Solid Desiccant Air Conditioning Research Articles

Solid desiccant air conditioning system using desiccant dehumidifiers with cooling technique and thermal recovery unit: Experimental investigation and performance analysis

The displayed experimental investigation pursues to design and fabricate high-efficient desiccant air conditioner that achieves the sustainable development by protecting the environment from harmful emissions, achieving thermal comfort conditions, and rationalizing energy consumption. To achieve this, smart innovative desiccant dehumidifiers and energy recovery unit were incorporated with the suggested air conditioner. The smart innovative desiccant dehumidifiers aimed to improve the air dehumidification capacity and avoid the effect of the adsorption heat by using larger cooling rates to cool the process air. To minimize power consumption, regeneration air was pre-heated using an energy recovery unit. The results showed that the ultra-efficient desiccant air conditioner suggested in the present study represents an effective design because it could achieve thermal comfort conditions and rationalize energy consumption. The ultra-efficient desiccant air conditioner could supply the cooling air with average temperature and humidity ratio varying between 11.9 and 14.6 °C and 6.89–8.9 gw/kgda, respectively. Also, the energy analysis presented that the proposed desiccant air conditioner is high-efficient where the average values of thermal coefficient of performance and electrical coefficient of performance reached 3.68 and 3.79, respectively. Moreover, the average saving in thermal energy was varying between 21.9 and 28%.

Experimental investigation on air dehumidification performance of metal organic frameworks and its application potential for solid desiccant air conditioning systems

In this paper, the air dehumidification performance of MIL-101(Cr) and MIL-101(Cr)-SO3H used for solid desiccant air conditioning (SDAC) system is experimental investigated, and compared with conventional desiccant materials including silica gel, molecular sieve and activated carbon. The results show that the moisture saturated adsorption capacity of MIL-101(Cr) is 1206–1392 mg/g at 25.0–33.5 °C/95%RH which is 4–6 times of the conventional adsorbents. MIL-101(Cr) presented an S-shaped isotherm with steep point between 30% and 50%RH which provide the possibility for low temperature regeneration. The water vapor desorption measurement results show that MIL-101(Cr) could have 96.3% (93.5%) desorption rate at 45 °C/15.95%RH (45 °C/30.60%RH) after saturated adsorption at 33.5 °C/58.0%RH. The modified material MIL-101(Cr)-SO3H didn’t show better moisture adsorption and desorption performance than MIL-101(Cr) at moderate relative humidity range but higher moisture adsorption capacity at low relative humidity cases. Its saturated adsorption capacity for moisture is 2–3 times of traditional adsorbents. MIL-101(Cr) has shown excellent moisture adsorption capacity and low-temperature regeneration property which makes it be a potential option for SDAC system optimization.

Performance analysis of different air conditioning systems in apartment buildings under different climates in China

Liquid desiccant air conditioning (LDAC) system and solid desiccant air conditioning (SDAC) system have strong dehumidification capability. To evaluate and compare their feasibility and applicability, performance analysis of these two air conditioning systems and the conventional split air conditioning (AC) system in apartment buildings was conducted under different climates in China. Results show that SDAC system has the best temperature control and LDAC system has the best relative humidity control with the same requirements. In hot and humid cities, 45% relative humidity can be reached and stably maintained by LDAC system in summer when the relative humidity set point is 50%. While for apartment building controlled by split AC system and SDAC system, indoor air relative humidity could even reach 65% in summer. LDAC system is most efficient in hot and humid cities. In cold and dry cities, split AC system performs better than other two systems. Moreover, a dividing line between areas where LDAC system is more efficient and areas where split AC system is more efficient is developed in this paper. Areas where LDAC system is more efficient are mainly distributed in the coastal areas, Yangtze River basin and south of the Yangtze River.

Experimental investigation of an integrated absorption- solid desiccant air conditioning system

Separate handling of sensible and latent components of building loads can be an energy efficient approach compared to simultaneous management of both. This paper presents a detailed experimental analysis of an energy efficient air conditioning system using solid desiccant integrated with absorption system for separate building thermal load handling. The experimental system consists of silica-gel based solid desiccant for latent load handling, whereas the gas fired air-cooled NH3-H2O absorption chiller is used to handle sensible load of the space. A chilled water-cooling coil heat exchanger is installed on the process side of desiccant cooling system to integrate it with the absorption chiller. The performance of integrated absorption- solid desiccant system is compared with a standalone conventional desiccant air conditioning system with a direct evaporative cooler considering it as baseline system under wide range of operating conditions including air temperature, air humidity, and regeneration temperature. The comparative analysis is performed in terms of supply air temperature, cooling capacity, and coefficient of performance. The experimental results exhibit that supply air temperature of the integrated system is 15.2 °C compared to 24.6 °C achieved by conventional desiccant system. Moreover, COPth of the integrated system is also 50–55% higher than its counterpart and it is almost comparable with double-effect absorption chiller. It is concluded that the integrated system using separate load management approach is more efficient for HVAC applications.

