Saturday, February 18, 2017

Furnace Door Switch

One of the first things most technicians do when troubleshooting a gas furnace is to disable the blower door switch. The blower door switch kills power to the furnace when the blower door is removed. Since the controls and blower are in that compartment, it is impossible to work on the electrical controls with the blower door removed if you do not jump out or physically disable the door switch. Many folks use duct tape to keep the switch closed. Many techs don’t know why the switch is there, and some make their life easier by just removing the door switch altogether. This is a bad idea.

The door switch is there to prevent the blower from sucking in vent gasses and circulating them through the house. The suction created by the blower can be stronger than the draft created in the vent. If the furnace is operating in an enclosed space and with the blower door off, the fan can literally suck vent gasses out of the vent. This can cause two problems. One, the negative room pressure can interfere with the furnace getting enough combustion air, and two, the vent stops working – dumping combustion gasses into the room. This creates a situation where carbon monoxide can be created, dumped into the room, picked up by the blower and circulated through the house. This is especially true for furnaces that get their combustion air from space in where they are installed.

What about sealed combustion systems which draw combustion air from outside through a PVC pipe? Although the combustion air for a sealed combustion furnace normally comes from outside via the PVC combustion air pipe, if you remove the panel to the burner compartment, the furnace will be pulling air from the surrounding area. More to the point, the vent gasses could conceivably be pulled out through the burner area. Although not likely, if both panels are off it is possible for the blower to create a strong enough negative pressure to interfere with the combustion process even with a sealed combustion furnace.

So after working on a gas furnace make sure the door switch is functional before you leave. Do not leave it jumped out or mechanically defeated. You do not want to be responsible for a tragedy.

Friday, February 10, 2017

2017 National HVACR Educators and Trainers Conference

There is still time to register for the HVAC Excellence National HVACR Educators and Trainers Conference is this coming on March 27-29 at the Florida Hotel and Conference Center in Orlando, Florida. I will be speaking at the conference and will be at the Pearson booth at the Expo. Please come by and say hello. I love to talk with other HVACR Instructors. Not an instructor? No problem. Techs and contractors are welcome as well. You can pick up on many of the latest topics. Better yet, you can meet the dedicated people teaching HVACR. You really can’t find this amount of quality continuing education anywhere else for the price of these conferences. Come and fill up at the all you can learn educational buffet being offered.

If you can find a way to attend one of this conference you won’t be disappointed. They are well worth your time. Unlike generic teacher’s conferences that target all subjects, these are specific to our field. And unlike industry showcases like ComforTech or the AHR show, these are specifically for teachers. As a result, everything you see will have a direct application to teaching HVAC/R.

I know that times are tough and getting funding and permission to go is difficult. When presenting the idea to your school administrators be sure to forward a copy of the program from the conference. The sessions at the National Educators and Trainers Conference in Orlando are high quality, professional programs, not sales pitches. The presenters are nationally recognized speakers from respected HVACR organizations. Be sure to note the large number of educational sessions. There are literally more sessions than you will have time to attend. Point out that attending will keep you informed about emerging technology like communicating systems. Point out that by attending you will be better positioned to integrate green mechanical concepts into your curriculum as a result of attending the conferences. Your attendance is tracked, so you can prove the number of hours you attended. Finally, you can get enough free instructional material and tools to help your program. Come gorge yourself at the all you can learn buffet! Here is a link for more information about the conference

Friday, January 27, 2017

ShurTape Mission HVAC

Shurtape Mission HVAC is looking for applicants who are willing to write small blog posts about HVAC in return for $500 per post at 10 posts per year. That is $5000 for researching and writing 10 short blog posts. We have had students participate in this program in the past and they found it very rewarding. Sadly, the Shurtape folks don't want worn out HVACR instructors, or I would be all over that. They want HVACR students. You need to move quickly, the cut-off date is February 3.
You can contact

Laura Pierce
lpierce@shurtape.com
Senior Media Manager
Shurtape Technologies, LLC
1712 8th Street Drive SE
Hickory, NC 28602
P +1-828-267-8506

To see more about the program look here

Saturday, January 21, 2017

Deja Vieux

We have been here before. An outgoing administration is promulgating lots of final rulings in their last gasp and an incoming administration is working hard to undo those rulings. We the regulated, are caught in the middle.

