How can commercial office buildings be made more energy-efficient? According to former ASHRAE president Gordon Holness, the answer starts with reducing “loads.” He suggests referring to ASHRAE Standard 100, Energy Efficiency in Existing Buildings, which lists energy efficiency measures that can be taken to lower overall energy use. For example:
· Building Envelope – Insulation, airtightness, infiltration, and so on.
· Water systems – hot water heaters, conservation, and so on.
· Energy Generating Systems – Boilers, chillers, pumps, and so on.
· Refrigeration Systems – Reducing loads, cleaning coils, and so on.
· Lighting Systems – Source and occupancy control.
· HVAC Systems – outside air ventilation rates, air distribution, temperature, and humidity control, and so on.
Before taking measures to conserve energy, you must understand how it is being wasted. Holness illustrates this with an anecdote.
“I recall a professor’s challenge to a student class at a technical college to improve the efficiency of a steam heating system at the student dormitory. Students were addressing the vacuum condensate returns and other functions, until one student pointed across the snow-covered campus at all the open windows in that very dormitory building, and said –‘there is your problem.’”
The heat output from the steam radiators was not properly controlled, so people coped with the overheating by using the simplest means at their disposal — opening the windows instead of reducing the heat.
Identifying the problem areas is just the beginning.
“Experience has shown us that even the best designed and energy-efficient buildings can deteriorate in performance by as much as 40% in just a three-year period," says Holness, “unless there are energy management plans and operation and maintenance plans that are implemented and adhered to.”
Most building codes are prescriptive, they tell you the “what” and “how” of installing building elements, for example, “use double- rather than single- glazed windows.” ANSI/ASHRAE/IES Standard 100-2015, however, is performance-based. “It doesn’t tell the building owner how to design or modify his building,” said Holness, but rather “what total energy use intensity target to achieve.”
ASHRAE 100 primarily tells the owner three things:
1. How to do an audit of the building to find out how much energy is being used in total and by system.
2. How to maintain the building, so once it’s modified it can continue be operated to sustain the intended performance.
3. What the energy target should be for a specific building type, climate zone, and number of hours occupied per week.
In addition, there are “Informative Annexes” that give detailed suggestions for achieving the energy-saving goals.
Section 5 of the Standard lays out the steps for establishing an energy management plan. The most important, is for the building owner to appoint an energy manager tasked with originating and overseeing the plan. After developing it, the manager should create an accounting system to record actual measured energy usage.
The goals for buildings are in terms of net energy-use intensity (EUI). This is defined as the net energy used by a building, from actual metered data, over the course of a year divided by its gross floor area. The actual measured EUI can then be compared to the plan’s targets, which are derived from the DOE EIA Commercial Building Energy Consumption Survey (CBECS) and Residential Energy Consumption Survey (RECS) data. The Standard has tables with extensive listings of desirable target EUIs for different types and uses of buildings in different climate zones. There is also a list of correction factors based on number of weekly hours occupied for each building type.
An energy management plan should detail energy efficiency measures (EEMs) aimed at reaching the target. An EEM is defined as “an action taken in the operation or equipment in a building that reduces the energy use of the building without negative impact within the building.” EEMs can be evaluated on a Simple Payback or Life Cycle Cost basis. For each EEM, there should be an operation and maintenance program, an implementation plan that includes initial commissioning, a training program for staff, ongoing commissioning plans, and a method to inform occupants about the benefits of efficient energy use.
Informative Annexes D and E of Standard 100 provide guidelines for operation and management (O&M) and EEMs respectively. These are arranged according to building systems such as, building envelope; heating, ventilating, and air-conditioning (HVAC); and lighting systems. The following are examples of EEMs identified in the Standard:
Operation and management measures include:
· At least every three years, inspect elements such as sealing of exterior joints and penetrations by utility services, to reduce air infiltration/exfiltration.
· Replace broken or missing windows.
· Repair or replace exterior door weather stripping as needed.
Energy efficiency measures include:
· Add exterior insulation to walls. Large wall surfaces are a major source of heat loss, especially at thermal bridges created where floors and internal walls are anchored in the exterior wall.
· Use “cool roof” (high-reflectance roofing material) with reroofing projects.
· Use draft seals on doors.
· Use self-closing doors.
Operation and management measures include:
· Prominently display a list of operating parameters such as temperature setpoint, pressure, and operating schedule for each piece of equipment.
· Display and maintain a service log for each piece of equipment.
· Analyze occupant complaints and how these relate to system operation.
· Maintain system schedules to account for whether or not a zone is occupied.
o Unoccupied: Automatic shutdown, setup, and setback modes.
o Start mode: Warm-up, , and optimum start.
Energy efficiency measures include:
· Convert a constant-air-volume system (CAV) into a variable-air-volume (VAV) system with variable speed drives (VFDs) on fan motors.
· Control VAV system VFD speed based on the static pressure needs in the system. Reset the static pressure setpoint dynamically, as low as is practical to meet the zone setpoints.
