Desiccant Evaporative Cooling Research Articles

Design and Energy Analysis of a Solar Desiccant Evaporative Cooling System with Built-In Daily Energy Storage

Heat storage with thermochemical (TC) materials is a promising technology for solar energy storage. In this paper, a solar-driven desiccant evaporative cooling (DEC) system for air-conditioning is proposed, which converts solar heat energy into cooling with built-in daily storage. The system utilises thermochemical heat storage along with the DEC technology in a unique way. Magnesium Chloride (MgCl2·6H2O) has been used, which serves as both a desiccant and a thermochemical heat storage medium. The system has been designed for the subtropical climate of Lahore, Pakistan, for a bedroom with 8 h of cooling requirements during the night. MATLAB has been employed for modelling the system. The simulation results show that 57 kg of magnesium chloride is sufficient to meet 98.8% of cooling demand for the entire month of July at an elevated cooling requirement. It was found that the cooling output of the system increased with increasing heat exchanger effectiveness. The heat exchangers’ effectiveness was increased from 0.7 to 0.8, with the solar fraction increased from 70.4% to 82.44%. The cooled air supplied to the building meets the fresh air requirements for proper ventilation.

Performance Assessment of Solar Cooling Systems with Energy Storage

The paper presents a complete solar cooling comparison. A detailed model of a tertiary sector building has been evaluated in three locations (Riyadh, Abu Dhabi, and Palermo) and coupled with four solar cooling systems: two solar thermal cooling systems (Li-Br absorption chiller and adsorption chiller), a solar Desiccant Evaporative Cooling system and a solar electric cooling (Photovoltaic coupled with Compression chiller). A multi-variable optimization procedure selects the optimal size of each component. The results show that the solar cooling system based on absorption chiller satisfied the cooling demand regardless of the site location whilst the performance of the Desiccant Evaporative Cooling system is dramatically affected by ambient conditions. The electric solar cooling option shows the best overall efficiency and appears a costeffective solution despite the high cost of the storage system.

Modeling and Simulation of a Desiccant Evaporative Cooling System

This paper studies the performance of a proposed desiccant assisted air conditioning system operating under the hot and dry climate conditions of Mosul city, Iraq. The proposed system consists of three stages: indirect/direct evaporative cooler, an enthalpy wheel, and a traditional vapor compression system. The performance of the suggested system is compared with that of the vapor compression system operating at the same conditions. The simulation results showed that an optimum rotational speed of 12.5 rpm is required for the enthalpy wheel to achieve the best system performance. The simulation results also showed the ability of the proposed system to achieve a power consumption saving of 51.03%, in the ventilation mode, and 22.93%, in the mixing mode with a ventilation mixing ratio of 0.4 when compared to the vapor compression system.

Performance Analysis of a Desiccant Evaporative Cooling System for Mango Fruit Storage in the Savannah and Transitional Zones of Ghana

Abstract Performance analysis of a 1.0 tonne desiccant evaporative cooling storage structure for mango fruits was studied. The study examined the effects of inlet air conditions and water flow rates through an absorber on the cooling performance of the system. The airflow rate was approximately 0.24 m3·s−1 and water flow rates through the absorber varied from 0 to 0.252 l·s−1. The system produced approximately 7 kW of cooling at water supply rate of 0.252 l·s−1. A simple linear correlation was established for condition line slope from inlet to exiting air conditions for all the water flow rates. Lines of best fit resulted in correlation coefficient better than 0.96. The observed temperatures with a direct evaporative cooler, tested with freshly harvested mango fruits were found to be between 15.1°C and 23.4°C and relative humidity between 81.8% and 97.7%. Physiological weight loss and firmness assessments of the fruits were also conducted.

Performance analysis of alternative HVAC systems incorporating renewable energies in sub-tropical climates

Over the past 40 years, energy consumption has increased dramatically to become a significant crisis faced today. The peak demand is growing at approximately 50% greater than the demand base growth in many Australian cities, which, in turn, requires greater finite resources and infrastructure to meet the required generation capacity needed. Currently, approximately 40% of electrical energy is consumed by HVAC systems in commercial building. This level of energy consumption emphasizes the necessity of developing an eco-friendly air-conditioning system, where possible, harnessing low-grade thermal energy such as solar energy rather than electricity. In this paper, a comparison of energy performances of three different HVAC is undertaken. Mathematical models are developed with TRNSYS17 to simulate the HVAC system within a typical small commercial building with various cooling options. The model is implemented to provide a comparative analysis across various cooling systems such as Vapour Compression System, Vapour Absorption System and Desiccant Evaporative Cooling System. This paper implements the developed model to investigate and compare the energy consumption and running costs over an eight-month cooling period of the widely used Vapour Compression System against alternative solar assisted cooling options for a sub-tropical location of Brisbane, Australia.

