Check the Draft

With the arrival of Fall weather technicians will soon be taking Fall furnace checkup calls. One of the things we should be doing is checking the vent draft pressure to insure that the vent is working properly. While many technicians are careful to check for cracks in heat exchangers, they sometimes neglect the vent. I believe that improper venting occurs far more often than cracked heat exchangers. Further, a vent that is spilling into the house has the potential to release far more vent gasses into the house than a crack in the heat exchanger. Of course it is right to check for cracks in the heat exchanger, just don’t neglect the vent operation. For all Category I furnaces, the vent should be a negative pressure. That is, it should be at a lower pressure than the room the furnace is operating in. Typically we want at least -0.02” wc. In other words, the vent pressure should be 0.02”wc less than the room pressure. This is true even with fan assisted Category I furnaces, which nearly all 80% AFUE furnaces are today. The fan helps pull the combustion gasses through the heat exchanger, it is NOT designed to PUSH vent gasses through the vent. Typical Class B vent is not air tight. If it is pressurized, it will leak out combustion gas.Even with fan assisted furnaces, the vent is supposed to operate at a negative pressure and the vent gasses leave because of their buoyancy compared to the surrounding air.

What can cause a lack of draft in a vent? One of the main culprits is lack of combustion air. The operation of the burners and the vent system can remove air from the room faster than it is being supplied, causing a negative pressure in the room. In older, leakier homes we often relied on infiltration for combustion air. Today, you really should provide outside air to the appliances. I have seen the operation of a furnace pull smoke out of a burning fireplace. There was enough air for the fireplace, but not both the fireplace and the furnace. The room went so negative that the fireplace vent was not lower than the room pressure. If the vent gasses cool off too much in the vent pressure will increase because the gasses are heavier, decreasing the draft. This can be a particular problem when replacing an older furnace with a newer one. Often, the vent is too big for the new furnace, causing the flue gas to cool off too much as it travels through. Another possibility is a plugged vent or vent cap. The flue gasses back up in the vent and then start to spill out of the appliance. 

Although most Category I furnaces with draft inducer fans have draft pressure switches to shut off the burners if the draft pressure is not at the minimum setting for the switch, I have seen furnaces operating with a positive vent pressure continue to run. Draft switches are, after all, switches and can fail. So don’t assume that because the draft switch is closed, the vent pressure is OK – measure it so you know.

Eco-Friendly Cooling

The folks at Greenheat in Australia wrote to remind me that there are ways to keep cool without using so many kilowatts. What follows is a short article from them on keeping cool the Green way.

Eco friendly ways to cool your home

Maintaining a comfortable temperature inside your home during fierce summer heat using eco friendly methods is often viewed as a faintly impossible ask. Many people are still labouring under the false impression that the only way to get proper relief from the heat is by installing a gargantuan, decidedly non eco friendly air conditioning unit. Sorry, environment. We’re too hot to bother with you.

Good news, lovers of cool temperatures and the earth. You can have it both ways. By implementing some of the measures suggested below, you’ll be minimising your impact on the environment without compromising your own comfort during the warmer months. To learn more about eco friendly ways to cool your home, visit Greenheat.

Let’s look at some eco friendly ways to cool your home:

• Keep the heat out! Seems obvious, but by properly insulating your home, ensuring your windows and doors are properly sealed, drawing the blinds at sunrise, and cutting down on your use of household appliances like washing machines, ovens, and stove tops, you’ll significantly reduce the amount of heat within your home.
• Become an Ivy Leaguer- covering your external walls with greenery is an effective and beautiful way to insulate your home from the punishing effects of hot weather. You’d be surprised at just how effective a measure this can be. Green walls can cut the surface temperature of walls by as much as 10 degrees Celsius.  Additionally, they help to filter air pollution.
• External shades and blinds- external blinds and shades are more effective than internal shades and blinds, simply by virtue of the fact that they block the solar energy before it hits your window.
• Split system air conditioning- inverter split system air conditioning units fluctuate according to the air conditioning requirements throughout the day. This makes them an energy efficient air conditioning option, minimising energy consumption by as much as sixty six percent.

NOT COOL

Not too long ago a morning television show did a “sting” type of operation on several HVACR contractors that were called out to service a system that had one simple problem. The good news is that all the technicians found the problem quickly. The bad news is that all the technicians then tried to pad the bill by replacing unnecessary parts. You don’t need to cheat people to make money. In fact, I think that cheating people ultimately ends in losing customers. Most satisfied customers will refer you to friends and family. The HVACR business works best with long term repeat customers, not a long string of patsies.There was once a contractor in Athens who specialized in getting their foot in the door and then condemning equipment. They are no longer in business. They literally ran out of people who would do business with them. When you cheat your customers, you are slitting your own throat. It does not take a high profile television program sting for folks to figure out something is wrong. Eventually, your customers will catch up to you. When they do, everyone they know will know about it.