· Identify if there are any rogue zones that determine the cooling or heating demand on the entire system.
· Reduce minimum flow settings in VAV terminals as low as is practical to meet ventilation requirements.
· Use night setback, or turn off HVAC equipment when the building is unoccupied.
· Install occupancy sensors with VAV systems and the system controls to reduce cooling/heating of unoccupied space.
· Schedule off-hour meetings in a location that does not require HVAC in the entire facility.
· Retrofit multiple-zone VAV systems with Direct Digital Controls (DDC) at the zone level, and implement supply air duct pressure reset to reduce supply air duct pressure until at least one zone damper is nearly wide open.
· Install programmable zone thermostats with appropriate deadbands.
Operation and management measures include:
· Review recorded trouble calls and occupant complaints and analyze how these relate to control operation.
· Check all setpoints.
· Check whether controls are overridden or in manual operation and make corrections as necessary.
· Check gauges, sensors, and switches.
· Check system’s backup batteries.
· For DDC, review applications programs and verify the system is working in accordance with the design sequence of operations.
ASHRAE 100 Paragraph 126.96.36.199.d specifies ongoing commissioning as a component of the Energy Management Plan. ASHRAE Standard 202-2013 covers “The Commissioning Process for Building Systems”. Lawrence Berkeley National Laboratory (LBNL) has published a guide to commissioning buildings.
“Commissioning ensures that a building’s operation is optimized. That is, it operates it least as well, if not better, than the designer intended… Commissioning is generally applicable to new buildings; however, commissioning goals are the same for new and existing buildings: to ensure that the building is performing efficiently,” [LBNL p.9] “Depending on the age of the building, existing building commissioning (EBCx) can often resolve problems that occurred during design or construction, or address performance problems that have developed during building operations.” [LBNL p. 13]
Commissioning requires dynamic measurements of system behavior under actual operating conditions. Control settings can then be reset in order to optimize system behavior as confirmed by the measurements. An important step in commissioning is benchmarking – measuring and recording past performance and energy use trends and comparing them to post-commissioning metrics.
Benchmarking can also be used to compare a building’s performance to its peers or to established norms, for example by using the Energy Star Portfolio Manager API, which is a useful tool for estimating the return on investment for energy-reduction. Lawrence Berkeley National Laboratory has developed an energy retrofit toolkit, Commercial Building Energy Saver (CBES), which uses benchmarking to help users evaluate retrofit alternatives.
The toolkit provides three levels of retrofit analysis, starting with no- or low-cost improvement. It analyzes building energy performance and estimates post-retrofit performance to evaluate energy savings economic payback of various retrofit measures. The toolkit includes a set of 100 energy conservation measures (ECMs). These include pre-simulated results of about 10 million Energy-Plus simulations, run on clusters, in the US Department of Energy’s National Energy Research Scientific Computing Center (NERSC).
Energy Use in Older Buildings
Larger buildings require larger amounts of energy, as do older buildings. In order to learn first-hand what can be done to save energy in these types of buildings, David Arnold, Ph.D. [ASHRAE J., Jan. 2015, pp. 52–59], visited three Chicago skyscrapers that were built between 1958 and 1969. He visited them in 2001 – 2003 and returned in 2012 to examine the results of their energy-reduction efforts. The Inland Steel Building illustrates what can and can’t be done when facing real-world constraints.
Completed in 1958, the 19-story Inland Steel Building was the first skyscraper built in the Chicago Loop after the 1930 depression. Its design is unusual in several ways, all of which are aimed at providing a wide-open interior space for flexible office layouts. For example, all of the building supports are steel columns around its exterior perimeter so that the office floors are unobstructed. Another unique feature is that services, including elevators and washrooms, are in a separate tower.
In 2003 the original plant was still in service, including boilers, chillers, cooling towers, air handling plant, and pneumatic controls. A new owner announced in 2007, plans to retrofit the building in order to achieve LEED platinum certification.
They proposed to add a secondary glass wall inside of the glass outer wall, and use programmable blinds in the space between them for climate control. In addition, they would install automatic daylighting controls and variable speed drives on fan motors. Single pass outdoor air supplies and integrated chilled beams would replace the original energy-inefficient dual duct system.
Two circumstances brought these plans to a halt. This is a landmarked building and was not able to win approval from the Commission on Chicago Landmarks because the changes would alter the appearance of the building. The project was then brought to a complete halt by the recession of 2008. By 2012, the building owners were once again investing in energy-saving renovations, but taking a more modest approach. This has included a new chiller, digital controls to replace the old pneumatic system, and the installation of a VAV system to replace the inefficient CAV dual duct system. Their application for LEED certification is now in progress.
“The measures in all three buildings have reduced energy use to a greater or lesser extent but in addition to reducing energy use, interventions of any degree need to be cost-effective if building owners are going to invest in improvements. This is why the low hanging fruit, the measures most likely to give the biggest return on investment have been applied in all three buildings. For example, converting CAV systems to VAV, installing digital control, and fitting pumps with inverters," says Arnold.