I’m in Maryland where the electric companies have been deregulated. KWH rate is about $.11 and will go up again in June. My greatest energy user is the water heater. Natural gas is not an option.
I have found a bit of information about drainwater heat recovery systems from the dept of energy. Are these systems worthwhile (i.e., how long will it take to recover the cost?) If you are a plumber, are you installing many and is the DOE’s estimate of installation between $300-$500 accurate?
Thanks – Jason
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I experimented with that 30 years ago when I built a little unit for the shower. Yes it works but.... The shower is a prime example, you use hot water at the same time you are supplying the warm water discharge to the heat exchanger, which then can be used to preheat the cold water input to the water heater. My notes show that I raised the cold water temp entering the water heater from 50 deg to 63 deg with 1.26 gpm of hot water flow into a 102 deg shower head discharge and a 90 deg tub drain discharge. With the data I have, it shows that even if the heat exchanger were 100% efficient, the cold water temp could only be raised 5 more deg to 68 deg.
While I achieved 18% savings, with a possibility of 25% savings maximum, these numbers are not laboratory scientific. This is coffee shop back of the envelope scribblings.
The shower is basically the only discharge of hot water you have, that is at the same time as the use of hot water. So while the system works, the gut feel here is that when all is considered, you will probably never economically pay for a heat exchanger system.
There is at least one system on the market that claims 40-50% savings in hot water heating costs but that is not real world figures IMHO.
I am sure there is a use somewhere for this idea but not enough incentive to make me put play with it anymore.
There are also drain-water heat recovery systems that use a two-coil storage tank to store the waste heat for later recovery as input to the water heater.
The website below claims a payback period of 2.5 to 7 years, depending on amount of hot water used and type of system.
If your family showers often and long, the shower is probably the primary point use of hot water and installing just a drain-type heat exchanger would be the least costly and quickest payback.
http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=13040
Solar & Super-Insulated Healthy Homes
Looking @ Riversongs Diagram it seams to be a simple cheap set up. My thought is if coupled with a passive solar water heater
the results might start to add up to something.
I installed one of these (http://gfxtechnology.com/)in a house once. Seems to me that the amount of heat you recover is going to depend a lot on how you use hot water...it will only recover heat if you are running hot water down the drain as in taking a shower. It won't recover heat from baths, doing dishes (unless you run a lot of hot water straight down the drain in the process), washing clothes. But if a significant portion of your hot water usage is in taking showers, I think it would be pretty effective. No idea of the payback period.
I think 3 to 5 hundred sounds like a reasonable number for installation labor, though that will depend a lot on the layout of your plumbing system. AFAIK you have to have either a two story house or a one story house on a basement.
Will your heater be ready for replacement soon anyway? They make some super insulated, very low heat loss electric units nowadays.
Thank you for the thoughts and advice. Not sure what I will do, but I am going to look into water heaters as well. Ours is 8 years old, so it may be smart to consider the water heater and a recovery system at the same time.Thanks again - Jason