Residential Heat Pump Systems Research Articles

Estimating electric power consumption of in-situ residential heat pump systems: A data-driven approach

International Energy Agency predicts that the global number of installed heat pumps (HP) will increase from 180 million in 2020 to approximately 600 million by 2030, covering 20% of buildings heating needs. Electric power consumption is one of the main key performance indicators for the heat pump systems from techno-economic perspective. However a common issue prevalent in many existing heat pumps is the lack of electric power measurement. The modern installations might be equipped with electric power measurement sensors but this comes at a higher system cost for the manufacturers and end-users. The primary objective of this work is to propose a virtual measurement for estimating power consumption, thereby eliminating the need for field measurement of power for heat pumps. To achieve the objective, a data-driven approach is proposed. Firstly, the in-situ data is preprocessed through data merging, cleaning, and normalization. Then, input features are pre-selected using Spearman correlation coefficients, and further refined by addressing multicollinearity problem. Following this, Extreme Gradient Boosting (XGBoost) models and polynomial models are developed by considering different features as inputs. All models are finally validated against the in-situ data from multi-units of ground source heat pump (GSHP) and air source heat pump (ASHP) installations. The results showed that the electric power consumption of GSHP can be estimated with high accuracy (99% for R2, 10 W for MAE, and 1% for MAPE) through generic data-driven models using only four easy-to-measure input features. Taking three input features as inputs for ASHP generic model, the accuracy can be reached to 83% for R2, 125 W for MAE, and 9% for MAPE. The method presented in this paper can be applied to estimate power consumption of millions of heat pumps and consequently add a significant value as well as provide different types of services, such as cost-saving benefits for manufacturers and end-users, flexibility services for aggregators and electricity grids.

Comparisons of Load-Based and AHRI 210/240 Testing and Rating for Residential Heat Pumps

The current testing and rating procedure for residential air conditioners and heat pumps is based on a steady-state performance measurement approach with a degradation coefficient to account for cycling losses at part-load conditions. Test equipment performance is measured under various ambient conditions with varying compressor and fan speeds, and the results are propagated through a temperature-bin method to estimate seasonal performance. Although the current rating approach offers a standardized performance metric for comparing the relative performances of different equipment, it involves disabling the native controls and, as a result, does not consider the impact of integrated controls for test units and their dynamic interactions with representative building loads. As an alternative, a load-based testing methodology (CSA EXP07) has been developed in which the dynamic performance of equipment is measured in a test facility by allowing it to respond to a simulated virtual building model. This study compares the steady-state and dynamic load-based performance measurement methodologies for use on a 5-ton residential heat pump system in order to understand the differences and their significance for the next-generation rating procedure. The differences in the two test methodologies' performance evaluation results are discussed with a causal analysis of the observed differences.

Evaluating Long-Term Performance of a Residential Ground-Source Heat Pump System under Climate Change in Cold and Warm Cities of Japan

A residential ground-source heat pump system often requires a long payback time to recover the capital cost. Long-term uncertainty in such a system’s performance increases as the climate changes. This study compares 20-years hourly heating/cooling demands of a typical residence in the present (2000–2020) and in the future (2076–2095) for two locations in Japan. This study also calculated soil temperatures as heat sources through 1D heat-transfer simulation based on the A1B climate scenario in the Intergovernmental Panel on Climate Change’s Special Report. System performance and simple payback times were compared in one cold and one warm city in Japan (Sapporo and Tokyo, respectively). Soil temperatures at a middle depth of a borehole heat exchanger were predicted to increase in the future by ~1 °C, with insignificant effects on a borehole heat exchanger. Seasonal performance factors increased in Sapporo because thermal demands would be kept even in the future, but decreased in Tokyo, which has a higher ratio of the energy used in operating the system in cooling mode compared with its small heating demand. The simple payback time was estimated at 16.2 and >20 years in Sapporo and Tokyo, respectively, both in the present and future, with the constant energy prices. If oil and gas prices doubled, the payback time would be halved in Sapporo to 8.4 years but remain around 20 years or more in Tokyo.

