Todd Intermill heats, cools and dehumidifies his 36-by-56-foot shop for $650 per year with an air-source heat pump and an electric furnace. The air-source heat pump moves heat from outside to inside the shop, and vice versa, to maintain the desired temperature. The electric furnace works as a backup in the winter. Its blower distributes the heat pump’s air throughout the shop.
The air-source heat pump is better than in-floor heat, says Intermill, Colman, S.D.
It’s more efficient than a combustion furnace, because nothing is burned to generate heat. Installation is simpler than in-floor heat. There are no valves or pipes to maintain as with in-floor heat. There are no worries about digging up the floor to repair a break in a line as with in-floor heat.
The heat pump works faster than in-floor heat. While it may take an in-floor heat system two days to raise or lower a shop’s air temperature 20 degrees, the heat pump with its forced-air system will do it in less than two hours in his shop, Intermill says.
An air-source heat pump consists of a compressor and two copper tubing coils, one coil indoors and one outdoors. The coils are surrounded by aluminum fins to facilitate the transfer of heat.
In the heating mode, liquid refrigerant in the outside coil extracts heat from the air and evaporates into a gas. The indoor coil releases heat from the refrigerant as it condenses back into a liquid. A reversing valve can change the direction of the refrigerant flow for cooling.
The system needs a little help on the coldest days of the winter, Intermill says. That’s why he has a backup electric furnace. The blower system also distributes the warm air generated by the heat pump.
Intermill insulated the wood-frame shop well. The 8-inch sidewalls have M\zn-inch thick OSB (oriented strand board) sheets on the inside and outside. The outside wall is clad in steel. The inside walls are covered with a high-quality gloss paint. The walls have R26 fiberglass insulation. There’s 18 to 20 inches of fiberglass insulation in the vaulted ceiling, giving it an R rating of 60-plus. The 16-by-24-foot hydraulic door is insulated to R20. Two-inch-thickboards insulate the concrete slab and foundation.
Sunlight from several 3-by-3-foot and 4-by-4-foot south-facing windows helps heat the shop in the winter.
Two 57-inch shop fans mounted on the ceiling recirculate warm air that collects in the peak of the vaulted ceiling. The air can be as much as 8 degrees F warmer near the ceiling than it is near the floor, Intermill says.
This article published in the November, 2010 edition of DAKOTA FARMER.