Paper 2: Volume 4 No.3 December 2005 Edition
Passive
and Low Energy Cooling of Office Buildings
U. Eicker,
M. Huber, P. Seeberger and C. Vorschulze
University
of Applied Sciences
Stuttgart
, Schellingstrasse 24, D-70174
Stuttgart
,
Germany
Abstract
In this work, the cooling
performance of night ventilation systems and different earth heat exchange
technologies were experimentally analysed in three office buildings in
Southern Germany
. One of the first passive energy standard office buildings in
Europe
was extensively monitored over a three year period to analyse the summer
performance of a highly insulated and well shaded building in which night
cooling ventilation was based on stack effect and cross ventilation. This
was combined with a mechanical ventilation system incorporating a ground
coupled heat exchanger to supply daytime fresh air.
For comparison, an energy
analysis was made of a mechanically driven exhaust air night ventilation
system and a supply and exhaust air system in the other two buildings. The
first of these was a passively cooled refurbished building in Tübingen
which utilises mechanical night ventilation to effectively discharge
ceilings with phase change material. In addition, fresh air cooling is
achieved using a horizontal brine-earth heat exchanger. The second
comparison building was a low energy office building in
Freiburg
which uses water based ground coupled heat exchangers for fresh air
cooling and an exhaust air ventilation system for night cooling.
During a typical German
summer, in which the number of hours that the ambient air temperature
exceeds 25 °C is less than 160, the passively ventilated building
performed excellently, even with relatively high internal heat loads of
200 to 400 Wh.m-2.day-1. However, when the ambient
air temperature was significantly higher, such as in the summer of 2003
(i.e. 3 K higher than the average summer temperature), nearly 10% of all
office hours recorded room air temperatures above 26 °C. In the case of
the two buildings that were night cooled by mechanical ventilation,
cooling performance was limited by the rather low air exchange rate of 2 h-1.
This resulted in overnight room temperature reductions of just 2 - 3 K
during hot summer nights. Also the coefficient of performance (COP) was
relatively low for this approach at between 4 to 6.
All the earth heat
exchangers showed excellent energy performances with COP's between 20 and
50. However, due to the limited fresh air volume flow in such buildings,
the earth heat exchanger only removed a small part of the total load.
Key words: passive
cooling, mechanical night ventilation, ground coupled heat exchangers,
summer building performance, passive building standard, phase change
cooling.
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