If your building isn't net zero, you can still be an energy hero. Drawing near can be just as good.
Targeting "near zero" instead – which the New Buildings Institute defines as an energy use index (EUI) of 16-20 kBTU per square foot per year or less – still brings staggering savings and green gains, even if true zero status isn't in the cards right now.
To hit anywhere near the bullseye of zero energy use, however, you need an extra-efficient building. Focus on optimizing your building's tightness, equipment, and operation inside and out before looking at renewables.
The Double-Edged Sword of Existing Buildings
Predictably, retrofitting an existing building to achieve such low energy consumption carries considerable challenges – but it may also offer previously unnoticed opportunity.
"You can look at any existing building and assess its existing green components, and if the building is currently in its end use, you can assess its actual performance. There's some benefit to having an existing building to work with," explains Ralph DiNola, executive director of the New Buildings Institute. "In a lot of historic buildings, you'll see features like high window head height, good daylighting, a design that favors natural ventilation, and a big thermal mass – you're potentially given a host of features that work well when aspiring to net zero."
You don't need the features of a historic building to put zero in your sights, however. Mark Frankel, technical director of the New Buildings Institute, says the key is integrated design and a strong, thorough team working with you, though some buildings can pose extra problems.
"Some of my favorite examples in our database are existing buildings that are not historic – they were total dogs, but now they're net-zero or super-efficient buildings because the design team was committed to making them work," says Frankel. "However, there are features that can be liabilities to net zero, primarily excessive glazing. That's a very difficult feature to work with because you have to fight solar gain and extreme heat loss, which are challenging features for managing energy."
Where to Start: Site, Facade, and Envelope
Start by assessing the building's orientation and the condition of the facade and envelope. Your location, climate, and building type will have a major impact on what strategies are feasible, says Jim Gabriel, partner of architectural firm Hanna Gabriel Wells, which renovated a former auto repair garage with cinderblock construction into its net-zero Bacon Street office in San Diego, CA, in 2009. The original structure was built in 1955.
"Office buildings have relatively low energy use compared to other building types, so they're a good target just because you're already part of the way to zero," says Gabriel. "The physical form of the building also plays a role. Ours is long and narrow in proportion, so it easily lends itself to natural ventilation and daylighting. The more things you can do passively, the more you start to drive down the energy consumption."
The Bacon Street office didn't require much insulation due to its breezy, temperate location, but more severe seasonal variations in other parts of the country make that step a must.
"If you can insulate the exterior and add a rainscreen on the outside of a relatively simple building, that will be less expensive than a total gut rehab of the interior spaces," notes Laura Blau, principal of sustainable architectural firm BluPath Design. "It's easier to attend to air sealing from the outside where more surfaces are open to you rather than trying to do things with existing interior conditions where floors meet walls and walls meet the foundation and roof. Maybe you have a building where you can change out the windows and put on a new facade. If you're adding a new wing, you can orient it to invite winter sun in or keep summer sun out, depending on the thermal dynamics."
The Historic Green Village on Anna Maria Island, FL, is a unique mixed-use combination of four 100-year-old buildings containing a cafe, outdoor equipment outfitter, and jeweler, as well as a new building with a small art gallery and bakery. The team opted for spray foam instead of exterior insulation because its historic buildings were unoccupied at the time of renovation.
"The biggest single factor in reducing energy is insulation, along with double windows and low-E glass," says Tom Stockebrand, the village's technical consultant and energy expert.
As Frankel noted, if your building is overglazed, sometimes a second skin can both mitigate the negative effects of too much glazing and contribute to a tight envelope, another requirement in creating an ultra-efficient building. Addressing envelope issues first will help clarify what to do inside and protect against envelope failure from condensation and freeze-thaw cycles, which invite rust, rot, mold, and mildew.
"With any deep energy retrofit, the first consideration is whether you're near the end of the useful life of your mechanical systems," says Blau. "That's a great time to think about putting money into the envelope so you reduce the load and can use smaller mechanical equipment. If you replace your mechanical systems and then look at your envelope afterward, you will have oversized systems that won't run as efficiently."
Address Electrical and Mechanical Systems
After addressing envelope and facade issues, turn your attention to the building's electrical and mechanical systems. Daylighting is a nearly universal strategy, according to the New Buildings Institute.
"You want to provide the right amount of light when and where you need it. Anything else is wasted," says Jenn Dolin, manager of sustainability and environmental affairs for lighting developer Sylvania. "Energy management and lighting control systems help you identify when lighting is being used incorrectly, and then you can adjust to that. Let's say you have a snowstorm and everyone is asked to stay home, but your lights are programmed to be on for 10 hours a day. If the entire building is lit for 10 hours but there are only three people in the entire building, you won't want those lights on because that's a huge amount of wasted energy. Some lighting control solutions will let you go in remotely, turn the lights off, and then adjust as necessary when people are back in the building."
The Leon County Extension Office in Tallahassee, FL, opted for a simple lighting retrofit when they targeted net-zero status during a 2012 renovation of their 1960s-era building. Lighting fixtures were upgraded from 40W T12 lamps with magnetic ballasts to 32W T8s. A survey of tasks then revealed that some occupants' needs were met with three lamps rather than four, allowing further savings. The team also added occupancy sensors to private offices.
HVAC did not escape the Leon County Extension's review. The office previously used zoned HVAC with multiple rooftop units. After the team decided to target net zero during the next renovation, closed-loop geothermal heating and cooling replaced roughly two-thirds of the building's heating and cooling capacity. The one remaining HVAC unit will later be replaced with one that has a higher SEER rating.
