Temperature And Humidity Independent Control Research Articles

A dynamic simulation study of temperature and humidity independent control system for temperate semi-humid continental monsoon climate regions

A temperature and humidity independent control (THIC) system is a promising solution for hot and humid indoor working environments. This study proposes a dual-source heat pump air-conditioning (DSHPAC) system composed of a dual-source heat pump (DSHP) and air handling unit (AHU) as a THIC system. The proposed THIC system indirectly adjusts the cooling capacity of the high-temperature evaporator (Eva1) and low-temperature evaporator (Eva2) by controlling the refrigerant mass flow rate of the system to meet the cooling and dehumidifying requirements under different operational conditions. The proposed THIC system can switch among three operational modes by using the designed operational strategy, ensuring that the requirements for indoor temperature and humidity are met. In addition, the mathematical model and equilibrium equations of the THIC system are established. This study uses an office building in Xi'an on a typical summer day as a simulation case in dynamic simulations. The coefficient of performance (COP), cooling capacity, and compressor power consumption of the proposed DSHP system are analyzed. The results demonstrate that the COP of the proposed system increases with the temperature of Eva1 (TEva1), the COP of the proposed system varies from 1.76 to 3.62, and the cooling capacity increases from 1.19 kW to 3.38 kW when TEva1 increases from 6.24 °C to 36.4 °C. The analysis of different values of φR (refrigerant mass ratio) shows that the highest COP is achieved at φR = 0.1. The results prove the application potential of the dual-source heat pumps to the THIC air-conditioning systems.

Techno-economic and environmental performance of a novel poly-generation system under different energy-supply scenarios and temperature and humidity independent control

The stand-alone energy production for power generation, heating or cooling is an usual method for low-medium grade energy utilization. To enhance the energy utilization efficiency, a combined cooling, heating, and power (CCHP) system, which is based on two-stage vapor compression cycle (TSVCC) and organic Rankine cycle (ORC), is proposed with temperature and humidity independent control (THIC). The essential parameters are changed to enhance the CCHP performances based on the thermodynamic model constructed. Moreover, the cooling performance are evaluated under different energy-supply scenarios, and the coupling effects of the CCHP are demonstrated through the THIC strategies. The results display that when the return air and fresh air are treated with energy of corresponding grade respectively, the higher outdoor relative humidity and the lower fresh air ratios are beneficial for enhancing refrigeration performance. The adverse effects of condensation temperature on both the economic and environmental performance far surpasses that of sub-cooling degree. With a rise of 10 °C in condensation temperature and sub-cooling degree, the economic performance decreases by 27.89% and 3.7% respectively, while the environmental performance decreases by 24.33% and 0.35% respectively. Furthermore, the proposed system can be switched to variant models according to different strategies in seasons to improve efficiency of energy utilization, which could be used in engineering applications.

Variations of Cooling and Dehumidification Degree Days in Major Climate Zones of China during the Past 57 Years

In previous studies, the concept of degree days has been widely used to indicate heating or cooling energy requirements, but it does not consider the dehumidification effect. In the present study, the concept of dehumidification degree days based on moisture content is used, and the degree days over the past 57 years for temperature decreasing and dehumidification in 4 cities belonging to major climate zones of China are analyzed. The results showed that the number of cooling degree days showed a significant increase (1.2–4.6 days/10 a) in all the selected cities, corresponding to the warming climate. In contrast, the degree days of dehumidification accounted for 19%–45% of the total days in summer and showed significant decreases (2.0–3.7 days/10 a) in the cold, hot summer and cold winter, and hot summer and warm winter climate zones. Comfortable days, i.e., days requiring no cooling and no dehumidification, accounting for 8–45% of the total days in summer, decreased significantly in the extreme cold and cold zones (0.9–1.8 days/10 a) but showed no apparent changes in the hot summer and cold winter and hot summer and warm winter climate zones. This study suggests that energy consumption for cooling increases linearly with climate warming, and only the energy consumed for dehumidification had an apparent decrease. The degree days of dehumidification, as well as those requiring no cooling and no dehumidification, should be fully considered in the capacity design of air-conditioning units, especially air-conditioning systems with temperature- and humidity-independent control (THIC). This study indicates that the assessment of energy consumption for requests for air-conditioning in relation to climate change should be carried out after separating energy consumption for cooling from energy consumption for dehumidification to improve building energy efficiency and indoor comfort.

