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Xu Z.,Berkeley Education Alliance for Research in Singapore | Liu S.,Berkeley Education Alliance for Research in Singapore | Hu G.,Nanyang Technological University | Spanos C.J.,University of California at Berkeley
Energy and Buildings | Year: 2017

Air temperature and speed play a critical role in the thermal sensation of comfort felt by occupants, especially in the tropics. It is of great practical interest to coordinate air conditioning and mechanical ventilation (ACMV) system and personal fans so as to enhance building demand response (DR) capability while minimizing energy cost in response to a specific electricity price signal and maintaining a thermal comfort level. In this paper, an optimization problem of coordinating ACMV and personal fans is addressed, which captures the coupling between ACMV and fans. A Lagrangian relaxation-based algorithm is developed to solve the problem by individually solving the subproblems of ACMV and personal fans with Lagrangian multipliers as the coordinated signals. This algorithm can separate the calculation of the cooling effect from the optimization procedure, so we do not have to solve the problem using a non-analytical model for evaluating the cooling effect provided by the fans. The performance of the proposed method is evaluated and validated using experimental and simulation results. Both the results show that coordinating ACMV and fans can substantially enhance building DR capability, save energy cost, and also improve customized thermal comfort microenvironment. © 2017 Elsevier B.V.

Fadeyi M.O.,Berkeley Education Alliance for Research in Singapore | Fadeyi M.O.,Nanyang Technological University | Tham K.W.,National University of Singapore | Wu W.Y.,National University of Singapore
Indoor Air | Year: 2015

The impact of asthma, exposure period, and filter condition downstream of the mixing box of air-conditioning system on building occupants' perceptual response, work performance, and salivary α-amylase secretion during exposures to ozone and its initiated chemistry products is studied. The experiments were conducted in a field environmental chamber (FEC) (240 m3) simulating an office environment. Experiments were conducted during periods when the air-handling system operated with new or used pleated panel filters at constant recirculation (7/h) and ventilation (1/h) rates. Average ozone and secondary organic aerosols (ozone-initiated chemistry products) measured during non-asthmatic and asthmatic subjects' 3-h exposures in the FEC were in the ranges approximately 20-37 ppb and approximately 1.6-3 μg/m3, respectively. Asthmatic subjects' perceived odor intensity and sensory (eye, nose, and throat) irritation ratings were generally lower than those of non-asthmatic subjects, possibly explaining why asthmatic subjects accept perceived air quality more than non-asthmatic subjects. However, asthmatic subjects' perceived physiological-like symptom ratings (flu, chest tightness, and headache) and concentrations of secreted salivary α-amylase were generally higher than those of non-asthmatic subjects. Asthmatic subjects had significantly lower accuracy than non-asthmatic subjects in a task that required higher concentration although they had higher work speed. Filter condition did not make any significant difference for subjects' responses. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Yang B.,Berkeley Education Alliance for Research in Singapore | Yang B.,Nanyang Technological University | Schiavon S.,University of California at Berkeley | Sekhar C.,National University of Singapore | And 3 more authors.
Building and Environment | Year: 2015

In warm environments, isothermal cooling by deliberately enhanced air movement can maintain thermal comfort using less energy than compressor-based air conditioning. To evaluate the performance of a brushless direct current (DC) stand fan, the cooling fan efficiency (CFE) index was measured in a climatic chamber under four dry-bulb temperatures (24, 26, 28, and 30°C), six speed settings (corresponding to centreline speeds in the range 0.6-2.5m/s at 1m distance), two fan-manikin distances (1 and 2m) and two orientations (front, side). The CFE index is defined as the ratio of the whole-body cooling effect generated by non-uniform airflow from the fan to its power consumption (°C/W). The CFE index overcomes the limitations of assessing the cooling effect based just on a few air speed measurements. The results show that the CFE index is influenced by dry-bulb temperature, fan speed setting, and fan-manikin distance, but not by fan-manikin orientation. The lower the temperature and the closer the fan, the higher is the CFE index. Increasing fan speed setting simultaneously enhances whole-body cooling and increases power use. Consequently, the CFE has a non-monotonic relationship with fan speed setting and the peak value is reached for an intermediate speed. As compared with previous testing results using an alternating current stand fan, the CFE index of the DC fan we tested is three times higher. As a complement to air-conditioning, the tested stand fan is a suitable energy-efficient technology for providing thermal comfort in warm environments. © 2014 Elsevier Ltd.

