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Long-term performance measurement of GSHP systems serving commercial, institutional and multi-family buildings

Measured long-term performance data for ground source heat pump systems serving commercial, institutional and multi-family buildings are rarely reported in the literature. Energy use intensity figures are occasionally published, but as they necessarily lump the building loads and the system performance together, they are of limited usefulness in understanding real-world system performance.
Annex 52 will bridge the gap between those who see the heat pump system as a complex environment and the ground source as a black box, and those who see the ground source as a complex environment and the heat pump system as a black box.

Funded by: Swedish Energy Agency

Time period: 2018–2021

Project partners: Sweden, Finland, Germany, The Netherlands, Norway, United Kingdom, USA

Background

Measured long-term performance data for ground source heat pump systems serving commercial, institutional and multi-family buildings are rarely reported in the literature. Energy use intensity figures are occasionally published, but as they necessarily lump the building loads and the system performance together, they are of limited usefulness in understanding real-world system performance.

Carefully instrumented long-term measurement and analyzed system performance data from recently installed GSHP systems of various sizes and types, or of GSHP systems that have been in operation for a longer period of time, are rare but highly valuable tools for researchers, practitioners and buildings owners. Such measurements help to show how the various system components and control strategies affect the overall performance, to identify best practices, design and installation issues that lead to poor performance and to give guidance on how unanticipated consequences of the design be partially or totally avoided.

The focus of the proposed annex is performance measurement of GSHP systems serving commercial, institutional and multi-family buildings. These buildings may, for example, have:

 Multiple heat pumps, which may be part of a central heating and cooling plant or be distributed throughout the building(s).

 Water-to-water (brine-to-brine), or water-to-air heat pumps.

 Depending on the above two items, a separate distribution system for heating and cooling may be needed, or the distribution system may only involve attaching ductwork to the distributed water-to-air heat pumps.

 Heating and cooling, with the cooling often being predominant for commercial and institutional buildings. Furthermore, heating and cooling may be provided simultaneously to different parts of the building, either by using both sides of the heat pump, or with some heat pumps providing heating and others cooling. In some cases, cooling or pre-heating may be provided directly by the boreholes without the aid of heat pumps (so-called free-cooling).

 In addition to the ground heat exchanger made up of multiple boreholes or doublets etc., complementary heat sinks or sources (e.g. cooling towers, fluid coolers, solar collectors) may be utilized, forming what is sometimes called a hybrid GSHP system.

 A range of pumping/piping system designs using variable speed central circulation pumps, distributed circulation pumps, primary/secondary pumping, and two-pipe or one-pipe configurations.

 Control systems that affect flow rates in part-load conditions, operation of the auxiliary heat sink or source, and other aspects of the system operation.

 Standby electrical losses from control boards in the heat pumps, circulation pump variable-speed drives, Legionella protection and other components.

 Heat pumps sometimes operating with only the fan running to assist in distribution of outdoor air.

These variations in the system configuration add several degrees of complexity to analyses of seasonal performance factors. E.g. when the heat pumps are providing both heating and cooling, how is the electrical energy used by the central circulation pump allocated? How should the free-cooling amount be quantified? How do heat pump stand-by losses affect seasonal performance factors?

The EU project SEPEMO (Nordman 2012) defined heating and cooling seasonal performance factors (SPF) for residential heat pump systems with a range of boundary conditions. The final report noted that heat pump system performance depends not only on the heat pump, but also on the climate and quality of installation. While the SEPEMO project guidelines serve as an excellent starting point for GSHP systems serving commercial, institutional and multi-family buildings, they do not address fully all of the features that may be found in these systems. The results from the proposed annex will make possible both improvements to GSHP system performance and direct comparisons with other heating/cooling systems installed in similar buildings.

One example of measured performance of an office-building GSHP system leading to system performance factors is descibed by Southard et al. (2014a, 2014b). This study involved a detailed analysis of two heat pump systems at the ASHRAE Headquarters building in Atlanta – an air-source variable-refrigerant flow heat pump system and a ground-source heat pump system. Features of the study not seen in the SEPEMO study are quantified uncertainty of the performance factors and the relationship between system COP and outdoor air temperature.

Another aspect of this work is that the long-term performance measurements will generate quality data that may be used for development and validation of models of components (e.g. heat pump with integrated tanks, different types of tanks, borehole heat exchangers) as well as GSHP systems. Developing and validating models based on measured data will facilitate further optimization of GSHP systems.

Aim and objectives

The Annex 52 aims to survey and create a library of quality long-term measurements of GSHP system performance for commercial, institutional and multi-family buildings. All types of ground sources (rock, soil, groundwater, surface water) are included in the scope. While previous work will be surveyed, the emphasis of the annex will be on recent and current measurements. The annex also aims to refine and extend current methodology to better characterize GSHP system performance serving commercial, institutional and multi-family buildings with the full range of features shown on the market, and to provide a set of benchmarks for comparisons of such GSHP systems around the world.

Analysis procedures that help diagnose poor performance and opportunities for system performance improvements will be investigated. Multiple case studies featuring GSHP system performance measurements for systems around the world will be included and these case studies will serve as reference sets for future benchmarking.

Outcomes

Case studies: performance analysis and monitoring.

Bibliography of published field studies.

Guidelines for instrumentation and monitoring of GSHP systems.

Guidelines for analysis and reporting of GSHP performance.

Publications

Lazzarotto A, Mazzotti Pallard W, Abuasbeh M, Acuña J. Performance evaluation of borehole thermal energy storage through energy and exergy analysis. Proceedings World Geothermal Congress 2020. Reykjavik, Iceland, April 26 – May 2, 2020. (Submitted)

Project contact persons

Project KTH Coordinator, researcher

Project Researcher

Case Study Responsible

Project Researcher

Page responsible:Oxana Samoteeva
Belongs to: Energy Technology
Last changed: Aug 25, 2021
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