David and Jane Marchant of River Berry Farm—an organic vegetable and fruit producer in Fairfax—were early adopters of biomass heating when they installed a corn and pellet furnace in one of their greenhouses in 2008. The furnace required manual lighting and, whenever a strong wind blew, the fire could be snuffed out, making it a real labor burden. Although it was rated for 165,000 BTU/hr input and had a relatively low initial installation cost of $5,200, the furnace never seemed to actually produce a reasonable amount of heat. The Marchants also had a variable load in the greenhouse that peaked at night and was non-existent during the middle of a sunny day inside the greenhouse. This made for a frustrating relationship with the appliance. “I kept thinking, there has got to be a better option,” recalls David, “It was a real labor burden, and you couldn’t count on it.”
This biomass heating demonstration was part of a UVM Extension project aimed at trialing several furnaces in agricultural heating applications with funding support provided by the High Meadows Fund. According to Chris Callahan, Ag Engineer with UVM Extension who assisted with some of the design and performance assessment, “The main lessons learned from these early installations were to buy high quality fuel, seek improved automatic ignition controls, invest in a good chimney and install it well, and know the actual heat output rating of the unit.” Modern biomass heating appliances generally include a fuel storage bin, an auger for feeding fuel to the appliance, the appliance itself (boiler or furnace) with an ignition system, a combustion chamber, a heat exchanger, and a heat distribution system. They also incorporate some means of controlling combustion, fuel feed rate, and air flow and often include emissions control measures and automated ash removal.
Boilers Can Provide Advantages Since Hot Water Can be Used in Many Applications
Based on their early experiences and bolstered by a commitment to long-term sustainability and reduced fossil fuel dependence, the Marchants hosted another demonstration project on their farm. This time, they opted for a higher-rated boiler rather than a furnace. Boilers produce hot water, rather than hot air, which allows more options for distributing the heat. The new system also had an automated propane ignition system. The selected boiler was a Central Boiler Maxim 250 with a 250,000 BTU/hr input rating, efficiency of 87.8%, and EPA Phase II Hydronic Heater qualification. “The boiler makes hot water which we can use in multiple greenhouses by plumbing it to them in insulated PEX piping. Once in the greenhouse, we convert to hot air with a hot water fan coil, put it in the ground for root-zone heating or on the benches in our mat-heating system for starts,” says David, “I like it. I keep trying to find something wrong with it, but I can’t. The payback period is a bit longer due to higher initial costs, but you have to expect that.”
The basic system cost was approximately $13,000 for the boiler, bin, pad, and plumbing to a hot water fan coil. The other heat distribution systems included in-ground PEX, heat exchange, and plumbing for a bench heat system and added approximately another $5,000. The system is more automated and reliable than the earlier furnace was, but the higher initial costs and the fact that the system is only used 3 months out of the year do prolong the payback period to about 12 years when compared with a propane furnace. If the system was used for 6 (space heating) or even 12 months (wash water, pasteurization) of the year the payback would be halved or quartered, respectively.
“In addition to the financial payback, the carbon emissions avoidance is also of interest to many people,” says Callahan, “In River Berry Farm’s case, the Maxim is helping them avoid 5,910 pounds of net CO2 emissions per year which is about equivalent to 5,000 miles car travel or the CO2 sequestered by half an acre of pine forest.” The EPA Phase II qualification of the unit refers to the emissions of criteria pollutants (e.g., sulfur oxide and nitric oxide).
The same analysis that shows the net CO2 emissions reduction also suggests the net criteria pollutant emissions are also reduced when using the biomass boiler compared to propane.
This story was prepared by the Energy Cross-Cutting Team of the Farm to Plate Network. Additional Food System Energy Success Stories are available on the Farm to Plate website.