by Tim Patricio

This is the final installment in our series on heating and cooling. We’ll continue from time to time with stories that are about the nuts and bolts of the building .. components you cannot necessarily see, hear, or touch, but depend on to be safe and comfortable at Park Tower.

You flip a switch, and whoosh! Ahhhhhhh .. air conditioning. But where does that cold air really come from?

In the spring, as warmer weather approaches, our team prepares to switch to cooling. This can be challenging. With all the glass on the tower, and the sun getting more powerful each day, it sometimes feels like a war with the elements, some residents being hot and others cold.

But when outdoor temperatures approach the 58 to 60 degree range, we prepare to make the switch. This starts with water already in the pipes, which may still be hot from being in heating mode. Should that be the case, we  wait a few hours for it to reach a safe temperature before beginning to cycle through the cooling system. Then the switch-over begins.

The equipment we rely on are two chillers and a cooling tower. Water is first refrigerated in the chillers, then moved to the risers and up into the building where it flows into branch lines that carry it to the convectors (heating/cooling elements) within your unit.

Water enters the coils of your convertors at about 45 degrees Fahrenheit. It leaves 5 to 10 degrees warmer – somewhere in the 50’s – depending on how warm your unit was. Turn your convector on and its fan forces air past those coils, thereby cooling it.

When water returns from your units to the chiller, the process begins again. The chiller’s several components –compressor, condenser, evaporator, and an expansion device – work together to remove heat before recirculating it again.

The refrigerants used by the chiller actually heat up as they remove heat energy from the circulating water. To re-cool those refrigerants, the honeycomb-like structures in which they’re contained are themselves bathed by cool water, thus draining away the heat and allowing them to work again to cool the circulating water.

But how to re-cool the water that re-cools the refrigerants? That’s where the cooling tower comes in.

Located on our building’s roof, the cooling tower receives the water that just finished cooling the refrigerant and needs now to be re-cooled itself. The tower passes this water through a series of ever-smaller screens, dividing it into smaller and smaller molecules. As these water molecules evaporate, the heat energy goes with them.

Two giant, high-speed fans assist the process. The hotter it gets outside, the faster those fans run to accelerate evaporation and cooling. (At lower temperatures, in fact, only one fan may be running.) Back goes the cooled water to the condenser part of the chiller, where the process starts all over again.

About the time you read this story, the first of June, we will have shut down the heating system for the summer.

Throughout the building there are sensors that feed temperature readings and other measurements into a computer control system. Our team will be monitoring this system continuously to determine the effectiveness and efficiency of our chiller and cooling tower.

When the dog days of Chicago’s summer are upon us – but the cooling components are operating optimally – then our residents can turn on their convectors and, voila, air conditioning!