Sunday, September 28, 2014

Manual J Resources



Are you looking for materials to teach load calculations? ACCA has free excel spread sheets they call speed sheets. You can download them from their web site. They also offer a curriculum for studying Manual J8, also free from ACCA. You do have to buy either Manual J8 or Manual J8 abridged to take full advantage of these. If you are looking for load studies coverage in a text, “Fundamentals of HVACR, 2nd ed” has a complete Unit on residential load studies. It includes examples using Manual J8 while working on a complete block load for a small house. Other Resources include Wright-Soft’s Right-J program or Elite Software’s RHVAC program. These are two very full featured commercial programs which are used a good deal in the industry. The good news is that you can download and use demo versions of them for free. Typically, there are a few limitations on the free download versions, such as not saving the files. However, you get a chance to try them out before purchase.

For teaching, I really like the ACCA Manual J Speedsheets. They are not too hard to learn, and I believe that students get a better understanding of Manual J because they do have to use the manual some to use the software. I also like the Manual D Speedsheet for ductwork. Both of these are a little limited – they are mainly for use in residential systems that are not too complex. But that is exactly where our students should be starting. We typically have our students do a block load on a small cabin and a room by room load on a 3 bedroom ranch style house. They then do a radial duct design on the cabin and an extended plenum on the ranch house. You will want to spend some time with the speedsheets before giving them to students. Although they are not difficult, there you do need to go through one a couple of times to feel completely comfortable. The instructions are in the sheets and there are ample examples on every tab. Links to the  resources mentioned are


Sunday, September 21, 2014

Thermostatic Expansion Valve Failures



There have been a run of TXV problems in new units stemming from a chemical used as a rust inhibitor on some of the compressor bearings in Copeland Scrolls. A reaction between the rust inhibitor and the POE oil used in the compressor causes the POE to coagulate and collect in the TXV. This appears to be an industry wide problem, not limited to a single equipment manufacturer. The chemical causes the valves to get gunked up and stick, usually resulting in a restriction at the TXV. The symptoms can look very similar to an undercharged system – very low suction pressure, low head pressure, and high superheat. Normally, the way I differentiate low charge from a restriction is by subcooling. A restriction typically has a normal to high subcooling. However, this is often not the case if the compressor in the system is a newer Copeland scroll. The Copeland scroll compressors designed for R-410A unload when the suction pressure drops below 55 psig. This is to keep them from operating at pressures which will damage the compressor. If the restriction is severe enough, the suction pressure on an R-410a system can drop below 55 psig. The compressor unloads, limiting how much refrigerant is pumped and holding down the head pressure.  You have low suction pressure, low head pressure, high superheat, and low subcooling: classic undercharge symptoms. However, adding charge does nothing unless you really go whole hog and grossly overcharge the system. Then you can build some head pressure, but it won’t fix the restriction or make the system cool. If the compressor is unloading, you can often hear it and even feel it in the piping. If you have what looks like an undercharged system with no detectable leak and adding refrigerant has no effect on the pressures, I bet you have a restriction. These days the restriction is often in the TXV. Several equipment manufacturers have service bulletins out regarding this issue. Below are links to a bulletin from Nordyne and a link to a YouTube video showing the bulleting from Emerson.



Saturday, September 13, 2014

Keep the Condensnot Moving!



The evaporator condensate drain is often one of the last things run when installing an air conditioner and sometimes is not given a lot of thought. The trouble is it can demand your attention if it does not work. A check list for constructing a working condensate drain that will continue to work and be easily maintained would be
1. The drain should have cleanouts near the unit and the trap to allow for routine maintenance.
2. Draw through coils should always have a trap after the drain pan.
3. The trap should be 4” deep and hold 2” of water.
4. The leaving side of the trap should be at least 2 inches lower than the drain pan outlet.
5. After leaving the trap, the condensate line should slope at least 1/8” per foot.
6. Except for the one trap at the unit, the condensate line should NEVER run up.
7. Long condensate lines may require a vent. If you install a vent, you MUST install a trap and the vent must be AFTER the trap, never before the trap.
8. In humid areas the parts of the condensate line closest to the unit may need to be insulated to prevent sweating.

