue. I've no idea what the required capacity would be, but i literally just mean as a vessel to heat water  into, to drop the charge level below 50% to allow it to accept the excess PV energy. I guess it's no different in some ways to just running a hot tap  constantly, but it would be there nice and warm at least for a while, for your use.

 

To summarise then - electrical setup aside; cold water along mains pipe, comes into house, hits (in this example) a cold water manifold and is diverted not only to outlets but also through the sunamp unit. Assuming this has charge it will heat the water passing through it and is then diverted on to a hot water manifold (ugly functional or @PeterStarck art installation type), where it can then get diverted to whatever source requires it, be that a shower, hot water tap, washing machine or whatever?

 

1 hour ago, Onoff said:

Dunno, thinking about Felicity Kendall now...

 

Always preferred Penelope Keith more. I'll be honest, her, Helen Mirren, Felicity Kendal and that Blonde Weather woman from the BBC get my nod any-day over the current lot of champagne barbies...

 

anyway - pipes and whatnot........

[Jeremy Harris]

I've spent an hour or so digging out scientific papers on research into the use of sodium acetate trihydrate as a phase change heat storage compound, and it's been quite interesting.  There is work going back decades that seems to highlight two recurring issues.

 

1) The cycle life of sodium acetate trihydrate when used as a phase change heat storage compound is limited to a few dozen cycles before it starts to degrade.  This seems to have been overcome by the specific mixture used in the Sunamp products, as they have now exceeded 40,000 cycles with only a tiny amount of degradation.  Some other research indicates that thickening agents may improve cycle life.

 

2.  When charging sodium acetate trihydrate there is a requirement to exceed the melting point (58 °C) by about 20 K, in order to ensure that all of the solid has melted.  Failure to do this results in spontaneous nucleation around "clumps" of solid within the primarily liquid mixture.  This implies that the charge temperature needs to be around 78 °C, just to be sure that all the PCM has melted.

 

Related to the second issue is the problem of getting heat evenly into the material when it is in the solid phase.  The viscous nature of the liquid phase, combined with its relatively poor thermal conductivity (similar to that of water, as far as I've been able to find out) and the tendency of the PCM to form a mixture which is not homogenous (lumps of solid PCM may well float around in the liquid) seems to be the Achilles heel of trying to heat the PCM evenly when using a relatively small area heat source.  Heating water from a small area heat source, like an immersion heater of kettle element, is aided a great deal by strong convection currents that readily establish in water as it is heated from the base of a container.  It seems that convection in sodium acetate trihydrate may well be nowhere near as vigorous or effective as it is in water, and this may well lie at the heart of the issue over trying to get a Sunamp heat cell evenly charged when it has only partially discharged, I think.

 

One thing seems clear.  There have been a lot of researchers working on using sodium acetate trihydrate as a phase change heat storage material for several decades, yet it seems that Sunamp, in conjunction with Edinburgh University, are probably the first to develop and engineer a practical product that uses a mixture of sodium acetate trihydrate, perhaps with a thickening agent to aid long term stability, and possibly an additive to improve the thermal conductivity (graphite powder seems to be something several researchers have investigated to do this).

[Guest Alphonsox]

Worth reposting this from Andrew Bissell of Sunamp on Ebuild in September 2015 and recovered from the wayback machine.

=====================================================================================================

 

Phase Change Materials

Phase change materials work by storing heat when they melt, and releasing it when they freeze again. Their mode of operation is simple in principle.

Melting/freezing stores/releases a lot of energy. As an example, think of water as a PCM that melts at 0^oC.

Water ice has a specific heat capacity of 2.000 kJ/kg/K at -10^oC (and density 918.9 g/L)
Latent heat of fusion of water (ice to liquid) is 334 kJ/kg
Liquid water has a specific heat capacity of 4.182 kJ/kg/K at 20^oC

Over the temperature range -10 to 20^oC there is (about) 10*2.000 + 334 + 20*4.182 = 20 + 334 + 84 = 438 kJ/kg of total heat capacity.
NOTE that over 76% of the stored energy in that 30 degree band is latent heat and less than 24% is specific heat.

For comparison, ice would store ~60 kJ/kg over 30 degrees from -31 to -1^oC; water would store ~125 kJ over 30 degrees from 1 to 31^oC.

(See:
http://www.engineeri...ties-d_162.html
http://www.engineeri...ties-d_576.html)

So the effect of having a solid/liquid phase change in the temperature range of interest is to dramatically increase the heat capacity over the range. That's why we use PCMs.

Of course not all materials are suitable to be PCMs. To be a PCM, a material has to have the right melting point for the application, a suitably high latent heat capacity (and ideally a high specific heat capacity too), and be safe and reliable over the long term.

Choice of PCMs

There are two main classes of Phase Change Materials for room temperature class applications (i.e. 10 - 90^oC):

• Organic - paraffins, waxes, fats, oils, fatty acids, etc
• Inorganic - salts, salt hydrates, metals (e.g. Woods metal)

It was easy to choose between these, and then hard to execute the choice.

Organic materials are common and easy to get, easy to work with, have a wide range of tuneable melting points, but suffer from defects that, in my view (and Sunamp's), make them fundamentally unsuitable for use in household heat stores.