Evaluating Evaporative Cooling Assisted Solid Desiccant Dehumidification System for Agricultural Storage Application

The study aims to investigate Maisotsenko cycle evaporative cooling assisted solid desiccant air-conditioning (M-DAC) system for agricultural storage application. Conventional air-conditioning (AC) systems used for this application are refrigeration-based which are expensive as they consume excessive amount of primary-energy. In this regard, the study developed a lab-scale solid silica gel-based desiccant AC (DAC) system. Thermodynamic performance of the developed system was investigated using various adsorption/dehumidification and desorption/regeneration cycles. The system possesses maximum adsorption potential i.e., 4.88 g/kg-DA at higher regeneration temperature of 72.6 °C and long cycle time i.e., 60 min:60 min. Moreover, the system’s energy consumption performance was investigated from viewpoints of maximum latent, sensible, and total heat as well as latent heat ratio (LHR), which were found to be 0.64 kW, 1.16 kW, and 1.80 kW, respectively with maximum LHR of 0.49. Additionally, the study compared standalone DAC (S-DAC), and M-DAC system thermodynamically to investigate the feasibility of these systems from the viewpoints of temperature and relative humidity ranges, cooling potential (Qp), and coefficient of performance (COP). The S-DAC system showed temperature and relative humidity ranging from 39 °C to 48 °C, and 35% to 66%, respectively, with Qp and COP of 17.55 kJ/kg, and 0.37, respectively. Conversely, the M-DAC system showed temperature and relative humidity ranging from 17 °C to 25 °C, and 76% to 98%, respectively, with Qp and COP of 41.80 kJ/kg, and 0.87, respectively. Additionally, the study investigated respiratory heat generation rate (Qres), and heat transfer rate (Qrate) by agricultural products at different temperature gradient (∆T) and air velocity. The Qres and Qrate by the products were increased with ∆T and air velocity, respectively, thereby generating heat loads in the storage house. Therefore, the study suggests that the M-DAC system could be a potential AC option for agricultural storage application.

Investigation on activated carbon-sodium polyacrylate coated aluminum sheets for desiccant coated heat exchanger

Adsorption and desorption properties of desiccants are of key significances to the dehumidification performance of a compact dehumidification component named desiccant coated heat exchanger. This work developed novel activated carbon (AC) - sodium polyacrylate (PAAS) composite coated aluminum sheets with high adsorption property and good desorption ability. Adsorption and desorption properties of AC-PAAS coated aluminum sheets were investigated under different air conditions. Cyclic adsorption-desorption features with internal-cooling/heating were conducted. Results showed that composite coated aluminum sheets had nearly 2∼3 times higher water uptake than an AC coated sample in the range of medium- to high-relative humidity (60%∼90% RH). More than 95% of adsorbed water in composite samples was released at 70 °C & 20% RH, and 86% was still desorbed when the air temperature was decreased to 40 °C. Adsorption capacities and rate coefficients of composite samples with internal-cooling could be 2.3 and 1.5 times higher than those without. This paper provides a way to develop composite desiccants with high cyclic water uptake performance in the fields of adsorption cooling, solid desiccant air-conditioning and atmospheric water harvesting.

Effect of changes in the regeneration temperature and the regeneration airflow velocity on the system performance of the solid desiccant air conditioning

This paper presents the effect of changes in operating parameters on the solid desiccant air conditioning system performance. It has consisted of the regeneration temperature and the regeneration airflow velocity parameters. These parameters were examined in two operation modes, the former ranging from 2 m/s–0.83 m/s at constant regeneration temperature, and the latter ranging from 75°C–46.4°C at constant regeneration airflow velocity. The results indicate a smaller decline in dehumidification performance for the constant regeneration temperature operating mode than the constant airflow velocity operating mode. On the contrary, the system performance and the recovery energy ratio at the latter operating mode gives a higher value than the former operating mode. These results suggest that when the dehumidification performance becomes the main function in the system, the regeneration airflow velocity should not be too low to avoid a significant reduction in system performance.

