Evaluation of a large dish‐type concentrator solar lighting system for underground car park

To utilize solar energy more efficiently and reduce lighting power consumption in underground public spaces such as car park, a large dish‐type concentrator solar lighting system is put forward along with its evaluation, which is a unique design to apply a laminated layer of beam split thin‐film coating and thin‐film solar cells onto the dish reflector. The collected sunlight is split into 2 parts, one being reflected into a fiber optical bundle and transmitted for daylighting, while the rest being absorbed by solar cells for electricity generation as the other way to replenish daylighting. A set of 4 solar lighting systems using 3.28‐m diameter dish are designed to meet the lighting requirement in a 1771‐m² underground car park. A mathematical model is adopted to calculate the output power and conversion efficiency of solar cells distributed on the parabolic dish surface. The indoor illuminance distribution is given by lighting simulation. The results indicate that the average daylight illuminance in the car park can vary between 62.7 and 284 lx on February 25, 2016 and between 62.7 and 353 lx on August 17, 2016 for 2 chosen days, respectively. For the presented design, the electricity produced by solar cells is just enough to power light‐emitting diodes for lighting meeting a criterion at night. Considering about 19% conversion efficiency of solar cells and the efficacy of 129.5 lm/W of light‐emitting diodes, the hybrid solar lighting system can have about 40% utilization ratio of solar energy, so it can be concluded that a sufficient lighting provision can be provided by the proposed large dish‐type concentrator solar lighting system for applications in underground car park.     

Novel glazing technologies to mitigate energy consumption in low‐carbon buildings: a comparative experimental investigation

Buildings play a key role in total world energy consumption as a consequence of poor thermal insulation characteristics of facade materials. Among the elements of a typical building envelope, windows are responsible for the greatest energy loss because of their notably high overall heat transfer coefficients. About 60% of heat loss through the building fabric can be attributed to the glazed areas. In this respect, novel cost‐effective glazing technologies are needed to mitigate energy consumption, and thus to achieve the latest targets toward low/zero carbon buildings. Therefore in this study, three unique glazing products called vacuum tube window, heat insulation solar glass and solar pond window which have recently been developed at the University of Nottingham are introduced, and thermal performance analysis of each glazing technology is done through a comparative experimental investigation for the first time in literature. Standardized co‐heating test methodology is performed, and overall heat transfer coefficient (U‐value) is determined for each glazing product following the tests carried out in a calibrated environmental chamber. The research essentially aims at developing cost‐effective solutions to mitigate energy consumption because of windows. The results indicate that each glazing technology provides very promising U‐values which are incomparable with conventional commercial glazing products. Among the samples tested, the lowest U‐value is obtained from the vacuum tube window by 0.40 W/m²K, which corresponds to five times better thermal insulation ability compared to standard air filled double glazed windows. Copyright © 2015 John Wiley & Sons, Ltd.     

An experimental study on the performance of enthalpy recovery system for building applications

In recent years, the attention of researchers has been focused on energy conservation demands due to the environmental impact of energy consumption throughout the built environment and global warming issue. Heat or energy recovery is one of the main energy-efficient systems that has been approved to overcome this problem. However, in conventional heat or energy recovery for building applications, only sensible energy has been recovered and neglecting the latent energy. In this work, enthalpy recovery system has been developed and the performances of sensible and latent energy have been investigated experimentally. The efficiency of close to 66% has been achieved for sensible energy and the latent energy efficiency was nearly 59% gained. Comparison of efficiency with effectiveness-NTU method showed both were in good agreement. Recovered energy was achieved up to 167 W at 3.0 m/s air velocity with 4.3 °C temperature difference.     

An investigation of thermoelectric cooling devices for small‐scale space conditioning applications in buildings

This paper presents the study of a thermoelectric cooler (TEC) designed for small‐scale space conditioning applications in buildings. A theoretical study was undertaken to find the optimum operating conditions, which were then applied in the laboratory testing work. A TEC unit was assembled and tested under laboratory conditions. Eight pieces of UltraTEC were shown to generate up to 220 W of cooling with a COP of 0.46 under the input current of 4.8 A for each module. Thermo‐economical analysis was carried out and results showed that a system with PV panel can compete with an equivalent system without a PV panel when PV costs fall down to or lower than £1.25 per Watt. For the cases without a PV panel, the system with a high level of TEC power input delivered a better performance in terms of the average cooling energy price than that system with a low level of TEC power input after critical interest rate (currently 4%). Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental and CFD study of ventilation flow rate of a Monodraught™ windcatcher

