Indoor Humidity Control Research Articles

TiO2@g-C3N4/SiO2 with superior visible-light degradation of formaldehyde for indoor humidity control coatings

Indoor air quality is a critical concern in people's daily life due to the adverse effects of formaldehyde and humidity on human health. The development of multifunctional indoor coatings which can photodegrade formaldehyde and regulate humidity is desirable. In this study, we use a simple route to synthesize a heterostructure photocatalyst (denoted as TiO2@g-C3N4/SiO2-x%) via combining TiO2, graphitic carbon nitride (g-C3N4), and enhancement silica fume (SiO2). The results indicate that the prepared TiO2@g-C3N4/SiO2-12% photocatalyst is capable of degrading formaldehyde with a removal efficiency of 83.5%, which is higher than those of pure TiO2 (10.8%) and g-C3N4 (67.8%) after 3 h of visible-light irradiation. The above findings may be attributed to the enhanced visible light absorption and the fast transfer of photogenerated electrons. Electron paramagnetic resonance spectra and Mott-Schottky plots show that the generation of ･O2− and ･OH active species via Z-scheme route on TiO2@g-C3N4/SiO2-12% are responsible for the decomposition of formaldehyde under visible light. For practical applications, the TiO2@g-C3N4/SiO2-12% photocatalyst is further employed to fabricate the sustainable coating (denoted as TGS coating), which exhibits a formaldehyde removal efficiency of 85.0% with outstanding humidity control performance over ten times higher than commercial coatings. The remarkable improvement of humidity control performance on TGS coatings is due to the effect of better textural properties. More importantly, this study demonstrates the valorization of waste silicas to fabricate sustainable TGS coatings with great stability, which may provide the practical applications in the indoor environment.

Experimental evaluation of three different dehumidifiers for greenhouses in cold regions

Selecting a dehumidifier is not easy for greenhouse growers because of its high capital and operation cost and new emerging technologies, besides selection variations with crop species, local weather climate, and greenhouse sizes. The technical performance evaluation of various dehumidification technologies in commercial-scale greenhouse settings and their comparative results can give growers the new information needed to select the best dehumidifier. In this study, the field performance of a newly developed state point liquid desiccant (SPLD) dehumidifier is compared with two other commercial dehumidification technologies; direct contact liquid desiccant (DCLD) dehumidifier, and heat recovery ventilator (HRV), in ornamental (rose) and tomato greenhouses. Under the test condition, among the three dehumidifiers, the HRV unit had the highest calculated moisture removal rate (MRR) of 189.1 kg hr-1, the lowest moisture removal cost of 0.022 $ kg−1, and the lowest electricity consumption (0.02 kWh kg−1 of moisture removal). The highest electrical consumption was found in the SPLD unit under the wet mode, with an average of 0.44 kWh kg−1. However, the SPLD-wet mode was the most efficient regarding net energy consumption (0.53 kWh kg−1). The DCLD showed a moderate performance on electrical energy (0.15 kWh kg−1) and net energy consumption (0.775 kWh kg−1) with good indoor humidity control. The SPLD unit under dry mode was similar to the HRV unit regarding moisture removal cost (0.026 $ kg−1) and electricity consumption (0.046 kWh kg−1). The comparative results of this study indicate that a single dehumidification technique cannot be both technically effective and economically cost-saving year-round. Thus, combining a low-cost technology, such as ventilation or a heat exchanger, and an internal dehumidification technology will be the most practical and feasible in cold regions.

Research on Prediction and Regulation of Thermal Dissatisfaction Rate Based on Personalized Differences

Thermal discomfort body language has been shown to be a psychological representation of personnel’s particular thermal comfort. Individual thermal comfort differences are ignored in public building settings with random personnel flow. To solve this issue, we suggested a Bayesian group thermal dissatisfaction rate prediction model based on thermal discomfort body language expression and subsequently implemented intelligent indoor temperature and humidity control. The PMV-PPD model was utilized to represent the group’s overall thermal comfort and to create a prior distribution of thermal dissatisfaction rate. To acquire the dynamic distribution of temperature discomfort body language, data on thermal discomfort body language expression were collected in a real-world office setting experiment. Based on Bayesian theory, we used personalized thermal discomfort body language expressions to modify the group’s universal thermal comfort and realized the assessment of the thermal dissatisfaction rate by combining commonality and personalization. Finally, a deep reinforcement learning system was employed to achieve intelligent indoor temperature and humidity control. The results show that when commonality and personalized thermal comfort differences are combined, real-time prediction of thermal dissatisfaction rate has high prediction accuracy and good model performance, and the prediction model provides a reference basis for reasonable indoor temperature and humidity settings.

