Addressing Sustainability in Ground Source Heat Pump Projects

Abstract

The use of ground source heat pump systems (also referred to as shallow geothermal or geo-exchange) is increasingly being considered as a means to service varied heating and cooling loads. Such systems have the potential to provide carbon emission and cost savings relative to traditional heating and cooling systems. A ground energy system comprises three key elements: 1. The load: the building, its controls and users resulting in a thermal load; 2. The heat transfer system: heat pumps, heat exchangers and associated controls; and 3. The source: the heat transfer system and its receiving environment, typically coupled via bores or ground loops. While the underpinning technology is not new, best practice in design is still evolving. One aspect of design requiring attention is sustainability, for which clear targets do not currently exist. Sustainability must address short and long term considerations for the environment. However, a true assessment of sustainability requires the wider system beyond hydrogeological elements to be assessed. To determine if a ground source system can be considered sustainable, a series of tests are proposed: 1. Can the thermal loads be serviced within the boundaries of the site? 2. What other thermally sensitive sites may need to be considered outside of the site? 3. Will there be unacceptable changes to the environment due to the long-term operation of the system? 4. Does the system operate as intended for the design life of the system, to maintain economic and environmental feasibility? In particular, thermal interference and water quality impacts require specialist assessment. While these tests may appear obvious to a ground source designer, they may be less obvious to others in the design team. A suitable framework for assessing sustainability should be capable of meeting the needs of designers as well as the regulators.