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Shading and Make-Up for Building Designers

Tuesday, March 26, 2013

I just returned from a meeting in Florida and I was reminded of a couple of basic concepts that apply to virtually all building designs.

Our meeting room faced an outside wall with a couple of French doors to a nice patio area.  The weather was unusually cool for Florida and everyone sitting on that side of the table was able to experience that coolness first hand...even though the doors were closed.  During breaks the smokers in the group would gather on the patio and, again, in spite of closed doors the meeting room started to smell of cigarette smoke.

The problem, of course, was a lower pressure in the meeting room compared to the outdoors.  Somewhere in the conference center there was an exhaust system churning away without a counterbalancing make-up air system.  The only way that the exhaust system could satisfy its demand for air was to pull that air from outside the building, through the conference room, to its final point of exit.  Cold, smoke-laden air was drawn into the meeting room and occupant comfort was compromised.  Simply adding a make-up air system similar to the Applied Air DFL-series would have improved the indoor environment and cost very little extra to operate.  Remember that all of that cold air that was being sucked into the building caused the occupants to raise the thermostat set-point in order to compensate for being cold and forced the large main air handlers to operate for more hours than necessary.  Maintaining a positive pressure in buildings controls infiltration of smoke, dust, and un-tempered air and it is relatively simple to achieve.

The other basic concept that popped into my head is how important the building envelope is to controlling operating costs.  This particular resort was built many years ago but employed some pretty effective passive shading for the guest rooms.  My room had a wall of windows for natural light and a view but had a deep setback that prevented direct solar radiation.  This deep setback meant that the air conditioning system would see far fewer operating hours than an unprotected glass exposure would allow.  Since solar radiation is also a significant portion of the building cooling load the setbacks allowed a reduction in HVAC equipment size as well.

Building design has changed since the days when this hotel was built and deep setbacks are much less common.  But effective solar shading is still feasible through the use of external shades and louvers.  External shade technology has advanced to the point where it is possible for the shades to track the location of the sun and automatically provide continuous reduction in solar radiation.  Some external shading systems such as those developed by Colt Group actually contain photovoltaic cells that can reduce the building electrical demand by more than providing shading alone.

So two basic concepts for sustainable building design:  maintaining a positive indoor pressure to eliminate unwanted and untreated outside air from entering the occupied areas; and using modern external shading technology to reduce the solar load in the occupied areas which, in turn, reduces operating and capital costs.