HVAC SYSTEMS - HFT Stuttgart

1. INTRODUCTION
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CHAPTER 01
Solar or waste heat driven closed absorption or adsorption chillers and open
desiccant evaporative cooling systems (DEC) offer the potential to provide
summer comfort conditions in buildings at low primary energy consumption
(Henning, 2004). As a consequence of the climate change debate and the
common goal to reduce the CO2 emissions in the European Union by at least
20% until 2020, interest in these innovative technologies has increased
significantly during the last ten years. Several test and demonstration plants of
the different technologies have been installed. However, not all of the installed
systems operate in an energy efficient way. From the primary energy point of
view some are even worse than comparable conventional systems with
compression chillers (Sparber, et al., 2009; Núnez, et al., 2009; Vitte et al.,
2008). Reasons for this are insufficiently designed solar systems and badly
dimensioned hydraulics with inefficient or over dimensioned pumps or fans or
badly controlled heat rejection systems. This leads to high additional heating
energy and electricity consumption and in consequence significantly reduces
their primary energy efficiency. Consequently, the requirement of appropriate
design tools and integrated energy efficient system control is attracting more
and more attention in research and development and therefore are main topics
of IEA task 38 (International Energy Agency Solar Heating and Cooling
Programme).
1.1 SOLAR DRIVEN ABSORPTION CHILLERS
For the often used single effect absorption chillers, the ratio of cold production
to input heat (COP) is in the range of 0.5-0.8, while electrically driven
compression chillers today work at COPs around 3.0 or higher. Solar fractions
on the heating energy demand of the absorption chillers therefore need to be
higher than about 50% to start saving primary energy (Mendes, et al., 1998).
The exact value of the minimum solar fraction required for primary energy
saving not only depends on the performance of the thermal chiller, but also on
the electricity consumption of the other components such as the cooling tower: