Experimental investigation of the potential of near infrared heating (NIR) in comparison to forced air heating.

摘要

In this study, the potential of near infrared heating (NIR) is assessed experimentally in comparison to forced air heating. To this end the night time heating needs for two identical, scaled down, experimental greenhouses located in central Greece were monitored for one thermal period. Four IR electric lamps were used to heat the first greenhouse whereas the second one was equipped with an electric forced air heater and an electric fan which was used for the homogenization of the temperature distribution. The output of several thermocouples located at the canopy area, on the cover and in the greenhouse air in both greenhouses were recorded every minute and 10 minutes averages were stored on a data logger, along with parameters characterizing the outdoors macroclimate, including outside and sky temperatures, wind speed and relative humidity measured by a suitable meteorological mast. The two heating systems were operated automatically to keep a reference temperature at the canopy within certain limits during nights (14-16 degrees C), suitable for the growth of lettuce, which was used as the test cultivation. Both heating systems maintained successfully the required conditions at the canopy for the growth of the plants. The energy consumption was recorded based on the time of operation of the heating systems. The internal air temperature in the IR heated greenhouse was always several degrees lower than the reference temperature of the plants resulting in significant energy consumption savings for the IR heated greenhouse. Savings of 38-50% were measured for the IR system in relation to the consumption of the conventionally heated greenhouse during the thermal period summing up to a total mean of 43%.