Positively Thankful

At thanksgiving we should all take time to reflect on our blessings. For me this has been a great year filled with an abundance of blessings for which I am truly thankful. Unfortunately, many of my students have had setbacks in their life the past couple of years. I suspect many of your students have as well. We are seeing a wave of students who are preparing for a second or third career because their previous career was abruptly terminated. The plant they worked for closed, the building contractor they worked for has no projects, or the company they worked for has gone out of business. These are good people whose life has been turned upside down. It would be easy for them to concentrate on the past and what they have lost rather than what lies ahead. Dwelling on past misfortunes can be harmful to your health, adversely affects your present and threatens your future. I believe that one of the most important things we can do for these students is to keep them focused on their future. I have seen economic downturns and displaced workers before and I know the end game. These folks will merge their current skills, knowledge and experience with the knowledge and skills they will learn in their HVAC/R program to quickly become leaders in their new field. HVAC/R needs them.

Here is a list of a few things today’s air conditioning students can be thankful for.

• The need for heating, cooling, and refrigeration systems is only going to increase.
• They are starting a new career in a field that desperately needs skilled workers.
• There are still openings for skilled air conditioning technicians even during this economic downturn.
• Installation and repair of HVAC/R systems cannot be outsourced to foreign country.
• The wages earned will remain competitive because the work cannot be done by unskilled workers.
• They will enter the field with training for new refrigerants at a time when this knowledge is crucial.
• They will enter the field with training for new high efficiency systems at a crucial time as well.
• They are entering a field that is consciously increasing the level of professionalism and certification.
• They have experienced HVAC/R educators to help them make this career change.

I wish for all of you an abundance of blessings for the coming year.

Sometimes HVAC/R technicians have an opportunity to do more than make people comfortable, we can save lives. More people are sickened or killed by carbon monoxide poisoning than any other type of poison. The Center for Disease Control and Prevention (CDC) reports that each year more than 500 people in the United States accidentally die from carbon monoxide. An estimated 10,000 people in the U.S. are treated for CO poisoning in hospital emergency rooms annually. It is believed that many more people suffering CO poisoning are misdiagnosed, or never seek medical care. This is because the symptoms of CO poisoning are very similar to influenza symptoms. One big difference is that influenza causes a fever and CO poisoning does not.

Carbon monoxide is an odorless, colorless gas that is highly poisonous. It is formed by the incomplete combustion of carbon based fuels, like natural gas, oil, coal, or wood. Incomplete combustion can be caused by lack of oxygen, improper mixing of the fuel and oxygen, or too low a combustion temperature. A correctly adjusted gas or fuel oil flame should produce very low levels of CO. Ideally a correctly adjusted gas or oil flame should produce no CO, but realistically, most produce at least trace amounts. Solid fuels almost always produce large amounts of CO, that is why charcoal comes with a warning that it is not to be used inside. Even people that should know better sometimes overlook the obvious. A friend of mine was conserving heat during a cold winter power outage by using his charcoal grill inside. His daughter became very ill and had to be rushed to the hospital where they correctly diagnosed her condition. This story ended well, she recovered and is doing well. Unfortunately there are many stories about CO that do not end well.

HVAC/R technicians are in a position to help. We can make sure all combustion appliances in the home are burning correctly, insure there is enough combustion air for proper combustion and venting, and finally by making sure the vent system is adequate and working correctly. For gas and oil furnaces also remember to inspect the heat exchanger for leaks. The heat exchanger separates the combustion products from the air circulating in the home. Although a defective or cracked heat exchanger can contribute to CO poisoning, more obvious problems are frequently to blame. Stopped vents, loose or leaky vents, and lack of combustion air are common causes of CO. While every technician should learn to look for conditions that can lead to problems, testing is required to verify that a system is operating at safe levels of CO and that there is no CO in the house. Every technician should have an accurate CO tester. Household alarms are not a substitute. While every house with gas or oil appliances certainly should have CO alarms, they are not a replacement for an accurate tool for diagnosis. I highly recommend a seminar done by Bob Dwyer for COSA (Carbon Monoxide Safety Organization) Make sure and take advantage of the opportunity if you have a chance to attend one of his CO Safety Seminars.

There are many units in Fundamentals of HVAC/R to help explain how to achieve safe, efficient combustion for gas and oil furnaces, including

• Unit 37 Gas Fired Heating Systems
• Unit 38 Warm Air Furnaces
• Unit 40 Gas Furnace Installation, Startup, Checkout, and Operation
• Unit 41 Troubleshooting Gas Furnaces
• Unit 42 Oil Fired Heating Systems
• Unit 43 Oil Furnace and Boiler Service
• Unit 44 Residential Oil Heating Installation
• Unit 45 Troubleshooting Oil Heating Systems

There are many good web sites for more research on carbon monoxide poisoning.

A few are listed below.

http://www.bbc.co.uk/health/conditions/carbonmonoxide1.shtml

http://www.cosafety.org/Aboutco.htm

http://www.clima-tex.com/consumer/carbonmonaction.html

http://annhyg.oxfordjournals.org/cgi/content/abstract/18/1/79

http://www.coheadquarters.com/colimits1.htm

http://www.coheadquarters.com/CarbonMonoxideHQ.com/index.html

Flue Season is Here!

No not the swine type, the furnace type! The weather is getting cold enough in many parts of the country that people are starting up their furnaces. Now is a good time to teach your students to check furnace flues during fall seasonal checks. The purpose of this article is not to discuss CO poisoning, but it deserves a mention since furnace flue problems can lead to carbon monoxide poisoning and CO poisoning shares many symptoms with influenza. One big difference is that influenza is normally accompanied by a fever and CO poisoning is not. For more information on CO poisoning check out the Carbon Monoxide Safety Organization web page.