The outright show-stopper for me is the high flammability of organic materials. I would not put tens or hundreds of litres of hot oil in a store in my home, and I wouldn't ask anyone else to do the same.

The other key defects of organic materials are lower energy density (typically half that of salt hydrates) and poor sustainability ("bio-derived PCMs" often derive from palm oil, which is strongly linked to tropical deforestation - sustainable sourcing may be available, but how can we be sure?; paraffins are directly derived from oil refining).

I don't absolutely rule out use of organic materials in future, in some capacity (perhaps in industrial heat stores, or ones buried underground), but I can't recommend their use inside homes.

Of the inorganic PCMs, the metals are costly, physically very dense (I mean g/L not kWh/m³) and toxic. Pure salts generally don't melt until much higher temperatures.

Salt hydrate PCMs

Sunamp uses salt hydrate PCMs.

We do so because they are non-flammable and have high energy density (very similar to water and water ice), and offer a range of melting points.

As you know we work with families of materials (where we have applied for patents) based on:

• Sodium Acetate Trihydrate (primary melting point: 58^oC; tuneability 46 - 58^oC)
• Strontium Bromide Hexahydrate (primary melting point: 88^oC; tuneability 75 - 88^oC)

Only SU58 (our 58^oC PCM using Sodium Acetate Trihydrate aka SAT) is in full-scale production as yet. It is our mainstay material, used in the heat batteries (HB58) used in SunampPV and other forthcoming products.

Our PCMs were developed with University of Edinburgh, and there are forthcoming academic papers due. For reasons of academic priority, I can't say everything I'd like to about the materials yet.

What I can say is that conventional SAT PCM is used (as some here have observed) for hand warmers. These can be stored at room temperature and can be activated by clicking a metal disk inside. They are recharged by fully melting the SAT inside by heating the hand warmers in a pan of hot water.

There is something to like in this approach - storability at room temperature - BUT there are some serious drawbacks:

• Conventional SAT materials used in hand warmers degrade after hundreds of cycles due to "phase segregation" - an anhydrous fraction precipitates out like a sediment; what is left behind is more dilute and less effective
• They need to be activated - when do you choose to do that?
• When the materials cool back to room temperature for storage,the specific heat is lost, so total energy storage is lower than it might be
• They don't reach 58^oC when re-activated and the energy released is less

Sunamp's SU58 is formulated differently. It contains additives that achieve two things:

• A polymer that eliminates the degradation effect. All the science points to the degradation being completely eliminated. Details to follow in the scientific papers, so please be patient. However what we have learnt does allow us to offer a 10 year limited warranty similar to the best electric batteries.
• It includes a nucleator, which means that the material starts to freeze cleanly when cooled to 58^oC. This means that there is no control issue about when to activate the material, no lost energy and we achieve the full 58^oC.

We have evaluated many other materials, and continue to do so. The 88^oC family is very exciting and essentially new. Many of the best ones at other temperatures are already in the public domain, though not always with their best formulations.

Sunamp Heat Batteries

A heat storage appliance like SunampPV needs to contain a heat store. In Sunamp's case we use Heat Batteries. After several generations of refinement (the first Sunamp heat batteries were deployed in field trials in 2013), we have arrived at a red plastic-cased cell, the shape of a large cereal box (115 mm wide x 463 mm long x 499 mm tall, externally occupying 26.5 dm³), weighing a little over 30 kg.

A heat battery cell offers:

• 45 Litres of instant hot water or
• 2.2 kWh of thermal energy

when discharged through a TMV set at 55°C, from 73°C to 45°C. Higher or lower performance may be delivered for other applications and operating conditions.


For example jsharris wants hot water at 42^oC. In that mode, two cells in series would deliver about 4.4 kWh before dropping below 42^oC. Three cells about 6.6 kWh, provided those cells were charged to an average 73^oC using, say, off-peak electricity or diverted solar PV electricity.

SunampPV includes two such cells (sitting side-by-side, connected in series) and hydraulics to allow the electric charging of the cells.

When discharged, cold mains water flows into the appliance and through heat exchangers in the cells. The cold water picks up heat from the PCM. Initially it transfers heat from the hot liquid PCM (which cools from 73 to 58^oC progressively), and then from the PCM as it freezes (at 58^oC). Finally once the PCM is all solid, the solid cools further (from 58^oC downwards), continuing to transfer heat to the mains water.

Is the end of useful energy when output drops below 45 or 42 or 40^oC (e.g. in a hot water application replacing a hot water tank with immersion heater or an instant hot water heater), or when the output approaches cold mains temperature (e.g. when SunampPV is connected as a pre-heat to a combo boiler**)? That's for you to judge based on your application. It affects useful heat output: there is about 20% of total heat to be had from 45^oC to ~11.5^oC. We quote heat capacity without this at cell level, and with this heat at SunampPV level (as SunampPV is designed for use with combis, where pre-heat is useful).

