Shower wastewater heat recovery

[Percival P. Cassidy]

On 10/26/05 01:45 pm Larry Bud tossed the following ingredients into the ever-growing pot of cybersoup:

Me too, but the shower doesn't switch on with the alarm clock.

Perce

[Chris Lewis]

According to :

It will? You dump a full tank of water every time you turn on the tap? No matter how little you turn on the tap?

Where is the rest of the water going?

Somewhat faster. Not "much". Further, in most cases, the heat is staying inside the house, which for at least most of the year here means you're wasting very little of it.

If you care about energy costs (which is the context of this thread), they would be.

Yes, I agree, you've wasted energy running the tank to 190F. It's illegal anyhow. That was just for purposes of the example. The same principle applies even if you set the tank to 140F (or in

120F). Setting the tank to the desired shower temperature (ie: 105F as opposed to 120F or 140F) saves very little money if any, and doesn't take into account things that need the higher temperature, like a dish washer. And means that you likely run out of hot water faster.

[ameijers]

Damn, Perce, how may years did you live on that submarine? :^/

aem sends (dearly missing the 400 gallon water heater and six-inch mains at the apartments, and still getting used to low pressure well water and only

40 gallon heater here is this house I bought a few months ago)....

[wkearney99]

If your hot water is too hot and you have to add too much cold to it to get the shower to a comfortable level then you're wasting energy. Better to drop the heat of the hot water down a few degrees instead. Think about it. Why take water that's already been heated and waste it?

[wkearney99]

Most dishwashers will bring water up in temperature if need be. Depends on what wastes more energy, overheating a big tank or warming up a small amount to do dishes.

[Percival P. Cassidy]

On 10/26/05 06:28 pm ameijers tossed the following ingredients into the ever-growing pot of cybersoup:

Never spent any time on a sub., but I did see one once, I think. And, no, it didn't frighten me.

I just don't believe in wasting water. And cold showers are very bracing

-- good for the constitution.

Perce

[Edwin Pawlowski]

I did think about it.

If the water is heated to 160 degrees, you use much less of it than if it was heated to 110 degrees. Same energy is expended. Where does the waste come in? If you take a shower with a 2.5 gpm flow, and you shower for 10 minutes, you use a total of 25 gallons. What is the difference in cost if I use 25 gallons of water heated to 110 degrees or if I use 8 gallons of water heated to 160 and 13 gallons of cold water to temper it for a total of 25 gallons?

[Ken]

The device you are looking for is commercially available. Here is one example:

Ken

[Mark]

the heated waste water heats up the drain pipes in the basement so most of the heat is recovered keeping your basement warm and dry...

check the temperature of the waste water that leaves your house...it's pretty low...

not much to recover

Mark

[HeatMan]

Considering they were almost giving these away a while back, they were worth it. You simply put the coil in-line with the supply line to your water heater and it reduces the load. If you insulate it, it'll do more.

[Wayne Whitney]

This is not true. It would be true if by adding cold water you were increasing the total flow rate out of the shower head. But the flow rate out the shower head is basically fixed, so mixing in cold water reduces the amount of hot water being used.

In other words, given a shower flow rate, desired shower temperature and incoming cold water temperature, the power (energy per unit time) that is required (flow rate) * (temperature rise required), for suitable units. It doesn't matter whether you use that power to heat a little bit of your shower water a lot, and then dilute it with cold, or use it to heat all the shower water a little bit.

The one place that lowering your hot water temperature will save energy is if you use a tank-style water heater. This reduces the temperature differential between the hot water in the tank and the environment, so it reduces the rate of heat loss. This savings by reducing the hot water temperature is independent of consumption, however.

Cheers, Wayne

[Wayne Whitney]

Yes, I will put in a solar collector at some point. But that's a purely independent issue, it makes sense to do a solar collector and a waste-water heat exchanger.

Cheers, Wayne

[Wayne Whitney]

Can you expand on this? When were they giving these away? A prefabricated exchanger now costs $275-$450.

Cheers, Wayne

[Wayne Whitney]

Well, the shower heat exchanger is simpler, as you know there will be hot water demand coincident with the drain water, so you don't need a storage-type heat exhanger.

Also, I would expect that most households have 4-8 times as many showers as dishwasher cycles. A shower also probably uses more hot water than a dishwasher cycle (10-15 minutes @ 1 gpm hot water for a shower, versus 5-10 gallon for a dishwasher cycle).

So I think that shower grey water heat exchange is the best place to focus on.

Cheers, Wayne

[William Brown]

Everyone who has raised teenagers knows that by lowering the water heater temperature, you reduce consumption, as they will take shorter showers because the hot water runs out.

Around here, since we have become ecologically aware, the cost of water is higher than the cost of heating it, so reducing consumption can save me quite a bit.