Managing Energy Use in Commercial BuildingsEd Brown | October 13, 2016
Engineers often worry about the energy used in commercial buildings. Topping the list of reasons why is that buildings “account for 36% of all U.S. electrical energy consumption,” and 21% of all primary energy. On average, 30% of that building energy is wasted.
Two main strategies exist for reducing both the total energy consumption and the waste. The obvious is to switch to energy-efficient devices such as LED lighting and cooling systems that use natural evaporation rather than compressors. A second strategy is to install programmable building control systems that ensure, for example, that lights don’t remain on in an unoccupied room.
But the benefits of energy efficiency in buildings can be slow in coming. In a 2010 speech, then-ASHRAE president Gordon Holness pointed out that “75 – 85%” of all buildings in existence would probably remain in use in 2030. Even if every building constructed from now on was a net-zero energy user, the “impact on our total environment would be small.”
A greater impact on total energy demand may come instead from improving existing buildings. One of the most cost-effective ways of doing that is to install devices that control systems that consume significant amounts of energy. The question then, is which systems? According to a report by the Alliance to Save Energy, two of the primary energy uses in U.S. commercial buildings are lighting and heating, ventilation, air conditioning and refrigeration (HVAC&R).
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Lighting uses about 20% of the electricity in a typical commercial building. Meanwhile, HVAC&R consumes about 37% of the primary energy and 34% of the electricity. The rest of the electricity is used by miscellaneous loads such as computers, personal lighting, heaters, and coolers.
Controlling Building Systems
Programmable infrastructure controls began emerging in the late 1970s and rapidly grew in sophistication and capability, said Holness in a recent interview. Today, wireless digital controls that can be easily and economically applied for programming systems such as lighting and HVAC are available for commercial buildings.
The most basic controllers can be programmed for time of day and day of the week. In this way, lighting can be automatically turned off at night and on weekends. Similarly, programmable thermostats can be set for different temperature levels at different time periods. Having basic controllers like these in place offers a starting point for installing more sophisticated systems.
A lighting controller with sensor inputs, for example, could be much more effective than a simple timer-based system. An occupancy sensor then could allow lights to be on only when someone is in the room, regardless of time or day. More complex control can be achieved by using dimmers and light level sensors so that the balance between daylight and artificial lighting can adjust to maintain constant illumination.
Beyond that, “multiscene” controllers allow two or more predefined lighting patterns within a given space. Wireless control, available from some manufacturers, eliminates the expense of additional wiring. With the open-source lighting protocol known as DALI, every lighting device has a unique address. This enables more targeted control, based either on distributed sensors or a programmable menu, so that lighting intensities can be varied within a single room.
Automatic control of HVAC is often more complicated than lighting, but is still achievable. Commercial buildings typically use circulating air for these systems. The temperature in different zones is controlled by blowers and motorized dampers. Some of the most flexible systems use variable frequency drives (VFDs) for blower and damper motors, which are operated by variable air volume (VAV) controllers. Using the appropriate sensors, these can modulate the flow of constant-temperature air to optimize temperature, humidity, and air quality.
In practice, these systems interact with each other. The heat from lighting, for example, affects the HVAC system and both are impacted by solar exposure and occupancy. These interactions must be taken into account when programming the systems. It is therefore most productive to treat the building as an integrated system. (Read a report from the Alliance to Save Energy on systems efficiency.)
Integrated control of building systems generally has been tied to proprietary protocols. But this has limited the ability to create networks, since buildings generally use a mix of devices from different manufacturers. Open-source protocols, such as ASHRAE’s BACnet, have been developed to address that problem. The protocol can be used to control HVAC&R systems, but also may be extended to other building systems, such as lighting, access control, and life safety as part of a building automation system (BAS).
Networking lighting controls is currently attracting attention due to the development of LED lighting that is capable of general illumination. The light output of LEDs is relatively easy to control and therefore simpler to integrate into networks. (Read “LEDs Get Smart with the IoT.”)
Key to developing a BAS is the use of direct digital controllers (DDC) that have embedded microprocessors and which can provide each device with a unique address.
The Internet of Things (IoT) offers a way of establishing direct communication between devices in a network, even down to the level of smart sensors. One benefit of IoT is that it provides real-time information about systems. This data is valuable for understanding trends, reacting to impending problems, and optimizing system performance. The information also can interface with the Internet so that it can provide data and a means of control from remote computers and mobile devices.
Next on the horizon may be machine learning, which offers a vision of building systems that can optimize themselves without the need for human intervention.
The People Factor
But even the best automated building system will not improve efficiency if people are not considered as a critical component of the feedback loop.
