Air Source Heat Pump Research Articles

Performance study of air source heat pump system applying two types of distributors

Abstract Air source heat pump heating is the most effective way to solve heating problems, and gas-liquid two-phase refrigerant in the uniform distribution and pressure drop problem of finned heat exchanger branch tube are the main factors affecting the heat transfer ability. To study the effects of two types of manifolds applied in air-source heat pumps on the system performance and pressure drop when the system is in operation, an engineering-based test system for the actual operation of air-source heat pumps was constructed. The study shows that the difference between the venturi distributor and the rectifier nozzle distributor in the impact on the system performance is relatively small, while the rectifier nozzle distributor compared to the venturi distributor in the pressure drop on the effect is obvious. The evaporator pressure drop will be transferred to the distributor part of the reduction of pressure drop losses in the evaporator on the impact of heat transfer performance. This paper summarizes the performance study of two types of distributors applied to air source heat pumps, which provides a meaningful reference for similar studies.

Optimization of solar-air source heat pump hybrid heating system

Abstract In order to construct a versatile, complementary, low-carbon, clean, and efficient heating system, this study explores the potential of a solar-air source heat pump (SAHP) hybrid heating system. A simulation model is established in TRNSYS, and the particle swarm algorithm (PSO) and genetic algorithm (GA) from GENOPT and MATLAB are employed. With the aim of minimizing the annual cost, optimization is conducted on the key parameters and operational strategies of the system. Comparative analysis between the two algorithms reveals that PSO slightly outperforms in cost reduction, while GA exhibits a slight advantage in enhancing system performance. Significantly improved energy savings are achieved by appropriately reducing the rated heating capacity of the air source heat pump and increasing the volume of the water tank.

Performance evaluation of underground thermal storage integrated dual-source heat pump systems

The increasing demand for electricity stresses the existing electric grids. Buildings consume 73% of all U.S. electricity and are responsible for 30% of U.S. greenhouse gas emissions. Integrating thermal energy storage (TES) in building heating/cooling systems, which consume considerable electricity, can mitigate the challenges to electric grids. This study reports on a novel thermal energy storage device integrated heat pump system to reshape the building electricity demand profile while maintaining thermal comfort. The annual performance of the proposed system has been evaluated through a dynamic system simulation with high fidelity in the Modelica platform. The dynamic model of the novel hybrid component named ‘dual purpose underground thermal battery’ was developed and validated. It was then incorporated into the system model. Given a time-of-use tariff, a rule-based control strategy was designed to shift the electric demand and switch the heat pump source for a typical single-family house in different climate zones of the United States. The system performance of the new TES-integrated dual-source heat pump was compared with that of a conventional air-source heat pump system. The results indicate that the proposed system can reduce the annual HVAC electricity cost by up to 52% while saving 45.2% on electricity consumption. In the Northern areas, the annual peak load of the HVAC system can be reduced by 64.9%. However, this reduction is less in the Southern areas as the system’s higher efficiency in winter dominates the overall energy-saving potential.

The advantage of running a direct expansion CO2 heat pump with solar-and-air simultaneous heat sources: experimental and numerical investigation

Dual-source solar-air heat pumps represent a promising solution for overcoming the limitations associated with single-source utilization, thereby enhancing heat pump performance. However, running the heat pump by alternatively employing the more advantageous source requires the integration of a controller capable of continuously monitoring and predicting the heat pump's performance in response to dynamic environmental and operational variables. Even so, a selective alternate operation does not allow to get the maximum possible performance from the use of the two heat sources. A different approach to address this challenge is the simultaneous utilization of the two sources, by properly combining two evaporators in the CO2 circuit. This paper presents an experimental investigation of a dual-source heat pump using CO2 as refrigerant, which can operate in three different evaporation modes: air-mode (using a finned-coil evaporator), solar-mode (using a photovoltaic-thermal PV-T evaporator), and simultaneous-mode (using both the evaporators simultaneously). The novel solution presented here does not require to split the refrigerant flow rate between the two evaporators and at the same time it solves the problem of possible maldistribution at the inlet of the evaporators. Experimental data indicate that the heat pump operating in simultaneous-mode allows to increase the evaporation pressure and the coefficient of performance compared to operation in air-mode or solar-mode. The measurements have been employed for validating a model of the system, capable of predicting steady-state and dynamic performance under various environmental and operational conditions. Simulation results show that the simultaneous-mode operation can be outperformed by the solar-mode only at high irradiance and low air temperature, when the evaporation temperature gets higher than the air temperature. Finally, the impact of the number of PV-T collectors and solar irradiance on the heat pump performance has been simulated and discussed. On this regard, the simultaneous use of the two heat sources adds more flexibility to the system and its design, because even the availability of a small solar area can contribute enhancing the performance over the mere air source heat pump.