Modelling and optimization of domestic thermal energy storage based heat pump system for geothermal district heating

In this study, a new residential heat pump system was designed for domestic use in the geothermal district heating system (GDHS). A heat pump system was integrated into the substations of the residences with this aim. The heat pump system was formed by replacing the conventional evaporator with thermal energy storage (TES) unit. In this regard, a shell and tube latent heat TES system was used and designed for the peak loads. 66 different systems were parametrically formed and analyzed thermodynamically. The observed cases were later evaluated from economical and environmental points of view. Finally, the most appropriate system was determined by a multi-criteria decision-making analysis named efficiency analysis technique with output satisficing (EATWOS). It was concluded that it is available to obtain an investable design with an NPV value of 6.35 million $, exergy efficiency of 15.24% and CO2 reduction of 1435.32 ktons per year.

Non-condensable gas in the refrigerant of air-source heat pumps: Interactions between detection features, charge level, and temperature

Non-condensable gas (NC) can be introduced into a vapor compression refrigeration cycle through improper installation or service, and decrease system efficiency, increase burden on the compressor, and reduce the compressor life span. Therefore, detecting this fault early can prevent energy waste and prolong the operating life of the system. However, diagnostic methods are not widely available, and neither are methods to quantify NC amounts based on easily measured variables. Therefore, an experimental test apparatus was built to provide data to improve understanding of NC-refrigerant interactions. Two NC fault intensities (50%, 100%), each at four charge levels (70%, 80%, 100%, 120%), were tested under five different ambient temperatures (0-40°C). Dry nitrogen gas was used for the NC. The results showed that the theoretical estimation method is inaccurate. The trends of the results from experimental tests are consistent with those from theoretical calculations, but the thresholds obtained from experimental tests are larger than those from theoretical calculations. This paper explains these differences, and provides a model to quantify the NC fault intensity using easily-measured variables. The specific model is applicable to typical residential air-conditioner and heat pump systems that use R410A refrigerant, but the general findings are applicable to other refrigerants.

Soft faults in residential heat pumps: Possibility of evaluation via on-field measurements and related degradation of performance

The growth of Internet of Things (IoT) technologies is leading to new opportunities in the heat pump sector for residential air conditioning, in which fault detection and diagnosis (FDD) techniques are being developed from measured data to better manage maintenance operations. This paper presents a physics-based digital model simulating the effects of soft faults (refrigerant leakages and condenser/evaporator fouling) concurring with different intensities on a residential heat pump system. Firstly, their effect on cooling capacity and COP has been analysed. Then, each thermodynamic cycle (as a sequence of measured pressures and temperatures) uniquely related to a peculiar combination of fault intensities is determined. In this way, the field of faults which can be uniquely diagnosed and evaluated has been calculated, and the interrelationship between this field and the uncertainty of the measurements has been demonstrated. The results are encouraging, since common instruments available on the market may detect penalizations of the energetic performance as small as 5%.

Clustering based on dynamic time warping to extract typical daily patterns from long-term operation data of a ground source heat pump system

While clustering has been commonly used to profile the building electricity consumption data, its application to HVAC system data is relatively less. Based on the operation data of a residential ground source heat pump (GSHP) system, a pre-processing procedure was set up, including acquisition, cleaning, missing-data fill-in, and standardization. Then hierarchical clustering was used, based on the dynamic time warping (DTW) distance calculation method. A new index, the sum of squares of errors based on DTW, was used to determine the best cluster number. The patterns were extracted based on clustering results.The heat exchange on the user-side during one cooling season was processed as a case study. We obtained 5 valid clusters and extracted patterns from each. For the studied case, the result based on the DTW method yields a better homogeneity compared to the Euclidean method. The method is then applied to a five-year operation data, where 9 and 6 patterns were obtained for the cooling and heating seasons, respectively. They mainly differed in shape, and the cooling patterns fluctuate more. Overall, clustering and pattern extraction can reduce the data dimension, and provide a data-driven view of how the system supplies the cooling and heating.

Assessing the performance limits of a variable-speed residential heat pump system

