Building Services Engineering Research & Technology

While water sounds have been used for soundscape improvement, little is known about their applicability in indoor environments. In order to investigate the effects of indoor water sounds on noise perception, a simple indoor water fountain system was used to produce water sounds over three different types of indoor intrusive noise (traffic noise, higher frequency dominated noise of a chair scraping the floor above, lower frequency dominated impact noise of a man running on the floor above) and speech in a test laboratory. Intrusive noise perception (annoyance and pleasantness) and speech recognition (KS-MWL-A) were assessed with three water sound levels (40, 50, 60 dBA) at two exposure times (immediate and 50 min) of water sounds by 54 participants. Short-term exposure to indoor water sounds improved the pleasantness of intrusive noise without increasing annoyance except lower frequency dominated impact noise. The increase in exposure time to indoor water sounds did not affect intrusive noise perception and speech recognition. The water to noise ratio significantly affected annoyance and pleasantness of traffic noise only; however, the level of water sounds did not significantly affect intrusive noise perception. Indoor water sounds can be used to improve intrusive noise perception except lower frequency dominated floor impact noise with no adverse effects on speech recognition dependent upon the speech to water sound ratio.

Practical application: This simple indoor water fountain can be directly applied to small offices or rooms to improve intrusive noise perception. When the simple fountain produces water sounds in a room, pleasantness of traffic noise throughout window openings or higher frequency dominated noise such as chair scraping noise can be improved without increment of annoyance and decrement of speech recognition. Short-term exposure to indoor water sounds is effective to increase pleasantness of the intrusive noises.

This paper presents a building performance simulation-based investigation to better understand the energy and comfort performance benefits of early detection of common sensor and actuator faults. Five types of air-handling unit faults and four types of zone-level faults were implemented to the energy management system application of the building performance simulation tool EnergyPlus. During 50-year simulation periods, the faults were randomly permitted to affect 75 different components of an archetype medium-sized office building model. The sensitivity of the simulation results with respect to three variables was studied: fault recurrence period, fault repair period, and discomfort threshold for simulated complaints. The results indicate that the energy use intensity and the predicted percentage of dissatisfied exhibit a power–law relationship with time, in which most of the performance reductions occur in the first 10 years. If the work-orders are issued only upon occupant complaints, the faults were estimated to cause a 16–62% increase in the energy use intensity for heating, ventilation, and air-conditioning and a 11–38% increase in the predicted percentage of dissatisfied at the end of the 50-year simulation periods. The results indicate that if the faults can be detected within a month after their first appearance, almost all their detrimental effects on a building’s energy and comfort performance can be mitigated.

Practical application: The methodology and results presented in this article are of practical use for those who study on-going commissioning, fault detection and diagnostics, and energy management systems in buildings. The simulation-based parametric analysis approach can be used to estimate the range of energy and comfort savings expected through early detection of common sensor and actuator faults in commercial buildings. Insights gathered from such an analysis can be used in planning the frequency of retro-commissioning and investments for automated fault detection and diagnostics systems.

This study proposes a novel decentralized sensor fault detection and self-repair method for heating, ventilation and air-conditioning systems. From the perspective of network structure, sensor fault diagnosis in heating, ventilation and air-conditioning systems is distributed to the updated smart sensors without the monitoring host, which is necessary in the traditional centralized method. A fully distributed flat sensor network is established based on fundamental physical equations. Similar to the structure, mechanism and characteristics of biological communities, a smart sensor needs only to communicate with adjacent nodes and operate collaboratively to complete sensor fault detection and self-repair tasks. These tasks are formulated as a constrained optimization and are solved by a decentralized algorithm with a penalty function executed in all the sensor nodes in parallel. The diagnosis model introduces an exponential function method to determine the precise location and undertake self-repair of a fault node. Simulation results on a chilled water system illustrate the effectiveness of the proposed method.

Practical application : The traditional sensor fault detection and diagnosis methods for heating, ventilation and air-conditioning systems are based on a centralized structure with several deficiencies, such as high maintenance and labor costs, link congestion and operational lag. This study presents a decentralized sensor network structure and exponential-function-based method that possess the advantages of plug-and-play, rapid deployment, high flexibility and convenience for engineering implementation without having to build a central monitor. The efficiency and effectiveness of the proposed method are demonstrated via a case study.

The liquid desiccant enthalpy recovery is an efficient way to save energy in air-conditioning systems. In this study, a counter-flow liquid desiccant enthalpy recovery device was proposed and experimentally analyzed. Enthalpy transfer capacity, enthalpy efficiency and pressure drop per height of packing were used as indices to describe its performances. Based on the experiment results, the heat and mass transfer model of a packed tower was used to simulate and optimize the performance of this device. The maximum enthalpy efficiency and enthalpy transfer capacity were achieved when the optimal air velocity (1.9–2.1 m/s in this study) maintained to be slightly below the air velocity at the loading point and the thermal capacity ratio of air to desiccant (m*) equaled to 1. These conclusions are valuable to both design and operation of such an enthalpy recovery device.

Practical application: A counter-flow enthalpy recovery device with liquid desiccant was proposed and experimentally investigated. Based on the experiment results, a numerical model for this device was built and validated. The optimal air and desiccant mass fluxes were analyzed to maximize the enthalpy efficiency of this device, which could be higher than the conventional device with cross-flow pattern. These results could provide guidelines for both design and operation management of counter-flow enthalpy recovery devices in liquid desiccant-based air-conditioning systems.

