The core components of vapor absorption refrigeration systems (VARSs) are the absorber, generator, condenser and evaporator. A pump is a critical component of a VARS to circulate the refrigerant–absorbent solution from the low pressure absorber to the high pressure generator. High quality mechanical/electrical energy is required to run this pump. Furthermore, the electrical pump is exposed to the high temperature corrosive solution. A thermally-driven bubble pump, which can be powered by waste heat or solar thermal energy, offers a simple and efficient technique for lifting a liquid from lower to higher levels, after which it can flow by gravity. In the vapor absorption refrigeration cycle, a bubble pump can be used to lift the solution from the absorber to the generator and also desorb the refrigerant vapor for achieving the necessary cooling effect. The performance of a VARS strongly depends on the bubble pump parameters. So the proper modelling and analysis of bubble pump parameters is a crucial to maximize the cycle performance. Extensive theoretical and experimental research has been performed in order to use the bubble pump for VARS. Some analyses have been developed based on air-lift pumps, some did not consider friction factor effects, two-phase flow, or the gas void fraction. Laminar flow is assumed and heat loss was not included for these analytical models. Beside these factors, thermophysical properties (such as specific heat, heat of vaporization, density, viscosity, surface tension) of the solution are also important for the evaluation of bubble pump performance as well as the overall performance of it in refrigeration systems. In this study, an analytical model of a bubble pump characteristics was developed and experimental work was conducted in order to use this pump in a VARS. In the simulation model, two-phase turbulent flow with heat loss, friction, surface tension effects and other thermophysical properties was considered. The model was validated by operating the bubble pump with water at atmospheric conditions. The bubble pump performance was investigated with tube diameters of 6 to 10 mm and lifting ratios (the ratio of the height of the liquid in the tube to the tube length) of 0.6 to 0.8, and at different heat inputs. Experimental results agreed with theoretical within 14%. The maximum liquid flow rate was obtained during slug flow at 180 watts heat input, a lifting ratio of 0.8, and tube diameter of 10 mm.

Absorption chillers represent a promising alternative to traditional vapor compression chillers, especially for the air conditioning systems. Indeed, they provide the same cooling supply without such a high electrical consumption, being driven by a low-temperature heat source. On the other side, they are not yet competitive with compression chillers because of their large size and high costs of investment. Their optimization becomes then a fundamental task to perform. Among the several components of these chillers, the absorber has been identified as the limiting one. The main obstacle is the low wetting on its tube bundle, which limits the absorption process. One way to overcome this problem is by the mean of additives. Indeed, small quantities of alcoholic surfactants in the working fluid lower the surface tension, promoting local turbulence at the vapor-liquid interface (Marangoni convection), which in turn leads to higher heat and mass transfer coefficients in the absorber. Nevertheless, only two kinds of additives are mostly used in these chillers and the experimental results available in literature are not in good agreement. The surface tension of water and aqueous lithium-bromide solution with different surfactants is experimentally investigated in this work. Common additives (e.g. 2-Ethylhexanol, 1-Octanol) as well as new additives are used. Their concentration in the solutions is varied in a wide range. The surface tension is measured according to the Pendant Drop Method. Several parameters are varied during the experiments, such as pressure, temperature and surrounding conditions. All the measurements are performed in a closed vacuum cell, in order to have the vacuum condition that occurs in the absorber, and to produce reproducible data. Results are discussed and compared with the available literature. The current study is carried out in the framework of the ITN Marie Curie “SHINE” research program financed by the European Union.

This presentation provides an introduction and overview of the current standards for rating positive displacement compressors.  It reviews the industry standard polynomial equation used for presenting ratings and the basis for the reference rating conditions.  It also explains the uncertainty limits associated with the standards and what they mean as they apply to a single compressor versus a batch/rack of compressors.  It explains the limitation of most compressor ratings and provides suggestions on how these ratings should be applied with zeotropic refrigerants as well as how to perform superheat corrections.

Positive displacement compressors with vapor injection are commonly used in the vapor compression cycle to increase the refrigeration effect of evaporators or the heat rejection of a condenser. It is important to characterize injection flow just like the suction flow in order to allow system designer to size the components of HVAC equipment. This seminar presents a method to characterize compressors with vapor injection.  The method is based on the AHRI 10-coefficient model with the addition of another independent and dependent variable.  The accuracy of the method will be presented and its effect on the number of test points required.