Use of Building Façade for Active Indoor Humidity Control

Regulating indoor humidity levels to healthy ranges is important to provide occupants with acceptable thermal comfort and air quality conditions. Conventional techniques relied on the supply of dehumidified outdoor air to dilute the indoor generated moisture. They use vapor compression cooling either as standalone system or integrated with desiccant dehumidifiers to generate the dry air. Such systems are energy intensive and require large footprint areas, especially in hot and humid climates. This work proposes thus an energy-efficient alternative where the indoor humidity is pumped directly from the space and discharged outdoors. This system integrates a metal organic framework-based dehumidifier with the building breathable façade. The dehumidifier dries the outdoor air that is used to ventilate the façade and create the necessary driving gradient for the moisture transfer, irrespective of the outdoor air conditions. Mathematical models are developed to evaluate the system performance for an office space located in the extreme hot and humid climate of Jeddah, KSA. The proposed system resulted in 89 % and 90 % reduction in the system size and energy consumption compared to conventional systems over the peak humidity month.

Thermodynamic performance analysis of a novel air conditioning system integrating solar absorption compression refrigeration and vacuum membrane-based dehumidification (SACV)

For solar absorption cooling systems, it is difficult to generate lower chilled water for dehumidifying and cooling, as well as facing intermittency problems. In this work, the novel SACV system for indoor temperature and humidity control is proposed, which integrates the SSAR subsystem, the VCR subsystem, and the VMD subsystem. The VMD subsystem and the VCR subsystem solve the dehumidification difficulty and all-weather heating and cooling problems, respectively. This work also proposes a method for determining the collector area that avoids frequent start-ups and shutdowns of the VCR subsystem. Besides, a thermodynamic model of the SACV system is established and validated, and a systematical performance analysis of the SACV system is carried out. For the SACV system, the sensitivity of the parameters to the MCOP is also discussed. Results indicate that the outdoor air temperature, the latent heat load ratio, and the solar radiation intensity are the key parameters for designing the SACV system; further, the evaporation temperature and the permeate side pressure are the key parameters for the SACV system optimization. The SACV system is more suitable for high-humidity environments. Moreover, during the cooling season, the SACV system of a commercial building can realize a power saving rate of 39.82% compared to the conventional VCR system. The proposed SACV system of a commercial building can reduce 19653.59 kg/year carbon emission compared to the conventional VCR system in Nanjing. The carbon reduction rate of the SACV system in the selected cities is rather similar, about 36.78%–39.79%.

Biopolymers impact on hygrothermal properties of rammed earth: from material to building scale

Three biopolymers were tested as rammed earth (RE) stabilizers, evaluating their impact on the hygrothermal behavior from material to building scale. Hygrothermal characterization included the determination of sorption isotherm, water vapor permeability, thermal conductivity at different moisture content, and specific heat capacity. The hygrothermal data were used as input for the simulation at whole-building scale considering combined heat and moisture transfer. The results were evaluated by comparing heating demand, thermal comfort during summer, and the contribution of walls for passively controlling indoor humidity. The results show that hygric properties were only slightly affected by the use of stabilizers, while the thermal conductivity was 33% higher for RE stabilized with lignin, consequently increasing the heating demand at whole-building scale. All RE walls were effective in reducing temperature oscillations in summer. In the particular case of a canicular event, the indoor temperature was reduced by up to 10° compared with the outdoor value. The indoor humidity also benefited from the passive regulation by RE walls, regardless of whether a stablizer was used.

