A cut from a thread in uk.d-i-y from 2006: Payback was 2 years, by a real
user.
"I cut my DHW heating by somewhere between 1/3 and 1/2 by installing a
waste-water heat-exchanger."

"daestrom" wrote in message
...

"Doctor Drivel" wrote in message
reenews.net...

"daestrom" wrote in message
...

"Derek Broughton" wrote in message
...
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/

What was the payback period?

I have a family of five. Even with a low-flow shower head, that works out
to about 34000 gallons of water a year. Of course it's mixed hot and cold
to create just a nice 'warm' shower of about 100F. The average year-round
water supply temp for me is 55F. So that works out to about 127 Therms of
NG a year. When I bought the thing, NG was $0.80/therm. The payback with
that 5% interest on $270 worked out to just about three years. With NG
prices running $1.30/therm, it's under 2 years. But mine has already paid
for itself.

Nice one daestrom, you obviously did your homework on payback. This company
have been threatening to setup in the UK (or have an agent) for a time.
Googling brings up some very encouraging feedback, and seems a better
investment than solar. The US government sites speak highly of it.

Unfortunately most homes here don't have basements, as they do in the USA,
so difficult to locate in a house. I see they have just brought out a batch
processing unit that can be located anywhere, so clawing back bathwater is
possible not just shower water. They use a controller and pump, so more
complicated. As my 4 year girl likes splashing about in a bath, the payback
might be a bit longer for me using the shower version.

But looks like they can be DIYed. One copper inside another, differential
controller and a pump. They work by the water spiralling around the pipes
and sticking to the sides as gravity pulls the water down. If a pump forced
water through too fast maybe it would not do this and heat wasted. Just a
thought. The pump's speed would have to be calculated.

Currently most people just would not believe they actually work.

"Andrew Gabriel" wrote in message
...
In article et,
"Dave Liquorice" writes:
On Wed, 11 Feb 2009 16:57:46 +0000, Richard A Downing wrote:

As you probably know it gets quite cold here and I continually plot
ideas to save heating oil - I used 1000l since the beginning of
November.

Only 1000? We've got through nearly 2000 since the end of November. Will
be due to order another 2000 in about 10 days time...

But is there a simple way of using the waste heat in the grey-water for
heating (aside from letting it go cold in the bath tub before pulling
the plug)?

Even if you can effectively recover it what are you going to do with such
"low grade" heat? Any medium you recover the heat into is only going to
be
around the upper 30's C at best. Too cool even for under floor heating.

How much actual energy is there in a bath full of water? Is it worth
recovering given that it is such low grade?

You could just leave it to cool down before pulling the plug.
That way, the heat has passed into the house. The moisture it
generates by evaporation might not be welcome though. Could
cover the top to prevent evaporation, but then it will take
much longer to cool.

If you're into DIY refrigeration, another option would be to
pump the heat from the bath back into the hot water cylinder.
You could affix evaporater pipework to the back of a (metal)
bath, and have a condenser coil in the bottom of your hot water
cylinder. Then you cool or even chill the bath water, dumping
the heat back into the hot water cylinder. Almost certainly
not worth it, but might be good fun. ;-)

I've thought about recovering the heat from a shower. That's
easier because you can just construct a reverse flow heat
exchanger to transfer the waste heat to the hot water cylinder
inlet flow, as they'd both be flowing at the same time.

See my post on the gfx. If can be DIYed by having a pipe in pipe and reverse
flow.

On Feb 13, 4:37*pm, Onetap wrote:
On 13 Feb, 10:59, wrote:

Rod wrote:
Onetap,

In many classes of substances there are some with bad effects. Jumping
to the assumption that there is bound to be an association with...............
It does seem one or 2 people lost the plot on that. Oils are a normal
part of skin & hair care.

It is mineral oil, meaning not animal nor vegetable.
It is not jojoba oil, nor olive oil, nor sunflower oil, nor rendered
butter, nor whale oil, nor goosefat, nor any of the other oils that
people have traditionally used to anoint their bodies or hair with.
It originated in a well in Saudi Arabia or in the bed of the North
Sea.

Why would anyone put mineral oil on their skin or on a baby's skin?


yes, it's a standard treatement for cradle cap in babies:

http://www.nlm.nih.gov/medlineplus/e...cle/000963.htm

Robert

On 24 Feb, 13:47, RobertL wrote:

yes, it's a standard treatement for cradle cap in babies:

Yes, apparently it softens the scaley coating, which must account for
something like less than 0.1% of the sales.

So why would you oil a healthy baby?

It was/is a by-product, an industrial waste until some smarmy sales
man found a market. Of course, every good mother knows that a healthy
baby must be kept clean and well-oiled, like a guardsman's rifle.

I repeat the question.

Why?


..

On 24 Feb, 10:54, Rod wrote:
Onetap wrote:

Yes; it's a daft idea. Oil (as in lubricating oil) forms a nasty
emulsion and will foul the heat exchanger. It's insoluble and the
drainage companies really don't want it because it sticks and can't
easily be dissolved away.

Response from Thames Water:

====

Dear Mr *****

Thank you for your email of 13 February 2009.

I can confirm that small amounts of oil going down the drain will not be
a problem. *Most hair and shower products, washing powders and soaps
contain fat, which wash into the sewers every day. *The fat and oil that
can causes problems with the sewers are cooking fat and oil; this must
not be put down the drain.

====

As I expected, they seem to have no problems with the small amounts of
mineral oil that would be required.


Bolleaux they did.

They don't want any amount of oil of mineral origin in their drains
and the Environment Agency are even more keep to keep it out of
surface water drains.
Compressors only loose a 'small amount of oil' to the condense drain.
So are all these oil absorbing filters a con? If I fill the sump with
mineral oil, will they find that acceptable.

You are evading the main point; putting oil into a bath will leave a
coating on the sides. It is a daft idea, dreamt up by the clueless.

Onetap wrote:
On 24 Feb, 10:54, Rod wrote:
Onetap wrote:

Yes; it's a daft idea. Oil (as in lubricating oil) forms a nasty
emulsion and will foul the heat exchanger. It's insoluble and the
drainage companies really don't want it because it sticks and can't
easily be dissolved away.
Response from Thames Water:

====

Dear Mr *****

Thank you for your email of 13 February 2009.

I can confirm that small amounts of oil going down the drain will not be
a problem. Most hair and shower products, washing powders and soaps
contain fat, which wash into the sewers every day. The fat and oil that
can causes problems with the sewers are cooking fat and oil; this must
not be put down the drain.

====

As I expected, they seem to have no problems with the small amounts of
mineral oil that would be required.


Bolleaux they did.

They don't want any amount of oil of mineral origin in their drains
and the Environment Agency are even more keep to keep it out of
surface water drains.
Compressors only loose a 'small amount of oil' to the condense drain.
So are all these oil absorbing filters a con? If I fill the sump with
mineral oil, will they find that acceptable.

You are evading the main point; putting oil into a bath will leave a
coating on the sides. It is a daft idea, dreamt up by the clueless.

I have never suggested that it is a good idea as originally described!
Merely pointed out that a small quantity of mineral oil going into the
sewer isn't an issue the water companies are bothered about. And it is
the person's choice whether or not they care about oil on their bath.

I have no experience of the oil used in compressors, oil absorbing
filters, etc. hence no comment on that bit.

--
Rod

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Although common it frequently goes undiagnosed.
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