News Article | December 22, 2016
Site: phys.org

In the latest issue of Indoor Air, an interdisciplinary team of researchers from the UC Berkeley, Nanyang Technological University in Singapore and Stanford University lays out the results of experiments conducted in the tropical city-state of Singapore. Some 50 percent of electricity in Singapore is consumed by commercial and residential buildings, mainly to supply air conditioning for occupant comfort and to dehumidify air conditioned spaces. In the United States, about 75 percent of electricity is used in buildings. Meanwhile, in the U.S. and worldwide, air conditioning accounts for 40 percent of total energy use and relative greenhouse gas emissions. "In 2050, most of the world population will live in the tropics, and the use of air conditioning is already exploding in tropical countries. Forecasts for an even hotter, more densely populated and wealthier planet just add to the significance of our research," said Stefano Schiavon, a UC Berkeley assistant architecture professor in sustainability, energy and environment and a researcher with the College of Environmental Design's Center for the Built Environment. A principal investigator on the Singapore research, Schiavon worked with fellow members of Singapore Berkeley Building Efficiency and Sustainability in the Tropics (SinBerBEST), a wide-ranging group of researchers from UC Berkeley, Nanyang Technological University (NTU) and the National University of Singapore (NUS). It is a program of the Berkeley Education Alliance for Research in Singapore (BEARS). For the cognitive tests, Schiavon collaborated with a doctoral student from Stanford. Air conditioning is needed to provide comfortable and productive working and sleeping environments, but its impact on the environment and the electrical grid is large, the team said. Lee Kuan Yew, Singapore's prime minister from 1959 to 1990, called air conditioning "a most important invention," without which work on the island city-state would be limited to cool early morning hours or dusk. "The first thing I did upon becoming prime minister was to install air conditioners in buildings…This was key to public efficiency," Lew wrote in a 2009 article for the New Perspectives Quarterly. The team's objective was to show that is possible to provide the same or more comfort with less energy. The typical set point for office building indoor temperatures has for decades been 23°C in Singapore, where the yearly average outdoor temperature during the day is 29°C (84°F). But Schiavon and his team wanted to see what would happen when they turned up the thermostat. They conducted five experiments in the summer of 2014, with 56 participants dressed in typical Singaporean office attire—long pants, a short-sleeved shirt, socks and close-toed business shoes—and assembled in a room at Nanyang Technological University featuring an open-office layout, with no cubicles. During the 90-minute tests, researchers asked participants to gauge their comfort levels when temperatures were adjusted to 23°C (73.4°F), 26°C (78.8° F) or 29°C (84.2°F). Relative humidity was controlled at 60 percent, a typical indoor level in Singapore. In two of the tests (26 and 29°C), subjects were allowed to control air movement with personal electric fans if they wished. The tests used smart, energy-efficient desk fans that run on more efficient, direct-current (DC) motors using between 3 and 17 watts, rather than alternative-current (AC) motors that use around 100 watts. Increasing the indoor temperature set point to values in the range of 26-29°C (79-84°F) and simultaneously providing occupants with personally controllable fans could be a cost-effective, sustainable and energy-efficient option for providing thermal comfort in new and existing buildings in the tropics, said Schiavon. "If applied to commercial building in Singapore, we could save up to 35 percent of the energy for air conditioning," he said. "Moreover, we are now working on smart fans that can adapt to the environmental conditions and provide the needed comfort" said Schiavon, adding that his team has a provisional patent on a smart control for a system of fans and is applying for a full patent. Explore further: In search of energy-efficient comfort through 'smart' ceiling fans and thermostats More information: S. Schiavon et al. Thermal comfort, perceived air quality, and cognitive performance when personally controlled air movement is used by tropically acclimatized persons, Indoor Air (2016). DOI: 10.1111/ina.12352

Fadeyi M.O.,Berkeley Education Alliance for Research in Singapore | Fadeyi M.O.,Nanyang Technological University
Sustainable Cities and Society | Year: 2015

Presence of ozone in indoor environment has implications on creation of sustainable indoor environment. A material mass balance model is used to summarize outcome of the review exercise that was conducted to understand what 15 years has taught us, with regards to the chemistry and concentration of ozone in indoor environment, since after a similar review effort by Weschler in the year 2000. Additionally, key knowledge gained on the impact of ozone and its initiated chemistry products on human health and comfort are summarized. This paper is concluded with recommendations for future research directions. © 2015 Elsevier Ltd. All rights reserved.

Yap H.G.,Nanyang Technological University | Tseng K.J.,Berkeley Education Alliance for Research in Singapore
9th International Conference on Power Electronics - ECCE Asia: "Green World with Power Electronics", ICPE 2015-ECCE Asia | Year: 2015

DC power distribution is becoming more prevalent in buildings, starting in niche applications such as data centers and gradually moving into more mainstream applications. There is need for the DC network in the building (termed as nanogrid) to interface with the external AC utility grid for energy exchange, security and reliability. In this study, we examined the power electronic converter topologies available for this function, as well as how to integrate the secondary objectives of metering, protection, communications and energy efficiency optimization. A three-phase bidirectional buck rectifier is chosen as a case study to interface the external AC grid to the internal DC nanogrid. The output of the bidirectional rectifier is chosen to be 380Vdc, while having to fulfill the requirements of smooth DC output voltage, unity power factor and low THD. The implementation of space vector PWM for this rectifier gives good dynamic response during the power flow change-over. The increase in number of power semiconductor switches may however lower the reliability of this topology. To assess the reliability of this converter, the possible internal faults of this topology are visualized using a polar plot of output voltage against phasor of the source voltage from the AC grid. The fault mode can be then identified easily from the fault pattern in polar plot. Simulation results are presented to support the analysis and recommendations. © 2015 Korean Institute of Power Electronics.

