Much has been written about energy efficiency and sustainability in relation to new-construction projects. But what about existing facilities? Are there significant efficiency gains to be realized?
With the latest revision of the U.S. Green Building Council's Leadership in Energy and Environmental Design for Existing Buildings (LEED-EB) Green Building Rating System, we have an answer, and that answer is yes. LEED-EB focuses on the issues most important to building owners: reduced energy and water consumption and improved operational efficiency. Its scope includes performance-based design, retrofit, commissioning, operation, and maintenance over the life of a facility.
This article will discuss investment trends related to energy efficiency, review proven cost-effective energy-saving measures for existing facilities, and provide real-world examples of successful retrofits.
An online survey of 1,249 North American executives and managers responsible for energy-management decisions commissioned by Johnson Controls and conducted in March 2007 revealed that:
Seventy-nine percent believed energy prices would rise significantly over the next year, with an average increase of 13.3 percent expected.
Fifty-seven percent expected to make energy-efficiency investments over the next year, with an average of 8 percent of their capital budget used.
Eighty percent expected to fund energy-efficiency improvements through their operating budget, with an average of 6 percent of their budget used.
Forty-eight percent of the respondents said environmental responsibility motivated their investment decisions at least as much as cost reduction did. Nonetheless, their organizations largely had not relaxed their return-on-investment requirements for energy-efficiency measures.
The organizations of 64 percent of the respondents had a maximum payback period between two and five years. The organizations of only 16 percent of the respondents would tolerate a payback period of six years or more. Overall, only 18 percent of those surveyed said their organization allowed a longer payback period than it did five years ago; however, 26 percent of larger enterprises (those with 500,000 sq ft or more) were tolerating a longer payback period. For organizations of all sizes, the payback period of about 45 percent had not changed over the previous five years.
It appears that economics prevail in investment decisions, with environmental responsibility almost on par. So, how do we best work with this investment mindset and help owners and managers optimize energy efficiency in existing buildings? The answer is with a combination of proven energy-efficiency strategies and solutions enhanced and enabled by new and available technology.
PROVEN ENERGY-SAVING MEASURES
An energy audit is the starting point and most powerful tool we have in creating effective energy-efficiency solutions. Technology, however, has vastly improved the ability of energy engineers to collect and analyze data. Hand-held computers and compact digital cameras, for example, have improved the speed and accuracy of gathering, cataloguing, and interpreting building-system and energy-usage inputs. In multibuilding and multi-location audits, electronic files and photographs can be shared easily and quickly, resulting in shorter response times and more comprehensive energy-efficiency recommendations.
While specific recommendations vary based on building type, use, and location; local utility-rate structures; and the related objectives and budgets of the building owner and management staff, there are areas in which energy-efficiency improvements are likely to be found in existing buildings, including:
Lighting typically accounts for 30 percent of energy use in non-residential buildings. A lighting retrofit, including the use of higher-efficiency ballasts and/or lamps, can directly reduce the energy used for lighting and indirectly reduce the demand for air-conditioning.
- Demand-response controls
Especially in capacity-constrained areas, it is critical to evaluate utility-rate structures and have the ability to reduce building electrical demand by turning off equipment or systems for defined periods of time. For example, with Internet Protocol-addressable ballasts, lighting could be reduced by 50 percent in selected areas during bright daylight hours.
- Premium-efficiency motors
Installing new high-efficiency motors on pumps, fans, and other components can yield substantial energy savings with a relatively short payback, as well as increase reliability and reduce maintenance.
- Chilled- and condenser-water temperature
Chillers typically spend less than 1 percent of their operating hours at design conditions; the other 99-plus percent are spent at off-design conditions coinciding with milder outdoor temperatures and/or lower humidity levels. Taking full advantage of these conditions is one way to reduce energy consumption.
- Variable-speed drives (VSDs)
VSDs continuously and precisely match motor speed to the demand on a motor. With a large-tonnage chiller system, a VSD retrofit can reduce annual energy consumption by 30 percent. (See “Chiller-Driveline Retrofits” sidebar.)
