As one of the main businesses in Jeju-do in South Korea, specialized local products are grown in greenhouses. For greenhouse farming, it is preferable to use geothermal heat pump systems for energy conservation because of the stable temperature of the ground. In the same manner, heat pumps using underground air is recommended for greenhouse farming since underground air can easily be obtained from porous volcanic rocks in Jeju-do. However, direct usage of the underground air is not feasible for planting in the greenhouse or livestock care because the underground air is relatively humid and its temperature is low. For the present study, the heating performance of an air-to-water heat pump which used underground air as a heat source for greenhouse farming during the winter was assessed through measurements. In addition, the economic impact of the air-to-water heat pump (AWHP) was compared with a conventional air heater. According to the results, an AWHP can save more than 70% of the total heating costs compared with a conventional air heater. In sum, the utilization of the air-to-water heat pump using underground air can have a positive impact on reducing energy consumption as well as provide direct economic benefits.

This study investigates control performance of daylight dimming control system under various sky conditions in order to examine the influence of daylight conditions on dimming performance. Field measurements were conducted in a full-scale mock-up model to collect actual data and computer simulations were performed to determine light output of fixtures. Results indicate that the variation patterns of desktop illuminance were similar to those of illuminance arriving at window. The direct component of daylight affected photosensor illuminance generating strong reflected components from wall surfaces. Relationship between desktop and photosensor illuminance was stronger than that of between window and photosensor. This implies that desktop illuminance was effective to predict the variation of photosensor illuminance. Compared to overcast sky conditions, dimming control was effective under clear sky and achieved good energy savings. Under overcast sky conditions, excessive dimming occurred due to the influence of electric lighting. It appears that control algorithm or photosensor conditions should be reset in order to block light input to photosensor and generate less dimming from lighting fixtures.

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