Fadeyi M.O.,Berkeley Education Alliance for Research in Singapore | Fadeyi M.O.,Nanyang Technological University
Building and Environment | Year: 2014

This preliminary study examines the influence of longer thermal history on building occupants' thermal sensation, perceived air temperature and thermal acceptability during the initial period of occupancy and after an extended period of occupancy in actual air-conditioned office buildings. Each of the subjects' forty-eight-hour thermal history was assessed using measured air temperatures with a wireless chip, "iButton," placed close to their skins. Subjects did thermal assessments of their offices through a web-based survey link while they had their "iButton" on them. In addition, the subjects were required to fill the survey 4 times in their offices: during initial occupancy, before lunch break, after lunch break and before they left their offices for the day. Subjects' thermal assessments followed typical transient perceptions during initial occupancy of their offices. However, subjects' thermal assessments followed typical steady-state perceptions after extended period of occupancy because of diminished influence of thermal history. Maximum thermal acceptability occurred around neutral point of rating scales of thermal sensation and perceived air temperature throughout occupancy periods. Additionally, gender and body mass index influenced building occupants' thermal assessments. These results provide understanding on how thermal history influences occupants' thermal sensation, perceived air temperature, and thermal acceptability should be accounted for in the design and operation of air-conditioned buildings where occupants spend considerable amount of time. © 2014 Elsevier Ltd.

Soudari M.,Kalasalingam University | Srinivasan S.,Berkeley Education Alliance for Research in Singapore | Balasubramanian S.,Kalasalingam University | Vain J.,Tallinn University of Technology | Kotta U.,Tallinn University of Technology
Energy and Buildings | Year: 2016

This investigation presents a personalized energy management system (PEMS) for heating, ventilation and air-conditioning (HVAC) systems in residential buildings based on economic model predictive control (EMPC) integrated with occupancy and occupant behaviour. The major building blocks of the PEMS are: weather forecasting tool, occupancy predictor, occupant behaviour model, cost-generator, and Economic Model Predictive Controller (EMPC). The occupancy is modelled using Hidden Markov Model (HMM), whereas Adaptive Neuro Fuzzy Inference System (ANFIS) is used to model the occupant behaviour. The cost generator computes the energy cost as the sum of personalized costs computed by using ANFIS model, time-of-use charges predicted from load-curve information, and fixed energy cost. The EMPC optimizes the energy consumption using a constrained optimization routine including the comfort margins specified by the occupant in a receding horizon manner. Performance of the PEMS is illustrated using experiments on a laboratory scale HVAC system. Our results show that the proposed controller not only reduces the energy consumption by 9.7–25%, and cost (from 8.2% to 18.2%), but also maintains the temperature within the personalized comfort band. The novelty of the proposed approach is the integration of demand response, occupancy and occupant behaviour within the PEMS framework. As a result, the proposed controller reduces energy, cost and peak-demand. © 2016 Elsevier B.V.

Deng Y.,University of Wisconsin - Milwaukee | Cao S.-J.,Soochow University of China | Chen A.,Berkeley Education Alliance for Research in Singapore | Guo Y.,Catholic University of Leuven
Building and Environment | Year: 2016

Multiple studies have been dedicated to particle emissions from three dimensional printer (3D printer). They collectively have shown that 3D printers will emit significant ultrafine particles during their printing processes. An important step forward is to investigate the printing process in detail and help reducing emissions. This study investigates particle emissions from two filaments of acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) according to four steps (loading, heating, printing, and unloading) during the 3D printing process in constraint of product quality assessment. The results show that ABS filament triggers at least times higher particle emissions than PLA filament (ABS-printed product presents higher quality with higher nozzle temperature (240 °C); however, higher nozzle temperature triggers substantially higher particle emission. This study further identifies that the particle emissions are mostly triggered by the heating process rather than the printing process. It indicates that filament undergoes decomposition during the heating period after being loading into the extruder. As for product quality in terms of surface roughness and production deformation, ABS is not compatible to fast neither printing speed nor low nozzle temperature; the PLA filament exhibits significant tolerance to temperature and feed rate changes. An optimization, which is externally heating up both the extruder and platform before the filament is loaded, shows that pre-heating reduces particle emissions by 75% for ABS filament when compared with the conventional procedure. © 2016 Elsevier Ltd.

Liu S.,Berkeley Education Alliance for Research in Singapore | Xie L.,Nanyang Technological University
2012 12th International Conference on Control, Automation, Robotics and Vision, ICARCV 2012 | Year: 2012

This paper considers the average consensus problem for multi-agent systems with continuous-time first-order dynamics. The communication channels among the agents are constrained in which the exchanged information is quantized. In this paper, logarithmic quantization is considered in the communication channels, and sampled-data based protocol is applied. It is shown that as long as the sampling interval is small enough, the consensus protocol is admissible under arbitrarily coarse quantization. To be specific, the consensus error is uniformly bounded and is proportional to the quantization error and averaged initial value. Numerical examples are given to demonstrate the effectiveness of the protocol. © 2012 IEEE.

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