Thermostatic Expansion Valve Research Articles

Performance of a direct-expansion solar-assisted heat pump for domestic hot water production in Algeria

The focus of this study is to investigate the energy performance of a direct-expansion solar-assisted heat pump water heating system (DX-SAHPWH). The system consists of an unglazed solar collector-evaporator, which can absorb heat from solar energy and air ambient simultaneously, a condenser in the form of a coil immersed in a hot water storage tank, a thermostatic expansion valve and a hermetic reciprocating compressor. The performance of the heat pump system is evaluated using a developed mathematical model under Matlab code. The modelling method is based on lumped and distributed parameter approach of different system components. Numerical calculations were carried-out to study the influence of different parameters, such as ambient temperature, solar radiation intensity and polytropic index on the system performance. Additionally, in order to evaluate the long-term system performance, the system’s model was applied on a case study of a single-family building located in Djelfa (Algeria), which represents the coldest arid region of the country. The results showed that the solar radiation intensity and ambient temperature have significant effects on the heat pump performance. A COP of 5.9 and a collector-evaporator efficiency of 1.9 were obtained at high solar radiation of 850 W/m2 resulting in lower heating time (29 min). In addition, results revealed that the system can operate even at lower ambient temperature due to its ability to take advantage of heat from the ambient air. The results from the case study gave a COP ranging from 2.3 to 3.8, which enhance the promising adoption of this system in domestic hot water production to respond to people daily life needs with clean, abundant and renewable energy.

Experimental study and semi-empirical model of a thermostatic expansion valve of a R290 direct-expansion solar heat pump

The expansion device plays a crucial role in the operation of heat pumps and refrigeration systems, making its study integral to advancements in the fields of refrigeration and heating. Among various expansion devices, the Thermostatic Expansion Valve (TEV) stands out due to its rapid response time and mechanical nature, which grants it high control capacity over refrigerant superheating. In this study, was developed a semiempirical mathematical model for a TEV incorporated in a DX-SAHP utilizing R290. The research was carried out in an experimental way, conducted using a fully instrumented DX-SAHP. A series of experiments tested different operational modes for water heating, subject to varying solar radiation intensities. A uniform methodology collected operational parameters, resulting in 150 experiments. The semiempirical model creation involved combining basic equations from the literature describing TEV operation and formulating an equation using multiple linear regression based on experimentally evaluated parameters. These parameters included solar radiation incidence, inlet and outlet pressures, and superheating degree. The regression model achieved an adjustment higher than 96 %. Combining this regression with equations suggested by previous researchers, resulted in a model with an adjustment exceeding 94 %. Furthermore, this study culminated in the derivation of a generalized model primed for broad application across various heat pump configurations for water heating purposes. Notably, the model underwent rigorous validation across a separate set of experiments, reaffirming its reliability and versatility. While excelling in steady-state operations, the model's transient data analysis falls short, as intended.

A Water-to-Water Heat Pump Model with Experimental Validation

An experimental validation of a steady-state model for water-to-water heat pumps is conducted on a 10 kW test bench. The objective of the model is to predict the capacity and the required compressor power, based on the inlet conditions of the secondary fluids in the evaporator and condenser. Detailed manufacturer performance maps based on the AHRI 540-2020 standard are utilized to model the fixed-speed scroll compressor. A new semi-empirical model for the thermostatic expansion valve incorporates condensing temperature effects on superheating prediction. Sub-models for individual components, including detailed representations of the evaporator and condenser, are integrated into a global model, resulting in a set nonlinear equation solved using an equation solver with appropriate guess values. The validation of the model is conducted in an experimental test facility equipped with two precisely controlled secondary fluid loops. The heat pump is instrumented to measure condensation and evaporation pressures, the compressor discharge temperature, compressor power, superheating, and sub-cooling. The results are divided into three sub-sections: the first validates the complete heat pump model by comparing its power consumption and COPs in heating and cooling; the second compares the predicted and measured operational conditions; finally, it is shown how the model can be used to predict the non-operational conditions of the heat pump for specific scenarios.