For example, a system can be rendered ineffective if someone changes a setting without considering the system design parameters. Gordon Holness, for example, recalls a hospital that was designed with a sophisticated energy management system. For the first year of its operation it achieved its energy use target. Within three years, however, energy use went up 35%. It turned out that a group of doctors in one diagnostic area wanted to work an additional shift. They reset the controls and turned on the lights and HVAC systems not only for their area, but for a much larger portion of the building. When the need for the additional shifts ended, the controls were never reset.
Michael A. Anthony, PE, senior manager of Infrastructure Standards Strategy at the University of Michigan, in an interview, speaks of an unspoken rule for programming building systems, what he refers to as the “Third Rail of Energy Conservation.” His own experience designing branch circuit wiring modifications for office space tells him that the temperature comfort range for men and women differs.
“You could probably take a large chunk out of your energy bill if you get men and women to live within a wider temperature range,” he says. So, for example, if they could learn to be comfortable within a 10-degree temperature range instead of a 5-degree range, energy consumption probably could be reduced by a great deal, he says. Additional savings also could come from reductions in construction material and labor costs spent on providing electrical power for personal space heating and cooling to customize the temperature of a workspace.
“Sometimes a sudden change in office temperature on an entire floor can be traced to misoperation of above-plenum smoke and fire dampers,” says Anthony.
One method of improving energy performance is by including people in the loop in a constructive way. An article “Improving Energy Performance in NYC Buildings,” published in the August 2012 issue of the ASHRAE Journal, discusses the use of dashboard displays for real-time energy use. In some cases these displays have motivated the building engineering staff to “tweak operation still further,” the article’s authors say. “We have observed that some operating staff manually change VFDs or change setpoints to lower peak demand based on the dashboard display.”
According to Holness, large-scale plasma TVs are being used in some places in Europe to display real-time energy use broken down by building zone. “People become aware of energy use, get interested in that and begin to wonder what’s happening and why, and then begin to try to change behavior.”
There’s plenty of optimistic talk about the great future for IoT (and machine learning) but conversations with industry veterans such as Holness and Armstrong highlight some difficulties when it comes to actually implementing systems.
According to Holness, one problem is that for these systems to do what was intended, adequate training must be provided for building operators, and systems must be properly commissioned and maintained.
Says Holness, “A major new driver and opportunity for saving energy in commercial buildings is ASHRAE Standard 100 Energy Efficiency in Existing Buildings.” Re-written and published in early 2015, the standard sets specific energy targets by building type, climate zone, and occupancy.
For example a bank building in New York City that operates 12 hours a day would have an energy target of 83 kBtu/ft2.yr. The standard includes detailed operation and maintenance requirements and identifies more than 300 energy efficiency measures (including building automation and control systems) that could be applied on a return on investment (ROI) or life cycle cost basis. The standard is written in code language for adoption by authorities having jurisdiction. “On an aggregate basis, the standard would save 30% of energy used by existing buildings,” Holness says.
When considering sophisticated building systems, the tendency is to think of high-rise buildings. But most commercial buildings in the U.S. are less than 25,000 square feet in size. And even the largest buildings have multiple subdivided units. Those configurations requires a “whole different level of sophistication,” says Holness. “You need systems and equipment that are responsive to those smaller modules.” One way to address that is to look at buildings as a collection of zones, each with individual modular control of its environment.
That presents its own problems. For example, for HVAC, it is most efficient to dynamically set the pressure to meet the lowest requirements of a zone. But if occupants of one zone complain that they are not getting enough air, the operator will change the zone pressure setpoint and the whole system receives a higher flow rate than what was intended.
Anthony talks about some manufacturers using their presence on energy conservation consensus standards committees to propose more sensing devices (such as temperature, carbon-dioxide and air flow sensors) that may contribute little to improving energy conservation. Instead, these devices may add another layer of wiring, firmware, and life cycle maintenance cost. Compounding that, says Anthony, much of his work on standards committees involves halting amendments proposed by manufacturers seeking to “make a market” for devices with little if any technical basis.
Economic gains may result from reducing energy costs by programming building systems. In addition to reducing total usage, economic benefits can be achieved by balancing the timing of loads in order to reduce peak demand. Because managing peak demand can be a challenge for utilities, a charge typically is imposed for the highest usage over a 15-minute period in addition to total consumption.
While potential savings may be had by cutting energy costs, one question is the length of time it takes to recoup investments in equipment and labor. At present, falling energy prices are extending the ROI time span, making investment in building systems a harder sell. There may be, however gains to be achieved in addition to savings on energy.
According to the U.S. Green Council, buildings with improved environmental conditions are better able to attract and retain workers and may increase productivity.
And according to High Performance Buildings Magazine, not only are energy costs lower, but total lifecycle costs are reduced by energy efficiency measures. What’s more, the median value of “green” buildings can be as much as 7% higher than traditional buildings.
Thus, building owners and engineers who automate building systems often can save money on energy, attract tenants, help utilities provide more reliable energy, and improve the environment, a potentially winning combination.