Abstract
Greenhouse cooling systems with three types of heat pumps: air source-air supply, water source-air supply and water source-water supply types, are evaluated by hourly calculations based on a simple heat balance model. Cases considered are for the current 4 most typical greenhouses at 4 locations in Japan. Cooling requirements for two combinations of day and night cooling as well as two night only cooling set points are determined. Peak daytime cooling requirements are similar for all locations and greenhouse types and may be too great to justify fully meeting without any ventilation. Meeting half the full day cooling requirements with heat pump systems may be more practical. In this case the water source-water supply system is shown to require only one sixth the size heat pump unit relative to the other two types, due to the utilization of the cool water storage. This type system sized to meet 90% of night heating requirements can meet almost all night cooling needs. Even modest sized systems are shown capable of meeting cooling needs many hours of the year extending the opportunity for closed operation with carbon dioxide enrichment.
