executive director of
facilities for the
University of New Mexico
Health Sciences Center
stands on a cooling tower
Heat is a formidable enemy in MR and CT chiller design
September 09, 2015
by John W. Mitchell
, Senior Correspondent
For Bernie Loeffler, executive director of facilities for the University of New Mexico Health Sciences Center, imaging cooling comes down to a basic value proposition. “Think of what happens when you have your laptop in your lap for too long — it gets hot,” he said. “The same thing happens with a CT or MRI. All those moving parts and pieces work hard to create an image. That creates heat. It’s my job to get rid of that heat.” With an older facility — some of the original UNM buildings date back to the 1950s — and summer temperatures that routinely hit over 100 degrees, Loeffler preaches the gospel of redundancy — building in a backup cooling loop if the primary loop fails. All of the medical center’s four MRIs and three CT scanners are on double loop-chilled water systems backed up with emergency power as well as the hospital’s stand-alone emergency diesel generators. The medical center relies on a wide array of manufacturers to meet their CT and MRI needs, including Siemens, Phillips and GE.
“You can’t just think about getting water to these units, you also have to get power to the units to run the chiller pumps in any kind of situation. We have power outages quite a bit,” said Loeffler, who speaks about system engineering with all the gusto of Scotty, the engineer from the TV series “Star Trek.” He said that in the eight years he has been at UNM they have doubled the chiller water capacity, which is just as vital for the IT functions that run the imaging computers and software as it is for the equipment itself.
In this time of rapidly advancing technology, MRI and CT have improved the lives of millions of patients. But as Loeffler notes, the laws of physics are also hard at work: nearly every milestone in imaging capability creates a corresponding increase in residual heat. Heat can cause these highly sophisticated machines to produce poor image quality and even fail with a patient on the table. A big job for imaging manufacturers and engineers is to dissipate growing heat loads to ensure outcomes and safety.
Turner Hansel, vice president at Filtrine Manufacturing Company, which makes medical chillers, can put a number on that heat. “An MRI on stand-by generates 28,000 BTUs of heat. As soon as a scan starts, that heat load goes up to over 200,000 BTUs, nearly tenfold,” he said. Hansel said it’s their job to engineer a chiller so a doctor, patient or technician never has to think or hear about imaging chillers undergoing downtime. But that doesn’t mean hospital leaders should not be thinking about chillers.
“There is a tendency for administrators who approve chiller purchases to think that if the new MRI fits into the old room, it’s all good,” said Mark Jelinske, a senior associate and mechanical engineer with Cator Ruma, an engineering firm with over 65 years of experience solving cooling challenges for its clients. Its recent projects include engineering design for the new $700 million St. Joseph’s Hospital in Denver.
“But it’s not a matter of swapping the old equipment out for the new,” Jelinske said. “Chiller cooling today works in tandem with the air cooling of a building’s HVAC system to adequately cool the air in the space in which the machine will operate — both the chillers and HVAC are part of the heat solution.” Jelinske noted that it’s important to pay attention to this, because funding for a new MRI install might require money from another bucket besides the capital budget. The costs to properly chill an MRI or CT and the space with the right HVAC configuration can be significant. For example, delivering additional air or water cooling with the right power supply down through a five-story building to a new machine on the ground floor will require money from the hospital building and maintenance budget, and require input from the hospital’s facility manager.
All of the experts interviewed agreed on two rules to keep imaging operational. In the first they stressed that imaging chilling does not stand alone but rather works in tandem with HVAC space cooling. Loeffler regularly deals with hot spots caused by external summer temperatures that have an impact on the computers and ambient temperatures. This creates discomfort for imaging technicians, radiologists, nurses and patients. The second point of agreement is that good planning and communication before a purchase is vital.
“If a client is slow in cutting a purchase order, sometimes getting complete and accurate information from the manufacturer about the machine that will go in the space is a challenge when we’re trying to plan the chilling and cooling load,” said Rick Wood, a senior mechanical engineer with Smith Seckman Reid, Inc. (SSR). He and his colleague Andre Fouche, also a senior mechanical engineer with SSR, both spoke to HealthCare Business News.
“So it’s not unusual for us to be working off generic drawings that might or might not be close to what’s going to be installed,” added Wood. He said about 70 percent of their work is for health care clients. This includes chilling and cooling needs for many hospitals, such as Rockingham Memorial Hospital in Harrisonburg, Virginia, Cook Children’s Medical Center in Ft. Worth, Texas, and Methodist Olive Branch Hospital in Olive Branch, Mississippi.
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.
“Regardless of the market or the application, the main objective is to ensure as close to 100 percent uptime as possible. The only downtime should be scheduled,” said John Carmody, vice president of sales and marketing for KKT Chillers, Inc. “Obviously any unplanned downtime is not favorable from a health care or revenue perspective.” Carmody said KKT designs a couple of features in their chillers to ensure performance longevity and redundancy. These include variable speed in such components as the compressor, pumps, and fans, which keep the chiller unit running at all times in response to the heat load. This prevents sudden on-and-off starts to reduce wear and tear, which in turn extends the life of the components.