A visual defrosting control method for air source heat pump system based on machine vision

Frosting on the coil of the air source heat pump (ASHP) significantly affects its performance. An accurate defrosting control method is essential for the ASHP unit. Here, a novel visual defrosting control method based on machine vision is proposed. The frosting degree of the unit is accurately obtained by frosting image analysis with digital image processing to achieve on-demand defrosting. Fractal dimension, frosting degree coefficient, and single-circuit frosting evenness value are introduced to evaluate the frosting degree of coil images. The image acquisition point is determined with confusion matrix. Based on this, the logical framework of the proposed method is constructed, in which the defrosting starting and termination conditions are set as the moment when the frosting degree coefficient is equal to 0.9 and 0, respectively. A multi-variable model of fractal dimension is fitted, which improves the generalization of the proposed method. Finally, comparative experiments are conducted between the proposed method and the traditional temperature-time (T-T) method in typical cases. The results indicate that the COP and total heating capacity increase by 11.8 %, 10.6 % and 7.4 %, 6.6 %, respectively, and the defrosting frequency is reduced by 75 %, which demonstrates dominant advantages of the proposed method in accuracy, energy-saving, and indoor thermal comfort management.

Research on Strategies for Air-Source Heat Pump Load Aggregation to Participate in Multi-Scenario Demand Response

Research on Strategies for Air-Source Heat Pump Load Aggregation to Participate in Multi-Scenario Demand Response

Analysis of a domestic air heat pump integrated with an air-geothermal heat exchanger in real operating conditions: The case study of a single-family building

The work presents an in-depth analysis of the real performance of an air heat pump unit installed in a single-family building and quantitatively determines the reduction in energy consumption achieved by the integration of an air-geothermal heat exchanger. The case study is a single-family building located in northern Italy. It is equipped with a heating, ventilation, and air conditioning (HVAC) system consisting of an air-geothermal heat exchanger coupled with a compact air source heat pump supported by an electric heater installed in a thermal storage and devoted to cover the peak demand. The main objectives of the work are to analyse the HVAC performance under real operating conditions compared to the design values and to highlight the existence of factors that affect this performance. The analysis was carried out by developing an accurate model of the heat pump system based on the real operating data acquired by the on-board monitoring system. The results confirmed the influence of the air-inlet conditions (temperature and humidity) and of the control strategy (more specifically, the ventilation flow rate) on the unit performance in both the heating and cooling modes. In particular, the analysis showed that minimising indoor ventilation in the case of low outdoor temperatures is of paramount relevance not only because it reduces the indoor heat demand, but also because it maintains the unit efficiency close to the design values. Furthermore, the installation of a geothermal heat exchanger guarantees a reduction in electricity consumption of approximately 30%.

Study on the performance characteristics of the substation PVASHP system based on TRNSYS

Taking the substation building as the research object, DeST software is used to simulate the annual building load of the case building, and the load results are connected to the TRNSYS software. At the same time, the G ENOPT software is used to optimize the solar inclination and azimuth, and the system simulation model of solar photovoltaic-air source heat pump is established and the data analysis is carried out. The results show that the peak cooling load of the substation building occurred on July 24th, The numerical value is the 49.28kW, The annual cumulative cooling load of the building is 20165.59 kWh; Based on Hooke Jeeves algorithm, the optimal inclination of photovoltaic panels is 44.18 and the optimal azimuth is 11.69; Typical days, The highest peak power of the air source heat pump appears at 1 a.m,Its peak power is 7.47 kW, The COP peak was 3.67; Within the typical week, Solar photovoltaic efficiency shows stable periodic changes, Peak aking around 12:00 noon, Its peak efficiency is 18.14%; There is a significant linear distribution relationship between the solar photovoltaic power generation capacity and the solar radiation, Its linear correlation coefficient was 0.85. Compared with the single air source heat pump system, the composite system saves 18.33% energy and has good application effect.

