Geothermal heat pump systems - closed and open-loop geo-exchange. Glossary: second selection of definitions provided by current legislation

A Geothermal Heat Pump (GHP) system is known to have enormous potential for building energy savings and the reduction of associated greenhouse gas emissions, due to its high Coefficient Of Performance (COP). The use of a GHP system in cold-climate regions is more attractive owing to its higher COP for heating compared to conventional heating devices, such as furnaces or boilers. Many factors, however, determine the operational performance of an existing GHP system, such as control strategy, part/full-load efficiency, the age of the system, defective parts, and whether or not regular maintenance services are provided. The omitting of any of these factors in design and operation stages could have significant impacts on the normal operation of GHP systems. Therefore, the objectives of this paper are to further investigate and study the existing GHP systems currently used in buildings located in cold-climate regions of the US, in terms of system operational performance, potential energy and energy cost savings, system cost information, the reasons for installing geothermal systems, current operating difficulties, and owner satisfaction to date. After the comprehensive investigation and in-depth analysis of 24 buildings, the results indicate that for these buildings, about 75% of the building owners are very satisfied with their GHP systems in terms of noise, cost, and indoor comfort. About 71% of the investigated GHP systems have not had serious operating difficulties, and about 85% of the respondents (building owners) would suggest this type of system to other people. Compared to the national median of energy use and energy cost of typical buildings of the same type nationwide, the overall performance of the actual GHP systems used in the cold-climate regions is slightly better, i.e. about 7.2% energy savings and 6.1% energy cost savings on average.

Geothermal heat pump (GHP) systems are more concentrated to moderate climate regions, although the potential for GHP systems in hot and humid climates is possible as past research efforts have demonstrated this using simulations and commercial case examples. This research investigates the use of residential GHP systems for the hot and humid climate found in southern Louisiana. The authors collected field performance information, including initial system cost, and electricity consumption and costs from two residential case studies in which each case included one home with a conventional heating and cooling system and one home with a GHP system. Using a comparative analysis and analysis of variance, results illustrate that initial cost of GHP system in the first case was $13,285 more and the second case was $17,588 more than the installation costs of a conventional system. Further, the GHP system payback period depends on the whether the design uses a horizontal or vertical ground loop, and the designer and contractor’s quality and experience in performing the GHP work as the first case resulted in a payback period of 70 years while the second case had a payback period of only seven years. Findings show that when an appropriate installation occurs, GHP system can save consumption and energy costs for residential homes in hot and humid climates.

Geothermal Heat Pump (GHP) systems are heating and cooling systems that use the ground as the temperature exchange medium. GHP systems are becoming more and more popular in recent years due to their high efficiency. Conventional control schemes of GHP systems are mainly designed for buildings with a single thermal zone. For large buildings with multiple thermal zones, those control schemes either lose efficiency or become costly to implement requiring a lot of real-time measurement, communication and computation. In this paper, we focus on developing energy efficient control schemes for GHP systems in buildings with multiple zones. We present a thermal dynamic model of a building equipped with a GHP system for floor heating/cooling and formulate the GHP system control problem as a resource allocation problem with the objective to maximize user comfort in different zones and to minimize the building energy consumption. We then propose real-time distributed algorithms to solve the control problem. Our distributed multi-zone control algorithms are scalable and do not need to measure or predict any exogenous disturbances such as the outdoor temperature and indoor heat gains. Thus, it is easy to implement them in practice. Simulation results demonstrate the effectiveness of the proposed control schemes.

Using natural sources of energy (solar, wind, biomass etc.) may potentially help to mitigate global warming. Low-temperature geothermal resources are among the more abundant natural energy sources. Methods of utilizing low-temperature geothermal resources include both direct use of warm groundwater and geothermal heat pump (GHP) systems. GHP systems may be subdivided into two basic types. One uses water circulated through a subsurface pipe without direct mass exchange between the pipe and the local groundwater aquifer (“closed system”). The other involves direct withdrawal of heated groundwater (“open system”). GHP systems are popularly used worldwide (Rybach et al., 2000; Fridleifson, 2001; Lund,2005). In Sweden, the number of GHP system installation per 100 people in 2005 is about two (Curtis et al., 2005). It is generally considered that GHP systems may be utilized everywhere because of stable temperature of the underground. However, the applicability of the GHP system is not clear for space cooling in tropical region where sufficient temperature difference between underground and atmosphere may not be expected. Aiming at grasping the applicability of GHP systems for space cooling in tropical region, an experimental operation of a GHP system was conducted at Kamphaengphet, Thailand from October, 2006 to March, 2008 (Yasukawa et al., 2009). The depth of the heat exchange borehole, in which U-tube was installed, was 56m. The authors set temperature sensors every ten meters inside the U-tube (at depths of 0, 6, 16, 26, 36, 46 and 56 meters, respectively). As the detail of the GHP system, the results of temperature measurements and calculation of system performances are presented in Yasukawa et al. (2009) in this issue, we attempted to estimate subsurface thermal influence of the GHP system for space cooling by acquiring temperature data of the underground from this test.