Application potential analysis of different control strategies for radiant floor cooling systems in office buildings in different climate zones of China

The application potential of radiant floor cooling systems is affected by climatic conditions. The meteorological parameters of 22 cities in five climatic zones in China (severe cold (SC), cold, hot summer and cold winter (HSCW), hot summer and warm winter (HSWW), and temperate) are analyzed to evaluate the applicability of four conventional control strategies of radiant floor cooling system in office buildings. The control strategies are modeled in the Transient System Simulation Program (TRNSYS), and the indoor thermal comfort, condensation risk, energy consumption, and carbon emissions are analyzed. Multi criteria decision-making is used to evaluate the radiant floor system. The results show that the control strategy with direct ground cooling produces the highest energy savings in the five climate zones. The energy savings are 25–66 % higher than those of the three control strategies using a heat pump as a cold source. Under the same indoor environment conditions, the three-step control strategy provides the optimum indoor temperature and humidity control. The number of hours when the three-step control strategy exceeds the thermal comfort zone is 5 % in 22 cities, and the number of hours with condensation risk is only 3%. The variable water supply temperature control and precooling control have better performance than the other strategies in the SC, cold, and temperate zones. In addition, the control strategies are ranked based on their application potential in 22 cities. The application potential of the radiant floor cooling system with a direct ground cooling source is the highest in the five climate zones in the two scenarios with equal weights of the four criteria and is preferable due to less carbon emissions. When the condensation risk is considered, the radiant floor cooling system with a direct ground cooling source exhibits better performance in the SC and cold zones. The variable water supply temperature control is the optimum strategy in the HSCW, HSWW, and temperate zones. The precooling control strategy ranks the highest in Changchun and Guiyang, and the three-step control strategy performs the best in Shanghai.

Effect of the indoor humidity control characteristics for amine grafted functionalized mesoporous silica nanomaterials

ABSTRACT In this study, the silicon source and aluminum source rich in stone mud were extracted, and the best alkali fusion process for different alkali fusion temperatures and alkali agent ratios was determined by the alkali fusion salt method. The surface of the material was grafted by 3-aminopropyltriethoxysilane to obtain an amine grafted functionalized groups MCM-41 material (APTES/MCM-41). The APTES/MCM-41 material was analyzed and water adsorption/desorption experiment was performed. Utilizing stone sludge to obtain APTES/MCM-41, which has a high specific surface area (25.19 m2/g) and, an adjustable pore size and an easy structural surface grafted can use different functional groups for the development of new materials. The 24-h moisture adsorption capacity of the APTES/MCM-41 with 2.5 vol.% amine functional groups was 37.02 g/m2, which conforms to JIS A 1470–1 specifications and far exceeds that of diatomaceous earth and inorganic materials in humidity control coatings (18.6 g/m2). APTES/MCM-41 could be used as an alternative to mechanical dehumidifiers.

Feasibility and optimization structure analysis on heat pump assisted desiccant cooling systems under dynamic conditions

• A horizontal comparison is conducted between the different forms of HPDC system. • The accuracy of the desiccant wheel model is verified by the analytic solution. • The indoor environment control issue of HPDC systems is clarified. • An optimal HPDC system enhances the temperature and humidity control performance. • The sensible heat exchanger is not suitable for HPDC systems. Heat-pump assisted hybrid desiccant cooling (HPDC) systems are generally placed with the evaporators located downstream of the desiccant wheel (HPDC-D) to deal with the adsorption of heat and control indoor temperature; positioning the evaporator upstream of the desiccant wheel (HPDC-U) can improve dehumidification performance. In this study, HPDC systems are established based on an analytic solution-validated desiccant wheel model, and the effect of the system configuration on the indoor temperature and humidity control is quantitatively analyzed in dynamic conditions. The proposed dimensionless parameters clarify the thermal performance of the dehumidification and regeneration processes. The simulation results propose an optimized HPDC-SE system with dual separate evaporators, and its energy consumption is compared. Finally, the feasibility of combining the HPDC system with a heat recovery plate is discussed. Due to the thermal imbalance between the condensing heat required for regeneration and the supply air cooling capacity required for the indoor sensible load, the HPDC-U system could not continuously control the indoor temperature below the control range in dynamic conditions, and the HPDC-D system could not continuously control the indoor humidity. The analysis of the dimensionless parameters shows that the thermal economy of the desiccant wheel decreases with the increase in the process inlet air humidity. The proposed HPDC-SE system can improve the indoor environment control effect and reduce the electricity consumption by 5%, 4.6%, and 11.7% compared to the HPDC-U system, respectively. The heat recovery plate has a low overall utilization and heat recovery rate for HPDC-U and HPDC-SE systems, and affects the indoor humidity control of the HPDC-D system. Therefore, the heat recovery plate is not suitable for HPDC systems.

