Long-Term Monitoring of a Campus-Scale Geothermal Heat Pump System Using Distributed Temperature Sensing

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.

The installation and operation of geothermal systems increased due to the expectation of good cooling and heating performance due to stable heat source temperatures. In actual geothermal system operations, heat source temperature rises or falls due to an imbalance of heating and cooling energy usage. Problems of source side temperature result in reduced geothermal system performance. The purpose of this study is to develop hybrid geothermal system operation technology to stabilize temperature and improve system performance by utilizing auxiliary heat source system. The auxiliary heat source system is operated by comparing the performance when operating the geothermal heat pump system alone and the performance when operating the hybrid geothermal heat pump system. The performance of a hybrid geothermal system is determined by the circulating water temperature of the geothermal system and the circulating water temperature of the auxiliary heat source system. Hybrid geothermal heat pump system performance is predicted through numerical analysis and collection of hybrid geothermal system performance data at various temperature ranges through field test. An operating method was developed using the predicted performance as the changeover operating point of the hybrid geothermal heat pump system. When applying the development and operation technology, it handled about 11% more load than the existing geothermal system operation. The addition of an auxiliary heat source increases the initial investment cost compared to the existing geothermal system, but decreases energy consumption, confirming that the initial investment cost of 15.3 years is recovered.

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.

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.

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.

Hybrid geothermal heat pumps for cooling telecommunications data centers

Design and optimization of the U-shaped well geothermal systems for heat production performance: A case study from Huangling, China

Geothermal heat pumps (GHPs) have been shown to have a number of benefits over other technologies used to heat and cool buildings and provide hot water, combining high levels of occupant comfort with low operating and maintenance costs. Public facilities represent an increasingly important market for GHPs, and schools are a particularly good application, given the large land area that normally surrounds them. Nevertheless, some barriers remain to the increased use of GHPs in institutional and commercial applications. First, because GHPs are perceived as having higher installation costs than other space conditioning technologies, they are sometimes not considered as an option in feasibility studies. When they are considered, it can be difficult to compile the information required to compare them with other technologies. For example, a life cycle cost analysis requires estimates of installation costs and annually recurring energy and maintenance costs. But most cost estimators are unfamiliar with GHP technology, and no published GHP construction cost estimating guide is available. For this reason, estimates of installed costs tend to be very conservative, furthering the perception that GHPs are more costly than other technologies. Because GHP systems are not widely represented in the various softwares used by engineers to predict building energy use, it is also difficult to estimate the annual energy use of a building having GHP systems. Very little published data is available on expected maintenance costs either. Because of this lack of information, developing an accurate estimate of the life cycle cost of a GHP system requires experience and expertise that are not available in all institutions or in all areas of the country. In 1998, Oak Ridge National Laboratory (ORNL) entered into an agreement with the Lincoln, Nebraska, Public School District and Lincoln Electric Service, the local electric utility in the Lincoln area, to study four new, identical elementary schools built in the district that are served by GHPs. ORNL was provided with complete as-built construction plans for the schools and associated equipment, access to original design calculations and cost estimates, extensive equipment operating data [both from the buildings' energy management systems (EMSs) and from utility meters], and access to the school district's complete maintenance record database, not only for the four GHP schools, but for the other schools in the district using conventional space conditioning equipment. Using this information, we were able to reproduce the process used by the Lincoln school district and the consulting engineering firm to select GHPs over other options to provide space conditioning for the four schools. The objective was to determine whether this decision was the correct one, or whether some other technology would have been more cost-effective. An additional objective was to identify all of the factors that make it difficult for building owners and their engineers to consider GHPs in their projects so that ongoing programs can remove these impediments over time.

We examine the problem of efficiency in both air-source and geothermal heat pumps in regions with low ambient air temperature, and the advantage of using a combination of both systems in one equipment. Both geothermal and air heat pumps have their advantages and disadvantages. Geothermal heat pumps are more expensive to install and, in colder climates, experience a progressive decrease in efficiency with constant use during the winter season because of chilling of the ground adjacent to geothermal heat exchangers during heat extraction. Air-source heat pumps are less expensive to install and experience a decrease in efficiency as ambient temperature is getting lower. A numerical model simulation was conducted using the program “INSOLAR.GSHP.12” for a 200 sq.m. house in Moscow. The model tested the efficiency of combined use of a ground heat pump at ambient temperatures below -10°C, and air heat pump for ambient temperatures above -10°C. The results were compared to simulation of using only a geothermal heat pump. The results show a 13.3% reduction in energy consumption using the combined ground and air heat pumps over the energy requirement of using only the geothermal heat pump.

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.

