The phrase "passive solar" is being heard increasingly. It's used primarily to describe the judicious use of solar energy for heating a building without having pumps, motors, heat exchangers and other complex special equipment to force fluids through special collectors, storage tanks or bins.

One of its simple forms is the Trombe wall. This consists of a masonry wall just inside a large south-facing glass wall or window. The winter sun shines through the glass onto the heavy wall and heats it enough so that the warmth lasts through part of the night. The open architecture of the rooms behind the wall encourage convection currents to carry that warmth through much of the house.

The masonry wall must be large and massive for maximum heat storage, and so must be the glass wall in front of it for maximum collection. The glass wall should be double glazed and perhaps also have a draw drape to close at night. Also required is a good deal of roof overhang. That is, the roof should jut forward over the glass wall far enough to prevent the high summer sum from pouring in.

Although it borders on violation of the term "passive," some sun-forced air across the Trombe wall may also help. And, in the Washington climate, don't expect these schemes to carry more than a portion of the heating load, especially in the grey days of deep winter.

There are more complicated techniques. One of is a variant of the sun-shower used by small yachts, a plastic container of water that resembles and oversize hot-water bag, transparentt on its top side and black on the underside. After a few hours flat on a sunny deck, it yields a warm shower or two. Similarly, there are schemes for larger containers of water in roof or wall arrangements, some with sliding covers, etc., being tried in the Sun Belts states.

But passive solar can have constructive meanings to the ordinary home-owner, too. For one designing his or her new home, it could mean contemporary architecture incorporating some version of the Trombe wall; or simply orienting the house so that the largest wall faces south and contains the most glass, plus sufficient eaves overhang to shade the summer sun.

For most of us it means opening shades and drapes on sunny windows to harvest as much of that energy as possible, and closing them when there is no winter sun.

Needless to say, the lower the house's heat requirements, the greater the fraction of the load contributed by passive solar. So, the house should be very well insulated, have double-glazed windows and doors, and be well weatherstripped