Generating electricity using household water... pressure or heat?
Generating electricity using household water pressure
I ran across this thread and smiled as I perused it. (click)
It was started by a man who wanted to put a tiny turbine in the city water pipe coming into his house, to generate electricity.
A lot of people found the thread and posted comments, asked questions, offered ideas and (I'm amazed at how patient they were) experts carefully told them why their ideas were impractical. It's an interesting read, for me at least.
I liked the guy that takes electricity from the phone line...
Here's an inventor that proposes a 'practical' version, for sinks, where 100% of the 'pressure' is otherwise wasted. (click)
My conclusion (because I DO know the math and have done a lot of experimenting) is that generating power from the city water pressure isn't worth the cost for me... because I pay about $2.25 per cubic meter (about 264 USG) for my water. I'd generate about 200 watts which would be 'worth' about $0.02 at my current electric utility rate.
But here's a thought, and the reason I stumbled onto that thread...
What if I took the energy from the HEAT in the water, and then gave the cooler water back? (reversing my water meter).
The heat energy in the water is MUCH greater than the available energy from the pressure of the water.
A BTU is 1°F per pound of water. (USG = 8.35 lbs)
So if in January, I brought in a cubic meter in an hour and dropped its temperature by 10°F, I would gather 22058.195 BTU/hour. That's enough to heat my home.
I'd use a liquid (city water) to vapor (evaporator) heat exchanger connected to a heat pump that would pump 120°F fluid through my in-floor and 'hot water' radiators in my zone-controlled system.
55°F is a LOT warmer than the air temperature in the wintertime, so the heat pump is a lot more efficient and practical. Yes... I would still have an electric bill but it'd be a lot less than if I heated the house with direct electricity.
The really nice part is that when I've taken the heat from the water, I don't have to pay for the water... because I give it back! The water, after it's gone through the heat exchanger, gets pumped back into the city system (reversing my water meter). I propose to pump it back 'in bulk' as soon as my heat pump shuts off or if the interim storage tank gets full.
Of course this only works if you have a type of water meter that can be reversed... otherwise you just paid about as much for the heat in the water as if you'd bought a gallon of furnace oil.
As very well pointed out in the 'water pressure' link; it doesn't take much energy to pump the water back, (about 250 watts or 850 BTU).
The cooler water would 'rewarm' itself underground as it makes it's way to be actually used by my neighbors.
In the summer, I reverse the process. I increase the temperature of the water from 60°F to 70°F and give 22058.195 BTU/hour. That's enough to cool my house!
In this case I use the same sort of liquid to vapor heat exchanger but it's connected to a mini-duct heat pump air conditioning system. I pump the water back using the same storage tank and pump system I use for the heating.
Of course, I do all the energy efficient things I can do with the house... insulate, seal leaks, low-e windows, HRV, etc. to reduce the size of heating and cooling system I need and the subsequent amount of energy I'd require.
I'm not likely to do this but thought of it as I'm examining alternate ideas once an energy evaluation told me that my yard was too small for a ground source heating/cooling system. I've just learned that 'direct exchange' ground source heat pumps only require about 1/3 the land area...
Other ideas I have include making a solar concentrator combined with a eutectic material to 'store' heat of the sun during the day (even in the winter) to use at night.
And for cooling, to store heat from the day into a eutectic and then radiate it out at night, when the temperatures are much lower. Thus to 'store' cool night temperatures in the eutectic, to act as a heat sink for the temperatures of the day.