Mathias Safarik1, Lutz Richter1, Carsten Heinrich2, Mike Otto3

1Institute of Air-conditioning and Refrigeration gGmbH, Bertolt-Brecht-Allee 20,
01309 Dresden, Germany; phone/fax +49 351 4081-684/635;

Email: mathias. safarik@ilkdresden. de; www. ilkdresden. de

2University of Applied Sciences Zittau/Gorlitz, Germany

3EAWEnergieanlagenbau GmbH, Oberes Tor 106, 98631 Westenfeld, Germany
phone/fax +49 36948 84-132/152;

Email: info@eaw-energieanlagenbau. de; www. eaw-energieanlagenbau. de

Abstract

Using solar thermal collectors to provide hot water or heating is a well established technology. To reach a higher solar fraction in heating bigger collectors areas are needed. These relatively big collector areas generate excess heat in summer which cannot be used for heating at that time. Storage for the winter time is possible but costly.

Solar thermal powered absorption cooling offers a good possibility to use these ex­cess heat to provide cooling during the summer and to increase the efficiency of the whole system. Solar cooling is also a promising opportunity to cut electrical peak loads during the summer and to reduce fossil fuel consumption.

One of the constraints for a wider use of this technology in recent years was the unavailability of a suitable absorption chiller in the capacity range below 50 kW which is interesting for many applications.

A water/lithium bromide absorption chiller with a nominal capacity of 15 kW was developed. A special heat exchanger design is used to reach small differences be­tween external and internal temperatures. The chiller can be driven by hot water generated by solar thermal collectors or other heat sources. It was designed for low driving temperatures to allow the solar thermal collectors to work with a good effi­ciency. Design conditions are 90 °C hot water input, 32 °C cooling water input, 15 °C cold water output. At these conditions the chiller reaches a COP of 0,7.

Three test installations with various configurations and at different locations have been installed. Different collector types (flat plate and vacuum tube) and cooling towers (wet and dry) have been tested. To predict the performance of the whole so­lar cooling system with different peripheral equipment TRNSYS simulations were done. The effects of using different collectors, storages, cooling towers and cooling coils were evaluated. Measurement and simulation results for some applications at different locations are presented.

Introduction

There is an increasing energy demand for cooling and climatisation in many parts of the world. The reasons are rising internal loads, the dynamic economic development of re­gions in warm and hot climates, growing standards of living and comfort needs as well as current trends in architecture (higher glass ratio in facades).

At present mostly electric driven compression chillers are used to satisfy the increasing cooling demand. Rising carbon dioxide emissions is one of the consequences. Because of the distinct distribution of the cooling demand over the day with a peak at noon and early afternoon there is also a peak in electric power consumption which impacts the grid and sometimes even leads to black outs.

It will be necessary to expand the capacity of the grid and to install new power plants to satisfy this power demand. Much of this capacity needed will not be used most of the year. One of the alternatives is solar thermal cooling with absorption chillers. Solar thermal col­lectors are widely used for hot water supply and heating in many parts of Europe. One problem is the distribution of insolation and heating demand over the year. Solar thermal plants for heating assistance produce a lot of excess heat in summer which cannot be used at this time. Storage for the winter time is possible but costly.

By using this excess heat for cooling the efficiency of the whole system can be increased. There is a high degree of congruence of the cooling demand and the insolation in many applications. Therefore only little storage capacity is needed.

In the small capacity range (below 35 kW) there was no suitable absorption chiller avail­able so far.