Limits and potentials of office building climatisation with ambient air

One of the first passive energy standard office buildings in Europe was extensively monitored to analyse the summer performance of highly insulated, well sun-shaded and mechanically ventilated buildings. During typical German summer conditions with less than 160 hours outside air temperatures above 25C these buildings perform excellently during summer, even if the internal loads are rather high. If ambient air temperatures are significantly higher like in summer 2003 with more than 3K higher average temperatures, nearly 10% of all office hours are above 26C. Detailed measurements showed that the night discharging of heavy thermal masses such as concrete ceilings was not very effective under free convection conditions, although night air changes were always above 5 h-1. Air temperature decreases due to night ventilation are limited to 2-3K. Three year measurements and simulation of the earth heat exchanger showed, that excellent performance is achieved with COPs between 35 and 50. Due to the limited fresh air volume flow in such buildings, the earth heat exchanger only removes a fraction of the total loads, here about 18% of the total internal loads.