International Journal of Low-Carbon Technologies - current issue

Experimental study of a thermoelectric heat pump system utilizing bent heat pipes for heat transfer

Jiang, L., Gillott, M., Riffat, S. — Tue, 17 Nov 2009 08:47:02 PST

This paper presents the study of the novel thermoelectric heat pipe heat pumping system. Bent heat pipes with sintered powder wicks were utilized in a configuration which used centrifugal forces, due to rotation, to enhance heat transfer. The revolving heat pipes worked both as a fan and as a heat exchanger; however, extra fan blades were required to improve the fan performance. Fan performance tests were carried out, followed by the thermal performance, within which eight pieces of thermoelectric devices were applied to provide the heat pumping. The results showed that the system could provide airflows of up to 168.7 m³/h with the revolving speed of 600 RPM, and maximum static pressure was up to 37 Pa. The system could supply the heating of up to 257.1 W with the coefficient of performance of up to 1.96. Comparisons were made between the revolving and stationary systems, and the results showed that the former increased the thermal performance by up to 10% in heating and up to 20% in cooling.

A generalized procedure to generate clear-sky radiation data for any location

Tham, Y., Muneer, T., Davison, B. — Tue, 17 Nov 2009 08:47:02 PST

Accurate estimation of clear-sky radiation is needed in many engineering and architectural applications. In this study, data from four different locations with differing climatic conditions are used to evaluate two clear-sky radiation models referred to as the Page model and the Yang model. Statistical tests were used to determine their performance. The locations chosen were Aswan in Egypt, Jodhpur in India, Bahrain and Gerona in Spain. Using readily available meteorological data, both models produced good results above 400 W/m², although the Page model was found to perform better in dry climates and the Yang model in more humid locations. Selective use of one model over the other according to the prevailing climate thus produces an overall improvement in the data generated. It is suggested that investigations should be undertaken to further improve the models under discussion.

Energetic and economic savings of free cooling in different European climates

Lazzarin, R. M., Noro, M. — Tue, 17 Nov 2009 08:47:02 PST

Free cooling is sometimes useful to face up not only ventilation load but also cooling load as well, taking advantage, directly or indirectly, of the enthalpy difference between inside and outside air in summer. The paper reports on the analysis of the energetic advantage of direct and indirect evaporative cooling (IEC) techniques conducted in summer in different European climates, in which external air flow is established by outdoor, indoor and inlet air enthalpies comparison. Psychrometric diagram has been divided into seven zones as a function of external air conditions; for each zone outside air flow control logic and obtainable free cooling effect have been developed and evaluated. As a function of indoor conditions, outdoor conditions (expressed hourly by Typical Meteorological Year), inlet temperature, external ventilation air flow and building cooling load, energy savings with free cooling techniques have been calculated, considering water consumptions in the adiabatic saturators. Interaction of free cooling, sensible heat recovery and IEC allows very interesting seasonal cooling load reductions, with the additional advantage of decreasing the chiller cooling capacity. All the energetic advantages have been evaluated by an economic point of view, in terms of net present worth and discounted payback period of the investment.

Energy and exergy analyses of an industrial wood chips drying process

Coskun, C., Bayraktar, M., Oktay, Z., Dincer, I. — Tue, 17 Nov 2009 08:47:02 PST

In this study, a comprehensive thermodynamic investigation through energy and exergy analyses is conducted to assess the performance of an industrial chips drying process and study how its operating conditions and efficiency can be improved further. In this regard, energy and exergy efficiencies are evaluated with the actual thermodynamic data available, as obtained from the factory, in Turkey. Energy and exergy efficiencies of the drum drying system (DDS) are found as 34.07% and 4.39%, respectively. The analysis results show that exergy efficiency is less than energy efficiency. The main reason of this low exergy efficiency for this drying process is high exergy destruction, as 41.5% of input exergy value. Energy can be recovered via an economizer from hot moist air leaving from the system. If stack gas temperature decreases from 130 to 90°C, regain energy and exergy values are to be 51 976 and 8162 kW, respectively. These recovered potentials can be used for district heating system in winter season and for district cooling system in summer season by using absorption cooling system. Energy and exergy efficiency values can be increased to 93.15 and 43.08%, respectively, by incorporating a heat exchanger into the system.

