Gang Pei

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.

A Comparative Study of PV Glazing Performance in Warm Climate

In this experimental study, the performance of ventilated double-pane glazing integrated with semi-transparent solar cells under the subtropical climate of Hong Kong has been investigated. The effects of a photovoltaic (PV) ventilated glazing system on the built environment — including heat and light transmission, thermal and visual comfort, and electricity generation — were analyzed and discussed. While the energy saving potential of PV glazing on air-conditioning demands was found promising, the same on daylight utilization was much inferior to the absorptive glazing applications. The purpose of the study was to gain experience on better use of the semi-transparent PV ventilated glazing technology, and on the energy/cost saving potential of some innovative arrangements.

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.

PV-Trombe Wall Design for Buildings in Composite Climates

The design of the novel PV-Trombe wall in Hefei is theoretically processed in this paper. The area of winter air vents and width of PV-Trombe wall are determined, the effects of two improvements (thermal insulation and shading curtain) are investigated, and the different operating results for winter heating and summer cooling are also obtained. Results show that if compared to the original PV-Trombe wall, after thermal insulating, the indoor temperature increases by 2.36 °C in winter and decreases by 2.47 °C in summer and the electrical efficiency decreases by <2%. After curtain shading, the indoor temperature decreases by 2.00°C in summer and the electrical efficiency increases by ∼1%. It is recommended that thermal insulation in both winter and summer and appending a shading curtain in summer are adopted for PV-Trombe wall, especially for the diurnally used PV-Trombe wall.

An Experimental Study on a Novel Heat Pipe-Type Photovoltaic/Thermal System with and without a Glass Cover

A novel heat pipe-type PV/T system was designed and constructed in the present study to solve the freezing problem associated with the traditional photovoltaic/thermal (PV/T) system. Outdoor tests were carried out from May to July 2010. The performances of the system with and without glass cover were also studied. The results showed that the average photothermal efficiency with glass cover was 41.30%, which was a little higher than that of the unglazed condition at 37.16%. However, the result of the tests on photoelectric efficiency was the opposite. The average efficiency was 9.42% with glass cover, which was lower than that without the glass cover at 11.51%. The unglazed condition efficiency curve showed a big fluctuation, whereas the glazed condition was almost a perfect parabola. The average first law efficiency of the glass-covered system was 48.52% compared with 44.24% without the glass cover. Conversely, the glass-covered system had a second law efficiency of 6.87%, which was lower than that of the unglazed condition at 8.01%.

Preliminary Experimental Comparison of the Performance of a Novel Lens-Walled Compound Parabolic Concentrator (CPC) with the Conventional Mirror and Solid CPCs

A conventional mirror compound parabolic concentrator (CPC) is limited by its half acceptance angle when pursuing a large geometrical concentration ratio with no tracking. A solid CPC, which is made from solid dielectric materials without notches, can achieve a larger half acceptance angle compared with the conventional mirror CPC of the same geometrical concentration ratio, which is attributed to the optical refraction caused by the dielectric material. However, solid CPCs are heavier and costlier. This paper presents a preliminary experiment on a novel lens-walled CPC. An experimental comparison of the conventional mirror and solid CPCs and the lens-walled CPC with the same geometrical concentration ratios of 2.5 is given for different incidence angles. Here the conventional mirror CPC chose the evaporated aluminium coating as the reflection layer, for short conventional CPC. Transparent acrylic was chosen as both the dielectric material and lens material. The three CPCs were all attached to a PV cell. Through the output characteristics of the cell, the optical performances of these CPCs can be obtained. The results showed that when the incidence angle was smaller than 35°, the optical efficiency of the lens-walled CPC remained above 46.7% and was more stable against incidence angle changes compared with the conventional CPC. It also weighed and cost less than the solid CPC. Thus, lens-walled CPC adequately combines the advantages of conventional and solid CPCs, and has great potential for use in large-scale practical applications.

Theoretical and Experimental Study of Spectral Selectivity Surface for Both Solar Heating and Radiative Cooling

A spectral selectivity surface for both solar heating and radiative cooling was proposed. It has a high spectral absorptivity (emissivity) in the solar radiation band and atmospheric window band (i.e., 0.2~3 μm and 8~13 μm), as well as a low absorptivity (emissivity) in other bands aside from the solar radiation and atmospheric window wavelengths (i.e., 3~8 μm or above 13 μm). A type of composite surface sample was trial-manufactured combining titanium-based solar selective absorbing coating with polyethylene terephthalate (TPET). Sample tests showed that the TPET composite surface has clear spectral selectivity in the spectra of solar heating and radiation cooling wavelengths. The equilibrium temperatures of the TPET surface under different sky conditions or different inclination angles of surface were tested at both day and night. Numerical analysis and comparisons among the TPET composite surface and three other typical surfaces were also performed. These comparisons indicated that the TPET composite surface had a relative heat efficiency of 76.8% of that of the conventional solar heating surface and a relative temperature difference of 75.0% of that of the conventional radiative cooling surface, with little difference in cooling power.

p-Hydroxybenzenesulfonic acid–formaldehyde solid acid resin for the conversion of fructose and glucose to 5-hydroxymethylfurfural

A novel solid p-hydroxybenzenesulfonic acid–formaldehyde resin (SPFR) was prepared via a straightforward hydrothermal method. The catalytic properties of SPFR solid acids were evaluated in the dehydration reaction of fructose and glucose to 5-hydroxymethylfurfural (HMF). SEM, TEM, N2 adsorption–desorption, elemental analysis (EA), thermogravimetric analysis (TGA), and FT-IR were used to explore the effects of catalyst structure and composition on the HMF preparation from fructose. The effects of reaction time and temperature on the dehydration of fructose and glucose were also investigated. An HMF yield as high as 82.6% was achieved from fructose at 140 °C after 30 min, and 33.0% was achieved from glucose at 190 °C in 30 min. Furthermore, the recyclability of SPFR for the HMF production from fructose in 5 cycles was good.

Structure optimization and annual performance analysis of the lens-walled compound parabolic concentrator

ABSTRACT The primary lens-walled compound parabolic concentrator (lens-walled CPC) has a significant advantage of a larger half acceptance angle as a static solar concentrator, but it also has a drawback of a low optical efficiency. In order to overcome this drawback, in this article, series of structure parameters were investigated and compared to further improve the optical efficiency within the half acceptance angle combined with the material properties. The average optical efficiencies of the improved lens-walled CPCs could achieve more than 82% within the half acceptance angle of 35ᵒ. Experiments were adopted to verify the credibility and validity of the simulation. Moreover, annual performance of the lens-walled CPCs comparison with that of the mirror CPC for Nottingham was analyzed. Results show that the improved lens-walled CPC has a higher optical performance for actual building application.

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.