If you run a large commercial property that uses chillers for space cooling, they are likely to have a higher energy consumption than any other electrical device in the building. A central chiller is more efficient than many window-type or packaged terminal air conditioners, but this does not mean that running a chiller is cheap – a more appropriate term would be “less expensive”.
The compressor is the chiller component responsible for most of the unit's electricity consumption. Modern compressors can adjust their speed to match a building's cooling needs, which is more efficient than the ON-OFF operation of older models. However, a chiller only achieves maximum performance if the complementary installations are well designed: selecting the right water pumps, air handlers and cooling towers is very important.
Optimize your HVAC design for superior performance.
An innovative concept is to complement the chiller with an ice storage system, which basically allows the storage of the air conditioning capacity. There are many ways this concept offers savings to homeowners.
Avoiding high electricity prices in daily tariffs
Many energy consumers are subject to time of day (TOD) electricity tariffs where the kilowatt-hour price changes throughout the day.
- During times of low demand, utility companies can only operate the cheapest power plants and kilowatt-hour prices reach their lowest point.
- During times of high demand, on the other hand, more expensive power plants must be brought into operation. As a result, kilowatt-hour prices are at an all-time high.
If a TOD rate is applied, any refrigeration equipment running during high demand times can cause a drastic increase in energy bills. Unfortunately, turning off space cooling systems is not an option for a busy building on a hot summer day. With ice storage , however, a chiller can reduce its output while the necessary cooling of the space is achieved by melting the ice.
- When electricity prices are low, the refrigerator works at full capacity to produce ice.
- On the other hand, when electricity prices are high, ice is used to provide as much cooling as possible. The chiller is only used for any additional cooling capacity that cannot be provided by the ice tank.
In TOD tariffs, off-peak electricity prices are often less than 50% of peak prices. As a result, there are huge potential savings from shifting consumption to off-peak times, and ice storage provides a way to achieve this for space cooling systems.
Avoiding capacity charges
Commercial and industrial energy consumers do not just pay for the total value of the energy used. There is also a capacity charge, which is calculated based on the highest kilowatt demand measured during a specified billing period. As a result, two consumers using the same number of kilowatt-hours can have very different energy bills, based on their demand behavior.
Just as ice storage can take advantage of cheap TOD electricity rates during off-peak hours, it can reduce the share of peak demand that comes from space refrigeration systems. Electricity demand can be monitored to determine times when peak demand occurs. Then, the cooling system can be programmed to use ice during peak demand.
- Assuming that a chiller consumes 0.60 kW/ton and the total building load is 500 tons, the energy consumption at peak load is 300 kW.
- If 200 tons of cooling can be provided with ice storage, the chiller must only provide the remaining 300 tons and the power consumption will be 180 kW.
- Capacity charges exceed $20/kW on many tariffs. In this example, 120 kW load shedding translates into savings of over $2,400/month.
Note that TOD rates are time-sensitive, but capacity charges are not. You are only charged high kWh prices for certain hours under a TOD tariff, but peaks in demand increase your capacity tariff regardless of when they occur.
Some electricity tariffs combine the concept of TOD pricing and capacity charges: your individual peak demand is charged at a higher rate if it occurs during hours when total grid demand is already high. To find the best strategy to mitigate your electricity bills, an energy audit of your building is strongly recommended.
Bonus: Ice storage can allow for reduced cooler capacity
Chillers only run at full capacity when your building requires it, which may only be for a few hours a day. If you can achieve this peak cooling load with a combination of ice storage and chiller operation, it may be possible specify a smaller chiller . The main advantage of this is a reduced initial cost, which makes supplemental ice storage easier to afford.