This presentation demonstrates determining the optimal method to predict compressor performance over the application envelope maximizing accuracy for a given number of test points. The uncertainty in each method is estimated as a function of measurement reproducibility and/or product-to-product variation, especially at the typical rating points given in the performance rating standard. The AHRI standard 540 was evaluated using three sets of compressor test data, and showed small uncertainty within the operating envelope. The study included uncertainty analysis in power and mass flow rate extrapolation outside the envelope.  The presentation also covers a study on the effect of superheat.

Vapor injection in conjunction with economized cycle is becoming more wide-spread as the unit efficiency requirements become more stringent and more difficult to meet with the new low-GWP refrigerants.   Economized cycle substantially boosts both efficiency and cooling/heating capacity.  A two-stage design is used in reciprocating compressors with vapor injected between the low and high compression stages. One of the most difficult tasks is to properly size the displacement of low and high pressure stages. This paper examines what controls this sizing to optimize vapor injected compressor performance with respect to operating conditions, refrigerant properties, and unit capacity and efficiency goals.

This session covers the background behind the movement to Low GWP and Natural Refrigerants, discussing regulations and phase-out dates, both nationally and internationally.  The case is made that owners need to begin reviewing alternatives, and why both Ammonia and CO2 are very viable alternatives.

This session presents several case studies in which low-charge ammonia systems were employed both in the US and Europe.  The case studies include details about the specific project constraints, and how low-charge ammonia systems were designed to fit within those constraints in an overall cost-effective manner.

The overall objective of any design engineer is to provide a cost-effective system that meets the owner's long-term needs.  This session reviews the issues and concerns of a refrigeration system from an owner's perspective, and the lessons learned from the deployment of low-charge ammonia systems.

There is a tremendous amount of activity using CO2 in addition to ammonia.  This case study reviews a refrigeranted storage and processing warehouse that was constructed using an existing building shell in the greater Chicago area.  Transcritical CO2 was used to serve multiple temperature areas as well as a portion of the facility that was dedicated to retail sales.  This seminar covers the design, installation, and operation stages of the project and provide lessons learned through the process.

Presented are a number of light commercial applications that were successfully converted for use with natural, low-GWP refrigerants. Among them are a chilled juice dispenser, originally designed for R134a, that was redesigned for use with transcritical carbon dioxide (R744). Another system successfully converted for use with a natural refrigerant was a platelet incubator typically used in pharmaceutical laboratories. The original R134a refrigeration system was redesigned to accommodate isobutane (R600a). Finally, several glass door merchandisers have been converted successfully to both propane (R290) and carbon dioxide. The technical challenges of each of these conversions will be presented and discussed in detail.

Ammonia is known to be one of the most energy efficient refrigerants, but its use has mainly been limited to large industrial system applications. Low-charge ammonia chiller technologies recently introduced to the U.S. market have the potential to improve efficiency in many commercial refrigeration applications while addressing previously-held concerns. The presentation showcases an ammonia chiller installation in Irvine, California and share preliminary performance information compared to the existing R-507A system.

Shifting to low-GWP refrigerants can drastically reduce the potential for greenhouse gas emissions from refrigerant leaks while improving energy efficiency. SCE recently completed laboratory testing of commercial freezer cases with R-404a and R-290 (propane). Results, including temperature and energy performance are shared along with potential plans for energy efficiency and low-GWP refrigerant rebates in California.

This presentation focuses on the application of low global warming potential (GWP) alternative fluids for commercial stand-alone applications. The presented non-flammable and mildly flammable molecules will cover HFO’s and HFO blends which provide lower or very low GWP (below 150). Experimental system test data as well as thermodynamic simulation and design characteristics are discussed compared to current solutions to underline the performance of these new fluid options.

Large commercial refrigeration systems have unique concerns/opportunities unlike those with a single compressor – single evaporator system.  This seminar will discuss Lubricant Management from the outlet of the compressors through all components including the oil separator, receiver, valving, headers and suction and liquid lines as well as risers and back to the compressor.