Performance evaluation of ecofriendly R1234ze(E) refrigerant in an automotive air conditioning system

AbstractA mathematical model for an air conditioning system used in five‐seater cars is developed with R1234ze(E) and R134a refrigerants, consisting of real system geometry like an evaporator, compressor, condenser, and thermostatic expansion valve. The mathematical model includes refrigerant properties, heat transfer, and pressure loss correlations for two‐phase and single‐phase regions. The performance parameters of a system like evaporator cooling duty, condenser heat loss, compressor power, refrigerant flow rate, and compressor volumetric efficiency obtained from a mathematical model are validated with the results of an experimental facility developed with R134a. The uncertainty analysis performed for the testing facility showed below 11% deviation. The simulation and experimental results showed an overall 10%–15% difference. It is found that the experimental cooling capacity with R134a and numerical cooling capacity with R134a show a 4%–12% variation, experimental cooling capacity with R134a and numerical cooling capacity with R1234ze(E) show a 7%–20% variation, and numerical cooling capacity with R134a and numerical cooling capacity with R1234ze(E) show a 5%–15% variation for the given range of compressor speed (500–1500 rpm), and condensing temperature (26–45°C). The study concluded that R1234ze(E) could potentially replace R134a because it has similar thermophysical properties and an average performance difference of up to 10% with R134a. Due to the limitations of the electric motor used to drive the compressor, tests in the current study were conducted at modest compressor speeds (500–1500 rpm). Future research will focus on experiments with high compressor speed (in the range of 1500–4000 rpm) and R1234yf and R1234ze(E) refrigerants for performance evaluation of automobile air conditioning systems.

Investigation on energy-saving potential from heat rejection pressure management in a CO2 transcritical vapor compression system

Heat rejection pressure is an important factor influencing the performance of a CO2 (R-744) transcritical vapor compression system. Previous relevant studies have investigated the optimum heat rejection pressure ensuring the maximum coefficient of performance (COP) and operating parameters affecting the optimum pressure value. However, studies presenting quantitatively how much energy can save when an R-744 transcritical system operates in the optimum heat rejection pressure are still rather limited. This work aims to investigate an energy-saving potential gain achieved by managing heat rejection pressure in an R-744 transcritical system and provides quantitatively how much energy can save with that. In that way, this work tries to fill out the research gap. Simulations were carried out employing prevalidated model, the system COP was investigated in various operating conditions, and the optimum heat rejection pressure securing the maximum COP was found. The optimum heat rejection pressure found in this work was compared to the existing correlations, thereby the comparison results are provided in this paper. The system's dynamic performance was also investigated in two different cases: when the expansion valve opening was regulated for the optimum heat rejection pressure, and when the valve opening was adjusted with a thermostatic expansion valve conventionally. In this study, it is observed the given system reduces the compressor power consumption by 62% when the refrigerant temperature at the main gas cooler outlet varies within a range of 33 ℃ to 45 ℃ and the evaporator temperature of 1 ℃. Consequently, in terms of energy-saving potential, this paper highlights the importance of heat rejection pressure management in an R-744 transcritical system and the significance of proper selection for the control target of an expansion valve depending on the system's operating regime.

Examination of Capillary Tube and Thermostatic Expansion Valve conduct in Domestic Refrigerator Using Hydrocarbon by Applying Graph Theory

Examination of Capillary Tube and Thermostatic Expansion Valve conduct in Domestic Refrigerator Using Hydrocarbon by Applying Graph Theory

Seeking a new throttle to substitute the thermostatic expansion valve in vapor-injection process for an air-source heat pump: An experimental study