(For SunampPV spec sheet please see:
http://sunamp.co.uk/...ure-for-Web.pdf
Apologies that it needs a little updating. For example it overstates the mass by 10 kg (it has come in below estimates at 80kg +/- 1 kg)

Power and Flow Rate

One very critical parameter that almost all other PCM system developers tend to fudge is power. This is because the thermal conductivity of PCMs tends to be very low (<< 1 Wm^-1K^-1), so its hard to get the heat in and out fast. Its all very well that PCMs offer high energy densities, but if you can't get at the energy, is it useful?

Sunamp Heat Batteries are designed to overcome this. A pair of heat batteries in series can sustain over 12 litres per minute of discharge when fed with cold mains water at 10^oC and deliver most of the energy in a plateau at just over 50^oC. Power is over 40 kW peak, 35 kW sustained, with over 30 kW still being delivered when falling to 45^oC.

A couple of points to note:

• The plateau temperature doesn't change much whether the mains cold inlet is 5, 10, 15 or 35^oC. This means power scales UP in cold conditions, when mains temperatures would be say 5^oC. This is desirable.
• There is very little water stored in the appliance - for SunampPV about 5 litres is present. This water comes out at high temperature (whatever temperature the PCM is at, whether 70+^oC at the end of charging or 58^oC during the freezing plateau) so there is IMMEDIATE hot water - no waiting for a heat exchanger to heat up; no initial slug of cold (except what is in pipework).

(Little water in the appliance, a different slug between each discharge and high temperature storage and, at least after every charging, over 65^oC, absolutely minimises legionella risk.)

Frankly I wanted to stomp the power problem into the ground, and I am proud that we have. One consequence is that SunampPV outperforms most combis it could be paired with (which is what we want). Another is that SunampPV can be used as a high flow rate electric hot water heater at >30kW when connected to a 3kW spur circuit (albeit not continuously, but if the average duty cycle is 10% it works).

We haven't yet tested maximum flow rate at maximum rated mains pressure. We'll update when we know.

Heat Loss

When building a small appliance, smaller than a water tank of equivalent heat capacity by 3 to 4 times, you risk being a mouse (i.e. having the surface area:volume ratio work against you). You also risk having total insulation volume end up close to or greater than your heat storage volume. For this reason SunampPV uses Vacuum Insulation Panel. We can do that because we have flat surfaces to insulate, and because the total surface is quite small (so we could afford to do the right thing - VIP is expensive per m²).

So far preliminary heat loss testing has been performed in-house using the approach used to test an electric storage water heater, wherein there is thermal draw-off and recharge using a tapping cycle during the hours of 07:00 to 22:00. This suggests 0.7 kWh / 24 hour heat loss from SunampPV. We are about to send a unit to a test lab for confirmation and other tests, so should have better data soon.

I am sorry that the 5W figure clouded this. That is the upper bound of the electrical standby load.

I hope we can further significantly reduce the thermal losses later.

Regulatory

If you read this after 26 September 2015, either we will have ErP certification from the above-mentioned test lab OR SunampPV will temporarily be off the market until we get ErP certification. Equally SunampPV doesn't yet have CE mark (although it has passed all the related lab tests for EMC and LVD). We believe SunampPV meets the UK water regulations, but WRAS certification is still pending.

SunampStack

Other Sunamp products will be composed of different numbers of cells in series, parallel or series-parallel arrangements. We offer cells to OEMs and for our own products. While we are not offering bare cells direct to the general public,we expect to offer SunampStack, a configurable product line, soon.

SunampStack is composed by integrating multiple layers of heat batteries

• Each layer is composed of 2, 3, 4, 5 or 6 cells
• Layers may be stacked up to 4 high (2,350 mm)
• High degree of flexibility and modularity to meet different storage requirements from 4 to >50kWh (90 to >1000 litres)

Example SunampStack:

• 5 cells wide by 3 layers high = 15 cells
• Occupies 655 mm wide x 540 mm deep x 1800 mm high
• Delivering 675 litres above 45^oC via a TMV set at 55^oC or 33 kWh

That's all for today folks.

Next I'll try to tackle some of your specific requests. Please be a little patient.

Andrew

[Onoff]

I've always thought organic compounds are a possibility like palm oil, cocoa butter or high sugar "jam". Think how hot a McDonald's Apple pie stays!

 

Place outside rather than inside the house!

[dpmiller]

I like the paraffin wax option.

[Guest Alphonsox]

19 minutes ago, dpmiller said:

I like the paraffin wax option.

 

I'm not sure your insurance company would be quite as enthusiastic, although you might be able to claim a huge vat of hot palm oil was due to your love of deep fried food. (Probably only a viable defence for those of us in Ireland or Scotland )

[dpmiller]

Paraffin wax changes state at a nice low temp and is used by the bucketful hot and liquid in Histo labs. Nothing to be afraid of...

[Onoff]

18 minutes ago, Alphonsox said:

 

I'm not sure your insurance company would be quite as enthusiastic, although you might be able to claim a huge vat of hot palm oil was due to your love of deep fried food. (Probably only a viable defence for those of us in Ireland or Scotland )

 

Chuck a few Toffee Crisps & pizzas in & who'd argue?

[Gone West]

15 hours ago, dpmiller said:

I like the paraffin wax option.

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