There is nothing wrong with making a profit, and there is nothing wrong with being paid well for your time, expertise, and investment. So be up front and charge people for your time, expertise and investment, not parts they don’t need. There is also nothing wrong with offering premium services. If you want to sell setback thermostats or other system improvements, you should make your argument based on the increased comfort, energy efficiency, or convenience that the customer will enjoy. We make money by solving problems for people, not creating them.

The Strength Remains

Eleven years ago, I was working in my office at school when a teacher from down the hall came in and said that a plane had flown into one of the World Trade Center Towers. While I was searching for information about the first plane, the second plane hit the other tower. It was only then that I realized we were under attack. I believe the trade center towers were chosen because they became an icon of American strength. Rather than weaken us, the attacks strengthened us in many ways. We proved our mettle immediately following the tragedy. Stories abound about how people rose to the challenge: from police and firemen risking their lives to politicians speaking with one voice as Americans. My favorite story involves St.Paul’s Chapel directly across the street. Somehow St. Paul's survived the shower of debris and was transformed into a round the clock hostel, providing care and support for eight months to the rescue and recovery workers. For months, volunteers came from all over America to work there. So many volunteers came that they had to be scheduled and their time helping was limited to allow everyone a chance to experience the blessing of helping. People cried when their time was up and they had to leave.

The towers came down. The strength remains.

To Stretch Your Budget, Roll Your Own!

Gary Recher is one of a group of instructors who communicate with me regularly, giving me feedback and ideas. In today's tough economy, we are all being asked to do more with less. Rather than focusing on what we don't have, I suggest we focus on what we DO have. Gary sent me this article on how he makes his own trainers. I hope it will stir your creative juices to see how you can use what is at hand to teach effectively in a challenging environment. If you have a favorite idea that you are willing to share, send it in and I will post it!

Electrical Troubleshooting Trainers

We as instructors want to provide our students with as much realistic troubleshooting scenarios as possible. We can use troubleshooting diagnostic software, manufactured trainers, and actual equipment that many times that we have to swap good parts for bad to provide troubleshooting tasks. Each has its place and can provide excellent opportunities for students’ to hone their troubleshooting skills.

Computer software can stimulate the student on various troubleshooting scenarios. This allows the students’ to develop problem solving skills without shorting out equipment or meters. However, it does not allow them to demonstrate those skills on actual systems using test equipment.

Use of manufactured trainers are many times boards that have the same components as an actual system that has trouble switches to simulate problems. The advantage of a trainer is that it allows the student to use their meter in an actual troubleshooting scenario rather than at a computer screen. Giving them the chance to use a meter and interpret their meter readings. The downside of these trainers that many times they are forced to use test points for the meter test prods rather than testing at points one would actually use in troubleshooting such as relay terminals.

Actual equipment allows students to get actual hands on experience. The limitations to using actual equipment is that to create a troubleshooting scenario the instructor or lab assistant will have to remove good components and install defective ones. This method is time consuming as the equipment will have to be set up for the troubleshooting scenario and then repaired at the conclusion of the troubleshooting session. If there is only one student this is ideal as the student can then demonstrate the removal and replacement of the defective component and then accomplish an operational test of the system. If several students have to troubleshoot the same fault there is always the downside of the fault being compromised to students that have not accomplished the troubleshooting task.

As HVAC/R technicians/instructors we are no strangers to solving problems. And there are ways to providing realistic troubleshooting scenarios without having to swap good parts for bad. Here is what our course has done that allows us to change troubleshooting scenarios using toggle switches. One of our troubleshooting stations is a cube air conditioner connected to an air handler with electric heat. On the back of the air handler a large hinged door component box was installed. Which is now becomes troubleshoot control center. Inside are mounted four motor starter rated toggle switches several lower amperage rated toggle switches and a dual run capacitor. Inside the compressor compartment the wires for the compressor and fan windings and wires spliced back to the control center. In the air conditioner’s electrical control box the contactor coil wire is unsoldered from one of the terminals. A 20 gauge stranded wire is soldered to the terminal and a second wire soldered to the coil wire. Both are run back to the control center to a toggle switch. Are you getting the idea now? With a flip of a switch there is a defective contactor. With the flip of a switch there is an open compressor or fan motor overload or run winding. The air handler cube relay was relocated to the control center. A similar relay was disassembled and the coil disabled and wires soldered to the internal terminals a hole drilled to the bottom of the relay and then through the mounting plate, grommet inserted into drilled hole, and back to control center through toggle switches. The thermostat was not immune either to our devilish modifications. By carefully grinding the current path etchings on the terminal board with a Dremel grinder wires can then be soldered to both sides of that break and then run to a toggle switch to the control center.

