Vertical-borehole ground-coupled heat pumps: A review of models and systems

General review of ground-source heat pump systems for heating and cooling of buildings

Experimental thermal performance evaluation of a horizontal ground-source heat pump system

The advancement of technology and renewable energy systems (RES) have evolved considerably through the years. Geothermal energy was first introduced in Italy in 1904 and has ever since dramatically increased in efficiency. One of the main types of RES, Ground Source Heat Pumps (GSHPs), are used for heating and cooling a space when coupled with Ground Heat Exchangers (GHEs). GSHPs extract or reject heat to the Earth via a network of tubes. The closed loop system, either vertical or horizontal, is the most common of the configurations. Alternatively, pipes can run all the way down to utilize natural underground water sources, when present, in an open loop configuration. GHEs have significantly higher performance over conventional air-to-air heat exchanger systems and the reduction of their cost and the improvement of their overall efficiency through their design are crucial in research. In this paper are presented and reviewed the design aspects of GHE systems. In particular are discussed the types of GHEs such as open or closed loop systems, vertical or horizontal, U-tube or spiral, energy piles and hybrid systems. A comparative analysis through the literature of the various geometrical aspects of GHEs and the geothermal investigation of the ground environment and the materials used in the construction of GHEs are also presented. Then is analyzed the modeling – experimental and mathematical – of GHEs, with terms that have been extensively studied, like borehole thermal resistance, thermal characteristics, thermal response test, line-source and cylindrical-source models, discussed in detail. Next a demonstration of designing a numerical model of a GHE system through a software, taking into consideration the thermal characteristics, is given. Finally, a comparative detailed list in the form of a table of more than 30 mathematical and/or experimental GHE studies is provided, focusing on the important factors analyzed and findings of each. The overall aim of the current review study is to help improve the efficiency and the total manufacturing cost of GHEs.

A review of the design aspects of ground heat exchangers

Combining solar energy and heat pump technology is a very attractive concept. It is able to eliminate some difficulties and disadvantages of using solar dryer systems or solely using heat pump drying separately. Solar assisted heat pump drying systems have been studied and applied since the last decades in order to increase the quality of products where low temperature and well-controlled drying conditions are needed. This paper reviewed studies on the advances in solar heat pump drying systems. Results and observation from the studies of solar assisted heat pump dryer systems indicated that for heat sensitive materials; improved quality control, reduced energy consumption, high coefficient of performance and high thermal efficiency of the dryer were achieved. The way forward and future directions in R&D in this field are further research regarding theoretical and experimental analysis as well as for the replacement of conventional solar dryer or heat pump dryer with solar assisted heat pump drying systems and solar assisted chemical and ground source heat pump dryers which should present energy efficient applications of the technologies.

Review of solar assisted heat pump drying systems for agricultural and marine products

A ground-coil heat pump system is defined as a heat pump in which the outdoor or evaporator coil is placed directly in the ground or exchanges heat with the ground through a secondary fluid (usually water or antifreeze solution), which is circulated through the ground in a closed loop. Ground-coil systems present a more challenging design problem than either air-source or well-water systems. For instance, the performance of the outdoor coil on an air-source system can be readily predicted once the outdoor air temperature and humidity are known. Well-water system performance can generally be determined at the time of drilling with established well-testing techniques. However, the performance of ground-coil systems is highly dependent on ground heat-transfer characteristics. Soil type (clay, silt, sand, etc.) and moisture content can cause ground thermal conductivities to vary by orders of magnitude from one part of the country to another, from one lot to another within the same town, or from one point in time to another for the same lot. Thus, there are many challenges and uncertainties in designing and installing ground-coil heat pumps. This project was undertaken with the objective of reviewing historical and current methods for designing ground-coil heat pumps. The effortsmore » concentrated on European and North American experience. The following discussion presents the historical background followed by a description of basic design configurations, operating experience, and some specific design methods that have been developed or are under development.« less

Design methods for ground-source heat pumps

The objectives of the program reported here were to gather design and performance information on historical and current ground-coil heat-pump systems, to assess the adequacy of available design methods, and to define near-future R and D needs to promote the use of this technology The project was generally separated into two parts: (1) a review of the North American technology conducted by Battelle-Columbus, and (2) a review of European technology conducted by Battelle-Frankfurt Descriptions of basic ground-coil design configurations, operating experience, design methodologies, and reviews of costs of existing installations are included It is found that further design-method developent efforts are necessary to provide installers and manufacturers with pertinent design information in order to stimulate further implementation of ground-coupled heat pumps in the United States Furthermore, a research effort is needed to develop parametric data on the design and performance of a ground-coil during cooling using heat and moisture models

State-of-the-art Survey of Existing Knowledge for the Design of Ground-Source Heat Pumps

The objectives of the program reported here were to gather design and performance information on historical and current ground-coil heat-pump systems, to assess the adequacy of available design methods, and to define near-future R and D needs to promote the use of this technology. The project was generally separated into two parts: (1) a review of the North American technology conducted by Battelle-Columbus, and (2) a review of European technology conducted by Battelle-Frankfurt. Descriptions of basic ground-coil design configurations, operating experience, design methodologies, and reviews of costs of existing installations are included. It is found that further design-method developent efforts are necessary to provide installers and manufacturers with pertinent design information in order to stimulate further implementation of ground-coupled heat pumps in the United States. Furthermore, a research effort is needed to develop parametric data on the design and performance of a ground-coil during cooling using heat and moisture models.

D. Hodgett

Papers

Design methods for ground-source heat pumps

State-of-the-art Survey of Existing Knowledge for the Design of Ground-Source Heat Pumps

State-of-the-art survey of existing knowledge for the design of ground-source heat pumps

Design methods for ground-source heat pumps

Design methods for ground: source heat pumps