Saturday, October 15, 2016

Personal Gas Safety

Time for furnace tune-ups is here. Soon you will be taking the first no-heat calls of this heating season. No doubt you will be inspecting equipment for safety concerns that affect the customer. Don’t forget to pay attention to your own personal safety. Gas leaks, leaky vent systems, incorrect combustion, and lack of combustion air can all create immediate hazards to the service tech working on the system. There are pro-active steps you can take to stay safe while working on gas fired equipment.

Gas Leaks
If there are existing gas leaks it is possible that a combustible atmosphere exists in the space. Ideally, you want to check the air in the space for combustible gas before entering. You can use an electronic combustible gas detector for this. Many techs now use these to check for gas leaks, so you might already have the tool. Just turn it on and let it sample the air in the room as you enter. There are also personal detectors which you can wear to monitor the conditions wherever you are. If you do detect combustible gas in the room, do NOT turn on or off any electrical switches and leave the room. Shut off the gas outside and ventilate the room before continuing. You will have to turn the gas back on to find the leak, but you can ventilate the room and start with a safe atmosphere while you are doing it.

Carbon Monoxide
Negative room pressure, incorrect or leaky gas venting, and lack of combustion air can all contribute to a build-up of carbon monoxide in the room. You can’t smell or see carbon monoxide, so it is especially dangerous. Again, you should test the atmosphere in the room. There are electronic detectors made to check for carbon monoxide in the air, and some are made to wear to monitor the air continuously. If the monitor indicates a build-up of CO in the room, you should shut off the gas outside the room and ventilate the room. Once the room is cleared of CO you can start to look for the cause. Before turning the gas back on make sure to check for obvious things such as blocked combustion air intakes or compromised gas vents. After restarting the furnace you should check the flame color and test the flue for proper operation. Also be sure to check the flue gasses for CO.

Gas Ignition Problems
When observing a gas furnace light, you should never place your face directly in front of the furnace. If there is a delayed ignition or flame roll-out you can be inside the fire-ball. I have made that mistake. It was over before I knew what happened. For a second all I could see was yellow because my head was in the fireball that came out of the furnace. Luckily it just singed my eyebrows a bit and gave my face a slight burn similar to a sunburn. Afterwards I worked out what had happened: a leaky gas valve had allowed a build-up of gas prior to turning the furnace on. Had my face been off to the side I would not have been in the flames when they came out.

Don’t leave your personal safety to chance. 
Take steps to detect and avoid possible personal safety hazards. It is an inconvenience to the customer to have to call 911.

Friday, October 7, 2016

Sorting Out Refrigerant Flammability

Most techs know that ASHRAE Standard 34 originally established three categories of refrigerant flammability: 1,2, and 3. They ranged from 1 – nonflammable, to 3, highly flammable. Category 2 was listed as mildly flammable, or somewhat flammable. Then they added a new category – 2L – for an even lower category of still flammable refrigerant. I admit that I always found that a bit confusing. In my mind, it either burns or it doesn’t.  In order to get a better handle on this I have done some studying.

Two characteristics are used to differentiate category 1 and category 2 refrigerants: the lower flammability limit and the heat of combustion. The lower flammability limit is the lowest percentage concentration of gas in a gas-air mixture that will ignite. Concentrations lower than the lower flammability limit will not burn. Even highly combustible gasses such as gasoline have a lower flammability limit. Refrigerants with a lower flammability limit of 3.5% or less are considered class 3, highly flammable. For comparison the lower flammability limit of gasoline is 1.4%  and propane‘s is 2.1%. Another way for a refrigerant to be considered class 3 is for its heat of combustion to equal or exceed 19 million joules per kilogram. In general terms, it does not take very much class 3 refrigerant to burn and when it does it is very hot.

Class 2  refrigerants have a lower flammability limit greater than 3.5%. It requires more than 3.5% concentration in order to ignite. Class 2 refrigerants do not burn as hot as class 3 refrigerants: their heat of combustion is lower. The lower heat of combustion is important because that is what sets other things on fire. It is possible for a class 2 refrigerant to burn without burning up everything around it.

So where does the 2L come in? Flammability class 2L is really a subclass of 2. Refrigerants with a 2L designation have a burning velocity of 10 centimeters per second or slower. The burning velocity is how fast the flame travels. A burning velocity of 10 cm/s means that the flame will travel about 4 inches in a second. In contrast, the class 2 refrigerant HFC-152a  has a burning velocity of 23 cm/sec.  – a little more than twice as fast.  Propane, a class 3 refrigerant, has a flame velocity of 39 centimeters per second – 4 times as fast.

Why is this important? The flame velocity and heat of combustion are what determine whether or not an explosion can occur. Rapid burning and high heat of combustion expand the air and combustion gasses so rapidly that great pressure is created, blowing things apart. Class 2L refrigerant cannot burn fast enough or hot enough to blow anything up. In many cases, a burning class 2L refrigerant will not even catch other combustible things around it on fire.

