I purchased a Drain Water Heat Recovery unit for our new house but have not started using it yet. Our utility provider has a rebate program that paid for 75% of the cost, so it was a no-brainer for us. However, I’m skeptical about how well it will work in a residential setting where our water use/flow rate is very low and showers are short…just curious if anyone can comment on their experience with these units??
Thanks
Shawn
Replies
Maybe this might bump your question up a notch. I have been skeptical of these contraptions for use in small scale applications such as yours. I believe to be efficient the waste water should run through an exchanger similar to the type used in a outdoor wood furnace to supply heat in a forced air furnace. This later type of exchanger is very efficient but it would easily get clogged up by running waste water through it. The WWHR units I researched keep a large I.D. because of the potential clogging problem and also so as to stay in code for the waste line diameter. If you are on a septic system I think it is better to let whatever waste water heat go to the septic tank to enhance the bacteria activity, especially in the colder regions.
I keep my hot water tank no hotter that 118 to 120 degrees which gives me greater kick for the buck than trying to recover a few degrees from the waste water.
Just my on two cents.
Virginbuild
Do keep in mind that most hot water ends up going down the drain, and as it goes down, generally the water heater is drawing in cold water. If most of the heat could be transferred from one to the other it would significantly reduce water heating costs.
The real questions are:
1) How efficient is the heat transfer in these things?
2) What is the expected lifetime of a unit -- how much does it cost to operate over decades?
Basically, with answers to these, and knowing how much hot water you use and how much it costs to heat, you'd be able to run the numbers with fair accuracy to determine if it's worth it.
But unfortunately, I haven't seen any data on the two questions above.
Hi,
There are some links to some tests and a link to a calculator that allows you to estimate savings for your situation here:
http://www.builditsolar.com/Projects/Conservation/conservation.htm#GWHX
Just looking over the material they look pretty good to me. Sending 90% of the energy you just put into heating the water from your shower right down the drain is what seems dumb to me.
Why would you not use it if you already have it?
Gary