looking for info on chillers for mri scanners, may have job with mfg. have exp. with everything from 1/4hp to racks but never worked on mri chillers/any info thanks.
What mfg? When you job, do you mean as a contractor or as an employee to the MRI mfg?
Do you have any specific questions? Or should I just rattle off the experiences I have?
the position is as a employee, the mfg. is fonar no specific questions. just any info you know about the system they use to cool these machines, i have worked on many types of chillers just not in the medical field,thanks again.
A chiller is a chiller. Uses gas. I would imagine A DX system of some sort. Maybe a constant suction. At any rate, it can not be much different than anything else.
work on these over the years they always have 2 stages of cooling for back up,and hgbp for low ambient loads and fan cycling to maintain suction.these come complete pump barrel all within the condensing unit just pipe it into the MRI related panel for the magnet. http://www.arctichill.com/Medical.htm
I haven't worked on any, but the mobil MRI unit at the Orthopedist's office I went to a while back has liquid helium as the primary coolant for the MRI magnets and liquid nitrogen to keep the helium in a liquid state. There's a secondary R22 chilled water system for cooling the cabinet frame and facings and then a package DX A/C to cool the space......all in a 40 ft semi-trailer out back.
[Edited by icemeister on 11-14-2004 at 05:42 PM]
Every manufacturer of chiller equipment for MRI equipment does it slightly differently and even the same manufacturer may have different models. Basically the refrigeration side is usually simple enough, Hot Gas bypass, low ambient controls etc. Chiller fluid can be plain water or Glycol mixture. There is usually some back up system using city water ( the magnets can run up-to $1,000,00.00 plus so a working backup system is a must), Normally the chiller section will be cooling the Helium loop that does the actual cooling of the magnet, but some systems do use direct cooling of certain areas of the MRI. The refrigeration side is easy, but you must have a good understanding of the control circuit. Be prepared for after hours work, the cost of these machines means that they can not afford to have them down for Pm's during normal operating hours.
"There is plenty of room at the top because very few people care to travel beyond the average route. And so most of us seem satisfied to remain within the confines of mediocrity." -- Benjamin Nnamdi Azikiwe, first president of Nigeria
Get your eyes and body checked for ferrous metal in a CAT scanner before you get near a MRI magnet even outside the vehical. If your planning to have children put the lead jacket over your nades before being checked in the CAT scanner. To many rads for your nads is not good. Been about 8 yrs. since I've worked on Cats or Mr's so some things may have changed.
Be safe not fast. body parts don't grow back
Fonar used to use Dunham Bush ACDS chillers, but when they started shipping them from Malaysia they kind of backed off of that. From what I know the last couple of years they have been buying 30 ton chillers from Trane, and having the pump system put together in the field.
The company I used to work for sold them 4 or 5 10 tons in 2000 (I think, maybe '99). We then sold them a 25 ton through KMA sales (a former DB rep). I actually went to the factory with the rep before the sale. They said it didn't keep up because it didn't work, we sent out a chiller guy, I think Chiller services it was called, and twice it was checked out OK. They never paid for the unit and sent it back aftet 6-8 months. No big deal, it happens. From then they were using Trane.
As far as I know, Fonar is the only MR outfit who buys an HVAC style chiller and has the pumps and all field built. But I haven't been in contact with them for a couple of years, so things could be much different now.
Generally you are cooling two things, a cryo compressor, and a bank of heat excahngers. The cryo compressor is kind of like a condensing unit, but for cryogenic helium. The liquid helium is what cools the actual magnet. The chilled water is kind of like condenser water (assuming you have a water cooled cryo compressor) for the cryo system. In fact on the Sumitomo compressors (used on GE and some Philips systems) it actually uses a coaxial hxr.
The heat exchangers use the chilled water to cool a loop of deionized water that cools the all of the electronics.
Don't know why I am wasting your time with this, the guys at your place can tell you all of this.