Daylighting performance of atriums in subtropical climate

Yi, R., Shao, L., Su, Y., Riffat, S. — Tue, 17 Nov 2009 08:47:02 PST

Design of an atrium aims to provide a good quality of daylighting. This paper deals with a parametric study of geometric effect on the daylighting performance of two typical types of atriums, enclosed and linear, in the subtropical climatic area. A case study of the daylighting of two existing atrium buildings is presented. The software, RADIANCE, is employed to simulate daylighting performance. The simulation results are compared with the field measurement and a 1:100 model atrium to validate the RADIANCE simulation. In the study of the geometric effects on daylighting performance in atriums, three combined geometric parameters, plane aspect ratio (PAR = W/L), section aspect ratio (SAR = H/L) and well index [WI = H(W + L)/2WL], are introduced to determine a proper design geometry. The relationships between the daylight factor (DF is defined as the ratio of the illuminance at a particular point within an enclosure to the simultaneous unobstructed outdoor illuminance under same overcast sky component) and these geometric factors are analysed for the two types of atriums. The results show that, for the enclosed atrium, the DF has an approximately linear relationship with either SAR or WI, while the DF of the linear atrium has an approximately linear correlation with the PAR. The recommended geometric factor may be WI = 1.5 for the enclosed atrium and PAR = 0.5 for the linear atrium if the comfortable DF is required. The results of this will provide a demonstration and general guide for the designers to predict daylighting performance of an atrium building in the subtropical climate region.

MHD effect on the development of thermocapillary convection in a two-layer fluid system

Zhou, X., Huang, H. — Tue, 17 Nov 2009 08:47:02 PST

To understand the effects of magnetic fields on the evolution behaviours of thermocapillary convection in a two-layer fluid system under the absence of gravity, we conducted a series of unsteady three-dimensional numerical simulations of thermocapillary flows in a rectangular cavity. The results show that the convective cell merging process under x direction magnetic field is decelerated in the encapsulant, but that in the melt is accelerated; magnetic field in z direction decelerates the convective cells merging in the melt and encapsulant greatly; the effect of magnetic field in y direction on the convective cell merging is weak. The maximum vorticity magnitude of thermocapillary convection 58.3 s^–1 at fully developed without magnetic field is reduced to 53.4, 54.4 and 20.7 s^–1 under magnetic fields in x, y and z directions, respectively.

Performance comparison and experimental study on several kinds of congregation-type solar concentrator

Tao, T., Hongfei, Z., Kaiyan, H., Xiaodi, X., Guo, X. — Tue, 17 Nov 2009 08:47:02 PST

Three types of congregated solar concentrators or so-called light funnels have been designed. They are a Compound Parabolic Concentrators (CPC) superposed light funnel, a CPC superposed light funnel with a deflector and a mirror focus superposition light funnel. Their light-concentrating principle and light conduction process have been analyzed. Their performances have been discussed after testing under real weather conditions, and also their conducting light rates and curve of conducting light performance for different incident angles have been calculated. The experimental results show that the conducting light rate of the mirror focus superposition-type light funnel is maximum, up to 35.1%. The CPC superposed light funnel has a minimum value, with only 25.6%. The CPC superposed light funnel is the most demanding regarding tracking accuracy. The other two types of concentrators are less demanding concerning tracking accuracy.

Sizing verification of photovoltaic array and grid-connected inverter ratio for the Malaysian building integrated photovoltaic project

Omar, A. M., Shaari, S. — Tue, 17 Nov 2009 08:47:02 PST

This paper discusses the sizing of PV array and inverter issues of grid inverters installed under the Malaysian Building Integrated Photovoltaic (MBIPV) project. The MBIPV project is jointly sponsored by the Government of Malaysia (GoM) and the United Nations Development Programme (UNDP) for the period 2006–2010. It covers all the DEMO, SHOWCASE and SURIA1000 grid-connected BIPV installations throughout Malaysia. Three types of cell technologies located at one site near Kuala Lumpur were selected as a case study. The data were collected for 1 year and analysed. The findings shall be used by relevant parties especially system integrator as a guide for sizing PV array and inverter under Malaysian climate.

Evaluation of simple all-sky models to estimate solar radiation for the UK

Tham, Y., Muneer, T., Davison, B. — Tue, 17 Nov 2009 08:47:02 PST

Detailed and accurate data are required for solar applications in the UK. In this study, the Yang model is evaluated for three locations in the UK, namely Camborne, London and Stornoway. Statistical tests were used to determine the performance of the model. Furthermore, the Yang model was compared with a previously evaluated meteorological radiation model (MRM). Note that MRM has been used by United Kingdom Climate Impacts Programme (UKCIP) to generate solar radiation for the UK for futuristic climate predictions. Bearing in mind that hourly solar radiation is a highly variable resource, particularly for the northern latitudes such as those in the UK locations, and also keeping in perspective the potential error regarding routine measurements, both models were found to perform well. From the data set under examination, more than 50% of recorded radiation values were found to be under 400 W/m². From the overall comparison, the MRM model performed better than the Yang model. Hence, it is suggested that the use of MRM model is continued for estimation of radiation for UK locations.