Most of the ducted split-type heat pump systems in the world feature fixed-speed compressors and fans. To meet forthcoming minimum energy rating requirements, reduce operational costs of the heat pump, and increase environmental sustainability, the efficiency of heat pump systems must be improved. Variable-speed equipment offers significant advantages for load modulation and has the ability to increase the seasonal performance significantly. Additionally, novel electrical motor technologies, such as permanent magnet (PM) motors can reduce the power consumption of the drives by up to 25-55% compared to the widely used permanent split capacitor (PSC) motor.In this study, a ducted fixed-speed heat pump system with a cooling capacity of 17.6 kW and a seasonal coefficient of performance (SCOP) rating of 4.11 is analyzed to quantify the theoretical performance limits that could be obtained by increasing the motor efficiency of the condenser fan, the evaporator fan and the compressor. Furthermore, the performance increase by replacing the fixed-speed components with variable-speed equipment is evaluated. A detailed charge-sensitive system simulation model that was previously developed by the authors and validated using experimental data obtained with the same unit was employed to carry out parametric studies to evaluate the impact of variable-speed compressor and indoor/outdoor fans on the SCOP rating.The study showed a 0.9% improvement of SCOP with every percentage increase of compressor motor efficiency. The dependence of the evaporator fan and condenser fan motor efficiency on SCOP was lower, but considering the generally low motor efficiencies of these components, a noticeable efficiency gain can be achieved. In variable-speed equipment, the motor efficiency of the component at minimum operational point was the significant factor on SCOP. The motor efficiency at intermediate and maximum speed had only marginal effects on the SCOP. This showed the importance of equipment with high motor efficiencies at low speeds for ducted split-system heat pumps. The change of the fixed-speed system to a fully variable-speed heat pump resulted in a high gain of SCOP, proving the superiority of a variable-speed system. Overall, the model predicted an SCOP gain of 35% when changing the system to a fully variable system with state-of-the-art high efficient motors.

Life cycle analysis (LCA) of residential ground source heat pump systems: A comparative analysis of energy efficiency in New Jersey

Developing clean energy policy supported by science-based research is essential for mitigating the hazards and risks associated with climate change. This study aims to explore ground source heat pump (GSHP) systems, an underutilized energy efficiency technology, as a means to promote emission reductions in the buildings sector. GSHP systems have the capacity to decrease the environmental impact of building space heating and cooling needs through fossil fuel displacement and higher energy efficiencies than baseline technologies. Although the benefits and engineering applications of this technology are established, it has not been adopted at scale, thus limiting potential emission reductions. Furthermore, energy economics can vary significantly across geographies which makes quantifying benefits of mitigation action challenging in regions with diverse electricity generator types and building heating fuels. This study uses life cycle analysis (LCA) to evaluate mid- and long-term sustainability metric impacts of GSHP systems operating in New Jersey, US, to assess the technology’s effectiveness while operating within the state’s electricity generating fuel mix. Results show that the state is a suitable location for residential GSHP systems, and that an electricity generation fuel mix with increased use of renewable energy sources would enhance the technology’s efficiency and decrease associated emissions even further. In addition, we compared GSHP technology to that of other common space heating/cooling methods and found that use of GSHP systems in conjunction with electric-based heating/cooling provides a substantial improvement in terms of environmental emissions. When compared to oil and gas-based heating, GSHP systems provided some improvement on mid-point impact factors and considerable improvement on end-point impact factors, most notably the economic improvement associated with decreasing dependence on fossil fuels. These findings suggest that GSHP systems should be considered for reducing emissions and end-use energy consumption and support new clean energy policies in the state.

Numerical modeling of an outdoor unit heat exchanger for residential heat pump systems with nonuniform airflow and refrigerant distribution

Multirow finned tube heat exchangers have been extensively used as an outdoor unit in heat pump applications. Several factors, including nonuniform airflow distribution, refrigerant circuitry arrangement, fin and tube configurations, and operating conditions, have a significant influence on its thermohydraulic performance. For accurate outdoor unit heat exchanger modeling and analysis, developing a robust and experimentally validated numerical model reflecting the influence of realistic nonuniform airflow and refrigerant distribution is necessary. This paper presents a general-purpose numerical model, implemented in MATLAB, for a multirow finned tube heat exchanger using a tube-by-tube modeling approach based on the log mean enthalpy difference method. State-of-the-art heat transfer and pressure drop correlations are used for each refrigerant-side's flow regime and airside fin configuration. An alternative iteration loop is also incorporated to solve the complex circuitry of the heat exchanger under wet conditions. Simulation results of the current model yield consistent and more real heat transfer, pressure drop, and temperature contours using nonuniform airflow velocity profiles than those of the simplified models that assumed uniform airflow. Therefore, higher accuracy of the performance evaluation for complex refrigerant circuitry was achieved. Furthermore, current model is able to identify the exit vapor quality that allows proper selection of tubes and mass flow rates to avoid unnecessary superheat or sub cooling. The model is also validated with available experimental data, and the maximum error is within ±10.0%.