Air source heat pump (ASHP) as a sustainable energy technology is playing an essential role in achieving carbon neutrality for almost countries. The operational stability of ASHP is related to throttles. The selection of thermostatic expansion valve (TEV) types is sometimes limited by a wide range of outdoor temperature conditions. In order to find a substitutable throttle of TEV, this paper compares a pulse width modulation driven (PWM-driven) solenoid valve coupled with a capillary with TEV to control vapor-injection based on a two-stage compressed air-source heat pump (TCASHP) prototype. The experiment results show that the TCASHP unit can operate in a wider temperature range if the TEV capacity is selected properly to control vapor-injection. While the on-off periods and times of PWM-driven set out of place make the TCASHP situate at a hunting problem state. The solenoid valve should be installed behind the capillary to control vapor-injection by experiments and entropic analysis. Furthermore, the shorter on-off periods and longer opening time of PWM-driven solenoid valve reduce the risk of hunting problems. Besides, the operation stability is the best for TCASHP unit with PWM-driven solenoid valve coupled with capillary to control vapor-injection, which has the same performance as the TEV.

Experimental investigation on the effect of expansion valves in a dual evaporator ejector refrigeration system using R134a and R456a

ABSTRACT The purpose of this study was to experimentally investigate a dual evaporator ejector system (DEES) operating with R134a and R456a. In order to see the effect of expansion valves in the system, the experimental setup was arranged in two different configurations. In the first configuration, DEES was operated with dual thermostatic expansion valves (DEES-DTXV). In the second configuration, DEES was operated with a single thermostatic expansion valve (DEES-STXV). In both configurations, the system was tested with R134a and R456a. The effective performance values of the system were investigated based on the entrainment ratios (ERs). It was found that DEES-STXV outperformed DEES-DTXV in terms of total cooling capacity and coefficient of performance. When the system was operated as DEES-STXV, the total cooling capacity obtained from R134a was 14% higher than that obtained from R456a at the ER value of 0.5. In addition, it was found that the ERs had a significant effect on the cooling capacities; therefore, it is not recommended to operate the DEES at the ERs greater than 0.8 in both configurations. Moreover, DEES-DTXV was found to be superior to DEES-STXV in that very low evaporation temperatures could be achieved in the secondary evaporator in DEES-DTXV. Finally, it was found that the performance values of R456a were close to those of R134a; so, R456a can be used as an alternative refrigerant in dual evaporator refrigeration systems with ejector.

Energetic and exergetic performance comparison of an experimental automotive air conditioning system using refrigerants R1234yf and R134a

In this study, the energetic and exergetic performance merits of an automotive air condition-ing (AAC) system using R134a and R1234yf have been investigated. For this aim, a laboratory AAC system was developed and equipped with devices for mechanical measurements. The refrigeration circuit of the system mainly had an evaporator, condenser, liquid receiver, fixed capacity compressor, and thermostatic expansion valve. The tests were performed by changing the compressor speed and air stream temperatures incoming the condenser and evaporator. Based on energy and exergy analysis, various performance parameters of the AAC system for both refrigerants were determined and presented in comparative graphics. It was found that R1234yf resulted in 0.4–10.9% lower refrigeration capacity, 5.5–11.6% lower COP, and 4.7–16.1°C lower compressor discharge temperature, while yielding 9.3–22.3% higher refrig-erant mass flow rate and 1.1–3.5°C higher conditioned airstream temperature in comparison to R134a. Moreover, the components of the R1234yf system usually destructed more exergy, and the total exergy destruction rate per unit refrigeration capacity of the R1234yf system was 4.1–15.3% greater than that of the R134a one.

Experimental performance evaluation of an R1234yf automobile air conditioning system employing an internal heat exchanger

