After a call from the arena’s director to the engineering firm where I worked, another engineer and I went to the facility to see if we thought we could help them. We negotiated a price for a study and report, and then it was my job to do the study and determine how utility costs could be reduced.
I understood the thermodynamics and the heat transfer issues but had never worked in an ice arena, so I had to do a lot of research. The ice in a skating rink is made essentially the same way ice is made in your freezer at home – by removing the heat using a refrigeration system. Your refrigerator blows the heat removed into your kitchen. The large compressors or “ice machines” in the rink were water-cooled and dumping the cooling water though a pipe into the creek running only a couple of hundred yards away. And it was a huge quantity of water – millions of gallons a month. It was city water and it was expensive. I measured the temperature of the discharge water and it was warm, in the 80s; it was carrying all of the heat removed from the ice surface.
The water was clean, essentially tap water, but its effect on the stream was unknown. However, it was hard water, which contained a lot of calcium, magnesium and iron. The ice machines were the same ones that had been originally installed in the mid-1950s, and gradually the hard water created a lime buildup inside of the heat exchangers. The buildup had to be removed periodically with acid, which in addition to removing the scale, also removed some of the metal and shortened the life of the ice machines.
When I calculated how much heat was being removed from the compressors and dumped into the creek, I discovered that it was more than the heat required to heat the arena. The ice machines were pulling heat from the ice and dumping it into the river. And to replace the heat being removed from the ice, the rooftop units had electric resistance heaters to heat the air. That heat would then travel from the warmer air into the colder ice and then to the creek. What if that heat could be recycled? Instead of dumping it into the creek, what if there were a way to put it back into the arena instead? Because the waste heat alone was more than the arena needed, the electric heaters could be shut off and a bundle of money saved. And if the solution eliminated using the hard city water, the life of the ice machines could be extended.
The next step was to figure out how to capture that waste heat and put it back into the rink. What equipment would be required? And how much would it cost for the engineering design and the construction? Following the traditional consulting engineer approach, I did all of the heat transfer calculations to determine the heat in and heat out.
I called a college fraternity buddy who was a sales rep for Baltimore Aircoil, a company that made the kind of equipment I thought we needed. He was an expert, and together we determined exactly what was needed and estimated what the cost would be. A closed-loop piping system could replace the present one; the setup would be very similar to the cooling system in your car. A water/antifreeze mixture would be circulated through the ice machines (the same as what happens in your car engine) to pick up the excess heat, and then it would be circulated through water coils that would be added to the rooftop heating units to heat the arena for free. The electric heaters would be off. If there was excess heat left, or in hot weather, the warm water would then flow through a large new cooling tower – very similar to your radiator, only on a much larger scale. You’ve all seen them sitting outside of most large facilities, hospitals, industrial and power plants, with a plume of moisture blowing out the top.
I wrote up a proposal for the park board with all of the information required to make a decision. Apparently it looked good to them, because they gave us the go-ahead to design the system, prepare the specifications, and take bids on building it. I believe the analysis showed that it would pay for itself in a couple of years from the savings – somewhere around a 50% reduction in utility costs. They were saving all of the water and sewer costs plus costs resulting from the electric heaters in the rooftop units. A two-year payback and 50% reduction in utility costs would be attractive to most building owners. The savings would amount to several million dollars over the life of the building.
The construction documents were prepared; bids were taken; and the systems were modified, exactly the way I designed them. They worked great and the utility costs were cut by at least 50%. In theory, the arena’s future was secure. The community would continue to have this tremendous asset. And it felt really good to have had a major role.
A happy ending? Not quite. There’s more to the story. My next post will detail what happened after the contractor hired to maintain the system changed the operation and lost all of the savings.
