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The aim of this study was to use life cycle assessment methods to determine the environmental impacts of manure utilisation by a biogas plant and by a typical manure composting system. The functional unit was defined as the average annual manure utilisation on a dairy farm with 100 cows. The environmental impact categories chosen were emissions of greenhouse gases (GHG) and acidification gases (AG). The GHG emissions were estimated as: 345.9 t CO2-equivalents (e) for solid composting (case 1), 625.4 t CO2-e for solid and liquid composting (case 2), and 86.3–90.1 t CO2-e for the biogas plant system. The AG emissions were estimated as: 10.1 t SO2-e for case 1, 18.4 t SO2-e for case 2, and 13.1–24.2 t SO2-e for the biogas plant system. These results show that a biogas plant system produces low GHG emissions, but comparatively high AG emissions with land application. It is suggested that land application using band spread or shallow injection attachments will decrease AG emissions (NH3) from biogas plant systems.

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The deployment of highly efficient cooling equipment is expected to promote energy savings and greenhouse gas emissions reductions in the tropics. A ground source heat pump (GSHP) has high energy-savings potential for use in Bangkok, Thailand. This study aimed to elucidate the operational conditions of a GSHP when used in Bangkok which was expected to achieve a higher efficiency than an air source heat pump (ASHP) over the long term. An operational experiment on a pilot facility in Bangkok and a simulation over a three-year GSHP operation were conducted. As a result of the operational experiment and simulation, the proposed operational condition was that the 90th percentile value of the hourly heat pump (HP) inlet temperature did not exceed 5 °C above that of the hourly annual ambient temperature during the third year of operation. When a GSHP designed based on this condition was utilized for a small government building, the required number of boreholes were 24, 4, and 3 for air-conditioned areas of 200, 40, and 25 m2, respectively, which achieved 40% energy savings. Thus, a small-scale GSHP in Bangkok designed based on the proposed condition can achieve high efficiency within space limitations.

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