Athol <athol_SPIT_SPAM@[EMAIL PROTECTED]
> wrote:
>Bernd Felsche <berfel@[EMAIL PROTECTED]
> wrote:
>> I've had SHW for about 35 years. The 'newer' system is 20 years old.
>> Sacrificial anode got replaced about 3 years ago when I had the
>> house re-roofed with steel (and insulated).
>My parents had a solar system with the tank under the house and the
>circulation between the tank and panels driven by a small mains
>powered pump. It worked for over 20 years with little maintainence
>but when the pump impeller failed after all 4 children had moved out
>of home, they worked out the the cost saving of solar vs off peak
>electric for just the two of them meant that repairing the solar was
>not cost effective.
>They now run straight off-peak electric.
At least until the price triples. :-(
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.
>> Installers tend to drop the heater on whichever surface looks
>> convenient.
>Just as long as it doesn't break. :-p
Use extra-thick custom-orb. :-)
>> The clever dicks will orient it for maximum insolation
>> during winter. You'll probably get too much in summer anyway.
>> Slightly away from North is probably better than true North. A few
>> degrees East may work better to get the water hot sooner in the day.
>The planned extension will be 2-stories high, and the roof should get
>pretty good early morning sun in spite of the place being in a valley.
Sounds good. One of the reasons why the valleys in the European Alps
are populated the way that they are. is because of the sun's position
in the morning.
>> It's somewhat dependent upon where the clouds tend to be in your
>> part of the world.
>Surprisingly, NE is probably the least cloudy direction. Probably a
>side effect of the hill...
Looks like you're a lucky fellow.
>> If in doubt, put panels on the NE and NW roof sides. :-)
>I think I might skip putting them on the NW face, which will be the
>front...
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). 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.
>> Keep the storage tank out of the wind, if you can.
>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.
>If I do end up with an ordinary storage tank near ground level, it
>will be inside a corner of the garage under the stairs to the top
>floor.
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.
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...
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.
>> Make sure that you get an inline gas booster, controlled by
>> thermostat. You should never need to touch it except to add gas.
>We are in a small area of a few blocks (maybe 100 houses) that
>don't have natural gas even though the areas around us do, so it
>would have to be LPG. Perhaps I should get a seriously decent
>sized tank, a bowser for the vehicle fleet and a separate take-off
>for the HWS and standby genset. :-)
>Seriously, my preference would be solar with heat pump backup but it
>seems that heat pump is seen as an alternative to solar, not a backup
>for it. :-(
I need about 300kWh a year of electric booster to heat the tank here
near the temperate coastline. The booster is operated by a timer to
take the chill off the water for my morning shower; and not left on
thermostat like many. The booster heats the whole tank so more water
is heated than needed. An inline heater only needs to heat what's
being used, when it's being used. Heating may not be the most
efficient but the heat lost in storage will be zero.
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.
--
/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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