Monodraught™ windcatchers are commercial natural ventilation devices, which are primarily driven by wind to produce both extract and supply air flow. The measurement of the net flow rate (extract minus supply) of a Monodraught™ windcatcher ABS 550 for various wind speeds and directions is introduced. The ventilation measurement system uses a cone flow meter and a blower fan. CFD standard k − ? turbulence model is employed to calculate the flow rate. The situation using a blower fan is considered in modelling and the effect of the manometer sensitivity is also discussed. The comparison has indicated a good agreement between measurement and simulation. CFD modelling of the windcatcher is then carried out for the situation of outdoor far field wind. At the same nominal wind speed, the calculated extract flow rate of the windcatcher in a far field wind is roughly twice that for the situation using a blower fan, the wind direction has a small effect on the extract flow rate. The extract and supply flow rates are also calculated for various room pressure due to various wall openings and installation on a flat roof or a pitched roof. The contribution of the buoyancy effect on the flow rates is discussed in simulation.     

Interactions between louvers and ceiling geometry for maximum daylighting performance

The impact of ceiling geometries on the performance of louvers was investigated using physical model experiments and Radiance simulations. Two performance indicators, the illuminance level and its distribution uniformity, were used to assess daylighting performance in a room located in a subtropical climate region. It was found that the performance of the louvers can be improved by changing the ceiling geometry. The illuminance level increased in the rear of the room, and decreased in the front—near the window—compared to rooms having horizontal ceilings. Radiance results were found to be in good agreement with physical model data obtained under a clear sky and high solar radiation. Louvers' daylighting performance was reduced by tilting the louvers downward. The best ceiling shape was found to be one that is chamfered in the front and rear of the room.     

Performance testing and comparison of turbine ventilators

A turbine ventilator is a device having a combined function of wind turbine and extract fan. Turbine ventilators are attractive replacements for electrical ventilation fans in terms of using wind energy. They are commonly used in attic, loft and rooftop spaces to facilitate ventilation in buildings at both domestic and industrial level. This study presents measurement of flow rates of four commercial turbine ventilators on a specifically designed experimental system. The ventilation flow rates and rotational speeds are taken at different wind speeds and compared with a simple open column and two standard vent hats. Use of a DC motor to power the ventilators in the absence of wind is described and power consumption against flow rate is given.     

Phase change material developments: a review

This paper presents a review of the latest developments on phase change materials (PCMs) for thermal energy storage (TES) applications in buildings. The paper provides information about material requirements for TES, classification of PCM, mathematical modelling and applications of PCMs.     

A review on wind driven ventilation techniques

Natural ventilation has gained prominence in recent times as a bespoke method of ventilating buildings. The two fundamental principles of natural ventilation are stack effect and wind driven ventilation. This paper reviews miscellaneous wind driven ventilation designs with respect to traditional means such as wind towers and more modern techniques including turbine ventilators and wind catchers. A distinction is made between specific types of wind driven ventilation techniques depending on their operation and mode of engagement with the wind. For example, a static wind catcher is classified as passive; a rotating wind cowl as a directed passive technique and a rotating turbine ventilator is classified as outright active due to its constant rotation with the wind. A table summarising the review is presented at the end with corresponding references.     

Performance evaluation of v-trough solar concentrator for water desalination applications

The working principle and thermal performance of a new v-trough solar concentrator are presented in this paper. Compared with the common parabolic trough solar concentrators, the new concentrator has two parabolic troughs which form a V-shape with the focal line at the bottom of the troughs. This is beneficial for the installation and insulation of the receiver, and the shadow on the reflective surface is avoided. The new v-trough collector does not require high precision tracking devices and reflective material. And therefore the cost of the system could be significantly reduced. Various experimental tests were carried out both outdoor and indoor using different types of receiver tubes. The results show that the collector system can have thermal efficiency up to 38% at 100 °C operating temperature. System modelling was used to predict the rate of fresh water produced by four different solar collector systems which include both static and one-axis solar tracking technologies. Comparison of the solar collectors at different temperature ranges for humidification/dehumidification desalination process using specific air flow rate were considered. At each temperature range, suitable solar collectors were compared in the aspect of fresh water production and area of solar collector required. Results showed that the new v-trough solar collector is the most promising technology for small to medium scale solar powered water desalination.