| "This program allowed us to further develop our relationship with the university." Sub-Zero Director of Design Engineering Paul Sikir |
According to the U.S. Department of Energy (DOE), refrigeration systems in the U.S. account for 41 percent of the energy consumed by residential and commercial buildings. Buildings consume about 36 percent of the energy used in the U.S. College of Engineering researchers are working to bring those numbers down.
When Madison Ice Arena upgraded its refrigeration systems recently, managers expected some energy savings from the modern equipment. When savings did not meet expectations, they turned to Assistant Professor Douglas T. Reindl (mechanical engineering and engineering professional development) and Professor Sanford A. Klein (mechanical engineering). Klein, Reindl and student Kyle Brownell evaluated the refrigeration system, found problems with its operation and came up with some alternative control strategies to improve the system's efficiency.
Working to improve efficiency at Sub-Zero products are (from left) Professor Douglas T. Reindl, Sub-Zero's Paul Siker and Professor Sanford A. Klein.
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"The arena rejects heat by using an evaporative condenser," Klein says. "In summer the refrigerant is pretty hot. The higher the refrigerant temperature, the harder the compressor works to reject heat. The arena was maintaining that kind of control year round. It doesn't make sense when it's 32 degrees outside to be blasting out 95-degree refrigerant."
When the outside air is very cold, the coolant releases heat more quickly. During the winter, the fans that control heat rejection were cycling on and off every couple of minutes. The team suggested that the coolant temperature be allowed to come down.
"They have six compressors. At first, five of six were running," Reindl says. "When the system came back down to equilibrium, two or three were running."
The cost to cool the Arena is about $40,000 a year. Reindl estimates the new control system will save 25 percent.
Madison-based Sub-Zero Corporation is also looking for increased efficiency with the help of Reindl, Klein and graduate student Andre Gan. Sub-Zero is a maker of high-end domestic refrigerators and freezers. The team is exploring changes to air flow and coil size to improve efficiency and meet DOE 2001 energy standards.
"We have a great university at our back door that we had not been tapping into," says Sub-Zero's Director of Design Engineering Paul Sikir. "This program further developed our relationship with the UW. It looks like we'll stick with the coils we have, but we learned a lot from their study in terms of where we are with the size of coils and energy consumption. That's what feasibility is about."
One feature of Sub-Zero products that distinguishes them from others is a two-compressor system. Most refrigerators have one compressor for both refrigerator and freezer. The refrigerator steals air from the freezer to keep cool. The downside is that freezer air is dry and tends to dry out food stored in the refrigerator. Sub-Zero uses separate systems for the refrigerator and freezer, which helps preserve food longer.
"One of the things we are proposing to them is that they keep the two systems but tie them together to improve the efficiency. It could result in a substantial improvement," says Reindl. "This isn't something they will be able to build next year but down the road it may prove to be pretty effective."
Reindl, Klein and another student, Joy Altwies, also found a method of improving efficiency for another company's freezer, but on a different scale. Agrilink Foods operates a massive cold storage warehouse in Darien, Wis. In it, they store more than 43 million pounds of frozen vegetables. The company wanted to lower its cooling costs.
"We have done a lot of active thermal storage systems for air-conditioning where you buy an ice tank or a water tank and you make ice at night when rates are low and melt ice or chilled water during the day," says Reindl. "That way you don't have to run expensive air-conditioning equipment during the day. You just run a pump. Instead of buying equipment, we proposed they use the product as the thermal storage equipment. Cool the vegetables at night and turn the refrigeration equipment off during day."
With millions of pounds of stored vegetables acting as the thermal mass, Reindl says the warehouse has more than enough capacity. Normally Agrilink Foods maintains a temperature of about minus five degrees. By bringing the air temperature down to minus seven or eight degrees at night and then shutting off the refrigeration equipment during the day, it's estimated the company will save $60,000 per year. Agrilink Foods Environmental Supervisor Joy Becker says the company is obviously pleased with the results. She says if the opportunity presents itself, Agrilink would certainly work with the college again.
--By Jim Beal--
| For further information, please contact: |
Douglas T. Reindl, 608/262-6381
dreindl@wisc.edu
Copyright 1999 The Board of Regents of the University of Wisconsin System
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Date last modified: Wednesday, 03-Mar-1999 12:00:00 CST
Date created: 03-Mar-1999
