A test solar house built by the federal government in Frederick has proved that some solar heating systems simply do not work, according to the HUD project's director.

"That is the value of testing," said Donald F. Leubs during a seminar sponsored last week by the Northern Virginia Builders Association. "It is to find what works and what does not work. There are many solar concepts that work and work well. We also found some that don't work as well."

The two-story, three-bedroom home, which was called "Energy Efficient Residence II," was built two years ago by the National Association of Home Builders Research Foundation with a grant from HUD

Leubs said the house used passive solar heat from a two-story solarium on its south side. It also had a variety of active solar heating systems, including a rock bin for storing surplus heat, a water pump to circulate water warmed by the earth and a system to recirculate heat from hot water used in the laundry and kitchen.

The total electric bill last year for the house was $652 and the glassed-in solarium saved only $50 to $60 in heating bills over a year, Leubs said.

"The family who rents the house is not as energy conscious as we would like," he said. "But we realized a substantial savings in the electric bill."

The researchers had worse luck with the rock bin in the basement. The 13 tons of rock were designed to store warmth pumped through air ducts from the solarium, but at times the rocks on the bottom of the pile were colder than the temperature inside the house, Leubs said.

But all was not a failure: Leubs said the earth heat pump worked better than expected. It sent water through pipes deep into the earth, where it was warmed in winter and cooled in the summer. Then the water was pumped back into the home where fans distributed the warm and cool air through ceiling ducts.

"That was the real winner," he said. He had equal praise for the extensive foam insulation used throughout the house. "It added immeasurably to heat retention."

Leubs said the foundation will continue to test building and solar ideas in test houses.

"There are a lot of things touted that really don't work," he said. "We want to keep providing the public with information on what exactly does work."