This paper presents an aggregation-disaggregation framework for the community-level management of widely-used Geothermal Heat Pump (GHP) systems in energy efficient buildings. In accordance with the layered operating architecture of the current power grid, this framework operates at two different time-scales. At a slow time-scale, each building predicts its GHP system future power consumption information consisting of both upper and lower bounds and the utility function, using aggregate thermal zone information and short-term disturbance forecasts. The information is then reported to a control center, i.e., an aggregator for all GHP systems in the community who determines and notifies their future nominal consumptions. At a fast time-scale, a distributed control scheme is designed based on a primal-dual gradient method, such that the nominal consumption can be tracked as closely as possible under real disturbances, using only local measurements and neighboring communications. In general, our framework provides an approach to scaling up the optimization and control for zone-building-aggregator interaction, which can be used to provide flexible ancillary services from a population of GHP systems to support the power distribution/transmission systems.

Heating application efficiency is a crucial point for saving energy and reducing greenhouse gas emissions. Today, EU legal framework conditions clearly define how heating systems should perform, how buildings should be designed in an energy efficient manner and how renewable energy sources should be used. Using heat pumps (HP) as an alternative “Renewable Energy System” could be one solution for increasing efficiency, using less energy, reducing the energy dependency and reducing greenhouse gas emissions. This scientific article will take a closer look at the different efficiency dependencies of such geothermal HP (GHP) systems for domestic buildings (small/medium HP). Manufacturers of HP appliances must document the efficiency, so called COP (Coefficient of Performance) in the EU under certain standards. In technical datasheets of HP appliances, these COP parameters give a clear indication of the performance quality of a HP device. HP efficiency (COP) and the efficiency of a working HP system can vary significantly. For this reason, an annual efficiency statistic named “Seasonal Performance Factor” (SPF) has been defined to get an overall efficiency for comparing HP Systems. With this indicator, conclusions can be made from an installation, economy, environmental, performance and a risk point of view. A technical and economic HP model shows the dependence of energy efficiency problems in HP systems. To reduce the complexity of the HP model, only the important factors for efficiency dependencies are used. Dynamic and static situations with HP´s and their efficiency are considered. With the latest data from field tests of HP Systems and the practical experience over the last 10 years, this information will be compared with one of the latest simulation programs with the help of two practical geothermal HP system calculations. With the result of the gathered empirical data, it allows for a better estimate of the HP system efficiency, their economic costs and benefits and their environmental impact.

Hybrid geothermal heat pumps for cooling telecommunications data centers

Ground heat accumulation caused by imbalanced heating and cooling loads in a building can cause the heat-source temperature to increase as the operating age of a geothermal heat pump (GHP) system increases. An alternative system to improve upon this situation is the hybrid GHP system. This study reviews existing research on GHP systems and hybrid GHP systems, variable water flow (VWF) control, and coefficient of performance (COP) prediction. Generally, constant flow control is applied to the circulating pump to provide a flow rate according to the maximum load. The need for VWF control was identified because the hybrid GHP system is used mainly as a heating and cooling heat source system for partial loads rather than the entire building load. Previous studies on predicting the COPs of GHP systems developed prediction models by selecting input values based on mathematical models, collecting data through multiple measurement points, and utilizing data from production environments. The model can be limited by the field environment, and it is necessary to predict the COP using machine learning based on existing field monitoring data.

Multi-Building Systems Thermal and Energy Management via Geothermal Heat Pump

The availability of geothermal energy as a renewable source and the favorable performance of heat pump systems provide an opportunity to meet the increasing heating and cooling needs in the building energy sector. However, developing a thorough understanding of how geothermal energy is used and how it affects the building energy performance provides motivation for studies conducted based on actual monitoring. The objective of this study is to examine the energy performance of a geothermal heat pump (GHP) system by means of monitoring the demand and consumption of electricity during heating and cooling operation modes in a commercial building. The literature review and several aspects of designing the particular GHP system related to enhancement of energy efficiency are discussed. The characteristic performance and results from actual monitoring of electrical energy demand and consumption of a GHP system are examined. It is observed that the need for cooling of the interior zones of the building r...

