Model Based Sensor System for Temperature Measurement in R744 Air Conditioning Systems

The goal is the development of a novel principle for the temperature acquisition of refrigerants in CO2 air conditioning systems. The new approach is based on measuring the temperature inside a pressure sensor, which is also needed in the system. On the basis of simulative investigations of different mounting conditions functional relations between measured and medium temperature will be derived.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

Experimental Test Rig For The Visualisation Study Of The Transcritical Flow In The Two-Phase R744 Ejectors

Recent studies have provided the significant number of approaches to enhance the performance of a twophase ejector, especially for transcritical CO2 cycles. However, the investigation of the mixing process is still challenging matter due to the highspeed fluid flow coupled with mixing of vapour and partially evaporated liquid stream. On the other hand, these phenomena directly influence the ejector efficiency. The behaviour of the aforementioned processes would be valuable for validation the numerical models as well as a required control of the system operation. Hence, in this work, the laboratory test rig for visualisation of the CO2 ejector mixing processes along suction nozzle, premixing chamber and diffuser was developed and manufactured. The visualisation techniques used for this study include the highspeed camera recordings and PIV measurements. The work consists of installation description, including the measurement approaches, solution predicted by the computational model for the transparent construction of the ejector and visualisation procedures. The selected onand offdesign operating points were described having regard ejector performance factors and its correlation with the output of the visualisation procedure

The Role of Internal Heat Exchanger in an R744 Vapor Compression System in the Air-conditioning Mode Under Various Conditions

This paper first presents a comprehensive review of the internal heat exchanger, followed by the discussion of experimental results of the role of an internal heat exchanger in an R744 air conditioning system. The effects of refrigerant charge amount on the performance of both basic and internal heat exchanger systems were investigated. Also, the control equations of COP-maximizing high-side pressure were developed and used for both systems. The experimental data show up to 13.8% improvement in efficiency by introducing the internal heat exchanger. The different roles of IHX in sub- and transcritical modes and the reason for the difference are discussed in the paper

Integration of a cold thermal energy storage for air conditioning demand in a CO2 refrigeration system of a supermarket

openThere is a significant transition in supermarket refrigeration, with a strong focus on reducing energy demand and installation costs. Generally, industry processes require cooling the most for short periods every day. The rest of the time, the cooling system runs at partial load with lower efficiency, but it is still designed for the highest capacity. Applying cold thermal energy storage (CTES) technologies, which can deliver some of the cooling during peak times, will reduce peak load demand and will allow for load shifting to periods with low electricity cost, free cooling capacity from the rack or high electricity production from renewable energy sources (e.g. photovoltaic panels). This will also contribute to a more flexible power system, and allow for an increased proportion of power production with variable renewable energy sources. Additionally, these units can also lead to a significant downsizing of the compressor pack, reducing the cooling system capacity. Currently, the air conditioning (AC) in REMA 1000 supermarkets, a leading supermarket chain in Norway, is supplied by a glycol circuit which is cooled by the CO2 (R744) booster refrigeration system. The design capacity of the refrigeration unit must handle all the refrigeration loads and the AC load during the warmest summer day, which results in overcapacity and part load operation for most of the year. This master’s thesis describes and investigates a proposed design for the implementation of a CTES dedicated to AC demand in a supermarket located in the Oslo region. This system aims to substitute the existing glycol circuit towards the air handling unit (AHU). Simulation results demonstrate that CTES offers substantial potential for reducing electrical peak power consumption during the warmest periods. The functioning of the CTES and its impact on the existing refrigeration system were simulated, revealing a peak reduction of up to 32,33%. The load shifting capability is demonstrated, absorbing 31,53% of the daily electricity consumption during the night, when the supermarket is closed, compared to 16,14% considering the instantaneous production of AC with the existing system. Consequently, electricity consumption can be increased by up to 74,8% during the night and decreased by up to 28% during the day. Even though energy savings are not the primary objective of this project, they are achieved by producing and storing energy required for AC during periods when the outdoor temperature is lower, and the coefficient of performance (COP) of the system is higher. The energy savings can reach up to 11,8% during the hottest day. Finally, the economic benefits of the system are assessed under spot pricing and tariff pricing systems, revealing potential electricity cost savings of up to 12,56% and 16,45%, respectively. The main big challenges of this system still remain its economical viability, in terms of payback time, and expanding its utilization during the winter period.There is a significant transition in supermarket refrigeration, with a strong focus on reducing energy demand and installation costs. Generally, industry processes require cooling the most for short periods every day. The rest of the time, the cooling system runs at partial load with lower efficiency, but it is still designed for the highest capacity. Applying cold thermal energy storage (CTES) technologies, which can deliver some of the cooling during peak times, will reduce peak load demand and will allow for load shifting to periods with low electricity cost, free cooling capacity from the rack or high electricity production from renewable energy sources (e.g. photovoltaic panels). This will also contribute to a more flexible power system, and allow for an increased proportion of power production with variable renewable energy sources. Additionally, these units can also lead to a significant downsizing of the compressor pack, reducing the cooling system capacity. Currently, the air conditioning (AC) in REMA 1000 supermarkets, a leading supermarket chain in Norway, is supplied by a glycol circuit which is cooled by the CO2 (R744) booster refrigeration system. The design capacity of the refrigeration unit must handle all the refrigeration loads and the AC load during the warmest summer day, which results in overcapacity and part load operation for most of the year. This master’s thesis describes and investigates a proposed design for the implementation of a CTES dedicated to AC demand in a supermarket located in the Oslo region. This system aims to substitute the existing glycol circuit towards the air handling unit (AHU). Simulation results demonstrate that CTES offers substantial potential for reducing electrical peak power consumption during the warmest periods. The functioning of the CTES and its impact on the existing refrigeration system were simulated, revealing a peak reduction of up to 32,33%. The load shifting capability is demonstrated, absorbing 31,53% of the daily electricity consumption during the night, when the supermarket is closed, compared to 16,14% considering the instantaneous production of AC with the existing system. Consequently, electricity consumption can be increased by up to 74,8% during the night and decreased by up to 28% during the day. Even though energy savings are not the primary objective of this project, they are achieved by producing and storing energy required for AC during periods when the outdoor temperature is lower, and the coefficient of performance (COP) of the system is higher. The energy savings can reach up to 11,8% during the hottest day. Finally, the economic benefits of the system are assessed under spot pricing and tariff pricing systems, revealing potential electricity cost savings of up to 12,56% and 16,45%, respectively. The main big challenges of this system still remain its economical viability, in terms of payback time, and expanding its utilization during the winter period

