One of the most daunting challenges facing architects and engineers in their struggle to deliver net-zero energy buildings is a four-letter acronym: HVAC. These systems today typically account for 25-50 percent of a building’s total energy use.
But the good news is there is “huge opportunity to improve” the way buildings are heated and cooled today, Peter Rumsey, PE, principal of Rumsey Engineers in Oakland, told the audience at Architectural Record’s 2009 Innovation Conference in his Oct. 7 session, “The New Generation of Super-Efficient HVAC Systems.”
The key to achieving a dramatic reduction in HVAC energy consumption? Accepting that VAV reheating systems are a solution “of the past,” said Rumsey—we should “throw them away and start afresh. We need to be looking at completely different mechanical systems.”
Work from Rumsey Engineers : Left: Betty Irene Moore Natural Sciences Building; Right: The StopeWaste.org building. Both projects are in Oakland, California
In lieu of VAV reheating systems, architects and engineers have a “diverse palette” of options to choose from, said Ramsey, including:
• Raised-Floor Systems (although he acknowledged some challenges here, including cost, under-floor cleanliness and accelerated rates of “temperature decay.”
• Radiant Heating & Cooling—which should have special appeal to architects, Rumsey surmised, because it means using 1-inch pipes instead of those design-ruining 20-inch ducts.
o And while Rumsey conceded that contractors may now be quoting a price of $10-15/square foot for tubing, he pointed out that he knows of four Walmarts that executed a system for $2.50/square foot. As moie and more contractors get comfortable with radiant heating and cooling, Rumsey predicted, the pricing premium will go away.
• Chilled Beams—which not only use less energy, but result in better air quality—and Rumsey cited a survey that poor air quality results in $5-10 billion of annual lost productivity in the United States.
• Night Sky—where water is sprayed on a roof at night; the chilled water is collected and used to cool the building during the day.
• Night Flushing (using cooler night-time air to flush heat of a building)—Rumsey noted that one reason why this process isn’t recommended more by engineers is that no modeling software allows engineers to dfo what they love best—calculate the benefits.
• Larger Ducts—For architects who can take the design implications, Rumsey explained that a slightly larger duct—24 inches vs. 20 inches—can yield dramatic energy benefits.
• Natural Ventilation, where the climate allows (watch our video tour of a noted building that uses natural ventilation: Thom Mayne’s Federal Building in San Francisco)
• Dedicated Outdoor Air Systems—decoupled from heating/cooling systems
• “True Integrated Design”—which Rumsey said “doesn’t mean doing BIM”, but means engineers and architects getting together early in the process to discuss how systems will affect each other.
o In an example of the possible benefits of this, he pointed to a building in California that, instead of being done in the standard steel, was done in concrete when the architect realized, in consultation with the engineer, that this material would allow a much simpler and cheaper HVAC system.
For architects looking for a firm engaging in HVAC best practices, Rumsey recommended they investigate what San Diego-based EHDD Architecture has done: “They get it,” he said, pointing to the firm’s Department of Global Ecology at the Carnegie Institution for Science as a prime example, a building that not only is a low-energy-usage star, but is a place that employees score as an exceptionally positive place to work.
Better HVAC systems, Rumsey said, are not about creating energy-stingy, but uncomfortable spaces—but about making “fundamentally better buildings.”
Rumsey began winding up his talk with his philosophical tenets re:HVAC. His first commandment? “Lower the loads” by considering building orientation, etc. Other “Rumsey Rules” include:
• right-size the building
• use simple engineering to achieve elegant solutions (“Victorian Engineering”)
• Use passive energy sources where possible
• Use controls where appropriate—but beware controls that are so complicated they don’t get used
And for those who believe that VAV reheating systems are timeless and eternal, he ended by reminding his audience that these systems emerged only in the 1980s—and where widely seen then as too complicated and expensive to use. VAV reheating systems have been “the reigning champ” for a long time, Rumsey concluded, “but they are about to be unseated.”