The thing about an MRI is that it means the chiller is at part load, sometimes 10-20% most of the time. It kind of depends on where it is and how it is used. In a smaller hospital, it probably is in standby more. If it is in an imaging center, that thing needs to run around the clock to make money, so it is usually cranking all the time. Since Fonar specializes in the Open MRI I would guess that most of them are in Imaging Centers. The chiller should have some way to unload, with either multiple stages or HGBP. HGBP is kind of ineffiecient if it running on standby most of the time. A large glycol reservoir kind of helps keep things stable.
Some one mentioned city water backup. At the bare minimum, you should have some way of putting city water through the cryo compressor. You can have it manual or some kind of automatic system. Filtrine, Arctichill, Liebert, and Schreiber all makes packaged boxes with everything inside so you can just hang it on the wall. If you lose water to the cryo compressor, it shuts off and then you boil off helium and then the Doctor goes nucking futs.
The hardest thing for a chiller manufacturer to deal with is that the MRI crew wants to spec one chiller that is sutiable in 100% of all sites. The chiller to sit in the direct sun in Vegas, must be the same chiller that will work in Pt. Barrow Alaska in January. This usually leads to problems. A base model should be specified to the chiller mfg, and then features specific to the site added.
Filtrine-IN the spec for Hitachi. Few others get in there. They are also speced for Varian (Linear Accelerator). They are not bad chillers, but super overpriced, for a machine that is just built out of Copeland condensing unit.
Arctichill- I don't think they have an OEM deal with anybody, but they get a lot of medical chillers out there. Make a nice chiller.They have a pretty nice switchover box.
Liebert- Used to have an OEM deal with Picker, who became Marconi and then bought by Philips. Unit cost too much and wasn't anything super special. Not a bad machine though.
Krause- Almost every Siemens sysem uses their 15 ton or their 25 ton. THe unit is super expensive. Like 50 or 60k. If Schreiber and arctichill get in there every once in a while.
Schreiber- They have an OEM deal with Philips, every Philips MR gets a Schreiber 10 ton. They used to supply a 4 ton for almost every CT, but the new CT doesn't need a chiller. THey also build a ton of 3 tons for GE.
Ellis and Watts- They build a pile of chillers for GE in an OEM situation. But a lot of others get chillers for GE machines because they give the siting people a lot of flexibility.
Doctors are the most demanding SOB's in the world. But if you come from market reefer then this won't be too bad of a transition.
Probably too much info, but this movie I am watching is pretty boring. Hope it helps.
[Edited by clydemule on 11-15-2004 at 11:54 PM]
Clydemule: Thanks for the detailed resource info. I have a question and perhaps your advice. I am a controls guy, not a mechanical guy, so I am not familiar with all the makes and models of chillers used in MRI apps.
I use a small web server device to monitor and alarm whatever variables the customer wants to monitor. Alarms are sent out over the customers network and routed as emails to wherever they want them to go (their service provider, etc.). I have a request to use this monitoring device on MRI machine chiller systems -- mainly just monitoring the temps of the cooling media for an MRI and a CT Scan machine. If the chilled water goes above a programmed setpoint, send out an alarm... The device I use comes with software that allows alarms and data to come from 100's of sites and the alarms and data to be stored and put into maintenance reports, etc. It also allows inquires to be made remotely into any MRI facility over the customer's network.
I asked them why they wouldn't want to monitor alarm conditions directly from the chiller itself. Wouldn't there be better ways to monitor these expensive machines than just by monitoring the chilled water temperatures? I can use modbus communication protocol to gather internal alarm information from the controllers on the chillers if they are using a standard PLC -- most all of them have a modbus interface. Are there remote alarm contacts provided in these MRI chiller packages?
Anyway, I appreciate your input and opinion. From a servicing standpoint, I think you would have a better feel for what kind of information would be of value from a remote monitoring standpoint. As you said, the most important thing is to keep these MRI's up and running.