Every component on the refrigerant side of a system comes into contact with the compressor’s lubricant.  This lubricant plays a key role in the performance and life of thermostatic expansion, electric expansion, and solenoid valves.    There are also interactions between the system lubricant and other system components such as piping, contaminant controls, and sealing surfaces.  This presentation explores good lubricant management practices and the challenges this part of a refrigerant system faces when transitioning to new lower GWP refrigerants.

Once oil leaves the compressor, it circulates through all components before returning to the compressor to perform its primary lubrication objective.  Oil induced wetting, foaming, and pressure drop impact heat exchanger effectiveness and pressure drop, sometimes in ways which are counterintuitive.  Oil disproportionately accumulates in regions of the heat exchanger which have the greatest effect on distribution of refrigerant flow, therefore the impact of oil is much larger than its circulation ratio would suggest.  Infrared photography and high speed videos are used to demonstrate changes in distribution and subsequent effect on heat exchanger and system performance.

When lubricant in the compressor circulates into the system, it may build up as a thin film on the internal surfaces of heat exchangers and acts as a thermal insulator. This robs the system of efficiency and increases energy consumption.  In addition, refrigeration systems have a fixed volume so circulating oil competes with the refrigerant resulting in reduce cooling capacity.  Oil separator technologies serve to regulate and minimize oil circulation by isolating the lubricant early in the discharge line and return it to the compressor.  This study examines the performance of various oil separation technologies using controlled experiments.

The transport refrigeration systems used in trucks and trailers are an integral component of the cold chain for perishable foods, pharmaceuticals and other temperature-sensitive products. The technology used in these systems is continually evolving to meet food quality standards, as well as current and future regulatory requirements for greenhouse gas emissions. Additional technologies have enabled greater fleet management and control, as well as reductions in customer operating costs. The present talk provides a summary of transport refrigeration requirements, along with an overview of available technologies used to address them and a discussion of the related technical challenges and design tradeoffs.

Advances in transport refrigeration and air-conditioning systems used in ships have evolved over many years. Today’s systems must incorporate the latest available technologies, taking into consideration current and future regulatory requirements for refrigerants with low Global Warming Potential, energy efficiency, indoor air quality, food quality standards and customer expectations around total operating costs. A summary of transport refrigeration system technologies generally, along with marine air-conditioning systems, is presented and includes associated technical challenges, trade-offs and potential design impacts.

Air cycle is the traditional refrigeration technology in the aerospace industry. Moving toward “more-electric” and “all-electric” aircraft concepts calls on high efficiency refrigeration technologies. Vapor cycle technologies are more efficient than the air cycle technologies and, therefore, the number of vapor cycle systems installed in aircrafts will increase in “more-electric” vehicles. At the same time advances in transport refrigeration systems used in airplanes have evolved over many years. A summary of transport refrigeration system technologies for aerospace applications is presented, focusing on vapor cycle systems integrated with environmental control systems (ECS).

Advances in transport refrigeration systems used in “Trailers” have evolved over many years. Today’s systems must incorporate the latest available technologies, taking into consideration  current and future regulatory requirements for refrigerants with low Global Warming Potential, energy efficiency, food quality standards and customer expectations around total operating costs. A summary of transport refrigeration system technologies generally, along with marine air conditioning systems, are presented and includes associated technical challenges, trade-offs, and potential design impacts.

The thermodynamic properties of refrigerants modeled in a simple single-stage vapor compression cycle can provide insight into the potential benefits or challenges associated with new generations of refrigerants.  This presentation outlines a simple thermodynamic cycle model and discuss various aspects important to system performance, including the impact of temperature glide when using zeotropic blends.  The thermodynamic performance of a range of next generation low GWP refrigerants will be reviewed, highlighting the potential benefits and challenges in front of us as we transition yet again.  Maybe not everything is going downhill?

The total environmental impact of leading lower GWP replacement refrigerants for R410A and R134a based chillers must be considered.   There are several alternate refrigerants with lower GWP’s than R410A and R134a, but the direct emissions are only one contributor to the total global warming impact.   The impact on efficiency must also be considered.   Chillers are very high efficiency and low leak products so the impact from direct emissions is low compared to indirect.   Results on annualized analysis of the efficiency including the impact of refrigerant cycle performance changes and heat transfer changes across all 19 climate zones will be presented.