A good place to start discussing furnace flues is to describe the four categories of vented appliances: Categories I, II, III, and IV. These categories are determined by the static pressure in the vent and the temperature of the vent gasses. For reasons of manufacturing and application limitations, Category II and III furnaces are rare. Most furnaces fall into either Category I or Category IV; 80% furnaces are category I while 90% furnaces are category IV. Category I furnaces are vented with type B gas vent. Category IV furnaces are usually vented using PVC. The combustion gas is cool enough to be safely vented through PVC and PVC is relatively easy to seal air tight.

In practical terms the vent gasses in a properly operating Category I furnace will not leak out small cracks because the vent gas pressure is less than the surrounding air. Vent gasses will generally not condense in a Category I flue because the temperature of the flue gas is considerably above dew point. Even though most 80% furnaces manufactured today have induced draft blowers, they still operate with a non-positive pressure vent because of the buoyancy of the hot combustion gas. However, the combustion gas coming from an 80% induced draft furnace is far more likely to condense in the flue than with older natural draft appliances. Oversized vents, single wall vents, masonry vents, or some combination of these can lead to condensation in the flue. Flue condensation can corrode metal vents and cause masonry vents to crack. Severe condensation can return water to the furnace and cause pre-mature heat exchanger failure. These situations most often occur when an older existing furnace is replaced with a newer, higher efficiency furnace. Even though the newer furnaces are designed for regular type B gas vent, they can not necessarily be connected to the old furnace flue. The extra heat in the combustion gas and the dilution air from the draft diverter of the older furnaces combined to make large single wall vent connectors and masonry vents work without condensation. The cooler combustion gas and lack of dilution air in the fan assisted furnaces makes their vent gas more susceptible to condensation. I have seen a single wall vent connector on an 80% induced draft furnace in a crawl space rust completely through and fall on the ground in a single year of operation. The furnace replaced a previous natural draft furnace that operated for many years without problems on the same type of vent. To prevent similar results when replacing an older furnace I recommend using only double wall vent and installing a metal flexible chimney liner when venting into a masonry chimney. An alternative to lining the masonry chimney is to vent horizontally using a power venter and not using the masonry chimney. More information on power venters is available from Field Controls

Another important step is to size the vent. The existing vent for the older natural draft furnace being replaced is often larger than is required for the 80% induced draft furnace. An oversized vent can also lead to condensation. You can download a pdf file on vent sizing from Hart & Cooley

Visual cues that furnace combustion or venting needs attention include: rust on metal vents, condensation weeping from vent joints, or carbon buildup anywhere in the vent system. Your students may run across non-condensing furnaces that were vented using a rigid plastic vent material called high temperature plastic vent, HTPV. This material has been recalled and should be replaced whenever it is found. HTPV recall If they see any of this material they should contact the furnace or vent material manufacturer or to find out what replacement vent material is recommended.

Fundamentals of HVAC/R can help your students prepare for flue season. Details on gas combustion can be found in Unit 37 Gas Fired Heating Systems. Furnace categories are discussed in Unit 38 Warm Air Furnaces. Vent sizing is discussed in Unit 40 Gas Furnace Installation, Startup, Checkout, and Operation. Gas combustion and venting problems are discussed in Unit 41 Troubleshooting Gas Furnaces.

The New 70

Many of the old timers I talk to who are still leery of R-410A want to know what the “new 70” is. They want a target number for the suction pressure of an R-410A air conditioning system. Many service technicians are in the habit of charging to a target number on the suction side. This is frequently 70 psig on R-22 systems. The saturation temperature of R-22 at 68.5 psig is 40°F and for many years the standard evaporator temperature at design conditions has been 40°F. But 70 is a nice round, easy to remember number and close enough for quickie rules of thumb. The problem is that systems seldom operate at design conditions. Another big problem is that conditions other than charge can cause low suction pressure. If a technician is only checking the suction pressure, they are not collecting enough information to recognize other system factors that can contribute to low suction pressure. A common error of inexperienced techs using the “70” method is overcharging systems that have low evaporator airflow. I have gone behind someone using the “70” method who had overcharged the system so severely the compressor stalled at startup and pegged my high side gauge past 500 psig. The customer was told that the compressor was bad. To be fair, most experienced technicians that use the “70” method understand how airflow and system operating conditions affect system pressures, they just don’t want to bother with manufacturer’s charts. They just modify the target up or down as they judge conditions affecting system pressures. These folks can usually get a system cooling; that is why they still have a job. However, the system will often not be performing optimally when they leave. Today’s customers are paying a premium for systems that are more efficient and have less environmental impact than older systems. Beginning January 2010, even the least expensive unit a customer can purchase will be non-ozone depleting and more efficient than the least expensive unit they could purchase just a few years ago. This means everybody is paying for efficiency and reduced environmental impact. However, if technicians don’t charge units properly, customers are not getting what they are paying for. Your students can be the vanguard of a new era that values professionalism. Make sure your students know how to handle new refrigerants like R-410A and know how to read and follow manufacturer’s charging charts. That will put them in a position of leadership early in their career.

Fundamentals of HVAC/R has a detailed discussion of system charging in Unit 27 Refrigerant System Evacuation and Charging. Variables affecting system pressures, common methods of determining the correct charge, and common methods of adding refrigerant are all covered. Charging is also discussed in other units including

• Unit 35 Residential Split system Air conditioning installations
• Unit 36 Troubleshooting Split System Air Conditioning
• Unit 52 Heat Pump Installation
• Unit 53 Troubleshooting Heat Pump Systems
• Unit 83 Troubleshooting Refrigeration Systems
• Unit 84 Installation Techniques
• Unit 85 Planned Maintenance
• Unit 86 Troubleshooting