Robust output regulation of the linearized Boussinesq equations with boundary control and observation

We study a temperature and velocity output tracking problem for a two-dimensional room model with the fluid dynamics governed by the linearized translated Boussinesq equations. Additionally, the room model includes finite-dimensional models for actuation and sensing dynamics; thus, the complete model dynamics are governed by an ODE–PDE–ODE cascade. As the main contribution, we design a low-dimensional internal model-based controller for robust output tracking of the room model. The controller’s performance is demonstrated through a numerical example.

Energy Saving and Charging Discharging Characteristics of Multiple PCMs Subjected to Internal Air Flow

One essential utilization of phase change materials as energy storage materials is energy saving and temperature control in air conditioning and indirect solar air drying systems. This study presents an experimental investigation evaluating the characteristics and energy savings of multiple phase change materials subjected to internal flow in an air heating system during charging and discharging cycles. The experimental tests were conducted using a test rig consisting of two main parts, an air supply duct and a room model equipped with phase change materials (PCMs) placed in rectangular aluminum panels. Analysis of the results was based on three test cases: PCM1 (Paraffin wax) placed in the air duct was used alone in the first case; PCM2 (RT–42) placed in the room model was used alone in the second case; and in the third case, the two PCMs (PCM1 and PCM2) were used at the same time. The results revealed a significant improvement in the energy savings and room model temperature control for the air heating system incorporated with multiple PCMs compared with that of a single PCM. Complete melting during the charging cycle occurred at temperatures in the range of 57–60 °C for PCM1 and 38–43 °C for PCM2, respectively, thereby validating the reported PCMs’ melting–solidification results. Multiple PCMs maintained the room air temperature at the desired range of 35–45.2 °C in the air heating applications by minimizing the air temperature fluctuations. The augmentation in discharging time and improvement in the room model temperature using multiple PCMs were about 28.4% higher than those without the use of PCMs. The total energy saving using two PCMs was higher by about 29.5% and 46.7% compared with the use of PCM1 and PCM2, respectively. It can be concluded that multiple PCMs have revealed higher energy savings and thermal stability for the air heating system considered in the current study.

The influence of an impedance obstacle on the acoustic field inside a rectangular room

The problem of sound propagation inside a rigid-walled room containing a rectangular obstacle was solved by dividing an acoustic field into subregions and using the continuity conditions. Acoustic waves were generated by a point source. The formulas valid for an impedance obstacle extending from a room floor to its ceiling were obtained. The considered obstacle can modeled such elements as a ventilation shaft, furniture or construction pillar. The solution was expressed in the form of convergent series. To obtain accurate results, the error resulting from the use of truncated series was controlled. Additionally, to check a correctness of the proposed solution and its computer implementation, the results obtained for a negligibly small obstacle were compared with those given by the empty room model. An excellent agreement was achieved which proves a high accuracy of the used methodology. The numerical analysis shown that the calculation time of acoustic pressure in a part of an empty room can be significantly reduced by using the obtained solution. An optimal source location for noise reduction was found. The distribution of acoustic field was illustrated and some conclusions were formulated. The changes in acoustic field due to the obstacle presence were predicted and discussed.

Subjective Effects of Sound Absorption and Investigation of Reverberation Times in Modern Japanese Dwellings

This study aimed to reveal the influence of sound absorption in general dwellings on the subjective evaluation of acoustics. First, a subjective experiment was conducted using a full-scale room model. The results indicate that the feelings of silence and serenity can be experienced at absorption coefficients above 0.17, particularly above 0.25. Additionally, we used the recorded binaural sounds for a subjective test instead of using a full-scale room model. This trial showed that the reverberance, feeling of silence, and feeling of serenity can also be evaluated using a headphone listening test. We also measured the reverberation times and recorded the sound environments in three bedrooms, three living and dining (LD) rooms, and three child rooms in modern Japanese dwellings. The average absorption coefficients of the LD and child rooms were lower than 0.17, in the range of 500 Hz to 4 kHz. Therefore, we analyzed the subjective effect of absorption through a psychological test using binaural recorded sounds. The bedrooms with absorption coefficients of 0.18–0.23 were significantly less reverberant, quieter, and more serene than the other rooms.

Mechanical and Thermo-Physical Performances of Gypsum-Based PCM Composite Materials Reinforced with Carbon Fiber

Phase change materials (PCMs) have received extensive attention due to their high latent heat storage density and isothermal behavior during heat charging and discharging processes. The application of PCMs in buildings would match energy supply and demand by using solar energy effectively, thereby reducing building energy consumption. In this study, a diatomite/paraffin (DP) composite was prepared through a vacuum-impregnated process. The thermo-physical performance, thermal stability, chemical structure and thermal reliability of the DP composite were evaluated. To develop a structural–functional integrated energy storage building material, carbon fibers (CF) were chosen as the reinforcing material. The mechanical and thermal properties of CF-reinforced DP/gypsum were examined. It is evident that the flexural strength and thermal conductivity of DP/gypsum containing 1 wt. % CF increased by 176.0% and 20.3%, respectively. In addition, the results of room model testing demonstrated that the presence of CF could enhance the overall thermal conductivity and improve the thermo-regulated performance of DP/gypsum. Moreover, the payback period of applying CF-reinforced DP/gypsum in residential buildings is approximately 23.31 years, which is much less than the average life span of buildings. Overall, the CF reinforced DP/gypsum composite is promising for thermal energy storage applications.

