2016 ASHRAE Winter Conference

Ground source heat pump (GSHP) systems are commonly used in Sweden for both residential and commercial buildings.  However, there are several key differences with GSHP systems utilized in the USA. Scandinavian systems are often heating-only, and instead of using grouted boreholes, groundwater-filled boreholes are often used.  These boreholes are cased from the ground surface to the usually-shallow bedrock.  A single or double U-tube is commonly suspended in the borehole.  These boreholes are often deeper than those commonly used in the USA.  This paper reviews current Scandinavian practice for borehole design and discusses several installations with boreholes 250 – 300 m (820-984 ft) deep or deeper.

The purpose of this paper is to explore the performance of shallow depth helical heat exchangers coupled with ground source heat pumps (GSHP) for residential HVAC applications.  This shallow depth system serves as an alternative to traditional vertical bore fields, which carry high installation costs.  These helical heat exchangers occupy considerably less land when compared to horizontal configurations, but are still influenced by changing ground temperatures driven by seasonal weather conditions.  Performance data and design information is limited for helical heat exchangers, which has limited their adoption amongst GSHP system designers and installers.  In Situ testing was performed for a GSHP system to provide designers with performance information and insight towards appropriate applications of this technology.

Heat pumps use less energy when the difference between the source and load temperatures is small. For a ground-source heat pump (GSHP), the source temperature is prescribed by the local ground temperature. As for the load temperature, it depends on the type of heating system. In this paper, the performance of a water-to-water heat pump coupled to two different heating systems is examined. The first one is a radiant type floor heating system operating at a relative low temperature (≈30 °C). The second system uses a fan-coil unit operating at higher temperature (≈45 °C) to supply space heat. The objective of the paper is to quantify the energy savings from running a GSHP at a low load temperatures.

Photovoltaic panels that provide electricity and thermal energy are now commercially available. These PV/T collectors use either the air or a liquid as the heat transfer fluid to collect thermal energy. This paper examines the overall system performance of PV/T collectors linked to a ground-source heat pump equipped with a four-pipe borehole. The system selected for this study consists of two independent fluid circuits. In the first circuit, the outlet fluid from a liquid-cooled PV/T collector is first pumped through a heat exchanger then to the ground heat exchanger. In the second circuit, fluid is pumped from the ground heat exchanger to the heat pump via the heat exchanger which provides a thermal link between the PV/T and GSHP circuits.

Studies have shown that neglecting borehole thermal capacity in annual simulations of ground-source heat pump systems can lead to an overestimation of the energy consumption by 3-4% when the heat pump is operating intermittently. There are various approaches to account for thermal capacity when simulating geothermal boreholes. The objective of this paper is to validate the TRCM procedure. Experimental data from two tests performed at the Canadian Centre for Housing Technology (Ottawa, Canada) are used for this validation.