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A load-based methodology for testing and rating the performance of unitary air conditioning equipment has been developed and demonstrated using a laboratory psychrometric chamber test facility. The methodology simulates representative sensible and latent loads of a commercial building as well as the thermal and latent capacitance of buildings using psychrometric chamber test facilities. The advantage of the proposed test methodology is that there is no requirement to disable the native control systems designed by equipment manufacturers. This results in more realistic representations of the installed performance of equipment that include interaction of their embedded controls with the building. The load-based control approach is described and applied to the control system of an existing psychrometric chamber test facility. Results using the developed test methodology collected from fixed-speed and variable-speed RTUs show significant differences between actual part-load performance and steady-state performance at equivalent ambient operating conditions. A test procedure that includes interaction of the equipment controls with a virtual building could enable future equipment ratings that are both climate and building-type specific. This would not be possible for the current testing approaches that override native controls with no building interaction. [ABSTRACT FROM AUTHOR]

• Addressed a real-world challenge for load-shifting multiple ON/OFF staged units. • Presented a unique MPC that shifts load while eliminating undesired peak. • Presented comprehensive 2-month experimental MPC demonstration results. • Achieved significant load shifting with over 30% demand savings. • Discussed experimental charging and discharging processes of building thermal mass. Small and medium-sized commercial buildings (SMCB) are significant demand response resources, and it is important to develop grid-responsive control algorithms that exploit those resources and create financial benefits for building owners and HVAC service providers. Furthermore, unlike large-sized commercial buildings, there is an opportunity to have universally applicable control solutions for many SMCBs since those buildings have a consistent HVAC system configuration: SMCBs are commonly served by multiple-staged air conditioning units controlled by their own thermostats. Despite the demand response potential and scalability, however, very few control solutions are available for SMCBs. Typical model predictive control (MPC) and heuristic control approaches for cooling load shifting that lower thermostat setpoints before an electric price jump are suitable mainly for large-sized commercial buildings where a continuous capacity modulation is possible, e.g., via dampers in variable air volume terminal units. However, those approaches can cause undesired, high peaks for SMCBs due to the nature of ON/OFF unit staging and narrow thermostat deadbands. This could discourage the use of advanced grid-responsive controls for SMCBs due to the concern of high demand charges, and has to be resolved. This paper presents a MPC solution that overcomes this challenge. It has a hierarchical MPC structure where an upper level MPC is responsible for electrical load shifting in response to an electric price signal while a lower level MPC is responsible for coordinating compressor stages to eliminate unnecessary peaks and follows the setpoints determined by the upper level MPC. Two one-month, comprehensive laboratory tests have been carried out to demonstrate load shifting and cost savings for the algorithm. Interesting trade-offs between energy efficiency and load flexibility were observed and are discussed, and lessons learned for applying MPCs for SMCBs are also presented. [ABSTRACT FROM AUTHOR]

Abstract: Multi-split ductless heat pumps are touted as an energy efficient option for air conditioning and heating in residential and small commercial applications. However, their use of multiple indoor units with variable speed compressor and fans and complicated controls leads to difficulties in understanding their characteristics by experiments only. A method to model the system using gray-box component models and an empirical control algorithm is described in this paper. The model was constructed from experimental results of an 8 kW R410A dual-unit ductless heat pump system having an accumulator. Strategies for modeling systems with accumulators and saturated control inputs are presented. Parametric studies with varying indoor air temperature, individual indoor unit load ratio, indoor fan speed and total indoor load were conducted. The results show that the model predicts system performance accurately and can help to understand the effect of saturated control inputs and changes of accumulator status on system performance. [Copyright &y& Elsevier]

Abstract: The paper provides results that show the impact of charge level on capacity and efficiency for several units tested in the laboratory. To evaluate the performance, capacity ratio and COP ratio were determined from measurements at various refrigerant charge levels and operating conditions. For all systems considered in this study, a refrigerant charge reduction of 25% led to an average energy efficiency reduction of about 15% and capacity degradation of about 20%. To evaluate the economic value of charge detection and correction, Seasonal Energy Efficiency Ratio (SEER) and annual cost of electricity were determined for some case studies based on the tested units. The results imply that charging inaccuracies could cause significant decreases in SEER, leading to increases in the operating costs. When the refrigerant was charged to 75% of design, the SEER value decreased by 16% and annual operating cost was increased by US$ 100 per ton of capacity. [Copyright &y& Elsevier]