"Our auditorium is one of the primary places we use for outreach, and a lot of nighttime functions are held there. In conjunction with solar PV producing energy during the day, we wanted the geothermal to primarily serve the nighttime load," explains Maggie Theriot, director of Leon County's Office of Resource Stewardship. "In addition to maximizing our heating and cooling dollars, it reduced the peak demand of the building. That brings more monetary savings, even if your energy use stays level."
Examine Benchmarking and Behavior
The most efficient building can still waste energy if occupants don't buy into your savings strategies, Frankel explains. Involve occupants early and often.
"What really separates successful from unsuccessful projects is when they address the way occupants will use the building and how it's operated over time," says Frankel. "If occupants aren't on board with good plug load behavior and turning off lights at night, you can totally destroy your energy budget. It's not just a design problem – it's a design, occupant, and operations problem."
Building energy dashboards are a popular way to help occupants visualize the impacts of their energy choices – the Historic Green Village meters all five buildings and displays data in a web-based portal and in dashboards for each building. The Leon County Extension Office took a similar tack with a kiosk comparing building energy consumption with the current production of the office's solar array. "People start using less power just because the display is sitting there," notes Stockebrand.
The extension office also used a more interactive strategy. Staying true to their teaching mission, occupants paired up with office mates to conduct self-performed audits, both in common areas and in their own offices.
"Throughout the audit, they're exploring their own spaces and reflecting on how they can improve personal behaviors and purchasing decisions, as well as how they interact with the space they're provided," explains Theriot. "From that came a list of recommendations that we boiled down. Some of the behavioral recommendations were achievable and free – any employee can start doing basic things like turning out the lights."
The audit also yielded more complex recommendations, Theriot added. Thanks to occupant requests, the infrastructure for an electric vehicle charging station was installed while the ground was already being disturbed to install the office's solar panels.
"Engaging your occupants sometimes means they come up with great unforeseen opportunities that otherwise might be missed," says Theriot.
In addition to showing occupants the numbers behind their actions, also target an often-overlooked energy consumer – plug loads.
"Traditionally plug loads are ignored because people focus on lights and mechanical systems," says Gabriel. "But the way we work today demands huge amounts of power from plugging in equipment – everyone has computers and mobile devices that are constantly recharging. Monitor plug loads and develop strategies for managing them, whether that's just making sure the equipment you buy is energy-efficient or buying occupancy sensors that shut off or step down equipment when people leave their areas."
The path to efficiency is difficult and can be fraught with complications, but it's combining a logical set of efficiency strategies that will draw your building close to zero.
"There's no shortcut to getting there," Gabriel adds. "You can't just bootstrap different thoughts together – often building owners and managers hear different strategies from different buildings and try to apply them to their own facilities in a piecemeal way. That's not going to get you the holistic kind of solution you need. When you properly analyze what you have, you get a building that can truly step out and move toward your goals."
CASE STUDY #1
Bacon Street Offices – Hanna Gabriel Wells
San Diego, CA
Building Size: 4,500 square feet
EUI: 13, with a net EUI of -9 due to a renewable production EUI of 22
Certifications: LEED Gold, Savings by Design Honor Award
- A wall of windows along the street side of the building provides daylight. Diffuse skylights at the back of the space provide balance.
- The design relies on daylighting first, then layers ambient light with advanced controls that turn off artificial light when it's not needed. Users control their own LED task lights.
- The building relies on prevailing coastal breezes for natural ventilation. Warm air is exhausted through the skylights.
- Each lighting zone is individually monitored for more effective commissioning and measurement.
CASE STUDY #2
Leon County Cooperative Extension (University of Florida)
Building Size: 13,000 square feet
Renovated: 2001 and 2012
EUI:19, with a net EUI of 0 due to a renewable production EUI matching consumption
- A closed-loop geothermal field of 60 wells at 90 feet deep moderates water temperature, enabling the building to discard or recover heat as necessary. The geothermal system allowed for a downsized compressor and provided a 40% energy savings compared to a conventional system.
- HVAC control setpoints are set back to 80 degrees F. on nights and weekends. During weekday morning operations, startup of the HVAC units is phased to avoid peak demand charges.
- Waste heat from the geothermal system is used to heat hot water in the kitchen.
- A 60 kW solar array of 253 panels, each producing 240W of electricity, is mounted on a steel beam structure so it can double as a canopy for the parking lot.
CASE STUDY #3
Anna Maria Historic Green Village
Anna Maria Island, FL
Building Size: 5,000 square feet (across five buildings)
Constructed: 1911 and 1915
EUI:28, with a net EUI of -7 due to a renewable production EUI of 35
Certifications: LEED Platinum
- Every structure is insulated above code levels and fitted with high-performance windows. One 1,000-square-foot building is insulated so thoroughly that its total monthly electric bill never exceeds $20.
- The geothermal heating and cooling system reaches 450 feet below the café into an aquifer with 72-degree F. water.
- Domestic water is heated to 170 degrees F. by a flat panel with copper tubing painted black.
- Data from the village's eMonitors (which track multiple circuits and main feeds) revealed that the dominant loads are air conditioning and café equipment, especially freezers, refrigerators, and the espresso machine. The team discovered that the air conditioners weren't phasing in as planned, due in part to excess heat created by a display case in the café. Simply adding a blanket reduced air conditioning loads by 25%.
Janelle Penny is senior editor of BUILDINGS.