Topic: German solar hotwater in NZ

German solar hotwater in NZ 

Guess what? will be pleased - www.solarrosahome.co.nz

Re: German solar hotwater in NZ 

Cam, what wrong with the best for godzone?

Re: German solar hotwater in NZ 

Hope they provide a challenge for the solar industry to jump two or three decades forward.

Re: German solar hotwater in NZ 

It might well be German, but their system hasn't been thought through.

If you happen to use a hot water heat pump and store water at 50 degrees, to comply with the 60 degree rule means taking water to 60 once a week. Doing this with straight electricity in a 300 litre cylinder costs 10c a day (3.5 kW hrs a week).

Is it worth fitting a "fresh water kit" (heat exchanger, pump and flow switch) to avoid this?

They also seem to suggest solar can be used to some extent for underfloor heating, and integrated with solar hot water. Yeh right. Even a 1000 litre cylinder only holds about 70kW hrs of usable energy, many houses need 100kW hrs a day to stay warm.

Unless you have access to cheap wood, the most cost effective heating solution today is with heat pumps - (but not high walls in a new house).

JK

Re: German solar hotwater in NZ 

Would they have to comply with the 60C rule? Though labelled as a HWC the system uses a heat exchanger so the potable water is heated directly and doesn't sit.

Actually it surprises me that you could heat water to usable temperature with a simple heat exchanger but I guess you only have to go to the end use temperature such as the shower temp.

Re: German solar hotwater in NZ 

JK,

you cost calcs for power are not taking reality in account. Reality is that power will go up even more if the asset sale goes ahead.
"Fresh water kits" are successfully used for years now and they are a safe way to use hot water, even for drinking from the tap !!!!!. Of course it needs a well trained plumber with up to date expertise to make it work.
And when it comes to technology, the Germans are like the All Blacks in rugby, they don't muck around.
And if you have a house which needs a staggering 100 KW a day to keep warm, it would be logical to invest into insulation and insulated windows , before even thinking about solar or heat pumps or whatever....

Re: German solar hotwater in NZ 

To Guess what? - JK said 100kWh a day - about right I would have thought - 20kW for 5 hours???

I also don't think power prices will keep rising - and have said that before. The reason has to do with what people will be able to do very, very soon: PV systems are plummeting in price, and I believe they have reached "grid parity" or, more importantly, "socket parity". Although there are a number of things to sort out so that we can make the most of PV for the average home, they are not insurmountable and the costs involved are falling by the minute.

This is going to have a revolutionary impact on the electricity sector - let's see what real "competition" looks like!

Seeker

Re: German solar hotwater in NZ 

In central Europe an average house build to 1998 German or Swiss or Austrian or Dutch......energy efficiency standards has an anual heat energy consumption of 100 Kw/ m2 living area.
In a 150 m2 house it would work at at about 41 Kw a day. Now if you take the cool, but not as cold as Europe NZ climate into account, it would be even less. 100 Kw a day is excessive and some serious work on the thermal envelope would logically be of higher priority to solar and whatever heating.

Re: German solar hotwater in NZ 

Guess what? I agree with you, unfortunately I can't change accepted building practice - only provide the most cost effective solution for an existing problem.

In round figures a complete underfloor heating system for a 200 sqm home is $16,000. 10 hours a day running of a heat pump consuming 25kWhrs, putting 100kW hrs into the house - for say 160 days a year. Costs about $800 a year for heating.

Investing another $10,000 in say better (ie uPVC windows) perhaps would save $200 out of the $800? Not worth it.

JK

Re: German solar hotwater in NZ 

Not worth it? Not true.
Every cold surface such as poorly insulated windows create discomfort. To compensate for this cold surface the room temperature must be increased and therefore the energy consumption.
A house with a highly thermally efficient building envelope is comfortable at 20 or 22 degrees and in NZ climate it can be heated for maybe 100 Dollars a year.
And the insulated windows have a service life about 4 times of your heatpump.
If you require 100 KW a day to keep a house warm you have either a house like a sieve or your heatpump system is not efficient at all.
If you have a ratio of 3 KW for 1 KW of power you should consume no more than 20 Kw a day with your heat pump

Re: German solar hotwater in NZ 

When JK said 100kWh/day, he was taking about heat energy, not the electricity needed to make the heat. With an efficient heat pump this would need 20-25kWh/day of electricity.

Could you explain how you arrived at the conclusion that 100kWh/day is excessive? Suppose we have a house which is a 20 x 10 x 2.4m box with R2.5 in the walls and floor, R5 in the ceiling, and 25% of wall area in R0.5 windows. The heat loss comes to 250W/degree, plus another 100 for ventilation losses, say 350W/degree. Average outside temp 5 degrees, inside 20, that's

350 * 15 = 5.25kW -> 126 kWh/day. And very few houses achieve this standard.

If I doubled everything to R5, R10, and R1.0, and used passive heat recovery I would be down to 45 kWh/day. With an efficient heat pump this would cost $3/day or $360 for the 4 cold months. How can a house be heated for $100 a year?

I would be very surprised if even 0.1% of NZ houses achieved this level of insulation.

Re: German solar hotwater in NZ 

Robert, my calc. was based on a house built in central Europe to 1998 thermal efficiency standard.
If you your sample house was built to this standard you would be at roughly 23 Kw a day to keep the entire house at 20 degree during the day and about 18 in the night in central European climate. Now if you take into account the lesser cold Winter in New Zealand you should be somewhere on the 1/2 mark.
If you build to passive house standards or near you would be spending even lesser or nothing.
The fact that just a few houses in New Zealand use less than 100 KW a day, doesn't change the fact that it is excessive. It means a lot of work is ahead and the energy saving potential is huge.
It is a bit like if 98 drivers speed through town and two don't, it is not an excuse for speeding.
Unless you building wrap is fully airtight you will never have R 2.5 insulation in the wall.
Unless your ceiling insulation is enclosed in an airtight cavity in the roof space, you will never have near R 5 ceiling insulation.
The insulation value given on the packaging is assuming an airtight still air cavity.

Re: German solar hotwater in NZ 

Guess what?, I don't think your information is correct. This 2007 chart
http://www.eurima.org/uploads/ModuleXtender/Publications/13/EURIMA-Ecofys_VII_leaflet_0412071.pdf

shows that that German standards in 2007 were:

Floor: U=0.45 (R=2.2)
Roof: U=0.25 (R=4)
Walls: U=0.33 (R=3)

which are very close to current NZ standards. Only the UK and Scandinavian countries are shown as having higher standards for insulation.

You have a point about airtightness, however, in my house my observed heat loss overnight matches my calculation using built R-values, so I am confident that there are no unexplained losses.

Re: German solar hotwater in NZ 

PS, I read here http://en.wikipedia.org/wiki/Energy_in_Europe
that energy use in Germany is 129kWh/person/day. If 30% of energy is used in houses, a 3-person household would use well over 100kWh/day (averaging over the year). I think the main reason that houses in Europe feel warm is that they have proper heating, not proper insulation (although I'm not denying that they're better on average than NZ, at least in northern Europe).