Bernd Felsche <berfel@[EMAIL PROTECTED]
> wrote:
> Athol <athol_SPIT_SPAM@[EMAIL PROTECTED]
> wrote:
>>Bernd Felsche <berfel@[EMAIL PROTECTED]
> wrote:
> It's "cost-effective" for just me with my SHWS. Off-peak electricity
> is a PITA here. Especially when they ask for more than 25 cents a
> day just to meter it, as well as charging premium rates above the
> norm during peak hours... At 25 c/kWh, I could operate a diesel
> genset.
I should have a look at the availability charge. I don't think that it
is that much here.
The thing is that if you're running solar with electric backup, you're
already going to have off peak available unless you're paying the even
higher rates of normal power.
We now have electronic meters that charge for power in 3 separate time
ranges. I don't remember the exact titles, but they are something
like "night", "shoulder" and "peak". The cheapest one of those is the
night one, which is about 30% more than off-peak 1. It applies between
10pm and 7am. Peak is about 5 times the night rate, and applies on
weekdays (excluding public holidays) between 2pm and 8pm. The shoulder
rate is about double the night rate and applies the rest of the time
(ie weekends and public hols 7am to 10pm, weekdays 7am to 2pm and 8pm
to 10pm). The huge rate for "peak" was a bit of a surprise.
> Looks like you're a lucky fellow.
That varies. :-p
> Rule of thumb for panel area is about 3 square metres per occupant
> at our latitudes (I haven't checked your quota of cloudy days - you
> need more panel in cloudy areas).
We are close to the coast and tend to get more rain than most of the
region. We do tend to get sunny patches even on rainy days.
> 200 litres/head of hot water
> storage. Those figures are somewhat above those quoted by those
> trying to minimise the price. Being the last under the shower in the
> morning shouldn't need booster in summer. But it's what you'd need
> with the typical 300 litres of storage. Solar energy is too diffuse.
We tend to have showers at night rather than sleeping dirty. :-)
The biggest problem we presently have is that, with my wife using warm
water in the wa****ng machine, we can exhaust the HWS if she does too
much wa****ng through the day then has a long shower in the evening...
It gives her an excuse to only do 1 load of wa****ng each weekday. The
off-peak is on all weekend, so most of the wa****ng gets done then.
>>I'm leaning towards an in-roof type to avoid the lossy pumping
>>arrangement that my parents had.
> Over here in W.A., there are traditionally many roof-top SHW
> systems, most with the roof-top tank operating purely on thermosyphon.
Yep. My inlaws actually had a thermosyphon system with a gravity
feed to the taps from the non-pressurised tank. That system died
and had to be replaced so they now run a pressurised tank type but
it's still in the roof.
> You can incor****ate some other passive solar design aspects, even
> if the orientation of the house isn't ideal (being longest sides to
> North and South). Arrange for external shades to the walls and
> windows East and West; the latter if there's not shade from the hill
> on a summer's afternoon.
> Roof wide enough to keep direct sunlight off the window glass at
> least 3 hours either side of noon in summer.
We will almost certainly have aluminium roller shutter on the outside
of every exposed window. That allows quite effective control of the
solar space heating, particularly if we take up the option of getting
electric motorised ones (it's an option) and controlling them from a
PC that also has temperature sensors, etc..
> Doors at bottom and top of stairwell to keep the ground floor warm
> in winter and the top floor cooler in summer. Insulate floors and
> walls, of course...
The top floor of the extension will be living space while the lower
floor will be the garage. It will have sound and thermal insulation.
The staircase will open from the existing lower floor to the new top
floor and I don't think that we've even considered doors on the stairs
to date. Hmm...
> Ventilation is im****tant. I heard a program recently on German radio
> (internet) recently where the heat from the air being exhausted is
> passed onto air entering the building (in colder weather of course);
> presumable by passing on either side of a large metal plate heat
> exchanger. Humidity control is im****tant in winter. You need to
> maintain levels of relative humidity around 50% after heating, which
> results in condensation on cold surfaces ... pretty nasty.
I'd rather keep the humidity below condensation levels, thanks. I am
already having that problem with my office shed after a few days of
persistent heavy rain.
> A heat pump doesn't have the intensity to heat the water as it's
> being used, so the energy has to go into storage; with associated
> losses. Even with a COP of about 3, the cost of operation wouldn't
> be much lower than with gas heating.
Yeah, and the heat pump has a much higher capital cost.
We keep having just enough power supply interruptions for me to be
seriously considering installing a genset large enough to power the
entire house. Obviously, in that scenario, using gas as the backup
for the solar water heating makes more sense than heat pumps.
The other piece of domestic equipment that I'll be looking closely
at when it comes time to replace is the dishwasher. It needs hot
and cold water but only has one input, which is intended to be cold,
meaning that all of the water is electrically heated in the unit.
I'd much rather have a dishwasher that had hot and cold inputs and
used solar heated water... I'd rather it use a bit more water and a
lot less electricity.
--
Athol
<http://cust.idl.com.au/athol>
Linux Registered User # 254000
I'm a Libran Engineer. I don't argue, I discuss.
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