OAKTrust :: Browsing by Author "Claridge, David E"

Browsing by Author "Claridge, David E"

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Active Remote Setpoint Optimization Utilizing BAS Trend Data
(2017-12-06) Paulus, Mitchell Thomas; Claridge, David E; Culp, Charles; Rasmussen, Bryan; Baltazar, Juan-Carlos
In this work, a new concept was explored for the optimization of heating, ventilating, and air-conditioning (HVAC) systems in buildings. The methods assume that only commonly trended sensor data would be available and that no live connection to sensor values would exist. An actual implementation would only require a small script to be written at the target building to request information from a centralized server and update setpoint values. A prioritization of sensors to trend at buildings is presented. Investigations into the feasibility were completed on a case study building on the Texas A&M Campus, the National Center for Therapeutic Medicine (NCTM) and the Preston Royal Library. The algorithms and models for the optimization are presented, along with uncertainty analysis into several key model parameters. 23-29% energy savings were found for AHU-2-3 at the NCTM building from June 1st, 2016 to January 1st, 2017. Missing fan power and air flow sensors reduced effectiveness, along with uncertainty in the plenum temperature for the series fan powered terminal units. Lack of readily available, accurate, manufacturers’ specifications were also limitations. A prototype of the system was developed on the web application CC-Compass, available at Texas A&M.
Advancing Embedded and Extrinsic Solutions for Optimal Control and Efficiency of Energy Systems in Buildings
(2017-05-23) Bay, Christopher Joseph; Rasmussen, Bryan P; McAdams, Daniel A; Claridge, David E; Datta, Aniruddha
Buildings account for approximately 40% of all U.S. energy usage and carbon emissions. Reducing energy usage and improving efficiency in buildings has the potential for significant environmental and economic impacts. To do so, reoccurring identification of hardware and operational opportunities is needed to maintain building efficiency. Additionally, the development of controls that continually operate building systems and equipment at energy optimal conditions is required. This dissertation provides contributions to both of the aforementioned areas, which can be divided into two distinct portions. The first presents the framework for the development of an automated energy audit process, termed Autonomous Robotic Assessments of Energy (AuRAE). The automation of energy audits would decrease the cost of audits to customers, reduce the time auditors need to invest in an audit, and provide repeatable audit processes with enhanced data collection. In this framework of AuRAE, novel, audit-centric navigational strategies are presented that enable the complete exploration of a previously unknown space in a building while identifying and navigating to objects of interest in real-time as well as navigation around external building perimeters. Simulations of the navigational strategies show success in a variety of building layouts and size of objects of interest. Additionally, prototypes of robotic audit capabilities are demonstrated in the form of a lighting identification and analysis package on a ground vehicle and an environmental baseline measurement package on an aerial vehicle. The second portion presents the development and simulation of two advanced economic building energy controllers: one utilizes steady-state relationships for optimizing control setpoints while the other is an economic MPC method using dynamic models to optimize the same control setpoints. Both control methods balance the minimization of utility cost from energy usage with the cost of lost productivity due to occupant discomfort, differing from standard building optimal control that generally addresses occupant comfort through setpoint limits or comfort measure constraints. This is accomplished through the development of component-level economic objective functions for each subsystem in the modeled building. The results show that utility cost and the cost of occupant productivity from optimal comfort can be successfully balanced, and even improved over current control methods. The relative magnitude of the cost of lost productivity is shown to be significantly higher than the cost of utilities, suggesting that building operators, technicians, and researchers should make maintaining occupant comfort a top priority to achieve the greatest economic savings. Furthermore, the results demonstrate that by using steady-state predictions, the majority of the performance gains produced with a fully dynamic MPC solution can be recovered.