With environmental concerns on high global warning potential (GWP) refrigerants used in HVACR industry, Carrier Commercial Engineering participated in the AHRI Alternative Refrigerants Evaluation Program (AREP). This study is to understand the Low GWP refrigerant options available to replace R-410A. A 10 ton Rooftop air conditioning unit was tested evaluating four Low GWP refrigerant candidates. The test consisted of EER and high ambient conditions. The refrigerants evaluated were R-32, R-454B, R-446A and R-447A as well as baseline refrigerant R-410A. The current and future regulations for Low GWP refrigerants, energy efficiency, and operation envelop were considered in the investigation.

A lower global warming potential (GWP) refrigerant blend, R448A, composed of hydrofluorocarbon (HFC) and hydrofluoro-olefin (HFO) refrigerants, has been proposed as an alternative to R404A.  An evaluation of these two refrigerants in a laboratory-scale commercial refrigeration system is presented in this session.  The system COP when operating with R448A was found to be up to 7% higher than that of R404A, while compressor power decreased by up to 6% when operating with R448A versus R404A.  Given that R448A exhibits lower GWP than R404A, with similar operating characteristics and no energy penalty, R448A is a suitable lower GWP replacement for R404A.

Industrial heating consumes a significant fraction of the energy consumed globally. Heating at temperatures higher than about 100°C is predominantly provided through combustion of fossil fuels with uncertain prices and well recognized environmental impacts. A significant fraction of industrial input energy is lost as low temperature waste heat (e.g. warm exhaust gases or cooling water) that could be lifted by high temperature heat pumps to process relevant temperatures. This paper assesses the potential for providing heating at temperatures between 100^oC and 150^oC through electrically-driven mechanical compression heat pumps. It reports the measured performance of a lab-scale reciprocating heat pump with HFO-1336mzz-Z (CF₃CH=CHCF₃; previously referred to as DR-2) as the working fluid over a range of conditions representative of intended applications (e.g. drying or steam generation). HFO-1336mzz-Z has attractive safety, environmental and thermodynamic properties and high chemical stability at high temperatures. Various compressor technologies, compressor lubricants, heat exchanger designs, expansion valve types and cycles with and without an internal heat exchanger were considered. Suitable equipment components were selected to meet the requirements for testing at evaporating temperatures between 30°C and 115°C and condensing temperatures in the range of 75°C to 150°C. Test results are compared with predictions based on ideal cycle thermodynamic modeling and the advantages of HFO-1336mzz-Z over other refrigerants are discussed. HFO-1336mzz-Z could enable more environmentally sustainable industrial heat pumps for the utilization of abundantly available low temperature heat to meet heating duties at higher temperatures, with higher energy efficiencies and lower environmental impacts than with incumbent working fluids.

The HVAC&R industry continues to evaluate low global warming potential (GWP) alternatives to R410A.  This paper reports performance of a 4 RT commercial rooftop heat pump with R410A as a baseline along with potential alternatives DR-55, DR-5A (R454B), and R32.  An adjustable frequency drive (AFD) was installed to allow the same capacity to be achieved with each refrigerant, matching compressor capacity to heat exchanger capacity.  Adjustable thermal expansion valves (TXVs) were installed to achieve the same compressor suction superheats in each case. 

Measurements of performance at the AHRI Standard 210/240 rating points were made with each refrigerant.  In addition, tests were run under outdoor temperatures ranging from 65F to 125F (18C to 52C).  A simple thermodynamic cycle model that matches average saturation temperatures in the evaporator and condenser along with a common compressor isentropic efficiency indicates that the capacity with DR-55 should be 2.5% lower than with R410A and should have an efficiency 1% higher.  Actual performance with DR-55 matched the capacity of R410A at the same compressor speed (60 Hz) with an efficiency 4% higher.  Similarly positive results were obtained with DR-5A.  With R32, the compressor speed needed to be reduced to 53 Hz to match the baseline capacity.  Efficiency was 3% higher than baseline.  As expected, R32 produced compressor discharge temperatures (CDTs) that were elevated by 20F and increased to 40F at the higher ambient conditions over R410A while DR-55 and DR-5A CDTs were only 10F above the baseline.  

