DOE Small Motor Efficiency Standards for 2015

You may have missed the news about required small motor efficiency minimum standards while you were focused on refrigerant changes; regional efficiency standards for air conditioners, furnaces, and heat pumps; and trying to stay ahead of the latest news on climate change. I know I did. I was looking at the Grainger web site the other day and up popped a bulletin regarding the Department of Energy requirement that certain small electric motors 3 horsepower and under meet a new minimum efficiency requirement beginning in March, 2015. I immediately thought “oh bother,” that would include most of the motors we deal with in residential HVAC. Then I looked up some details and breathed a bit easier.  Motors which are exempt include multispeed, enclosed, specific purpose, or special mounting bracket. That just exempted most of the motors in residential air conditioning equipment. If you deal with regular mount, general purpose, 42, 48 or 56 frame capacitor start or capacitor start-run motors, you WILL be affected. An example might be ventilation fan motors. Grainger was not saying replacement motors would not be available, just that they would now have run capacitors and would be longer due to the extra windings required to meet the new efficiencies. Basically, this DOE ruling makes what was once the premium, high efficiency motors the minimum motor design for certain motor types defined by NEMA. I found several links with discussion and details on this requirement. They are listed below. You might want to take a look at some of these links to determine if you work with any of the affected motors. That way you can develop a replacement strategy before you get to a job and find that you will not be able to replace the old motor with another just like it.

Baldor http://www.baldor.com/news/article.asp?id=1014

US Department of Energy  http://www1.eere.energy.gov/buildings/appliance_standards/product.aspx/productid/40

Weg Industries http://ecatalog.weg.net/files/wegnet/WEG-motor-global-energy-efficiency-legislations-2015-and-beyond-energyeffleg-training-english.pdf

Design News   http://www.designnews.com/author.asp?section_id=1365&doc_id=271471

NOx Nox Who's There?

Cracked. Cracked who? Cracked heat exchanger. OK – not the funniest knock knock joke – especially if it is YOUR furnace. Low NOx emission inserts are causing pre-mature furnace heat exchanger failures. You can read more about this at http://ncidavid.blogspot.com/

I want to talk a bit about what NOx is, why an insert can help reduce NOX emissions, and why NOx inserts can cause trouble. NOx is a generic term for nitrogen compounds NO and NO₂ which are formed when nitrogen is present during combustion at high temperatures. These are major contributors to air pollution and acid rain. Laws requiring reduction of NOx emissions in areas of particularly high air pollution (California) have required the development of low NOx furnaces. Since the air is 78% nitrogen, any combustion process that uses air for its oxygen source has lots of nitrogen present. NOx will only form at high temperatures, but the burners in gas furnaces are definitely hot enough to form NOx. One quick and easy solution is to put something in the flame to cool it down. NOx rods and NOx inserts work by cooling the burner flame temperature, thus reducing the NOx emissions. These NOx rods or inserts are typically metal. Stick some metal in the flame, cool it down, and you have a low NOx furnace. The problem is that metal held directly in a flame eventually burns up. It does not burn quickly, but it does burn. That is why we don’t want the furnace flames actually touching the heat exchanger. The heat exchanger material cannot withstand direct flame contact, called impingement. NOx inserts stick inside a tubular heat exchanger. Unfortunately, the insert eventually degrades from being exposed to the flames. In some cases, it can twist or deform and change the flame pattern. This can cause the burner flames to touch the sides of the heat exchanger, and the heat exchanger fails prematurely. Before the heat exchanger fails, the furnace will be producing higher levels of carbon monoxide and carbon particulates because of the change in flame pattern. So you trade one type of pollution for another. If you work on furnaces with NOx inserts, be sure to check them – and watch the flames to see that they are not touching the heat exchanger. If you work in an area that does not require the NOx inserts, you can solve the problem by removing them. However, now you are increasing the amount of air pollution the furnace produces. Low NOx burner technology does exist – where NOx reduction is achieved through burner design, but I don’t know if there are any true low NOx burners for residential appliances. Keep an eye out for furnaces with low NOx inserts. It might be worth a few extra moments to wath the flame pattern and measure the CO in the flue gas. Abnormally high CO might indicate a developing problem. 

Playing with Your Phone on the Job

Many companies now issue company cell phones to their service techs. The phones are intended for communication, so the company can find the techs and talk with them virtually anywhere, anytime. Now those phones may need to be considered part of the technician’s toolbox. There are already many great apps, including free pressure-temperature apps – usually from refrigerant companies. Equipment and parts manufacturers have started producing apps for looking up parts and equipment service specs. Now you can use your phone or tablet to read the system pressures, line temperatures, superheat, and subcooling. Stride Tools (Imperial) released the i-manifold last year. It is a four port manifold without a display. It sends the information wirelessly to your phone or tablet, and your device becomes the display. Since the display is literally on a small computer, the app can do all kinds of cool things. For one, they have wireless thermometers that can work with the i-manifold to determine system operating conditions, capacity superheat, and subcooling. But wait – there’s more! Now Yellow Jacket has come out with a small device they call the mantooth. It connects to the system and has a tethered temperature probe. It also has no display, but sends the information to your smart device via Bluetooth. So you can see system pressures, temperature, superheat, and subcooling all on your phone. The advantage of this device is that you don’t have to fill up a hose with refrigerant to get a reading – so refrigerant loss is minimal. The “short” gauge concept is perfect for simply testing system performance. Another well known manufacturer is also testing “short” gauges that connect to smart phones and tablets. Their devices are also “short” gauges – eliminating the refrigerant loss from connecting hoses. Their gauges do have their own display as well as connecting to your device through Bluetooth. They are developing wireless thermometers to work with these gauges. Again, you will be able to see all relevant system operating conditions on your smart device and you won’t have to lose several ounces of refrigerant just to perform a check-up. You may soon be playing with your phone on the job – to improve your productivity!

Condenser Subcooling

What happens to the refrigerant subcooling when condenser airflow or water flow are reduced? Many people instinctively say that the subcooling would decrease if the airflow across the condenser decreased. After all, the air is what is cooling the refrigerant – if you have less of it, the refrigerant will not be cooled as well – so you might expect subcooling to decrease when airflow decreases. The only problem with this is that it is exactly backwards. In fact, decreased airflow in an air cooled condenser usually causes an increase in condenser subcooling. Remember subcooling is just telling you the difference between the condenser saturation and the liquid temperature leaving the condenser. Condenser pressure and saturation temperature both increase with reduced airflow. Most techs understand that. While the condenser saturation temperature increases a lot, the liquid temperature does not rise as quickly. The increased condenser pressure also contributes to increasing the compression ratio, so the compressor moves less refrigerant. The increased compression ratio and the increased saturation temperature cause the condenser to hold more liquid refrigerant than normal. The liquid sits longer in the condenser and has longer to be cooled below saturation temperature. Since the liquid is starting at a higher temperature compared to the air circulating over it, it tends to lose temperature faster than it normally would. All this adds up to increased subcooling. 

This is easy to verify. Start a unit, let it run a while, and check the subcooling. Now block the condenser airflow and watch the condenser pressure and liquid line temperature. You should see a big increase in the high side pressure while the liquid line temperature stays about the same or increases just a little. One caveat – don’t let the unit run too long with a blocked condenser – unless you want to run the “what happens when the compressor overheats” experiment. Monitor the compressor temperature to be on the safe side. I am not responsible for you destroying your unit while checking this out. Better to use one at school. (After asking the instructors of course)