Ed Davies

But how much will the charge to take the tank away if somebody decides that, e.g., an ASHP would be better than LPG? Perhaps it's free (though I suspect not) but it would be good to know for sure.

A third reason that's likely silly: the advertised capacity of the SA includes, in addition to the latent heat which is the main function, the sensible heat stored when it's heated above 58 °C and that available when it cools below that to some other value I forget at the moment (40 °C?) which would obviously be lost if it supercooled.

Why do you care? There are three parameters of interest: price, power output and number you can fit in the intended area. Efficiency obviously affects the total power you can get from an area but since you can't fit n+½ rows or columns it's only of secondary importance. You pay more per watt for high efficiency panels (ones with smaller area) so think carefully whether that's actually important to you.

Like a handwarmer? But would they do that if there was any solid in there to seed the phase change? I suspect not. I actually put in another sentence after the one you quoted then deleted it as a) an additional complication and b) too speculative, but let's try now: My guess would be that if a unit was fully charged (all liquid) then was left to stand then it might supercool like a handwarmer; that is, it might drop well below 58 °C while still remaining liquid but when some water was drawn off so a part solidified that would seed further solidification so that whole lot rose to 58 °C where it would reach an equilibrium of solid/liquid mix which would change slowly as it lost further heat. On reflection, though, I think that's silly for two reasons. The trivial one is that the temperature sensors wouldn't work for state-of-charge sensing. More seriously, if the whole cell supercooled to ambient temperature then there wouldn't be any sensible heat available to warm water flowing through (assuming the “cold” water is at ambient temperature, too) so nothing would trigger further solidification. So I'm going to stick with my view that any charged cell is likely at around 58 °C except the last bit of the charge/first bit of the discharge where it's a bit hotter and the last bit of the discharge/first bit of the charge when it's cooler. I think they must have something which triggers solidification as soon as the temperature reaches the appropriate point, like the clicker in a hand warmer but “always on”.

Yes, the things clearly work so obviously it doesn't. But it must take some cleverness in the design to make sure. I imagine that's at least part of what their secret sauce is about. Yes, the last bit of energy stored is as sensible heat warming up the liquid above the melting point. Yes, again. I imagine it goes over a fairly narrow range of temperatures but you'll need an extra few degrees (say an extra 7 °C → 65 °C) to get the heat flow in to work quickly enough to be useful. If left on its own it'll likely just sit at 58 °C. As heat is lost (slowly) through the insulating panels and pipework, a small amount of material will solidify releasing replacement heat to keep the temperature stable.

A litre of LPG contains less energy than a litre of oil. Per kg LPG has more energy but it's quite a lot less dense which more than cancels that out. Another disadvantage of LPG is that you're tied to a single supplier (you typically rent the tank and suppliers only fill their own tanks) whereas if one supplier ups the price of their oil too much you can try somebody else.

I'm supposing, too, but my supposition is the opposite one: there's no particular voodoo in the Sunamp PCM to stop or start the phase change, it just happens with temperature. The voodoo there will be to do with not having the liquid in contact with the heat exchangers which turns solid when the first batch of cold water flows through not immediately sticking to the exchanger and insulating the rest of the liquid. This is the classic problem with all phase-change heat stores. My assumption is that, unlike the hand warmers, the contents of the Sunamp are at around 58°C so the liquid-solid phase change doesn't spread in the way it does in the super-saturated solutions in hand warmers which are stored and used at much lower temperatures. If all the latent heat turned to sensible heat on the first use then there'd be little point in having the PCM in there in the first place. Also, the temperature would rise a lot (at least 75 °C) yet the water comes out at pretty much the same temperature throughout most of the discharge.

Really? We wouldn't have guessed from your comments. ?

