Insights: Is Ice Storage Right for Your Next Project?
Ice storage is an HVAC technology that can be applied to so many different industries, but what exactly is it and when should it be considered?
Firstly, ice storage does not save energy or increase the environmental impact of an HVAC system, per se. The reason for this is making a chiller operate cold enough to create ice is less efficient requiring more electricity per ton of HVAC (typically). Then why utilize ice storage? It is a tool to save the client electricity costs and potentially get more useful capacity out of their HVAC systems.
What is ice storage?
To explain this, let’s first talk about how an ice storage system operates. The chillers cool a loop of chilled water that contains glycol (anti-freeze) down to 19°F. This below freezing chilled water is run through tanks filled with regular water, which freezes into ice. This cycle is called ice build mode. For cooling the building, the chillers typically cool the water down to 42-45°F. This warmer water can be run through the ice tanks and be cooled by the ice in the tanks. This is called ice melt or ice burn mode.
How does ice storage allow for more useful HVAC capacity? Ice can be melted during the highest need time of the day, along with the chillers to artificially increase the available capacity at that point in the day. This approach is called load shifting. The system works to save up cooling energy in the ice during the cool hours of the night or anytime the building is unoccupied. Then that energy can be used in conjunction with the chiller operation to produce more cooling than the total chiller capacities.
If the chillers are less efficient while making ice, meaning they need more electricity per ton, how can this save the building owner money? This savings is derived from how commercial buildings are charged for electricity. Residential power billing only charges the home owner for how much electricity they use, but commercial buildings are charged for how much they use (consumption) and the maximum amount of power they need at any given time during that month (demand). The reason for this is the power company is required to be able to provide the power that all of their clients need. The demand charge makes sure they can cover spikes in energy needs, even if those spikes are for short periods of time.
Ice storage can allow for the owner to have lower demand costs, by spreading out the cooling load as described above by load shifting the peak portions of cooling during the day to night time. Also, electric companies tend to charge commercial clients less money for electricity during off-peak hours (differs from season to season, by typically 9pm to 6am when most businesses are closed). By storing up cooling energy at night, the owner can pay the lower off-peak rate for consumption costs.
Many electric companies also provide rebates for HVAC equipment that will lower the peak demand costs. For example, a project C&S completed at Port Canaveral received $600/ton for hourly load shifted to off-peak hours. For this project, C&S designed the system to shift all of the tonnage to off-peak. So the whole day was cooled by the ice tanks. Our load was 600-tons, so the rebate was $360k, which paid for much of the ice plant right up front.
Is ice storage right for your next project?
The best project applications for ice storage are facilities with regular schedules, time off late and at night or off days to allow for ice building, and cooling peaks during the day like schools, churches, and places of assembly. Higher education tends to have later and earlier hours where cooling is needed, so it may be more appropriate for a different type of thermal storage, like chilled water storage tanks. Hospitals or other 24-hour operations are typically not good thermal storage candidates.
Finally, an ice storage system is more complicated and requires a slightly more complex maintenance routine than a traditional chiller plant. The owner’s maintenance capabilities or willingness to have a service contract must be considered. Also, consideration must be made for project locations where chillers running at night time could be audibly objectionable to adjacent properties, though purposeful acoustic treatment and chiller plant location can help mitigate these concerns. Local noise ordinances will set what target sound levels must be.
Matthew McQuinn, PE
C&S would be happy to help you determine if ice storage is right for your project or facility. Matt can be reached at firstname.lastname@example.org or (407) 956-6612.