Heat is a formidable enemy in MR and CT chiller design

by John W. Mitchell, Senior Correspondent | September 09, 2015
From the September 2015 issue of HealthCare Business News magazine

Fouche said they have worked with designs for both water- and air-cooled imaging machines. The two agreed that more often than not, the equipment manufacturer provides any cooling that is specified, but they will work up specifications for a chiller if needed.

“If we are spec’ing the chiller, it’s not just a matter of finding the best matched unit,” said Wood. “We have to work with the architect to find space. For example, is there enough ceiling clearance for a bigger chiller if it’s a retrofit? The machine will also need delivery of electrical load and water if needed. I recommend to clients that they purchase the imaging unit and the chiller as a package deal. This helps to prevent change orders later in the project.”

He cited a project in a New York hospital where a CT and MRI were being installed and both had different specified chilling temperatures. While both had closed chilling systems using glycol, the plan also called for domestic water to supplement the cooling. “If you’re removing heat with circulating fluids, it’s easier to build in redundancy,” said Fouche. “There are three typical options that can be provided for back-up chilling if they meet the manufacturer’s specifications.”

These options, according to Fouche, are: chilled water from the building chillers, chilled water from dedicated chillers, and domestic water. He added that the drawback of domestic water is that it can be wasteful, expensive and may not be cold enough. If building chillers are used, the operation schedule must be confirmed to make sure the chiller plant is not shut down in the winter. Jelinske agreed that any design for MRI and CT must include chilling redundancy.

No power or chilled water and the MRI is out of service. A back-up source of emergency chilling lowers helium loss if a problem develops. According to Jelinske, spending decisions about redundant cooling, as well as power supply, come down to a decision about the worst-case scenario. What failure mode are both outpatient and hospital operators willing to accept?

In an outpatient setting, an operator may be willing to accept downtime and equipment damage that only results in a loss of income. For a hospital, he said the primary cooling system should be relatively robust, but a domestic water-chiller backup is the very minimum that should be engineered into the system, because lives can be at stake if imaging equipment fails. Other options are for a stand-alone imaging equipment chiller to back up the in-house water chiller with a redundant chilled water loop and portable temporary units that can be located as necessary around the facility, or with portable chillers mounted on truck trailers.

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