It's not drinkable. Well, it is but whoever did would probably get at least a bit ill. Any water that goes through the ASHP and/or the UFH has to be kept completely separate from the “wholesome” (DHW) water that'll get fed to taps, showers, etc. For the cylinder you have a choice: it can be full of DHW and heated by a coil containing the primary water (from the ASHP, boiler, solar thermal, whatever) with inhibitors and anti-freeze as required for the source. This is a conventional hot water cylinder. Or the cylinder can contain primary water and heat the DHW via a coil through it. Terminology varies but that's usually referred to as a thermal store. Other combinations are available: e.g., tank-in-tank or using plate heat exchangers. With a conventional hot water cylinder you may or may not have a separate smaller buffer tank containing primary water which is there to stop the ASHP from short cycling. If you have a thermal store then there's typically no need for a separate buffer as the thermal store does that function.

Thereby reducing the humidity and therefore increasing the drying rate. Just like a dehumidifier.

From a water regulations point of view, isn't flow in the opposite direction the possible problem: from hot to cold rather than cold to hot? I.e., there's a theoretical possibility that mucky hot water could flow back into the cold supply. Very unlikely in practice because the cold's normally at much higher pressure but could happen if there's a limitation to the supply and another cold tap open lower in the house so the cold suctions back. So to be completely compliant with water regulations you ought to have a (double?) check valve on the cold side, too?

Am I right in thinking that the logic of requiring double insulation, rather than just an equivalent extra thickness of single insulation, is that any cracks or splits in one are unlikely to line up with any in the other or propagate through or is there more to it than that? That one will act as a strain relief for the other?

Bath's off the mains here; no tank except header for the vented DHW cylinder so all the colds are. No real problems except that the electric shower cuts off if anything else is running, even the cistern refilling, presumable as a result of a low pressure/flow sensor. So that makes me wonder whether running cold into your bath at high speed might drop the pressure for anything else which cares about that sort of thing. Other shower? Washing machine?

Ask the manufacturer if the individual cores are to an appropriate standard for use like that? Would individual cores like this need to be in conduit through the wall and to the consumer unit as they're otherwise only single-insulated?

No experience or information beyond the obvious you can find on the net but quite interested. Thinking likely candidate for my second set of batteries once the first lot of LiFePO₄s die.

Yep, Danfoss here.

I think that must depend on the model of actuator head. For the ones in this house pushing the lever up turns the pump and boiler on. Just checked, turning the DHW valve on with DHW off on the programmer and indeed the pump and boiler ran. The electrician mentioned doing that as a work around in the case of a faulty programmer or thermostat when he explained the system to me. The ones in John Ward's video I referenced above look different in that the external level only seems to half open the valve. He doesn't show if the cam to operate the microswitch moves far enough in that case but I suspect not.

Paul at the end of the road got a single post lift himself quite recently and seems pleased: https://lifeattheendoftheroad.wordpress.com/2018/10/20/on-her-way/

Thanks for removing that video @PeterW . The one I meant was: https://youtu.be/mYwm7SmslyM?t=1246 The other video specifically about zone valve insides: https://www.youtube.com/watch?v=0MKnKj5bdzY

Opps, sorry, Part 1 of that series is better on the actual operation of Zone valves. He also has another one on the insides of the actuator head. It's not immediately to me how to delete that video from the previous post.

The lever isn't directly connected to the motor/valve. You can use it to push the valve into the open position against the spring when the motor is not being driven (and can be latched at the top of the movement to hold the valve open) but it can't be used to push the valve shut against the motor power. When the motor is driving the valve open the lever is free to be moved, hence floppy. The only purposes to doing that are to feel what state the motor/valve is in and to latch the valve open if you want it to stay open after the motor switches off. In what way does there appear to be current going to the valves? Have you measured with a meter? On which connections? In case you don't realise, the motor also has a switch in it which is typically used to control power to the boiler and/or pump. The idea is that programmer and thermostat drive the motor open at which point the switch closes which then runs the boiler and pump. If the valve jams or the motor fails then the valve won't open so the switch won't operate and boiler and pump won't run against a closed valve. Are you sure the “current” you're seeing isn't the voltage on one side of that switch?

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. 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.

Exactly. This might just turn out to be a simple software fix. Or maybe software + changed temperature sensor string, or something like that. Let's hope Sunamp give some indication soon but until they do discussion is so speculative as to be mostly a source of confusion.

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.

Any 3-pole rotary switch with sufficient positions will do it.