Performance Evaluation of Ground Heating and Cooling Systems - Long-term performance measurements of two case buildings

Abstract

Geothermal energy is one of the oldest and most sustainable energy sources and has been used
for thousands of years. The temperature of the ground at shallow depth is fairly constant,
above the air temperature in winter and lower than the ambient temperature in summer.
Shallow geothermal energy systems can thus be used to provide heating and cooling with or
without heat pumps.

This study aims to analyse the long-term performance measurements of two shallow geothermal heating and cooling systems. The first system is installed in a small clubhouse in Gothenburg, whereas the second system is installed in a large office building in Stockholm. For both installations, high-frequency data has been collected for several years, which enables evaluating and analyzing the performance of these systems.

The first system provides space heating and domestic hot water (DHW). It is a water-to-water
heat pump connected to a single 230-m deep borehole heat exchanger. This study uses longterm high-frequency measurement data from this clubhouse and investigates the energy performance of the GSHP system for the three years between 2014–2016.

The second system is installed at the Entré Lindhagen in Stockholm. The system is primarily
a direct ground cooling system but also preheats the ventilation air to balance the ground
loads. The system was taken into operation in January 2014 and serves a heated floor area of
65,265 m². The ground system consists of 144 boreholes with double U-tubes, each with an
active-depth of 220 m. This study provides the performance evaluation of the ground system
for five years between 2014–2018 using high-frequency measurement data.

Within the scope of this work, seasonal performance factors for both systems are evaluated
corresponding to the SEasonal PErformance factor and MOnitoring (SEPEMO) and/or Annex 52 system boundary schemes. Results are analysed to show how the various system components affect performance. The outcome of this research provides a set of benchmarks for comparison of such systems around the world.

Popular Abstract

Nowadays it is becoming popular to use ground-source heating and cooling systems for residential as well as commercial buildings. This technology offers both environmental benefits and high energy efficiency. The performance of these systems depends upon the design,
operation, and control of several sub-systems. Hence, in order to understand the real performance of ground-source heating and cooling systems, it is necessary to study it with different system boundaries such as for heat pump, ground source, supply side, and the whole system. The objective of this study is to analyze the long-term measured data of two case study buildings using ground-source heating and cooling systems. The aim is to determine the measured performance of the two systems according to the established methods of performance
evaluation reported in the literature.

The first system is installed in a small sports clubhouse in Gothenburg, whereas the second system is installed in a large office building in Stockholm. For both installations, high-resolution data has been collected for several years, which enables the evaluation and analysis
of the performance of these systems. The first system provides space heating and domestic hot water (DHW). It uses a heat pump coupled to a single 230-m deep borehole heat exchanger. The second system is primarily a direct ground cooling system with no mechanical cooling. It
also preheats the ventilation air to balance the ground loads over the year. The ground system consists of 144 boreholes with double U-tubes, each with an active-depth of 220 m.

The energy performance of the GSHP system of the first system is analyzed for three years time period between 2014-2016. The performance evaluation of the first system has been studied using two popular boundary schemes: SEPEMO boundary scheme and Annex 52 boundary
scheme. The second system has been evaluated for five years time period between 2014-2018. The performance evaluation of the second system has been performed using the Annex 52 boundary scheme. The performance evaluation of both systems has been carried out using seasonal performance factors, which present the ratio of delivered thermal energy to purchased electrical and thermal energy.

For the first system, the annual seasonal performance factors for different system boundaries range in a very wide range. The difference between the seasonal performance factors for different system boundaries is caused by the auxiliary components in the system. The always-on auxiliary electric heating for legionella protection is observed to affect the system performance the most. The measured seasonal performance of the second system with direct ground cooling is several folds higher compared to the traditional ground cooling systems with mechanical cooling. However, auxiliary components such as pumps are also observed to affect the performance of this system considerably.

The outcome of this work shall serve as a reference set, and provide monitoring experience and guidance for analyzing and optimizing the measured performance of ground heating and cooling systems.

• author: Liu, Hao and Zhang, Hongyi
• supervisor: Saqib Javed
• organization: Division of Energy and Building Design; Department of Architecture and Built Environment
• course: AEBM01 20201
• year: 2020
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Ground source heat pump (GSHP), System performance, Long-term monitoring, Geothermal, Borehole heat exchangers, Office building, Uncertainty analysis, Deep Green Cooling, Free cooling, Heating, Cooling
• language: English
• id: 9026913
• date added to LUP: 2020-08-24 09:32:01
• date last changed: 2022-06-01 03:41:32