Hi Noyers - are Rega Ventilation delivering and installing to SW France as well?

I'm still not sure what to opt for. We're under pressure to sign up a plombier and electrician by September or risk a major rant from the builder about his chantier being bloqued. The Passivhaus doc says : insulation, solar and MHRV but I haven't found anyone locally who does this.

On the other hand, we have found a traditional plombier (works with copper and something he calls 'multi-skin') who is happy to integrate solar, UFH and a wood burning stove with back boiler. Let's see what he quotes for the job ...

....soooo... no takers then....?

Come on people - hot water in the winter when its cloudy?

So far

- biomass
- electric immersion
- electric instant hot water
- mains gas
- huger winter optimized evac tube array

any others without the inefficient electricity the finite mains gas or the particulate nasties of biofuels, also any other reasons than mine why these options are a bit duff...? (that should temp a bit of debate methinks )

J

What temperature can evacuated tubes get to on overcast days?

Looking at these numbers:

http://www.apricus.com/html/solar_collector_efficiency.htm

and various meteorological stations' output showing that 100 W·m⁻² is plausible global radiation for a cloudy day gives a stagnation temperature difference over ambient of 38 °C. With output (actually, average temperature in the collector) 20 °C above ambient the output power would be 20 W·m⁻².

The trouble is, those calculations are using the fitted parameters for the performance right at the end of the range for which they were made so I'm not that confident of the results. Anybody got some ETs and can say how far out this all is?

Posted By: James NortonCold showers may work for Biff and Tony but not for my misses I can guarantee that!

Are these misses your daughters or your girlfriends? Either way, I appreciate the urgency of your enquiry!

ED

There were many, many days this summer where my solar pump ran for less than an hour. We went to Cornwall for two weeks and the weather in Chesterfield was warmer the whole time came home to a heat store at 45degrees; pump had run for 30 odd hours - totally pathetic performance.

Conclusion - the performance of evac tubes in overcast conditions days is overstated by orders of magnitude yet the 'dull day' claims persist.

That said if you have a coil in the top of your water cylinder or a stratifier you can still get some useful heat out.

"Come on people - hot water in the winter when its cloudy?"

It wouldn't be that difficult to provide solar on a mass scale (using concentrators, thermal banks and distributed heating). However, if you're talking about designing for a completely cloudy winter then the banking would become un-economic (unless interseasonal starts to look better economically)so one would need a back up source.

Hmm.

Where can you put a modest water tower/dam in Sheffield.

Blimey Jacky it may be inefficient but very, very cool.

Actually a Stirling engine with solar mirror might be better than PV - output is mechanical.

Of course, in the UK there's no such thing as "excess" solar energy...

Skywalker, yes, I realise the output of the ETs on cloudy days are going to be cooler than you might want a hot water tank to be to kill legionnaires. However, for many purposes cooler water would be fine - I've just measured the temperature of water I'd use for a shower with a mercury and with an IR thermometer and they both showed about 35 °C.

Hence my question, anybody got any idea what sort of temperature could actually be achieved by ETs on cloudy cool days?

If you've got a large mass of water (many tonnes, accumulated over many cloudy days with a big array of ETs) at, say 30 °C then you've got a good head start when the sun does come out for an hour or two to boost some to 50 °C or you can use a fairly small amount of electricity, wood or gas to do the same boosting. Also, you can use the "lukewarm" water for space heating, e.g., using UFH.

Absolutely!

Roof with 90 -180 tubes or more OR (or indeed AND - if you see what I mean) heat less water when there is less sun. Most solar controllers (other than the budget ones) can switch between heating two things. Some can do more. Importantly these two things can be two vessels (heat stores/tanks whatever) or two levels in the same store. I regret I did not cotton on to this earlier (before I bought my store) as I would have had a coil put in at the top (to heat the first 50l say) along with my bottom one. The other option is a stratifier i.e. wookeys home made one or a proprietary one where if there is a teacup full of hot water available you will get it (system losses excepted).

I think the original Q was about DHW during the winter without bought-in energy, the holy grail! From my researches for a new detached 3-bed, it seemed:
GSHP needs too much elec.power to run (even if you have the ground area or are willing to drill down), ASHP is inefficient and unsightly for most UK dwellings except flats, PV Panels are too expensive and require costly inverter for 240v.single phase, Wind Turbines ideal in the right location but planners hate them. So back to wood or pellets if you have a source, even then the technology is expensive and mostly designed for communal dwellings or industrial use.
So it seemed to me that that for a basic system I'd install a 1Kw or 2Kw Wind Turbine with 120v.output connected direcly to a suitable immersion heater (wind blows more in winter and with a large enough store excess can be diverted to space heating), plus probably two PV panels of 100w. to provide some back-up plus power for any low voltage pumps I could fit (circulating pumps don't use much power but it's v.difficult locating low voltage ones) and Solar Thermal collectors about 3m2 to provide spring/summer DHW and driven by PV output. This might - if the technology works - make me independent of grid energy but I'd still need large battery banks if I were to smooth out the natural weather patterns. A high quality inverter would probably also be a good idea if I wished to use a computer, watch TV, boil a kettle etc. Unfortunately I would probably have to live in an east-west valley and more than 2 miles from the nearest other dwelling to be allowed all this, negating the Wind Turbine efficiency.

If I were you I would go for the 9 m^2

How many days can you survive without a shower?

To start with the immersion idea is a good stop gap and necessary as a back stop too.

....another after thought...

I guess the store should be sized either on a basis of 100l per m2 of panel or I have to dump some heat - possibly through a heat main to a DHW tank in my mother-in-laws house which is next door...

Also I went ofr a big store and was confident about the lack of heating load wouldn't I be better using the heatexchanger to heat/preheat mains cold water, shove it up to the top floor into a small stupidly insulated DHW tank in a stupidly insulated cupboard, with a smaller immersion there rather than trying to heat 30% of a enormous Akvatherm just to get 150l of hot water...?


J

Thermodynamic Solar Panels for Winter DHW