On Wednesday we signed the contract with the builder who is doing the ground works. Holes for the foundations have been dug this week and the concrete may be being poured as I write. They are also putting in the pipes for the heat recovery / ventilation system. We are going to take some photos tomorrow. If the weather stays mild and dry all the ground works should be finished in two to three weeks’ time.
We are now trying to work out how we are going to finance the next stages. We should order the wooden construction and windows as soon as possible (and we need down payments for these). Once we have ordered them they will take six to eight weeks to arrive. Then the house can be built within a few weeks! In order to get a mortgage though, the walls need to be built to 1m above ground level. As our house is being pre-manufactured offsite, this is not going to be easy. We might have to persuade the land registry office (which will value the house with its “1m high walls”) that this criterion does not apply in our case. Peter has an investment fund that he may be able to borrow from, or we might have to sell the flat we are living in and rent a place for a few months if we just can’t get a mortgage at this stage!
Here are the contents of some recent e-mails from Bjorn. We will be discussing all the options and hopefully making some decisions on Sunday.
Some explanation as to the Zemný Výmeník (SOLE collector). Planned were 165 running meters of tube for pre-heating (winter) or cooling (summer) the air. I added another 100rm (it will be close to 300rm) to make it more effective, both winter and summer. In fact it is now long enough so that you theoretically could connect it to a heat pump (tepelné čerpadlo) up to 5KW. I made a calculation - such a heat pump would cost around 220 000.- including installation. But it would not be very reasonable to do so, because of the temperature gradient being too big (from about 1° to 55° for heating and warm water) the power ration (výkonové číslo) is only 3,2. (For 1KW el. you get 3,2 KW heat).
I now propose a different solution: Longer SOLE collector to boost passive gains (Winter and Summer) + larger solar panels (5 panels instead of 2) with cca. 10m2 + and direkt heating with electricity for the rest (el. spiral in solar heat tank). No pellet oven. Extra cost: 45 000 SOLE, 80 000 Solar. Saved money: 300 000 pellet oven + installation and exhaust pipe. The Solar panels will cover your need for hot water to about 68% and passive gains from the SOLE collector and especially solar collector will cover about 1/4 of your heating demand.
I calculated the need for electricity for 1 year for your house. You will need 1300KWh to heat hot running water during winter time, and about 2000 KWh to heat your house. All in all this is 3300 KWh per year for heating. Compared to that you need about another 4000KWh for all your other appliances (light, washing, cooking etc.). The price for you is 1,87 per KWh if you heat the house + 400 per month (tarif D11 from ZSE, 20hours a day, peak is more expensive, but you will not use that for heating). Because your heat losses are so small, heating directly with electricity makes sense.
Soon it will be possible to buy wind powered electricity (in Germany you can do that already) and it is probable that in 10 years time it will be feasible to mount photovoltaics for a reasonable price that will produce 3300KWh/a or more on your roof - this makes only sense if that gained electricity can be sold directly into the grid. This is possible in Germany and Austria today. This seems to me a sounder ecological strategy.
The pellet oven could save you the 3300KWh in electricity - but the price of the pellets would be comparable to the price of the electricity - and for the 4000KWh you need for other appliances you would get a higher tariff so effectively you would pay more. Failure of electricity: any power loss up to 24 hours will not change the inside temperature by more than 1°C.
There are small free standing ovens that burn bioethanol and produce only water vapor and CO2. These can be used for extra heating (up to 2KW) in passive houses. Bioethanol is expensive though, and is only meant for a once in a time use. These ovens are new and cost about 80000 SKK. I don´t think that would be necessary, I mention this only to inform you about possible back ups.
One more possibility:The heat pump is only slightly more expensive than the solar panels. So if we would skip the solar panels completely, we could replace them with the heat pump. With an overall need for heat of 7000KWh/a we would probably only need 2200KWh electricity, even less than with solar panels....life expectancy of a heat pump is a bit lower than solar panels, but the system is more compact and easier to install.
Finally, here is another website that is good if any of you in the UK want to make ecological changes to your homes: http://www.est.org.uk/ And it explains some of the things mentioned above.