A. Napolitano 12*, G. Franchini1, G. Nurzia2, W. Sparber2

1 University of Bergamo, Department of Industrial Engineering, Viale Marconi n. 5, 24044 Dalmine (BG), Italy
2 EURAC, Institute for Renewable Energy, Viale Druso, n. 1, 39100 Bolzano, Italy
* Assunta Napolitano, assunta. napolitano@unibg. it

Abstract

The present work reports the main issues of coupling solar collectors and cogeneration units for heating and cooling purposes which have been derived from the detailed analysis of a study case. The work suggests a procedure for planning such systems so that solar collectors and a cogenerator do not interfere in their respective operation. The procedure includes the selection of a layout, the definition of a control strategy and the sizing of each component of such a plant. The outputs of the procedure are used in TRNSYS dynamic simulations to assess the performance of the planned plant.

Keywords: solar heating and cooling, co-generation, planning, simulation

1. Introduction

In Solar Heating and Cooling (SHC) plants, solar collectors are typically assisted by auxiliary technologies to match the entire user’s heat demand. Gas boilers are commonly employed as heat back up systems, but further machines fit to the same use. Among the possible supplementary technologies, Combined Heat and Power (CHP) generators, also known as Cogeneration systems, offer some advantages.

Many technologies are available for cogeneration but in this work only gas engine based CHP units are considered in combination with solar collectors, both for heating and cooling purposes. The latter is supposed to be achieved by means of an absorption chiller. When heat recovered from a CHP system is used to power an absorption machine, this not only meets the cooling load, but also reduces the peak electric demand caused by the cooling request [1]. Moreover, a balanced heat demand over the year, due to the presence of an absorption chiller, improves cogeneration application project economics by increasing its operating hours per year [2]. When CHP units are selected to assist solar collectors for heating and cooling purposes, further advantages are added to the above mentioned ones. In fact, CHP systems support solar collectors by providing a heat source which derives from thermal recovery. Hence, such a back up results in a more efficient energy supply and fuel saving compared to conventional systems (e. g. boilers), especially in cooling season as heat driven chillers require heat amounts larger then the electric demand of conventional chillers.

Despite of these advantages, coupling solar collectors and a CHP unit (SHC-CHP systems) for heating and cooling purposes present certain critical issues, as shown by the study case below reported. The main issue is to fit to each other a typically unsteady heat source (the solar radiation) and a system which needs steady working conditions (N. B. the primary function of an engine heat recovery
equipment is to cool the engine [1]), with the aim of meeting the heat demand, both in winter and summer. As planning such systems can be rather complex, a research work is being carried out to identify the main criteria for optimal designing and sizing. This work is based on dynamic simulations on TRNSYS platform to test on one hand first selected layout and control strategy, on the other hand the influence of various choices of sizes.