Abstract: Models for unitary air conditioners and heat pumps typically have difficulties in providing accurate predictions for the following situations: 1) charge modeling over a large range of charge levels, 2) two-phase refrigerant entering fixed-orifice expansion devices, 3) two-phase refrigerant entering compressors, and 4) non-uniform refrigerant mass flow allocation among evaporator circuits at low indoor air flow rates. This paper gives descriptions and assessments of improved modeling methodologies for all four issues. The study utilizes data obtained from extensive testing at a wide range of operating conditions for two R-410A units and one R-407C unit. [Copyright &y& Elsevier]

Refrigerant pressures are critical measurements for monitoring, control, diagnostics, and optimization of vapor compression cycle equipment. Direct refrigerant pressure measuring practices are expensive and more than often problematic. This paper describes a method, termed virtual pressure sensing, wherein refrigerant pressure values are indirectly derived from low-cost temperature sensors that can be surface-mounted. In this manner, physical pressure sensors are eliminated and pressure sensing can be achieved at a much lower cost and in a non-invasive way. Five virtual pressure sensors are developed to obtain the five most important pressures in vapor compression cycle equipment: compressor discharge line pressure, condensing pressure, liquid line pressure, evaporating pressure, and suction line pressure. The performance of the proposed virtual pressure sensors, in terms of accuracy in estimating pressures and inferring liquid line subcooling, suction superheat, compressor power consumption, and refrigerant flow rate, is evaluated extensively using laboratory data collected from four systems. These systems include air conditioners and heat pumps, split and packaged systems, refrigerants R-22 and R-410α, fixed-orifices and thermal expansion valves, and reciprocating compressors and scroll compressors. Ultimately, the virtual sensors are used as a part of a decoupling-based fault detection and diagnosis (FDD) technique to diagnose multiple simultaneous faults. The impact of the virtual pressure sensors on the FDD performance is evaluated extensively using the laboratory data collected from the four various systems. [ABSTRACT FROM AUTHOR]

Adjustable throat-area expansion valves (ATAEVs), including thermostatic and electric expansion valves, are used commonly in air-conditioning equipment and lead to improved system performance as compared to the use of fixed-orifice expansion devices. However, ATAEV modeling literature is limited. Typically, an ATAEV is modeled by specifying the superheat entering the compressor or by empirically correlating experimental data. In order to model system behavior more accurately and effectively over a wide range of conditions, more accurate ATAEV models are necessary and a more general modeling methodology is desired. This paper presents a general model format that utilizes manufacturers' rating data. Model structures for three types of valve geometries are derived. Two model formats and corresponding parameter estimation procedures using manufacturer performance rating data are considered. The proposed method is validated using experimental data and compared with results from the literature. Both the experimental validation and the theoretical analysis demonstrate that the proposed method is more accurate and more generic than other methods presented in the literature. [ABSTRACT FROM AUTHOR]

This paper presents a detailed experimental validation of a simple transient model for cooling and dehumidifying coils that is developed in a companion paper (Zhou and Braun 2007). In all cases, the model provided very accurate predictions of exit air and water states. This appears to be the first experimental validation of a transient coil model under conditions where moisture condensation occurs. [ABSTRACT FROM AUTHOR]

Dynamic coil models are useful in the development and evaluation of feedback controllers and fault detection and diagnostics algorithms. Existing models in the literature have not been validated fully using experimental data and have not been evaluated in terms of trade-offs between model accuracy and computational requirements. This paper develops a computationally fast, distributed model for the transient behavior of cooling and dehumidifying coils. The model utilizes several steady-state performance indices that simplify dynamic modeling, including fin efficiency, air-side effectiveness, and water-side effectiveness. Predictions from the simplified model were compared with a detailed reference model and with other simplified models from the literature. Comparisons with detailed experimental measurements are given in a companion paper (Zhou and Braun 2007). The model provides very accurate predictions of coil transient performance and executes more than 1000 times faster than real-time on a 1.2 GHz personal computer. As a result, it is very practical for implementation within system simulation programs that execute over long time periods, such as a year. [ABSTRACT FROM AUTHOR]