- Outdated-equipment replacement
Dramatic efficiency gains have been made in all categories of HVAC equipment. In many cases, other energy-efficiency measures (e.g., new lighting systems) or changes in building-use patterns have reduced cooling or heating load, meaning new equipment can be smaller in capacity (or staged to meet demand more efficiently).
- Variable air volume (VAV)
Constant-volume air distribution, especially at high static pressure, is a known energy waster. Converting to a VAV system, whether overhead or underfloor, can reduce energy consumption by more closely matching airflow to temperature set points at, in many cases, lower static pressure.
- Solar power
A power-purchase agreement (PPA) is a long-term agreement to buy power from a company that produces electricity. With a solar PPA, a provider builds a solar-energy facility on a customer's site and operates and maintains it for a defined period of time (usually, 15 years or more). Generally, it ensures energy rates that are lower and less volatile than those of the local utility. What's more, operating and maintenance costs are covered, with the building owner paying for only the electricity that is consumed.
OPPORTUNITIES WITH NEW TECHNOLOGY
For energy performance truly to be optimized, proven energy-saving measures need to be augmented with newer technology. Two technologies that apply well to existing buildings are:
With a modern, integrated building-management/automation system, continuous optimization is possible. Such a system knows the set points and tolerances of all equipment, which it continuously monitors, alerting operators of problems. This allows operators to continuously fine-tune a building, realizing extra energy savings.
On-site renewable energy
Combining a renewable energy source, such as biomass, geothermal, solar, or wind power, with an overall energy-efficiency strategy can be an elegant solution to high energy costs, uncertainty of energy supply, and the need to reduce greenhouse-gas emissions. Consider, for example, a biomass-gasification plant covering 85 percent of a university's energy consumption (see “Biomass-Gasification Plant” sidebar) or a geothermal heat pump and an in-floor radiant heating and cooling system in a “net-zero”-energy building (see “Net-Zero-Energy Building” sidebar). Creative solutions such as these can be implemented with available technology. Plus, there are organizations capable of taking responsibility for the design, engineering, installation, commissioning, operation, and maintenance of renewable-energy solutions.
Equipping an older chiller with a new compressor-motor driveline while retaining the heat-exchanger shells is uncommon, but merits consideration under any of the following circumstances:
- Chiller capacity exceeds the maximum building load
Downsizing a compressor driveline to match chiller capacity to actual load would result in more-efficient operation. If retained, the now-oversized heat-exchanger shells would provide greater heat-transfer-surface area, further increasing chiller efficiency.
- The chiller is aged, and maintenance costs are escalating
Because of the number of maintenance-intensive parts involved, a new compressor-drive system can upgrade a chiller plant significantly — and at less cost than a completely new chiller system. For example, some new compressors eliminate oil management from chiller operation. Additionally, the new modern control center that generally is part of a driveline retrofit may include a variable-speed drive.
- The equipment room is not easily accessible
Removing an older chiller from a sub-basement or other difficult location may require extensive work, including partial building demolition and reconstruction. New driveline components usually can be delivered through standard doorways.
At the University of South Carolina, where energy is one of the largest annual budget items, the escalating price of natural gas had university planners concerned. From that concern came plans to develop a world-class biomass-gasification cogeneration plant that would furnish steam and electricity fueled by local wood-product waste.
The plant was one of 18 projects recommended as part of an audit of energy- and water-saving opportunities on campus. After the university reviewed and prioritized the opportunities, the plant construction was bundled with the other priority projects into a performance contract. The $19 million investment in the biomass project will be paid back over 14 years.
The integrated gasification-based system will reduce the university's use of natural gas by almost 390,000 dekatherms and produce 302 million lb of steam a year. It not only will provide energy, it will reduce harmful greenhouse-gas emissions. Another benefit of the project is that it will provide the university's engineering department with a hands-on laboratory for students to study and optimize this alternative fuel technology.
When Integrated Design Associates (IDeAs) Inc., a consultancy providing electrical-engineering and lighting-design services, bought a 7,200-sq-ft former bank building in San Jose, Calif., to serve as its new headquarters, David Kaneda, principal, saw an opportunity to bring the concept of a zero-energy building to life.