The effects of regeneration temperature of the desiccant wheel on the performance of desiccant cooling cycles for greenhouse thermally insulated

The use of solar energy for cooling greenhouses in the hot period in Mediterranean climate is an important issue. Desiccant evaporative cooling (DEC) system is advantageous because it uses a low grade thermal energy and preserves the merits to be friendly environmentally technology. In this paper, a numerical investigation was carried out on a desiccant cooling system powered by air solar collectors coupled to an insulated greenhouse. The influence of the regeneration temperature on the air stream properties at every system component state point was studied. The performance of the desiccant cooling system was evaluated in terms of thermal and electric coefficient of performance. Results show that the best performance of the system (COPel = 14 and COPth = 0.94) was obtained for a 60 °C regeneration temperature and a supply flow rate ratio of 0.2. An economic analysis shows that the use of the DEC system for greenhouse cooling is attractive and profitable since the payback period is 1 years. The use of the proposed system allows saving 9396 kWh/year of electric energy compared to conventional system.

Performance Analysis of Solar-Assisted Desiccant Cooling System Cycles in World Climate Zones

The demand for affordable, environment-friendly, and reliable water conditioning systems has led to the introduction of several standalone and/or hybrid alternatives. The technology of desiccant evaporative cooling (DEC) has proven to be dependable and has gained success at places where initially it was deemed unfeasible. Today, a number of related technologies and configurations are available. Among them, solar-assisted desiccant cooling system (SADCS) offers a cheap eco-friendly alternative, especially in hybrid configurations. Most studies have investigated the performance of numerous SADCS configurations in specific climatic conditions; however, at the global- and system-level scale, no such study is available. The current study investigates five different SADCS configurations using equation-based object-oriented modeling and simulation approach in five different climatic conditions. The selected climatic conditions cover a wide range of global weather data including arid/semiarid (Karachi), dry summer tropical (Adelaide), and mesothermal (Sao Paulo, Shanghai) to continental conditions (Vienna). The performance of all selected SADCS configurations (ventilation cycle, recirculation and ventilated-recirculation cycles, dunkle and ventilated-dunkle cycle) is analyzed for specified cooling design day of the selected cities. A uniform system control strategy based on the idea of displacement distribution (ventilation) system is used for each configuration and climatic zone. By monitoring their performances based on the values of cooling capacity (CC) and coefficient of performance (COP), the best SADCS configuration is proposed for each considered climatic condition in the world. The results revealed that the climates of Vienna, Sao Paulo, and Adelaide favor the use of ventilated-dunkle cycle configuration with average COP of 0.36, 0.84, and 0.93, respectively, while ventilation cycle based on DEC configuration suits the climate of Karachi and Shanghai with an average COP of 2.32 and 2.90, respectively.

Preliminary study of the hybrid solar DEC “NAC wall” system integration in building façades in urban context

A new concept of hybrid/natural air conditioning system, “NAC (Natural Air Conditioning) wall”, with a high level of architectural integration is presented. NAC wall concept is that of a solar DEC (Desiccant Evaporative Cooling) open cycle with very low pressure drops, thus drastically reducing, or even avoiding, the electricity consumption for driving fans. The supply air is dehumidified by an adsorption bed and is cooled indirectly by an evaporative cooler, through a low pressure drop heat exchanger. Adsorption bed is a finned coil heat exchanger coated with a SAPO-34 zeolite layer realizing both heat and mass transfer in a unique component. The assembling of NAC wall components is analysed in order to optimize architectural integration and performances. Experimental data carried out in different operation mode offered promising optimization suggestions to increase the specific cooling power for a better building integration. The integration at a building level would represent an architectural innovation, and the NAC wall production would not impact the supply chain with disruptive changes.

