While more efficient lighting fixtures and water conservation programs reduce energy costs, heat recovery is the money saver that keeps on saving, observed Jeff Dearduff, veteran bakery engineer and chairman of the American Society of Baking.
Mr. Dearduff, who oversaw a recent heat recovery system installation, noted the exhaust leaves the oven chamber around 300°F. Instead of sending it to the atmosphere, it can be used to heat a secondary medium — usually food-grade propylene glycol — that can be routed to proofer heating coils, process water heaters and even fermentation room systems. The glycol is recycled through a closed-loop system so there is no effect on oven airflow or pressure.
“The idea of using the waste heat from the oven stack simply allows you to get a full bang for the buck on each cubic foot of natural gas or other fuel that you are purchasing,” Mr. Dearduff explained. “By using this waste heat, you are not buying fuel for steam boilers, water heaters and other systems. It is this full use of the purchased fuel and overall reduction of fuel purchases that becomes the sustainable feature. If you factor your fuel purchases into the entire business unit’s productivity, you can calculate a cubic foot of fuel per pound of finished product formula. This can be reported as a monetary savings and a conservation of natural resources, which makes the big customers very happy.”
Scott Houtz, AMT’s president, said heat recovery is just common sense. “When you look up to the roof of a bakery and see these heat plumes, you just think, ‘What a waste of energy,’” he noted.
The glycol tanks and other main parts of the system can be installed outside of the bakery and are tolerant enough to operate in either extreme heat or cold, according to Mr. Houtz. The actual heat exchanger sits inside the stack with a damper arrangement that can divert all, some or none of the oven exhaust through the heat exchange coils, depending on the bakery’s needs.
“If we need only 50% of the heat coming out of the oven, the damper will modulate accordingly to match up our heat loss through the loop to make up that load,” Mr. Houtz said.
In the case of a system failure, he added, the damper can be fully opened so it doesn’t disrupt the baking process.