Monday, August 31, 2015

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.      

Monday, August 17, 2015

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)







Monday, August 10, 2015

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

Friday, August 7, 2015

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.










  

Thursday, July 30, 2015

Send Superman Over to Fix my Unit

I have noticed something that is happening now in many companies - employees are often asked to be superhuman because of the amount of work to be done and the chronic short handed situation many companies find themselves in. This can lead to looking the other way as employees do things they should not do while trying to do the impossible. I had a recent graduate complain that the company he worked for scheduled him to do an installation by himself which he did not complete until 11:30 PM. He did not even get to the job until after his normal scheduled quitting time. He had a company meeting at 7:00 AM the next morning, which he made. However, in the 7.5 hours between completing the job and returning to work he had to get home, sleep, and return to work. His truck still had the old equipment in it from the night before. He was reprimanded for having a messy truck - a violation of company policy. In my mind, the problem started when he was scheduled to do the impossible. I have heard more than one story like this. Another student told me his wife went from asking when he was going to get a job to asking when he was coming home. Upon graduating, he had responsibility for the large rack refrigeration systems in 15 grocery stores spread across 2 states. He was not left entirely on his own – they gave him a cell phone. Trying to service these far flung, complicated systems which he was just learning about had led to 60 and 70 hour weeks. Students are glad to have the job, but they are often covered up in work before they even have a year in the field. When they demonstrate that they can perform, they are rewarded with more work. I believe as an industry we need to allow new techs a bit of breathing room and time to develop into the techs we want them to be. That means we have to still provide time for education and training, time to sleep, and time to de-compress a bit. The fact that so much responsibility is being shouldered by brand new techs shows our great need. This provides opportunity for people who are looking for a rewarding career which provides the income needed for a good standard of living.  The danger we face in pushing the most promising too hard is that we could literally run our best new prospects out of the trade.  

Saturday, July 25, 2015

How Does an Air Conditioner Cabinet Become Energized?

The last two weeks I have been talking about electrical safety. Specifically, discussing the electrical hazard of an energized system cabinet. This week I would like to discuss ways that the cabinet of a system can become energized. First, for a cabinet to have a voltage other than ground, the cabinet is either not grounded, or the ground has failed. Failure to properly ground a metal cabinet is the first condition that sets up the electrical hazard. But another mistake or failed component is required to actually energize the cabinet. Some are obvious – such as a loose energized wire touching the cabinet. Others are less obvious, such as a grounded electric motor. If a motor is grounded (not shorted or open) and the equipment cabinet in which the motor is mounted is not grounded, when the motor is energized the cabinet will also become energized. Motors can sometimes be grounded and still operate. So you touch an operating unit and get shocked. Another failure that can energize a cabinet is a broken or missing insulator on heat strips. Most heat strips have one side that is wired hot all the time. If the ceramic insulators break and allow the strips to contact the frame holding them, the cabinet can become energized.

A sneaky way for a cabinet to be energized is to wire a 110 volt device into a 230 volt unit using one leg and ground. Basically, current will be going through ground anytime the 110 volt device operates. This alone won’t cause an energized case. But if the ground between the unit and the panel breaks or just gets a bad connection, now there will be a voltage between the case and the actual ground – and the case will be energized. To avoid this, don’t wire 110 volt devices this way. You either need a separate neutral AND a cabinet ground (4 wires), or you need a 230 – 110 transformer. This is why newer electric dryers have 4 prong plugs: two for the 230 volt hot legs, one for neutral for the motor, and one for a cabinet ground.

So here are a few simple rules to help you avoid creating an electrical hazard:

1. All metal cabinets and pipes should be grounded
2. Ground wires should never be used as part of an operating circuit.
3. When equipment has both 230 volt and 110 volt loads, the equipment either requires a neutral wire AND a separate ground wire, or a 230 volt to 110 volt transformer.

Thursday, July 16, 2015

Basic Electrical Safety Tips

In light of the tragic story I posted last week, I thought an article on electrical safety would be appropriate. Here are a few things we ALL should do while working on units:

Assume all units you work on are dangerous
When you inspect hundreds of units and most are safe, it is easy to assume the equipment you will be working on is safe. Don’t assume units are safe, assume the opposite. When approaching a unit, particularly one that you don’t know anything about, assume it is dangerous.

Test BEFORE you Touch
Carry a non-contact voltage detector with you at all times. Test all disconnects and units with the non-contact voltage detector BEFORE touching ANYTHING. While you may go your entire career without ever seeing an energized case or disconnect, they do occur and it only takes a few seconds to test.

All Units and Power tools SHOULD BE GROUNDED
Everything that operates on electricity should have a ground wire. The purpose of the safety ground is to provide a good path for power should electricity contact the exterior metal parts. The idea is for the ground wire to be a better path then you are. The only exceptions are double insulated tools with non-conductive cases.

You should NOT be grounded
Try to avoid grounding yourself. If at all possible, don’t lean on grounded equipment and don’t sit or stand on wet ground or pavement. The idea is to make yourself a poor path. Wearing shoes with thick rubber soles helps.

If possible, turn the power off before working on a unit
Don’t do any more live work than necessary. If you can perform the service or maintenance with the power turned off to the unit, turn the power off. Obviously this is not always possible. For example, the power must be on and operating to check the system charge.

Use only Category III or IV electric meters on HVAC Systems
That “free” meter from El Cheapo Freight is not safe to use on an air conditioning system. You have no assurance that it can withstand voltage surges. Remember, when using an electrical meter the meter quality is what separates you from the electricity you are testing – that includes the leads. They should also be rated as Category III or IV.

Always Use a Fuse Puller to Change Cartridge Fuses
Channellocks, Vise grips, and pliers are NOT fuse pullers. That bit of rubber on the grip is NOT a very good electrical insulator.

NEVER change a fuse with the circuit still energized
Removing or inserting a fuse with the circuit energized can create an arc flash. An arc flash is an electrical fireball which can hurt you even if you are not touching any energized surface.