At 22 Degrees we have been exploring mixed mode options on projects for some time now. As Robert Mannes mentioned in his August post, Auckland has a reasonably mild climate and is ideal for mixed mode operation. We have developed a model using our own 22 Degrees premises as an example of a combination of a ‘mixed mode’ and a ‘sealed’ building. Given our tenancy is only 12m deep and has 2 external walls we have a good base for cross ventilation.
At 22 Degrees we use natural ventilation as much as we can and have a very reliable ‘Fred-Ometer’ who adjusts the windows to suit the weather. This for us removes the need for any electrical modulation, however not every tenancy has a Fred so the simulations are based on typical mixed mode protocols.
Overall we found a difference between the mixed mode and sealed operation as being 25 kWh/m². For us, this equates to an approximate saving of $600-1000/annum depending on power costs. To accompany this we have simulated the effects of natural ventilation through our office using CFD. This was done using the highest allowable inlet velocity and is helpful for the production of air movement in and around the built environment.
In Wynyard Quarter, the newly constructed ASB head office at North Wharf, incorporates mixed mode planning. It is a prime example of environmentally sustainable energy efficient design. The design incorporates rain water harvesting, modulated work space layouts and mixed mode ventilation. Our building, although on a much smaller scale, demonstrates the positive effects of a hybrid approach to ventilation.
Not all buildings are able to run mixed mode, however if the potential is there for this to be incorporated at building design stage, there are considerable financial savings to be made.