Environmental Building NewsTM The Leading Source for Environmentally Responsible Design & Construction A Publication of BuildingGreen, Inc. www.BuildingGreen.com Volume 23, Number 8 · August 2014 or less energy than the project team Natural Ventilation: The Nine Biggest anticipated. Most importantly, a successful natural ventilation system Obstacles and How Project Teams must be attuned to the local micro- Are Beating Them climate and the occupants’ micro- culture in a way that most other Designers are reinventing the art and science of passive comfort control design strategies simply don’t require. even where climate and culture favor mechanical systems. All this makes some project teams balk By Paula Melton at the idea from day one, and most never even consider it—yet even in The Eastgate building in Harare, savings to a decrease in sick days due the U.S., where climates and cultural Zimbabwe, is world-famous for its to the amount of fresh air. “Air-con- expectations typically make mechan- biomimetic passive cooling system, ditioned offices recirculate the air at ical HVAC a given, there are project inspired by termite mounds. The least six times; otherwise you waste so teams pursuing natural ventilation for fan-assisted network of thermal much energy. In my system, there is no its energy and air-quality benefits. labyrinths and chimneys cools the recirculation at all; it’s all fresh air.” space economically and “uses about Why Natural Ventilation? 10% of the energy” consumed by a As the contrast between these two mechanically conditioned building buildings demonstrates, the reasons There are three primary reasons to next door, architect Mick Pearce told for natural ventilation differ by design a building for natural ventila- EBN. project, and the system may cost more tion. or less upfront than a conventional Necessity was the mother of Pearce’s mechanical system. It may save more invention. The expense of importing the equipment needed for a mechan- ical HVAC system drove the strategy. Ten years later and seven thousand miles away in Melbourne, Australia, Pearce employed natural ventila- tion again for Council House 2, with profoundly different results. That’s because the natural ventilation system pulls in air “for breathing, not for cool- ing.” Instead, radiant cooling makes the ceiling “like the roof of a cave.” In Melbourne, the economic driver wasn’t the cost of equipment; it was worker productivity. “The building actually cost about 20% more than the cheapest office block at that time,” he said. The team expected a ten-year payback, but revised that down to seven years after a couple years of data had come in. Energy savings were actually weaker than anticipat- ed—about a 60% reduction compared Photos: Courtesy Mick Pearce with the building it replaced, not the Similar technologies for different climates, cultures, and economies: Eastgate Center and Council House 2 85% modeled—but Pearce attributes share an architect and a strategy involving concrete thermal labyrinths, but that is where the similarity ends. Environmental Building News • August 2014 Copyright © 2014 BuildingGreen, Inc. All rights reserved. • Energy savings can be dramatic in Viability vs. Potential climates and building types where natural ventilation is feasible for most or all of the year. Estimates vary wildly and depend on climate, but Shaun Fitzgerald, Ph.D., cofounder of natural ventilation products and consulting firm Breathing Buildings, cites savings on fan energy alone of 10% to 30% in the mild U.K. climate where he works. • Occupant satisfaction often drives the decision in the developed world, according to many design- ers EBN spoke with. “The notion Source: Payette that you can just open a window The climate may be friendly to natural ventilation, but the microclimate and other factors can reduce the potential significantly. and hear a bird chirp or feel a little breeze is psychologically very refreshing,” notes Steve Tatge, a Kita Schloss-Geister, that has been natural ventilation viability—based lead architect at the University mostly successful but also problem- simply on the local climate—and of Washington, which is pioneer- atic; his firm helped the architects natural ventilation potential—based on ing natural ventilation strategies fine-tune the daylighting scheme for the site, microclimate, and other finer in a number of new and existing the design, which initially was over- details (see chart). After the topic is in- buildings. glazed, in Marais’s judgment. “LEED troduced and vetted based on viability, was the number one priority,” so day- the second set of calculations guides • Indoor air quality is closely related lighting was “very heavily weighted. whether the project should be natural- to occupant satisfaction. “If you can At that stage, I don’t think anyone was ly ventilated, mixed mode (a combina- introduce copious amounts of fresh giving natural