Viability of an Open-Loop Heat Pump Drying System in South African Climatic Conditions

Drying agricultural produce consumes a considerable amount of energy. As an energy-efficient system, a heat pump can improve the energy efficiency of the drying process and hence reduce the energy consumption, especially in South Africa, where both sub-tropical and temperate weather conditions dominate. The objective of this research is to experimentally investigate the impacts of weather conditions on the operational conditions and thermal performance of an open-loop air-source heat pump drying system. The experimental investigation was conducted in a climate chamber where the climate conditions were simulated from −10 °C to 20 °C with an interval of 10 °C for the typical temperature range of the harvesting season in South Africa. The findings indicate that ambient temperatures have a significant impact on both the operating conditions and thermal performance of an open-loop heat pump system; the change in ambient temperatures from −10 °C to 20 °C leads to a 141.6% improvement in the suction pressure, a 214.2% increase in the discharge pressure, and 30.1% increase in the compression ratio, as well as a consequent increase of 130.6% in the refrigerant mass flow rate (from 0.0067 to 0.0155 kg/s), resulting in a corresponding increase in the coefficient of performance (COP) of the heat pump drying system by about 42.1%. Therefore, this study suggests that, while using an open-loop air-source heat pump drying system utilising R134a refrigerant is feasible in South Africa, it may be practically limited to regions with warm climates or during warmer seasons.

A Review on the Heat-Source Tower Heat Pump Systems in China

Based on air-, water-, and ground-source heat pump systems, a novel type of heat pump system, named the heat-source tower heat pump system (HSTHPS), has recently been developed in the southern area of China. The HSTHPS overcomes the evaporator frosting problems of the air-source heat pump system (ASHPS) when the ambient temperature is lower, and it avoids the geological condition constraints of the water- and ground-source heat pump systems. However, studies on the HSTHPS are insufficient, thereby limiting its development and applications. Thus, the present review provides a detailed literature review on the advancements of HSTHPSs in China, including the HSTHPS operation principle, heat-source tower (HST) structure, heat and mass transfer characteristics, HSTHPS performance, antifreeze solution use, and antifreeze solution regeneration. Studies on the heat and mass transfer characteristics of HSTs are sufficient for guiding the application. Regarding open systems, the solution drifting to the air needs to resolved, and future studies need to focus on structure optimization for heat exchangers in closed systems. Moreover, advanced defrosting technology should be applied to closed-type HSTs, and a suitable operation strategy for HSTHPSs should be developed. Future priorities should involve integrating HSTHPSs with additional renewable energy in order to achieve continuous, stable, and efficient heating in winter based on the characteristics of local climate and renewable energy.

Performance comparison of air source heat pump coupling with solar evacuated tube water heater and that with micro heat pipe PV/T

Air source heat pump (ASHP) has been generally regarded as energy saving devices for winter heating, yet for low-income households, the operational costs for heating in low-temperature conditions may be prohibitively high. Solar evacuated tube water heater (SETWH) and photovoltaic/thermal are economical solar energy conversion devices. Integrating them into ASHP has been proven globally to significantly reduce heating costs. However, a performance comparison between the SETWH combined with ASHP (SETWH-ASHP) and of micro heat pipe photovoltaic/thermal (MHP-PV/T) combined with ASHP (MHP-PV/T-ASHP) heating systems remains unexplored. Therefore, for a 120 m2 building with underfloor heating water pipe, SETWH-ASHP and MHP-PV/T-ASHP heating systems were respectively developed on the TRNSYS software platform. Their accuracy was confirmed using prior experimental data, followed by performance simulation for the heating season. The result is that MHP-PV/T-ASHP heating system outperformed SETWH-ASHP heating system, showing a 19 % increase in solar fraction, a 2.2 boost in system energy efficiency ratio, a 12.3 % rise in primary energy saving rate, a 0.9-year shorter payback period, and a reduction of 494.7 kg in CO2 emissions over the heating season. The results offer practical guidance for the promotion and application of heating systems that combine efficient and low-cost solar conversion devices with ASHP.

