Dreadnaught

Oh, of course. Less of a factor.

Very good point. I am tempted to plan for PV but not install it until an economic case becomes clear. Two complications about this decision are: (i) the possibility of recovering VAT at the time of build, should that sway the choice; (2) I am expecting the cost of PV to continue falling, especially as material science continues to advance.

What a kind offer. I will PM you. I am slowly learning that. Much more to learn. It is indeed a rather intimidating prospect having read some of the blogs and threads, although thus far is not deterring me, although I am rather apprehensive. Ben Adam Smith of the House-Planning-Help podcast seems to be going down the route of doing as little himself as possible for his newly-started build. I now can understand why. Makes sense. Thank you.

Oh, very good point. Just store the energy in the slab. Obvious now you say it. Truly excellent point. Not at all sure how to do this. I assume PHPP and an eagle-eye on the builders will not be enough. Have more to learn. By the way, @TerryE do I understand your arrangement correctly that you generate DHW from your Willis heater (at least as for showers)? I think that can't be so but I was confused about your comment of a SunAmp being only useful in your case for baths.

Ah, I see. So all the new 3rd-generation Sunamp would need to add is separate circuits for DHW and UFH so that they don't mix (and no doubt lots of other goodies that I can't even imagine). And now I also understand @Nickfromwales's point about the different phase-change materials (PCMs). They are simply to cope with different sources of energy. The lower temperature PCM is for heat derived form an air-source heat pump (ASHP), which cannot generate high temperatures without sacrificing COP (or using a complex multi-stage heat pump). I am also aware that, with a SunAmp that does contain both high- and low-temperature PCMs within, then the low-temperature PCM can be used to preheat water that then feeds into the high-temperature PCM, and then this higher-temperature water can be blended down to the target temperature. So in my scenario, using E7 and PV, a high-temperature PCM Sunamp would be the choice unless I anticipate possibly adding an ASHP later, when having both PCMs might be desirable. Anyhow, it seems @Nickfromwales has some good news up-his-sleeve about some thing for early March!

Ooh, can't wait!

Yes, I was thinking about that. Assuming that the UFH water circuit is a closed loop, would you bypass some of the water around the Sunamp and re-blend the unheated water with heated water from the SunAmp outlet using a thermostatic blending valve? Sorry for my basic description, I know next to nothing about plumbing.

@Visti, at the risk of going off at tangent, given that @Bobnjudi was asking a specific question about a cylinder, I am learning that one of the greater risk with a passive house is not the winter space heating but the complication of keeping the home cool in the summer. I believe @JSHarris found this and somewhat to his surprise. I therefore weigh the overheating benefits of SunAmp highly given how costly cooling can be in terms of either house design (shading installation, etc.) and possible cooling technology (such as air-to-air or air-to-water heat pumps, etc.). Also the ability to have a (marginally) smaller plant room (not applicable to @Bobnjudi I assume given their advance stage) is another cost to be considered. Just a thought. Hope its not too off topic. Sorry @Bobnjudi!

Yes. As I understand it the new version of the SunAmp will contain two types of cell, with two different phase-change materials to cater for two different hot water temperatures: one well suited to DHW (higher temperature) and one good for UFW (lower). The SunAmp PV always had the equivalent of a Willis heater built-in. It is what converted the PV (or any electrical supply for that matter) to heat energy which was then chemically stored, so no change their. The advance with the new version of the SunAmp, as I understand it, is the ability to output water sufficiently low temperature to be suited to UFH (and presumably on a separate circuit so that UFW and potable water is not being mixed), all in one package. Others will surely be along to correct me if I am wrong.

Great news!

Thanks @Nickfromwales. Now that's a great idea. Music to my ears!

At the risk of going off-topic, as @PeterW mentioned, SunAmp(s) would take up less space and the lower heat loss would in the summer lessen the risk of overheating for your Passive House. An alternative?

Modifying what I said in my first post, I have just read a host of @TerryE's splendid posts about his own build and I am now persuaded by the merits of a Willis Heater heating the slab and the ingenious use of the slab as a heat store. Thus my my latest best guess for internal services or my build is to drop the ASHP and add a Willis heater and stick with UFH, E7, SunAmp (especially the new model with two temperatures, one of which is suited to UFH) with E7 and PV. And maybe plan for the possibility of a heat pump later if cooling turns out to be needed or if the economics of a HP is justified by realised space-heating requirements, which I suspect will be unlikely as I plan to build only a small-ish two-bedroom house. And even if cooling is needed, as @JSHarris said in a post, a cheap commoditised air-to-air HP may well be a wiser purchase particularly as the floor slab is probably not the best location for the delivery of cooling, given the nature of convection and the risk of condensation (which is probably small if well controlled and cooling is only by a few ºC). I admire the simplicity of this approach. It is just what I am seeking. And could require very little maintenance. As @TerryE well said, the only traditionally mechanical part will be the water pump(s).

Fair point @richi and well said. (should probably have skipped the bit in brackets). Thanks @JSHarris I have not read that. I will do so with interest, appreciated. I agree that Cochrane surveys are the gold standard. Jeremy, more generally I am impressed by your breadth of knowledge and that of many on this forum. I am learning a lot by following threads on a great range of diverse subjects (even the splendid sparring with @Fredd).

This PDF from Southern Water in my view summarises fairly the difference between (i) salt-based softeners, (ii) phosphate-based ones, and (iii) "physical-softeners". https://www.southernwater.co.uk/Media/Default/PDFs/2835b_WaterSofteners_A4Notes_Nov12.pdf (By the way, I hold a different view on the sodium-health issue, a more conventional one in line with that of scientific-advisory councils around the World. As far as I can see, the evidence is strong that a high-sodium diet leads to higher blood pressure, which in-turn leads to increased cardiovascular disease, all on a population-wide basis (@JSHarris result not withstanding). Cardiovascular disease is a major cause of death. (Degree in physiology and PhD in biochemistry). Interesting thread. I plan to add a salt-based water softener to my build, when I get to it (and a non-softened tap for in the kitchen for cooking/drinking). Having done so past research on water softeners some time ago, I am tempted to use an older design of softener, a single-tank type, and one that has a tried-and-tested mechanical mechanism for timing and managing the resin ionisation step (no power supply needed). My research suggested to me that the modern two-tank systems are a marketing gimmick. Anyone can tolerate a few minutes of hard water once in a while if one attempts to draw water while the tank is regenerating. The added complication of two tank system provide only that marginal benefit for rather more complication. Having said this, it seems from what I have read that most salt-based water softeners are low maintenance (other than feeding them salt), no matter the type, so its probably marginal.

Thanks all. Advice much appreciated.

A very interesting insight. Good to know. I have not started my build yet but I am a convert to the simplicity and speed of SIPs. I will be looking out for this issue. Am reading your blog and finding that to be very informative too.

Hi, Tom here. New to the site. I am a passive-house enthusiast, already planning designs for a new build but I have not even found a plot yet, so I am probably letting my enthusiasm get ahead of me. I aim to build a small home in the South East of England, probably around Hertfordshire or Buckinghamshire. I have no experience in building but have been reading intensively for a few months now and have learnt a lot from this site and many other blogs, including Jeremy Harris' and podcasts, including Ben Adam Smith's House Planning Help podcasts and by visiting houses on the Passive House open days. I am fully convinced that Passive House is the best way. And have been persuaded that SIPs above a floating concrete slab might be a good construction approach. For DHW and heating, my latest best guess for internal services is an ASHP, UFH, SunAmp with E7 and PV. Best regards, Tom