The design of mixed-mode ventilation and comfort cooling systems have taken another step forward with the construction of the Centre for Mathematical Sciences in Cambridge - the new home for the mathematical genius Stephen Hawking. But how energy efficient are the buildings likely to be?

When it is required to predict the local mean age of air, the calculations are often carried out assuming that there is no recirculation that is that all of the supply air is fresh. However, local mean age values will be greater than in the fresh air case when some of the exhaust air is recirculated. This paper examines and discusses the effect of recirculation and shows that, for many systems the increase in local mean age due to recirculation can be calculated by means of an elementary analysis that leads to a simple algebraic expression.

Nearly 20 years after it was ordered by Parliament, the f'.230 million parliamentary building is ready to welcome its inmates: 200-odd constituency MPs and their staff. Does the building's controversial luxury extend to the engineering services?