A bench-top automobile air conditioning (AAC) system using a thermostatic expansion valve was developed. The system was equipped with a coaxial internal heat exchanger (HEX) and charged with R1234yf, a new refrigerant used as an alternative to R134a. The system was tested at the compressor speeds ranging between 1000 rpm and 2600 rpm with increments of 400 rpm. For each compressor speed, the air temperatures at the evaporator and condenser inlets were concurrently changed between 30 °C and 40 °C with increments of 5 °C. The system was operated for the cases of employing and not employing the HEX, and totally 30 test runs were performed. Then, the first law of thermodynamics was applied to the system components to evaluate various steady state performance parameters. The considered parameters were the refrigerant mass flow rate, evaporating temperature, cooling capacity, compressor power, coefficient of performance (COP), condenser heat dissipation rate and discharge temperature of the compressor. It was determined that the experimental system employing the HEX yielded on average 0.8 °C lower evaporating temperature, 2.2% higher cooling capacity, 2.0% lower compressor power and 3.0% higher COP values relative to the system not employing the HEX. These findings reveal that the use of HEX causes a better system performance in terms of the cooling capacity, compressor power and COP. Consequently, the performance of R1234yf AAC systems can be improved with the use of HEX, and thus, the AAC systems using R1234yf can be more competitive with those using R134a.

Feasibility study and in-depth performance assessment of needle valve using as expansion device in refrigeration system

The needle valve (NEV) has high potential for further using as the automatic expansion device in the refrigeration system. However, the experimental proof is required for further developing the automatic controller for operation. This paper proposes the feasibility study and performance map of the needle valve (NEV) using as the expansion device in a small vapour compression refrigerator (VCR). The relevant parameters produced by NEV are compared with those using capillary tube (CT) and thermostatic expansion valve (TEV) which are the conventional device. The system COP, superheated degree at evaporator outlet (SHDevap-out), subcooled degree at condenser outlet (SCDcon-out), mass flow rate, volumetric refrigeation capacity, compressor's specific work and refrigerant quality are considered for comparisons. Additionally, the economic assessment of using NEV compared with the other two devices is proposed. It is found that COP produced by NEV are similar to TEV which is better than CT. The ecomnomic assessment indicates that the NEV produces similar useful cooling energy per unit cost to that using TEV which is higher than CT. Overall results indicate that the NEV can efficiently be used as the expansion device in VCR which is alternative to the conventional expansion devices.

Enhancement of condensate water quantity and coefficient of performance of an air conditioning system: An experimental study

AbstractThe objective of the present work is to increase the quantity of condensate water from atmospheric air during the air conditioning (A/C) process by using two techniques: increasing moisture content in atmospheric air by adding steam and passing compressed air instead of atmospheric air, respectively. The experiment was performed with both capillary valve and thermostatic expansion valve operations for assessing the volume flow rates (VFRs) of condensate and coefficient of performance (COP) concerning the air A/C arrangement. The control valve operated for the steam supply case was at half valve opening and one‐fourth opening, respectively. The R‐22 refrigerant was used in this study. From this study, it was perceived that the condensate water quantity was increased by adding the moisture to the inlet air for the A/C system simultaneously with the usage of compressed air. Furthermore, the COP of the system was also compared to normal atmospheric air admission conditions. The compressed air and steam admission to the A/C system has shown a tremendous increase in COP together with the VFR of the system rather than atmospheric air admission conditions.

Experimental investigation of vapour compression chiller based on transient cooling performance influenced by expansion devices

This paper proposes the experimental investigation of a vapour compression refrigerator working as the water chiller (VCR-chiller) influenced by the expansion devices. The comparative cooling performance is implemented based on the transient operation (parameters of interest as a function of time). The expansion devices, thermostatic expansion valve (TEV), needle valve (NEV) and capillary tube (CT), are investigated under the same condenser, evaporator and compressor. The external performance parameters (cooling temperature, cooling load, electricity consumption, and COP) influenced by the expansion devices are assessed. The internal performance parameters (refrigerant temperature, refrigerant pressure and refrigerant mass flow rate), which indicate the flow state of the refrigerant, are also used to assess the deep impact of the expansion devices on the cooling performance. It is found that the cooling performance of VCR-chiller is strongly influenced by the expansion devices. The highest possible COP based on transient operation is achieved when using NEV while that produced by TEV is not much lower than NEV. However, using CT provides the lowest COP due to an uncontrollable refrigerant mass flow rate and its own characteristics. The findings indicate that attention must be paid to the selection of the expansion device for the VCR-chiller.