The downside of this is that you will have to do it yourself, and it does take time to make. The upside to doing this is that the student will be troubleshooting equipment as near world as possible and troubles can be changed with the flick of a switch from a thermostat to a fan relay to a compressor problem, etc..

This same procedure can be accomplished using manufactured demonstrators. By installing faux relays and toggle switches a demonstrator can be turned into a troubleshooting trainer.

The bottom line of this article is to hopefully to inspire you to use your mind, innovate and create the training devices that provide more realistic training situations.

Practicing for Success

"We are what we repeatedly do. Excellence, then, is not an act but a habit." – Aristotle

I would like to propose a slight revision to Aristotle’s line of thought: Success is not a condition, but a habit. Have you ever known someone that is lucky and seems to go from one success to another? It is sometimes difficult not to be envious of their success and wish we were so lucky. If the primary action you take towards becoming successful is to wish for success, chances are you will not find it. People are not successful because they are lucky; they are successful because they prepare for their success through repetitive practice. So the question is: “Are you practicing for success or failure?” You might ask “Who would practice for failure?” However, I have seen many students diligently practicing for their inevitable failure. They practice for failure by not preparing for class, arriving late, and making endlessly creative excuses for their failure to complete their work. Eventually they become expert at failing – eliminating all chances of success. I will not tell you that if you work hard and put your best effort into everything you do that you will always be successful. But I can guarantee that if you do not work at being successful, you will most certainly fail.

A big part of achieving success is preparing for opportunity. Opportunity comes in different forms at different points in everyone’s life. But to take advantage of opportunity when it comes around, you have to be prepared. That is one of the main reasons for going to school – to prepare for your future opportunities. You should practice being successful to prepare for opportunities that are sure to come. Show up to class early, prepare for class by studying the assigned material, ask questions when you don’t understand something, and don’t settle for good enough to get by, always strive to improve. I can not tell you exactly when or where opportunity will present itself in your life, but I do know that you must prepare yourself to take advantage of it when it arrives.

So if you have been practicing for failure, I suggest you reconsider your strategy. Put yourself out there, throw yourself into your studies, and risk being successful.  

Centrifugal Blower Motors

Since air is what we work with it makes sense to insure that our students understand airflow and fan performance. Fan motor performance is one of the most often misunderstood aspects air conditioning systems. The amp draw on a centrifugal fan with a standard AC inductive motor goes down as resistance to airflow is increased. For most people this seems counterintuitive. It is easy to picture the fan motor pushing harder to overcome the resistance and increasing in amp draw. However, this is exactly backwards. Centrifugal fans move air by throwing the air outwards through centrifugal force. The amount of air the fan is moving decreases as the resistance to airflow increases. If the fan blades are moving less air, they can actually spin easier because there is less air to sling. This causes the motor RPM to increase and the motor amp draw to decrease.

The most convincing way to teach this concept is to have students figure it out for themselves using a centrifugal blower. Have them operate a centrifugal blower in free air with no restriction and measure both the amp draw and the fan RPM. Note that most centrifugal blowers cannot operate in free air for an extended time without overheating, so try and keep the free air operating time to a minimum. Next have them block one side of the air intake with a piece of cardboard and recheck the amp draw and RPM. Typically the increase in RPM is immediately obvious, but measurements prove the point. Have them slide the cardboard to block the intake only half way while watching the amp draw. A few minutes of experimentation will convince the students that blocking the intake actually causes an increase in RPM and a decrease in the motor amp draw. Next have them partially block the fan outlet while checking the amp draw. Once again, the amp draw will decrease. Allow them a few minutes of play time to convince themselves. This experiment does more to explain centrifugal blower motor performance than a week’s worth of lectures.

Although the noise and increased air velocity make it seem like the fan is actually moving more air, the truth is that it is moving less. The air that it IS moving is traveling at a very high velocity, or speed. This is what makes the increased noise. But since you are effectively making the hole that the air travels through smaller, less air is able to get through, even at higher velocity. This is more difficult to show. To get accurate readings, you really need the air to be moving through some ductwork.

Another point to discuss is the difference between a blower with a traditional PSC motor and one with an EVM blower. The behavior we have been discussing is typical of an AC induction motor, like the PSC motors that come standard on most blowers. However, an ECM blower motor senses the change in work and increases its speed enough to actually overcome the resistance, so that the fan moves the same amount of air even against increased resistance. Since this requires more electrical energy, the amp draw for an ECM blower will increase when the fan is restricted. The ECM technology solves one problem: losing airflow due to increased resistance. But is creates a new one: increased electricl use to overcome the resistance. 

To read more, check out Unit 41 Fundamentals of Psychrometrics and Airflow and Unit 75 Fans and Air Handling Units in Fundamentals of HVACR 2nd edition. You can find the blower labs in the new Lab Manual for Fundamentals of HVACR, 2nd edition. They are labs 75.3 AC Induction Motor Blower Properties and lab 75.4 ECM Blower Properties.