Buildings and their power and cooling systems are built to last for decades. However, they must respond to market conditions on an hourly basis to operate efficiently. This requires not only selecting the right equipment, but designing a strategy for it to operate at the lowest possible cost. Fuel prices can double in a month. Electricity prices can have even wider swings in a single day, and prices are highest just when air conditioning is most in demand. Further complicating the issue: A building owner can earn money by agreeing to participate in a utility's demand-response (DR) program, in which he or she agrees to curtail electricity use on the demand of the utility or wholesaler.

"The real gains are when you can automate your demand response, you can preprogram your strategies, and you can optimize which ones you want to use for certain conditions," Chuck Goldman, a staff scientist and group leader of the Electricity Markets and Policy Group at Lawrence Berkeley National Laboratory, said. "You can shave 5 to 15 percent off your peak demand and have the capacity to participate in emergency programs."

Demand Response
No nuclear plants have been built in decades. Coal plants already are hard to permit and will become expensive to operate if Congress passes a carbon tax. Natural-gas and oil prices are on the rise. Nevertheless, the demand for electricity keeps growing. To ensure reliability without adding new generating capacity, utilities are adopting various strategies to reduce peak electrical demand or shift it to other times of the day.

"A decrease in usage is just as valid as an increase in generation, and sometimes it is a lot faster," Ray Dotter, a spokesperson for PJM Interconnection, a regional transmission operator that manages the wholesale electricity market in 13 states and the District of Columbia, said. "You can open a circuit a lot faster than you can ramp up a generator."

According to the Federal Energy Regulatory Commission, the 274 entities that offered a DR program in 2008 had the combined ability to reduce peak load by 40,000 mw. Each region of the country has its own rules and incentives for participating in a DR program. In PJM's region, building owners typically signed up with one of more than 80 curtailment-service providers (CSPs), a company or organization that specializes in DR or offers it as a service. A CSP monitors power conditions and prices and sends a signal—which can be something sophisticated or as simple as a phone call or fax—to their customers requesting a usage adjustment.

"We would like to see that signaling become more sophisticated as some of the smart-grid technology gets deployed," Dotter said.

The Building Owners and Managers Association of Chicago (BOMA/Chicago), which represents more than 250 office buildings, is working on a $185 million smart-grid project that will link 262 buildings with a network operations center (NOC) at its CSP, Metropolitan Energy. The local electric utility, Commonwealth Edison, will install new electric meters to transmit usage data from the office buildings to the NOC every minute or less. Building-automation systems will be programmed to respond to the NOC's price signals, and, depending on price, reduce electrical usage through various methods, such as slowing down an HVAC system’s variable-speed drives.

"The system will allow them to rapidly change the power the building is consuming," Dotter said.

Hybrid Chillers
Additionally, hybrid cooling systems can cut costs while increasing reliability. Hybrid cooling systems can be set up in a variety of ways. For example, in 2009, testing firm ACT Inc.'s data center became the first in the United States to receive Leadership in Energy and Environmental Design (LEED) Platinum certification from the U.S. Green Building Council (USGBC). The data center's hybrid design uses outside air for cooling during winter and geothermal cooling during summer.

However, a more common approach is to use two different drivers, such as a steam turbine and an electric motor or gas engine, to power two centrifugal or absorption chillers. Depending on the price of electricity, gas, or steam, an energy manager could select which of the chillers to use at a particular time of day. In most cases, the motor-driven chiller would operate during the cooler hours of the day and be supplemented or replaced by the engine or steam turbine during peak hours.

The downside is a hybrid chiller system increases initial capital expenditures because two compressors, as well as piping and valving, are required to complete connections to an evaporator. However, this is offset quickly when operating costs decrease.

HVAC manufacturer York International Corp. compared the capital and operating costs of two 500-ton electric centrifugal chillers with the costs of six hybrid designs that could meet the same cooling requirements. York discovered that the hybrid systems could pay for themselves within six months to five years. (Note: Payback calculations were based on specific temperature ranges, as well as particular pricing structures for gas and electricity that may not be applicable to every building's conditions.)

Dual-Drive Chillers
One way to cut a hybrid system's capital costs while achieving the same amount of energy savings is to connect multiple drivers to a single compressor (Figure 1). While new to building HVAC systems, this approach has been used successfully with natural-gas pipeline compressors for years, allowing them to operate with natural gas or electricity, depending on cost.

Driving a chiller compressor with an electric motor and reciprocating engine or steam turbine can provide demand-side management capability, emergency or standby electricity, and/or chiller power while saving energy costs. First-cost savings can be greater with this method than with separate standby engine generators and electric-driven chillers.