An Experimental Investigation of the Thermal Behavior of a Fixed Bed Regenerator
(2023-05-10) Verlekar, Jay Rohit; Pate, Michael B; Claridge, David E; King, Maria D
Heating, Ventilation and Air-Conditioning (HVAC) systems consume large amounts of energy to maintain acceptable thermal environments for occupants; therefore, it becomes important to develop energy efficient systems to support this primary HVAC system goal. The Fixed Bed Regenerator (FBR) is a type of energy recovery system that offers preconditioning of fresh supply air without compromising on Indoor Air Quality (IAQ). This device consists of a cylindrical core made of ceramic for thermal energy storage and laced with numerous hollow channels for air flow so the device can act as a regenerative heat exchanger. The FBR also contains a reversible fan that facilitates air movement between the outdoors and indoors by alternating channel airflow in two directions. The ceramic core absorbs energy from the hot outside air flowing through channels during the supply cycle, which spans 50 seconds for this particular unit, thus cooling fresh outdoor air before it discharges to the indoor space. Next, the core transfers energy to the indoor space air flowing back through the channels during the exhaust cycle, which also spans 50 seconds. Thus, a complete cycle, which consists of a combination of the supply cycle and the exhaust cycle, lasts 100 seconds. The objective of this project is to evaluate the thermal behavior, the core charging and discharging phenomenon, and the effectiveness of the FBR for a range of indoor-to-outdoor temperature differences. Before taking data for analysis, it was necessary to develop a methodology that ensures the onset of pseudo steady state after an initial FBR startup by monitoring how long it takes the core temperatures to stabilize; it was determined that pseudo steady state was reached after about 16 minutes for all cases. As a first step in the FBR analysis, the temperature change of air flowing through the core provided an indication of the FBR effectiveness. For example, at an outdoor-to-indoor temperature difference of ΔTmax =25℉, the inlet-to-outlet air temperature difference during the supply cycle decreased from 22.9℉ to 11.8℉ from the cycle beginning to the end. For the exhaust cycle, this inlet-to-outlet temperature difference decreased from 15.4℉ at the cycle beginning to 8.6℉ at the end. These decreasing temperature differences from the start to the end of both cycles is an indicator that the core has a decreasing ability to exchange thermal energy with the air or, in terms of this FBR study, a decreasing effectiveness as time passes during a cycle. For example, in the ΔTmax=25℉ case, the effectiveness, which is calculated from temperature data, decreased from 0.90 at the start to 0.47 at the end of the supply cycle, and similarly from 0.80 to 0.39 for the exhaust cycle. The effect that ΔTmax has on mean and peak effectiveness was also evaluated. An analysis of the complete cycle, which is a combined supply and exhaust cycle, showed that the mean effectiveness increased slightly from 0.50 at ΔTmax=20℉ to 0.53 at ΔTmax=30℉. The peak effectiveness showed a similar trend of a slight increase from 0.85 at ΔTmax=20℉ to 0.94 at ΔTmax=30℉. Thus, it was determined that, among the three ΔTmax samples analyzed, the optimal operating conditions for the Fixed Bed Regenerator were at ΔTmax=30℉.
Building Energy Simulation Using Constrained Optimization
(2019-03-29) Davis, Clinton Paul; Culp, Charles H; Claridge, David E; Rasmussen, Bryan P; Pate, Michael B
This thesis presents an equation-based approach to steady state building energy modeling using constrained optimization. Models using this approach can be built from algebraic equations that describe a building and its HVAC equipment and knowledge of the system’s overall control strategy. The equation-based nature of this approach allows arbitrary systems to be represented, and simple rules can be followed to construct models that produce a valid energy balance overall operating conditions, including atypical scenarios such as temperatures drifting above or below their desired set points. The theory behind constrained optimization modeling of steady state HVAC systems is presented, and methods for constructing typical HVAC systems are given. Mathematical methods for integrating dynamic effects such as thermal mass into these models are also presented. To efficiently solve these models, a prototype program named Beryl is presented along with a performance analysis of the computer resources required for different types of modeling. Finally, future areas of research are given such as modeling improvements and improvements to numerical solvers for the specialized problems being solved. The solver developed in this work was able to perform yearly building energy simulations on single AHU in 0.5 to 5.0 seconds using hourly time steps on a single thread. Factors that affect simulation runtime were also analyzed. Based on these results and the robustness of the simulations, constrained optimization based building energy modeling was shown to be a valid and potentially useful approach.