Data-driven modeling of residential air source heat pump system for space heating

Air source heat pump systems must operate efficiently during the winter to ensure that energy-saving targets are met and occupants of residential and commercial buildings have acceptable thermal comfort. Investigation on the behavior of air source heat pump systems based on the analysis of real data is important to improve the system performance and attain optimum performance during winter. This will assist governments and industry sectors in formulating energy policies and improving this technology efficiently. Currently, there is no available studies relating the use of data-driven models for improving air source heat pump system. Thus, a large experimental dataset was obtained from four real projects in Beijing, and a hybrid and general model (ambient temperature –20 °C to + 17 °C) coupling various data-driven models was established. A methodology was developed to assess and detect outliers in the dataset that cause incorrect results for the developed model. After removing the outliers, a regression analysis revealed an excellent agreement between almost 8000 experimental data samples and the predictions, with a coefficient of determination of 0.87. Two scenarios were considered for improving and optimizing the thermal performance of air source heat pump systems using the developed predictive model. A growth of 8.18% was observed in the coefficient of performance compared with that of the real operation when the indoor temperature was 18–20 °C. The total system performance increased by an average of 15.93% when the indoor temperature was set between 18 and 20 °C and the rated capacity increased from 11.5 to 12 kW.

An experimental investigation on frosting characteristics of a microchannel outdoor heat exchanger in an air conditioning heat pump system for electric vehicles

To increase the driving range of electric vehicles in cold climate, air conditioning heat pump (ACHP) system is supposed to be the most effective solution. Working near 0°C with high humidity, the microchannel outdoor heat exchanger (OHX) in system would experience badly frosting process, like traditional residential heat pump system. It would lead to a significant reduction of system performance without defrosting in time. In this article, experimental investigation has been implemented on the frosting process of ACHP system of electric vehicles which is with a microchannel OHX. The phenomenon of frosting distribution was observed, the frosted part on surface shows uneven with various flows paths. The typical frosting characteristics of an outdoor microchannel heat exchanger were also obtained. In a self-designed three-heat exchanger ACHP system, the inlet and outlet refrigerant temperature of OHX as well as the outlet air temperature of system decrease with increasing frosting coverage rate. The frosting phenomenon was analyzed with variation of ambient temperature and humidity. System influence by frosting was also studied with under different ambient conditions. When OHX begins to frost, the heating capacity reduction of system under different ambient conditions were both increased but the differences in the coefficient of performance (COP) variations under different ambient conditions were small as frosting progressed.

Analytical and numerical sizing of phase change material thickness for rectangular encapsulations in hybrid thermal storage tanks for residential heat pump systems

Thermal energy storage is essential to the operation of many systems. It plays a vital role in many renewable and CO2-reducing technologies which have a mismatch in time between when thermal energy is available and required. Water is the most commonly used thermal storage medium in many applications, however, for systems with a small temperature operating range, large storage volumes may be required since the energy storage capacity of water is proportional to the temperature range. In contrast, phase change materials (PCMs) can maintain high energy capacity under limited temperature conditions, but they typically have low thermal conductivities which results in slow melting/solidification rates. As such, careful design of the encapsulation geometry is required to take advantage of phase change thermal storage. Systems using phase change materials must ensure complete melting, and the encapsulation thickness must be designed according the system needs.Models of hybrid storage tanks employing both water and PCM are investigated, with PCM encapsulations embedded in water. This study uses a novel application of analytical formulations of 1-D melting to size rectangular PCM encapsulation to match the requirements of a residential heat pump system. With boundary conditions that reflect the heat pump and storage characteristics, the proposed analytical solution links encapsulation thickness to system requirements. The analytical formulation is derived for encapsulation thickness in terms of heat pump rating, temperature differential, storage material, and storage volume. The solution was verified through system-level numerical simulations using TRNSYS and an in-house enthalpy-porosity modeling tools detailed in the paper. The verifications have shown a good agreement, and the melt thickness predictions were within 4% between both models. The study proposes using the methodology as a standard for designing hybrid water-phase change material thermal storage for heat pumps, which can be expanded to various PCM geometries and thermal systems.