The MRI only cares about 2 things in terms of chilled water:
1. Is the water cold enough?
2. Do we even have water available?
So yes, you could look at the alarms from the chiller, but as a bare minimum, you only need the two above points. What alarms you can get out of the chillers depends on how what the chiller manufacturer gives you. FOr example, I densigned an MRI chiller with a microcontroller that can generate some 15 different alarm conditions. However, all of these alarms fire a single alarm contact. A newer version of the software hsa two alarm contacts, an OH CRAP I AM TOTALLY SCREWED alarm and an OK, I HAVE A PROBLEM BUT I THINK I CAN STILL DELIVER COLD WATER ALARM.
The major alarm can be used to send a signal to an automatitc city water switchover device, whereas the other alarm just fires a light that says "come check me out.
For example, on a two compressor unit, if one refirgeration system goes down, the maint. alarm will fire first. In general, if a chiller has a big enough reservoir, you can get thorugh a scan with only 50% capacity. If the chilled water temperature runs away, or if both reefers go down though, the controller will fire the failure alarm. If the glycol level gets low, the maint alarm fires, not the failure alarm. You get the idea.
So what is the adavantage of detecting that the unit has kicked off on high head pressure? There really isn't one, other than for diagnostics. But you will have to have a tech out there anyway, and he SHOULD be able to figure that out. ANyway, when the unit kicks off on high head, the end result is the water temperature will go up because you reefer system is not running. You have the same end result. Plus to actually determine the actual failure, you will have to somehow scab into the wiring to hook up to the HP switch.
Then there is the fact that you could look at more information, suction pressures, head pressures, etc. to look for trends. But who is going to look at the data and determine a potenital problem before the machine goes down? No on at an imaging center, I can tell you that much.
I would say the most of the controllers do NOT have MODBUS
built into them. The controller I use (Carel) have a Modbus gateway, but you have to add a RS485 card first, and then wire that to the gateway.
One thing you may want to look into is being able to hookup into the MRI service system. A lot of them have webgateways with spare digital inputs, that are setup to call a field service engineer from the MRI mfg. if there is a problem. That will have to be cleared through the MRI people first though. This way the customer doesn't have to have parallel systems.
Thanks for the thorough reply. I am familiar with Carel (been over to their plant in Italy and offered shot after shot of espresso all day long .. lol)
I see what you are saying .. keep the alarms simple because a tech will need to go to the site anyway.
The service company that has requested this tie in to the MRI chiller is looking to take the service business away from a competitor ... I believe Philips has a service group that is taking care of the chillers (big $$$$).
This HVAC service company is well able to service the chillers and are looking for a fast and convenient way to handle the alarms over the customer's network (not a modem) and aggregate the info. The small system I have would allow the ability to diagnose a pending failure if it is able to grab the pressure info and such and run the trended data through a program in the small ethernet web server we'd install at each MRI facility. That's why I was hoping for a modbus interface that would expose the registers holding those points of information.
Well, it sounds like monitoring the chilled water temp and the maintenance and failure alarm contacts (if they are available) would be less complex and would achieve the primary objective of immediately identifying a down chiller and getting the alarm to the service dispatch.
Is the webgateway you refer to a built-in OEM function that comes with the MRI machine for self-diagnostics? Once hooked up, where would its alarms go? Does it use special software to set up and configure the destination and content of the alarm strings?
Thanks for taking the time to post ... I appreciate your advice and look forward to your reply.
Dunno if you are comforatble telling me, but who is this service company, and what brand MRI is this for?
Also, who is the chiller mfg?
I would love to go to the Carel plant in Italy. I have only been to Carel USA in Manheim PA. Do you use Carel controllers and write code for them?
I don't have a whole lot of details about the MRI mfg web interface. All I know is that is ties into a service center somewhere. I know that Philips can actually run a scan remotely.
I have used the Carel Webgate. You connect to the controller (Carel PCO2) via Rs485 serial card plugged into the controller. YOu then hook up the webgate to a router, and assign it an IP address (deault IP is 192.168.1.1).
You know what? WHy don't you just call me, if any of the other members want to know more I will post the info.!
I am in San Diego.