Ice Energy's "Ice Bear" Keeps Off-Peak Kilowatts in Cold Storage to Reduce HVAC's Peak Power Costs
In many regions of the U.S., utilities are feeling the heat. Peak power demand threatens their ability to deliver as much energy as customers need on hot afternoons. Ice storage air conditioning shifts a major commercial energy load into off-peak evening hours, saving money for businesses and reducing pressure on the grid. California's new building energy code makes load shifting a necessity for many new facilities. (podcast) (photo)
January 16, 2007
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By night, the Ice Bear turns the air conditioner's condensing unit into a big ice maker. By day, the ice turns the Ice Bear into an energy-efficient condensing unit. (Ice Energy photo).
California adjusts building energy standardsIn warm climates, such as the California desert, customers may soon call for more energy on hot afternoons than the utility can generate or deliver.
California has gone as far as to modify its building energy efficiency standards to align them with the state's commitment to resolve this problem. It's a trend that could affect businesses in other states.
"California continues to lead the nation in its energy efficiency standards for building envelopes," says Greg Tropsa, president of Ice Energy in Windsor Colorado. "But they remain plagued by summer air conditioning peak demand problems."
California has recently redesigned their efficiency standards to consider the time and location of energy demand. The legislature's objective was for building standards to model the real cost of delivering a kilowatt.
Relatively new rules in California's Title 24 Part 6 now affect most new homes and buildings in the state. They've complicated the task of calculating a building's energy efficiency. Designers now must take into account a multiplier called the Time Dependent Valuation, or TDV.
Time Dependent ValuationSupplying energy generally costs more when demand is high, because a utility must resort to their most costly sources of energy -- firing up older power plants, or buying on the spot energy market, for example. The cost differential can be significant, and the TDV quantifies it.
A building designer must predict not only the building's overall energy consumption, but the consumption by time of day and season, as well. It's not enough that buildings are more efficient than a national standard, if their collective power consumption jumps up at the same time in the afternoon. The new rules force designers to compensate by applying a higher weighting factor to on-peak loads.
"If you build a building in Palm Desert and consume 100 kilowatts of energy on a hot August afternoon, the Time Dependent Value would multiply that 100 kilowatts by a factor of perhaps up to 40," Tropsa explains. "That same 100 kilowatts in Redondo Beach on a Christmas evening may only carry a weighting factor of zero."
Location Dependent ValuationThe time of day aspect has an immediate cost implication for a utility, but what does location have to do with it? The location weighting takes transmission constraints into account.
Utilities deliver power over a grid mostly designed and built between World War II and 1980. Urban growth patterns in the last 25 years have created large population centers where the grid does not have capacity to deliver sufficient electricity.
Utilities are faced with a sort of Hobson's choice: Build more lines, construct local plants, buy energy from another region, or force conservation, any of which costs utilities (and their customers) dearly.
California has created an incentive to make buildings more energy efficient when they are to be built in areas affected by transmission constraints. Along with the TDV multiplier, there is a Location Dependent Value.
TDV vs. TOUMany utilities have adopted time-of-use tariffs, at least for business customers. In California, customers have an incentive to take advantage of lower rates in off-peak evening hours, rather than pay higher rates in on-peak hours of the day.
Business customers also pay demand charges, which are an attempt by the utility to discourage customers from contributing to the peak power problem.
"The problem that business face is that they're dependent on their air conditioning," says Tropsa. "Fifty percent of peak power, and a third of all energy on the grid during the day, is air conditioning and thermal loads. To solve the peak demand problem, customers need to be able to reduce their air conditioning demand, but historically they've been unwilling to do that because it's bad for business."
A conventional air conditioner is an energy-hungry machine. The refrigeration cycle is typically driven by an electric motor. And, Tropsa explains, "the hotter it gets during the day, the less efficient that motor becomes, the more energy it draws, and the less cooling it provides. That is what creates part of the power problem for the utilities."
An enabling technology would let businesses to have cooling comfort, while taking advantage of lower off-peak prices at night. It would also help the utilities accomplish what they have been trying to achieve: getting customers to shift their air-conditioning loads.
Ice storage air conditioningA rather simple but clever technology is providing a storage mechanism for energy, enabling customers to run air conditioning units in off-peak hours. It's called the Ice Bear, a product of Tropsa's company, Ice Energy.
"The Ice Bear uses a common, commercial-style, refrigerant-based air conditioner as its mechanism for creating a block of ice," Tropsa explains. "The Ice Bear simply uses the condensing unit at night when temperatures are cooler. Rather than running it on a rooftop, where it might be 125 degrees, we're running it later that evening, when it might be 72 degrees out."
The condenser runs steadily, consuming energy at the off-peak evening rates, says Tropsa, "and we're storing all that energy as ice. That ice doesn't cool the building. It's used to condense the refrigerant. The Ice Bear is essentially an ice condensing unit."
During the day, when a building's controls calls for cooling, an electric motor pumps refrigerant up into an evaporator coil, where it changes from a liquid to a vapor. In a conventional air conditioner, the heat in the vapor is then rejected through a power-hungry electrical condenser. But the Ice Bear returns the refrigerant instead through the block of ice, re-condensing the vapor into a liquid without consuming large amounts of electricity at the same time.
Incentives for ice storage air conditioningMany utilities are offering time-of-use electric rates that reward customers for load shifting. In California, the Public Utilities Commission and municipal utilities offer rebates for installing ice storage air conditioners. Some programs are quite attractive.
"The Anaheim Utility District has passed the most attractive incentive in the country to drive the commercial adoption of energy storage," Tropsa says. "They're offering to cover the costs of the equipment and installation for the customer. And in return for using energy storage, they're offering a 20 percent reduction in the customer's annual electricity bill."
While commercial customers are saving on their power bills, California hopes to save even more. The California Energy Commission says the state's building efficiency standards (along with those for energy efficient appliances) have saved more than $56 billion in electricity and natural gas costs since 1978. It is estimated the standards will save an additional $23 billion by 2013.