ventilation a thought.” tion of mechanical and passive strat- air without using fans, you’ve cre- egies), or mechanically conditioned ated an amazing environment for By the time the firm had turned its year-round. If the system will involve the people inside,” says Fitzgerald. attention to ventilation, they discov- sensors or automation sequences for In some climates, he remarks, ered certain windows were too large: windows, fans, or other components, “About 70% of the year, the idea of “Even if you just opened them a little it’s best to discuss that early in design being cocooned in a glass box that’s bit, there was a lot of air”—a problem as well, Menchaca cautions, because air-conditioned is just anathema.” in cold weather. But it was too late these will need to be budgeted for. to change the windows; as a work- The list of reasons not to attempt natu- around, some rooms in the finished Engineering good relationships ral ventilation is considerably longer, building have to be ventilated while but experts EBN spoke with have dis- the children and teachers are else- Even if the client is convinced, the covered that many of these obstacles where in the building. mechanical engineer may not be. have a lot more to do with perception “They want to avoid liability and and habit than with physics. We’ll ex- How early? risk,” says Blake Jackson, AIA, of plore nine of these barriers, and how Tsoi/Kobus. “You really have to get project teams are overcoming them. “What we do is assist the teams in the them on board.” (See #2 below for very, very early design stages, guiding more on the perceived risks of natural 1. Conventional Design them toward more efficient choices in ventilation.) Process terms of design,” explains Alejandra Menchaca, Ph.D., one of two in-house It helps when architects educate them- “The architect wants to sell a proj- building scientists at Payette. Their selves, Jackson suggests. “You have ect with good-looking pictures,” guidance compares options for orien- to have a few factors working togeth- argues Jean Marais, B.Eng., of the tation, massing, and shading to inform er and a team that’s in agreement,” Berlin-based engineering firm decisions about daylighting, natural including architects who understand b.i.g. bechtold. “There is a lot of glass, ventilation, and other strategies. how building geometry, ceiling height, and the fenestration is not always glazing, and other features affect the effectively used.” When considering natural ventila- feasibility of the scheme. “There’s tion, the “first step is to evaluate the nothing keeping architects from Marais relates the story of a 7,000 ft2 climate,” but it doesn’t end there. picking up the CIBSE guidebook,” he naturally ventilated daycare center, Menchaca draws a distinction between says (CIBSE is the U.K. equivalent of Environmental Building News • August 2014 p. 2 ASHRAE; AM10 is its natural ven- it took me three days to get the right do. Somehow, we’re okay with that.” tilation standard, and AM13 covers settings.” That said, she admits, “I have seen mixed-mode ventilation). “It’s rela- so many buildings where the natural tively visual, considering it’s an engi- That situation may be improving ventilation doesn’t work,” whether neering tool.” soon, reports Philip Haves, Ph.D., because of the design itself or because leader of the simulation research “everything was properly designed, No supermodels group at Lawrence Berkeley National and then the control systems failed.” Laboratory (LBNL). A team of re- Control systems can be re-sequenced Ideally, the project team would be able searchers led by Paul Linden, Ph.D., (more on this below), but if the system to provide a rough sense of energy chair of the Department of Mechanical doesn’t provide enough airflow, or if savings early on, but “the decision to and Aerospace Engineering at the occupants are not comfortable enough use natural ventilation or not comes University of California–San Diego or not flexible enough, “you can’t just way before we have a full building en- has developed new models of vari- ‘fix’ your occupants. All you can do is ergy model,” says Menchaca. “Many ous modes of natural ventilation, and reduce the amount of natural ventila- times, we don’t have the answer other LBNL has been integrating these new tion that you’re using.” than knowing the climate outside is models into EnergyPlus. One of the nice.” models, he explains, deals with eddies Most buildings in the U.S. make that form against buildings and can this possible by installing a backup Menchaca calculates roughly what cause “pumping action” that either mechanical system that’s already percentage of the time the building draws wind in through the window being used for a certain percentage of will be using natural ventilation and or forces interior air out in hard-to- the year, with natural ventilation re- creates a spreadsheet showing “how predict ways.