Recirculating heat systems capture and reuse excess heated air that would otherwise be vented to the atmosphere, improving system efficiency and lowering power consumption. Because the heat is recirculated, the intake air stream through the blower and heater is at a much higher temperature than in a typical process heat system. Non-specialized heaters and blowers are designed with the assumption that the intake air is at or near room temperature, the higher inlet temperatures associated with recirculating systems will damage these tools. Specialized equipment is available that is designed to withstand the high inlet temperatures of recirculating systems. In this article we discuss these specialized pieces of equipment and how they differ from the equipment used in non-recirculating process heat systems.
Many standard heaters have built-in electronic controls or supply power connections which are in close proximity to the input air stream. These components are not able to withstand the elevated temperatures involved in a recirculating system. Recirculating air heaters overcome this problem by using appropriate connections for the temperature and standing off the connection terminals from the supply air. These heaters usually do not have any inbuilt control electronics and therefore require an outside control system incorporating a Solid State Relay or Silicon Controlled Rectifier in order to regulate temperature output. See our article on Temperature Control of Air Heaters for more information about control options.
Maximum rated intake temperature can vary by heater, so always be sure to check the specifications to ensure they meet your requirements.
As with heaters, the elevated inlet temperatures of a recirculating system can damage a standard blower’s bearing, grease, and electric motor components. Blowers designed for heat recirculation have the bearings and motor isolated from the blower volute, usually using an air gap and insulator plate, which protects them from the high temperature. Maximum rated operating temperature can vary by blower, so always be sure to check the specifications to ensure they meet your requirements.
Consideration much also be given to the hose and other connectors that are used in the system. The standard plastic parts used in low temperature systems generally cannot withstand the higher temperatures of a recirculating system. High temperature components must be sourced.
At STANMECH, we have experience building heat recirculating systems. Let us help design the right system for you. Contact us at firstname.lastname@example.org or 1-888-438-6324.