Coil Condensation Detection For Humidity Control
(2014-05-12) Kaneb, Charles Peckitt; Culp, Charles H; Claridge, David E; Rasmussen, Bryan P
Conditioning the air inside a building requires controlling both primary components of its enthalpy: temperature and humidity. Temperature sensors used in buildings are sufficiently reliable, durable, accurate, and precise that they can be relied on for sophisticated building control systems. Commercial resistive and capacitive humidity sensors become inaccurate near saturation and often fail permanently when exposed to liquid water. Excessive humidity can cause both occupant discomfort and permanent damage to buildings. In American climates dehumidification accounts for the vast majority of the energy used to control humidity. Therefore, a sensor which can survive and accurately measure humidity in hot, wet conditions will allow considerable savings. Simulations of the energy consumption and savings available from enthalpy economizer control and supply air temperature resets were performed for buildings in Houston, Dallas, and Philadelphia. Temperature economizers were shown to attain between 90% and 95% of the savings of an enthalpy economizer. A spreadsheet simulation of enthalpy economizer use showed that the savings available are heavily dependent on the ability to avoid its use on very hot, humid days. A newly-designed condensation sensor was developed for this project. It relies on the order-of-magnitude difference in AC reactance between humid air and liquid water. When installed on an AHU, it detects water condensing off the cooling coil as the temperature of the air drops below the dew point. Electronics were designed to provide the 0.25 V, 131 kHz current required and to obtain a 0 V output when dry and a 5 V output when wet. A field reliability test was successfully performed with the sensor passively monitoring the transitions from wet to dry at Langford Building A and the Jack E. Brown Building at Texas A&M University, College Station, TX. The sensor was shown to be able to provide the reliable state change detection needed to control an economizer. The main limitation of this sensor is slow response on dry-to-wet and wet-to-dry transitions. Most measured dry-to-wet response times were between 5 and 10 minutes, which were driven by the time required to saturate the cooling coil.
Development of a Data-Driven Model-Based Anomaly Detection Method for Whole Facility Level Energy Use Data Using the Energy Balance Load Variable
(2018-05-07) Masuda, Hiroko; Claridge, David E; Culp, Charles H; Haberl, Jeff S; Pate, Michael B
The continuous monitoring of building energy use provides useful feedback to building owners and operators to achieve persistent energy efficiency and to make important engineering and financial decisions. The practice of managing the quality of metered data is essential to the successful utilization of energy data because metered energy data often contain errors and biases. This dissertation develops a method for automatically detecting anomalies in whole-building energy use data. The method can assist time-consuming and expensive tasks in monitoring and managing energy use data collected from a large portfolio of buildings. The method uses a variable called the energy balance load (EvBL), which is calculated from separately metered electricity, cooling, and heating energy use data. Anomalies are detected based on the distance between the EvBL value that is predicted by a data-driven reference model and the actual EvBL value. For the EvBL reference model, a simple regression model with weather variables is used so the model can be applied to various types of buildings with minimal information. Updating reference models to account for the dynamic use and operations of buildings is a challenge. To address this challenge, this dissertation develops an anomaly detection method using the adaptive recursive least squares (RLS) filter as a reference model estimator and the standardized cumulative sum (CUSUM) test as a change detector. In the application to actual data, the new method demonstrates the ability to detect anomalies in a timely manner. The measurement bias in the chilled water use, caused by a drift of the temperature sensor reading, was detected on the fourth day after the temperature began to drift. Furthermore, the start of a disabled time schedule for the heating, ventilation, and air conditioning (HVAC) systems was detected on the seventh day, and the change-back to the previous schedule was detected on the second day. Both the physical interpretation of the EvBL model parameters and the sensitivity and uncertainty analysis on the key parameters are presented such that they can be used as aids to warn analysts against physically impossible reference models.
Embodied Energy Calculation: Method and Guidelines for a Building and its Constituent Materials
(2013-10-23) Dixit, Manish Kumar; Culp, Charles H; Fernandez-Solis, Jose L; Claridge, David E; Clayton, Mark J; Yan, Wei
The sum of all energy embedded in products and processes used in constructing a building is known as embodied energy. According to the literature, the current state of embodied energy research suffers from three major issues. First, there is little agreement on the definition of embodied energy. Second, the existing embodied energy data suffers from variation and are regarded as incomplete and not specific to a product under study. Third, there are various methods for calculating embodied energy with varying levels of completeness and accuracy. According to the literature, the input-output-based hybrid method is the most appropriate method but it needs further improvements. Some of the studies also found a positive and strong correlation between the cost and embodied energy of a building but this correlation needs to be analyzed at a building material or product level. This research addressed the three issues identified by the literature. First, using a rigorous literature survey, it proposed an embodied energy definition, a complete system boundary model, and a set of data collection, embodied energy calculation, and result reporting guidelines. The main goal of proposing the guidelines was to streamline the process of embodied energy calculation to reduce variations in embodied energy data. Second, three improvements were carried out in the current input-output-based hybrid approach, which included process energy data inclusion, human and capital energy integration, and sectorial disaggregation to calculate material-specific embodied energy. Finally, the correlation between the embodied energy and cost and price was analyzed at a material level. The study concluded that an input-output-based hybrid method was the most appropriate method for calculating the embodied energy of a building material in a complete manner. Furthermore, incompleteness in the results of a process-based method was significant (3.3 to 52% of the total). The energy of human labor and capital inputs was up to 15% of the total embodied energy. It was also found that the sectorial disaggregation could provide results specific to a material under study. The results of this study indicated a strong and positive correlation between the embodied energy and cost (and price) of building materials under study.