Assessment of energy self-sufficiency of a smart farm through integrated modeling of air-source heat pumps and solar power generation

This study explored methods to operate a sustainable system by improving energy independence and integrating renewable energy into a microgrid. However, there are challenges associated with the intermittency of renewable energy and difficulties in predicting the energy demand of energy systems. Therefore, this study emphasizes the need to analyze solar power generation and predict the cooling and heating demands of energy systems. The target system was a smart farm in which hot and cold water was supplied to the smart farm using a heat pump during seasonal changes. A prediction model for the smart farm was developed to calculate power consumption according to the ambient temperature in summer and winter. The results suggested that additional consideration is needed to optimize system operation and renewable energy use to improve the balance between energy consumption and supply. A comparison of the total power consumed to solar energy generation highlighted the challenge of attaining 100% self-sufficiency rates, reaching 44% in summer and 40% in winter. Analysis of solar power generation and air-source heat pump usage trends provided insights into strategies for achieving energy independence in smart farms. In conclusion, this study provides a model for managing energy demands on smart farms and insights into the optimization of system operation with renewable energy. It also provides a foundational framework for evaluating microgrid systems based on renewable energy and contributes to identifying methods to increase the energy self-sufficiency rates to enable sustainability of smart farms.

Heating performance of a vapor compression heat pump cascaded with a thermoelectric heat pump

Air source heat pumps (ASHPs) are widely utilized for heating and cooling in residential buildings; however, their effectiveness in heating mode is compromised during extreme weather conditions. Extensive research endeavors have been undertaken to develop, test, and assess a cost-effective vapor compression ASHP suitable for cold climate regions. This study takes an innovative approach by developing component and system prototypes for a cold climate heat pump. This design combines a thermoelectric heat pump (TEHP) with a traditional residential split ASHP to augment heating capacity in low ambient temperature conditions. The component and system prototypes underwent experimental testing in the psychrometric chambers. The experimental findings revealed a 13.6 % to 13.7 % increase in total heat pump heating capacity, accompanied by a 3.1 % to 5.0 % decrease in the coefficient of performance (COP) at ambient temperatures of −15 °C and −19 °C, when compared to the original ASHP. The COP of the TEHP is relatively constant, ranging from 1.63 to 1.76. This prototype offers a solution to address the challenges associated with reduced heat pump capacity at low ambient temperatures. The experimental results indicated that the lower the ambient temperature, thermoelectric heat pump auxiliary heating can increase the heating efficiency 60 % in comparison to electric resistance.

Optimization study of the circuitry for 5 mm small-diameter finned-tube heat exchanger in air-source heat pumps

Finned-tube heat exchangers (FTHXs) are currently extensively utilized in residential air-source heat pumps (ASHPs), but their escalating costs pose an urgent issue needing resolution. This study investigated the feasibility of replacing the 7 mm diameter FTHX in the outdoor unit of an ASHP with a 5 mm small-diameter FTHX, aiming to reduce material consumption without compromising performance. Based on the Intelligent System for Heat Exchanger Design (ISHED), a 6–3-1 circuitry (6 circuitries merging into 3 then 1) optimization scheme tailored for the 5 mm diameter FTHX was proposed under non-uniform airflow distribution. The performance differences between this circuitry and the baseline were then analyzed through numerical simulations. Finally, comparative tests were performed between the original FTHX and the modified 5 mm diameter FTHX. Overall, even with a 5.10 % reduction in total heat exchange area, its heat exchange capacity and efficiency still meet the performance standards for the initial ASHP. Notably, the proposed 5 mm diameter FTHX reduces the material costs and refrigerant charge by 19.76 % and 12.28 %, respectively. This phenomenon illustrates the considerable economic benefits of reducing the volume of FTHX. Additionally, it holds significant practical value in promoting the use of natural refrigerants including hydrocarbons according to the new international legislative framework.

Characteristics and Application Analysis of a Novel Full Fresh Air System Using Only Geothermal Energy for Space Cooling and Dehumidification

