Passive House Hot water

[johnuready]

I have a post going elsewhere on the use of PV power to heat hot water and struggling. Hence this post to see what other people have managed in a similar situation.

Our bungalow is a refurb that I'm building to a Passive spec and have every reason to belief we are going to achieve the "Annual Specific Space Heat Demand" of 13 KWh/M2. That's great but the MVHR will only need small amounts of heat to supplement the recovery and as the wife likes warm towels in he bathroom I have 2No. 850 BTU rails that will run for 1 hour ish in the morning. If my calculations are wrong we have a fall back of a possible radiator in the hall. That's fine but as the towel rails are only 3m away from the heat source the gas boiler idea will not work on such a small load and short runs. Hence the 2Kw electric boiler idea that run the towel rails as required. I think that the performance of the house with the MVHR will limit the "on time" for the towel rails anyway.

That leaves me with a hot water problem. I have space for a 200l tank and as I have no gas boiler on the plan for CH, I'm looking at Solar Thermal and topping up with electricity (mains and or the free PV diverted from the grid) to top in the winter.

Only my wife and I, no bath just shower, 4Kw on roof, no solar thermal as yet.

Note:

The 2kw electric boiler to run the 2 No. towel rails, purchase costs £250 and will cost me about 30p a day to run during the winter months. A low power gas boiler, including all parts and labour (no tank) £1000 to £1200.

Anybody have solution ideas?
 

[clockmanFR]

I come at this a different way.

Yep, i get bricked by those on this forum that have vested interests in the present status Qua.

Passivehaus standards, yes great its a start, but i tend to go further with minimal use materials, minimal costs and importantly in this day and age minimal future maintenance costs.

For example the concept of Gas boilers water tanks, plumbing header tanks etc is just a nightmare of costs and what about future costs?.

I honestly can not see gas getting cheaper, but PV there you go get a few KW up, to feed that Hot tank.

And talking of Hot water tank, go European with direct pressure non vented, very different to the nonsense sold in the UK.

[martin]

"go European with direct pressure non vented" - it's a subject that's been long discussed on this forum, and I must hold up the flag for the simplicity/safety/convenience of the good old-fashioned cold water header tank in the loft, and a proper vented system.
It is intrinsically safer, simpler, doesn't require regular inspections to ensure it's ongoing safety, and most important of all, in the increasingly unsure conditions we face, is splendidly "low tech", easily repairable, AND gives you the reserve tank of water to tide you through water cuts (we get them fairly regularly already)

Personally I'm amazed that someone who goes for  "minimal use materials, minimal costs and importantly in this day and age minimal future maintenance costs" has been bamboozled by the "wisdom" of over-hyped pressurised systems....

[billi]

Hi

Get a Domestic hot water heatpump  something like this  

http://www.schueco.com/web/za/content/solarpower_and_heat/products/heat_pump/hot-water_heat_pump/wpsol_300


about 1500 GBP delivered (similar model)

and use your PV    and even install more PV or connect a solar thermal idea to it , with FIT or without it , to make a passiv house to an active house  


Billi

[clockmanFR]

See brickbats, never seen it, don't know about it, don't want to know about it, must be costly, looks unsafe, is unsafe, not good old fashioned UK stuff, so must be dangerous. (3 English Plumbers).

Ah the word 'LUDITES' comes to mind.

Sorry Martin, but when You live and work with other concepts you see all sides of the story.

Actually, its good on costs, very robust, simple to install and minimal materials.

UK is UK, but to me now working with other systems, that are as standard made for normal incoming pressure of 6 bar, when i see the complicated UK stuff, sharp intake of breath.

PS, want to talk about European electrics? UK Ring mains, UK single pole MCB's, truly the Dark Ages.

[martin]

I'm not talking electrics, just simple "fail safe" domestic plumbing that fits well with a "keep it simple ethos", that also has the decency to give you a very useful reserve tank of water (for which I have been very grateful several times!)

[johnuready]

Thanks for that notes. I think I'm getting on with the issues that need bottoming out. The CH, as it's a very low requirement I'm going to use the 2Kw hot water boiler running on a timer and thermostat per bathroom towel rail, that will give me instant heat as required. Boiler cost £250 and come complete with pump, pressure tank etc. Really plug and play. As the passsive house requires very liitle CH input, that works out as a good comprimise.

The HW, I'm going for the VailXXXX Solar system. This will give me a 200l tank with 2 coils, direct system. One coil for Solar Thermal and one for another heat source when / if required. The roof panel comes with all the controls etc and integrates.

That leaves an immersion to play with on the diversion of PV power V load on house or just 100% PV during the winter combined with Solar Thermal and see where we get to. A good excuse to brush up on the old electroic skills.

It also leaves me the spare coil just in case it all goes wrong and I fit an Air Source / something in the future.

I'm looking at MVHR units next week, another issue to resolve.

John

[martin]

For solar hot water you'd be hard put to better the house brand evacuated tube panel, tank and ancillaries both for quality and price!

[Baz]

Solar water undoubtably the way to go and a quality brand (as above) not the cheap stuff of ebay. However see other threads for all the discussion about how many to have to extend the season but bear in mind mid winter it is only a starter to take the chill off not to actually get a shower out of it.
As for the towels the simplest and most efficient will be an electric towel radiator. On the switch put a picture of a starving Biafran and tell you wife she can turn it on if she has no conscience.