EVALUATING AND OPTIMIZING UTILITY PLANT OPERATION USING TREND DATA
(2020-04-13) Cu, Khanh Nguyen; Claridge, David E; Culp, Charles H; Pate, Michael B
Trend data have been the main source for utility plant evaluation and optimization. However, the current practice of trend data processing has not been well addressed in previous research as an important part of the workflow. As a consequence, the evaluation and optimization process can fail due to unreliable data, as the performance indicators are improperly estimated. The chilled water systems in the Texas A&M University utility plant have been investigated in this thesis. The hourly average timeseries data of chilled water systems are categorized with various methods in order to validate the reliability of meter records and performance benchmarking. After-processing, data are input for characteristic performance mappings and anomaly detection, which will help the plant operator in fault diagnosis and improving the performance of the chilled water systems. The outputs of this data-only–based validation process have been aligned with an on-site commissioning report, which requires an investment of labor and resources. It can be applied in other utility plants with similar configuration.
Heat Transfer Performance and Piping Strategy Study for Chilled Water Systems at Low Cooling Loads
(2012-12-05) Li, Nanxi 1986-; Claridge, David E; Culp, Charles H; Pate, Michael B
The temperature differential of chilled water is an important factor used for evaluating the performance of a chilled water system. A low delta-T may increase the pumping energy consumption and increase the chiller energy consumption. The system studied in this thesis is the chilled water system at the Dallas/Fort Worth International Airport (DFW Airport). This system has the problem of low delta-T under low cooling loads. When the chilled water flow is much lower than the design conditions at low cooling loads, it may lead to the laminar flow of the chilled water in the cooling coils. The main objective of this thesis is to explain the heat transfer performance of the cooling coils under low cooling loads. The water side and air side heat transfer coefficients at different water and air flow rates are calculated. The coefficients are used to analyze the heat transfer performance of the cooling coils at conditions ranging from very low loads to design conditions. The effectiveness-number of transfer units (NTU) method is utilized to analyze the cooling coil performance under different flow conditions, which also helps to obtain the cooling coil chilled water temperature differential under full load and partial load conditions. When the water flow rate drops to 1ft/s, laminar flow occurs; this further decreases the heat transfer rate on the water side. However, the cooling coil effectiveness increases with the drop of water flow rate, which compensates for the influence of the heat transfer performance under laminar flow conditions. Consequently, the delta-T in the cooling coil decreases in the transitional flow regime but increases in the laminar flow regime. Results of this thesis show that the laminar flow for the chilled water at low flow rate is not the main cause of the low delta-T syndrome in the chilled water system. Possible causes for the piping strategy of the low delta-T syndrome existing in the chilled water system under low flow conditions are studied in this thesis: (1) use of two way control valves; and (2) improper tertiary pump piping strategy.