Design of solid desiccant air conditioning system

Currently, solid desiccant air conditioning system (SDACS) is an alternative to utilize solar energy to resolve environmental and energy issues resulting from the use of conventional vapor compression of air conditioning systems. SDACS can maintain the thermal comfort of a room with optimization of solar thermal energy and minimal use of electrical power. Present work in this paper is to design a solid desiccant air conditioning system of a closed room with 18 m3 of total volume. The desiccant wheel is used to dehumidify air in the room, and evaporative cooling will be decreasing the temperature of the air. The result shows the lower temperature can be reached 24°C.

An experimental investigation on solar powered solid desiccant air conditioning (SPSDAC) based on regenerative evaporative cooling system with PCM unit

ABSTRACT A solar powered solid desiccant air conditioning (SPSDAC) with PCM unit was explored for cooling purposes for the duration of sunlight and sunset hours. Two unique modes of the indirect evaporative cooler (IEC) was adopted during the operation of the SPSDAC. During mode-1, the water circulated through the copper coil and annular space of the hollow circular pipe was vacant. Whereas in mode-2, the water circulates through copper coil and annular space. It was concluded that COP of the system is more than the exergy efficiency and exergy efficiency varied from 1.83% to 1.99%. The desiccant wheel thermal effectiveness (28.81% and 46.06%) is lower than the indirect and direct evaporative cooler effectiveness. The setup under mode-2 is advantageous as compared to mode-1. The pay back time of the setup is 23.2 months. The mean overall thermal storage capacity of the system in mode-1 is 1796.1 W whereas in mode-2 is 1817.7 W.

Thermodynamic investigation of M-cycle assisted open-cycle desiccant air conditioning systems

There is a necessity of low cost air conditioning (AC) systems for the agricultural sector of Pakistan e.g. product storage/preservation, greenhouse growing and thermal comfort of animals etc. Solid desiccant air-conditioning (DAC) system can be a handy solution in this regard. The present study gives a detail overview of DAC assisted with the Maisotsenko cycle (M-cycle) system and its applicability for the agriculture sector and livestock applications. Ideal humidity and temperature requirements for the agricultural and livestock applications have been represented on psychometric charts. Comparison between M-cycle assisted DAC and conventional DAC systems has been given which shows the significance of DAC technology in the AC sciences and also represented this difference as graphically. Desiccant AC systems are getting lots of attention in order to control the humidity in various air conditioning applications e.g. product storage, greenhouses and thermal comfort for the livestock. Different materials and arrangements of the desiccant air conditioning system are checked whether which arrangement is suitable for Pakistan situation. Additionally, some analysis has been made to investigate the DAC system assisted with M-cycle and checked the feasibility of system for ambient conditions of Multan. Results show that the DAC system can be low cost heat driven air conditioning system for the human comfort as well as agricultural sector of Pakistan.

Performance study of desiccant coated heat exchanger air conditioning system in winter

Conventional air source heat pump system faces several challenges when adopted in winter season. Solid desiccant air conditioning system can provide humidification and heating power simultaneously and can be driven by low grade thermal energy; it provides a good alternative for air source heat pump systems. However, conventional solid desiccant air conditioning system adopts desiccant wheel with high cost as core component, which hinders the development of such system. Recently, desiccant coated heat exchanger (DCHE) with low initial cost and high efficiency was developed and this paper aims to investigate performance of DCHE air conditioning system adopted in Shanghai winter season. Performance of the system is predicted by a developed mathematical model where supply air states, mass of humidification and coefficient of performance (COP) are adopted as performance indices to evaluate the feasibility and energy utilization ratio of the system. Effects of regeneration water temperature on system performance are analyzed. It is found that under the simulation condition, relatively low regeneration temperature (such as 20°C) cannot meet the designed standard and relatively high regeneration temperature (such as 40°C) provides too much extra heating power, thus moderate regeneration temperature around 30°C is recommended. Meanwhile, switch time is a crucial operation parameter for the system to obtain satisfied supply air, switch time from 40s to 80s and from 70s to 240s are recommended for transient and average supply air states, respectively. Both mass of humidification and COP increase with increasing regeneration temperature under simulation condition. Also, influences of ambient air temperature and humidity ratio on system performance are discussed to study the feasibility of such system regarding different climatic conditions. Results show that higher humidity ratio of ambient air results in increased humidity ratio of supply air, temperature of ambient air has neglectable effect on supply air. In conclusion, DCHE air conditioning system can be adopted for winter operation with moderate selection of regeneration temperature as well as switch time.