Recycling light-emitting-diode waste quartz sand and stone sludge for the synthesis of amine grafted mesoporous humidity control material

This article proposes a cost-effective development method to recycle two types of waste material (i.e., light-emitting-diode (LED) waste quartz and stone sludge) to produce mesoporous materials. The proposed method is simple yet effective. Extraction of the precursor liquid from the silicon and aluminum sources respectively contained in the waste quartz and stone sludge is based on the alkali fusion method, and the mesoporous material is synthesized after the hydrothermal reaction. The novelty of this work lies in our functionalization of Mobil Composition of Matter No. 41 (MCM-41) through amine group grafting (AGG-MCM-41). The results show that the structure of the mesoporous MCM-41 grafted by the amine functional groups remains orderly. The 29Si nuclear magnetic resonance spectrum confirmed that the supported surface of the MCM-41 features a large number of silanol groups, which verifies that modification of the amine functional group improved the effect. The results show that when the addition amount of amine functional group is 5 vol% (when relative humidity = 95%), the highest equilibrium moisture content of the material is 26.5 kg/kg. The wet performance of the material was studied, and it was proved that 5.0-AGG-MCM-41 complies with the standard of Japanese Industrial Standard (JIS A 1475) (equilibrium moisture content>5 m3/m3). The research results also show that the optimal equilibrium moisture content is more than 44 times that of metal-organic frameworks humidity pump. Therefore, the synthesized AGG-MCM-41 offers excellent humidity control performance in the practical application of building materials as it narrows the indoor humidity fluctuation spontaneously without any energy consumption. This creates new opportunities for smart indoor humidity control. The amine-group-grafted MCM-41 effectively reduces the shortcomings of high energy consumption, high costs, and insufficient space caused by mechanical dehumidifiers. In addition, the production of AGG-MCM-41 from LED waste and stone sludge achieves 100% recycling. Transformation of two problematic industrial byproducts into humidity-conditioning materials with beneficial technical and environmental properties represents a significant contribution towards the goals of sustainable development.

On energy-efficient HVAC operation with Model Predictive Control: A multiple climate zone study

This paper aims to quantify the performance of Model Predictive Control (MPC) for a typical commercial building heating, ventilation and air conditioning (HVAC) system across a wide range of climate and weather conditions. The motivation of the study comes from the fact that although there is a large body of work on MPC for HVAC systems, there is a lack of studies that examine the range of possible performance of MPC, in terms of both energy savings and maintaining indoor climate (temperature and humidity) as a function of outdoor weather. A challenge in conducting such a study is developing an MPC controller that can be used in a wide range of weather. The root cause of this challenge is the need for a tractable cooling and dehumidification coil model that can be used by the MPC controller, since the coil may operate in quite distinct modes depending on weather. We present such an MPC controller, and then leverage it to conduct an extensive simulation campaign for fourteen climate zones in the United States and four weather conditions (winter, spring, summer, and fall) in each climate zone. The performance of the proposed controller is compared with not only a rule-based baseline controller but also with a simpler MPC controller that ignores humidity and latent heat considerations. There are several results the arise from this comparative study. One such result is that energy savings from MPC over baseline can vary dramatically based on climate and season. Another is that the effect of ignoring humidity in the MPC formulation can lead to poor indoor humidity control more in milder weather rather than in hot weather. The results from this study can help practitioners and researchers assess costs and benefits of proposed MPC formulations for HVAC control.

Solar-driven smart ceramic fiber-based monolithic adsorbent for autonomous indoor humidity control

Even though designing new sustainable buildings has become a main consensus in mitigating the energy crisis, it is equally important to reduce energy consumption of established architectures. Herein, we present a simple and efficient strategy for low-energy management of indoor humidity in established buildings. Solar-driven humidity-controlled ceramic fiber is fabricated by layer-by-layer assembly of chitosan/CuS backbones and dual-ligand metal organic framework (DMOFs) layer on a substrate. The hydrangea-type DMOFs layer exhibits high-efficient water collection as well as rapid adsorption and transport kinetics, supporting the high atmospheric hygroscopicity (0.45 g/g) of resultant ceramic fiber at 90% relative humidity (RH). The photothermal CuS layer shows high solar thermal conversion and efficient thermal conduction, allowing that adsorbed-water water to rapidly ooze out from DMOFs under the solar energy. Relying on attaching super-hygroscopic DMOFs and CuS particles with high solar absorption, the customized ceramic fiber achieves moisture collection at night and adsorbed-water release during daytime, thereby maintaining stable indoor humidity (41.8%–52.8%). By uniting these two daytime and nighttime management pathways, the resulting closed-loop system will offer a promising and low-energy solution for indoor ambient regulation in existing architectures.