The results here demonstrate that DR-55 and DR-5A are "design compatible" alternatives to R410A.  That is, they can be used in existing equipment designs with very little modification.

This paper explains the drop-in test results of R410A and R32/1234ze blend to a R32 dedicated mini-split air conditioner as well as simulation results. Usually, R32 and blends are dropped in to R410A units, but here the tests were carried out in opposite direction. As the test unit employs variable speed compressor, the paper clarifies the relative performance between these refrigerants under wide range of capacity. Since 32/1234ze blend is zeotropic, the impact of the change in flow velocity of refrigerant in heat exchange is clearly observed. Tests and simulations of the sample unit are also performed at high ambient conditions with these refrigerants. Such operation is now focused on due to the Montreal protocol discussion.

In response to environmental concerns raised by the use of refrigerants with high Global Warming Potential (GWP), the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) has launched an industry-wide cooperative research program, referred to as the Low-GWP Alternative Refrigerants Evaluation Program (AREP), to identify and evaluate promising alternative refrigerants for major product categories. After successfully completing the first phase of the program in December 2013, AHRI launched a second phase of the Low-GWP AREP in 2014 to continue research in areas that were not previously addressed, including refrigerants in high ambient conditions, refrigerants in applications not tested in the first phase, and new refrigerants identified since testing for the program began. Although the Ozone Depletion Potential of HFC-410A is zero, this refrigerant is under scrutiny due to its high GWP. Several candidate alternative refrigerants have already demonstrated low global warming potential. Performance of these low-GWP alternative refrigerants is being evaluated for various applications to ensure acceptable system capacity and efficiency. This paper reports the results of a series of compressor calorimeter tests conducted for the second phase of the AREP to evaluate the performance of R-410A alternative refrigerants in a reciprocating compressor designed for air conditioning applications. It compares performance of alternative refrigerants ARM-71A, L41-1, DR-5A, D2Y-60, and R-32 to that of R-410A over a wide range of operating conditions. The tests showed that, in general, cooling capacities were slightly lower (except for the R-32), but energy efficiency ratios (EER) of the alternative refrigerants were comparable to that of R-410A.

Faced with more stringent regulatory pressures, the demand for environmentally friendly substances is high. The number of low global warming (GWP) refrigerants entering the market is rapidly increasing to meet market needs.  Many of the new low GWP refrigerants are “mildly flammable” or “2L” as classified by ISO 817 and ANSI/ASHRAE Std 34. The new refrigerant flammability class provides the heating/air-conditioning/refrigeration industry potential options to meet environmental regulations with equipment designed to meet reduced flammability concerns.  Mildly flammable refrigerants are defined as refrigerants which have burning velocity less than 10 cm/sec and heat of combustion (HOC) less than 19,000 kJ/kg.  Although not part of classification requirements, mildly flammable refrigerants have higher lower flammability level (LFL) and exhibit higher minimum ignition energy (MIE).  Current MIE testing of 2L refrigerants has employed ASTM E582, which use an electrical spark ignition source.  Results from that testing has shown that typically, class 2L refrigerants have MIE values which are two to four orders of magnitude greater than highly flammable or ISO 817/ANSI 34 class 3 refrigerants. The high MIE values determined for mildly flammable refrigerants denotes that they are typically very difficult to ignite. A relatively unexplored potential ignition source is a hot surface which can be found in air conditioning auxiliary heaters and other refrigeration systems.  Maximum hot surface temperatures are also specified in several equipment standards.   Recently, work was conducted to review potential ignition/non-ignition for several 2L refrigerants which were released onto a hot surface. A new test was designed to simulate a 2L refrigerant leak onto a hot surface within a piece of equipment.    In particular, individual refrigerants were released onto a heated metal surface and potential ignition was observed for a set time period after the refrigerant was released.  Interestingly, ignition values noted were several hundred degrees higher than literature auto-ignition temperature (AIT) values. This work summarizes the test apparatus used, the hot surface ignition testing conducted with various 2L refrigerants, and ignition testing results.