Optimized low pressure solar DEC with zeolite based adsorption

This paper presents a new concept of hybrid/natural air conditioning system with a high level of architectural integration. A solar DEC (Desiccant Evaporative Cooling) open cycle with very low pressure drops, drastically reduces the electricity consumption for driving fans. The supply air is dehumidified by an innovative zeolite coated adsorption bed and cooled indirectly by an evaporative cooler, through a low pressure drop heat exchanger. The adsorption bed is a finned coil heat exchanger coated with a SAPO-34 zeolite layer realizing both heat and mass transfer in one component. Low thermal grade heat is used to regenerate the adsorbent material, showing high compatibility with low temperature solar systems such as flat plate or evacuated tubes solar collectors. Experimental data have been used for validating a CFD model of the coated coil. The possibility to remove the adsorption heat during dehumidification reduces the air temperature with a positive effect on cooling power.

Experimental analysis of “NAC-wall” for hybrid ventilation mode

Reducing the energy demand for residential cooling systems is crucial in order to limit CO2 emissions, consistently with the EU climate change policy. Within this context, solar DEC (Desiccant, Evaporative Cooling) technologies can represent a valid answer to the energy saving targets. This experimental analysis aims to present the last results of a scientific campaign on a solar DEC prototype, named NAC-wall (Natural Air Conditioning), operating with a hybrid ventilation mode. Heat and mass transfer happens in an innovative dehumidification component, a finned coil coated with a layer of Zeolite SAPO-34, presenting very low pressure drops. Different tests have been performed in the flow regime Reynolds 750–3500 to analyze dehumidification effectiveness. For a better comparison between each test, a preliminary complete regeneration of the adsorbent mean have been always carried out with hot water circulation, produced by a solar thermal system. A theoretical optimized working cycle, i.e. one regeneration stage followed by one adsorption stage, has been studied starting from the experimental results and its performance has been compared with the optimized natural ventilation operating case, reported in a previous work.

Parametric Analysis of Design Parameter Effects on the Performance of a Solar Desiccant Evaporative Cooling System in Brisbane, Australia

Solar desiccant cooling is widely considered as an attractive replacement for conventional vapor compression air conditioning systems because of its environmental friendliness and energy efficiency advantages. The system performance of solar desiccant cooling strongly depends on the input parameters associated with the system components, such as the solar collector, storage tank and backup heater, etc. In order to understand the implications of different design parameters on the system performance, this study has conducted a parametric analysis on the solar collector area, storage tank volume, and backup heater capacity of a solid solar desiccant cooling system for an office building in Brisbane, Australia climate. In addition, a parametric analysis on the outdoor air humidity ratio control set-point which triggers the operation of the desiccant wheel has also been investigated. The simulation results have shown that either increasing the storage tank volume or increasing solar collector area would result in both increased solar fraction (SF) and system coefficient of performance (COP), while at the same time reduce the backup heater energy consumption. However, the storage tank volume is more sensitive to the system performance than the collector area. From the economic aspect, a storage capacity of 30 m3/576 m2 has the lowest life cycle cost (LCC) of $405,954 for the solar subsystem. In addition, 100 kW backup heater capacity is preferable for the satisfaction of the design regeneration heating coil hot water inlet temperature set-point with relatively low backup heater energy consumption. Moreover, an outdoor air humidity ratio control set-point of 0.008 kgWater/kgDryAir is more reasonable, as it could both guarantee the indoor design conditions and achieve low backup heater energy consumption.

Solar-Powered Air Conditioning for Buildings in Hot Climates: Desiccant Evaporative Cooling vs. Absorption Chiller-based Systems

In many countries, solar cooling systems are one of the best candidates to tackling global warming and summer peak loads of building air conditioning systems. In this work, based on the collaboration with the Saudi research institute “King Abdullah City for Atomic and Renewable Energy”, two types of solar driven cooling systems are investigated and compared: the open-circuit Desiccant Evaporative Cooling technology and the system based on single-stage LiBr absorption chillers. A computer code has been developed in Trnsys® to simulate a well-insulated single-family residential building, starting from a 3D model of the building architecture, and the solar cooling systems. The simulations have been carried out for two different locations: one in a dry desert area (Riyadh, KSA), the other one on the seaside (Abu Dhabi, UAE). The results show that absorption chillers need a very effective heat rejection system to work properly, whilst DEC systems exhibit a dramatic performance reduction in wet climates.