Hygroscopic photothermal beads from marine polysaccharides: demonstration of efficient atmospheric water production, indoor humidity control and photovoltaic panel cooling

A sorbent-based atmospheric water generator is developed via facile integration of marine polysaccharide, hygroscopic salt and photothermal polymer in a bead-like hollow structure, demonstrating promising energy-wise and sustainable applications.

Research on the Influence of Ventilation Mode on the Condensation Risk at the Wall Radiant Terminal

The separate control of indoor heat and humidity in radiant air conditioning has more energy-saving advantages than convection air conditioning that use the same cold source to handle heat and humidity loads, which is in line with the international trend of carbon reduction and emission reduction. However, the surface of the radiation terminal is prone to condensation, which poses a health and safety hazard. In order to reduce the risk of condensation at the wall radiant terminal, this paper uses CFD to study the effect of ventilation mode on the risk of condensation at the wall radiant terminal, and evaluates the risk of condensation by using the term of the minimum supercooling condensation temperature. The simulation results show that the thermal boundary layer on the surface of the radiant terminal under different ventilation velocity is different, which affects the minimum supercooling condensation temperature, and makes the condensation risk of the radiant air conditioning system different. When the wind speed of the attached jet is 1.07 m/s, the thickness of the thermal boundary layer is 0.045 m, and the minimum supercooling condensation temperature at the radiation terminal is 1.79 K. By further increasing the wind speed and reducing the thickness of the thermal boundary layer, the minimum supercooling condensation temperature can be further increased to 2.2 K, reducing the risk of condensation.

Research on Intelligent Control System of Air Conditioning based on Internet of Things Intelligent Control System of Air Conditioning

The current air conditioning intelligent control system cannot achieve the ideal energy-saving effect. The indoor temperature and humidity control is not good enough either. Therefore, an intelligent air-conditioning control system based on Internet of Things technology is designed. The hardware part of the system includes system control motherboard, sensor module, execution control structure, wireless communication module and access layer. The software includes the design of communication layer, the design of monitoring management, and the design of intelligent indoor air-conditioning temperature remote control algorithm. The experimental results show that the control effect of the intelligent air conditioner is more accurate and energy-saving, the opening degree of the air conditioning valve is larger, and the comfort is improved. The indoor temperature and humidity of the proposed system are both more ideal.

Indoor temperature, humidity and illumination control system based on Android

The temperature, humidity and illumination control system designed in this paper is based on Android platform. It is controlled by connecting the mobile phone wifi with the single chip microcomputer, and uploaded to the mobile phone client through wifi serial port technology. Users can collect indoor temperature and humidity data and illumination data through sensors. Through the mobile phone client to control the LED lights and relay switches of household appliances, such as the control of air conditioning, and finally achieve the goal of adjusting indoor lighting and controlling the on-off of household appliances.

High Water Adsorption MOFs with Optimized Pore-Nanospaces for Autonomous Indoor Humidity Control and Pollutants Removal.

The indoor air quality is of prime importance for human daily life and health, for which the adsorbents like zeolites and silica-gels are widely used for air dehumidification and harmful gases capture. Herein, we develop a pore-nanospace post-engineering strategy to optimize the hydrophilicity, water-uptake capacity and air-purifying ability of metal-organic frameworks (MOFs) with long-term stability, offering an ideal candidate with autonomous multi-functionality of moisture control and pollutants sequestration. Through variant tuning of organic-linkers carrying hydrophobic and hydrophilic groups in the pore-nanospaces of prototypical UiO-67, a moderately hydrophilic MOF (UiO-67-4Me-NH2 -38 %) with high thermal, hydrolytic and acid-base stability is screened out, featuring S-shaped water sorption isotherms exactly located in the recommended comfortable and healthy ranges of relative humidity for indoor ventilation (45 %-65 % RH) and adverse health effects minimization (40-60 % RH). Its exceptional attributes of water-uptake working capacity/efficiency, contaminants removal, recyclability and regeneration promise a great potential in confined indoor environment application.