Geothermal source heat pump (GSHP) systems as renewable energy systems are being more frequently installed as part of the zero-energy building drive. However, in South Korea, where a large amount of heating load can be required, maintaining high system performance by using only a GSHP is difficult owing to the gradual degradation of its thermal performance. The performance of a solar-assisted GSHP system was therefore experimentally analyzed and compared with a GSHP-only system. The results showed that the heating coefficient of performance of the GSHP-only operation was 5.4, while that of the solar-assisted GSHP operation was 7.0. In the case of the GSHP-only system, the maximum temperature of the heat pump water supply on the heat source side was initially 13.1 °C, but this rapidly decreased to 11.4 °C during operation. For the solar-assisted GSHP system, the temperature of the water supply to the heat source side of the heat pump was controlled at 15–20.9 °C, and the power consumption for system operation was reduced by about 20% compared with that for the GSHP-only system. Much higher temperatures could be supplied when solar heat is used instead of ground heat, as solar heat contributes to the performance improvement of the heat pump system.

Numerical simulations were performed with a non-isothermal multi-phase reactive geochemical transport code, TOUGHREACT for predicting changes in temperature, permeability, porosity, and injectivity resulting from a long term operation of a geothermal heat-pump (GHP) system. A one-dimensional model was developed to simulate a GHP system for a potential geothermal reservoir with down-hole water temperature of 200°C. The GHP system was developed for (1) an open-loop system with a set of extraction and injection wells 600 meter apart, and (2) a closed-loop system with a heat exchanger. The same ground water was either injected into the ground through the injection well of the open-loop system or placed in the heat exchanger in the closed-loop system. Injecting water temperature (65°C or 35°C), pressure (+2MPa or +5MPa), chemical composition, and well casing (stainless stell or PVC) for the closed-loop system were varied. The feedback effects of changes in permeability and porosity resulting from mineral dissolution or precipitation on liquid injectivity and heat extractability were evaluated. The results showed that the impacts of the mineral precipitation on liquid injectivity and heat extractability were significant in the open-loop system than in the closed-loop system. This study also showed the injecting water temperature and well casing material would not be significant to improve the performance of a closed-loop GHP system. For the comprehensive evaluation of a GHP system performance, a system-level modeling considering economic and technical aspects was suggested.

Geothermal heat pump (GHP) systems are known for their higher energy efficiency, lowermaintenance, and lower environmental impact compared to conventional heating systems, but theirdisadvantage is higher capital cost. The objective of this study is to examine the feasibility ofgreenhouse heating with GHP systems. Both closed- and open-loop systems are examined at fourlocations across the U.S. and a net present value analysis is conducted for a 20-year life-cycle forvarious GHP base-load fractions. Results show that it is only under situations of relatively lowgeothermal loop installation costs and/or relatively high natural gas costs that some portion of agreenhouse could be economically heated with a closed-loop GHP system. Open-loop GHP systemsshow considerably more favorable economics than closed-loop systems. Of course, open-loopsystems would need to be sited at locations with sufficient ground water supply.

A simulation study on the performance of the solar and geothermal hybrid heat pump system by using R22 was carried out with a variation of operating conditions. The system was consisted of solar system (concentric evacuated tube solar collector, heat storage tank) and geothermal heat pump system (double pipe heat exchanger, electric expansion valve and compressor). As a result, the heating capacity is linearly decreased from 13.2 kW to 11 kW as the heat pump operating temperature increases from 40 o C to 48 o C. Besides, the heating COP decreases by 13.6% from 4.4 to 3.8 when the ground temperature raises 13 o C to 17 o C. The heating capacity is increased by 4.7% from 11.5 kW to 12.2 kW and the heating COP rises by 19% from 4.7 to 5.6.

An experimental geothermal heat pump system for space cooling was installed in Kamphaengphet, Thailand in 2006 and used for 17 months. Temeprature changes in the subsurface heat exchange tube and its surroundings were monitored to evaluate subsurface thermal properties and short- and long-term effects of operation of the system. Subsurface temperuatre increase due to the system operation recovered in few days and no long-term effect was observed after a year of operation. Room and atmospheric temperatures and electricity consumprion of the system were also measured through the period. Temperatures and flow rates of primary and secondary fluids were measured as well. As a result, a system COP (coefficient of performance) of around 3 was obtained for its stable operation period. The results of temperature measurements and calculation of system performances is presented in this paper.