The cowls serve two needs: ventilation and heat recovery. With the cowls no energy is required for ventilation, and in the colder months the heat kept in the house by the supertight envelopes is not lost in the process. The British Isles may not need air conditioning like, say, Florida, but the architects and engineers still had to address cooling.
For one, internal heat gains from computers and other equipment in the north-facing work spaces (living spaces in the mixed-use development face south) are addressed through vents and the building's thermal inertia. The latter means that the buildings' roofs and walls absorb the heat from the equipment as well as a good deal of the outside heat in warmer months, therefore minimizing temperature swings between the day and night. After the sun goes down and the temperature drops, the built-up heat is released.