SEER 13 SEER 12 SEER 13
Just before January 20, 2001 when Bill Clinton left office, the Department of Energy upped the minimum SEER from 10 to 13. The change was to take effect in 2006. ARI objected and the Bush administration agreed to drop the minimum from 13 to 12. The DOE published the new 12 SEER standard in May 2002. Several states as well as national environmental and consumer groups successfully sued.  On Jan. 13, 2004, the U.S. Appeals Court for the 2nd Circuit, based in New York, ruled that the DOE did not follow "proper procedures" when it adopted its 12 SEER standard in May 2002. The more stringent 13 SEER standard was reinstated.

This is an oversimplification of the actors and events, but tell the basic story. Instead of having from 2001 until 2006 to reinvent their product line, manufacturers had only from May of 2004 until January of 2006 because of the regulation wars. In retrospect, it would have been far easier to shoot for the 13 SEER target from the beginning and have several more years to accomplish it.

HFC Phasedown
Like a case of deja vieux, the outgoing Obama administration just signed a Global Warming amendment to the Montreal Protocol this past October and the incoming Trump administration wants to scrap all Global Warming initiatives. However, AHRI is not beating the drums to slow down or scrap the HFC reductions. Instead they are saying that what they really want is regulatory consistency and certainty. In other words, they don’t want to relive the 2001 – 2006 SEER wars.

Nothing is Constant but Change
There are mid-term elections in two years, and the ruling party almost always take a beating, meaning the senate may change hands in two years. If this election has taught us anything, it is that we cannot know for certain who will be heading up the government in four years. In eight years we are guaranteed to have a change at the top. It takes years to develop and test new products, and the last thing any manufacturer wants is to have the design parameters altered drastically and capriciously based on the latest election. Even if the challenges are steep, they can be met with a reasonable time for development if you don’t keep moving the goal posts.

To read more about the history of the SEER wars read this excellent article in the NEWS.
http://www.achrnews.com/articles/97373-how-we-got-to-13-seer

To read more about AHRIs position on the HFC phasedown, read this NEWS article
http://www.achrnews.com/articles/134252-kigali-agreement-creates-orderly-phasedown-of-hfcs

Saturday, January 7, 2017

CSST Gas Lines

If you use flexible gas connectors or CSST (corrugated stainless steel tubing) when hooking up the gas to a gas appliance, you need to make sure and do it safely. Flexible gas connectors are made of corrugated stainless steel and generally have no outer covering or protection. They are often used to connect a gas appliance to a rigid iron gas line. 

CSST, on the other hand, has an outer covering over the corrugated stainless steel, comes in large rolls, and is often used instead of black iron when piping gas lines. There are some installation practices for each of these products that need to be followed to avoid setting up a dangerous situation.

For flexible connectors, it is important that they not be used to go through walls, floors, or the unit cabinet. Iron pipe should pass through the unit cabinet to the gas valve. Contact with the metal side of the furnace cabinet can rub a hole in a flexible connector. Another reason for keeping flexible connectors out of the cabinet is the potential for loose electrical wires or connections to arc against the flexible connector and blow a hole in it. While this could also happen with black iron, there is far less likelihood of the arc blasting a hole in the iron. 

Flexible connectors can be used to make the final connection between the black iron leaving the furnace cabinet and the black iron piped into the furnace area. When using a flexible connector, the flared connectors are generally considered “unions.” Don’t forget to install a gas shutoff. Some flexible connectors are provided with a gas shutoff.

CSST is similar to flex connectors in construction with an outer layer of protective plastic. CSST can be pulled through interior walls, but metal nail protectors are required anywhere the CSST is inside the wall. CSST manufacturers make striker plates for this purpose. Protection needs to be approved by a listing agency, such as CSA or UL. Also, it is still best to use black iron to go into the furnace cabinet. The best practice is to penetrate exterior walls with black iron. If CSST is used to penetrate an exterior wall, protection is required.

