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Routes to Energy Savings
Programs to reduce energy costs have greatly evolved from those of the 1970s that stressed turning loads off and setting back thermostats. While it is still important to limit equipment and system operation to only those times when they are needed, and to see that space temperatures are matched to the needs of the occupants, today’s energy cost control programs must do much more if they are to be successful.
There are two primary forces driving the change in energy cost control programs today: new technology and the way in which facilities are charged for energy. New technologies have greatly increased the operating efficiencies of today’s building systems, in some cases cutting energy requirements by as much as 50 percent from those that were available during the 1970s.
Equally important is the way in which facilities are charged for energy. The steadily increasing demand for energy has created a number of problems for the energy industry. Today, the biggest concern is over electricity generation capacity. Simply stated, demand for electricity has risen faster than utilities have been able to add generation capacity. These capacity concerns, combined with the deregulation of the electricity industry, have resulted in increased emphasis on demand charges for users.
But even if utilities were able to rapidly bring new generation plants online, this would not solve all of the problems. While generation capacity is the big concern today, in the near future it will be the ability of the transmission and distribution infrastructure to get the power where it is needed. Therefore, energy cost control programs must address the demand portion as well as the use portion of the electrical bill.
These concerns are not limited to electricity. The demand for natural gas in recent years has outstripped both new gas wells and gas production. With many new electricity generation plants burning natural gas instead of oil or coal, natural gas has the potential of becoming the energy concern of the near future.
The most common strategies in use today to help control energy costs include improving the operating efficiencies of building systems, shifting electrical loads from peak rate times, reducing or shaving peak electrical loads, switching to alternative fuels, and most recently, demand-response metering. By using these techniques to develop their facility’s energy cost control program, facility executives can make a significant reduction in their facility’s energy costs.
Advances in building technology have resulted in major improvements in the operating efficiency for building energy-using systems. While these improvements have been made in almost every type of energy-using system, the most significant improvements have come in the areas of lighting, chillers and boilers.
Lighting system upgrades offer facility executives a way of reducing their energy costs while improving the performance of lighting systems and reducing maintenance costs. More efficient light sources and fixtures combined with better control techniques allow most lighting system upgrade programs to achieve reductions of 25 to 50 percent in energy use.
One of the most popular and cost effective lighting system upgrades has been the installation of T8 fluorescent lamps and electronic ballasts. When compared to the standard T12 lamp and magnetic ballast configuration, energy use can be reduced by an average of 35 percent. Additional benefits of the upgrade include less lamp flicker and quieter operation. Upgrading to T8 lamps is cost effective in any applications where T12 lamps are currently used, particularly those having a high number of hours of operation per day.
Another lighting system upgrade is the replacement of incandescent bulbs with compact fluorescent lamps. Compact fluorescent lamps use between one-quarter and one-fifth of the energy required to produce the same amount of light by an incandescent lamp, while offering a lamp life that is 10 to 15 times longer. New compact fluorescent lamp designs can be used in practically any application, including those requiring dimming. Replacing incandescent lamps with compact fluorescent lamps is cost effective in all applications.
The new generation of lighting controls also offers significant improvements in energy efficiency. Occupancy controls can be used to limit the operation of the lights in an area to only those times when they are needed. Dimming fluorescent ballasts allow occupants to match the light output of their system to their individual needs while reducing lighting energy requirements. Dimming ballasts, when used in portions of a building having large areas of glass, can be dimmed in response to how much daylight is available. Dimming ballasts can also be controlled by a building automation system to reduce the electrical load during periods of high demand.
Chiller energy efficiencies have steadily climbed over the past years. Today’s best centrifugal chillers operate at less than 0.50 kilowatts per ton, a 40 percent increase in energy efficiency over the best models from 10 or 15 years ago. Even greater gains have been made in part-load efficiencies, thanks in part to the use of variable frequency drives. The result is that a new chiller can cut seasonal HVAC energy use in half. Any facility that currently operates centrifugal chillers that are more than 15 years old is a candidate for upgrading to a new, high-efficiency chiller. In addition, any facility that is currently operating CFC-based centrifugal chillers that are in need of an overhaul should also consider a new, high-efficiency chiller.
The greatest advances in boiler energy efficiency are the result of the use of digital controls. Digital controls are more accurate, more responsive and more reliable than their pneumatic predecessors. By constantly monitoring building loads and boiler operation, digital controls can maintain the optimal air-fuel mixture over a wide range of loads and operating conditions. While upgrading to digital controls will improve the operating efficiency of any boiler by at least 10 percent, they are most cost effective in larger installations, particularly those having multiple boilers.
Load shifting is a program designed to move large electrical loads from high cost, on-peak periods to lower cost, off-peak periods. To benefit from load shifting, facilities must be on a rate schedule that is based on time-of-day rates with separate demand charges. The greater the differential between on-peak and off-peak rates, the greater the potential savings.
The most widely used technology for load shifting today is thermal energy storage. With thermal energy storage, building chillers are operated during off-peak periods to generate brine or ice, which is stored in a central tank system. During on-peak hours, chilled water is circulated from the storage system and used to fully supply the building air conditioning system or to supplement chilled water generated by a smaller chiller.