Abstract: The most promising applications for standing-wave thermoacoustic cooling were investigated from the perspective of the ratio of coefficient of performance (COP) to the reversible COP or COPR. A design optimization program based on the thermoacoustic simulation program known as DELTAE was developed. The program was applied to two standing-wave thermoacoustic cooler configurations in order to determine the best possible COPRs for various temperature spans between hot-side and cold-side stack-end temperatures. It was found that the COPR of standing-wave thermoacoustic coolers increases with temperature span and reaches a maximum for temperature lifts around 80°C. Analysis of the results and the losses clearly shows that the efficiency of these systems may be good for refrigeration, but not for air-conditioning and cryogenic cooling. The COPRs determined from measurements for various thermoacoustic coolers developed so far show similar trends, and generally support the optimization results. [Copyright &y& Elsevier]

Abstract: This paper presents results of experiments performed on different combinations of five types of filters of varying efficiencies (MERV4, 6, 8, 11, and 14) and four types of evaporator coils with depths and fin geometries under clean and fouled conditions. The fouled conditions were obtained after injection of 600g (1612g/m2 of coil face area) of dust upstream of the filter–coil combination, which was meant to simulate a year of operation in the field. The air-side pressure drops of the coils and filters and air-side effective heat transfer coefficients of the coils were determined from the measurements under the clean and fouled conditions. Depending upon the filter and coil, the coil pressure drops increased in the range of 6–30% for an air velocity of 2.54m/s. The impact was significantly greater for tests performed without an upstream filter (the coil pressure drops increased from 43% to 200%). The largest relative effect of fouling on pressure drop occurs for coils with fewer rows, primarily due to higher fin densities. The impact of fouling on air-side effective heat transfer coefficients was found to be relatively small, which ranged from −14% to 4%. In some cases, heat transfer was actually enhanced due to additional turbulence caused by the presence of dust. However, with large dust deposits, heat transfer is degraded because the dust also acts as insulation and creates an uneven air velocity. [Copyright &y& Elsevier]

Abstract: This paper describes the development and evaluation of features and virtual sensors that form the basis of a methodology for detecting and diagnosing multiple-simultaneous faults in vapor compression air conditioning equipment. The features were developed based upon a physical understanding of the system, cost considerations, and heuristics derived from experimental data and modeling results. Virtual sensors were developed in order to reduce the cost of implementation. The validity of the features and virtual sensors was evaluated using measurements from a variety of different air conditioners tested in a laboratory environment. More detailed evaluation results are presented in separate papers. [Copyright &y& Elsevier]

Abstract: The goal of the study presented in this paper was to evaluate the impact of different filter types on the performance of three typical packaged air conditioners under both clean and fouled conditions. In a companion paper, combinations of six different levels of filtration and four different coils were tested under clean and fouled conditions. From the tests, it was found that fouling has a relatively small impact on air-side effective heat transfer coefficient, but can have a large impact on coil pressure drop. Data from the experimental study were used in developing simulation models for the three packaged air conditioners. Simulations show that the equipment cooling capacity is reduced with fouling primarily because of a decrease in air flow due to the increased pressure drop. In most cases, EER (energy efficiency ratio) was reduced with fouling primarily due to increased fan power. However, the changes in EER were relatively small, in the range of 1–10%. Equipment having low efficiency filters had higher EER after fouling than equipment with high efficiency filters, because high efficiency filters result in significantly higher pressure drops than low efficiency filters. The impact of the evaporator side fan efficiency was found to be significant. The energy penalty associated with high efficiency filters was reduced greatly when fan efficiency increased. Although high efficiency filters cause higher energy penalties they provide considerably better air quality. The quantity of dust passing through the coil with an MERV14 filter was approximately 30 times less than the dust passing the coil with an MERV4 filter. This difference was doubled when the MERV14 filter was compared to a case with no filter in place. [Copyright &y& Elsevier]

Existing methods addressing automated fault detection and diagnosis (FDD) for vapor-compression air-conditioning equipment have good performance for faults that occur individually but have difficulty handling multiple simultaneous faults. In addition, these methods either require high-cost measurements or measurements over a wide range of conditions for training reference models, the development of which can be time consuming and cost prohibitive. This paper formulates model-based FDD in a generic way and demonstrates that decoupling is the key to handling multiple simultaneous faults. To eliminate a cost-prohibitive overall system model, an alternative physical decoupling methodology to mathematical decoupling is developed. During the mathematical development, a previously developed FDD method termed the statistical rule-based method is reexamined and cast within the general mathematical framework. The paper also includes an evaluation of the FDD method in terms of both sensitivity and robustness. [ABSTRACT FROM AUTHOR]