Ejector for the world: simplified ejector-supported CO2 refrigeration systems for all climates

The novel configuration presented in this work simplifies the layout of ejector-supported booster systems while maintaining all the benefits of an ejector implementation. The basic version of the solution is based on: i) MT and LT compressor suction groups, ii) flooded MT evaporation with increased evaporation temperature, and iii) ejector utilization throughout the year. The ejector is actively operated as a high-pressure-control device at elevated ambient temperatures ('summer mode'). With lower ambient temperatures the ejector is operated passively, and the high-pressure control is performed by individual metering devices upstream of the different evaporators ('winter mode'). The feasibility tests performed in the laboratory proved that energy-wise this novel system configuration outperforms traditional and parallel compression supported booster systems under any condition. The pressure lift measured with active ejector is sufficient for liquid refrigerant distribution to the evaporators, while the pressure drop recorded in passive mode is negligible for practical applications.Ejector for the world: simplified ejector-supported CO2 refrigeration systems for all climatesacceptedVersio

Laboratory Evaluation of a Commercial CO2 Booster Refrigeration System

The traditional multiplex direct expansion (DX) refrigeration system used in commercial applications is prone to significant refrigerant leakage, especially older existing systems. EPA (2012) estimates that the U.S. supermarket industry-wide average refrigerant emission rate is approximately 25%. The use of high Global Warming Potential (GWP) refrigerants in these systems, combined with high refrigerant leakage, can result in considerable direct carbon dioxide equivalent (CO2eq) emissions. In addition, commercial refrigeration systems consume a substantial amount of electrical energy, resulting in high indirect CO2eq emissions. Thus, there are ongoing efforts to reduce both the direct and indirect environmental impacts of commercial refrigeration systems through the use of leak reduction measures, refrigerant charge minimization, low GWP refrigerants and energy efficiency measures. Based on prior energy and life cycle climate performance (LCCP) analyses, it was determined that a transcritical CO2 booster refrigeration system for supermarket applications has the potential to reduce carbon emissions and increase energy efficiency. To that end, a lab-scale transcritical CO2 booster refrigeration system was fabricated and installed in the environmental test chambers at the Oak Ridge National Laboratory (ORNL). This system consists of a transcritical CO2 compressor rack, an air-cooled gas cooler/condenser, medium-temperature (MT) and low-temperature (LT) refrigerated display cases, and MT and LT “false†loads. The lab-scale refrigeration system has a low-temperature cooling capacity of approximately 9.1 kW at −30°C and a medium-temperature cooling capacity of approximately 34 kW at −6.7°C. One 4-door vertical display case, 3.0 m in length, as well as a “false†load provided by a plate heat exchanger and a glycol loop, constitutes the low-temperature load. The medium-temperature load consists of one open vertical display case, 2.4 m in length, as well as a “false†load provided by a plate heat exchanger and glycol loop. The air-cooled gas cooler/condenser is installed in a temperature and humidity controlled “outdoor†environmental chamber while the compressor rack and refrigerated display cases are installed in a separate temperature and humidity controlled “indoor†environmental chamber. For both chambers, the temperature can be controlled between −18 to 65°C and the humidity can be controlled between 30 to 90%. The performance of the transcritical CO2 booster refrigeration system was determined at four ambient temperature conditions (15.6°C, 21.1°C, 26.7°C and 32.2°C). After the refrigeration system achieved steady-state operation at each of the four ambient temperature conditions, system performance data was collected for a 24-hour period. Over the temperature range of 15.6 to 32.2°C, the total load on the system was found to remain relatively constant. In addition, the compressor power was found to increase by approximately 78% over this same temperature range. Thus, the resulting coefficient of performance (COP) of the system was found to vary from 2.2 (at 32.2°C) to 4.1 (at 15.6°C). Based on the laboratory evaluation, the transcritical CO2 booster refrigeration system demonstrates promise as a low emission, high efficiency alternative to the traditional multiplex DX systems currently in use

