Passive Water Heaters

The last topic I’m going to cover in this series on passive design is passive water use. Heating water consumes a considerable chunk of the energy that the typical house uses, so if you can cut your active water heating it can pay off both in terms of cutting energy use and cutting your bills.

While passive solar water heating systems are less efficient than their active counterparts, they tend to be cheaper, reliable, and long lasting. There are two basic types of passive water heaters, the integral collector-storage passive system or a thermosyphon system.

Integral Collector-Storage  (ICS) Passive Water Heater

An ICS system works best in more moderate climates, where the temperature rarely falls below freezing.  The ICS system has exposed pipes, so above freezing temperatures are necessary to keep the pipes from freezing and ruining the system.  The ICS system is made up of an insulated storage tank, a solar collection tank and the pipes that connect them. The solar collection tank is used to heat water in batches using solar energy. Once heated, the water passes into the insulated storage tank, and cool water fills the solar collection tank again.

Thermosyphon Passive Water Heater

A thermosyphon consists of a tank, pipes and a solar circulator. In this case instead of the sun heating a large tank of water, the sun heats winding pipes of water. Cool water flows from the high positioned tank into the lower circulator where it is heated. Warm water flows from the circulator back into the tank due to natural convection caused by the temperature gradient.  An indirect thermosyphon that uses glycol fluid in the circulator loop can be used in colder climates if the piping is adequately insulated.

If you’re interested in building your own passive water heater, you can find some good information here.

photo: “Solar Water Heater boiler” by gmourits CCBY