Designing a building holistically, and making sure that its components and systems work together according to design intent, can pay big dividends in energy savings and occupant satisfaction, according to a study by scientists at the Lawrence Berkeley National Laboratory of the performance of The New York Times Building in New York City.
Measured results from the post-occupancy evaluation showed a 24 percent reduction in annual electricity use and 51 percent reduction in heating energy use, compared to expectations from a design that just met the prescriptive energy-efficiency code in effect at the time of construction (ASHRAE 90.1-2001), and a 25 percent reduction in peak electric demand. In addition, a significant fraction of occupants indicated a high level of satisfaction with the overall building and its design features.
The Times Company’s investment in advanced energy-efficiency technologies is estimated to yield a 12 percent rate of return on their initial investment.
Located near Times Square in New York, the 52-story building has 1.5 million square feet of commercial office space, and the Times Company has occupied floors two through 21 since the building’s opening in 2007. A Berkeley Lab research team from its Environmental Energy Technologies Division (EETD) began working with the Times Company in 2003 to design, evaluate and specify an integrated solution with energy-efficient lighting and automated shading systems for the windows in a full-scale mockup at a nearby Times Company site in Queens.
The goal of the 18-month collaboration at the mockup, supported by The New York State Energy Research and Development Authority, was to determine whether the advanced technologies could provide comfortable working conditions for the building occupants while maximizing energy savings. The test results in the mockup led to new performance specifications, a positive response from the manufacturing community, and ultimately the incorporation of these high-performance lighting, shading and HVAC systems into the final building design.
The completed building was occupied in 2007. Since then, and because of the innovations incorporated into the design, the Times Building has attracted a lot of attention in the architectural and energy efficiency community. The key unanswered question for this building, and most buildings, is: how is it performing?
Members of the Berkeley Lab team and collaborators from the University of California, Berkeley’s Center for the Built Environment, who assisted with the commissioning of the innovative HVAC system, returned to the Times Building in 2011 and 2012 as part of their participation in the US Department of Energy Commercial Buildings Partnership (CBP) program to conduct a monitored evaluation of three installed energy efficiency measures — dimmable lighting, automated interior roller shades, and the underfloor air distribution system (UFAD).
CBP aims to demonstrate validated, cost-effective low-energy technologies and systems that can be widely replicated nationwide in both new construction and retrofit projects in the commercial buildings market.
In an occupied building for technical and practical reasons, the energy use of each system of interest cannot always be directly measured. To evaluate this building, the research team measured energy use and other data from the automated shading system, dimmable lighting system, and underfloor air distribution system on a typical floor in the building and gathered other data throughout the building. The team used the measured data to calibrate the EnergyPlus model then used the model to predict annual energy savings.
EnergyPlus is building simulation software developed by Berkeley Lab.
The team also used occupant survey data gathered by Sustainable Energy Partnerships, which was conducted for another report, to evaluate the success of the building in maintaining comfortable working conditions.
The building uses automatically dimmable lighting controls together with an automated shading system to minimize energy use and maximize occupant comfort. Occupancy-based controls turn off light fixtures when occupants leave the area after an eight-minute delay. The digitally addressable, dimmable lighting system enables staff to tune the lighting to their preferred lighting levels, called setpoint tuning. Whenever the daylight is present in the perimeter areas, the lighting control system dims or turns off the overhead lights automatically.
Annual lighting energy use savings from the lighting control strategies (occupancy, setpoint tuning and daylighting) was 56 percent (3.94 kWh/ft2-yr) across a 40-foot deep perimeter zone compared to a code-compliant building with only the standard scheduled lighting controls.
The Sustainable Energy Partnerships survey results report that 57 percent of the occupants responded with greater than neutral satisfaction with the automatic lighting controls (occupancy sensors, dimming in response to daylight conditions). Some 78 percent of the occupants were very satisfied with the overall quality of the lighting in their workspace from daylight and the overhead lighting system (average rating was 5.53 on a seven-point scale where a value of four is neutral).
The automated motorized shading system regulates sunlight entering through the windows to reduce cooling and can reduce glare from the sky. Its control algorithm is programmed to maximize incoming natural light but minimize the negative effects of glare and direct sunlight on occupant comfort.
The system is also designed so that occupants can override the automatic system and raise or lower the shades if they aren’t satisfied with their environmental conditions.
The automated shading enabled lighting and cooling energy use reductions, and reductions in peak electric demand. Energy savings due to the shading system alone could not be measured directly, but the reduction in annual site energy use due to the combination of the three systems was estimated to be 26 percent (10.17 kBtu/ft2-yr) across a typical tower floor compared to a code-compliant building.
Occupants on all floors overrode the automated shading system infrequently. For motors overridden at least once, 80 percent of these motors were overridden an average of 18 times per year (1.5 percent of the year) for an average total time of 38 hours per year during primary work hours.
Forty-one percent of the occupants responded with slightly greater than neutral satisfaction with the automatic window shades, with an average rating on all 20 floors of 4.12 on a seven-point scale.
An underfloor air distribution (UFAD) system distributes air from the plenum under the floor to ventilate and condition the space above. A UFAD helps save air conditioning energy by maintaining comfortable conditions in the lower occupied zone of the space, while allowing warmer and less comfortable conditions to exist in the higher space elevations. The air conditioning setpoint can be higher — therefore lowering the airflow and reducing cooling — while still allowing the average conditions in the occupied zone to remain comfortable.
Temperature measurements in the interior zone showed a reasonable amount of air stratification (2-3 degree F difference between standing head height (67 inches) and ankle height (4 inches) in the occupied zone — an indicator of good UFAD cooling performance
After some fine-tuning of the systems for a year after occupancy, Patrick Whelan, the Times Company’s facilities director, said that maintenance and operations needs for the three systems were surprisingly minimal given the advanced technology incorporated into the three systems.
This study confirms that office buildings in an urban environment can deliver measured energy performance that substantially beats the energy codes with a combination of smart design, efficient technology and properly integrated building systems, carried from design to construction and commissioning and into operations.
The lesson for replicating the success of this building on a large scale is that the technologies and systems solutions are available, but that is essential to pay attention to details such as procurement of building equipment, and verifying the proper performance of the equipment after it is installed.
Projections published by Berkeley Lab in January said spending on energy efficiency programs funded by electric and natural gas utility customers will double by 2025 to about $9.5 billion per year.
Photo Credit: The New York Times Company