Life cycle cost analysis of different residential heat pump systems

Nowadays, the application of air-source heat pumps for heating and cooling in residential buildings has been increased significantly. The main occasion for this is the accessibility of a heat source for these devices - the external air. Nevertheless, the increase of the energy efficiency of the air source heat pump systems is a difficult design problem because their capacity and performance are a function of the dynamically changing parameters of the outdoor air. Because of that, the main aim of this study is to develop an approach for choosing a structural scheme of an air-to-water heat pump system under specific climatic conditions. The considered systems are monovalent, bivalent-parallel and bivalent-alternative heat pump systems. In the current paper is conducted a dynamic energy modeling of heating and cooling demand of a typical residential building situated in Varna, Bulgaria and applying the bin temperature data. It is assessed the effect of the heat pump capacity over the annual and seasonal energy performance of the heat pump systems. It is established the effect of the bivalent temperature, cut-off temperature and on-off cycles duration on rates of the criteria for techno-economic assessment. The seasonal coefficient of performance (SCOP), seasonal energy efficiency rate (SEER) and life cycle costs (LCC) of the analyzed heat pump systems are adopted as assessment parameters.

Load Shifting Assessment of Residential Heat Pump System in Japan

With the economic growth and increasing requirement of indoor thermal comfort, the load of building sector presents a greater variability.This paper aims at analyzing the energy consumption characteristics and influencing factors of the residential heat pump system. Firstly, we selected residential households as investigated objective in Kitakyushu, Japan, and compared the energy saving performances of heat supply systems between heat pump and natural gas boiler. The results were based on real measured residential load during winter period, and calculated the cost saving performance of residential heat pump system compared with traditional natural gas boiler. We also did a survey of residential occupation behavior for the 12 selected residential customers. The result indicated that there was low relationship between power consumption and occupation hours, and the number of family members had a significant impact on the power consumption. The results indicate that residential heat pump system presented promising energy saving and cost reduction potential.

Seasonal Performance Investigation for Residential Heat Pump System with Different Outdoor Heat Exchanger Designs

A finned tube heat exchanger is a key component used as a condenser or an evaporator in residential air-conditioning (AC) and heat pump systems. The overall cycle performance of these systems is significantly affected by the heat exchanger’s geometric design. This study investigates outdoor heat exchanger designs with varying geometric parameters such as the fin pitch, number of tube rows, and tube length, and their effect on system performance based on seasonal energy efficiency ratio (SEER) and seasonal coefficient of performance (SCOP). Air face velocity profiles for each operating condition along the outdoor heat exchangers are determined using CFD, with subsequent cycle simulations for 10 different operating conditions. Results have been validated with the available experimental data. The number of tube rows, fin pitch, and length of tube have been varied from 2–10, 1.4–2.5 mm, and 800–2800 mm respectively. The numerical results reveals that SEER increases 3.21% while SCOP increases 5.32% up to fourth and fifth tube row respectively and remain unaffected thereafter. Similarly, SEER increases by 3.55% as the tube length is increased from 800–1800 mm, while it increases only 0.67% for 1800–2800 mm and the maximum variation of 4.32% has been found for SCOP. Moreover, increasing the fin pitch reduces SEER and SCOP (except for fin pitch from 1.4 to 1.8 mm). Finally, the performance of the system with four different fin configurations have also been investigated and it has been found that slit fins are more effective.

Numerical study of the electrical load shift capability of a ground source heat pump system with phase change thermal storage

The inclusion of thermal storage into a residential heat pump system provides an opportunity for electrical load shifting in order to reduce peak electricity demand. To assess this potential, a detailed numerical system model for a ground-source heat pump coupled with thermal storage was developed for residential heating applications. Water-based thermal storage and hybrid storage containing water and phase change materials (PCMs) were considered. The amount of thermal buffering needed to shift the heat pump operation to off peak electricity periods was numerically assessed for a house of 180 m2 floor area in Toronto, Ontario, Canada. A very cold day ambient profile was considered as the extreme case to reach the study conclusions. Results indicated that total electrical load shift to off-peak hours was achieved by a 2.5 m3 water tank or a 1 m3 hybrid tank containing 50% PCM by volume. This implies around 65% reduction in storage volume without compromising the space heating capability. This is attributed to the higher storage capacity offered by the hybrid system when the temperature operating range is limited by heat pump operation. The influence of operating temperature ranges and packing ratio was presented. Lower operating ranges and higher packing ratios lead to better thermal buffering of the hybrid system at smaller storage volumes. However, careful choice of the PCM encapsulation geometry is needed to guarantee complete melting/solidification during the charging/discharging period.