“We felt we should walk the talk, not just talk,” Kaneda said.
The goal was to transform the 1960s-era, windowless concrete structure into a highly efficient and comfortable building using a full complement of sustainable-design techniques and technologies. The result is a building that:
Uses renewable energy to meet 100 percent of its energy requirements.
Burns no fossil fuels.
Produces zero net greenhouse-gas emissions.
The building's HVAC system was designed to maximize performance, energy efficiency, and indoor-air quality while keeping construction costs comparable to those of more traditional designs. The energy efficiency of the HVAC system and building envelope is estimated to be 40-percent below 2005 California Title 24 requirements.
The HVAC design incorporates a geothermal heat pump, which takes advantage of the fact that the temperature below ground remains constant year-round — about 50°F in this case. Water flows through pipes laid under an open-landscape area and enters the building, where a heat exchanger collects heat from the water during winter and uses the cooling effect of the water during summer. A radiant floor system with cross-linked-polyethylene (PEX) counterflow tubing uses the water to convey heating and cooling. The system uses less energy to provide the same level of comfort as traditional forced-air systems because of the temperature variance between the occupant and the floor. Radiant systems typically can use higher-temperature water to provide effective cooling and lower-temperature water to provide effective heating, meaning equipment operates at higher efficiency levels.
“Since the system has been operating, it has already provided a very cool and comfortable environment during some very hot weather,” Kaneda said. “It is a very efficient system that will help us meet our net-zero-energy target.”
A building-management system accurately controls flow rates and slab temperature to enable maximum performance using the least energy. Pumps are kept at their lowest demand speed using power-inverter technology. Floor condensation is monitored; if needed, dehumidification is provided by the air handler, which uses chilled water and condenser water for temperature control via a pair of dual coils.
The building receives its energy from a photovoltaic system, the panels of which are part of the single-ply-membrane roof. The electrical system is tied into the grid, drawing power at night and sending excess energy back to the grid during the day. The result is “net-zero” energy use.
To reduce the amount of energy used for lighting and to take advantage of available daylight, Kaneda's team added windows and skylights. High-efficiency windows block infrared and ultraviolet light, which helps to keep the office cool. South-facing windows are shaded by an overhang, while east-facing windows incorporate electrochromic window glazing. Low-energy fluorescent bulbs used throughout the building either are controlled by occupancy sensors or use dimming ballasts. Sensors turn off select lights when daylight is sufficient.
Energy conservation extends to computers and office equipment as well. Flat-screen liquid-crystal-display monitors are used in place of traditional monitors, which use 50-percent more energy, while laptop computers are used in place of desktop computers where possible. Office equipment is integrated with the building security system, automatically shutting down when the security system is armed.
“All of the technologies we are using are readily available,” Kaneda said. “Some of them are more expensive from a first-cost standpoint, but the reduction in energy use will pay long-term dividends. And, it's the right thing to do from the standpoint of reducing our impact on the environment.”
MORE ABOUT THE MECHANICAL SYSTEMS
Additional facts concerning the IDeAs headquarters building's mechanical systems:
High pumping efficiencies are achieved with a low-pressure-drop piping system coupled with open-port ball-type control valves.
The electric water-source heat pump has a cooling energy-efficiency ratio of more than 19.
The PEX piping is buried 6-ft and 4-ft deep.
When outside air is too cold or too hot for the operable windows and doors installed throughout the building to be utilized, a dedicated outside-air handler with high-performance filtration and constant temperature control provides the required ventilation.
Global and regional climate-change policy will continue to drive energy efficiency. Green-building practices can be applied to optimize all types of existing facilities. Achieving continuous optimization requires a combination of proven energy-efficiency strategies and new technology, including monitoring and control capabilities and clean energy via on-site renewable-energy sources. The technology is readily available, and the improvements can pay for themselves. Performance contracting is an effective approach, as it can help achieve the scale necessary to address climate change while offering a proven model for financing significant energy-saving projects.
For past HPAC Engineering feature articles, visit www.hpac.com.
David Clark is vice president of North American systems sales for Johnson Controls Inc. He has more than 20 years of building-automation experience.