Performance analysis of a novel dual-evaporation-temperature combined-effect absorption chiller for temperature and humidity independent control air-conditioning

Temperature and humidity independent control (THIC) air-conditioning (AC) systems are promising alternatives to conventional AC systems. A novel dual-evaporation-temperature combined-effect (DETCE) absorption chiller for THIC AC application is proposed. It can produce high-temperature (16–18 °C) and low-temperature (7 °C) chilled water with a thermal coefficient of performance (COP) above 1 by the deep utilization of heat source at around 100–120 °C. Theoretical models were established to investigate effects of generation temperature (Tgen), evaporation temperature and high-temperature cooling capacity ratio (HCR) on thermal performance of the novel chiller. The results show that the COP of the proposed chiller (COPch,prop) is largely affected by Tgen and HCR. The COPch,prop is 24.1 %-50.4 % larger than that of the conventional single-effect absorption chiller (SEABC) under typical HCRs (0.5–0.7). Performance comparison of the DETCE absorption chiller-based THIC AC system and the conventional SEABC-based AC system was also conducted under different room sensible heat ratios (RSHR), fresh air ratios (FR) and ambient conditions. It is found that the proposed system has a greater energy-saving potential when applied in an air-conditioned space with a large RSHR and FR. Under typical RSHRs (0.6–0.8), both the thermal energy saving rate (ESR) and the heating fluid saving rate of the novel system are over 20 %. Besides, the proposed system can achieve an average ESR of around 30 % under a wide range of ambient conditions. This study provides a novel solution for the deep utilization of solar energy or waste heat at around 100–120 °C to achieve efficient and environmentally friendly THIC AC.

Impacts of temperature and humidity changes on air‐conditioning design load under the climate change conditions in different climate zones of China

AbstractMeteorological parameters, as the important basis for improving building energy efficiency, will show apparent changes under climate change conditions. In this study, outdoor design temperature and humidity for air‐conditioning system in 12 cities, representing major climatic zones of China, were analysed to determine the impacts of temperature and humidity on the design load of air‐conditioning system. The results showed that outdoor design temperature largely increased during the last few decades and relative humidity apparently decreased except for two cities belonging to the severe cold and hot summer and cold winter climate zones. The increase in temperature and decrease in humidity have made obvious changes in the design load of air‐conditioning system. The design loads for cooling increased 1.8%–10% in these selected cities during 1991–2017 compared with 1961–1990. By contrast, the design loads for dehumidification decreased 0.8%–7% in 1991–2017 relative to 1961–1990. When the cooling and dehumidification were considered together, the design loads changed from −1.5% to 4.1% in the two periods, depending on cities or climate zones. These results demonstrated that, under the condition of climate change, the combined changes of humidity and temperature rather than temperature alone should be fully considered to determine the design capacity of air‐conditioning system, especially for temperature and humidity independent control (THIC) air‐conditioning system, to save energy and improve indoor comfort.

Adaptability of a temperature and humidity independent control air-conditioning system in green office buildings

In order to reduce the energy consumption and improve the economy of air conditioning system, theoretical analysis and energy consumption simulation are used in this paper to explore the adaptability of temperature and humidity independent control (THIC) air-conditioning system in green office buildings. On the basis of the air moisture content and working hours of staff in green office buildings, China was divided into four humidity-hour zones, and several typical cities were selected in each zone for the same building to carry out the analyses of energy consumption simulation and dynamic recovery period of different THIC air conditioning systems in office buildings. The results indicated that in Urumqi, as the representative city of humidity-hour zone I, green office buildings do not suit THIC system; THIC air conditioning system shows obvious advantages over traditional air conditioning in terms of energy saving and economy, and the energy saving rate of the most suitable THIC air conditioning system in Harbin, Beijing and Haikou, as the representative city of humidity-hour zone Ⅱ, zone Ⅲ and zone Ⅳ, reached 28.04%, 24.64%, and 24.42% respectively. Based on the number of humidity-hour, the most suitable THIC air conditioning systems for typical cities in different zone were raised, and a reference for the use of THIC air conditioning system in green office buildings was provided in this paper.

