This project investigates the possibilities of supplying a new residential area, Rosborg Ø in Ny Rosborg in Vejle, Denmark with ground source based heating and passive cooling utilizing foundation pile heat exchangers (heat exchanger is abbreviated HE in the following) commonly referred to as energy piles. The energy pile foundations are connected to a distribution system of uninsulated pipes buried at shallow depth (referred to as Cold District Heating and abbreviated CDH in the following) from which connected energy consumers are supplied with heating with heat pumps as well as passive cooling.
To achieve this goal, the project has developed a geothermal screening procedure based on geophysical mapping, borehole information, pile testing and laboratory measurements of soil thermal properties. A prototype computational model for CDH has been developed and used for assessing the potential for heating and cooling supply of Rosborg Ø, a small, residential subarea of Ny Rosborg. Finally, the project has developed a complete business model for energy pile based, collective heating and cooling with a well-defined cost structure in which total fixed and variable costs can be quantified in specific projects such as e.g. Rosborg Ø.
The comparative case study of the geothermal potential and the estimated energy demand of the planned buildings on Rosborg Ø in Ny Rosborg shows that CDH can fully supply the heating demand as long as the ratio between the building footprint and liveable area exceeds 26%. Thus, Ny Rosborg is well-suited for CDH based on energy piles, however, recalculation of the scenario is necessary once additional information on the planned buildings becomes available. This conclusion is further supported by operational data from the energy pile foundation at Rosborg Gymnasium, demonstrating excess heating and cooling possibilities. A further analysis of operational data from the energy pile foundation at Rosborg Gymnasium shows an energy efficiency ratio of 24.8 for the passive cooling during the summer of 2018 which is roughly ten times more efficient than traditional Air Conditioning (AC). Moreover, the analysis shows that Rosborg Gymnasium can supply their cooling needs passively with energy piles 97% of the time where cooling is required. As such, the variable costs of building cooling with energy piles is exceptionally low.
The initial investment is higher for energy piles, however, the variable costs of heating and cooling are greatly reduced relative to traditional District Heating (DH) and AC. In WP 5 the estimated payback periods for collective heating and cooling supply of Rosborg Ø are 3.76 and 6.29 years assuming office and residential buildings, respectively. The relatively short payback periods are due to a drastic reduction in the variable costs of heating and cooling with energy piles of ca. 80% relative to traditional DH and AC. The contributing factors to the short payback period are the relatively low costs of electricity, the high COP of the Ground Source Heat Pump (GSHP) system, the relatively high power tariff (effektbidrag) from traditional DH and finally the exceptionally low costs of passive cooling/seasonal heat storage.
In the current project, the partners have developed a truly renewable, economically competitive heat pump technology to supply collective building heating and passive cooling/seasonal heat storage for the future energy supply in Denmark.