Postprint version. Published in Acta Horticulturae, Volume 801, January 1, 2008, pages 1317-1324.
The objective of this study was to evaluate the effects of relative humidity, light management levels, minimum ventilation rates, CO2 enrichment and canopy size on energy consumption in three different greenhouse systems (conventional, open-loop heat pump, and confined heat pump) in winter, spring, and summer months. No difference was observed in energy consumption with relative humidity set point levels in winter due to the already low relative humidity levels. Some differences were observed in spring and summer due to extra dehumidification required to maintain the inside relative humidity at lower levels. Energy consumption in summer was reduced up to 25.5% by using an 80% relative humidity set point instead of 70% in the open heat pump system. Using a 250 W/m2 light management level instead of 350 W/m2 resulted in a 5% reduction in energy consumption in summer, but the energy used for ventilation and heating did not change in summer. The only change was observed in the energy required for cooling. However, the energy consumption was significantly affected by the minimum ventilation rate. A 50% reduction (using 0.005 m3/s.m2 instead of 0.01 m3/s.m2) in the minimum ventilation rate resulted in 26%, 21%, and 1.5% decreases in total energy consumptions in winter, spring, and summer, respectively. Using a CO2 enrichment level of 1000 ppm compared to an enrichment level of 350 ppm resulted in a slight decrease in leaf temperatures during the day. This decrease caused a decrease in the air temperature resulting in slightly higher energy consumption for heating the greenhouse. This small increase in the energy consumption was about 1.7%. The partial canopy (0.4 m) systems had more energy consumption than the full canopy (2.0 m) greenhouse systems.
Bioresource and Agricultural Engineering
The original publication is available at http://www.actahort.org