In addition, according to Carmody, pump failure tops the list of components that fail in a chiller, so KKT is introducing a new chiller model — the cBoxX line — which uses two pumps. Hansel, with Filtrine, said a common cooling design known as storage method is prominent in their chillers. “We build our units with a 55- to 550-gallon tank, filled with a combination of glycol and water to cool both the cryo compressor and the gradient coils. Each component has different cooling needs,” he explained. Hansel said additional backup could be provided either from city water (if below 75 degrees) or building chill water.
According to Donald Decker, national account manager for health care with Daikin, many of their hospital clients are operating in buildings constructed earlier than the 1970s. Daikin generates $18 billion in space cooling revenue a year. “Adding new technology tends to change the design of these buildings from how the space use was originally intended,” said Decker. “They need more cooling tonnage, but only have the same amount of space available to put a new unit in.” He said new design and technology advances, such as magnetic bearings, variant refrigerant flow, and centrifugal design, produce very little heat, save energy and are much quieter, all of which helps fit more powerful units with higher capacity into existing spaces.
“This is a very common problem and solution,” said Decker. “We understand the pain points that administrators have with behind-thewall costs that don’t directly touch the patient, so we work to make a case for upgrades as an investment.”
To this end, Mark Kearschner, vertical market manager for health care, also at Daikin, cited the advantages in considering the entire cooling needs of a hospital, not just spot solutions. He said the payback on a facility redesign with the new available designs and technology can actually produce much-improved cooling and pay for a project through energy savings in as little as three years or less. Daikin client Methodist Dallas Medical Center, for example, achieved payback with a new HVAC system design in 18 months.
Bill Bonneau, principle engineer, MR heating and cooling at GE Healthcare, said the trend is for their customers to order MRI systems with a chiller package. He said that customers are seeking standardization and a few vendors to work with on major installation, expansion or a new-build program.
Bonneau noted that several recent chiller technology advances reduce chiller load and power consumption. Free cooling is a design that uses ambient air to remove excess heat from the MRI system and room environment prior to using the chiller. Free cooling is typically a standalone optional piece of equipment supplied by the chiller manufacturers and designed to work with the outdoor chiller directly.
Also, advances in temperature-controlled, variable-speed condenser fans and compressors on the chiller help reduce power consumption. Bonneau noted for chiller manufacturers, the environmental trend to reduce hazardous waste limits the selection of cooling fluids that are currently optimal.
Loeffler at UNM said they do not include chiller packages with their MRI and CT purchases. Instead, they engineer both primary and redundant chilling requirements into their existing in-house chiller systems. This consists of three, large, industrial 300- to 400-ton chillers and three 800-ton cooling towers.
“These units will run 25 years if you take care of them, and another five [to 10] years past that if you don’t overuse them,” Loeffler said. Bob Bachman, president of Advanced Mobility, a subsidiary of KY Trailers, is a man who knows a few things about imaging chillers. The company builds specialty trailers for clients who need everything mobile, from television production studios to mobile MRI and CT scanners. “We have to design specs that meet the OEMs’ specifications for temperature range, chilled water temperature and flow, and present solutions that meet or exceed those specifications,” said Bachman.
He added that the units have to be capable of running 24/7. To engineer this kind of performance, Advanced Mobility has been working with just a few chiller makers for the past decade. He said that with only one exception, there has not been any significant OEM change in the past 10 years in mobile imaging — so familiarity works in their favor. But even so, the chillers in their rigs are designed to operate under extreme and stressful conditions.
“We design-in overcapacity and redundancy,” Bachman said. He noted the chilled water and air-cooling to keep the imaging technicians and patients comfortable in the trailer are designed off the same unit. Depending upon the need, the load between water and air can be weighted one way or the other. “We have two compressors and fans, so if one shuts down the unit will continue to operate,” he said. “Our typical chiller is at 225,000 BTUs, so we over-engineer the design. And, of course, the first priority is to keep the chilled water around the shield collars for the imaging equipment.”
He said that while customers are responsible for maintaining the mobile units they sell after the warranty period, they have not received any complaints about chiller malfunctions. According to Bonneau, there are several potential reasons why chillers fail. These include: corrosion on the equipment or in the plumbing associated with the chiller MRI system; blockages in the coolant lines prohibiting proper coolant flow; and mechanical failure of components, such as fans.
Jeremy Fox, a project manager at Direct Medical Imaging, which refurbishes used MRI and CT equipment and distributes KR Product chillers, pointed out that it’s not just hot weather that is hard on chillers. “Any extreme weather takes a toll on chillers. They can be degraded as much by freezing and thawing as heat in cold climates,” he cautioned. “The part of the chiller that is exposed to the elements is always at risk of failing.”
He said the average lifespan for a chiller is about 10 years. None of the sources interviewed felt that the market for chillers was leveling off or declining. Bonneau, with GE, reported that overall demand for chillers is increasing because of the growing need to manage the imaging operating environment. Despite the challenges and cost, MRI and CT service cannot be provided without chillers. “It’s amazing what you can accomplish with 54-degree chilled water,” Loeffler from UNM summarized.