Thermodynamic performance assessment of vacuum membrane-based dehumidification and air carrying energy radiant air-conditioning system (VMD-ACERS)

Temperature and humidity independent control (THIC) air-conditioning system is a promising technology. In this work, a novel temperature and humidity independent control (THIC) system is proposed, namely VMD-ACERS, which integrates vacuum membrane-based dehumidification and air carrying energy radiant air-conditioning system. This work establishes a novel coefficient of performance (COP) model of VMD-ACERS. The main parameters affecting the COP of conventional fan coil unit cooling system (FCUCS) and VMD-ACERS are investigated. The performance of FCUCS and VMD-ACERS are compared, and the energy-saving potential of VMD-ACERS is proved. Results indicate that, for FCUCS, the importance ranking of parameters is basically stable. However, for VMD-ACERS, the importance ranking will be affected by FCU and refrigerant. The most important parameters of VMD-ACERS are condensation temperature and permeate side pressure. On the contrary, superheating, subcooling are relatively less important parameters. For VMD-ACERS, it is not necessary to pursue the membrane with very high selectivity, because the selectivity of membrane would also be a less important parameter when it reaches 500. The COP of VMD-ACERS is higher than that of FCUCS when the permeate side pressure is higher than 8 kPa. The VMD-ACERS solves two technical problems about power-saving and thermal comfort of conventional THIC, and can extend the application of THIC air-conditioning system.

Performance of a temperature and humidity independent control air-conditioning system based on liquid desiccant for industrial environments

Saving energy consumption of air-conditioning systems is becoming increasingly important in industrial buildings. In this study, measurements were conducted to reveal on-site performance of a full fresh air-conditioning system based on liquid desiccant applied in an industrial factory. Operating the system, temperature and humidity independent control (THIC) can be realized. The results reveal that the THIC system requires higher-temperature chilled water and no reheating process because of the adoption of a liquid desiccant dehumidifier, compared with the conventional vapor compression air-conditioning system. Therefore, a competitive system's coefficient of performance of 3.6 can be realized under the THIC system and an annual electricity-saving ratio of 23.3% can be achieved. In this system, the process air is divided into two parts, and the flow rate ratio of these two parts is discussed to further improve the system's performance. An optimal range of the ratio is determined in this study. When adjusting the ratio from the current 0.72 to 0.5, annual electricity consumption of the THIC system can be further saved by 5.4%. This study would provide valuable experience and reference for energy conservation of industrial air-conditioning systems.

Entransy analysis on the performance of the counter-flow heat exchangers for a double evaporating temperature chiller

The double evaporating temperature (DET) chiller has been considered as a credible method to realize temperature and humidity independent control (THIC). Energy performance optimization is of great significance for the extensive application of the DET chiller. In this paper, entransy method is employed to analyze heat transfer performance of heat exchangers based on the extremum principle of entransy dissipation (EPED) and the minimum entransy dissipation-based thermal resistance (EDTR). The entransy dissipation rate and EDTR are discussed in detail to indicate the impacts of tl,c, th,c (i.e., temperature of low temperature chilled water, high temperature chilled water), MC(R32): MC(R236fa) (i.e., mass concentration ratio of R32 to R236fa), and structural parameters on heat transfer performance of heat exchangers. The results indicate that the lowest entransy dissipation rate of heat exchangers are achieved when MC(R32): MC(R236fa) is 40%: 60%. The design tl,c/th,c are suggested to be set at 7/16 °C to reduce the entransy dissipation rate and EDTR of heat exchangers, which is beneficial to strengthen energy utilization of the chiller for energy saving. Considering the significant effect of heat capacity ratio of two steams on the EDTR, mr (i.e., mass flow rate of refrigerant) and ml,c/mh,c/mc (i.e., mass flow rates of low/high temperature chilled water/cooling water) should be increased and decreased, respectively.