To effectively reduce building energy consumption, a novel full fresh air system with a heat source tower (HST) and a borehole heat exchanger (BHE) was proposed for space cooling and dehumidification in this paper. The cooling system only adopts geothermal energy to produce dry and cold fresh air for space cooling and dehumidification through the BHE and HST, which has the advantage of non-condensate water compared to BHE systems integrated with a fan coil or chilled beam. Based on the established mathematical model of the cooling system, this paper analyzed the system characteristics, feasibility, operation strategy, energy performance, and cost-effectiveness of the proposed model in detail. The results show that the mathematical model has less than 10% error in estimating the system performance compared to the practical HST–BHE experimental set up. Under the specific boundary conditions, the cooling and dehumidification capacity of this system increases with the decrease in the air temperature, air moisture content, and inlet water temperature of the HST. The optimal cooling capacity and the system COP can be achieved when the air–water flow ratio is at 4:3. A case study was conducted in a residential building in Shenyang with an area of about 1800 m2. It was found that this system can fully meet the cooling and dehumidification demand in such a residential building. The operation strategy of the cooling system can be optimized by adjusting the air–water flow ratio from 4:3 to 3:2 during the early cooling season (7 June–1 July) and end cooling season (3 August–1 September). As a result, the average COP of the cooling system during the whole cooling season can be improved from 6.1 to 8.7. Compared with the air source heat pump (ASHP) and the ground source heat pump (GSHP) for space cooling, the proposed cooling system can achieve an energy saving rate of 123% and 26%, respectively. Considering that the BHE of the GSHP can be part of the proposed HST–BHE cooling system, the integration of the HST and GHSP for space cooling (and heating) is strongly recommended in actual applications.

Modelling and analysis of heat pump integrated Photovoltaics-Wind systems for an agricultural greenhouse in Turkey

This study focused on modelling and analysing photovoltaics and wind systems to meet the heating demand of a commercial greenhouse. The aim is to evaluate technical, economic, and environmental performances of the related systems and to determine the optimum configuration. A novel approach was introduced by integrating hybrid energy systems with large-scale wind turbines and developing a dynamic heat transfer model. A large commercial greenhouse with an area of 26,640 m2 located in Izmir, Turkey was selected for considering Mediterranean climate, and a detailed heat transfer model of the greenhouse were developed considering heat transfers by convection, radiation, ventilation, and infiltration. A combination of air source heat pumps, photovoltaic panels and wind turbines were used for meeting the heating demand of the related greenhouse. Five different on-grid energy systems scenarios, namely (i) Photovoltaics-Heat Pump, (ii) Photovoltaics-Wind Turbine- Heat Pump, (iii) Wind Turbine- Photovoltaics- Heat Pump (iv) Wind Turbine- Heat Pump, and (v) only Heat Pump were considered. The system modelling with a detailed heat transfer analysis of the greenhouse was made by MATLAB. The energy analysis of the systems was performed on an hourly basis for one calendar year. The annual heating demand and the corresponding electricity consumption of the greenhouse were calculated as 497.37 and 114.07 kWh/m2, respectively. Net Present Value, Levelized Cost of Energy and CO2 savings were used to evaluate economic and environmental performances of the systems. Among five on-grid energy system scenarios, the first scenario, consisting of 5271 photovoltaic panels and 20 heat pumps, emerged as the most economically attractive choice with Net Present Value and Levelized Cost of Energy of $547,440.40 and 0.080146 $/kWh, respectively. Critical parameters affecting the economy of this scenario were found to be electricity prices, tomato yield, and photovoltaic panel prices. For environmental evaluation the fourth scenario, integrating wind turbines and heat pumps, achieves the highest CO2 savings of 2,064.73 tons due to increased renewable electricity production and lower life-cycle CO2 emissions of wind turbines compared to photovoltaic systems. This analysis enhanced the understanding of energy dynamics in greenhouse environments, contributing to the advancement of sustainable practices in agriculture.

Environmental footprint analysis of domestic air source heat pumps

Air source heat pumps (ASHP) are increasingly being recognised as a low carbon alternative to traditional fossil fuel type heating systems for residential buildings, with many countries targeting their mass deployment to meet their emissions reduction goals. However, the environmental impacts of ASHPs throughout their entire life cycle to include manufacture and end-of-life, as well as operation, have not received comprehensive attention to date. This study addresses this gap by conducting a review of research quantifying the life cycle impact of domestic ASHPs, coupled with an examination of technology uptake and deployment. By analysing the entire life cycle, from production to end-of-life, the global warming potential of a 6 kW ASHP is estimated to be 35.8 t CO2 equivalent over the lifetime of 17 years identified by the study. Additionally, the study conducts a comparative analysis of the operational footprint based on a range of electricity carbon footprint and suggests possible improvement of 1200 % with targeted improvments. Furthermore, the study calculates the global warming potential using both the seasonal performance factor specified by a heat pump manufacturer and real-world field trial data. The findings unveil a significant disparity of 20 % between the two methodologies, underscoring the paramount importance of incorporating in-field heat pump performance data when evaluating their environmental impact.

