A Tool to Assess Heating Efficiency of Direct-fired Heater with the Impact of Humidity Control
Creators:Lee, Wee Fong
Advisor:Ling, Peter P.
air exchange rate
decision support tool
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Series/Report no.:Food, Agricultural, and Biological Engineering. Graduate student poster competition, 2014
Heating is one of the top two expenses of greenhouse operations in northern climates. Direct-fired heater (DFH) that has been promoted having high heating efficiency, 99.9%, compared to 80-94% of conventional indirect-fired heaters (IFH), could be an energy efficient choice. However, the high efficiency claim does not consider energy lost through air intake during combustion process. Fresh air intake is important for clean combustion and extra dehumidification for the water vapor generated from the combustion process to maintain a healthy environment for plant growth. The actual heating efficiency of a DFH is affected by amount of fresh air intake where higher air intake rate causes lower heating efficiency. A decision support tool (the tool, thereafter) was developed to determine the minimum air intake needs for the combustion and water removal, thus, the highest net heating efficiency of a DFH can achieve. In a case study, the tool predicted that a DFH had a net heating efficiency of 86%. The prediction was verified with field experiments to compare heating performance of the DFH to a popular IFH. The results showed varied DFH heating efficiency that was affected by the heater operation strategy to regulate fresh air intake rate. A higher heating efficiency was achieved with a fresh air intake rate determined by the tool. The DFH consumed 8.8% less fuel than that of the IFH. The field tested DFH heating efficiency was 87% which was in close agreement with the prediction of the tool.
Ohio Agricultural Research and Development Center
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