Performance analysis and evaluation of desiccant air-handling unit under various operation condition through measurement and simulation in hot and humid climate

In hot and humid climate such as in Japan and south east Asia, dehumidification in summer is really important for air conditioning. Temperature and humidity independent control (THIC) of air conditioning system can handle sensible heat and latent heat separately, and provide good indoor environment and achieve energy conservation. Desiccant air handling unit is one of the major solution for THIC of air conditioning system. It needs hot water to regenerate sorbent which absorbs moist in the air. Combined heat and power can supply hot water at almost constant temperature for desiccant air handling system and also contribute to the business continuity plan of commercial buildings. However, there are still uncertainties about the factors which affect energy performance of desiccant air handling unit and the optimum design and operations in hot and humid climate. The objectives of this paper are to prove factors which affect energy performance of desiccant air handling unit by measurement analysis and show optimum condition of the desiccant air handling unit under various room conditions by simulation. Measurement analysis shows that energy performance of desiccant air handling unit depends not only on the inlet air condition to dehumidification wheel but also on designed supply air humidity. Furthermore, simulation results show the optimum inlet air condition entering dehumidification wheel under various supply air absolute humidity which is determined by design room conditions. These results provide useful information of desiccant air handling unit during design and operation phase of buildings in hot and humid climate.

Exergy and energy analysis of a double evaporating temperature chiller

Temperature and humidity independent control (THIC) has been demonstrated as an effective way to improve the performance for air-conditioning systems. As an alternative option of THIC method, a double evaporating temperature (DET) chiller using zeotropic mixture refrigerants of R32 and R236fa has been proposed to substitute the traditional water-cooled chiller. The low temperature chilled water of 7 °C and high temperature chilled water of 17 °C will be produced simultaneously by this DET chiller, and the latent and sensible cooling loads of buildings can be afforded by the produced low temperature chilled water and high temperature chilled water respectively. In this paper, the experiments with different concentration ratios of R32 to R236fa are carried out on a 4.0-kW DET chiller. To further improve the energy performance of the DET chiller, the exergy analysis is used to investigate the effects of chilled water temperature and mass concentration of zeotropic mixture on the DET chiller. The exergy loss for each component is discussed in detail to identify the inefficient components, and then indicate the ways to improve the performance of DET chiller. The results show that the DET chiller achieves the lowest exergy loss and highest exergy efficiency when the mass concentration ratio of R32 to R236fa is 40%: 60%. Furthermore, the design temperature of high temperature chilled water should be at 16 °C to improve the energy utilization of DET chiller. This study will help to understand the design and operation for the DET chiller based air-conditioning systems.

Analysis on the Utilization of Temperature and Humidity Independent Control Air-conditioning System with Different Fresh-air Handling Methods

The presented research illustrates the characteristics of Temperature and Humidity Independent Control (THIC) system with different fresh-air handling methods through engineering case studies. The investigated methods include dehumidification with the application of cooling, liquid desiccant, dual cooling sources dehumidification and dehumidification wheel. By analyzing the dehumidification processes on psychrometric charts, this study summarized main design focus then conducted detailed calculation for equipment sizing. Furthermore, this study compares energy consumptions for the four methods. Results show liquid desiccant and dual cooling sources dehumidification are more suitable for general office buildings in terms of energy conservation. Dehumidification wheel method consumes too much energy therefore not applicable for comfort air conditioning systems.

