Keeping the ice cream hard while cutting the refrigeration bill by two-thirds

When Charlie Hall was building his passive solar house here, he realized he could readily recess his refrigerator-freezer into the kitchen wall. That way he would have more room in the kitchen as the bulk of the refrigerator would protrude into a small storage room where there was free space.

While he was at it, it seemed sensible to encase the refrigerator in additional insulation as any slowing of heat transfer from outside would save on energy.

It did - and by more than Hall figured.

A consultant in alternative-energy systems, Hall placed a double layer of 3 1 /2-inch fiberglass batts flush to the sides and top of the refrigerator. He then added a similar thickness at the back, but left a 2-inch gap between the insulation and refrigerator.

Hall also placed narrow one-inch-wide vents along the bottom and top of the back wall of insulation to allow the refrigerator motor and refrigeration coils to ''breathe.'' The insulation, supported by a wooden frame (stud-wall construction), was covered on the outside by conventional plasterboard to give it a smooth exterior finish.

It was mid-August of last year when this was done. At the time the appliance was on a setting (3) which kept the interior of the refrigerator at 41 degrees F. and the freezer at 5 degrees F.

The refrigerator was moved into its insulated recess without changing the setting. By the following morning the temperature in the refrigerator had dropped low enough to freeze a cucumber in the crisper while the freezer section registered zero.

Hall found he had to reduce the setting to 1 (least energy use) to prevent any freezing from taking place inside the refrigerator. At the same time the freezer temperature remained only a degree or two above zero - or ''low enough to keep the ice cream hard,'' Hall reports.

Put another way, the Halls now are getting acceptable refrigeration by ''using one-third the electric current we used to use,'' he adds.

For the first two weeks after moving the refrigerator into its insulated box, some condensation took place and leaked out onto the kitchen floor. Hall isn't sure what caused this to happen, but he conjectures that some moisture in the insulation had condensed after being placed alongside the cool surface of the refrigerator. However the unwanted moisture disappeared of its own accord.

Those two major users of electricity, refrigerator-freezers, and hot-water heaters, both perform more efficiently if surrounded by additional insulation to reduce heat-loss or heat-gain by conduction. That appliance manufacturers do not do this is only partly a cost-cutting measure.

The principal disadvantage is bulk. Most adequately insulated refrigerators would be far too bulky to fit into most conventional kitchens. Thus, most households pay for the convenience of compact appliances by footing a larger energy bill.

But when space is no great obstacle, home-refrigeration bills can be cut, as in Charlie Hall's case, by up to two-thirds.