Saturday, March 27, 2010

3 Ways to Save Energy That are a Bit "Out There"

Here are three areas where significant energy might be saved in a home with fairly simple systems.  One has to do with using some of the heat in the hot air up in your attic, and the other two have to do with recovering some of the heat we waste in showering.

Regular showers are a major waste of energy.  Typically we spend about 3 KWH heating water for a shower, and then send about 85% of that energy right down the drain.  It amounts to about 300 KWH for a family of 4 per month.

Using The Heat In Your Attic
This page looks at some of the ways that all that heat up in the attic might be used productively.  This includes recovering heat for domestic water heating, space heating, pool heating, and cloths dryer air preheat. 
Some of these look fairly practical (to me).

I've been logging the temperatures up in my attic for about 6 months and the plot of these temps is included.  We live in a very cold climate, and it still looks like there is some potential.

Details here...

Recovering Heat From Shower Water Drain Pipes
This page looks at all the energy we send down the drain when taking a shower, and in some of the ways that are currently out there to recover some of that energy. 
It considers one (as far as I know) new method, which is basically to rearrange the drain plumbing to retain the shower water in the homes heated envelope long enough to recover the heat in the water for space heating. 
Some ways of doing this, the resulting energy saving, and a small test to examine the potential of this method are discussed.

It may seem like there is not really much potential here, but for heating climates, the potential energy saving for a family might be of the order of 1200 KWH a year.

Details ...

A Very Energy (and Water) Efficient Shower Design
This is a look at a shower design that was looked at for potential use on very long range commercial jet airplanes.  It is a very efficient design both from a water use and energy point of view.  It may not be for everyone, but have a look.


So, I'm particularly interested in whether you think any of these ideas have some merit and are worth pursuing (or not). 
Or, maybe you have some of your own "Out There" ideas you would like to share?

UPDATE: Turns out Kenneth has built and uses a recirculating shower... 
Kenneth's interest were more in getting long showers with very high flow (6 shower heads) without breaking the bank on energy use.  Its a nice simple design.

Note that Kenneth has also done a very nice Solar Shed project that does both solar space and water heating -- hope to have the details on this up soon.
Thanks Kenneth!



  1. Hi Gary, looked at your attic temperature data, seems to me that in a heating climate, and if both summertime cooling can be avoided and one faces high midday electrical rates - one could mount a mini-split heat pump in the attic so that the HP efficiency is bolstered during expensive hours.

  2. For a cooling climate (Central TX), nighttime radiation/coolth is signifigant.
    If you wanted to make a water based collector for the attic air, would Richard Heiliger's MTD(Modified Trickle Down) with enclosed funnel at the bottom be a good collector? Since its automatically drainback, no UV issues either. Its a bit crazy talking about water in the attic but water does catch the heat/coolth.

  3. Hi Gordon,
    Interesting idea.
    I guess that the mini-split would maintain its high COP with the hot attic air as the source?
    Seems like it might also get some benefit from the attic temperatures being warmer that outside ambient temperatures, even when they are not hot enough to use directly?

  4. Hi Dan,
    Are you envisioning the collector on the outside of the roof (so it sees the night sky)?

  5. Hi,
    Note the update to the recirculating shower item above -- Kenneth has already built and uses a kind of recirculating shower.
    Kenneth has also done a very nice Solar Shed project that provides both solar space and water heating -- hope to have the details up soon.

  6. I was envisioning the MTD collector internal to the lower attic. I could "charge" the MTD from both sides in the attic. I see it as a cheap thin flat plate collector for attic temperature using the rafters as a frame. I have a large internal chimmney(not a full masonry stove but pretty close)which I will not use for fires. The fireplace would hold 150 gallons in a tank It could be cooled in the summer with night cooling or warmed in the winter with daytime attic heat. I have severe winds and am mostly interested in keeping the house from freezing. Some cooling would be great. . Its sits on bedrock and is easily the coolest temp in the house.
    I would only start the pump when all conditions were perfect towards heat or cold.
    IF winter mode and Temp high, pump water from tank.
    not summer mode and temp low, pump water from tank to attic. Max height to pump 12 feet.

  7. Hi Dan,
    So, I guess what you are looking for is an efficient and cheap attic air to water heat exchanger.
    I guess the MTD might work for that. It seems like you would still need the glazing on it to prevent evaporation of the water and humidification of the attic. Once you have glazing on it, it might not be that good a heat exchanger on the glazed side. The back side should make (I guess) a pretty good heat exchanger.
    Another thought would be to use the style of car radiators that come with electric fans. These are very efficient heat exchangers at a pretty reasonable price -- as this paper by Nathan shows:
    Not sure if it would drain back or not for freeze protection.

  8. There are several styles MTD collectors. One(Richard's design) has the felt totally enclosed in a mylar package with a header at the top and a funnel at the bottom which attaches to plumbing. If the pump turned on or filled a reservior at the top of the MTD at the target temperature and then stopped, it would use a limited amount of power and still accomplish drain back isolating the storage. It might be against a metal back plate in the attic to allow heat or cool collection from both sides. Glazing would not be necessary,same with UV deterioration. You would have a winter and a summer setting to activate the pump and collector for heat or coolth.
    The radiator implies two fans and the pump. Theses could be solar powered but that would also entail batteries as night cooling has no sunlight.
    I am still learning how to collect coolth, probably need that trip to New Mexico to learn from the Gurus.

  9. Yes Dan there are a number of variations on the MTD theme as a matter of fact the one you are proposing sounds like it should be in a class by itself. The essential ingrediants of MTD include a Trickle Down distributor at the top of the collector, a trickle down platform on which the water is dispursed, an inner film to prevent the evaporation of water an outer glazing to trap heat, a gutter and built in mounting brackets so that a collector array may be easily assembled from many individual collectors.


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