Wednesday, May 23, 2012

Post #13 Reusing the energy in hot water

Question: How hot is the water that comes out of your shower head?  Answer: Somewhere between 105 and 120 degrees F (depending on your preference).  Question: How hot is that water as it goes down the shower drain?  Answer: Still hot, perhaps 90 degrees F.  Question:  What happens to that energy in that water?  Answer:  Usually it is completely wasted- at the Armstrong House, the energy is reused.  Question:  How?  Answer:  I'll explain the process in a bit, but first:

Think of boiling a pot of water on your stove.  Have you ever tried to boil a pot of water that started out really really cold?  Once in Maine I had to fetch water from a spring that had frozen over the night before.  I had to break the ice to get to the liquid water and when I returned to the cabin with our cooking water it had chunks of ice floating in it.  That morning, it took more time and energy to boil the  near freezing water.  Similarly, it takes less time and energy to boil water that is already hot- like when you reboil a kettle that was recently boiled.  

Now, think of a picnic on a hot summer day.  The night before you prepared an awesome potato salad and set it in the fridge over night.  Once the picnic is underway and the food is spread, your cold potato salad starts to loose its chill.  After an hour or so, your potato salad has totally lost its chill (and its appeal) so you decide to put it back in the fridge.  What has happened to your potato salad?  More importantly, what does the potato salad and Tate's frozen spring water what have to do with saving energy at the Armstrong House?

At the Armstrong House Education Center we have installed a drain water heat recovery unit, which is a fancy way of saying 'we passively heat up the potato salad so we don't have to boil frozen spring water'!  What the heck am I talking about?

He have one of these:

The Armstrong House's drain water heat recovery unit.  

Notice the copper piping that runs vertically through the photograph- this is our drain water heat recovery unit, which takes the hot waste water from the shower and preheats the cold water coming into the house.  The following two diagrams are of the installed unit that I took from the manufacturer's website.

The waste water heat recovery unit connected to shower and water supply.  

The waste water heat recovery unit in action.  It takes hot water from the shower and preheats the cold water coming into the house. 

But, why is the water coming into the Armstrong House cold?  Like everyone in Pound Ridge, I get my water from a well.  The temperature of well water is governed by the temperature of the earth and rock that it collects in- which for our area is somewhere in the low 50's F.  50 degree water is cold- very cold.  50 degree water must be heated like crazy before you can even think about using it to clean dishes, wash clothes or use in a shower.  With the use of our drain water heat recovery unit, we can essentially split the difference between the hot waste water and the cold water from the ground.  For example, if it comes into the house at 50 degrees F. and the waste water is 100 degrees F. the new preheated water will be 75 degrees F.  If the water comes in at 60 degrees and the wasted shower water is 90 degrees, the new preheated water will be 75 degrees F.  By using preheated water, we have to use less energy when heating it back up to 100 degrees F (remember the pot of boiling water).  For more information and a formal energy/cost savings review of the drain water heat recovery unit click here.
This is just one of the many ways that we are reducing our energy consumption at the Armstrong House.  Stay tuned for more.


Charlie Hohn said...

This is a great idea! Don't penguin feet do this too?

Solar NJ said...

Genius! I love the concept.

-Sharone Tal