Applicability and energy efficiency of temperature and humidity independent control systems based on dual cooling sources

Temperature and humidity independent control (THIC) systems demonstrate promising energy-saving potential compared with the conventional air conditioning systems. One type of THIC systems is proposed to use dual cooling sources with different temperatures since they could be produced easily by traditional vapor compression refrigeration chillers. This paper investigates the applicable condition of the THIC system based on dual cooling sources (DCSTHIC system). It is found that the DCSTHIC system has limited conditions (such as scopes of the heat moisture ratio and the fresh air rate) when applied, otherwise the indoor air temperature and humidity can’t be fulfilled, and further available scope of the heat moisture ratio realized by the DCSTHIC system is disclosed for air conditioned spaces. The minimum realized heat moisture ratio depends on the temperature of low-temperature cooling sources (tLCS). A parametric study is also conducted to analyze effects on the energy efficiency of DCSTHIC systems. These parameters include the heat moisture ratio (ε) and temperatures of dual cooling sources. Results show that DCSTHIC systems show more significant energy-saving potential in the air conditioned spaces with higher ε. The system COP improvement ranges from 3.1% to 17.5% compared with conventional air conditioning systems when the heat moisture ratio changes from 8000kJ/kg to 15,000kJ/kg. This study helps to guide the design and optimization of DCSTHIC systems.

A novel air-conditioning system for proactive power demand response to smart grid

Power demand response is considered as one of the most promising solutions in relieving the power imbalance of an electrical grid that results a series of critical problems to the gird and end-users. In order to effectively make use of the demand response potentials of buildings, this paper presents a novel air-conditioning system with proactive demand control for daily load shifting and real time power balance in the developing smart grid. This system consists of a chilled water storage system (CWS) and a temperature and humidity independent control (THIC) air-conditioning system, which can significantly reduce the storage volume of the chilled water tank and effectively enable a building with more flexibility in changing its electricity usage patterns. The power demand of the proposed air-conditioning system can be flexibly controlled as desired by implementing two types of demand response strategies: demand side bidding (DSB) strategy and demand as frequency controlled reserve (DFR) strategy, in respond to the day-ahead and hour-ahead power change requirements of the grid, respectively. Considerable benefits (e.g., energy and cost savings) can be achieved for both the electricity utilities and building owners under incentive pricing or tariffs. A case study is conducted in a simulation platform to demonstrate the application of the proposed system in an office building.

Performance analysis of a hybrid air-conditioning system dehumidified by liquid desiccant with low temperature and low concentration

Abstract For temperature and humidity independent control (THIC) air-conditioning systems that integrated liquid desiccant dehumidification technology, it is very good idea to use condensation heat of the vapor compression system for the liquid desiccant regeneration. However, the system is unable to work in situations of humid climate or high latent load, since the condensation heat may not satisfy the regeneration of the liquid desiccant. This paper proposed a novel THIC air-conditioning system based on liquid desiccant, in which liquid desiccant with low-concentration and low-temperature was used in air dehumidification, and the condensation heat could meet the need of the regeneration of desiccant solution. A validated mathematical model was used to investigate the performance of the novel system under different operation conditions. The results showed that under typical indoor condition in Nanjing summer, mass concentration range of 25.4–26.9% was suggested in the dehumidification process using LiCl–H 2 O, and the dehumidification temperature range of the desiccant was around 17–19 °C. The effects of the ratios of indoor sensible load to latent load, and the outdoor air temperature and humidity on the system performance were discussed. Performance comparisons showed that COP sys of the system was 13.6–116.1% more than that of the conventional system under different operation conditions.

A Novel Air-conditioning System for Proactive Power Demand Response to Smart Grid

This paper presents a novel air-conditioning system with proactive demand response to smart grid. The system consists of a chilled water storage system (CWS) and a temperature and humidity independent control (THIC) air-conditioning system. Using this system, building power demand can be flexibly controlled as desired by implementing two demand response strategies: demand side bidding (DSB) strategy and demand as frequency controlled reserve (DFR) strategy, in respond to the day-ahead and hour-ahead power balance requirements of the grid, respectively. Considerable benefits can be achieved for both power companies and end-users under incentive pricing mechanisms. A case study concerning on the demand response performance of the proposed system is also conducted in an office building.

