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of D 300-390 per MWh for the office in Madrid with low internal loads and D 200 per
MWh for the best case of the office with longer operating hours (see Figure 6.27).
In comparison, Scholkopf and Kuckelkorn (2004) calculated the cost of conven-
tional cooling systems for an energy-efficient office building in Germany with D 180
per MWh: 17% of the costs were for the electricity consumption of the chiller. The
total annual cooling energy demand for the 1094m 2 building was 31 kWhm 2 a 1 .
Our own comparative calculations for a 100 kW thermal cooling project showed that
the compression chiller system costs without cold distribution in the building were
between D 110 and 140 per MWh.
Henning (2004a) also investigated the costs of solar cooling systems compared
with conventional technology. The additional costs for the solar cooling system per
Megawatt hour of saved primary energy were between D 44 per MWh in Madrid and
D 77 per MWh in Freiburg for large hotels. It is clear that solar cooling systems can
only become economically viable if both the solar thermal and the absorption chiller
costs decrease. This can be partly achieved by increasing the operating hours of the
solar thermal system and thus the solar thermal efficiency by using the collectors also
for warm water production or heating support.
6.1.6 Summary of Solar Cooling Simulation Results
In this work the design, performance and economics of solar thermal absorption chiller
systems were analysed. Different absorption chillers were modelled under partial
load conditions by solving the steady-state energy and mass balance equations for
each time step. The calculated cooling power and coefficient of performance fit the
experimental data better than a constant characteristic equation. The chiller models
were integrated into a complete simulation model of a solar thermal plant with storage,
chiller and auxiliary heating system. Different cooling load files with a predominance
of either external or internal loads for different building orientations and locations were
created to evaluate the influence of the special load time series for a given cooling
power. The investigation showed that to achieve a given solar fraction of the total heat
demand requires largely different collector surfaces and storage volumes, depending
on the characteristics of the building load file and the chosen system technology
and control strategy. To achieve a solar fraction of 80% at the location in Madrid,
the required collector surface area is above 3m 2 kW 1 if the generator is operated
at constant high temperature of 85 C and the solar thermal system operates under
low-flow conditions. In this case, it is highly recommended to increase the collector
field mass flow, so that temperature levels cannot rise too much. Doubling the mass
flow decreases the required collector surface area and thus solar thermal system costs
by 30%.
For buildings with the same maximum cooling load but different load time series,
the required surface area varies by a factor of 2 to obtain the same solar fraction.
The influence of building orientation with the same internal load structure is about
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