Deconstructing Energy Efficient Buildings
Finding the Happy Medium Between Net Zero and Passive House
No matter what time of day or season, most of us move from one well-lit, temperature-controlled space to another, blissfully unaware of the energy required to do so. We’ve had it pretty good. The bad news is that Mother Nature is fed up and getting her climate-change revenge via extreme weather events, rising sea levels and wild swings in seasonal temperatures. So achieving energy efficiency is no longer an “if” proposition. Now, it’s all about “how.”
The term generating the most buzz in the energy-efficiency arena is undoubtedly “net zero,” which, simply means a building creates enough of its own juice to meet its cooling, heating and electricity requirements. As defined by the primary net zero energy building (NZEB) certifying body, the International Living Future Institute (ILFI), the concept has grown to include the use of alternative energy sources like solar, wind, and thermal energy, as well as a reduction in consumption. For some building owners, achieving ILFI’s NZEB standard is their only goal, but its requirements can also be incorporated into Living Buildings, ILFI’s premium certification.
How a flower relates to and impacts its surrounding environment is the inspiration behind the concept. Each carefully considered element of Living Building design, such as site selection, water use, health, and beauty, is referred to as a “petal.”
Very much in contrast to the wider, holistic nets that NZEBs and Living Buildings cast, the Passive House Institute US (PHIUS) standard focuses on a well-insulated and tightly-sealed building envelope. To that end, Passive House also incorporates the use of high-performance windows and doors, a balanced ventilation design, the smallest conditioning system possible and a season-appropriate solar gain plan. Passive House is all about the numbers, with more of a “miles per gallon” focus, according to PHIUS Co-Founder and Executive Director Katrin Klingenberg.
The certifications themselves are not required to achieve net-zero energy use or energy efficiency, but they do often serve as a badge of honor. Rocky Mountain Institute (RMI) Program Manager Craig Schiller said, “For commercial buildings, part of the drive for certification is around marketability, especially if you’re planning on selling a building. It’s a verifiable way of showing what you’re actually doing in terms of energy conservation, but you don’t have to be certified.”
Taking Schiller’s train of thought one step further, and throwing certification to the wind, consider a hypothetical monument to energy efficiency that integrates an optimal mix of features from NZEB, Living Building, and Passive House structures.
The first decision is where to build. Los Angeles is a no-brainer as it is in one of the most energy-friendly states with – bonus! – a temperate climate that does not require the extraordinary design measures necessary to battle extreme heat or cold.
The next step is site location. Although trees are great for summer shade, too much cover can minimize the benefits of solar. Both the Living Building and NZEB standards limit potential sites to greyfields and brownfields, so an existing one-story office building in a commercial area is ideal – as long as the building is oriented in such a way that it maximizes solar gain.
Ideally, the building would be no more than 2,500 square feet, already built out for a one–entity operation, even though energy-efficient methods can be utilized in buildings with a leasing component, like the Living Building-certified Bullitt Center in Seattle. Bradley Kahn, spokesman for the Bullitt Center, explained tenants agree to energy budgets when they sign their leases and that they have “risen to the challenge.” As a result, the building, through solar panel energy production and a use-reduction strategy, creates 60% more energy than it uses, plug loads included.
Since our hypothetical model uses an existing building, it likely is already connected to the local electrical power grid. Now a few decisions have to be made. Both the Living Building and NZEB standards require that one or more renewable energy sources be maintained on site to meet 100% of the building’s energy needs. In the middle of a city like LA, wind turbines and hydroelectric energy are out. Solar, which is relatively accessible and cost-effective, should do the trick.
Passive House, being the numbers-focused option that it is, has no requirement for onsite power or renewable energy, which also helps keep costs down. Its objective is energy efficiency, period. But for sustainability’s sake, not to mention federal tax credits, solar panels positioned on the roof still make sense. If old mechanical systems on the roof prevent this option, a possible workaround could be found in the flat canopy installed along the Bullitt Center roof’s edge where solar panels are affixed. Another example of a clever solution can be seen in DPR Construction’s NZEB-certified office in Phoenix, where the covered parking was outfitted with solar panels. However, if there is any hope of covering daily energy needs with solar, conservation is also key.
DPR Project Executive Derek Kirkland said a few of their energy-saving tricks are the use of solar tubes instead of light fixtures, as well as a vampire switch. “The last person out at night hits the vampire switch, and it cuts the noncritical power load – photocopiers, laptops, etc.,” said Kirkland, reducing plug load by 37%. These kinds of energy conservation measures make sense, and a feature like the vampire switch can keep employees engaged and on board.
Although all energy-efficiency methods make insulation a priority, Passive House dominates in this area. After insulating our hypothetical model, sealing the envelope, and installing appropriate doors and windows for maximum air-tightness and low heat transfer coefficients (U-values), it’s time to evaluate the ventilation. “It’s very important to have an air-tight building so that you’re not losing heat or getting heat gain in the summer time through the building envelope,” said Hayes Zirnhelt, RMI senior associate, “but you do need fresh air, and the best way to do that is to have a dedicated mechanical ventilation system. ”
One unique requirement of Passive House, and uncharacteristically demanding, is that the ventilation system must also include a heat recovery function. This allows warm exhaust air to be transferred to the incoming fresh air without the two air streams mixing. In hot weather, the heat exchange process can be reversed so that hot incoming air transfers to the exhaust air and is cooled before entering occupied space. Most of these heat recovery systems also come with bypasses so that cool air or warm air can flow directly into the space, if the weather allows.
Even though they generate their own power, many Living Buildings and NZEBs pursue some level of passive heating and cooling as a way to conserve energy. Kirkland boiled DPR’s heating and cooling scheme down to this: circulate the cool air in, hot air out, all within the confines of an incredibly tight building envelope, and you’re done.”
He also credited three key elements with keeping the indoor temperatures pleasant in the Phoenix heat: automated windows, shower towers (evaporative cooling towers) and more than a dozen 8-foot fans. The shower towers draw in cool air, which the fans then circulate to one side of the building to be drawn up and out via a zinc-clad solar chimney. Temperate air is kept inside, due in large part to 20-foot automated paneled windows, programmed to open and close at certain outside temperatures.
RMI uses a similar window setup, and much like the vampire switch, the windows are connected to a red light that turns on when one is open. “We’ve trained all of our occupants to look at that light,” said Shiller, “if the light is red, you can’t leave yet.”
The insulation, ventilation, and heat recovery benefits in the Passive House playbook can address most heating and cooling requirements. Shower towers and 8-foot fans sound cool, but they’re overkill for our hypothetical space. However, programmable windows and a small standard heating and cooling system to take up the slack in the event of unexpected extreme weather – or in case someone leaves a door or window open – are smart extras that provide eco-friendly finishing touches.
As always, the final question comes down to cost. Passive House could incur higher upfront payments for more insulation, a tighter shell and a dedicated ventilation system with heat recovery. Meanwhile, mandatory on-site power, along with the intangibles like “beauty” and “education” could eventually send the price tag for meeting NZEB and Living Building standards sky high. The yearlong certification and documentation requirements for NZEBs and Living Buildings, versus Passive House’s almost immediate approval, could add a premium to the bottom line as well. Perhaps, there is something more to our hypothetical hybrid than pure whimsy. The unassuming, simple energy efficiency formula in Passive Houses, spiked with touches of high-tech net zero implementations could offer a more cost-effective option than simply selecting one over the other. But if a choice must be made, just don’t forget to hit the vampire switch on the way out.