Because the cost of the electricity used to generate chilled water during off-peak periods is one-fourth or less than its cost during on-peak periods, the savings in energy costs can be significant. And with the building’s chillers offline or operating at reduced capacity when the peak demand is set for the billing period, additional savings will be achieved in demand charges by using thermal energy storage.
Load shifting is best applied in applications where the occupancy of the building varies with the time of day, where cooling loads account for at least 30 percent of the total electrical load, and where the ratio between on-peak and off-peak electricity rates is at least 4-to-1.
Electricity demand charges are based on the highest rate at which electricity is used during the billing period over a specified time interval, typically 15 or 30 minutes. Peak shaving is a strategy that was developed by users in response to these demand charges. Facility executives found that they could significantly reduce their demand charges by monitoring their demand for electricity, and, when it approached a predetermined level, temporarily turning off loads to keep the demand under that level. Loads that were turned off included lighting systems, building fans and building chillers. The hope was that the load peak would pass in a few minutes and the temporary reduction in services would not be disruptive.
Today, building automation systems and new HVAC system designs have provided facility executives with a powerful tool for peak shaving while maintaining building indoor air quality. When meters connected to the system detect electrical demand levels approaching the desired upper limit, chilled water temperatures can be reset for a few minutes, unloading the chillers. Fans in VAV systems can be slowed for reduced flow and energy use until the peak passes. Lighting systems can be scaled back without having to fully turn them off.
In larger facilities, standby and emergency generators have been used to help shed loads during peak time. In these facilities, when the peak is approached, the generators are started and loads transferred. The generators are operated several hours at a time or until the connected load drops off sufficiently.
There is one point that facility executives should be aware of if they plan to use onsite generators to reduce demand. Usually, generators are set up to operate only those loads that are critical in the event of a power outage — some lighting, elevators and only critical air conditioning systems. If a generator is to be used to reduce demand, then it is likely that additional electrical loads, beyond what is normally considered to be critical, will have to be connected.
In order to use peak shaving, facilities must be equipped with central metering equipment that can be remotely read, a building automation system that controls sufficient electrical loads to be able to reduce peak loads, loads that can be temporarily reduced or turned off, and a rate structure that places a high premium on peak loads.
Fuel switching is the ability to use alternative fuels to provide heat or air conditioning within a facility. It was originally implemented by electrical utility companies as a protection against fuel shortages or price spikes, but it has been adopted by facilities as a means of protection against high demand charges as well as shortages.
To protect against price spikes or shortages in natural gas, boilers can be converted to be able to burn two different fuels, such as natural gas and number two fuel oil, or natural gas and residual oil. Having dual-fuel capabilities offers the additional advantage of allowing the facility to operate under an interruptible service contract with the natural gas company. Interruptible rates are lower in cost than non-interruptible rates. Dual fuel boilers are most cost effective in applications where both an interruptible service contract is available for natural gas, and there is a steady supply of alternative fuel at a competitive price.
To reduce the impact of electrical demand charges, facilities can install natural gas or steam-fired absorption chillers or gas-engine-driven chillers alongside electric centrifugal chillers in a hybrid plant configuration. When the demand for electricity rises, the absorption or engine-driven chiller can be brought online, reducing the facility’s need for electricity and its demand charges. Using a combination of centrifugal and absorption or gas-engine chillers is most cost effective in applications having a large central plant serving multiple buildings or a large single building.
Demand Response Programs
A demand response program is the latest strategy to be used to reduce electrical demand charges. The program is developed by utility companies and offered to customers on a voluntary basis. Customers that agree to participate commit to a minimum mandatory reduction in their electrical demand, typically 15 percent, when notified by the utility company of a need to reduce electrical demand. While program details vary, the programs operate basically the same. The utility company notifies participating customers of the need to reduce electrical demand. Customers then have 30 minutes to reduce demand by the agreed upon amount.
Reductions last four hours and usually occur between the hours of 11 a.m. and 7 p.m. Most agreements set a maximum number of times that reduction can be implemented in a billing period. Programs are usually set up to operate between June 1 and Sept. 30.
In return for reducing their electrical demand, customers receive payments at an agreed upon rate in addition to the quantity of energy that they saved. But should a customer fail to achieve the agreed upon demand reduction, the contract carries a penalty clause that can charge the customer on the basis of how much demand they failed to reduce.
If facility executives are to take advantage of a demand response program, they must have a metering infrastructure in place that allows them real time access to their facility’s electrical demand. They must have the tools in place that will allow them to rapidly reduce their electrical loads, such as a facility-wide building automation system. They must have the personnel available to disconnect electrical loads that are not controlled by the building automation system. And the facility must be able to operate effectively with the identified loads disconnected from the system for up to four hours. Unless all of these conditions can be met, and the load reductions carried out in a very short time frame, demand response programs can end up costing facilities money.
James Piper, PE, PhD, is a consultant and writer with more than 25 years of experience in the facilities field.