NAC wall: An open cycle solar-DEC with naturally driven ventilation

This paper presents the general concept of the NAC (Natural Air Conditioning)-wall system and some experimental results on a first prototype. The originality of the system is to perform a solar DEC (Desiccant, Evaporative Cooling) open cycle by exploiting natural buoyancy driven ventilation, thus avoiding the use of fans.The supply air is dehumidified by a zeolite based adsorption bed and is cooled indirectly by an evaporative cooler, through a low pressure heat exchanger.Eight days measurements were performed, each including a sample with five adsorption/regeneration cycles. During the first measurements, thermal COPs were in the range 0.30 1.01, depending on duration of regeneration and absorption phases. This led to a better tuning of the system, which gave for the remaining samples an average COPth of 0.64, with an average electrical COP of 12.7, calculated considering electrical consumption of water loops pumps.

SHC Task 48 B2 – Three GOOD Practice Examples of Solar Heat Driven Desiccant Evaporative Cooling Systems

Within the activity B2 of IEA SHC Task48, an exhaustive report on GOOD Practice examples of existing solar heat driven desiccant cooling (SDEC) systems was written. Three SDEC systems from Austria, Australia and Italy are well documented from the design phase to the operational phase. The authors of the GOOD Practice SDEC systems belong to research entities and the selected SDEC projects were scientifically accompanied by these partners from the very beginning on. The energy performance of all three SDEC systems in operation is indicated by monthly energy fluxes and key performance indicator as a result from measurement data of a scientific monitoring campaign. The GOOD Practice SDEC report on each system closes with findings and lessons learned in order to guide next projects by answering; What quality and support measures lead to a successful SDEC system implementation with high energy performance figures, high quality of indoor comfort and high user friendliness for facility manager? The SHC Task48 B2 report is published on the official SHC Task48 website.

Life Cycle Assessment of a compact Desiccant Evaporative Cooling system: The case study of the “Freescoo”

The paper aims at exploring the performances of a compact Desiccant Evaporative Cooling system called “Freescoo” (Free Solar Cooling) in comparison to standard conventional technologies. The Freescoo – that aims at applications in the residential sector and in small office buildings and includes a photovoltaic–thermal system – is analyzed, its monitored performance discussed and reported: under cooling conditions an Energy Efficiency Ratio of 12.8 is calculated, that reaches 50.7 if also photovoltaic generation is considered. To assess the performance of the proposed system a Life Cycle Assessment study was performed to investigate the system covering all its life, from the production, going through its use and its disposal. Results are compared to those obtainable by standard conventional systems with comparable heating and cooling power outputs to further explore the performances of the system.The electricity consumption of the investigated solar cooling system proves to be equal to only the 5% of the equivalent conventional system having the same thermal output during a year. The production phase of the Freescoo shows a predominant role among the other life cycle steps, reaching a 95% share on the total for some indicators, such as human toxicity.If the life cycle phase of a conventional system is compared with the whole life cycle of the Freescoo system, the former would report many indicators values higher by 200% in comparison to the latter.If use of water is considered, although the Freescoo system would require 2590l of fresh water during a year in comparison to none consumed by a conventional system, the higher water footprint of conventional systems would result in water uses higher by three times if compared to the Freescoo.

Experimental testing of the buoyant functioning of a coil coated with SAPO34 zeolite, designed for solar DEC (Desiccant Evaporative Cooling) systems of buildings with natural ventilation

This work reports the experimental testing of a prototype of a new adsorption stage for solar DEC (Desiccant Evaporative Cooling) systems, in which airflow is activated by natural forces. The adsorption stage takes place in an air/water coil, coated with a thin layer of zeolite SAPO34 material. The thin coating configuration allowed testing of a concept of natural buoyant airflow on the coil, both during adsorption and during desorption phases. The heat released by the sorption phenomenon drives the airflow on the coil, whereas during the desorption, hot water flows through the coil and activates the convection.The tests proved the feasibility of the concept, though revealing the need to optimize the system configuration.

