Measured Performance of a Mixed-Use Commercial-Building Ground Source Heat Pump System in Sweden

Abstract

When the new student center at Stockholm University in Sweden was completed in the fall of 2013 it was thoroughly instrumented. The 6300 m2 four-story building with offices, a restaurant, study lounges, and meeting rooms was designed to be energy efficient with a planned total energy use of 25 kWh/m2/year. Space heating and hot water are provided by a ground source heat pump (GSHP) system consisting of five 40 kW off-the-shelf water-to-water heat pumps connected to 20 boreholes in hard rock, drilled to a depth of 200 m. Space cooling is provided by direct cooling from the boreholes. This paper uses measured performance data from Studenthuset to calculate the actual thermal performance of the GSHP system during one of its early years of operation. Monthly system coefficients-of-performance and coefficients-of-performance for both heating and cooling operation are presented. In the first months of operation, several problems were corrected, leading to improved performance. This paper provides long-term measured system performance data from a recently installed GSHP system, shows how the various system components affect the performance, presents an uncertainty analysis, and describes how some unanticipated consequences of the design may be ameliorated. Seasonal performance factors (SPF) are evaluated based on the SEPEMO (“SEasonal PErformance factor and MOnitoring for heat pump systems”) boundary schema. For heating (“H”), SPFs of 3.7 ± 0.2 and 2.7 ± 0.13 were obtained for boundaries H2 and H3, respectively. For cooling (“C”), a C2 SPF of 27 ± 5 was obtained. Results are compared to measured performance data from 55 GSHP systems serving commercial buildings that are reported in the literature.

Addressing the building energy performance gap with measurements

“…This difference is sometimes referred to as the building energy "performance gap" (de Wilde 2014). Spitler and Gehlin (2019) reviewed some of the work exploring the performance gap based on energyuse intensity (EUI). The results are eye-opening, to say the least.…”

A Study on the Effect of Performance Factor on GSHP System through Real-Scale Experiments in Korea

“…The ground heat exchanger length is an important performance factor for the GSHP system, and most GSHP system design software is used to calculate the required length of ground heat exchanger. Most studies, however, have been conducted through the numerical analysis or the transient analysis of TRT [13][14][15][16]. Few studies [16] have examined the performance change according to the length of ground heat exchanger through real-scale experiments.…”

“…In the previous studies, performance analysis of various performance factors of the GSHP system was performed. [5][6][7][8][9][10][11][12][13][14][15][16]. However, most previous studies analyze the effectiveness of the design factor through numerical simulation [5,6,8,10,11,14].…”

“…It, however, does not provide quantitative values for newly developed systems, such as the shape of the ground heat exchanger and the introduction of the heat storage tank. To address this problem, various studies [5][6][7][8][9][10][11][12][13][14][15][16][17][18] have been conducted using experimental and numerical methods.…”

“…GSHP linked heat storage tank system has a higher 15% heat pump COP compare to the GSHP system. Spitler et al [13] analyzed the performance measurement method and the performance factor of the GSHP system in a university building in Stockholm, Sweden. As a result, the measured COP is more affected by the amount of heating and cooling provided than by the entering fluid temperature to the heat pumps.…”