Performance assessment and transient optimization of air precooling in multi-stage solid desiccant air conditioning systems

Renewable energy is one of the most promising solutions to both energy and global warming crisis. Energy consumption can be minimized considerably by utilizing solar energy in air conditioning systems operation. One of the popular solar air conditioning technologies is desiccant air conditioning. Nonetheless, conventional desiccant air conditioning systems have a relatively low coefficient of performance (COP). In consequence, two-stage desiccant air-conditioning systems are proposed to improve desiccant air conditioning systems’ COP. Moreover, a recently commercialized cooling method named Maisotsenko cooling cycle which is capable of cooling air near to its dew point temperature is considered to be integrated within the proposed multi-stage desiccant cooling systems.In this paper, three new two-stage desiccant air conditioning systems incorporating Maisotsenko cooling cycle are proposed and investigated in details for hot and humid climates such as UAE. Furthermore, air precooling is considered to improve two stage desiccant air conditioning systems’ COP. Moreover, full transient analysis and optimization are carried out in UAE within June–October. The proposed system can minimize the required solar heating during noon time as the ambient air dry bulb temperature rises. Average COP of the system during electricity load peak hours (10:00–14:00) for all five considered and combined months is 1.77. Average rate of heat input required to operate the system and average building cooling load are determined to be 100.3kW and 46.2kW, respectively. Therefore, system average COP is computed to be 0.46.

Performance assessment of integrated PV/T and solid desiccant air-conditioning systems for cooling buildings using Maisotsenko cooling cycle

Hot summer days coincide with high solar insolation periods and high peak demands in the UAE. Solid desiccant air conditioning systems are capable of utilizing low-grade sources of energy such as solar energy. In this paper, two new air conditioning systems combining solid desiccant and Maisotsenko coolers are examined for use in humid climates such as the UAE. Solar energy in the form of a solar PV/T module is selected as the primary source of energy to operate the desiccant air cooling systems while an auxiliary heater is devised for supplementary air heating. A detailed thermodynamic analysis is performed to illustrate and evaluate the proposed air conditioning systems’ performance in the UAE under different operating conditions. A comparative analysis is carried out to signify the advantages and disadvantages of integrating the Maisotsenko cooler with conventional desiccant air conditioning units. In addition, a seasonal analysis is conducted to examine the performance of the proposed systems throughout a summer day in Abu Dhabi. Average COP for two proposed configurations during the investigated period are 0.2495 and 0.2713. Furthermore, their corresponding solar shares are 32.2% and 36.5%, respectively. Finally, with PV/T module collectors’ area of 681.0m2 and 656.3m2, annual electricity generation of 145.0MWh and 139.7MWh are reported, respectively.

農業用デシカント空調システムの実験的研究

農業用デシカント空調システムの実験的研究

Interpolation procedures for the effectiveness method to account for the influence of the inlet airflow states on the desiccant wheels performance

The prediction of the dynamic global behaviour of solid-desiccant air conditioning system continues being a complex task. It is still difficult to get access to a simple model representing with enough accuracy the behaviour of commercialized desiccant wheels.The present work is focussed on the investigation of the feasibility of different interpolation procedures based on the effectiveness concept to predict the influence of the inlet states of the process and regeneration airflows on the pair of independent effectiveness parameters and, consequently, on the global behaviour of a desiccant wheel. The interpolation procedures require a relatively low number of reference operating cases, which can be obtained experimentally, provided directly by the manufacture or derived by validated software.A comprehensive set of airflow inlet states is considered, covering the typical range of inlet states in real operating conditions of dehumidification wheels. The output results of the different version of the interpolation procedure are compared with a set of reference data for desiccant wheels having process–regeneration splits of 50–50% and 67–33%. Moreover, the approach is tested using different number of base points to define the interpolation domains for the process and regeneration inlet air states. The results of this study lead to the conclusion that: (i) the version A with only one operating point in each domain, an approach corresponding to the constant effectiveness assumption, is not recommended if it is to cover the whole range of inlet states considered, (ii) good results are obtained if the interpolation is based only on the four basic points defining each domain; (iii) the best agreement is achieved with versions of type B using 6 points in the regeneration air domain, provided that the two additional points refer to the same air temperature and different moisture contents, (iv) the best option is version B1, requiring only a total of 24 operating cases for the interpolation.The approach can be seen as an easy and quick prediction method of the global behaviour of a real desiccant wheel, suitable to be used in dynamic simulation tools for complete HVAC&R systems like TRNSYS or EnergyPlus.