Second Generation of Freescoo Solar DEC Prototypes for Residential Applications

Freescoo is an innovative all-in-one compact solar Desiccant Evaporative Cooling (DEC) air conditioner concept. Results of the first prototype developed were presented at SHC Conference last year. Now a second generation of freescoo prototypes for applications in residential and small office buildings have been installed in Italy at ENEA Casaccia and at UNIPA. The thermodynamic cycle is based on the use of fixed and cooled adsorption beds and advanced evaporative cooling concepts. The adsorption bed, which is a fin and tube heat exchanger packed with silica gel grains, allows simultaneous dehumidification and cooling of the process air. The indirect evaporative cooling process, operated downstream to the dehumidification, is realized usingan optimized configuration with two wet plate heat exchangers connected in series. Low wet bulb temperatures reached on the secondary flow, allow supply air temperatures to the room below 20 °C. Systems are designed also for stand-alone operation thanks to a battery accumulator and PV cells installed. No auxiliary device is used for cold production. The main features of the second generation prototype system are first discussed, as well as some optimizations carried out from the first to the second generation prototype. Results are related both to field monitoring data. Performance indicators such EER and thermal COP, maximum cooling power achieved, stand alone operation data and control issues are presented and discussed.

Performance investigation of solid desiccant evaporative cooling system configurations in different climatic zones

Performance of desiccant evaporative cooling (DEC) system configurations is strongly influenced by the climate conditions and varies widely in different climate zones. Finding the optimal configuration of DEC systems for a specific climatic zone is tedious and time consuming. This investigation conducts performance analysis of five DEC system configurations under climatic conditions of five cities from different zones: Vienna, Karachi, Sao Paulo, Shanghai, and Adelaide. On the basis of operating cycle, three standard and two modified system configurations (ventilation, recirculation, dunkle cycles; ventilated-recirculation and ventilated-dunkle cycles) are analyzed in these five climate zones. Using an advance equation-based object-oriented (EOO) modeling and simulation approach, optimal configurations of a DEC system are determined for each climate zone. Based on the hourly climate data of each zone for its respective design cooling day, performance of each system configuration is estimated using three performance parameters: cooling capacity, COP, and cooling energy delivered. The results revealed that the continental/micro-thermal climate of Vienna, temperate/mesothermal climate of Sao Paulo, and dry-summer subtropical climate of Adelaide favor the use of ventilated-dunkle cycle configuration with average COP of 0.405, 0.89 and 1.01 respectively. While ventilation cycle based DEC configuration suits arid and semiarid climate of Karachi and another category of temperate/mesothermal climate of Shanghai with average COP of 2.43 and 3.03 respectively.

Results of System Configurations to Optimize Solar-driven Desiccant Evaporative Cooling Systems in Full Year Operation

The already shown high potential of desiccant evaporative cooling (DEC) systems in full year operation by using the sorption rotor for temperature and humidity recovery is here further analyzed to investigate the potential of certain system configurations. First, the disadvantages of activating the supply air humidifier in full cooling operation regarding the indoor comfort and the reduction of evaporative cooling potential in the overall process are discussed. Secondly, different control strategies for solar thermal systems with triple use (cooling, heating support, domestic hot water preparation) for different applications and climates were analyzed. These scenarios were compared with reference systems using conventional air-conditioning technologies to evaluate the primary energy savings of each case.

Grey-box modelling and in situ experimental identification of desiccant rotors

This work focuses on grey-box modelling of desiccant rotors. The main objective is to enhance the accuracy of the desiccant wheel model at off-design conditions, including unbalanced flows and variable rotational speed, by introducing tuneable parameters which can be experimentally identified. In order to perform parameters’ identification on full-scale Desiccant Evaporative Cooling (DEC) units, an ad hoc measurement apparatus has been developed and tested, along with a suitable identification procedure. The core of the measurement apparatus consists of a set of eight sensors which allow measuring the process air temperature profile at the dehumidifier wheel outlet. The apparatus was installed in an experimental DEC setup. With the support of numerical modelling, a methodology to identify the physical parameters of the desiccant wheel has been developed. The method is based on a one-dimensional physical model of the generic rotor channel. The results show that the recorded temperature profiles in a few operating conditions are sufficient to identify the model’s tuneable parameters and that the model’s output is valid over a different and wide range of operating conditions. Moreover, the influence of tuneable parameters on the model predicted temperature profile and the comparison of the experimentally identified parameters with their theoretical expected values are discussed. Finally, it is concluded that the accuracy of the one-dimensional model can be improved when its physical parameters are experimentally identified rather than estimated on the basis of literature data. Therefore, grey-box models of commercial wheels would be very helpful in cases where numerical simulations are employed for the design and control optimization of real life DEC systems.