Planning For Optimal Performance

Feb. 1, 2000
By taking advantage of energy-saving opportunities, schools can meet needs of the future without increasing energy demands.

Because of more stringent indoor air quality standards, and more equipment and technology in schools, educational buildings are requiring more energy. But by implementing certain energy-saving measures, schools can meet educational needs without using more energy, depleting natural resources or adding cost to already-tight budgets.

Changing habits Reducing energy consumption can have significant effects, yet be accomplished at minimal cost. The Alliance to Save Energy has instituted a green schools program that focuses on changing people's behavior in schools. Pilot programs in New York, Pennsylvania and Washington are showing an average savings at each school of $8,700 per year.

Twenty-three schools in the Seattle School District are participating in the green schools program. The schools are all more than 30 years old and do not have the energy-efficient features common in newer buildings. The program trains custodians, teachers and students and focuses on identifying broken equipment, operating equipment more efficiently and tailoring building systems to the school schedule.

"It takes a combined effort of building staff and students to achieve success," says David Broustis, resource conservation specialist for the Seattle School District. Broustis recommends offering incentives to help motivate participants. This can be done in the form of rebates based on a percentage of the actual savings.

In Seattle, each school receives 90 percent of its energy savings to buy equipment and tools; the schools shared $90,000 in rebates last year.

The changes were simple: The kitchen staff turned off the refrigeration units over the summer at one school; another school provided unit heaters for staff working after hours and shut off mechanical systems; custodians performed building surveys to identify leaking fixtures and steam traps; turning off the lights in vending machines saved $15,000 at another school; instead of waiting until 10 p.m. to turn off all the lights, teachers and custodians coordinated their schedules and keyed switches were modified so equipment and lights could be turned off in unoccupied parts of the building at the end of the school day.

Energy-saving ideas The following ideas can provide even more opportunities to conserve energy. Many of the suggestions involve direct digital control (DDC), which defines the computer process and electrical energy operating for the various components of building systems, and energy management control systems (EMCS), which are basically direct digital controls that have logic routines to operate building systems efficiently.

Typical EMCS routines for saving money:

-Timeclock. Within the EMCS is a programmable calendar that schedules when the building will be occupied, including holidays and special weekend events. When the building is occupied, all devices (lighting, heat, etc.) go active. When the building is unoccupied, the building operator can pick the level of turndown.

Use of occupancy sensors is increasing, and can hone energy savings even further. Originally, occupancy sensors were used to control room lights. Now, additional connections are being used to turn the room's HVAC unit off or shut down required ventilation air if the room is unoccupied.

-Temperature setpoints. An EMCS is capable of manipulating setpoints in order to achieve energy savings. Examples of temperature setpoints that are changed anywhere from seasonally to hourly are: room temperature, HVAC-unit supply air and heating water loop temperature.

-Optimal start routine. The EMCS tracks the outside air temperature and the occupied building start time. It starts the morning warmup cycle (bringing the room from unoccupied to occupied temperature setpoint) at the time that will use the least energy.

-Controlling ventilation air. Ventilation air, or outside air, is a big energy user in most heating and air-conditioning systems. A typical classroom may require that half of its supply air be ventilation air regardless of outside air temperature. This leads to significant mechanical heating or cooling of that air in order to keep the room temperate. In large spaces, such as common areas, gymnasiums and multipurpose rooms, using a CO2 sensor to control ventilation air quantities can save energy.

-Maintenance records. EMCS logic can alert building operators when equipment requires service; record service work orders; and keep records of parts lists.

-Real-time energy use. The EMCS can be programmed to turn off equipment when it senses that electrical use in the building is too high. This feature is used to avoid paying demand charges on electrical usage.

-Energy use and tracking. An EMCS can track energy consumption (both electricity and gas), energy-use trends and system operations. System operators can view information at the desktop interface-it is a matter of understanding and using the information.

Equipment selection To save energy through equipment selection, the sky is the limit regarding design concepts. Energy-saving equipment and systems are everywhere, and everyone is jumping on the bandwagon. The energy-efficiency ratings for individually packaged pieces of equipment are increasing all the time. The various elements of energy-efficient systems (variable-air-volume, water-loop heat pumps, gas heat, etc.) are numerous. How these systems are combined depends heavily on building operator preference and local energy costs.

A life-cycle cost analysis is one of many valuable studies during the design phase that combines building operator preference with energy usage. Different HVAC systems (typically three) are modeled on computer software to generate expected energy usage. This output is combined with estimated first costs, periodic maintenance costs and future replacement costs to calculate an expected 25- or 30-year lifetime cost of the system in current dollars.

Building owners are rightly concerned about first costs when initiating a capital expenditure, but may find that a specific system costing more upfront will pay for itself in significantly decreased energy usage.

Saving measures Some energy conservation measures for building operators to consider:

-Capturing leaving heat. The addition of ventilation air, as required by code, to anyspace means that some already heated or cooled air has to leave the space. When these quantities are large, consider adding some kind of heat recovery, such as an air-to-water-to-air transfer via a closed water loop.

-Established system types. Certain systems have a reputation for being energy savers; good examples include variable-air-volume (VAV) systems and heat pumps. VAV systems save energy by slowing down the fan in response to heating and cooling demands. When the rooms need cooling, the fan is at full speed; when the rooms require heat, the fan slows down.