Development of temperature and humidity independent control (THIC) air-conditioning systems in China—A review

A temperature and humidity independent control (THIC) system is a way to regulate indoor temperature and humidity separately through different approaches. Because of this distinction, THIC air-conditioning systems can satisfy the adjustment requirements of indoor temperature and humidity better than conventional systems can, and they show significant potential for energy conservation. In the past ten years, rapid improvements have been achieved in both theoretical research and the development of equipment related to THIC systems, and more and more applications are being put into use in non-residential buildings in China. This paper focuses on the development of THIC systems in China and reviews recent achievements and progress related to the main devices used for temperature and humidity control, including outdoor air handling dehumidification processors, sensible heat terminals, and high-temperature cooling sources. The energy performance of THIC systems is examined based on an analysis of established applications. Both the performance of key components and the energy consumption of entire systems indicate that THIC systems result in significant improvements in energy performance compared to conventional systems. Developmental trends and recommendations about design methodology, ways to improve the performance of handling devices, and feedback from applications of THIC systems are also discussed.

Research of Temperature and Humidity Independent Control Air-Conditioning System

In this paper, the working principle, relevant equipments and characteristics of temperature and humidity independent control (THIC) air-conditioning system were presented. And authors summarized the application status, design conditions and application conditions of THIC air-conditioning system. Through the research of the system application at home and abroad, authors pointed out the engineering limitations and the way to improve and popularize the technology application.

Performance simulation of a joint solid desiccant heat pump and variable refrigerant flow air conditioning system in EnergyPlus

Temperature and humidity independent control (THIC) system has become an attractive alternative to conventional HVAC systems for its merits of energy-saving. In this paper, a novel solid desiccant heat pump is introduced and integrated with a conventional variable refrigerant flow air conditioning system (VRF) to form a THIC system. A standalone module of the SDHP is developed and the integration of the proposed THIC system is established based on EnergyPlus. Performance of this joint SDHP and VRF system (JDVS) is investigated in an office room. Parametric investigation results show that performance of SDHP varies greatly with the change of ambient air condition and part load ratio. Then, performance of JDVS in terms of capacity, energy consumption and system coefficient of performance (COP) is studied under summer and winter conditions. Finally, comparison study with the conventional joint heat recovery ventilator (HRV) and VRF system (JHVS) is conducted. Simulation results show that JDVS could obtain a better indoor thermal comfort while consuming less energy compared to JHVS. Through the whole year, JDVS consumes 18.7% less energy compared to JHVS. In addition, 85.5% of the indoor condition provided by JDVS falls in the comfort zone, and 35.4% provided by JHVS falls in the comfort zone.

Performance analysis of the air-conditioning system in Xi’an Xianyang International Airport

Reducing the energy consumption of air-conditioning systems is becoming increasingly important. This paper focuses on the air-conditioning system in Terminal 3 in Xi’an Xianyang International Airport, the first airport terminal to adopt radiant cooling in China. In the large spaces of this airport terminal, a temperature and humidity independent control (THIC) system has been adopted instead of a conventional nozzle air supply method, which significantly reduces the energy consumption of the air supply. The radiant floor is the main mechanism for indoor temperature control, while a liquid desiccant outdoor air processor combined with displacement ventilation is responsible for humidity control. Ice storage is adopted to reduce operating costs, and the supplied chilled water temperature can be as low as 3°C. This paper examines the performance of the THIC system in detail. The indoor environment is determined through measurements to be comfortable, and the on-site performances of key components in both the airport terminal and the cooling plant are investigated. The outdoor air processor supplies air of appropriate temperature and humidity ratio; two kinds of radiant floors are used for temperature control, both with measured cooling capacities of about 30–40W/m2; and the energy efficiency ratio (EER) of the cooling plant is 2.62.