Elsevier

Energy and Buildings

Volume 45, February 2012, Pages 211-218
Energy and Buildings

Performance evaluation of a building integrated semitransparent photovoltaic thermal system for roof and façade

https://doi.org/10.1016/j.enbuild.2011.11.008Get rights and content

Abstract

In this paper, analytical expressions have been derived for room air temperature of building integrated semitransparent photovoltaic thermal (BISPVT) and building integrated opaque photovoltaic thermal (BIOPVT) systems each integrated to the roof of a room with and without air duct. Comparative studies have also been carried out between BISPVT and BIOPVT system each integrated to the façade and roof of a room with and without air duct for the cold climatic conditions of Srinagar, India. However, the present thermal model is also valid for different climatic conditions. It is observed that there are maximum (18.0 °C) and minimum (2.3 °C) rise in room air temperature for semitransparent photovoltaic thermal (SPVT) roof without air duct and opaque photovoltaic thermal (OPVT) façade with air duct respectively. Further, on the basis of sensitive analysis, it is also observed that increase of air mass flow rate (0.85–10 kg/s) through duct increases the room air temperature from 9.4 to 15.2 °C for SPVT roof for a given climatic and design parameters.

Highlights

► Semitransparent/opaque PV modules are integrated on façade and roof of a building. ► Room temperature is higher in semitransparent than opaque PV. ► Maximum room air temperature of 22.0 °C is achieved in BISPVT system for roof.

Introduction

Solar energy is one of the renewable energy which is available in abundance. Photovoltaic (PV) module converts solar energy into electrical and thermal energy. Further, use of this thermal energy for space heating in a building increases the electrical efficiency of PV module. Therefore, PV modules integrated to the façade or roof of a building enhance its effectiveness. The classification of such integrated PV modules to a room is given in Fig. 1. Agrawal and Tiwari [1] developed analytical expression for room air temperature for an opaque type BIPVT system mounted on the rooftop of a building. They concluded that for a constant mass flow rate of air, room temperature is higher in series combination than any other type of combination of BIPVT system. System performance and system efficiency for a PV module installed on the roof and façade for a Samsung Institute of Engineering and Construction Technology (SIECT), Gihung were evaluated by Yoo et al. [2]. They observed that the BIPV system on the building provide about 10% of the required electricity for a typical day. Guiavarch and Peuportier [3] observed that the overall efficiency is higher for semitransparent than opaque PV collector in case of preheating the ventilation air of the building. Fung and Yang [4] developed the semitransparent photovoltaic module heat gain (SPVHG) model and experimentally verified the thermal performance of semitransparent BIPV modules. They found a 4.1% of net heat gain difference between the experimental and simulated results.

Fossa et al. [5] carried out experiments to investigate the natural convection in a vertical channel under different uniform and non-uniform heating modes, channel spacing and heat fluxes. A two-dimensional thermal network model to predict the temperature distribution for a section of photovoltaic solar wall was proposed by Dehra [6]. Besides this, he also tested solar ventilation through solar wall with an exhaust fan in the outdoor room laboratory. A minimum air gap of 0.14 m between a single PV module and building envelope was recommended by Gan [7]. Ordenes et al. [8] installed a PV system on rooftop of a building and concluded that it yields more energy than on any of the vertical façade. They observed that more than 45% of energy will be produced on the rooftop portion of PV installation. Sadineni et al. [9] found save in annual electrical energy by installing a 3.19 kWp PV system on the south-facing roof of the home in Las Vegas. Karava et al. [10] developed forced convective heat transfer coefficient for the roof (inclined at 30°) of a low-rise building. From the results of above mentioned researches it has been concluded that BIPVT system is helpful in space heating of cold climatic city and depends upon the ambient temperature, amount of solar intensity on an inclined roof or façade, latitude of the place, type of PV module (semitransparent/opaque), total area of PV module, heat transfer mode (natural and forced) and insulation of the building.

In the present paper comparative studies have been carried out between BISPVT and BIOPVT system each integrated to façade and roof of a room, with and without air duct (refer Fig. 1) for a cold climatic conditions of Srinagar, India situated at 34°1′, 74°51′E. The comparison is based on variation in room air temperature found in both systems. For this study, analytical and numerical approaches have been considered which are valid for other climatic conditions.

Section snippets

Description of BIPVT system

Following two types of BIPVT systems are considered in the study:

  • (i)

    BISPVT system – In this system a number of semitransparent (glass to glass) PV modules are integrated to a room of building.

  • (ii)

    BIOPVT system – In this system a number of opaque (glass to tedlar) PV modules are integrated to a room of building.

Combinations of these systems with and without air duct are described below.

Thermal modelling

The following assumptions have been made to write the energy balance equation of a BIPVT system:

  • 1

    One-dimensional heat conduction is considered for the present study.

  • 2

    The system is in quasi-steady state.

  • 3

    There is no temperature stratification in the air of a room due to forced mode of operation.

  • 4

    Glass cover is at a uniform temperature.

  • 5

    The room is thermally insulated.

  • 6

    Air properties are constant with time and temperature.

Methodology

Solar radiations (diffuse and beam) and ambient air temperature data for Srinagar city have been taken from Indian Metrological Department (IMD), Pune, India. Input design parameters of room and PV modules have been taken from Table 1. Matlab 7.1 software has been used for evaluating the performance of BISPVT and BIOPVT systems.

On the basis of analytical studies, it has been decided to compute the room air temperature for mass flow rate range, i.e. 0.85–10 kg/s. The following equations have been

Results and discussion

The hourly variation of ambient air temperature and solar intensity on a horizontal and inclined roof (34°) for a typical day of January of cold climatic conditions of Srinagar has been shown in Fig. 5. The figure further shows that the solar radiation is higher on the inclined roof as compared to horizontal roof.

Hourly variation of room air temperature (Tr) and solar cell temperature (Tc) for both SPVT and OPVT systems each integrated to façade and roof of a room, with air duct and air mass

Conclusions

  • Room air temperature difference in SPVT façade and OPVT façade, and SPVT roof and OPVT roof with air duct is 1.46 °C and 1.13 °C, respectively. Room air temperature difference in SPVT façade and OPVT façade, and SPVT roof and OPVT roof without air duct is 9.80 °C and 9.55 °C, respectively.

  • Maximum room temperature achieved is 22.0 °C in SPVT roof without air duct for an ambient temperature of 4.4 °C. This high temperature is obtained by semitransparent photovoltaic roof.

  • Increase of mass flow rate of

Future scope

The present study is limited to analytical analysis of performance of BIPVT system integrated to façade and roof for a specific PV modules area with specified solar radiation. The same can be extended to experimental verification with site-specific conditions for validation of analytical data.

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