What Flavor is Your CO2 System?

If you work in any phase of refrigeration, you undoubtedly have heard about the emergence of CO2 refrigeration systems in commercial refrigeration. I had the pleasure of touring the HillPhoenix Refrigeration plant in Conyers today, and I was impressed by both the number and variety of CO2 systems they are currently building. They had Cascade systems, Trans-critical systems, Glycol systems and Booster Systems all using CO2. These are distinctly different approaches to working with CO2.

The transcritical has probably received the most press. It derives its name from the fact that the high side operates above the critical point while the low side operates below the critical point. The name indicates that the system operates on either side, or across, the critical point of the refrigerant. The critical point is the pressure and temperature at which the refrigerant can no longer condense to a liquid. So the “condenser” is really just a gas cooler. The refrigerant does not condense to a liquid until AFTER the pressure is dropped. The critical temperature of CO2 is 88°F, so any time the high side temperature rises above 88°F, the refrigerant will not condense. The pressures are bit higher than you might be used to – over 1200 psig, so not just any compressor and piping will do. However, in a way, the transcritical systems are a bit simpler than the other flavors.

Cascade systems use two complete refrigeration systems – one system’s job is really to cool the condenser of the other system. If you keep the CO2 cold enough, say 40°F, the pressures are not that high. However, to have a 40° condenser requires a system whose evaporator is in that same temperature range and whose condenser is at the normal operating temperature for an air cooled condenser. This system typically uses HFC refrigerant. So you have a heat exchanger and an HFC system to keep the CO2 system cool. This allows wider range of compressors because the CO2 compressors are not operating at 1200 psig. However, the system operating with the normal temperature condenser (80°F – 100°F) will have a refrigerant OTHER than CO2.

And then there are the booster systems. The booster systems incorporate both low and medium temperature racks into a single unit. The low temp CO2 compressors pump into the suction of the medium temp CO2 compressors, which operates at transcritical temperatures and pressures. This way the low temp compressors don’t have to be heavy duty transcritical compressors, just the medium temp compressors. The system uses only CO2, no HFC refrigerant is required, as in a cascade system.

There are also glycol systems, where the refrigeration system cools glycol, which is pumped through the store to the cases. This reduces the amount of refrigerant in the system and reduces leaks by reducing the amount of piping, fittings, and braze joints. What became apparent in my visit was that there are many ways to solve the same problem, and you can expect to see different solutions at different locations. It also is apparent that in commercial refrigeration, CO2 is here to stay and HFCs are on their way out.      

OSHA Updates Confined Space Safety Rules

Contractors who work in crawl spaces and attics may find the latest confined space regulations ... confining! Until recently, residential contractors rarely had to worry about confined space regulations. Now they will need to address confined space regulations on most jobs - both installation and service. OSHA just made changes to the confined spaces rules which will affect everyone that works in residential attics and crawl spaces. Considering that a large amount of residential HVAC equipment is installed in an attic or crawl space, these changes will affect residential HVAC contractors. A confined space is now defined as

1.         Large enough to get your body in
2.         Limited means for getting in and out
3.         Not designed for continuous occupancy

The employer is responsible for providing a competent person to inspect all confined spaces before work begins. This person is looking for any other hazards which can make the confined space more dangerous, such as toxic fumes, low oxygen, electrical hazard, fall hazard, or extreme temperature. (Note this is only a partial list.) If the confined space has any additional hazards it becomes a permitted confined space. Workers can only enter a permitted confined space for the purposes listed on the permit under the conditions and restrictions listed on the permit. A hazard warning must be posted at the entry to a permitted confined space and a permit issued that lists all the details regarding work in that particular confined space. There must be an attendant posted outside a permitted confined space any time a worker is in the space. There are many more regulations. This is honestly only the tip of the iceberg. Suffice it to say, you want to avoid having to declare the confined space a permit required confined space. 

You are allowed to remove hazards to accomplish this. For example, a typical attic with no floor is a permitted confined space based on the fall hazard. If you put boards down for the workers to walk on you remove that hazard, and it no longer requires a permit. Similarly, an electrical hazard can be removed by turning off all power to the confined space. If a confined space has no additional hazards, then you can use what OSHA refers to as an alternate procedure. For this, the competent person must determine that no additional hazards exist, or that they have been removed. The space needs continual positive ventilation while work is being performed. However, the permit and the attendant are not required. Note that this still requires a competent person to inspect the pace BEFORE work begins.

Some logical questions come to mind, such as

Who is the competent person?

The competent person can be one or more of your employees who have been trained to recognize hazards in confined spaces and can use test equipment to test for oxygen level, combustible gasses, or toxic gasses. In the event of an incident, they will be asked to clearly tell OSHA what procedures they used identifying the risks involved with the space. 

Where do I get the permit?

For confined spaces requiring a permit, your company generates the permit – not some government agency. The purpose of the permit is to clearly communicate the conditions under which the space may be entered and who may enter.

When does this go into effect?

The new rules will start being enforced on October 2, 2015.

Where can I read more about this? (Trust me, you NEED to even if you don’t WANT to)

 Final Ruling

Training Webinar Video

Enfocement Date 

OSHA Confined Space Page

Legionnaires Cooling Tower Article

I just saw this article in the NEWS discussing Legionnaires and cooling towers - very good info. Since this ws the subject of my most recent post I thought I would share this important information.

http://www.achrnews.com/articles/130330-legionnaires-disease-sickens-108-in-new-york

Defeating Legionnaires Disease

Legionnaires disease is back in the news. It is caused by the legionella bacteria. The disease is most commonly spread by dirty cooling towers. The legionella bacteria grows in dirty tower water, and is transported to the surrounding area in the mist droplets leaving the tower. When someone breathes in water mist contaminated with legionella, they may contract a pneumonia that can kill people in a few days. 

The good news is that this is relatively easy to prevent by simply keeping the cooling towers clean.  Normal tower water maintenance will prevent the legionella from growing in the tower in the first place. If you have ever had a back yard wading pool for the kids, you know how quickly water left outside can develop slime – literally in a couple of days. Now think how quickly stuff can grow in water that is being heated, as in a cooling tower. Cooling towers need constant maintenance to stay clean. 

This can be done by testing the water weekly and adding chemicals as needed, or by using an automated chemical feed system. Even with an automated system, the water should be checked monthly to insure everything is working properly. Every building that uses a cooling tower should have someone on staff or contracted to keep an eye on the water condition. Some chemical salesmen will perform this service in exchange for buying all the chemicals from them. Obviously, the cost of their service is built into the price of the chemicals. In general, you want to maintain a slightly acidic ph to discourage calcium deposits and critter growth. 

Another reason to keep your cooling tower clean is that the same water circulating through the tower is also circulating through your condenser. A coating of green slime inside your condenser will insulate the condenser from the water passing through, reducing system efficiency. This translates into higher operating cost. You are not saving money by skipping cooling tower maintenance, you are spending it on increased system operating cost. Here are a few links with more details on cooling tower maintenance.

Aqua Chem

Chem-Aqua

SPX

BAC

NALCO