During the 1970s and early 1980s, the world witnessed the worst oil crises ever following an oil embargo imposed by producers from the Middle East. Due to power reliability problems that were triggered by these events, chilled water storage systems were born. District cooling itself is a very old technology —it emerged in 1889 thanks to innovative work of Colorado Automatic Refrigerator Company, a Colorado based company—. Today, combining district cooling and thermal energy storage (TES) technologies can create an unbeatable system devoid of interruptions. However, challenges still abide for district cooling plants.
What are these challenges?
Maybe the question should be “what do district cooling systems need?”. District cooling plant managers and customers are looking for the following solutions:
- Energy efficiency
- Water flow reliability
- Environmental friendly processes
- Minimal maintenance cost
Another important question: what should a modern water chiller do to offer this need? It should have uninterrupted and adequate water flow at the correct temperature.
Sensitivity of critical facilities
Consider the level of cooling reliability needed in a critical facility. We are talking about facilities such as emergency theaters, banks, laboratories, data centers and clean rooms. These facilities need emergency cooling otherwise, there will be data loss, equipment failure or product damage. In case the system malfunctions, the cooling system may shut down temporarily. The three common causes of interruption are:
- Planned Maintenance
- Mechanical Failure
- Power Loss
Solution for the problem: available technologiesYou can counter the above disturbances using several technologies. Here are some of those possibilities.
- Standby generators: they may provide the cooling power as needed, but they increase running cost significantly. Furthermore, most generators start up in several seconds, which adds to the delay restarting the chillers.
- Source: http://www.cbecl.info/2013/04/gnerators.html
- Battery uninterrupted power supply (UPS): this system’s role is to provide power before standby generators ignite. The drawback is in the complexity and high cost of such a combination.
- Thermal Energy Storage: cool storage designs are applicable in several instances including load leveling, load shifting, full recharge, partial recharge and standby. ARANER’s TES technology provides the perfect remedy for cooling in the event of power outage or any other problem occurring. It takes over when chillers stop. Valves in the thermal accumulation tanks release cold water into the main supply feeder line to maintain the low temperatures of the chilled water supply.
More about thermal accumulation tank
Fig 1: An Accumulation Tank
This is a special tank used in emergency cooling systems. Tank sizes vary immensely because they depend on temperature differences and cooling level. It is mostly popular for storage of ice or stratified water because both mediums are cost effective to handle. Chilled water storage suits plants that have ample space because thermal stratification is more attractive for large storage tanks. Since ice is compact, ice storage can apply in smaller spaces.
What are the benefits of the tank?
Facilities benefit from thermal accumulation tanks in terms of both cost savings and reliability. Consider a sizeable data center that suffers power outage for 2-3 hours. Chiller shutdown means that temperatures in the center will increase dramatically within a few minutes. If the data center has several thermal accumulation tanks, the facility manager will not worry over power blackout. As long as the reservoir supply can last long enough for the engineers to fix mains power, the data center operates normally. When the chillers go down, the system can use water from the tanks to maintain the normal low temperatures. The air handlers and chilled water pumps can continue working normally using a combination of generator backup power and UPS. Depending on operational level at the time of power blackout, the system can continue running for hours. As facility managers strive to restart the chillers , thermal accumulation tanks help dissipate server residual heat and maintain cooling. ARANER can design a thermal accumulation tank system and help you in the following:
- Reduce plant cost
- Reduce plant size / footprint
- Reduce plant maintenance cost
- Lower energy bills
- Reduce equipment size
- Provide backup capacity
Source: ARANER TES Tank Reference Book
Ask yourself, would you rather risk losing an entire data center or laboratory than pay for a one-time thermal accumulation tank installation? Protecting a critical facility from damage is obviously the priority here.
TES is the most reliable method of optimizing district cooling systems where critical facilities need chilled water security system. These facilities cannot afford a few seconds of delayed cooling. While there are alternatives, their drawbacks are not manageable for most cooling plants. Contact ARANER for more analysis of this technology.