This study investigates the thermal performance of closed-loop advanced geothermal systems under the influence of groundwater flow in deep sedimentary formations. By integrating advective heat transport into a 3D numerical model, we evaluate the combined effects of groundwater flow in deep sedimentary aquifers and geothermal heat transport and extraction using U-shaped closed-loop geothermal wells. The model is developed to simulate heat-transfer dynamics, incorporating well design with realistic casing and cement layers, layered geology with associated petrophysical uncertainties, and varying operational conditions. As study area, we selected the Midyan basin in Saudi Arabia, characterized by thick sedimentary formations and an elevated geothermal gradient. The results show that the advective heat transfer, induced by groundwater flow, significantly enhances system efficiency. Improvement in thermal power output increases by up to 27% over a 40-year operational period compared to conduction-only scenarios, particularly if groundwater flow is perpendicular to the lateral section of the wellbore. Sensitivity analysis reveals that geothermal gradient and reservoir depth are the most impactful geological parameters. Operational parameters such as injection rates (10—100 kg/s) and injection temperatures (25—45 °C) can be adjusted to further optimize the system performance, with 30 kg/s identified as the optimal injection rate that balances energy extraction and parasitic pumping losses. Well-design parameters, including diameters (0.114–0.245 m) and lateral length (0.5–3 km), also play a critical role, with longer lateral sections and larger diameters increasing the overall power output. These findings show the potential of U-shaped closed-loop advanced geothermal systems in sedimentary basins with dynamic groundwater flow and provide insights for optimizing geothermal energy systems in similar geological settings.

Geothermal heat pump (GHP) system for heating and cooling purposes may be powerful alternative to reduce energy consumption and to contribute to environmental issues. Its intensive utilization may reduce emissions of CO2 and other toxic gases by replacing fossil fuel boiler into GHP. It may also greatly contribute to solve the problem of urban heat island (UHI) phenomenon. Combination of high performance of GHP and reduction of UHI result in a few percent of saving electricity for air conditioner in highly populated cities. GHP is generally not appropriate for space cooling in tropical regions. Since subsurface temperature is generally higher than year-average atmospheric temperature and atmospheric temperature is almost constant through a year in tropics, underground may not be appropriate as “cold heat-source”. However, according to the result of groundwater temperature survey in the Chao-Phraya plain, Thailand, subsurface temperature is lower than daytime atmospheric temperature for 5K or more over four months in several cities (Yasukawa et al., 2009, in this issue). Thus underground may be used as cold heatsource even in parts of tropical regions. A GHP system, borehole heat exchanger, heatpump and fan-coil, was installed for room cooling in Kamphaengphet, Thailand. Temperatures in the subsurface heat exchange tube and of secondary fluid, etc., were monitored during operation of the system. The results of temperature measurements and calculation of system performances are introduced in this paper. Capacity of the subsurface heat exchange system is presented in Tenma et al. (2009) in this issue. Although shallow subsurface temperature in Kamphaengphet is rather high and not quite suitable for a cooling system, the experimental results can be applied for other regions. Thus places more suitable for GHP system will be found as a result of this experiment and regional groundwater survey.

The National Certification Standard for the Geothermal Heat Pump Industry adds to the understanding of the barriers to rapid growth of the geothermal heat pump (GHP) industry by bringing together for the first time an analysis of the roles and responsibilities of each of the individual job tasks involved in the design and installation of GHP systems. The standard addresses applicable qualifications for all primary personnel involved in the design, installation, commissioning, operation and maintenance of GHP systems, including their knowledge, skills and abilities. The resulting standard serves as a foundation for subsequent development of curriculum, training and certification programs, which are not included in the scope of this project, but are briefly addressed in the standard to describe ways in which the standard developed in this project may form a foundation to support further progress in accomplishing those other efforts. Follow-on efforts may use the standard developed in this project to improve the technical effectiveness and economic feasibility of curriculum development and training programs for GHP industry personnel, by providing a more complete and objective assessment of the individual job tasks necessary for successful implementation of GHP systems. When incorporated into future certification programs for GHP personnel, the standardmore » will facilitate increased consumer confidence in GHP technology, reduce the potential for improperly installed GHP systems, and assure GHP system quality and performance, all of which benefit the public through improved energy efficiency and mitigated environmental impacts of the heating and cooling of homes and businesses.« less

Modeling and performance evaluation of ground source (geothermal) heat pump systems

Simple SummaryA geothermal heat pump (GHP) was installed in a pig house, and production performance, housing environment, energy efficiency, noxious and carbon dioxide (CO2) gas emissions, and economics were compared between GHP and the control (conventional heating). The CO2 gas emission, usage, and cost of electricity were reduced in the GHP-installed pig house. The GHP also maintained the inside temperature of the pig house more effectively. Furthermore, the concentration of noxious gas (NH3) was also lower during the growing and finishing phase in the GHP-installed pig house. Therefore, the results indicate that the GHP system can be used for sustainable pig production and food security as a climate-friendly renewable energy source for livestock.This study examined the effects of a heating system using a ground source geothermal heat pump (GHP). A GHP was installed in a pig house, and a comparative analysis was performed between the GHP and the control (conventional heating system) in terms of the production performance, housing environment, noxious gas emissions, electricity consumption, and economics. The geothermal system performance index, such as the coefficient of performance (COP), inlet, and outlet temperature, were also evaluated. The outflow temperature during each period (weaning, growing, and finishing) was significantly higher than the inflow temperature in all three components of the GHP system. Similarly, the average internal temperature of the GHP-connected pig house was increased (p < 0.05) during each period. The carbon dioxide (CO2) concentration, electricity usage, and cost of electricity during the 16-week experimental period were reduced significantly in the GHP system relative to the control. The concentrations of ammonia (NH3) during the growing and finishing period and the concentrations of formaldehyde during the weaning phase were also lower in the GHP-installed pig house (p < 0.05). These results indicate that the GHP system can be used as an environmentally friendly renewable energy source in pig houses for sustainable pig production without harming the growth performance.