e Ji

Dynamic performance of hybrid photovoltaic/thermal collector wall in Hong Kong

Abstract This paper presents a computational thermal model that has been used for analyzing the annual performance of facade-integrated hybrid photovoltaic/thermal collector system for use in residential buildings of Hong Kong. In the study, the applications of EPV (film cell) and BPV (single silicon cell) panels in this hybrid photovoltaic/hot-water system were investigated. Simulation results based on test reference year data showed that the annual average electrical efficiencies of the hybrid EPV and BPV modules are, respectively, 4.3% and 10.3%, the corresponding annual average thermal efficiencies to hot water are 47.6% and 43.2%, and the reductions of space heat gain in summer season through the collector wall are 52.9% and 59.1%. The overall thermal efficiencies are 58.9% and 70.3% respectively, which are much better than the conventional solar collector performance.

Domestic air-conditioner and integrated water heater for subtropical climate

The technology of using a heat pump for space conditioning and domestic hot water heating in residences has been developed for half a century. The earlier air-to-water heat pumps and water-heating heat pumps suffered from drawbacks like high costs, unreliable operation, and inflexible applications. They were not well positioned in the market to attract customers. This paper introduces a novel air-conditioning product that can achieve the multi-functions with improved energy performance. The basic design principles and the laboratory test results are presented. The results showed that by incorporating a water heater in the outdoor unit of a split-type air-conditioner so that space cooling and water heating can take place simultaneously, the energy performance can be raised considerably.

Photovoltaic-Thermal Collector System for Domestic Application

Photovoltaic-thermal (PV/T) systems integrate photovoltaic and solar thermal technologies into one single system with dual production of electricity and heat energy. A typical arrangement is the direct attachment of PV modules onto a solar thermal collector surface. For a given collector surface area, the overall system energy performance is expected higher than the conventional side-by-side PV and solar thermal systems. In the development of PV/T collector technology using water as the coolant, the most common design follows the sheet-and-tube thermal absorber concept. Fin performance of the thermal absorber has been identified as one important factor that affects much the overall energy performance of the collector. Accordingly, an aluminum-alloy flat-box type PV/T collector prototype was constructed and tested in Hong Kong. Our test results indicate that a high combined thermal and electrical efficiency can be achieved. The primary-energy-saving efficiency for daily exposure approaches 65% at zero reduced temperature operation. With a simple and handy design, the product is considered to be very suitable for domestic application.

Performance of the photovoltaic solar-assisted heat pump system with and without glass cover in winter: A comparative analysis

Abstract An application of photovoltaic/thermal (PV/T) technology in heat pump, known as the PV solar-assisted heat pump (PV-SAHP) system, is presented. Comparative performance tests were conducted through an experimental rig under two different working conditions of the PV/T collectors: with and without glass cover. The energy performance in terms of PV/photothermic conversions and refrigeration cycle was compared in typical winter days of the temperate climate zone in China. It was found that with a single glass cover, the exergy efficiencies of PV/photothermic conversions and overall PV/T conversion were, respectively, 12.83, 5.26, and 18.09 per cent, and the heat pump coefficient of performance (COP) was 4.85. Without the glass cover, the exergy efficiencies and COP were 13.36, 3.04, and 16.40 per cent, and 3.41, respectively. The results imply that although the presence of the glass cover leads to a small reduction in the PV exergy efficiency, it is able to improve considerably the photothermic exergy efficiency, the overall PV/T exergy efficiency, and the COP of the PV-SAHP system in winter.

Environmental Life-Cycle Analysis of Hybrid Solar Photovoltaic/Thermal Systems for Use in Hong Kong

While sheet-and-tube absorber is generally recommended for flat-plate photovoltaic/thermal (PV/T) collector design because of the simplicity and promising performance, the use of rectangular-channel absorber is also tested to be a good alternative. Before a new energy technology, like PV/T, is fully implemented, its environmental superiority over the competing options should be assessed, for instance, by evaluating its consumption levels throughout its production and service life. Although there have been a plenty of environmental life-cycle assessments on the domestic solar hot water systems and PV systems, the related works on hybrid solar PV/T systems have been very few. So far there is no reported work on the assessment of PV/T collector with channel-type absorber design. This paper reports an evaluation of the energy payback time and the greenhouse gas payback time of free-standing and building-integrated PV/T systems in Hong Kong. This is based on two case studies of PV/T collectors with modular channel-type aluminium absorbers. The results confirm the long-term environmental benefits of PV/T applications.