Performance comparison of liquid, vapor, and liquid–vapor injection of single-screw compressor for an air-source heat pump

Refrigerant injection techniques are usually proposed to improve the performance and reliability of compressors when a single-screw compressor applied to an air-source heat pump works at low temperatures in winter. In this study, an experimental study was conducted to present the performance comparison of the single-screw compressor in the air-source heat pump under liquid, vapor, and liquid–vapor refrigerant injection at evaporation temperatures between −19 and −8 °C. The results indicate that, when the evaporation temperature decreases from −8 to −19 °C, the heating capacity under liquid–vapor and vapor injection increases by 16.7% and 12.7%, respectively, compared with that under liquid injection and that the COPh increment under liquid–vapor injection and vapor injection is, respectively, from 11.23% to 39.21% and from 17.18% to 30.82% compared with that under liquid injection. Therefore, the liquid–vapor injection method is conducive to the operation of the air-source heat pump at a lower ambient temperature. The experimental results can provide the basis for the future design of single-screw compressors applied to air-source heat pumps.

Techno-economic evaluation of a seawater source heat pump system with auxiliary heat source in cold region of China

The utilizing of renewable seawater energy through seawater source heat pumps (SWHPs) in coastal areas is considered as a sustainable technology with minimal environment impact. Promotion of this technology needs clear understanding of its techno-economic performance but there are limited relevant studies. An empirical study was conducted in Qingdao, China, based on a practical installation comprising SWHPs supplemented by electric boilers. On-site measurements revealed considerable COP of 3.81 for SWHP and COPs of 2.87 for the whole system, implying SWHP as a viable and efficient solution for space heating in mild winter in this region. Results from TRNSYS simulations showed SWHP with auxiliary gas boilers (SWHP-GB) achieved the lowest annual primary energy demand and best economic and environmental benefits compared with other three schemes, namely SWHP with electric boilers (SWHP-EB), chillers with gas boilers (Chiller-GB) and air source heat pumps with gas boilers (ASHP-GB). SWHP played important roles in energy efficiency of the whole system with a considerable seasonal COP of 3.72 and 3.22 respectively for heating and cooling. Annual primary energy demand of SWHP-GB accounted for 55 %, 78 % and 56 % of SWHP-EB, Chiller-GB and ASHP-GB, respectively. SWHP-GB achieved the lowest life cycle costs and a rapid payback period of 10.9 years. Moreover, using direct or indirect heat exchange with seawater was found with limited impact on techno-economic performance of the system. To conclude, SWHP-GB could be used as an efficient solution for building heating and cooling in northern coastal cities in China.

Performance analysis of a novel air source ammonia/water cascade heat pump for heating buildings in subarctic climate

Performance of available air-source heat pumps (ASHP) for buildings is extremely influenced by the outdoor air temperature (OAT). When OAT falls below –20 °C, especially in subarctic climate, most commercially available ASHPs lose their defined functionality. To address this issue, a novel cascade heat pump (CHP) is proposed that utilizes two natural (with zero global warming index) refrigerants: ammonia, aka R717, as the low stage (LS) refrigerant, and water, aka R718, as the high stage (HS) working fluid. The proposed system is equipped with two rotary vane compressors for LS and HS. To desuperheat the compressor discharge temperatures and increase the HS heating capacity, liquid refrigerant is injected into the chamber of both LS and HS compressors. The wet compression is thermodynamically modeled and validated against experimental data available in the literature. Optimum design parameters such as the maximum allowable temperatures during compression and the minimum vapor quality after injection are obtained where the COP is maximized. Total exergy destruction, number/location of injectors and the injected amounts are also investigated. The proposed CHP can deliver 6.35 kW heating load at 50 °C with a COP of 1.985 when OAT is –40 °C. From a broader perspective, the proposed CHP not only proves its efficacy in extremely cold subarctic climates but also emerges as a pivotal player in addressing the global warming issue. This is accomplished through a dual approach to decarbonization—firstly, by electrifying heating processes and secondly, by substituting phased-out refrigerants with environmentally friendly natural alternatives.