High Water Adsorption MOFs with Optimized Pore‐Nanospaces for Autonomous Indoor Humidity Control and Pollutants Removal

AbstractThe indoor air quality is of prime importance for human daily life and health, for which the adsorbents like zeolites and silica‐gels are widely used for air dehumidification and harmful gases capture. Herein, we develop a pore‐nanospace post‐engineering strategy to optimize the hydrophilicity, water‐uptake capacity and air‐purifying ability of metal‐organic frameworks (MOFs) with long‐term stability, offering an ideal candidate with autonomous multi‐functionality of moisture control and pollutants sequestration. Through variant tuning of organic‐linkers carrying hydrophobic and hydrophilic groups in the pore‐nanospaces of prototypical UiO‐67, a moderately hydrophilic MOF (UiO‐67‐4Me‐NH2‐38 %) with high thermal, hydrolytic and acid‐base stability is screened out, featuring S‐shaped water sorption isotherms exactly located in the recommended comfortable and healthy ranges of relative humidity for indoor ventilation (45 %–65 % RH) and adverse health effects minimization (40–60 % RH). Its exceptional attributes of water‐uptake working capacity/efficiency, contaminants removal, recyclability and regeneration promise a great potential in confined indoor environment application.

Chemically Stable Carbazole-Based Imine Covalent Organic Frameworks with Acidochromic Response for Humidity Control Applications.

Isoreticular chemically stable two-dimensional imine covalent organic frameworks (COFs), further denoted as DUT-175 and DUT-176, are obtained in a reaction of 4,4′-bis(9H-carbazol-9-yl)biphenyl tetraaldehyde with phenyldiamine and benzidine. The crystal structures, solved and refined from the powder X-ray diffraction data and confirmed by high-resolution transmission electron microscopy, indicate AA-stacked layer structures. Both structures feature distorted hexagonal channel pores, assuring remarkable porosity (SBET = 1071 m2 g–1 for DUT-175 and SBET = 1062 m2 g–1 for DUT-176), as confirmed by adsorption of gases and vapors. The complex conjugated π system of the COFs involves electron-rich carbazole building units, which in combination with the imine groups allow reversible pH-dependent protonation of the frameworks, accompanied by charge transfer and shift of the absorption bands in the UV–vis spectrum. The sigmoidal shape of the water vapor adsorption and desorption isotherms with a steep adsorption step at p/p0 = 0.4–0.6 in combination with excellent stability over dozens of adsorption and desorption cycles ranks these COFs among the best materials for indoor humidity control applications.

Improved indoor air temperature and humidity control using a novel direct-expansion-based air conditioning system

Many approaches have been tried to obtain an improved indoor thermal environment in small-to medium-sized buildings located in hot-humid climates when using direct-expansion (DX)-based air conditioning (A/C) systems. However, inadequacies still existed in these approaches. Therefore, to address these problems, a novel DX-based A/C system with a two sectioned cooling coil (TS-DXAC) has been proposed. In this paper, a control strategy to operate the TS-DXAC system for achieving an improved indoor air temperature and humidity control in hot and humid climates is presented. Firstly, the detailed configurations of the TS-DXAC system and the control strategy of the TS-DXAC system are presented. The developed strategy included two control algorithms, i.e., Algorithm I and Algorithm II, enabling the TS-DXAC system to be operated under two different indoor conditions, i.e., hot-humid, and hot-dry, respectively. Secondly, a test TS-DXAC system was set up and the controllability tests for the control strategy were carried out. This is followed by presenting the experimental results and related discussions. The experimental results demonstrated that in all the tests, indoor air temperature could be directly controlled at the two indoor conditions, while indoor air temperature and relative humidity could be simultaneously controlled over a relatively long period at a hot-humid indoor condition using Algorithm I. The control strategy enabled the TS-DXAC system to respond the changes in either indoor settings or cooling loads by outputting variable sensible and latent cooling capacities at a higher energy efficiency compared to conventional On-Off controlled DX A/C systems. However, to improve the control sensitivity under Algorithm I, consideration should be given to the variable speed operation of the compressor in the TS-DXAC system.