Performance benefits of chiller plants with ice storage


23 May 2019
air conditioning chiller ice storage new york US USA North America energy
Michael Tobias
Michael Tobias is the founder and principal of New York Engineers. He leads a team of 30+ mechanical, electrical, plumbing, and fire protection engineers from the company headquarters in New York City and has led over 1,000 projects in Chicago, New York, New Jersey, Pennsylvania, Connecticut, Florida, Maryland and California, as well as Singapore and Malaysia.
Chillers are commonly used as a cooling solution for large commercial buildings and industrial processes. Chilled water can be pumped vertically with ease, providing air conditioning for the upper floors. On the other hand, air ducts do not work for long vertical distances. Water can also absorb more heat per unit of volume, making the installation more compact.

Chillers have a high demand for electricity, since their nameplate capacity is often in the hundreds of tons. The combined load from the chiller plants of multiple facilities can be very high, especially on the hottest days of summer. This is a significant engineering challenge for grid operators: if the transmission and distribution capacity is not enough for the peak demand, blackouts can be expected.

There are also applications that require cooling all year long, even during winter. Some examples are data centers, industrial processes and cold storage facilities. A high-efficiency chiller offers increased savings in these cases, since it operates all year long.

The impact of chiller plants on electricity bills
Considering their scale, chillers have a high demand for electricity. Their monthly consumption in kilowatt-hours is high, but they also increase the demand charges that are applied to large commercial and industrial consumers.

  • These charges are based on the highest demand measured during the billing period. Typically, it occurs at a time when the chiller plant is running at full capacity.
  • Some demand charges are based on the highest measurement during the last 12-month period. In these cases, chillers can increase power bills even in months when they are not used.
  • Cumulative demand from chiller plants can cause a significant burden on electricity grids, taking the transmission and distribution capacity to its limit. A power network with insufficient capacity is prone to blackouts under high air conditioning loads.

High-efficiency chillers, such as water-cooled units with variable speed compressors, can achieve significant savings. In addition, measures that reduce the peak demand from chiller plants are beneficial for both building owners and power companies. Buildings have lower capacity charges, and grid operators handle a reduced load.

How ice storage can enhance chiller plants
Ice storage tanks are a promising addition for chillers, since they allow cooling even when the unit is turned off. With this configuration, a chiller can be configured to make ice when demand is low, and it can be ramped down or deactivated to mitigate peaks in energy consumption.

In applications where cooling is not needed 24/7, a chiller can use ice storage to meet loads above its rated capacity. When the building does not require cooling, the chiller can make ice. Then, the building has access to both the chiller capacity and the ice tank capacity, which can provide a cooling output above the chiller’s output alone.

Energy storage is normally associated with batteries, but thermal storage methods are equally viable. The concept of chiller plants with ice storage was deployed successfully in a commercial district in Chicago, reducing its peak electricity demand by 30 megawatts.

The widespread use of ice storage across many buildings can improve the reliability of power grids. Since the maximum demand on the grid determines the required capacity, power companies can postpone expensive upgrades if demand is kept under control. Considering that network ownership costs are reflected in electricity tariffs, peak demand mitigation can help stabilise prices.
When can ice storage reduce electricity expenses?
Ice storage is always beneficial for the power network operators, since it reduces peaks in demand. However, the benefits for building owners can vary depending on how electricity is obtained. Ice storage can reduce energy expenses when the electricity tariff includes demand charges or time-of-use energy prices:

  • If demand charges are present, ice storage can reduce the demand contribution from chiller plants.
  • If time-of-use electricity prices are present, a chiller plant can take over the cooling load when the highest kWh prices are being applied.

The savings from ice storage are unavailable when the user pays a fixed tariff regardless of demand peaks and the time of use. While the benefit for the power company remains, in this case there are no savings for the end user. HVAC engineers can determine the most suitable configuration for a building, based on cooling needs and operating schedules. Cooling systems operate at their best when they are suitable for the application and sized optimally.
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