Abstract: Air conditioning is a non-critical application for fault detection and diagnosis (FDD) where decisions about servicing faults should involve the use of economics. Existing methods for evaluating impacts of faults on equipment performance only consider some individual factors such as the equipment coefficient of performance (COP) or cooling capacity. This paper develops an overall economic performance degradation index (EPDI) for air conditioning equipment that includes the combined effects of degradations in COP, cooling capacity, and sensible heat ratio (SHR). EPDI quantifies the performance degradation caused by faults based on economics so it can be used as part of the decision making process in an overall FDD system. Furthermore, EPDI can be used along with estimates of typical field performance degradations to assess the economic benefits associated with the application of automated FDD. A case study is presented where EPDI was applied to measurements for an existing unit where faults were artificially introduced. [Copyright &y& Elsevier]

Abstract: It is necessary to know CO2 source generation rates and system flow parameters, such as supply flow rate and overall room ventilation effectiveness, in order to evaluate cost savings for demand-controlled ventilation applied to commercial buildings. This paper presents a methodology for estimating schedules for generation rates and flow parameters using short-term testing. These parameters are used within a model that predicts return air CO2 concentrations as part of an overall energy analysis model. As a first step in developing the methodology, two different parameter estimation techniques were evaluated using simulated data. Each method gave models that provide good predictions of return air CO2 concentrations, but differed in terms of the identified parameters. The preferred parameter estimation method provides estimates of both average hourly source generation rates and day-to-day variations. This technique was applied to three different types of commercial buildings using field monitored data. The sites are small commercial buildings with packaged HVAC equipment and included modular schoolrooms, children''s play areas in fast food restaurants and a pharmacy retail store. The impact of the length of model training data period on estimated CO2 generation rates was investigated. Eight weeks of data is sufficient for training. Expressed in terms of the coefficient of variation, the errors in predicted CO2 concentrations ranged from 4% to 15% depending on the sites. The predicted frequency of time that CO2 concentrations were within a given range agreed well with the field measured data. [Copyright &y& Elsevier]

Abstract: Evaluation of a building for application of demand-controlled ventilation (DCV) typically involves the use of computer simulations to predict energy use/costs for both fixed ventilation and ventilation adjusted to maintain fixed CO2 levels within the space. The simulation tools incorporate models for predicting CO2 concentrations in response to internal sources (people), infiltration/exfiltration, and ventilation. This paper presents a detailed evaluation of different modeling approaches for predicting levels of CO2 in occupied spaces for small, single-zone commercial buildings employing packaged air-conditioning equipment. Two-zone and three-zone transient models were compared with a quasi-static equilibrium model applied to three distinctly different building types. Baseline data were derived from computational fluid dynamic models that were developed for field sites. A complete building system simulation model was then used to compare the impact of the different modeling approaches on the predicted energy cost savings associated with application of DCV in each building type. The use of a transient CO2 model did not have a significant impact on model prediction accuracy and energy cost savings predictions as compared with the quasi-static model. The difference in predicted annual energy costs between the various CO2 modeling types were small and less than might result from errors introduced by factors such as CO2 sensor uncertainty. Therefore, the use of an equilibrium model is sufficient for use in evaluating DCV for small commercial buildings. [Copyright &y& Elsevier]

Current air-conditioning system models seek to balance the level of code complexity with the speed of execution. Ideally, the simplest code possible that can accurately predict system performance is desired. To further understand this issue, two methods of modeling unitary air-conditioning systems are compared: a detailed, local approach and a simplified, global approach. These methods have been applied to two commercial unitary air conditioners for which extensive experimental data were obtained. The global approach predicted absolute system performance as well as or better than the local approach. In a separate analysis, the effects of two-phase modeling parameters on system model predictions were considered. The two-phase friction factors, heat transfer coefficients, and void fraction models were independently varied. The resulting system performance predictions were sensitive to variations in the air-side heat transfer coefficients and the void fraction model and not as sensitive to variations in the friction factor. Both the void fraction model and the condenser parameters mainly affect the compressor discharge pressure and the compressor power consumption. The evaporator parameters mainly affect the refrigerant mass flow rate and the heat transfer rates in both heat exchangers. [ABSTRACT FROM AUTHOR]