Effect of flow channel dimensions on the performance of a box-frame photovoltaic/thermal collector

Abstract The hybrid photovoltaic/thermal (PV/T) collector technology is a new trend in solar energy application. For the thermal absorber, a box-frame water-channel design is able to enhance better heat transfer between the solar cells and the liquid coolant, thereby improving the combined electrical and thermal performance of the collector. This article reports the findings of the effect of water-flow channel dimensions on the energy performance of a box-frame PV/T collector design. A mathematical model of this PV/T collector system was first developed. Dynamic simulation results the authors obtained show that both the number and the height of the water-flow channels can significantly affect the collector performance. With a reduction in the channel height and an increase in the number of channels per unit width, better convective heat transfer between the working fluid and the channel wall can be achieved. This improves both the thermal and the electrical efficiencies of the collector. However, this also leads to an increase in the friction loss at the water circuit and, therefore, more pumping power is required. The optimal designs are discussed.

Modelling and validation of a building-integrated dual-function solar collector

A novel building-integrated solar thermal system known as building-integrated dual-function solar collector is proposed. The system has two independent operating modes: passive space heating mode and water heating mode, and it uses the following criteria to select the operating mode that during cold days such as winter days it works in passive space heating mode, but in warm seasons such as summer it works in the water heating mode. A testing system was established, and it performed in thermosiphon water heating mode for water heating. Two dynamic numerical models were, respectively, presented for the two operating modes of the testing system. The experimental data on the testing system were used to validate the two models. The results show that the numerical model for the system in the thermosiphon water heating mode can give a fairly good prediction and the model for the system in the space heating mode also gives a good prediction.

Distributed dynamic modelling with experimental validation on a photovoltaic solar-assisted heat pump

Abstract The photovoltaic/thermal solar-assisted heat pump is a system that directly integrates a Rankine refrigeration device with a photovoltaic/thermal solar collector. A specially designed direct-expansion PV evaporator is employed in the system to acquire thermal energy and electricity from solar radiation simultaneously. In this paper, a distributed model is presented that describes the dynamic performance of the system. Numerical simulation was performed with instantaneous solar irradiance and ambient temperature based on the model. A testing rig was built in Hefei, China, and experiments were conducted to verify the model. The results show that high photovoltaic and thermal performance can be obtained by the system. The average electrical efficiency is around 13.02 per cent. The output electricity is about 85.5 per cent of the power consumption, which means that the system can offer most of the power consumed by itself. Neglecting the heat loss of the water box, the highest coefficient of performance (COPc) can reach up to 7.3 and the average value is around 3.41. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions.

Numerical study of the use of photovoltaic-Trombe wall in residential buildings in Tibet

Abstract In the current paper, the thermal and electrical performance of photovoltaic (PV)- Trombe wall (PV-TW) used in Tibetan residential buildings is investigated, and two performance influencing factors are analysed. Based on the original model, the PV-TWs model for residential buildings is updated, and then a simple design is performed for a given residential building in Tibet. The results show that the indoor temperature increases linearly, whereas the electrical efficiency remains almost constant, when the PV-TWs width increases. In addition, thermal insulation is found to be quite effective to improve the thermal performance, whereas it decreases the electrical performance only a little. After choosing a width of 1.70 m, the average indoor temperatures are 10.2 °C and 24.0 °C for PV-TW system with and without thermal insulation, respectively. Besides, the average electrical power can satisfy the requirement of 100W, with an electrical efficiency of 10–11 per cent.

Performance of Solar Assisted Heat Pump Using Pv Evaporator Under ` Different Compressor Frequency

A novel photovoltaic solar assisted heat pump (PV-SAHP) system was constructed with the PV cells laminated onto the evaporator-collector plate. So a portion of the solar energy received was converted to electricity and the rest was converted as heat. The heat energy was then absorbed by the refrigerant and carried over to the condenser. Photovoltaic efficiency was increased in this way due to the lowered PV cell operating temperature as a result of the refrigerant evaporation process. The COP of the heat pump was also substantially improved because of the solar energy absorption. Performance tests under frequency 40Hz, 60Hz of compressor were conducted on the experimental rig. The dynamic performance of this PV-SAHP system was analyzed and the influencing factors were identified. The results indicate that this PV-SAHP system has a superior performance than the conventional heat pump system and at the same time, the photovoltaic efficiency is also higher.