Improvements and Applications of the Methodology for Potential Energy Savings Estimation from Retro-commissioning/Retrofit Measures
(2010-03-24) Liu, Jingjing; Claridge, David E; Culp, Charles; Heffington, Warren
This thesis has improved Baltazar's methodology for potential energy savings estimation from retro-commissioning/retrofits measures. Important improvements and discussions are made on optimization parameters, limits on optimization parameter values, minimum airflow setting for VAV systems, space load calculation, simulation of buildings with more than one type of system, AHU shutdown simulation, and air-side simulation models. A prototype computer tool called the Potential Energy Savings Estimation (PESE) Toolkit is developed to implement the improved methodology and used for testing. The implemented methodology is tested in two retro-commissioned on-campus buildings with hourly measured consumption data. In the Sanders Corps of Cadets Center, the optimized profiles of parameter settings in single parameter optimizations can be explained with engineering principles. It reveals that the improved methodology is implemented correctly in the tool. The case study on the Coke Building shows that the improved methodology can be used in buildings with more than one system type. The methodology is then used to estimate annual potential energy cost savings for 14 office buildings in Austin, TX with very limited information and utility bills. The methodology has predicted an average total potential savings of 36% for SDVAV systems with electric terminal reheat, 22% for SDVAV systems with hot water reheat, and 25% for DDVAV systems. The estimations are compared with savings predicted in the Continuous Commissioning assessment report. The results show it may be helpful to study the correlation by using generalized factors of assessment predicted energy cost savings to estimated potential energy cost savings. The factors identified in this application are 0.68, 0.66, and 0.61 for each type of system. It is noted that one should be cautious in quoting these factors in future projects. In the future, it would be valuable to study the correlation between measured savings and estimated potential savings in a large number of buildings with retrocommissioning measures implemented. Additionally, further testing and modifications on the PESE Toolkit are necessary to make it a reliable software tool.
Optimization of a Combined Cooling, Heat, and Power Plant Design for Existing Central Utility Plants
(2023-05-02) Abeyawardhane, Kushan Buddhika; Claridge, David E; Rasmussen, Bryan P; Culp, Charles H
Cost and emission savings with load-following capability are essential factors in the design optimization of Combined Cooling, Heating, and Power (CCHP) systems. This thesis presents a methodology for evaluating CCHP system design options for large central utility plants to minimize operating costs and emissions. Central utility plants can be considered the backbone of large campus systems providing critical supplies such as cooling and heating energy. In this strategy, multiple Power Generation Units (PGUs) are considered to meet different load profiles annually to improve system utilization and resilience. The systematic process was applied to a case-study plant and identified the most economically viable CCHP design to minimize the annual total cost, including operation, maintenance, and utility costs, while also addressing redundancy issues. A Pareto frontier of design solutions containing wider total operational capacity is recognized using a mixed integer linear program algorithm. The final results of the case study showed that the CCHP system could achieve 23.8% operational cost savings and 30.2% and 60.7% in CO2 and NOx reductions, respectively. In addition, multiple PGU systems provide two percent additional cost savings compared to a single PGU system while avoiding downtime and increasing energy resilience. A sensitivity analysis indicated that utility cost fluctuation could drastically change the optimal operating cost. An increase in natural gas cost and a decrease in electrical grid cost can make the optimal design infeasible.
An Optimized Plant For A District Heating And Cooling System Using Low-Grade Geothermal Fluids
(2019-08-18) Liao, Jiajun; Claridge, David E; Pate, Michael B; Culp, Charles H; Weijermars, Ruud
An optimized plant is developed for a district heating and cooling system using low-grade geothermal fluids from depleted hydrocarbon wells. The optimum geothermal fluid flowrate and temperature supplied to the surface end-use system are determined as 29 gpm and 191°F from inactive wells on the Texas A&M RELLIS Campus. The absorption chiller, the desiccant dehumidification, and geothermal district heating systems are modeled for cooling, dehumidification, and heating and simplified with relationships between the required geothermal fluid temperature and its output at different outside air conditions. The desiccant wheel dedicated outside air system with heat exchanger and condenser water cooling shows the ability to avoid the most cooling coil load and therefore is selected for the surface integrated system. The surface end-use system modeling is developed by combining these three heat-operated system models with load profiles of typical campus buildings. The inlet temperature requirements and the maximum temperature drops of each system are studied, and possible system arrangements are investigated using the bin method. Both the site energy load to energy ratio (LER) and the cost LER are introduced and calculated. When the building loads are large and the integrated system operates at its full capacity, the optimized arrangement is with the desiccant dehumidification system and the geothermal district heating system operated in parallel. When the outside air temperature is lower than 75°F, the geothermal district heating system is operated; otherwise, the desiccant dehumidification system is operated. Its yearly total energy output is 8,572 MMBtu with a total LER of 14.08 – 23.76, i.e. it requires 14-24 times fewer electric Btu than the energy output. When the integrated system matches the building loads well, the optimized arrangement is that the absorption chiller system and the geothermal district heating system are in parallel, and then in series with the desiccant dehumidification system. Its yearly total energy output is 3,264 MMBtu with a cooling LER of 4.72 – 7.89 and a heating LER of 4.25 – 7.24. Thus, all the integrated geothermal systems described above would have an operating energy use less than one-fourth that of a traditional heating and cooling plant meeting the same loads.