To summarize:
Class 3 Refrigerants have a lower flammability ratio of 3.5% or lower and/or a heat of combustion equal to or greater than 19Mj/kg. They burn fast and hot.

Class 2 Refrigerants have a lower flammability ratio exceeding 3.5%. It takes more of them to burn and they do not burn as hot as class 3 refrigerants.

Sub-Class 2L Refrigerants in addition to a lower flammability ratio exceeding 3.5% also have a flame velocity of 10 cm/sec or less. They burn slowly and without releasing as much heat.

Class 1 Refrigerants do not burn.

Friday, September 30, 2016

New EPA Rules

On September 26, 2016 the EPA issued a new Final Ruling updating the regulations for handling refrigerants. Don’t panic, there is plenty of time to prepare. For technicians, the first important enforcement date is not until January 1, 2018 and some parts do not take effect until January 1, 2019. However, you do need to prepare. There are more changes than I can list in a short blog post, but I will provide an overview and plenty of links to the information.

Mostly about Global Warming
Most of the changes have to do with limiting global warming by reducing the use and release of HFC refrigerants. Some of the more significant changes include requiring certification to purchase and handle HFC refrigerants, reducing the allowable leak rate for ozone depleting and global warming refrigerants, specifying regular leak inspection for equipment which has exceeded the allowable leak rate, and requiring record keeping when disposing of systems with more than 5 pounds of refrigerant.

Technician Certification
Staring January 1, 2018 technicians must be certified to purchase and handle nearly all refrigerants, not just ozone depleting ones. One curious exception is that sales of small cans of refrigerant for use in car air conditioning systems will not require certification. The cans will be required to have a valve, but sales to the general public will still be allowed.

Leak Rates Lowered
Starting January 1, 2019, the leak rates will all be lowered and will apply to HFC and replacement refrigerants as well as ozone depleting refrigerants. A few specific refrigerants are exempted from the venting prohibition and the leak requirements. These exempted refrigerants include carbon dioxide, nitrogen, water, ammonia, chlorine, hydrocarbons, and R441A. The leak trigger rates which require repair are now 30% for industrial process refrigeration, 20% for commercial refrigeration, and 10% for air conditioning and “other” uses. Note that the refrigerant charge level for these trigger rates remains at 50 pounds or more.

Leak Inspection
Beginning January 1, 2019, the new rules require regular leak inspection for systems that have reached the “trigger rate” requiring leak repair. The frequency of the required inspections is determined by the type of system and the size of the system charge. Quarterly inspections are required for commercial refrigeration and industrial process cooling systems which hold 500 pounds or more refrigerant. Commercial refrigeration and industrial process cooling systems holding at least 50 pounds of refrigerant but less than 500 pounds require an annual leak inspection. Air conditioning systems holding at least 50 pounds require annual leak inspections. When leaks are repaired, an initial system tightness verification is required before adding refrigerant. A second system tightness verification is required after the system is up and operating. Records of all of these tests are required.

System Disposal Record Keeping
Starting January 1, 2018 technicians disposing of systems with at least 5 pounds of refrigerant must keep records regarding the equipment and the refrigerant charge. Specifically, you must keep
The location, date of recovery, and type of refrigerant recovered for each disposed appliance
The quantity of refrigerant, by type, recovered from disposed appliances in each calendar month;
The quantity of refrigerant, and type, transferred for reclamation or destruction, the person to whom it
was transferred, and the date of the transfer. Note that you are not required to report the quantity of refrigerant recovered from each individual system, but rather, the cumulative quantity of refrigerant recovered each month.

Links to EPA Documents
This is just an overview. To really understand all the details you should consult the information published by the EPA. Here is a list of links to some of that information.

Advance Copy of Final Rule

Subpart F—Recycling and Emissions Reduction

Fact Sheet on New Regulations

EPA Page on Revised Regulations

EPA page on leak requirements

Friday, September 23, 2016

HFCs not Going Anywhere

HFCs are not going away any time soon. I am sure you have all hear about the push to reduce or eliminate HFC refrigerants because of their global warming potential. This past weekend at Comfortech 2016 I sat in on a very informative session by Rob Yost on refrigerants. One big point was that low GWP replacement candidates for R410A are all rated at 2 or 2L for flammability. The reason is pretty straight forward. To be non-flammable a chemical must be relatively stable. However, that stability means it lasts longer in the atmosphere, which increases its global warming potential. In other words, low flammability and low global warming potential are somewhat opposites in terms of chemical properties.

The newest low GWP blends being developed are actually blends of both HFOs and HFCs. The highest pressure HFO developed at this time is very similar in pressure to 134a. Obviously that won’t replace 410A. However, mixing it with some higher pressure HFC refrigerants yields a much lower global warming potential than 410A at working pressures that are similar to 410A. However, this mixture will be flammable.

