4:00pm - 4:15pm
Determining the impact of sensor orientation on moisture content measurements in Eastern White Pine
As buildings become more airtight and more insulated, the movement and accumulation of moisture within the building envelope become paramount in determining its resiliency. Current methods for quantifying the moisture content (MC) of wood species involve the measurement of electrical resistance between two installed electrodes and the use of existing empirical correlations to evaluate the MC. However, these correlations do not adequately consider the uncertainty of how the sensors are oriented within a sample or wall assembly. The objective of this paper is to determine the impact and uncertainty of MC readings within a wood sample due to sensor orientation. Experiments were conducted using multiple fastener types consisting of various materials and geometries. A total of 126 Eastern White Pine samples were tested with electrodes placed along the grain of the wood (longitudinal), across the grain of the wood (tangential), and in a diamond pattern. To investigate the relationship of electrical resistance between the two directions, resistance measurements were also taken in a third direction (45° relative to the grain). The samples were placed in a controlled laboratory environment until steady state was achieved at approximately 14%, 18% and 22% MC. At each MC, electrical resistances of the wood samples were measured in all three directions at temperatures ranging from -10℃ to +40℃. These data were then compiled and the relationship between the MC, grain orientation and temperature was determined. It was found that the orientation of the sensor relative to the grain impacted the resistance measurements, with the tangential direction having a significantly higher resistance – this impact was most noticeable at lower MCs and temperatures.
4:15pm - 4:30pm
Influence of the disparities between lab and in-situ application on the penetration depth of a hydrophobic agent
1Building Physics and Sustainable Design, Department of Civil Engineering, KU Leuven, Kasteelpark Arenberg 40, 3001 Leuven, Belgium; 2Research Foundation (FWO) - Flanders, Belgium
In the last few years, the application of a hydrophobic agent has gained popularity as a measure to reduce the absorption of wind-driven rain in masonry walls. In practice, several layers of a hydrophobic agent are sprayed on the surface of a wall where it penetrates and reaches a certain depth. Previous research into this penetration depth has shown that the hydrophobic zone closest to the treated surface transitions into a partially hydrophobic zone where the influence of the hydrophobic agent is still present albeit less pronounced. These conclusions are derived from experiments on single bricks hydrophobised by capillary absorption rather than a masonry wall hydrophobised by several sprayed layers of hydrophobic agent. Therefore both the influence of the method of hydrophobisation as well as the nature of the hydrophobised material on the penetration depth are the subjects of this study.
To investigate the influence of the method of hydrophobisation on the penetration depth, brick samples are hydrophobised by capillary absorption either continuously, to replicate the lab environment, or in several intervals, to replicate the application of several layers. Results have shown that applying the agent in several layers causes it to penetrate further into the bricks.
The second part of this paper focuses on the penetration depth of a hydrophobic agent into bricks and mortar joints which are destructively removed from a hydrophobised masonry wall. While the aforementioned hydrophobic and partially hydrophobic zones are visible in the ceramic bricks, the mortar joints solely display a completely hydrophobised zone which extends half as deep as in ceramic brick. This can be attributed to the limited liquid permeability of lime mortar which makes the penetration of the hydrophobic agent more difficult and limits its influence to a zone near the treated surface.
4:30pm - 4:45pm
Development of an autonomous humidity control material by using metal-organic frameworks (MOFs)
Latent cooling load accounts for around one-third of the total load of air-conditioning, and its proportion is even higher in some subtropical and tropical areas. To maintain indoor comfort and to prevent microorganism growth, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) recommends that indoor relative humidity should be maintained between 40% and 65%, which is the desired comfort relative humidity range for the human being. To meet the requirement, the vapor-compression air-conditioning system is the most commonly used method for dehumidification. However, this approach is energy-consuming.
In this paper, a novel autonomous humidity control material (AHCM) based on Metal-Organic Frameworks (MOFs) is synthesized. This material has an S-shape isotherm, high porosity, large pore volume, and very high water vapor uptake of 1.62 g/g at 80% RH. MOF-AHCM can autonomously control indoor relative humidity within the desired comfort range (i.e. between 40% and 65%) at room temperature. Hygrothermal properties of the new material are measured. Numerical simulations have been carried out to study the effect of MOF-AHCM on indoor hygrothermal conditions and building energy consumption in different climates. The results show that MOF-AHCM can effectively control indoor relative humidity fluctuations and reduce building energy consumption in most climates without any additional energy input.
4:45pm - 5:00pm
Experimental investigation of a novel metal-organic framework (MOF) based humidity pump under high humidity conditions
Technical University of Denmark, Denmark
Latent heat load accounts for a significant proportion of air-conditioning energy consumption and particularly for specific environment in humid climates. Traditional vapor-compression refrigeration dehumidification faces the problem of refrigerant leakage, overcooling and complicated mechanical systems. Here, we report a novel humidity pump that uses semiconductor refrigeration and metal-organic frameworks (MOFs) dehumidification technology, which can efficiently transport moisture from a relatively ‘low-humidity’ space to a high-humidity one. The working principles of the humidity pump were introduced that the process air flows through the cold desiccant coated heat exchanger and then comes into direct contact with the MOF coatings to transfer heat and mass. The dehumidification performance of humidity pump was investigated in high humidity. The dehumidification coefficient of performance (DCOP), dehumidification rate and moisture removal efficiency using MIL-100(Fe) coatings was calculated. The results indicated that the MOF humidity pump possesses excellent moisture transfer ability.
5:00pm - 5:15pm
Study on ultrasonic assisted regeneration of activated alumina — A potential technology used in dehumidification system
1School of Energy and Environment, Southeast University, Nanjing, 210096, PR China; 2Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, PR China; 3Jiangsu Institute of Urban Planning and Design, Nanjing, 210036, PR China
Activated alumina used in dehumidification should be regenerated at more than 110 °C temperature, resulting in excessive energy consumption. A new regeneration method using power ultrasound was put forward to overcome the limitations of activated alumina in air-conditioning applications. Comparative experiments were conducted to study the feasibility and performance of ultrasonic assisted regeneration so as to lower the regeneration temperature and raise the efficiency. The mean regeneration speed, regeneration degree, and enhanced rate were used to evaluate the contribution of ultrasound in regeneration. The effective moisture diffusivity and desorption apparent activation energy were calculated by theoretical models, revealed the enhanced mechanism caused by ultrasound. Also, we proposed some specific indexes such as unit energy consumption and energy-saving ratio to assess the energy-saving characteristics of this process. Our analysis illustrates that the introduction of power ultrasound in the process of regeneration can reduce the unit energy consumption and improve the recovered moisture adsorption, the unit energy consumption was decreased by 68.69% and the recovered moisture adsorption was improved by 16.7% under 180 W power ultrasound compared with non-ultrasonic assisted regeneration at 70 °C when initial moisture adsorption was 30%. Meanwhile, we proposed a simplified transverse-flow bed model to investigate the effects of some parameters (e.g., ultrasonic power and frequency, temperature and humidity of inlet air and the porosity of activated alumina in the steel sheet) on the working performance of rotary dehumidifier. The key variables during the ultrasonic-assisted regeneration are then investigated based on the simulation data, including the acoustic pressure distribution and corresponding oscillation velocity induced in the packed bed, the temperature and moisture ratio distribution in the packed bed and the enhancement of activated alumina regeneration brought by ultrasound. Finally, the mechanism and energy flow of ultrasonic assisted regeneration in the dehumidification process are depicted in this work.