Performance and Optimization of an Underfloor Air Distribution System in an Educational Building in a Hot and Humid Climate
(2015-05-01) Khmelenko, Vasiliy; Claridge, David E; Culp, Charles; Baltazar, Juan-Carlos
Today there is a proliferation of different HVAC system configurations. Design and performance of each HVAC system are dependent on climate and the intended use of the building. Energy recovery ventilation is becoming more common in new buildings and is one of the more popular retrofit options in hot and humid climates. Currently there is a lack of optimization strategies that involve the underfloor air systems combined with Energy Recovery Ventilation (ERV) especially in hot and humid climate. This thesis examines the performance and optimization of underfloor air distribution systems (UFAD) in hot and humid climates. This thesis also compares the UFAD system performance to a typical overhead air handler unit (AHU) system found in Texas. The performance comparison is done with EnergyPlus modeling software. Separate sets of models are created to examine performance of at different operational parameters. The minimum air flow rates are modeled at 0.1 cfm/ft2, 0.2 cfm/ft2, 0.3 cfm/ft2, 0.4 cfm/ft2 for both UFAD and overhead (OH) systems. The supply air temperatures were modeled at 55 °F, 60°F, and 63 °F. Outside air strategies include simple economizer, energy recovery ventilation (ERV), as well as a combination of both economizer and ERV. The study found that at low minimum (0.1 cfm/ft2) flow rates an overhead system will slightly outperform a UFAD system (OH 2.6% cheaper to operate than UFAD) while at 0.3 cfm/ft2 a UFAD system is more efficient (UFAD 14.8% cheaper to operate). The outside air strategies have the same energy savings effect on both systems. The UFAD system has a higher peak cooling load and a lower peak heating load compared to the overhead system. This thesis also covers the stratification and supply air temperature measurements within two offices inside the Mitchell Physics building, located on the Texas A&M campus. The stratification measurements showed that on average the stratification was lower than expected for such systems with office 411 having average stratification of 1.8 °F and office 423 average stratification of 1.5 °F. Temperature measurements at the diffuser level showed some reheat, especially during unoccupied periods such as early mornings, late evenings and weekends, even when the outside temperature was above the interior thermostat set point. System level total supply air flow rate showed little variation with a minimum of 0.47 cfm/ft2 and a maximum of 0.59 cfm/ft2. The analysis of energy recovery wheel operation concluded that the low exhaust air flow of only 0.2 of the outside air is responsible for the low temperature difference observed in the outside air stream through the ERV.
Thermodynamic Modeling of a Membrane Dehumidification System
(2012-11-28) Bynum, John 1983-; Claridge, David E; Culp, Charles; O'Neal, Dennis; Pate, Michael
In warm and humid climates, a primary source of building energy consumption is dehumidification of conditioned air supplied to the building spaces. The proposed system utilizes a selective membrane to remove water vapor from ambient air as opposed to a vapor compression cycle or a desiccant. This work provides an analysis of the membrane dehumidification system with a focus on the energy performance of the system. A system performance goal was set at the beginning for a given inlet and outlet ambient air condition and a total cooling load of one ton. The target COP of the combined sensible and latent cooling is 3.58 with a target value for only the latent system of 3.34. Two different simulations were developed including an initial simulation which uses a basic mass transfer model and a simpler condenser model. The initial model was used to develop the system, analyze operating parameters and provide initial performance results. The initial simulations indicate that the system requires two optimizations to meet the target performance: condenser pressure optimization and the use of multiple membrane segments operating at different pressures. The latent only COP including the optimizations was a maximum of 4.23. A second model was then developed which uses a more detailed mass transfer model and a more detailed condenser model based on the operating conditions. This simulation yielded a maximum latent only COP of 4.37 including the optimizations. The work also analyzes two different combined systems capable of providing both sensible and latent cooling. The first utilizes a conventional vapor compression cycle for sensible cooling and has a maximum COP of 3.93. The second uses multiple evaporative coolers in between multiple membrane dehumidification steps and was found to have a maximum COP of 3.73. Second law analysis of the systems was also conducted and found that the greatest reduction in latent system exergy loss can be obtained by improving the selectivity of the membrane. Apart from improving the membrane selectivity, the results show the greatest improvement can be found in improving the operation of the gas compression devices.

Browsing by Author "Claridge, David E"

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