This paper brings together a rapid evidence assessment of impacts of elevated CO₂ concentrations on human cognition with IPCC projections of atmospheric CO₂ concentration by the end of the present century, and an analysis of potential consequences of increased atmospheric CO₂ concentrations for ventilation systems in buildings and other enclosed spaces. Whilst only limited research has been done on the effect of CO₂ on cognition (as opposed to air quality in general), half of the studies reviewed indicate that human cognitive performance declines with increasing CO₂ concentrations. Hence, given the likelihood of increasing atmospheric CO₂ concentration by the end of the 21st century, direct impacts of anthropogenic CO₂ emissions on human cognitive performance may be unavoidable. Attempts to minimise these direct impacts are likely to result in significant indirect impacts on the engineering of ventilation systems and associated energy use in all enclosed spaces including buildings and transport systems.

Practical application : This paper concerns what may well be one of the most important long-term drivers of the design, management, operation and regulation of ventilation systems over the remainder of the 21st century. It will be relevant to professionals, particularly at senior levels in the building industry.

In this paper, the influence of the solid-solid phase change material on the novel micro-channel flat-plate heat-pipe–based building integrated photovoltaic/thermal system has been investigated, which has been expected to store the excess heat, enhance the overall efficiency of the system and maintain the stable photovoltaic temperatures. The proposed system was divided into two parts, i.e. the outdoor part formed by flat-plate glass, photovoltaic panel, micro-channel flat-plate heat pipes, solid-solid phase change material layer and insulated material, and indoor part including the storage tank, water pump and storage batter. The experiments were conducted at the Guangdong University of Technology, China, to investigate the thermal and electrical performance of the proposed system. When the simulated radiation was at 300 W/m² and water flow rate was at 600 L/h, the maximum average thermal, electrical and overall efficiency were found at 52.9%, 7.9% and 60.8%, respectively, when the xenon lamps were turned on, and the maximum average efficiency of 86.6% were found when the xenon lamps were turned off, indicating the most appropriate working condition of the proposed system due to the thermal storage and release of the solid-solid phase change material during the system operation. Compared with the previous studies of the conventional building integrated photovoltaic/thermal systems, it was found that the overall efficiency of the system averagely increased 5–30% and the daily water temperature difference of the system averagely increased 1.8–10.5℃, indicating that the solid-solid phase change material can significantly increase the thermal efficiency of the system.

Practical application The proposed micro-channel-flat-plate-heat pipe based BIPV/T (MCFPHP-BIPV/T) system with SS-PCM will be potentially used in buildings to provide amount of electricity and thermal energy. The generated electricity will be used by the residential electrical devices or connected to the grid, and the thermal energy can be used for hot water, even for space heating and cooling. The proposed building-integrated system can be assisted in realising the targets of energy saving and carbon-emission-reduction in buildings.

This research work presents shading of building in hot and dry climate areas using rooftop photovoltaic arrays. Electrical power generation using photovoltaic arrays helps in reducing dependency on the utility grid. Areas with high intensities of solar radiation for a longer duration of time create high daily temperature. The Kingdom of Saudi Arabia (KSA) falls in high temperature and very low humidity climate zone. KSA has increased electricity tariff rates by 260% since 1 January 2018, has planned goals of generation of 9.5 gigawatts of renewable energy by 2030, and has ideas of constructing a self-sustainable city by the Red Sea. Energy analysis performed in this research is to calculate benefits of placing photovoltaic arrays on a rooftop of Buildings. These benefits include the electrical energy production and reduction of building cooling load by shading effect on a rooftop. By placing photovoltaic arrays on rooftop, up to 23% energy saving of cooling load can be achieved. The net annual output of photovoltaic generation per panel is discussed by adding energy generation and saving in cooling load of the building. The distance between the photovoltaic arrays is optimized for maximum benefits of electrical energy and saving in cooling loads.

Practical application: Photovoltaic arrays on rooftops for shading effect have practical benefits of energy savings in hot environment areas where high solar irradiance heat up the buildings. Photovoltaic arrays provide shading and energy generations which is a step towards zero energy buildings.

Electrical heating, ventilation and air-conditioning loads in buildings are suitable candidates for use in demand response activity. This paper demonstrates a method to support planned demand response actions intended explicitly to reduce carbon emissions. Demand response is conventionally adopted to aid the operation of electricity grids and can lead to greater efficiency; here it is planned to target times of day when electricity is generated with high carbon intensity. Operators of heating, ventilation and air-conditioning plant and occupants of conditioned spaces can plan when to arrange shutdown of plant once they can foresee the opportune time of day for carbon saving. It is shown that the carbon intensity of the mainland UK electricity grid varies markedly throughout the day, but that this tends to follow daily and weekly seasonal patterns. To enable planning of demand response, 24 h ahead forecast models of grid carbon intensity are developed that are not dependent on collecting multiple exogenous data sets. In forecasting half-hour periods of high carbon intensity either linear autoregressive or non-linear artificial neural network models can be used, but a daily seasonal autoregressive model is shown to provide a 20% improvement in carbon reduction.

Practical application : The forecast method demonstrated in the paper would enable building operators to plan demand response activity to target times of high carbon intensity on the UK electricity grid. The method would be easy to implement as the only data required are publicly available.