Ground heat exchangers: Applications, technology integration and potentials for zero energy buildings

doi:10.1016/j.renene.2018.05.089

Renewable Energy

Volume 128, Part A, December 2018, Pages 337-349

https://doi.org/10.1016/j.renene.2018.05.089 Get rights and content

Highlights

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The latest research and applications on ground heat exchangers are reviewed.
•
Air-based GHEs, water-based GHEs and their applications are introduced.
•
Both passive and active applications of GHEs are presented and analysed.
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Various cooling and heating technologies integrated with GHEs are introduced.
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A technical route for GHEs to be used in zero energy buildings is provided.

Abstract

Ground heat exchanger takes the soil underground as heat source or sink to supply cooling or heating. It has been widely used in building heating and cooling systems due to high efficiency and environmental friendliness. This paper reviews the latest research on ground heat exchangers from several new perspectives and demonstrates their potentials in achieving zero energy buildings. Firstly, ground heat exchangers are classified into water-based and air-based ones based on the heat transfer medium. They can be used in a passive or active approach. Associated research and projects for each approach are introduced and analysed. Then the integration of ground heat exchangers with various cooling and heating technologies and related studies are reviewed. These technologies include solar thermal collectors, cooling towers, nocturnal radiative cooling technology, solar chimney, etc. Finally, a technical route for ground heat exchangers to help realize zero energy buildings is presented, which provides a promising solution to improve energy efficiency of buildings.

Introduction

Ground heat exchanges (GHEs) are buried underground and exchange heat with the surrounding soil via water or air [1]. They become increasing popular in building heating and cooling systems due to its long-term durability, high efficiency and environmental friendliness [1,2]. The high efficiency results from the stable temperature of soil below a certain depth (i.e. 10 m) underground, which is lower in summer and higher in winter compared with the outdoor air [[3], [4], [5]]. Due to the high thermal inertia of the soil, the temperature variation is largely delayed and almost completely immunes to the intensified solar radiation and fluctuated air temperature. The benefits of GHEs in improving the building energy efficiency have been demonstrated by many researchers [[6], [7], [8], [9], [10], [11]].

Energy shortage and environmental pollution problems are concerned worldwide and it is generally believed that decreasing building energy demands is an effective solution to this problem [[12], [13], [14]]. Researchers around the world spare no effort to optimize the design and operation of buildings and their energy systems. Zero energy building (ZEB) therefore appears with much higher energy performance than conventional ones. Many applications [[15], [16], [17]] have demonstrated the benefits of ZEBs on mitigating the energy shortage and the environmental pollution. Some countries or institutions, which have ambitious targets on their future energy consumption, attempt to take ZEBs as their future building energy targets, such as Building Technology Program of Department of Energy in US and the EU Directive on Energy Performance of Buildings [18,19].

As a clean and sustainable energy technology, GHEs can be used to help achieve ZEBs. However, the potentials of GHEs in ZEBs are still not fully recognized and need to be further exploited. There are already some reviews on the applications of GHEs in buildings. However, most of them focus on ground source coupled heat pump (GSHP) systems, where GHEs are connected to the evaporators or condensers of heat pumps. The direct applications of GHEs (without heat pumps) for heating and cooling are rarely reviewed. In addition, many of these reviews pay more attention to the performance of ground source heat pump systems or GHEs, rather than the integration with various cooling/heating or renewable energy technologies.

To fill the above research gaps, this paper therefore presents a comprehensive review on the application of GHEs in buildings from several new perspectives and illustrates the potential for ZEBs. The GHEs are classified into two categories according to the heat transfer medium: water-based GHE and air-based GHE. Relevant studies are introduced in Section 2. The application of GHEs is separated into two approaches: active application and passive application. Associate research and projects are reviewed in Section 3 and Section 4. Then the integration of GHEs with various cooling/heating and renewable energy technologies is introduced in Section 5, including solar thermal collectors, evaporative cooling technology, nocturnal radiative cooling technology etc. The potentials of GHEs to realize ZEBs and a technical route are presented in Section 6. Finally, conclusions and recommendations on GHEs are summarized in Section 7.

Section snippets

Classification of GHEs based on heat transfer medium

GHEs, also called as ground source coupled heat exchangers, have been widely used for cooling and heating in buildings [1,20]. They can be classified into three categories according to the heat transfer medium: water-based GHEs, air-based GHEs and direct-expansion GHEs. The water-based and air-based GHE use the circulating water or air through the buried tube to exchange heat with the soil. For the direct-expansion GHE, the refrigerant from heat pumps flows through the pipe directly and the GHE

Passive application of GHEs

The soil temperature at 10–15 m below the ground surface stay constant all the year. The cold or heat energy stored underground therefore can be directly used for cooling and heating. The GHE can be used independently or coupled with mechanical heating and cooling systems. In the passive application of GHEs, the energy consumption of mechanical heating and cooling systems can be reduced or even eliminated. The GHEs are often integrated with ventilation systems and building envelopes.

Active application of GHEs

The active application of GHEs in this paper mainly refers to the ground source heat pump (GSHP) system. In winter, the GSHP system extracts heat from the relatively warm ground and releases it into the building for heating. In summer, the process is reversed and the GSHP system extracts heat from the building and releases it into the ground. The GSHP system is more applicable for the buildings with both heating and cooling demand considering the annual heat balance underground. Compared with

Integration with various cooling and heating technologies

As an energy efficient technologies, the GHE can be integrated with various cooling and heating technologies such as solar thermal collectors, evaporative cooling technology (mainly referring to the cooling tower), night radiative cooling technology, etc. Relevant studies are reviewed as follows.

Potentials of GHEs for zero energy buildings

Zero energy building has been obtained increasing attentions in recent decades [101]. It refers to the building that the annual energy used is almost equal to the on-site renewable energy generation. There are many similar definitions about ZEBs, including zero carbon building, net zero energy building, nearly zero energy building, etc. The concept, definition and calculation methods on ZEBs have been summarized in Refs. [19,102].

Many efforts have been made to achieve ZEBs and these studies can

Conclusions

This paper reviews the research and applications of GHEs for heating and cooling in buildings and demonstrates the potential contributions of GHEs to achieving ZEBs. The GHEs are classified into two categories based on the heat transfer medium: water-based GHE and air-based GHE. Water-based GHEs are often integrated with building envelopes and used in GSHP systems. The air-based GHE is often adopted to precool or preheat fresh air before supplying it to buildings.

GHEs can be utilized in a

Acknowledgements

This work presented in this paper is financially supported by a grant (No. 51678263) of National Science Foundation of China and Startup Fund for Talented Scholars (No. 3004261108).

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ReviewGround heat exchangers: Applications, technology integration and potentials for zero energy buildings

Highlights

Abstract

Introduction

Section snippets

Classification of GHEs based on heat transfer medium

Passive application of GHEs

Active application of GHEs

Integration with various cooling and heating technologies

Potentials of GHEs for zero energy buildings

Conclusions

Acknowledgements

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Renew. Sustain. Energy Rev.

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Int. J. Refrig.

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Energy Build.

Energy Procedia

Renew. Sustain. Energy Rev.

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Renew. Energy

J. Clean. Prod.

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Geomech. Energy Environ.

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Review
Ground heat exchangers: Applications, technology integration and potentials for zero energy buildings