Cleanout
Drains are getting a little more attention these days because the newer mechanical codes require cleanouts. In the past condensate drains were often cleaned by cutting out the old trap, blowing out the line, and installing a new trap. Now you are required to leave a way to access and clean the drain without cutting into it. Some people use tees or crosses at places where elbows would normally go. You can also purchase some fittings to install in the drain line that make accessing and cleaning the drain line easy. One is called “ALL-Access” Link http://www.allaccessdevice.com/
Another is offered by Rectorseal http://www.rectorseal.com/index.php/easy-klear/
Rectorseal also makes a manufactured trap which is clear, allowing you to see when the trap is full of “condensot.” It has service access built in as well. http://www.rectorseal.com/index.php/ez-trap/

Trap
A trap is always required with a draw through coil, otherwise, water will be held in by the negative pressure and the air flowing in through the drain. Many people don’t trap positive pressure coils, such as a coil installed on a furnace. Usually, they will drain because the pressure is pushing the water out. One argument for leaving the trap off on positive pressure coils is that traps tend to get clogged more quickly with “condensnot,” the slimy brown algae that grows in drain pans and drain lines. However, if the air velocity on a blow through coil is high enough, it may still have a negative pressure at the drain outlet. Adding a trap on a blow through coil also provides an air seal between the coil and the outside Manufacturers often specify traps even on blow through coils. Packaged units often specifically warn NOT to trap because they sometimes have a built in trap, and adding another would amount to double trapping. The trap needs to hold enough water to offset the negative pressure of the coil. A common specification calls for a 4” deep trap with a 2” riser so that the trap holds 2” of water and the outlet is 2 “ below the drain pan outlet.

Vent
Ever notice that plumbing systems have vents? The vent keeps the draining water and effluent from creating a suction which can slow or even stop drainage. On longer condensate lines, a vent may be required to insure drainage. Vents can also help on lines with minimal slope. The vent is just a tee with a riser which is open to the air. When used, there MUST be a trap and the vent should be AFTER the trap. Putting a vent before the trap pretty much undoes any good the trap would do by allowing air to pass through the vent. The vent should be at the start of the condensate line (but after the trap) and the riser should go above the rim of the drain pan.  

Slope
One of the laws of plumbing is that waste products run down hill. After the line leaves the trap at the unit it should never go back up. Running the line up after dropping down creates a second trap. Remember that the line is not under pressure, it is gravity flow. It is easy for “condensnot” to accumulate at this second trap and cause the drain to overflow at the unit. I am embarrassed to admit that I have personal knowledge of this. An unintended second trap is a messy service call waiting to happen.

Insulation
If your unit runs a lot and the coil is located in a humid area, the condensate line can sweat. Usually, the PVC is enough insulation to prevent this, but in some areas people have had problems with dripping condensate lines from sweating. Insulating the trap and all the drain between the trap and the unit with armaflex takes care of this.

Instructions
Finally, always follow the manufacturer’s instructions. They usually are pretty specific about how the drain is to be run. Trapped or not trapped, vented or not vented – those things are all typically in the instructions. Here is a link to another online posting that shows one manufacturer’s instructions and a drain run according to those instructions. 

Thursday, September 11, 2014



Thirteen 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. The trade center towers were chosen because they became an icon of American strength. The terrorists intended to strike fear into our hearts by taking down our most visible symbols of strength and power. Rather than weaken us, 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 that provided round the clock care and support for eight months to the rescue and recovery workers. 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.

Friday, September 5, 2014

Left Handed Piano



I took Labor Day weekend off from blogging, I hope you didn’t miss reading my weekly post too much. Actually, I hope that you REALLY, REALLY missed it and can’t wait for the next article. One of the great things about Labor Day is the chance to spend time with your family relaxing, telling stories, and recalling family history and legend. One story about my grandmother struck me because it so clearly describes her. She contracted Parkinson’s disease as a young woman. In fact, I never knew her when she did not have Parkinson’s. Dad tells the story of her first meeting with the doctor to look for a treatment for her Parkinson’s. Grandad had taken her to a doctor to see if L-Dopa would help her. The doctor asked “Mrs. Stanfield, how long have you been disabled?” to which she quickly shot back, “I am NOT disabled!” The doctor tried a different approach. “How long have you had trouble walking?” Grandmother,” I walk just fine, thank you!” The doctor tries again, “Can you walk across the room for me please?” Grandmother gets up and slowly walks across the room, dragging her right leg behind her. In her mind, she was NOT disabled. She got where she needed to go and did what she needed to do. The palsy also crippled her right hand. She had been a world class piano player, but now she could not open her right hand. She started playing left handed piano music. When she died, she had a large collection of left handed piano music – music written intentionally for ONLY the left hand. With her one palsied hand, she could play better than 99% of the rest of us who have two good hands. She was a very able woman. You did not dare call her disabled or tell her what she could not do. There are many young people returning home who suffered a multitude of injuries while serving overseas. Our industry needs their talent and abilities. Please, lets give them a chance to play some left handed piano.