This paper provides an overview of research related to automated fault detection and diagnosis for chillers, packaged air conditioners, and other vapor compression cooling equipment. The paper discusses the benefits, constraints, and possible products for FDD applied in the HVAC&R industry, presents results of fault surveys for packaged air conditioners and chillers, outlines the general structure and elements of an FDD system for HVAC&R equipment, describes specific methods associated with different FDD elements, and presents results from some specific case studies. The paper also attempts to provide an assessment of the state-of-the-art in FDD for vapor compression equipment and to identify the steps necessary to achieve widespread application. [ABSTRACT FROM AUTHOR]

[Display omitted] • First non-isothermal selective membrane-based HVAC system. • Detailed derivation of thermodynamic governing equations and performance metrics. • Thorough analysis of power reduction compared to several state-of-the-art designs. • Case study using EnergyPlus building simulations for hospitals. • Highest efficiency membrane-based HVAC system with up to 66% second law efficiency. As much as 40% of the total load on air conditioning systems can be attributed to condensation dehumidification. However, new water vapor-selective membranes present a unique opportunity to greatly reduce the power requirements for moisture removal by avoiding phase change and have thus been ranked as a top alternative to traditional HVAC systems. To date, however, all such systems have relied on the assumption of constant temperature, even terming the technology "isothermal dehumidification." This work proposes a membrane-based air cooling and dehumidification approach, referred to as the Active Membrane Energy Exchanger (AMX), which is the first to provide simultaneous, yet decoupled, air cooling and dehumidification. The suggested AMX configuration uses two vapor-selective membrane modules with a water vapor compressor in between them, using the second membrane module to reject vapor into the exhaust stream. Cooling and heating coils in each membrane module channel move heat between the air streams using a vapor compression cycle. A detailed steady-state, thermodynamic model is presented for the AMX integrated within a 100% outdoor air conditioning system. The AMX's limiting parameters and design considerations like compressor efficiency are systematically analyzed for a broad range of outdoor air conditions and compared against standard and state-of-the-art dedicated outdoor air systems. This new high efficiency approach is found to outperform all other standard and state-of-the-art systems, achieving 1.2–4.7 times the COP over conventional dedicated outdoor air treatment. Lastly, a building simulation case study predicted cooling energy savings as high as 66% in hospital buildings with 100% outdoor systems in hot, humid climates. [ABSTRACT FROM AUTHOR]

• Shown that thermostat controls for multiple RTUs inefficiently operate economizers. • MPC that optimally operates economizers for open space buildings is proposed. • A CFD-coupled model was developed/validated for the control evaluation. • Significant energy savings up to 35% was achieved by the proposed MPC. "Free cooling" with cool outside air can meet or reduce a building's cooling loads in an energy efficient manner when conditions are favorable. For rooftop air conditioning units (RTUs), this is achieved with air-side economizers that are integrated with the packaged RTU. However, current RTU economizers are independently controlled at the unit level and may not fully leverage the free resource for economic benefit especially when multiple units serve a common zone of a building, such as in retail stores. That is, the independent control of multiple RTUs could lead to some units operating with mechanical cooling even when the outdoor air temperature or enthalpy is low enough to meet the load with economizer cooling. This paper presents a model-predictive control (MPC) approach to optimally supervise multiple RTUs in order to fully utilize the free cooling resource. The algorithm is applied to the evaluation of the energy savings potential for a case study building served by four identical RTUs under various climate zones over a cooling season. [ABSTRACT FROM AUTHOR]

Condensation dehumidification in conventional air conditioning technologies is energy-intensive, accounting for up to 50% of building cooling energy used in some climates. Selective vacuum membrane dehumidification (VMD) is one of the leading alternative dehumidification technologies due to its potential for significant energy savings, and the "dual-module humidity pump" is one of the most promising VMD concepts. This work is the first to provide experimental proof-of-concept for the dual-module humidity pump system and provides the first thermodynamic modeling framework that accounts for realistic steady-state operating limitations, both of which are lacking in the current literature. Additionally, this work is the first to provide a system design solution that overcomes practical challenges associated with air accumulation in the vacuum channels. The experimental results in this work show that the current prototype can remove up to 45% of the water vapor in the air stream, and the vapor pressure difference in the vapor rejection module needs to be approximately 2–4 times greater than that of the dehumidification module in order to maintain balanced mass transfer. The thermodynamic model applied to typical air conditioning conditions shows that the ideal dehumidification (latent) COPs can reach up to 40, but practical COPs are limited to approximately 10. Furthermore, the model shows that the overall energy efficiency increases as the membrane air selectivity increases, though this improvement gradually starts to diminish when the membrane selectivity is increased above 10,000. [Display omitted] • First experimental demonstration of the efficient dual-module humidity pump. • Benchtop prototype can remove up to 45% of the humidity in the air flow. • Thermodynamic model that accounts for realistic inefficiencies is presented. • Ideal latent COP can reach up to 40, practical COP limited to approximately 10. • Membrane selectivity beyond 10,000 yields diminishing efficiency enhancements [ABSTRACT FROM AUTHOR]

