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Air conditioning units consume a large amount of energy, so if you want to make an environmentally friendly choice, opt for off-peak systems.
vlynder/iStockphoto.comGreen energy has become a prominent topic, and the list of methods for generating and using energy more efficiently continues to expand. One smart way to utilize energy effectively is through off-peak cooling systems. These systems are designed to operate at night when energy demand is lower. Air conditioning systems use a lot of energy, and when electricity is used during off-peak hours, it reduces strain on the grid during peak demand times.
This helps balance electricity demand, preventing brownouts and blackouts, while also taking advantage of cheaper electricity during off-peak hours. There are additional advantages to off-peak cooling systems as well. Conventional air conditioners consume more energy as they heat up, and the more power they draw, the less efficiently they operate. Off-peak cooling systems not only shift energy demand to a later time, but they also offer a more consistent cooling environment, achieving the same cooling results with less energy usage.
Utility companies must meet energy demands during peak times by whatever means necessary. They often resort to activating less efficient and more polluting plants or purchasing expensive energy from other plants on the grid, passing on those extra costs to consumers. They also expand their infrastructure when they can't meet current or forecasted demands. By improving the efficiency of the energy grid through spreading out electricity demand and cutting energy consumption through optimal air conditioning performance, greenhouse gas emissions are reduced, and the need for additional power plants is delayed. This benefits the environment and helps keep energy prices manageable [source: Katz].
Next, we'll explore how off-peak cooling systems operate overnight, yet still manage to keep the air cool during the hottest parts of the day.
Off-peak Cooling Basics
Off-peak cooling systems work by using electricity to freeze water in special insulated tanks with refrigerant-filled coils. These coils circulate a mixture of ethylene or propylene glycol and water, chilled to well below freezing. Once the water has frozen during off-peak hours when energy demand is low, it's ready to cool the air the following day. This process, known as charging, means the system requires very little energy to stay cold while on standby until it's used to cool an office or home.
As the building warms up during the day, the air conditioning activates, and the chilled refrigerant from the off-peak cooling system cools the air. The glycol circulates through the ice-filled tanks, re-chilling after being exposed to hot air, and eventually, this exchange of heat causes the ice to melt. At night, the system charges again by freezing the melted ice with a chiller, preparing it for the next hot day.
This is an example of a basic off-peak cooling system. More advanced systems may use alternative refrigerants or employ different methods for storing ice. Some systems utilize off-peak storage for only a portion of their overall cooling needs, with chillers running during peak energy periods to supply the rest. While these partial systems have higher operational costs, they offer lower capital investment because the chillers can be smaller, making the equipment less costly.
Off-peak cooling, also known as thermal energy storage (TES), has traditionally been used in large buildings such as office complexes, hospitals, or schools. Older TES systems required large tanks, making them difficult and expensive to retrofit into existing structures or residential settings. Today, smaller and more affordable systems are being developed for residential use, and larger systems can place tanks almost anywhere—from underground to within the building itself.
The majority of the savings in off-peak cooling systems come from taking advantage of lower energy rates during off-peak hours. If energy pricing structures change and off-peak savings become less favorable, the financial benefits of off-peak cooling could diminish significantly. In this case, the advantage of off-peak cooling lies in utilizing the current energy pricing models offered by power companies, not in the design or cost of the equipment itself.
In the upcoming section, we’ll take a closer look at some of the components of off-peak cooling systems and how they apply to residential settings.
Off-Peak Cooling Systems For Light Commercial and Residential Use
Innovative off-peak cooling system designs are constantly being developed. While large systems typically use large, insulated polyethylene tanks, chillers, and a dedicated distribution network to cool and circulate air indoors, newer, smaller configurations are making off-peak cooling feasible for smaller-scale applications, such as light manufacturing, commercial, and residential use.
The size of the cooling system needed for a building depends on the area that requires cooling. Air conditioning capacity is measured in tons, and one ton (0.9 metric tons) can cool 12,000 BTUs ( kilowatts) per hour. If that seems unclear, it translates to about 500 square feet (46.45 square meters) of space [source: ACU Air].
The Ice Bear 50 system by Ice Energy is designed for large residential or small commercial spaces. This unit is compatible with both roof and split systems, working with the existing ductwork of an air-conditioning system to cool up to 30-ton hours at a maximum load of 5 tons (4,536 kilograms). Ice Energy states that integrating the Ice Bear with your current HVAC system during off-peak hours can reduce peak energy demand by as much as 95 percent from day one. The Ice Bear can range in cost from $4,000 to $18,000, depending on the air conditioner involved and installation specifics [source: Ice Energy].
IceCycle also manufactures a unit for retrofitting called the IceCycle Retro, which, like the Ice Bear, works with roof and split-system installations, utilizing the existing setup to convert conventional air conditioning into off-peak cooling.
Industry leader CALMAC, known for providing off-peak systems to major companies like IBM, American Airlines, McDonald's, Kohl's, DuPont, Marriott Hotels, and JC Penney, is now branching out into large residential installations with its ICE-BANK model 1045 C tank, which offers 45-ton hours of cooling capacity [source: Miller].
In the next section, we’ll explore what the future holds for off-peak cooling systems.
In 1902, Willis Carrier invented the first air-conditioning system to solve a problem with smudged pages at a printing plant. His system was designed to remove humidity and lower temperatures. This invention led to the creation of the air conditioner. A few years later, in 1928, the first home air conditioner, called the Weathermaker, was introduced.
The Future of Off-peak Cooling
As long as power companies continue to provide incentives for using electricity during off-peak hours, the future of off-peak cooling looks promising. Moreover, in locations like Southern California, where energy demand is high, businesses are being discouraged from using power during peak times through time-of-use rates and demand charges. Meanwhile, many utilities offer attractive incentives for businesses to switch to off-peak energy systems, even covering the cost of the equipment and providing energy discounts [source: Du Bois].
On the residential side, several power companies already offer time-of-use pricing for their customers, and this trend is expected to grow as power demands increase. Starting January 1, 2010, the R22 refrigerant used in many air-conditioning systems will be phased out in favor of the more eco-friendly R410A. If your system’s evaporator or condenser needs repair, you may have to pay for an expensive conversion, which could be the perfect time to consider off-peak alternatives to meet your air-conditioning needs [source: ACU Air].
On the following page, you’ll discover more articles that delve into green energy practices and much more fascinating information.
With the help of a grant from the U.S. Department of Energy, Richard Bourn developed a roof-mounted cooling system that utilizes water, cooled by the night air, to keep buildings cool during the hottest parts of the day. The system was tested on flat and low-sloped roofs with different installation methods. An analysis of five systems revealed a reduction in peak cooling demand ranging from 50 to 90 percent. Additionally, it was projected that a NightSky system could potentially double the lifespan of a roof. The NightSky project is one example of how innovative energy conservation techniques are reshaping our understanding of power needs [source: Night Sky].
