ASHRAE Journal - September 2012 - 76

2012 Technology Award Case Studies
flat plate solar collector panels. To further optimize the system, one of the manifolded AC units was converted to a 100% outside air unit, and the existing air-distribution system was converted to a dedicated outdoor air system (DOAS). The converted outdoor air-conditioning unit was also modified with a desuperheater heat exchanger that uses refrigerant superheat from the AC compressor to preheat the solar hot water heating system in the morning at system startup. Chilled water generated by the absorption chiller is then circulated to individual chilled water fan coil units located throughout the existing air-conditioned areas. The addition of fan coil units throughout the building solved the zoning issues and provided more controllability of thermal comfort, and the conversion of the previous constant-volume AC system to a DOAS also improved indoor air quality in the building because ventilation air quantities can be continuously maintained in accordance with ASHRAE Standard 62.1 at all times. The cooled and dehumidified outside supply air also helps to maintain thermal comfort and humidity control in the building. In Hawaii, more than 97% of all electrical power is produced by imported oil. The annual electricity consumption due to the installation of the solar thermal AC system has been reduced by 64,846 kWh, which corresponds to a reduction of 45 metric tons of CO2 emissions. Prior to implementation of the new solar thermal airconditioning system, the facility consumed approximately 387,360 kWh/year at an average electrical cost of $85,582/ year. This corresponds to an average cost of electricity of 22.1 cents/kWh. The air-conditioning system at the SSFM facility was the largest consumer of electricity, accounting for roughly 45% of the total electrical load. Based on the monitored energy consumption data after the completion of this project, the solar cooling system has reduced facility electrical demand by more than 28 kW on average, and now saves 64,846 kWh/year or $14,266/year in electrical energy cost. Based on the energy savings achieved with the new solar thermal AC system and overall cost for the new system, the simple payback is calculated at 12 years after taking state and federal tax credits into consideration. Besides the energy savings, another advantage of the new AC system design is that it provides more zoning throughout the space, which improved thermal comfort. The occupants have multiple thermostats and zone temperature controllers so that more occupants are satisfied with the conditions in their work area. This is a pioneer project for solar thermal air conditioning in Hawaii. Compared to photovoltaics, using solar flat plate collectors or parabolic solar collectors can be a more cost effective way to offset building energy cost in Hawaii. With Hawaii’s abundance of solar energy, solar thermal air conditioning could prove to be an efficient means for cooling buildings as technology improves in the design of the collectors and in the efficiency of absorption chillers.

ASHRAE Journal

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September 2012

ASHRAE Journal - September 2012

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