A Net Zero Building Property Tour
My class recently had the opportunity to tour what is believed to be California’s second ever certified Net Zero Energy Building. The 12,000 square foot public library in Alpine, CA opened to the public in 2016 and was certified Net Zero two years later.
Net Zero Energy refers to the fact that the library produces at least if not more energy on-site than it consumes. The building is also certified LEED Gold, which is the second highest of four rating levels that look at issues such as carbon emissions reduction, energy use, waste, water, indoor environmental quality, and other similar factors.
The building designers squeezed as many photovoltaic solar panels onto the roof as they could. Still the panels are only visible from a distance and are for the most part not even noticeable. In using the panels, they’re able to produce about 108,500 kWh annually. At different times of the year the panels produce more energy than the building uses. This excess energy, which is about 8% more on average than they use, is sent back to the local power grid allowing the County (which owns the library) to receive a credit.
The building’s life cycle is estimated to be 50 years, while the cost of designing a net zero building, purchasing equipment, and maintaining it for those 50 years is projected to be paid for through energy savings in approximately 12 years. That leaves 38 years of pure benefit.
Building Design Elements
The building was designed in such a way that the walls are higher and windows are larger and more plentiful on the northern facing side of the building. This was done because in the Northern Hemisphere the sun shines brightest from the south (closer to the Equator). This means that the northern facing side of the building receives indirect sunlight, which provides a source of illumination with less intense heat transfer. With less heat from the sun’s infrared rays, the air conditioning doesn’t have to work as hard, which saves energy and reduces carbon emissions normally produced via the use of energy that would otherwise be used to cool off the building.
On the side of the building where the direct sunlight hits, the architectural team designed vertical fins (concrete pillars) that serve a dual purpose. To the average person the fins are nothing more than an architectural design feature, or part of the aesthetics. But they also serve to shade the windows as the sun moves through the sky over the course of the day. When your goal is net zero energy, the little things add up and make a real impact.
From inside the library, glancing up towards the ceiling, you would see an open and industrial look. The high and open ceiling design allows hot air to naturally rise and occupy space where there are no people. If they had a lower ceiling height, the heat wouldn’t have as much space to fill before it would be felt by the building’s occupants and require air conditioning.
On one end of the building there is a butterfly roof, which from a cross section view looks almost like the letter V, with the center of the ceiling/roof being lower than the sides. This allows for the collection of rainwater that if properly managed can be used for vegetation or at the very least gradually returned to the ground below in such a way as to avoid flooding.
Active Energy Saving
While the building’s design offers a form of passive energy savings (e.g. indirect sunlight generates less heat which means less energy is used to cool the building), there are other measures that the design team and engineers implemented to further reduce the library’s energy usage.
The lights inside the building all use LEDs, which are more energy efficient. Not only that, but the building management system is able to monitor the amount of daylight coming in through the windows and will automatically adjust the artificial lighting up or down to maintain a steady brightness level inside. There are also occupancy sensors in the smaller rooms where the lights will turn off completely if the room is empty. This means only using energy to light the library when needed.
The windows have a coating that blocks specific wavelengths of light such that visible light is allowed through the windows, while infrared rays (those that cause heat) are reflected outwards. The is known as low-emissivity glass.
The engineer I spoke with also explained that there is a lot of phantom energy usage in the building, an issue that they didn’t fully realize the extent of ahead of time. Phantom energy refers to the consumption of energy by devices that are plugged in, but not actively in use. For example, the microwave in the staff lounge or the printers connected to the computers use energy even when nobody is cooking or printing.
In an effort to deal with this sort of energy loss, the outlets are set to turn off when not in use. Doing this means that staff do not have to physically unplug items when they’re not using them to have the energy saving effect of actually unplugging them. Security systems and other equipment that need to run 24/7 are on separate circuits.
The engineer also explained how he’s disappointed every time he looks into the computer room and sees a dozen or so screens all lit up. Despite the fact that it consumes energy, the design team had to make a compromise as the library staff likes the appearance of having all the monitors remain on. They feel it looks more invited to patrons.
With 60% of a typical building’s energy use being associated with the HVAC (heating, ventilation, and air conditioning) system, this became a major area of focus. A traditional heating and cooling system pumps in cool air to warm rooms and warm air into cool rooms. By contrast, this library uses an “energy recovery system” that can actually move air from one room to another. For example, it can move warm air from say an equipment room to a colder conference room.
There is also another system known as “demand control ventilation”. The heating and cooling system (as well as the lighting) are controlled by a series of carbon dioxide sensors, that allow the building to monitor occupancy. As more people enter the building, more carbon dioxide enters the air (as people exhale). Thus, by measuring the amount of CO2 in the air, the system can tell how busy the library is at any given point in time.
When more people enter an enclosed space, their body heat will naturally warm the air, and so the system knows that when CO2 levels reach a certain point that more air conditioning will be necessary. Similarly, it can reduce the amount of air conditioning used when it senses that the building is nearly empty, such as after closing when the custodial staff are the only people present.
This was the first time I had the opportunity to see a net zero energy building in practice. It was really interesting to hear about some of the features that were included, such as how the vertical fins provide shading to the windows while looking like nothing more than a design feature or the fact that carbon dioxide levels can be used to measure building occupancy. Being able to take a tour first hand helped to make the academic material we’ve been learning in the classroom feel more practical.
The other noteworthy thing is that had I not been told that the building had a net zero energy usage, I would’ve never known. It was a nice library. It has a clean, open, and modern look. The space was bright and felt comfortable. In other words, although there may have been some tradeoffs behind the scenes (such as the compromise made about the computer monitors) the functionality and overall appearance was not compromised in making the space energy efficient.
If you’re interested, there are a few pictures of the library on the Property Tours page of my website.