On Jul 16, 9:57*am, Tim Lamb wrote:
In message , Bob Minchin
writes
Roger Mills wrote:
In an earlier contribution to this discussion,
Dave Liquorice *wrote:
On Wed, 15 Jul 2009 18:56:49 +0100, Tim Lamb wrote:

20m3/day or 833kg of water per hour. Extract 5deg. C is how much
energy?
Specific heat capacity water 4.187 kJ/kgK

20000 * 5 * 4.187 = 418.7MJ
*Yes, that answers the question asked - "how much energy per day?"
*However, a more useful calculation would be the *rate* of extracting
energy *(i.e. power) in kW. Have you worked that out?
*[I'd be interested to know whether your calculation arrived at the
same *result as mine].
Yes it does work out the same

418.7MJ divided by number of seconds in a day (3600 x24) gives 4.84kW

Unfortunately the pumped concept falls at several hurdles.

More than 4.84kW is needed.

Have you calculated exactly what you need to maintain 19C on a cold
winter day? As well as heat from the river you can also collect a bit
more from the pipe run from house to river, plus additional insulation
may sometimes be an option, plus other heat sources.


Although river Lea water is *warm* (largely
sourced from effluent treatment plants upstream) 5deg.C seems a
realistic figure considering prolonged adverse winter weather.

Do you actually know the winter river temp? It might be better.


The EA website gives abstraction charges of 15 to 28ukp per 1000m3 and
trade effluent discharges are charged on anything exceeding 10m3 per day
so it looks as if the project is doomed!

However, by cleaning out an existing drain paralleling the river bank, I
can probably create a flow which would improve the performance of the
slinky version. I am beginning to think that gas is best!

regards


NT