[Display omitted] • First experiments for simultaneous cooling and vacuum membrane dehumidification. • Cooling provides up to a 6% increase in prototype dehumidification performance. • Crossflow cooling tubes provide a 4–8% increase in dehumidification performance. • Straightforward framework for understanding practical latent COP limitations. • Development of a CFD model for air channel pressure drop estimates. Vacuum membrane air dehumidification has gained significant interest in recent years as a highly efficient means of air dehumidification. Prior theoretical modeling work by the authors introduced the Active Membrane Energy Exchanger (AMX) concept, which combines active heat exchange and vacuum membrane dehumidification into one non-isothermal system, and found that it could outperform other air conditioning technologies under many conditions. However, no experimental literature exists on combining active heat exchangers and vacuum membrane dehumidification. The goal of the present study is to evaluate the dehumidification (mass transfer) performance of the AMX concept relative to isothermal membrane dehumidification through three main methodologies: (1) membrane material-level characterization, (2) experimental prototype development and testing, and (3) computational fluid dynamics (CFD) simulations. The dense membranes used in this work showed up to a 40% increase in water vapor permeance at cooler temperatures, and the prototype system showed up to a 6% increase in humidity removal when the air was simultaneously cooled. Furthermore, the membrane module-integrated heat exchange tubes provided additional mixing and turbulence, leading to a 4–8% increase in humidity removal. The upper limit coefficient of performance was equal to approximately 2.2, necessitating advanced system designs to improve efficiency. This study is the first to highlight that combining the cooling and vacuum dehumidification processes can improve dehumidification performance. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a residential air conditioning compressor designed for vapor injection has been modified in order to inject large quantities of oil into the working chamber in order to approach an isothermal compression process. The compressor was tested with oil injection mass flow fractions of up to 45%. At an evaporating temperature of −10 °C and condensing temperature of 30 °C, the overall isentropic efficiency was up to 70% at the highest oil injection rate. Overall, over the testing envelope investigated, there are no significantly negative effects experienced for the compressor and the compressor isentropic efficiency and refrigerant mass flow rate improve monotonically as the oil injection rate is increased. [Copyright &y& Elsevier]

[Display omitted] • First system design with membrane dehumidification and indoor air recirculation. • Consideration of energy consumption for both indoor and outdoor air conditioning. • Energy savings potential up to 50% compared to conventional systems. • Enables efficient supply of 3x outdoor air flowrates compared to current standards. • Simulation of buildings in 114 cities implemented into a contour energy savings map. It is widely known that increasing outdoor air ventilation rates in buildings can help improve indoor air quality and mitigate the spread of diseases. However, cooling and dehumidifying outdoor air requires significantly more energy than treating indoor recirculated air. Recent developments in water vapor-selective membranes, which use a vapor partial pressure gradient to remove water vapor from air, offer a unique opportunity to provide highly efficient dehumidification in HVAC systems that can justify high outdoor air ventilation rates without drastic increases in energy consumption. This work presents an analysis of a novel membrane HVAC system referred to as the Active Membrane Energy Exchanger (AMX), which couples a refrigeration cycle with selective membranes to simultaneously cool and dehumidify air. While past selective membrane dehumidification systems have been isothermal, the AMX is the first to deliberately target non-isothermal operation by combining membrane dehumidification and active heat exchange. A thermodynamic model is developed for the AMX in a system that uses both outdoor air ventilation and indoor air recirculation (AMX-R) to elucidate the limitations around increasing ventilation rates. This study is among the first to consider recirculation for selective membrane processes, rather than only 100% outdoor air. The AMX-R can achieve up to 50% cooling and dehumidification electricity savings in warm and humid climates under current ventilation standards. Furthermore, ventilation rates can be nearly tripled with the AMX-R while consuming similar amounts of energy as conventional HVAC systems. Lastly, the incorporation of EnergyPlus building simulations for 114 US cities shows that the AMX-R has the greatest potential in the southern regions of the US. [ABSTRACT FROM AUTHOR]

