One of the ways a building’s energy consumption can be reduced, as part of an energy management plan, is to incorporate a heat-recovery system, which intercepts waste gases before they leave the industrial process or before they are exhausted from a building. The system then extracts some of the heat these gases contain, and recycles that heat back to the process or for use in building applications.
“The technology involved in heat-recovery systems may be air-to-air through a fan and heat-exchange arrangement; direct recirculation to the process; or an oil, glycol or water system consisting of a pump skid and coil arrangement,” said Tim Golden, aftermarket services manager for Megtec Systems Inc., De Pere, Wis.
Common to all heat-recovery system technologies, however, is thermal transfer and thermodynamics.
In industrial processes, heat-recovery systems are generally used where exhaust heat is available at more than 200°F and at flow volumes more than 5,000 standard cubic feet per minute.
“Returning energy to the industrial process is typically preferred as it provides greater benefit,” Golden said.
According to Golden, specific industrial applications include flexographic and lithographic printing plants, pharmaceutical facilities, can and wood product manufacturing plants, and foundry and agricultural applications.
According to John Borzoni, national sales manager for the heat-recovery unit division of Doucette Industries Inc., York, Pa., heat-recovery systems in commercial applications can be used anywhere substantial air conditioning and refrigerating loads and simultaneous water heating needs exist.
“For example, grocery stores are a great application, as well as restaurants, hotels, schools or healthcare facilities,” Borzoni said.
Waste heat-recovery systems’ role in an energy management plan is to reduce or eliminate fuel usage for building or process heat as a supplement to the existing heating and cooling systems, Golden said.
“When a building makes use of the waste heat produced by cooling a space instead of externally exhausting it, that air cooling system’s efficiency will be increased by 10 to 15 percent,” Borzoni said.
That can become extremely important in light of federal government mandates that require a minimum of a 15 seasonal energy-efficiency ratio (SEER) rating for new or retrofit construction of a building’s heating, ventilating and air conditioning (HVAC) system to qualify for stimulus money from the American Recovery and Reinvestment Act of 2009.
“An existing air conditioner with a 13 SEER rating already increases to a 14 SEER rating just when a heat-recovery system is applied,” Borzoni said.
Since heat-recovery systems exchange the temperature between incoming and outgoing air streams, they reduce the electrical loads associated with introducing the outside air. In addition, passive desiccant wheel technology also exchanges humidity and can provide up to 50°F of free heating, 15°F of free cooling, and 30 percent dehumidification, Smith said. A passive desiccant heat exchanger is normally composed of a rotating cylinder filled with an air-permeable material resulting in a large surface area. As the wheel rotates between the ventilating and exhaust air streams, it picks up heat energy and releases it into the colder air stream. The driving force behind the exchange is the difference in temperatures between the opposing air streams or thermal gradient.
“There are numerous benefits to using heat-recovery systems,” Golden said.
In addition to overall reduced fuel usage and costs, heat-recovery systems reduce carbon emissions and greenhouse gases. Further, when heat-recovery systems are applied, older, inefficient equipment can be upgraded, extending the life of other equipment.
“This reduces the bottom-line costs for products and services and makes companies more competitive,” Golden said.
Many states now have grants, loans, and tax or financial incentives to help finance at least a portion of such projects.
“Heat-recovery units are a quick and easy way to improve efficiencies without scrapping perfectly good equipment,” Borzoni said.
For most commercial buildings, he added, a heat-recovery system will allow the facility to have all the hot water it requires. Perhaps most importantly, however, heat-recovery systems can enable buildings to comply with the American Society of Heating, Refrigerating and Air-Conditioning Engineers energy-efficiency standards, the U.S. Green Building Council’s Leadership in Energy and Environmental Design credits, and the Environmental Protection Agency’s Energy Star certification requirements.
Electrical contractors that take advantage of the opportunities afforded by heat-recovery systems should partner with reputable companies with the necessary process knowledge to ensure the installed systems are safe and do not have an adverse effect on the facility’s process, quality or production, Golden said.
“Applying a heat-recovery system is a simple, straightforward method of improving a building’s energy efficiency and streamlining its energy management. Promoting its use to a client will add value to the contractor’s offering without adding substantial new equipment or electrical costs to the project,” Borzoni said.
BREMER, a freelance writer based in Solomons, Md., contributes frequently to ELECTRICAL CONTRACTOR. She can be reached at 410.394.6966 and firstname.lastname@example.org.