ASHP to heat water for a shower or electric shower?

doodling

Hi,

wittynamegoeshere said:

[...]

Also even with good insulation ideally it needs to be heated reasonably soon before use.  Don't heat it at 5am if you're not having a shower until 8pm.
[...]

The thing to remember is that the performance of ASHPs is linked to ambient temperature. Where an ASHP is providing heat that will be stored then it makes sense to run the ASHP to provide that heat at the warmest time of day (probably early afternoon).

If your thing that stores heat (e.g. a hot water cylinder) loses a lot of heat then it (or the pipes going to.it) needs more insulation. Saying that you shouldn't store heat because it leaks out is admitting that you haven't insulated things well enough.

Reed_Richards

doodling said:

The thing to remember is that the performance of ASHPs is linked to ambient temperature. Where an ASHP is providing heat that will be stored then it makes sense to run the ASHP to provide that heat at the warmest time of day (probably early afternoon).

Everything stores heat to an extent, your hot water cylinder, your house.  So logically it also make some sense to get the ASHP to make your house really warm at the hottest time of the day, particularly if that is hot enough to allow it to use weather compensation.

wittynamegoeshere

Reed_Richards said:

wittynamegoeshere said:

 I'm going to look at thermal storage ....The idea of this is that it's a way of storing heat so that it doesn't constantly lose energy - once it's in its locked away.  

No that's completely wrong.  It will still constantly lose energy, anything above ambient temperature will.  Now because a phase-change thermal store is more compact than a tank of hot water (which is also a thermal store) then you can insulate it very well, although I strongly suspect that you still lose a lot of heat down the pipes.  The main virtue of the Sunamp product is that you can fit one in a smaller space than a hot water tank of equivalent heat storage capacity.

You've misunderstood, as I did when I first encountered it.

My (rough) understanding is that it stores heat using a phase-change.  The heat changes some fluid from a crystallised to liquid state.  Then it sits there are as a liquid at ambient temperature, for as long as you like, losing no energy at all.

When you turn the tap on, somehow some of this stored magic liquid gets turned back into crystals - this reaction releases heat, which passes through a heat exchanger that heats the flowing water as it passes through it.

Then the next time your heat pump heats it, it turns back into a liquid again.  If you haven't used any hot water since the last time then presumably the heat pump doesn't bother - either because of some control system or perhaps just because no heat gets absorbed from its circulated water so it gives up.

It works like an instant hot water boiler, but is powered by stored potential energy that was previously heat from the heat pump.

wittynamegoeshere

My understanding is that it's a lot like these pocket hand warmers, but on a bigger scale with added cleverness...

https://www.youtube.com/watch?v=Oj0plwm_NMs

doodling

Hi,

wittynamegoeshere said:

Reed_Richards said:

wittynamegoeshere said:

 I'm going to look at thermal storage ....The idea of this is that it's a way of storing heat so that it doesn't constantly lose energy - once it's in its locked away.  

No that's completely wrong.  It will still constantly lose energy, anything above ambient temperature will.  Now because a phase-change thermal store is more compact than a tank of hot water (which is also a thermal store) then you can insulate it very well, although I strongly suspect that you still lose a lot of heat down the pipes.  The main virtue of the Sunamp product is that you can fit one in a smaller space than a hot water tank of equivalent heat storage capacity.

[...]
Then it sits there are as a liquid at ambient temperature, for as long as you like, losing no energy at all.

When you turn the tap on, somehow some of this stored magic liquid gets turned back into crystals - this reaction releases heat, which passes through a heat exchanger that heats the flowing water as it passes through it.
[...]

Unless you can explain the mechanism by which heat is released, other than simple heat transfer, then this doesn't sound real to me. The Sunflow brochure shows a simple heat exchanger, no magic control which somehow commands heat to be released on cue.

In general, materials have a single temperature at which melting and freezing occurs.

There are substances which do exhibit a hysteresis at a macro level (agar is the well known one) but this is not at a material phase change level and consequently you don't get the energy storage benefits.

There may well be benefits using phase change materials to store heat but a reduction in insulation (other than as a result of a smaller physical amount of heat storage material required) is not one of them.

Reed_Richards

wittynamegoeshere said:You've misunderstood, as I did when I first encountered it.

My (rough) understanding is that it stores heat using a phase-change.  

No I really have not misunderstood.  Yes it is a phase change material; I think it's probably a solid to solid phase change.  Anyway whatever the temperature at which the phase change occurs is the temperature you get to heat your water to and just below the ambient temperature at which your thermal store needs to be kept.  In the case of the Sunamp material this is about 58 C.  See https://www.energylivenews.com/wp-content/uploads/2019/07/sunamp-introduction-to-heat-storage-batteries-2.pdf or find the discussion on the Green and Ethical board about two years ago. 

FreeBear

Sea_Shell said: Does a heat pump system get the water hot enough to kill nasties like Legionnaires disease??  60⁰c+

Or is that only a risk in pipes that are "stagnant" rather than in daily use?

If you maintain a water temperature of 50°C or higher, bacteria will die within a few hours. You don't need 60°C to do the job.

wittynamegoeshere

Reed_Richards said:

wittynamegoeshere said:You've misunderstood, as I did when I first encountered it.

My (rough) understanding is that it stores heat using a phase-change.  

No I really have not misunderstood.  Yes it is a phase change material; I think it's probably a solid to solid phase change.  Anyway whatever the temperature at which the phase change occurs is the temperature you get to heat your water to and just below the ambient temperature at which your thermal store needs to be kept.  In the case of the Sunamp material this is about 58 C.  See https://www.energylivenews.com/wp-content/uploads/2019/07/sunamp-introduction-to-heat-storage-batteries-2.pdf or find the discussion on the Green and Ethical board about two years ago. 

OK, I get it.  It stores heat but can store more of it than water, due to the phase change at around 55 degrees C.  Plus it has a lot of energy to give at a "hot" temperature, rather than turning cooler as soon as you start using hot water.  I think so anyway.

Told you I was starting off understanding all this stuff.

Reed_Richards

wittynamegoeshere said:

OK, I get it.  It stores heat but can store more of it than water, due to the phase change at around 55 degrees C.  Plus it has a lot of energy to give at a "hot" temperature, rather than turning cooler as soon as you start using hot water.  I think so anyway.

Told you I was starting off understanding all this stuff.

That's correct.  It stores more heat per unit volume than water and it does not turn cooler until it has lost nearly all of its stored heat.  Nor does it turn hotter until it has gone a little beyond being "fully" charged.  The Sunamp unit would not work well with an ASHP!  This is because it takes in its energy at 58 C and 58 C is beyond the temperature that an ASHP can typically achieve on its own and/or efficiently.  That means you could only charge it by running the ASHP and an immersion heater in tandem (or some ASHPs might be capable of 60 C but only at the cost of poor efficiency).  My hot water cylinder is set to 50 C and in order to use a thermal store like the Sunamp one instead you would need a phase change material where the phase change occurs at 50 C (or very close thereto).

Reed_Richards

Reed_Richards said:
....or find the discussion on the Green and Ethical board about two years ago. 

which is here: https://forums.moneysavingexpert.com/discussion/6060969/heat-battery/p1