Heat pumps use a refrigeration cycle to generate heat from a tepid source. Water-loop heat pumps that essentially get their heating and cooling from cycling the water loop through the earth are considered the most efficient. In those systems, the only energy used to reject or add heat from the loop is pump energy; there is not a boiler or chiller involved.

-Thermal storage. If the daytime electricity demand charge is an issue, building operators need to shed electrical usage during the day. Ice storage has emerged as a new standard in daytime load-shedding; ice is made during the night, when electrical demand charges are lower, using a chiller. The ice is then used to chill the cold water loop during the day.

-Economizer function. "Economizer" is the capability of the control logic on the air-side system to recognize that the best temperature air for supplying to the room or zone is outside air. The unit mixes some percentage of the return air with this outside air so the unit does not have to heat or cool the incoming air, as it is the optimum temperature already. This function usually comes into play in spring and fall when outside temperatures are more moderate. Typically, local codes require this function when the unit is of a certain size, but the economizer cycle should be considered for inclusion in all air-side system logic.

-Commissioning. While this is not specifically a system type, it is high on the list of ways to save energy in new installations. Commissioning is a process in which a trained professional takes a new system through all the paces before construction is finished. Once all the equipment and systems are in place, the commissioning agent makes sure all the pieces work together as efficiently as possible.

-Ease of maintenance. No matter what system you choose, proper maintenance is necessary for optimum efficiency. To help ensure this, allow easy access to mechanical units, preferably without entering instructional spaces.

Bright ideas Lighting is one of the biggest sources of energy consumption and therefore offers some of the biggest savings potential. With careful design, schools can use all sources of light efficiently and effectively. Minimizing use of the lighting system and designing lighting systems with efficient fixtures to provide appropriate light levels will reduce energy costs.

Classroom, office and corridor fixtures outfitted with lighting fixtures with electronic ballasts and T8 lamps provide substantial energy savings. Electronic ballasts provide cooler operation and prolong lamp life. Schools that have old-style T12 lamps can save approximately 38 percent in energy costs by switching to T8 lamps.

Another source of energy savings is the maximum use of daylight zones. By using photocell sensors and putting lights that are next to windows on a separate zone, lights turn off automatically when enough natural light is available.

Occupancy sensors in classrooms and offices also will decrease energy usage. Occupancy sensors with individual manual controls eliminate the need for dimming ballasts and provide optimum energy savings. A study by U.S. EPA Energy Star,

Building and Green Lights, shows classrooms equipped with occupancy sensors can save up to 61 percent in lighting costs.

Controlling corridors, common areas and exterior lights via the building's EMCS also can provide significant savings. A time clock, photocell or programmable controller can turn lights on or off. Automatic lighting control minimizes the use of lights by turning them off at night and during unoccupied periods.

The rapidly growing Lee's Summit, Mo., School District is planning two new elementary schools. The district has not been satisfied with HVAC systems in elementary schools built within the past five years. Their gas-fired heating/electric cooling rooftop units have had problems with comfort control, indoor air quality, energy consumption and maintenance. The district had chosen the systems primarily for their low first cost, which fit the available capital budget.

To ensure a high level of indoor air quality (IAQ) in the new schools, the district's architect recommended that energy recovery ventilators (ERVs) be used with any HVAC system chosen. ERVs bring in large quantities of fresh air, while recovering up to 80 percent of the energy in the stale air being exhausted from the building.

The district also considered water source heat pump (WSHP) systems for the new facilities, which had a moderate first cost, high energy efficiency and low maintenance costs.

Unfortunately, the district had budgeted the new elementary schools for a rooftop system. The WSHP system coupled with ERVs would cost about $2 more per square foot to install, an amount not covered by available funds. The Missouri Department of Natural Resources provided the solution with its Energy Efficiency Loan Program. The program provides loans to districts at a 2 percent interest rate for any project that can demonstrate at least an eight-year payback based on energy cost savings.

The district architect used a computer program to compare the projected annual energy consumption of the new buildings using the rooftop system and the WSHP system. The WSHP system saved $29,138 a year-a 7.9-year payback on the additional $230,000 cost. The state approved the loan application and will provide funds to the district. The district in turn will repay the loan with savings from its operating budget.

Energy conservation was critical in designing a classroom addition for Needham Elementary School in Durango, Colo. To address this concern, the following design elements were integral:

-Classrooms were arranged with south- and north-facing insulated glazing for easier sunlight control.

-As part of the "connector" between sections of the existing buildings, a light court (or atrium) was created by widening the passage and providing a large window area. This allows passive heating into an area that can accept a swing in temperatures without making the space unusable. A fan-coil unit takes this heated air and distributes it to the adjacent entrance area in the winter, and exhausts the warm air when it is warm outside.

-The windows at the south-facing classroom walls were large; a roof overhang was provided; and a light shelf (exterior and interior) was incorporated into the fenestration to control and distribute natural lighting into the classroom. The classroom ceilings were placed higher than normal to allow light to penetrate deeper into the rooms.

-To provide additional natural lighting in interior spaces, large corridor skylights serve the circulation spaces (where control is not critical). The interior portion of the classroom ceiling was raised to the maximum height, allowing the classroom windows to "borrow" the natural lighting from the skylighted corridors.

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