"daestrom" wrote in message
...
"Derek Broughton" wrote in message
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Ron Purvis wrote:
I think you are off on your figures. According to
http://www.fsec.ucf.edu/solar/apps/sdhw/dhwsave.htm the typical home
uses
20 gallons of hot water per day for the first two persons and 15 gallons
of hot water for each additional person. That would be 25,550 gallons of
hot water per year for a family of four.
OK, I'll accept those numbers. Anyone got a better figure on the average
cost of heating water? My numbers for heat required are, if anything, on
the low side, but at $25/million BTU, and only 25,000 gallons per year,
you're talking $250/year (somebody else said $20/month, so same
ballpark).
Still plenty to make a commercial solar water heater pay off.
I cut my DHW heating by somewhere between 1/3 and 1/2 by installing a
waste-water heat-exchanger. Running hot water for a shower and letting
all the energy go down the drain (literally), just doesn't make sense. Of
course, this system only recovers heat from *running* water, so baths and
dish washing doesn't affect it.
I have one of the largest units and it is a two-pass type so is not the
most efficient model they have. Mine cost only about $270, did the
installation myself.
http://www.gfxtechnology.com/
Use one of these and save 1/3 of DHW costs, install solar panels and cut 50%
of that and add one of these and DHW should cost a penny or two.
Zenex, in Plymouth has introduced a "top box" that fits on a condensing
boiler's flue (patented). Out of the boiler into the box and out again to
outside. The return pipe pass through the top-box and out to the boilers
return. This appears a big "leap" in making condensers more efficient.
They announced it pre-Xmas, but now it is on sale.
http://www.zenexenergy.com/downloads/HVR10-REPRINT.pdf
http://www.zenexenergy.com/
It extracts even more latent heat from the flue of a condensing boiler.
They claim, with some independent validation, that a "condensing" boiler can
save 30% of its heating bills. There are no moving parts.
They claim that a combi (for US people a combined hydronic boiler and
on-demand DHW heater) can deliver 50% more water flow for the same input -
so a 12 litres per min job will be 18 litres, a big hype that fills a bath
pretty fast instead of a leisurely fill.
They are developing a 15kW combi that delivers 12 litres/min - a little
better than the average combi around. 12 litres is normally only achieved
by a 28kW boiler. So, at 15Kw it is not oversized for the CH in flats, and
the case size can be kept down.
They plan a box for a non-condensing boilers too, that will bring
non-condenser into condensing territory.
They claim the price will fall from £595 as production gears up. If it gets
to half, and it does what they say, then this is copst effective and can
save a lot of fuel, the bigger the house the more fuel saved.