Linear model predictive control for the reduction of auxiliary electric heating in residential self-assisted ground-source heat pump systems

This article presents a linear model predictive control strategy for the operation of a “self-assisted” ground-source heat pump (GSHP) to reduce auxiliary electric heating in residential applications equipped with undersized boreholes. The self-assisted configuration uses an electric heating element at the heat-pump outlet to inject heat into the bore field when approaching peak power demand. A linear control-oriented model is proposed to account for both the source-side and load-side GSHP dynamics. The ground heat transfer is predicted using the bore field’s ground-to-fluid thermal response factor, thus allowing for any bore field configuration while accounting for thermal capacity effects. Real historic ambient temperature forecasts and their corresponding historic recorded ambient temperatures from Montreal are used in this article. The coefficient of performance (COP) nonlinearity is circumvented with an iterative approach. A Kalman filter is used to dynamically adjust the bias on the predicted returning fluid temperature. On a borehole undersized by 15%, the control strategy reduces auxiliary electric heating by 96% over 20 years at the cost of a 5.53% increase in total energy consumption. Due to the occasional simultaneous heat injection and auxiliary heating, the yearly peak power demand is increased.

Performance analysis of low GWP refrigerants mixture as a substitute for R410A in residential air conditioner in tropical region

The issue of global warming has triggered more critical issues, and today’s refrigerants with high global warming potential (GWP) are facing the challenges of being phased out. According to 2014 Assessment Report of the Refrigeration, Air-Conditioning and Heat Pumps Technical Options Committee (RTOC Assessment Report 2014), the R410A has GWP of 2100 and is widely used in residential air-conditioning and heat pump systems. Currently, in the market, the potential refrigerant that can be used to replace R410A in the air-conditioning system is R32. The purpose of this project is to create a new refrigerant mixture using low GWP refrigerant as a base that can replace for R410A in an air-cooled split air conditioner. Simulation works have been developed using Refprop software to simulate the refrigeration cycle with the operating conditions of the air-cooled split air conditioner, in the tropical region. The chosen cycle was an ideal vapour compression cycle with the evaporating and condensing temperatures of 5 °C and 47 °C, respectively. Through this study, two potential refrigerants mixture was found to be suitable to replace the R410A. The two refrigerant mixtures, R32/R1234ze and R32/R600a, both based on R32, were found to have similar thermodynamic properties as the R410A. They were found to be able to produce the coefficient of performance (COP) very close to the R410A when used in an air-cooled split air-conditioning system. Hence, the use of this refrigerants will avoid significant modifications on the present air-conditioning system configurations. Refrigerant R32/R1234ze has the potential to reduce the GWP of R410A by 70 % while refrigerant R32/R600a by 73 %. At the end of the equipment lifespan, refrigerant R32/R1234ze would reduce the direct of Total Equivalent Warming Impact (TEWI) by 23 % while refrigerant R32/R600a by 20 %.in constructing both.

WITHDRAWN: Life-cycle assessment of various types of residential ground-coupled heat pump systems: Wisconsin, US case

Abstract Within the heating, ventilation, and air conditioning (HVAC) sectors, ground coupled heat pumps (GCHPs) offer a potentially economical, low-carbon energy approach to lowering of the global energy budget. This study investigates the performance of a conventional vertical GCHP configuration with three boreholes (VERT), a conventional horizontal GCHP (HORZ), an unconventionally deep (300 m) single borehole GCHP (SING) system, and a conventional split natural gas air conditioning unit (NGAC). This study also compares potential for reduced greenhouse gas (GHG) emissions via the GCHP systems in Wisconsin, USA, using a comprehensive “cradle-to-grave” life-cycle analysis (LCA), which is implemented using SimaPro. Assuming the current Wisconsin electrical grid of 5.5% renewables, heating and cooling loads of a 186 m2 residence, a coefficient of performance (COP) of 4 and a 25-year lifetime, an average of 272 metric ton CO2 equivalent emissions is calculated for SING. Top contributors are heat-exchanger operation (93.3%), borehole drilling (2.4%), and circulation pump operation (1.5%). This amounts to GHG emissions savings of 10% and 19% over VERT and HORZ GCHPs, respectively, and 27% over NGAC. Sensitivity analyses determine that a grid with renewables penetration of 50% could save 68% GHG emissions over natural gas. As the use of fossil fuel decreases and the grid becomes cleaner, GCHP systems become even more beneficial from the perspective of lifetime GHG emissions. A COP of 5 could further reduce GHG emissions by 38%, indicating that the COP is a significant factor of GCHP environmental impacts.