"Hidden" Strategies in Duda/Paine LEED Gold Buildings

A few years ago I took a three day seminar on Residential Energy Efficiency.  The first day’s emphasis was on ways to tighten the building envelope; insulation, spray foam sealant, conditioned crawl spaces, radiant barriers and more.  On the second day, the instructor casually mentioned that a tight building envelope would not allow fresh air into the house and would therefore adversely affect indoor air quality.  A 30 minute conversation ensued about possible remedies.  The conversation centered on where to place an exterior wall opening to minimize discomfort from drafts, possible locations where one would not notice it, and ways to dress it up with louvers.  At the time I thought, if you are losing heat by creating a hole in an exterior wall, why bother tightening up the building envelope?  The cold air coming in would waste all of one’s effort.

Today’s buildings face the same dilemma; how to introduce fresh, unconditioned air for high indoor air quality without wasting energy to raise the temperature before it is used. What if there was a way to capture the heat from the air you are exhausting or somehow pre-condition the cold air coming in?  The solution we have used on several projects at Duda/Paine is called a “heat-wheel”, sometimes called a thermal wheel, rotary heat exchanger or even an energy wheel. 

 

This process is reversed in the cooling cycle.

 

The air being exhausted from interior spaces (from toilets, kitchens, or hoods) is routed through a matrix of heat absorbing material that draws the heat from the exhaust air.  This material is rotated into a chamber where cool air is coming into the building and the heat transfers from the material into the fresh air, effectively pre-conditioning the fresh air before it is mixed with air circulating through the system.  The wheel of heat absorbing material rotates back into the exhaust stream and the cycle continues.  Approximately 70% to 90% of the warmth from the exhaust is transferred into the fresh air stream for gross energy efficiencies around 15%.

 

These wheels can be very large for commercial buildings.  At Democracy Tower, Duda/Paine’s project in Reston Town Center, Virginia, the heat-wheel is located in the penthouse mechanical area and accessed through doors into the chambers.  Invisible to most building users, but continually benefitting all of its occupants with fresh indoor air.

 

 

 

By David Davis