The Green Geek

Ice Cooling Technology

Posted by Steve on 08 3, 2006

As summer temperatures soar, people without air conditioners must endure the high temperatures, while the people with air conditioners must endure the high cost of being cool. Because the hottest time of the day also coincides with the highest demand, electricity prices are the highest just when people need that energy to run their air conditioners. Ice cooling systems save money by shifting the cooling load to night time, where rates are the cheapest. But there’s a way to save even more money, by shifting the cooling load even further away.

An ice cooling system, like the one used at the IBM Canada office in Toronto, operates at night when electricity is cheaper to make large amounts of ice. This ice melts during the following day, cooling the building. This allows the air conditioning unit to be shut down during the peak electrical loading time, saving money for the company. This type of system is available for smaller commercial and residential use as well, from Ice Energy.

Ideally an environmentally-friendly passive system would be used, such as good ventilation and shading, or ground source heating and cooling. But for instances where below ambient cooling must be achieved, such as for older buildings that can’t be retrofitted with geoexchange pipes or shade trees or where cost is a limiting factor, ice cooling is a viable option.

Shifting the ice creation step to night time saves money by using cheaper electricity rates, but for geographical regions that are suitable, why not switch the ice creation by several months to winter when the ice can be made for free?

The practice of seasonal ice storage is very old, used before mechanical refrigeration systems became available. These ‘ice houses’ were made to store milk and other perishable food items over the summer, and consisted of an underground space that was packed with ice blocks during the winter and insulated with sawdust. This ice stayed frozen all summer, and was replenished the following winter.

A very simple system could be set up with plastic drums or containers that are heavily insulated. Inside these drums would be a heat exchanger coil, surrounded with a glycol solution. Suspended in this glycol solution are ice packs. During the winter, a ground level heat exchanger is plumbed into the loop and glycol is circulated through the storage tanks, freezing the ice packs. When the temperatures start to rise above freezing, the pumps shut off and the ice remains frozen until summer when the temperatures rise enough to require cooling. Valves are opened and the pump starts up again, this time cycling the chilled glycol to the building’s cooling system. The storage system needs to be sized to provide adequate ice for the summer months, and the more insulation the building has the longer the ice will last.This system could be retrofitted to almost any kind of building that had available land for burying the tanks.

On a related topic, the same type of insulated underground storage system could be used to store heat from the summer for use in the winter, using rocks or a cement slab to hold the heat; although a system like this would be massive.

related story on Treehugger