by Gordy Slack
The United States has more than 4.8 million buildings, and that number is steadily increasing at nearly two percent a year. Energy-wise, these buildings are monsters. They gobble up about 39 percent of the power produced and are responsible for an equal amount of the nation’s carbon footprint.
As buildings are planned, architects and engineers may devote time, attention, and money to designing energy-efficient buildings. However, once those buildings are inaugurated and occupied, there is little follow-up.
“It is not uncommon for designers to estimate the energy requirements of a building and then find that those estimates are off by a factor of two when the building is up and running,” says Arens. Once that is discovered, though, the building has already been occupied and simply keeping it going is more than enough work for its operators. The owners are thus forced to absorb the costs of these unforeseen inefficiencies.
That approach was never sensible, says Arens, but today’s energy costs and the realities of global climate change make it downright impractical and unattractive. Arens and his colleagues at CBE are trying to find ways to sustain the good intentions that go into designing a building throughout the construction phase and, if possible, all through the building’s life.
Their interest is partly in making existing buildings work better and partly in understanding how to make the next generation of buildings better still.
“Most buildings are built as prototypes. But they never get tested,” says Tom Webster, a research specialist at CBE. “Imagine if Detroit did that with cars!”
Monitoring and adjusting a building's energy performance on a long-term basis, known as “commissioning,” can lower the building's energy consumption by as much as 50 percent, according to LBNL research. For all commissioned buildings, the median energy reduction is 15 percent, no small amount in this era of rising energy costs, both financial and environmental.
One obstacle to the study and monitoring of building performance has been the difficulty of getting detailed and timely feedback from the buildings themselves. Big commercial buildings have surprisingly complex energy systems, says Arens, and it has been hard just to gather good data, let alone do the kind of analysis that would help engineers pinpoint and correct inefficiency.
The Berkeley group, employing sensors and wireless network technology developed by CITRIS scientists and engineers, is trying to make that data collection and analysis more efficient. If they can monitor a building and track its performance, Webster says, they can identify and correct problems or just tune it up to restore maximum efficiency.
Toward that end, the CBE team has developed portable commissioning carts, building-monitoring SWAT teams on wheels. The technology-laden hand trucks can be quickly rolled in to monitor healthy buildings or to diagnose ailing ones. The team recently developed a cart specifically to monitor air conditioning systems installed in the new, highly acclaimed, 55-story-tall New York Times (NYT) Building in Manhattan.
“The NYT building is remarkable,” says Fred Bauman, a research specialist at the CBE who works closely with Webster and Arens on the project. The building is best known for its innovative exterior screen made of horizontal ceramic rods that are designed to maximize diffuse natural light in the building while blocking direct rays that would require more air conditioning.
The NYT building also employs underfloor air distribution (UFAD), a raised-floor system that has the potential to use less cooling than more traditional, ducted cooling systems that pump conditioned air in from above. Under suitable weather conditions, UFAD systems can also increase the use of free-air cooling, which draws cool air in from outside, further reducing the need for air conditioning.
The Berkeley team received funding from the NYT to make a mobile cart to monitor and evaluate both the installation and the performance of the underfloor system.
“The basic idea,” says Webster, “is to gather a lot of data quickly and turn it directly into useful information so the commissioning agent can easily make adjustments and corrections.”
The cart features a telescoping pole that can be hoisted to the ceiling to measure the temperature of a room at different heights. Ideally, a building’s “occupied zone” (OZ) has a vertical temperature difference in the range of three-to-five °F, says Webster. The cart also has a tubular tether connected to a pressure gauge that can be stuck into floor air diffusers to measure the flow. The cart also picks up readings from small wireless sensors planted throughout the building that constantly gather plenum and room temperature data and then upload them to a database on the cart.
Old-fashioned top-down air distribution systems aim to create a uniform environment, mixing the air with overhead diffusers. “The underfloor system only requires a comfortable temperature in the OZ—between four inches and sixty-seven inches above the floor—and can sustain variability vertically while maintaining uniformity horizontally,” says Webster. In fact, such vertical variability is necessary to fully realize the benefits of the underfloor system. For example, in a UFAD system, supply air is introduced through floor diffusers and returned at ceiling level. This produces an overall floor-to-ceiling airflow pattern that takes advantage of the natural buoyancy produced by heat sources in the office and more efficiently removes heat loads and contaminants from the space.
Researchers or commissioning agents periodically push the cart around the building and gather data on the average temperature in the OZ, the rate of airflow the supply temperature to the zone, amount of stratification, normalized airflow to the space, and measures of variation between different locations,” says Webster.
The cart’s onboard computer crunches the numbers in real time, which is what makes it such a leap forward, both as a research tool and as a building management tool. Until now, if a building was monitored at all, it was done so employing relatively large and cumbersome stationary sensors that gathered data; turning that data into usable information took a lot of time, which few building operators have to spare, even if they have the expertise needed to do such analysis.
"We have certain criteria we want the building to meet, and we model that in the software, then we compare the actual measurements to the data. We can see questionable stuff right away and then decide whether to wait and fix it later or tend to it immediately,” says Webster.
Eventually, the Berkeley group is hoping to integrate the monitoring and analysis from commissioning tools such as the cart with the building management system (BMS) so that building operators can monitor their buildings in enough detail and in real time to allow correction of problems right away, and seize opportunities to save energy and money, as they occur.
It is a vision whose time has come, says Arens. If all existing commercial buildings adopted commissioning practices, it would save the energy equivalent of taking ten to twenty million cars off the road.
Could any other achievable practice take such a huge bite out of our national energy debacle? “I can’t think of one,” says Arens.