Visualization of the Opening Process of a Discharge Reed Valve in the Presence of Oil

Oil in circulation in refrigeration systems generally degrades their thermodynamic and reliability performance. The vast majority of compressors used in the residential, automotive and light commercial air conditioning and refrigeration use pressure actuated reeds as the discharge valves. These valves are the gateway for the oil to leave the compressor to the rest of the system. This work is focused on the breakup process of the film that is formed between a reed valve and its seat. Emphasis is given on visualization of the breakup pattern and determination of the critical valve lift and velocity at which the film breaks during typical compressor operation. Preliminary experiments were carried out outside of the compressor environment, using a typical valve plate from a reciprocating compressor for household refrigerators. Observations of the breakup pattern show that the liquid film does not remain continuous until breakup into ligaments and droplets. In fact the stretched liquid film is first broken up into equally spaced liquid columns and then by means of the drag force promoted by the vapor flow due to the pressure difference it is blown away from the valve edge and starts the atomization process into a fine mist. Additional experiments were also carried out with two different oil viscosities (32cSt & 120cSt), and four different operating frequencies ranging from 30Hz-60Hz in a scroll type compressor operating under typical residential air conditioning conditions. The valve lift was inferred by visualization and determined using image processing techniques implemented in MATLAB.. The visualizations were also utilized to quantify the droplet cloud velocities, and also valve critical lift before oil is ejected from the gap between valve and seat

An Experimentally Validated Model for Microchannel Heat Exchanger Incorporating Lubricant Effect

In the microchannel heat exchanger model that is developed in this study, the thermodynamic and transport properties of refrigerant-oil mixture are taken into account as well as their impact on boiling heat transfer and pressure drop. This model is validated against experimental results (R134a-PAG 46 oil) at various oil circulation rates (0.1%-8.3%). The agreement between measurement and prediction is ±4% for capacity, ±10% for pressure drop and ±3? for superheat at compressor inlet. Inclusion of lubricant in the new model has provided better prediction over models using pure refrigerant. Simulation results also indicate that lubricant addition improves refrigerant distribution, thus decreases the capacity degradation due to maldistribution

Energy efficient multiejector CO2 cooling system for high ambient temperature

Experimental evaluation of a multiejector CO2 cooling system of 33 kW cooling capacity is conducted for an Indian supermarket at high ambient temperature context. The test-rig is designed to depict the actual supermarket cooling requirements in India with three different cooling temperature levels simultaneously; freezing, medium refrigeration and air-conditioning. The rig is equipped with a novel design consisting of two multiejectors; low ejection ratio ejector (LERE) and high ejection ratio ejector (HERE), in a series configuration. It is observed that the maximum pressure lift of 5.5 bar is obtained with this new design. Moreover, improvement in the overall system performance with the support of the internal heat exchanger (IHX) is evaluated. Enhancements observed in the maximum COP and PIR are 7.2% and 6.2% respectively. Furthermore, the test-rig performance with the flooding and non-flooding of the medium temperature evaporator (refrigeration) is evaluated. It is observed that the evaporator flooding reduces its superheat at the exit by 83.84%, leading to the overall reduction of PIR by 6.51%. The performance of the proposed system is also compared with the reported field data obtained at a low ambient temperature context. The results projected that the proposed cooling system with series multiejector configuration is a reliable choice for higher ambient temperatures and it is expected to outperform the existing systems at lower ambient temperatures.acceptedVersio