Sunday, March 3, 2013

Point of Use Water Heating

Imagine going to the kitchen sink and dialing in the water temperature you want.  Then open the single tap and voila - water at the temperature you want, at any volume.  When you close the tap and re-open it, the water is at the same temperature.  Again and again.  No having to adjust to the right temperature every time you open the tap.  Wouldn't that be luxurious?  The technology to do this was available decades ago, but we keep doing things the old way...

Achieving this is simple.  One need only provide a single water line to the faucet.  In that line is a point of use (electric) water heater with a remote control.  The remote control is mounted near the faucet (EcoSmart makes this kind of unit).  The heater is somewhere nearby, but out of sight.  The only issue with implementing this is that the efficiency of water heating is always just 100%. However, one advantage is that there is no hot water anywhere in the system - just at the last two feet of water tubing before the faucet.  No standby losses, although these days they are small in better tanks.

Consider the shower.  Imagine again, only one water line supplying the shower, with an inline point of use water heater with remote.  In the shower, we dial in on the digital display the water temperature we want.  Shower water comes out of the spout at precisely that temperature.  The warm water leaves the shower via the drain, but here, we have a heat recovery device which is some 80% effective.  We give most of the waste heat to the incoming cold water stream just before it contacts the POU heater.  Then the heater finds it very easy to raise the water temperature just the last say 10 degrees Celsius.  In this way, we minimize the heat that leaves the house and the energy and power needed to heat shower water.  If we want a bath, things are quite a different story, and I haven't really thought about what I'll do in that case.

The drain water heat recovery devices out there right now are only some 50 to 60 percent efficient.  Even that is saving half our energy to heat the water, so yay, but for some untold reason, none of these devices take advantage of heat pipes, which I plan to experiment with.