Moisture buffering effect of hygroscopic materials under wall moisture transfer

Hygroscopic material can moderate the indoor humidity variation due to its moisture buffering effect. This effect would change when used as interior finish mainly due to air exchange and wall moisture transfer. The author focused on clarifying the extent of the wall'’s influence on indoor moisture buffering and building humidity environment. A room model was established and the situation of no wall moisture transfer was simulated by adding a vapour barrier between the interior finish and the wall. Comparing this result with wall moisture transfer, the moisture buffering effect of the wall can be quantitatively analysed. The results verify that the buffering effect and the humidity environment, especially the seasonal buffering, change with the wall moisture transfer. The wall has great impacts on buffering in the cases of thin interior finish, high moisture production and low ventilation. Because the layer under the hygroscopic material also has buffering capacity, the difference of using various thicknesses of material is not obvious. Frequent ventilation reduces the buffering effect but improves the RH optimality.

Analysis of Optimum Thickness of Glass Wool Roof Thermal Insulation Performance

Countries in south east Asia are mostly experiencing tropical climate conditions. Therefore, the use of the air conditioning has been increased to reduce the tension and achieve thermal comfort inside the buildings. In order to reduce the energy consumption, thermal insulation has been introduced to lower down the indoor temperature. The main objective of this study is to determine the optimum thickness of the glass wool insulation. To conduct the study, a wooden room model is built based on the classroom that located at one of the Malaysian universities. The thicknesses of the glass wool insulation used in the experiment is 25 mm (one layer), 50 mm (two layers) and 75 mm (three layers). According to the results, the maximum temperature reduction for one layer of insulation is 1.0°C. Two layers of insulation reduces the indoor temperature by 1.3°C followed by the reduction of 1.5°C after applying three layers of insulation. The convection coefficient outside and inside is determined to calculate the heat flux of the roof with different insulation thickness. The heat flux gained by the roof reaches the highest value at 1 pm which is 0.648 W/m² without insulation. The heat flux has been reduced to 0.629 W/m² after applying one layer of glass wool insulation. The heat flux gained by the roof is further reduced to 0.573 W/m² and 0.518 W/m² when two and three layers of insulation are applied, respectively. Throughout the experiment, the temperature inside the room is reduced with the increase of the insulation thickness. Two layers of glass wool insulation has been selected as the optimum insulation thickness which is validated after performing calculation using the polynomial function as well as the cost analysis. Two layers of glass wool insulation yields a 27.40% of ROI per annum.

Safety of a ‘swing room’ surgery model at a high-volume hip and knee arthroplasty centre

Aims The practice of overlapping surgery has been increasing in the delivery of orthopaedic surgery, aiming to provide efficient, high-quality care. However, there are concerns about the safety of this practice. The purpose of this study was to examine the safety and efficacy of a model of partially overlapping surgery that we termed ‘swing room’ in the practice of primary total hip (THA) and knee arthroplasty (TKA). Methods A retrospective review of prospectively collected data was carried out on patients who underwent primary THA and TKA between 2006 and 2017 in two academic centres. Cases were stratified as partially overlapping (swing room), in which the surgeon is in one operating room (OR) while the next patient is being prepared in another, or nonoverlapping surgery. The demographic details of the patients which were collected included operating time, length of stay (LOS), postoperative complications within six weeks of the procedure, unplanned hospital readmissions, and unplanned reoperations. Fisher's exact, Wilcoxon rank-sum tests, chi-squared tests, and logistic regression analysis were used for statistical analysis. Results A total of 12,225 cases performed at our institution were included in the study, of which 10,596 (86.6%) were partially overlapping (swing room) and 1,629 (13.3%) were nonoverlapping. There was no significant difference in the mean age, sex, body mass index (BMI), side, and LOS between the two groups. The mean operating time was significantly shorter in the swing room group (58.2 minutes) compared with the nonoverlapping group (62.8 minutes; p < 0.001). There was no significant difference in the rates of complications, readmission and reoperations (p = 0.801 and p = 0.300, respectively) after adjusting for baseline American Society of Anesthesiologists scores. Conclusion The new ‘swing room’ model yields similar short-term outcomes without an increase in complication rates compared with routine single OR surgery in patients undergoing primary THA or TKA. Cite this article: Bone Joint J 2020;102-B(7 Supple B):112–115.

On-site measurement and simulation of indoor particulate matter distributed in a single room with stratified flow field

This study combined on-site measurement and model simulation to characterize the spatial distribution of indoor particulate matter (PM) in a single room with stratified flow fields. The concentration of PM spatially distributed in a single room with natural ventilation was measured at different heights for different PM sizes. This study revealed that the PM concentration varied with height and time. Moreover, chamber test results showed that by burning Chinese worship incense, fine particles (PM0–4) accounted for 97.33% of total PM with an average emission factor of 39.54 mg/g. The results were then applied to determine the gross emission of PM and describe its spatial distribution in a single room. Model simulation results indicated that only a small amount of PM flowed out of the room due to the trap by an indoor vortex under natural ventilation. The results are crucial for characterizing the stratified PM concentration and determining the sites for PM monitoring in indoor environments.

PUMICE LAYER: A SOLUTION TO DIMINISH THERMAL ON HORIZONTAL LEFTOVER PLACE IN ROOFTOP

There are many ways to solve thermal on buildings, such as the installation of horizontal and vertical sun-shading devices on four-direction facades. However, rooftops are often ignored. In low-rise to high-rise buildings’ rooftop, there are leftover places exposed to solar heat radiation all day. Some rooftop places are equipped with polymer thermal roof insulation, and some are even without outer thermal insulation. The research aims to find a solution to diminish the horizontal thermal radiation by using eco-friendly material, pumice, as an outer thermal insulation. Exploiting method was used on one roof model as a conventional rooftop (without outer insulation), and another as a modified rooftop model covered with pumice. Couple HOBO data logger U12-012 temperature sensors were used to measure rooftop surface temperatures and room model temperatures. Results show that the thermal radiation were blocked efficiently: 26oC on pumice covered rooftop. It saved 8.4oC room temperature.