The current building codes in the US don’t allow flammable refrigerants inside buildings in most circumstances, so none of the refrigerants presently being studied can be used under the current building codes. The next revision for building codes is due out in 2018. However, the window for incorporating exceptions for lower flammability refrigerants into the 2018 code has already passed – and no exceptions or conditions for the use of 2L flammable refrigerants are in the upcoming 2018 code. That makes 2021 the closest date that flammable refrigerants could possibly be used inside buildings. Even though that is only a little over four years from now, we can be reasonably sure that no mass extinction of HFC refrigerants will occur any time soon.

Before we transition out of 410A to something else, the issue of using lower flammability refrigerants inside buildings will have to be addressed, and even then, it is likely that HFC refrigerants will be some of the components in the next generation of refrigerants.

Friday, September 16, 2016

Are You Keeping Up?

Technology is changing the HVACR industry so quickly that many techs get vertigo from the dizzying changes. It is tempting to try and “opt out” of the technological revolution and stick to the old familiar technologies you are comfortable with. However, your lack of participation will not slow the train, you will simply be left behind.

Before heat pumps were common in the southeast, I remember many techs declaring that they would not work on heat pumps. Today, any tech in Georgia who does not work on heat pumps does not work very much. I remember another time an older tech  telling a story of how he retrofitted a system with a stack control and threw away that electronic junk. So the customer ended up paying a lot to downgrade their system because the tech did not understand it. Worse, it did not work well afterwards.

I know many techs today are leery of communicating control systems, variable refrigerant flow systems, electronically controlled compressor motors, and WiFi thermostats – just to name a few things. These things are not going to go away. Customers like them. They like the energy efficiency and convenience these products bring. If you don’t sell and service them, someone else will. The only logical course of action is to educate yourself on the emerging technologies found in the HVACR industry. This is a lifelong process. This year is not the same as last year, and there will be more to learn next year. I am older than most practicing HVACR techs, but I do not long for the “good old days.” I am too busy having fun with the new toys, there is just so much I need to learn.

Sunday, September 4, 2016

Primary and Secondary Drain Connections

Have you ever wondered why evaporator coils often have several drain connections? It is not because the manufacturer had extra PVC drain plugs they needed to use. Most coils have both primary and secondary drain connections. Sometimes they have more than one set for convenience, and sometimes they have multiple sets because the coil can be positioned more than one way. It is important to recognize the difference between a primary and secondary drain connection and pipe them correctly.

The secondary drain provides an outlet for the water in case the primary gets plugged up. Since the secondary connection is a backup drain, it is located slightly higher than the primary connection. Sometimes this is done using an internal dam which forces water to go through the primary drain unless it is plugged up.
Primary drain on the right and secondary drain on the left.
Notice the internal dam on the secondary drain connection.

Most manufacturers recommend that the primary drain be trapped, but the secondary is typically not trapped. The secondary and primary should not run to the same drain line. If the drain line gets plugged up and both drain connections run to it, there is really no point in having a secondary drain connection. Often, the secondary drain line runs  very short distance to an overflow drain pan or a condensate pump.

Another way to utilize the secondary drain connection is to install a condensate overflow switch on the secondary drain connection so that the system shuts down if water builds up to that level. I like that because the customer knows there is a problem and calls for a correction. If the secondary drain handles the water without incident it might not be noticed until it stops up as well.

Overflow switch connected to secondary drain connection on the left.

I saw a system this summer which was several years old and had never been piped correctly. The primary and secondary drain connections had been swapped. The primary drain was piped to an overflow drain pan under the unit  and the secondary drain was connected to the actual condensate drain line which was completely dry and clean. The overflow pan was full of brown slime, and the drain to that overflow pan had stopped up and the water was now overflowing into the ceiling. The difference in the two drain connections was obvious – the secondary drain connection was located higher. But maybe not so obvious to the installer. Just know that there is a reason for the two connections: one is for your primary drain and the other is to avert disaster. If you get them confused you are creating a future problem.

Friday, August 26, 2016

Keep Your Cool

This week I am passing along a tip contributed by a reader, Mike Lilley. He keeps cool by wearing a cooling vest. After doing a little research I found three types of vests for sale: one that circulates air, some that use evaporation, and some that use phase change gel. For attic work I think we can rule out the air vest because it works by circulating ambient air through the vest. In dry heat the evaporative vests should work well, especially outside. However, in an attic in the southeast, I think their performance would not be enough to keep you cool. Mike said that the workers at his company use cooling vests with phase-change gel packs.

The gel packs are similar to the blue-ice packs you might use for your cooler, with one big difference. This gel freezes and melts at 58°F. Remember that the temperature of a substance stays the same as it changes state. This is an important concept in making air conditioning work. This gel stays at 58°F until all of it has melted, and 58° is comfortable, as opposed to keeping a 0°F gel pack next to your body. Further, you can freeze the removable gel packs in a refrigerator or in a cooler with ice. A couple of users commented that it is important to keep the packs flat during the freezing process. Otherwise, the hard, lumpy gel packs make the vest uncomfortable. Here is a link to learn more about these cooling vests. I must tell you that I have not personally used one – yet. But is certainly sounds like a cool idea.

Here are a few links to learn more about cooling vests.