Oven Preheat vs. Duct Loss/AHU efficiency

[easypilot]

I am trying to improve the efficiency of a painting facility. Five natural gas fired ovens randomly heat 1,000 to 5,000 cubic feet each of 20ºC to 40ºC (midwest US climate) ambient air initially. Upon process completion, 200ºC to 250ºC oven air is ventilated down to <50ºC whereupon oven doors are opened, the finished product is removed, and oven reloaded for the next cycle. Random product size and volume causes random heat cycle times. Approximately 60,000 cubic feet of hi-temp air is exhausted daily. Approximately 400 feet of well insulated 24 inch duct could interconnect these ovens. I would like to rewrite the PLC program to include overall operation of ductwork baffles, valves, AHU, etc., so that a ventilation cycle of one oven would provide preheat for another. Would real world daily ductwork heat loss and AHU power consumption exceed the cost of heating this amount of air? In other words, is using exhaust for preheat worthwhile and feasible?

 

[butelja]

Could some type of pebble bed heat regenerator heat exchanger be used to store the heat?

 

[easypilot]

Butelja;
Thank you for the response. I suppose heat storage might be a future consideration. As oven operators were asked to record time of day at process start, it was discovered that ventilation and heating were simultaneaous several times daily. Simple ducting and air handling between ovens is all that is needed right now IF FEASIBLE. Is moving 60,000 cubic feet of hot air worth the effort?

 

[butelja]

The total amount of heat you are talking about (based upon 60,000 cubic feet) is between 375,000 and 400,000 BTU, or 110 to 117 kW*hr. Look at the cost of the energy saved compared to the cost to implement and decide based upon the economics.