Come on people are you men or mice (women / lady mice)...?

This seems to me to be a pretty big question....

Your gas creates C02 and will run out...
PV doesn't well enough in cloudy winter... same for Evac Tubes...
Wind turbines can't beat the planners or low urban wind speeds...


So what ya gonna do....?


(Cold showers may work for Biff and Tony but not for my misses I can guarantee that!)

J

In a city (where I don't agree with burning wood) I would just use the E7. You aren't adding to peak load so won't cause any new power stations to be built and we will certainly start to have excess night time supply if we build a load of new nuclear power stations in partnership with the French, plus add a lot of wind, wave, tidal etc. If you are using evacuated tubes for the solar then it isn't going to be a vast amount of electricity over a year and think of the savings in capital cost! Sometimes I just don't think it is worth investing large sums of money to save small amounts of energy, diminishing returns and all that.

Likewise with the space heating. Design to the highest standards of insulation and air tightness and stick a cheap wall spilt ASHP in your main living room for £799. What's the point of spending any more on systems that will hardly ever be used? Just a waste of resources.

Posted By: James NortonOk...
...So I design to passiv-haus standards, including airtightness insulation, MHRV I have some evac tubes on the roof with , even a little PV but is there any way I can get a family's worth of hot water during the winter without mains gas backup (or oil or LPG)...?

I am scratching my head over the same issue for a house in west Wales. GSHP and underfloor heating sounds great but there's no way my wife is going to accept tepid water in the winter time or probably any other time. For DHW I think 60C is overkill, but even a modest 48C is quite a step up from the 35-40C I assume you can expect to get from a GSHP. I'm leaning towards a log boiler and a large thermal store that supplies both the domestic hot water and hot water for the UFH. Add solar water heating and you probably could get by with very little wood over the summer months. But then there's the electricity for the UFH pump to consider and maybe for the log boiler as well...

Chris Wardle commented: "Design to the highest standards of insulation and air tightness and stick a cheap wall spilt ASHP in your main living room for £799. What's the point of spending any more on systems that will hardly ever be used? Just a waste of resources."

Totally agree about insulation and draught-proofing. The problem with the ASHP approach is that each room you're actively using will need an ASHP. I live mostly in Japan, where central heating is not used. The result is that the house ends up festooned with external ducts and boxy fan units for multiple aircon/heaters (one in each room) which is ugly in the extreme and gets expensive quickly. The alternative is to have only one of these devices and never use the other rooms in the winter because it's too cold, or heat them with inefficient fan blowers. I've experienced houses without central heating and to me it's not the answer. Personally I would prefer to pay for the comfort and security of a central heating system and use it sparingly than save the money and struggle to keep the house warm during an unexpectedly chilly winter. I do accept that notions of "cold" vary from person to person and we all have our own ideas on how much should be spent.

Dan

Dan, are the houses in Japan designed to PassivHaus standards? I doubt it so certainly a central heating system is required. The idea behind PH is that you design out the need for central heating by spending more on getting the insulation and airtightness etc right and off-set that additional cost against the savings from not installing a conventional heating system.

As soon as you start plumbing heat distribution systems and boilers in that saving is lost and they just cost more to build. You end up paying a lot of money for piece of kit you only actually need for a few weeks a year. Just seems like a waste of money to me.

At 60ºC the bacteria can not survive

Unfortunately there are also other less common pathogens that can survive to 114C or so. Ideally any system routing water might take the temperature up to perhaps 130C before storage.

There are possible new technologies that could solve the dilemma. However any new technology that might be visible to the public (almost all new renewable technology) will not have been planned for by the planners and so will have difficulty being introduced into this country until proven elsewhere with the UK planning laws subsequently re-written to account for it.

Jon

Interesting, domestic indirect systems could only ever get up to about 80ºC and the norm is around 60ºC. Are we all at risk from these other pathogens?

Health and Safety legislation tends to concentrate on Legionella although systems should be flushed and possibly disinfected before use.

Jon

Well as I have got to nearly 50 I’m not going to start worrying now!

You wouldn't necessarily need evac tubes. There are other more economic ways to obtain very hot water (100C+) from stationary arrays by considering the house or structure itself as a solar collector. However, it would need a rethink of construction and planning so I think we're a good decade away and perhaps an alternative (probably nuclear) will be found in the intervening period?

I haven't been able to get any real data on how many evac tubes would be required. Will be very interested if you find any data.

Hi Tom

There are various solar mirror reflection arrangements that allow fixed concentration with one or more moveable receptor(s): This allows medium to high grade energy production but you almost certainly wouldn't use it to its full potential in residential use. You would just need to design the roof or the facade as one of these reflector types adding a cost of about £30 a sq m assuming mass production together with the receptor apparatus (the larger cost): Means that the house shape and layout with regard to solar movement is partly dictated by the type of reflection gathering system you choose (which is why it is currently infeasible in the UK: Our planning system is not geared up to use innovative renewable energy)

Back to original question: design to passiv-haus standards, including airtightness insulation, etc.
Live in France and heat domestic hot water by electricity, cheap rate. EDF (Electricity de France) generates electricity as follows: -

Nuclear 87.5%
Renewables 5.9%
Coal 3.3%
Gas3.2%
Oil 1.6%
Other 0.3%

Look no oil! (Well all right 1.6%).
Of course the downside is that fission nuclear reactors can hardly be described as "green" and everyone here lives too near to one.

Posted By: jonDidn't say it would be easy Tony, just ideal: You can also get away with 115C but this tends to be a less economic way of doing it. Steam only gets produced at 100C as a forced change of state, given sufficient energy input, at standard atmospheric pressure. I don't think we are at serious risk from pathogens that can survive at greater than 60C Cds but it's not my area of expertise.

According to my father (retired anatomy lecturer), 120C for 20mins is the rule of thumb. That leaves water sterile for all practical purposes - only real exotics can survive that. But we've all been getting by with hot water that's a lot less hot that that (obviously), and bathwater-related deaths seem mercifully rare.

The other option for your DHW is instantaneous heating as the water is used. With a thermal store with built in heat exchanger this is easily achievable, and this will reduce the risks of legionalle and E-coli bacteria (the two worst offenders) as the water is mains cold water until it is heated just before use. This is how our system works anyway, and it is used in civic buildings and hospitals, hotels factories and domestic dwellings all over Germany, Austria, and to a smaller degree, Australia, Dubai and Ireland. Plus, when the Thermal Store is above 60 degC, the water is heated to above that anyway, and then mixed with cold water to achieve 45 degC at the taps.

Hi "mrswhitecat"
Will a house to passivehaus standards + MHRV need any heating over and above the wood burner with back boiler you need for spring/summer weather such as we now have in SW France (where it's rained most days since March). Any solar system would need to be pretty efficient to make much impact this year!

"spynappels" - Have there ever been deaths from Legionella of fit people living in private homes? The risks must be minute. I'd be more worried about drunk drivers, lightening strikes.....

James,
I too am building a PassivHaus/CSH level 6 house and I posted a very similar question on the UK PassivHaus Forum. If there is to be no conventional central heating and if mains gas isn't available, as in my case, the replies split into two camps. The first one thinking a simple low cost immersion was best, the other was to use an ASHP and reduce CO2 production. I have decided to use the simple option. To get around the Legionella problem I will be using a 300l heat store with an external heat exchanger giving me mains pressure hot water. I hope that helps.

Hi mrswhitecat,
MHRV from Rega Ventilation, 21 Eldon Way, Biggleswade, Beds SG18 8NH - not installed yet but have heard fans running at factory and doubt you'll be able to hear them at all once installed.