S. Thomas* and P. Andre

Department of sciences and environmental management, University of Liege 185 Avenue de Longwy, 6700 ARLON, Belgium Corresponding Author, sebastien. thomas@ulg. ac. be

Abstract

To minimize environmental impact and CO2 production associated with air-conditioning system operation, it is reasonable to evaluate the prospects of a clean energy source. The targets of the study are to evaluate cooling energy consumption to maintain thermal comfort in an office building and to point out solar energy to satisfy these cooling needs. Simulations were carried out with three different cooling systems in the same operating conditions to determine as accurately as possible the potential use of solar energy. For comparison purpose, the base case is a classical air-conditioning system (heat pump for cooling, gas boiler for heating). Two other configurations were simulated: a classical vapour compression system fed by photovoltaic panels and electricity grid as back-up and, absorption chiller fed by solar thermal panel field and by gas boiler. In the three chosen locations (Paris, Lisbon and Stockholm), results shown that installing photovoltaic panels on the roof is really interesting from the primary energy consumption point of view.

Keywords: Solar cooling, absorption, photovoltaic, TRNSYS

1. Introduction

The present energy context is characterized by the imminent end of the era of fossil fuels and the environmental impact of their operation. Energy demand growth, local pollution, global climate change, … are problems that must be taken into account. It seems urgent to reconsider our way of life and design equipments as to minimise their energy consumption. Most air-conditioning equipments are currently electrically driven vapour compression systems. According to the International Institute of Refrigeration (IRR) [1], 15% of the world’s electricity is used for refrigeration and cooling. Moreover, the growth of cooling needs and consequently electricity consumption for cooling is an indisputable fact.

Using renewable energy such as solar energy is really feasible for air conditioning in building. Different technologies exist and can be compared based upon different characteristics: energy consumption, cost of the whole equipment, … The study is dedicated to office buildings which require especially high comfort levels and have often high heat gains due to glazed facades and electrical equipment. Small scale (round 5-10 kW) applications became recently market available. For large scale absorption and adsorption chillers the technology is more mature because of existing system driven by waste heat (coming generally from a cogeneration unit). In this work the emphasis is put on available technologies, key equipments are market available and data is taken directly from manufacturer.

The comparison exercise is realized on a theoretical office building. To point out use of solar energy in this building, three test cases have been defined. The first one is used as reference as it is a usual system implementation in real office building. For each case, three locations have been simulated using Meteonorm data files: Paris (Montsouris station), Stockholm (Arlanda station) and Lisbon.

Especially for the last two cases, several aspects are to be addressed in order to provide a suitable solar air conditioning solution:

• Solar collectors

• Refrigeration equipment (chiller)

• Building

• Climate

Simulation of all these elements as well as links between them requires a very flexible simulation software. The dynamic simulation environment TRNSYS [2] is applied in this study. It makes possible the whole system simulation as well as the implementation of new models.