Drying hay with renewable energy is cheaper than with natural gas, propane or oil, and using two heat sources instead of one gets the job done faster, says Philippe Savoie, an Agriculture and Agri-Food Canada research scientist.

Savoie and research engineer René Morissette recently installed an outdoor wood furnace 75' from a hay-drying shed on a commercial hay farm near Neuville, Quebec. The furnace heats water that then is pumped through underground pipes to the building, through heat exchangers and back to the furnace. That heat combines with solar heat collected beneath the shed's roof to dry up to 8,000 small square bales at a time.

The farmer, Richard Matte, grows timothy and orchardgrass hay, mostly for the horse market. But field-drying hay in Quebec's humid climate is challenging. So Matte built a shed with four 7,500-cfm fans and a perforated floor and dried 16%- to 25%-moisture hay using natural-air ventilation. It worked, but took up to 30 days to remove the excess moisture from bales, and moldy spots sometimes developed in the upper layers before they dried.

In 2007 he installed solar collectors on the roof to absorb the sun's heat and modified the inner roof to force incoming air to flow near the panels. That increased the air temperature about 15° F on sunny days, shortened the drying time and reduced the risk of moldy hay. But solar heat isn't effective on rainy days or at night, and when Matte kept the fans running, cool air sometimes caused condensation within bales.

Supplemental heat from the wood furnace lets him run the fans continuously, shortening the drying time and eliminating the condensation problem.

“It accelerates the drying so that the last layer will dry within four to five days,” Savoie reports.

The fans pull ambient air into the building through inlets under the eaves on the north side. The air flows beneath the solar collectors and down through a duct adjacent to the south wall to a below-floor plenum, then is forced up through the hay. Roughly a third of the air passes through a heat exchanger in the duct, gaining about 54°. Then it mixes with the other air for a net gain of 18°.

The combined temperature gain from biomass and solar heat, just over 30°, would be significantly higher if the heat exchanger was big enough so that all the air could pass through it, says Savoie. The 4-sq-ft exchanger was chosen because of its cost, about $500, space constraint and availability, he adds.

Matte loads the dryer 18 bales at a time using a bale fork, and stacks them eight layers high. The perforated floor is actually formed of removable wood panels that are placed over the entire width of the barn dryer in 8' sections. More sections are added as more hay is stacked in the dryer. Matte usually stacks a day's harvest, typically 700-1,500 bales. Initially, a single fan begins the drying process. The second, third and fourth fans are started as more bales are added.

Roughly 60% of Matte's hay is field-dried and goes directly into storage, Savoie reports. The drying shed has enough capacity to dry the remaining 40% of each cutting.

Savoie's idea for drying hay with a wood furnace is linked to his ongoing biomass research. He's been looking at the feasibility of harvesting corn stover and woody crops such as willow and utilizing them on farms.

“We thought there might be an opportunity of having a furnace installed at the farm so that the farmer could use locally grown biomass that's available at fairly low cost,” he says.

Heating buildings is one possibility, and the profitability would be enhanced if the biomass furnace had multiple uses. It might be used to heat a home, garage or shop plus dry hay or grain, for example.

“This, of course, implies adding a second piping system, and typically it should be in the ground between the furnace and the building, and having a heat exchanger,” says Savoie.

Matte paid $10,000 for his piping system and heat exchangers and installed them himself. Agriculture and Agri-Food Canada provided the furnace.