[Display omitted] • A vapor-selective membrane-integrated heat pump dryer is proposed. • Integration of hollow fiber membranes with partial pressure-driven ε-NTU method. • Membrane geometries are the dominant factors compared to physical properties. • Optimized COP increases by an average of 460% under a wide range of conditions. • Multiple smaller units in parallel perform better than a single large unit. Dehumidification and drying processes significantly contribute to energy consumption in air conditioning and dry material manufacturing. Conventionally, water is removed by cooling the airstream below its dew point, demanding substantial energy for phase change and reheating. Vapor-selective membranes mitigate these energy penalties by selectively separating water vapor without condensing it, offering notable energy savings for transitioning to sustainable drying processes with heat pumps. However, efficient membrane dehumidification requires a large surface area, necessitating innovative designs for high efficiency and compactness. This study proposes a new drying cycle combined with vapor-selective membranes, focusing on the design optimization of hollow fiber membrane-based energy recovery ventilators. Hollow fiber membrane properties, geometry, and pressure drops are integrated into a model of the partial pressure-driven ε-NTU method. The simulation is validated within a 10% error range against experimental data. Global sensitivity analysis emphasizes that membrane geometries significantly influence dehumidification performance more than physical properties. Design optimization is then conducted with four competing objectives: water vapor removal, fan power consumption, sensible heat loss, and compactness. The optimized design demonstrates a compactness of 13.05 cm2·cm−3 and an exceptional equivalent coefficient of performance of 16.8 under nominal conditions. Compared to the baseline, this optimized design showcases a 20% increase in compactness and an impressive 460% increase in coefficient of performance, even under varying operating conditions. Scale-up design guidance suggests that employing multiple small units in parallel is more efficient than a single large unit when dealing with dehumidification at high air flow rates. [ABSTRACT FROM AUTHOR]

• Combining membrane dehumidification and dewpoint evaporative cooling (M−DPEC) • Thermodynamic model based on first and second laws to assess energy performance. • M−DPEC achieves up to 50–90% energy savings compared to desiccant wheels. • Up to 50% carbon emissions reductions compared to conventional technologies. • System dehumidification step self-supplies up to 12x the water required for cooling. Investigating new energy efficient and sustainable designs for air conditioning has become imperative due to air conditioning's contribution to global warming. The combination of membrane-based dehumidification and dewpoint evaporative cooling provides a possible solution that eliminates the energy-intensive process of condensation dehumidification, while also avoiding the use of harmful refrigerants. This paper is the first to present a straightforward thermodynamic model and initial assessment of a hybrid system that combines a vacuum membrane dehumidifier inspired by the Claridge-Culp-Liu (CCL) cycle with a dewpoint evaporative cooler with the additional investigation of reusing the dehumidification water to provide the evaporative cooling. A parametric study is performed for different ambient conditions. Results show the maximum achievable coefficient of performance (COP) for cooling and dehumidification with the system to be as high as 15 for very dry climate conditions, with a median value in the range of 4 over the range of typical ambient conditions. The system also displays the potential for having a self-sustaining water supply for evaporative cooling, producing up to 12x the amount of water required for the evaporative cooling portion of our system in highly humid conditions. An energy savings analysis yielded positive savings at low humidity conditions when compared to a baseline vapor compression system. Additionally, the system outperformed a baseline desiccant wheel system under all conditions. The absence of harmful refrigerants lowers overall (direct and indirect) greenhouse gas emissions associated with the M−DPEC system to as low as 50% of the baseline vapor compression system. Therefore, the model shows potential for the technology to efficiently fulfill building cooling demands while employing an environmentally friendly system to reduce greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Abstract: A detailed mechanistic model has been developed for scroll compressors and scroll expanders with liquid flooding for application to the Liquid Flooded Ericsson Cycle. This model is based on the integration of a set of differential equations that arise from the conservation laws. The impact of the flooding liquid on the working process is also included through mixture properties as well as treatment of two-phase flow pressure drop. With the working process known, it is then possible to solve for the compressor power, total mass flow rate and other model outputs. The fine level of detail in the model allows for the investigation of the impact of design changes to the scroll machines. This model can also be readily extended to allow for the analysis of liquid flooded vapor compression refrigeration. [Copyright &y& Elsevier]