“Visible” Strategies in Duda/Paine LEED Gold Buildings

Green Roofs are often promoted as a new invention, but sod above a structure is an old idea.  On ancient buildings, sod was a useful roofing material because it was easy to install, available regionally and since it was living, did not deteriorate rapidly.  The sod also absorbed rainwater and would hold much of it, slowing its passage into the structure below.

 

On modern buildings, better waterproofing technologies are required than sod can offer, especially in commercial buildings where flat roofs are often incorporated.  Sod on the roof does little to protect against leaks today and its use is not for shedding water as it was before.  So is a green roof a gimmick used only as a demonstrable, popular green building technique? 
 

 A green roof is easily identifiable and signals a different strategy is being employed than buildings in previous few decades, but it also serves an important environmental function.  Urban settings have been documented to be 15 to 20 degrees warmer than outlying spaces because of a dense concentration of dark roofs and paving.  Soil and plant material on a roof avoids a large, dark surface condition and diminishes the potential for warming.





 

Green roof technology takes advantage of another aspect of the old sod roof and that is rainwater absorption and retention.  Without a green roof, smooth roof surfaces allow rapid movement of water toward drains and storm water systems in a large storm event.  With the large percentage of smooth surfaces in an urban setting, rain events can easily create flash flooding conditions as all of the water moves quickly toward the point of discharge.  The force demonstrated with rapid water movement can damage infrastructure as well as erode and alter natural waterways. 

Building a system to handle the worst case conditions would be prohibitive or create waterways similar to the Los Angeles River. 

The goal of recent roof and site design is to slow the discharge of water to roughly equal the rate water leaves a wooded site.  A green roof can reduce rainwater discharge by %. 

By David Davis

 

"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