Performance of Automotive Air Conditioning System with R134a and R1234yf

A steady-state mathematical model of a small-capacity Automotive Air Conditioning System (AACS) working with the refrigerants R134a (1,1,1,2-tetrafluoroethane) and R1234yf (2,3,3,3-tetrafluoropropene) is developed. The model considers the major components of the system, namely, the swash plate compressor with fixed stroke, thermostatic expansion valve (TXV) and the compact heat exchangers (flat-tube, louvered-fin evaporator and condenser). In order to verify the mathematical model, an experimental facility has been developed for testing the AACS and experiments are conducted with R134a. The experimental results are also validated with published data. The effects of various operating conditions, namely, the condensing air temperature, condensing air velocity and the compressor speed, on the performance of the AACS are predicted for both R134a and R1234yf. The results of the simulations with R134a and R1234yf are compared with the experimental results obtained with R134a. The results show good agreement with the experimental results, with most of them showing less than 10–15% of variations from the experiment results. The uncertainty analysis is performed and showed that the most of validations follow below 10% difference.

Experimental analysis of a novel gas-engine-driven heat pump (GEHP) system for combined cooling and hot-water supply

Abstract Heat pump technologies have been widely used in air conditioning and hot water application. However, most of the heat pump systems adopt an expansion valve to complete the cooling and heating modes currently. The flaw is that as the four-way valve is switched, the expansion valve cannot be guaranteed to be very close to the inlet of the evaporator in both modes, making the performance of the cooling or heating mode worse. In addition, for gas-engine-driven heat pump (GEHP), the utilization of engine waste heat is insufficient. Based on the above two shortcomings, a novel GEHP unit with an advanced finned tube heat exchanger and three thermostatic expansion valves was built in this work. The performance was evaluated under an experimental operating range of engine speed from 1300 rpm to 2000 rpm, air temperature from 23.8°C to 27.7°C, and evaporator water inlet temperature from 13.2°C to 22.4°C. Experimental results showed that when the engine speed and ambient temperature increased, the compression ratio increased, whereas the coefficient of performance (COP), primary energy ratio with heat recovery (PER1), and primary energy ratio without heat recovery (PER2) of the system decreased linearly. As the evaporator water inlet temperature increased from 13.2°C to 22.4°C, the COP, PER1, and PER2 had an improvement of 23.6%, 20.8%, and 27.6%, respectively. The averages of COP, PER1 and PER2 were 3.67, 1.57 and 0.96, respectively. The results indicated that the novel GEHP unit was able to maintain expected high performance.

Effect of thermostatic expansion valve tuning on the performance enhancement and environmental impact of a mobile air conditioning system

In this work, the performance enhancement of a HFO-1234yf mobile air conditioning (MAC) system with a suction/liquid line heat exchanger (SLHX) was carried out experimentally by tuning the thermostatic (constant superheat) expansion valve (TXV) and its impact on the environment was also evaluated. The optimum charge of HFO-1234yf and HFC-134a systems was found to be 670 g and 740 g, respectively. The results showed that the HFO-1234yf system with SLHX had better coefficient of performance (COP) and exergy efficiency when compared to HFC-134a system with SLHX at idling condition, whereas it had reduced performance at other speed conditions. The tuning of the TXV in the HFO-1234yf system had a positive influence on the COP, cooling capacity, and exergy efficiency and those were higher than that of existing HFC-134a system by 4.3–8.6%, 6.5–10.1%, and 3.7–5.1%, respectively, at idling and city speed conditions, whereas those were slightly lower at high-speed conditions. The total CO2 equivalent emission of tuned and un-tuned HFO-1234yf system was 27.98% and 24.64% lower than that of the existing HFC-134a system. The outcome of this study indicated that the SLHX implementation in the HFO-1234yf MAC system with tuned TXV could be a possible option to replace HFC-134a.