One of the biggest safety concerns with both flexible connectors and CSST piping is properly grounding the gas piping system. There have been many instances where lightning strikes near a building have blown holes in CSST gas lines or connectors. The grounding is to avoid this. The most common practice is to connect a bonding ground wire to the rigid black iron pipe outside the house BEFORE the first CSST connection. This bonding ground is connected to the ground rod or run inside to the ground bus of the electrical panel.

Here are a couple of links for more information”
Grounding: http://www.csstsafety.com/CSST-solution.html

Installation: http://www.tracpipe.com/Technical/CSST_Installation_Instructions/  

Monday, January 2, 2017

Don't Forget the V

I recently spent some time in Hawaii and noticed that many buildings, both residential and commercial, had no heating or cooling systems. Instead, many only had provisions for ventilation. You see, the temperature in Hawaii rarely gets too far out of the comfort zone, so they condition through ventilation. Now to be sure, there were certainly times when I wished where I was staying at least had a dehumidifier, but the temperature was never an issue. Larger commercial buildings did have air conditioning, but smaller stores usually did not. All  buildings had lots of provision for letting the outside air in.
Hawaiian Air Conditioning

In talking about HVAC we often forget to spend any time discussing the V – ventilation. Even if your building has heating and air conditioning, some amount of ventilation is necessary to maintain healthy comfort conditions. The more people and activities you have inside, the more ventilation you need. Most commercial buildings with large central ducted systems have the ventilation built into the duct system. Another common arrangement is to have a dedicated ventilation system whose only purpose is to pull in ventilation air from outside and expel stale air from inside. These systems are often used for buildings which do not have centrally ducted systems. For example, a building which uses VRF systems to heat and cool often have dedicated ventilation systems.

For years residential buildings have depended upon infiltration to provide ventilation. With increasingly tight houses, this method is becoming unworkable. Even for leaky houses this is far from ideal because  you don’t have any control over how much “fresh” air leaks into your house, or where it is coming from. Some may be coming in through your fireplace or crawlspace. In that case, it may not be very “fresh.”

Residential ventilation systems are now available that allow you to control the amount of outside air entering your house. By adding the outside air into your duct system, you can also control where it enters. Another benefit to adding outside air purposefully with a ventilation system is that it can be filtered and conditioned before entering the living space. I encourage you to think a little more about the V in HVAC. You might find it to be a breath of fresh air.

Sunday, December 18, 2016

Refrigerant Line Sizing

Refrigerant line sizing is an overlooked aspect of system application and installation. Incorrectly sized refrigerant lines can rob your system of capacity and reduce its efficiency. In a worst case scenario, incorrectly sized and applied refrigeration lines can cause multiple compressor failures. For most applications, the two lines involved are the liquid line and the suction line. 

Pressure drop in the liquid line can create flash gas in the line before the refrigerant reaches the metering device. This causes a drop in system capacity because it reduces the amount of liquid entering the evaporator. Some pressure drop is inevitable. It is important to have enough liquid subcooling to offset the pressure drop through the liquid line. 

Suction line pressure drop also hurts the system performance by increases the compression ratio and reducing the amount of refrigerant being circulated. The general rule is to try and keep suction line pressure drop below an equivalent saturation temperature drop of 2F. The actual amount of pressure this represents depends on the refrigerant and the evaporator saturation temperature. Suction lines have another very important design criteria: the refrigerant traveling through them must have sufficient velocity to return oil. While larger lines help reduce pressure drop, they also decrease refrigerant velocity. In general, you want your suction line to be as large as possible while still having enough velocity to return oil. 

There are far too many variables to mention in a blog post, but I can point you toward some excellent materials available online. DuPont and Lennox both have excellent refrigerant piping handbooks available on the web in pdf form. The Dupont document is applicable to all forms of refrigeration while the Lennox material is primarily for air conditioning. Virginia Air has a great excel file which does a lot of the heavy lifting for you in calculating pressure drop and velocity. They also have several line sizing tables on another tab of the excel file. I guarantee that you will learn something about line sizing if you download and examine these three wonderful resources. I know I did.


Lennox

Virginia Air