Exploding Refrigeration Containers

Prices for HCFC 22 are finally rising to the levels that were expected this past summer. With the rise in refrigerant price will come increased interest in replacement refrigerants. For your safety as well as your customers safety, make sure you know where your refrigerant comes from. Avoid bargains from people you don’t know. This is not just about obeying the law, it is also about safety. Several container refrigeration systems have exploded after being charged with counterfeit R-134A. Container refrigeration is more difficult to patrol because the containers travel all over the world. Three articles discussing the accidents involving the mystery replacement refrigerant can found World Cargo News, ACHR News, Huffington Post.

Although flammable refrigerant s can be used safely, systems using flammable refrigerant use components designed for that use. Systems designed for flammable refrigerant also have limits on the amount of charge in the system and carry warnings regarding the flammability of their refrigerant. To stay safe, only use SNAP approved replacement refrigerants and only purchase refrigerant through the normal supply chain.

AHR Expo 2012

The AHR 2012 Expo is happening this week at the McCormick Place in Chicago. It runs Monday January 23 – Wednesday January 25. The AHR Expo is the granddaddy of all air conditioning industry shows. It is co-sponsored by two of the HAVC/R industry heavy hitters: ASHRAE and AHRI. This is truly a world class show with people and companies from all over the globe. My experience has been that it is really impossible to look at all the exhibits in a day because there is so much to see. If you are located anywhere close to Chicago and can find a day to visit the expo, it is well worth your time. Instructors and students can get so much free literature that it will take you hours just to read it all. There are many free seminars every day for discussion of new technologies and products. The AHR Expo is usually where HVAC/R companies roll out their latest and greatest, so it is a perfect place to see where the industry is heading. Perhaps most useful to instructors are the contacts you can make with OEM suppliers, manufacturers, wholesalers, and industry technical gurus of all stripes. You may not be able to swing by this year, but you can still see who is there and even take a look at some of their info via a virtual show feature on the AHR Epo web site. On the main page of their site are photos and tweets. At the top of the main page is an Exhibitors menu. One selection in the middle of the list is AHR Expo TV. Videos of different vendors booths are available to see the the booth without traveling to Chicago. Also, check out the exhibitors list. There are so many, that it is organized as a search. When you get to a specific vendor, their contact information is listed. This is a great tool for searching who's who in the HVACR field. So if you can't swing by the Windy City, take a virtual tour.  

Transcritical Refrigeration

There has been a lot of work in the last decade on using carbon dioxide as a refrigerant. It is inexpensive, non-flammable, non-toxic, compatible with most materials, relatively friendly to the environment compared to fluorinated refrigerants, and has the potential to be quite efficient. There is one large obstacle to using CO² as a refrigerant: its critical point. The critical point is the highest pressure and temperature where the refrigerant can still condense. At and above the critical point there is no distinction between gas and liquid, so no condensation or evaporation can take place. The very top of the hump in a refrigerant enthalpy diagram is the critical point. A normal refrigeration system is a subcritical system because all the system components operate at pressures and temperatures below the critical point. (See Unit 18 in Fundamentals ofHVACR for more details on refrigeration enthalpy diagrams.) The problem is that critical temperature for CO² is 88°F. The condenser saturation temperature for most refrigeration systems is above 88°F, especially for air cooled systems that must use hot outdoor air for cooling the condenser. This prevents the use of CO²  in a “normal” refrigeration system which uses an evaporator to absorb heat and a condenser to reject heat.

One application of CO²  refrigerant is called a transcritical system because part of the system operates above the critical point and part of the system operates below the critical point. Subcritical, supercritical, and transcritical all describe a refrigeration system’s operating pressures and temperatures relative to the critical point of the refrigerant in the system. A typical “normal” refrigeration system is a subcritical system because everything happens below the critical point. In a supercritical system, all the components operate at pressures and temperatures above the critical point. A supercritical system operates on gas compression and expansion with no change of state. All heat transfer occurs by the gas changing temperature. A transcritical system operates both above and below the critical point. Heat is absorbed in an evaporator where liquid evaporates to a gas, but heat rejection takes place above the critical point, so there is no condensation in what normally would be considered the condenser. The refrigerant does not condense back to a liquid until after the pressure is reduced. For more details on transcritical refrigeration systems, see Unit 85 Commercial Refrigeration Systems in Fundamentals of HVACR, 2nd edition.