Стабилизация хладагента как энергоэффективное решение поддержания параметров микроклимата серверных помещений

Among all known methods for energy saving based renewable energy sources, those aimed at improving the quality of equipment regulation are of particular importance. The use of renewable energy sources ensures an increase in energy saving; however, the equipment used in engineering systems should also be reliable. At present, almost every office building has a special facility for server equipment. Such facilities are rarely furnished with devices for removing excess heat, which may hinder stable operation of computer equipment and shorten its service life. In the present study, the energy efficiency of a method for stabilising the refrigerant in air conditioning systems operating on freon is experimentally verified. The stabilisation of the refrigerant is based on bringing the gas-liquid freon in the circuit to a uniform state prior to its entry in the thermostatic expansion valve (TEV). A refrigerant stabilisation device was embedded in the circuit of the on/off type split system, the working substance in which was R410A. During 3 months, the temperature of the server mobile station and the power consumption of the split system were monitored in real time, 24/7. On the basis of the obtained results, the energy saving was calculated. The test results were independent of external factors. Reasons for a more efficient cooling of the split system by bringing the refrigerant to a homogeneous state with a decrease in its temperature prior to its entry in the TEV were investigated. It is shown that, in the evaporator, freon requires more time and energy for the phase transition, which process consumes more heat from the facilities under cooling.

Management of Condenser Fan Speed and its Influence on the Split Air Conditioner Performance

Energy saving is the challenge of decreasing the quantity of energy consumption needed. This can be done by employing reliable and smart control system. In this article, an experimental study has been carried out to investigate the performance of a split air conditioning unit having a variable speed condenser fan. The rate of heat rejection airflow has been controlled according to the outdoor air temperature via a Proportional Integral Differential (PID) controller. The control algorithm allows increasing the condenser fan speed with the increase of outdoor air temperature and vice verse. The maximum rate of air flow of the fan is 0.43 m3/s at 42ºC outdoor air temperature and the minimum flow is 0.28m3/s. To facilitate variation of refrigerant flow rate according to the evaporator load, the traditional capillary tube was replaced with a suitable thermostatic expansion valve and liquid refrigerant reserve. The influence of condenser airflow modulation and its temperature on the air conditioner performance and also on the compressor power consumption has been investigated and presented at different evaporator loads. It has been found that a 10 % reduction in compressor power is achieved by increasing the condenser air flow by about 50%.

Experimental study of the static and dynamic behavior of a novel heat driven electronic controlled expansion valve

In this work, a heat driven thermostatic valve is described and tested. The proposed valve is based on a thermostatic expansion valve, where a heating element is wounded to its sensing bulb. By means of controlling the power supplied to the heating device, the degree of superheating at the outlet of the evaporator can be easily controlled. Such arrangement has not been proposed in the open literature. The proposed setup has been tested in an experimental rig operating with R134a. The system behavior for both steady state and transient loads has been compared for the original thermostatic expansion valve setup and the modified one. A mathematical model of the installation has been developed to perform parametric analyses regarding the type of control loop to be used for the heating element. It has been found that the proposed arrangement is able to control the superheating successfully, with a maximum deviation from the set point of 0.02 °C and 0.17 °C for the steady and transient state respectively. Furthermore, the superheating oscillations are reduced in relation with the original valve configuration, thus preventing hunting in the evaporator at low loads.

히트펌프의 양방향 전자식 팽창밸브 개도 따른 냉방성능

Heat pumps consist mainly of compressors, evaporators, condensers and expansion valves, and change the flow of refrigerant to allow cooling or heating in a single unit. The expansion valve used in the heat pump is mainly used with the electronic expansion valve for the conventional manufactured cooler, which flows in a single direction, requiring a separate bypass line and check valve, thereby reducing the performance of the freezer. Therefore, in this study, the cooling performance according to the opening step was analyzed using a interactive expansion valve for R-404A, which does not require a bypass line and a check valve during the design of the heat pump. The cooling performance coefficient for R-404A was 3.633 for thermostatic expansion valve, 3.795 for conventional electronic expansion valves and 3.851 for interactive electronic expansion valves. This is an improvement of 6.001% compared to the temperature formula and 1.476% over the conventional electronic system.