Bryan holds a Kalos meeting all about residential system commissioning best practices. He goes back to the basics and talks about the ABCs - airflow, balancing, and charging.
Every time we do a major repair on a residential unit, we would be wise to do a system commissioning. When we do commissioning, we focus on the ABCs, which are Airflow, Balancing, and Charging (or Combustion) or Airflow Before Charging (or Combustion). Condensate can also count as the "C" in the ABCs. In any case, the ABCs describe the order of system commissioning.
The first way we confirm airflow is by checking the blower motor and the condenser fan. Airflow has to exist from both sources, and you can do that by listening to the motors and feeling for the airflow. (The condenser fan will exhaust hot air; if it doesn't exhaust hot air but is running, then it could be running backward.) After you confirm airflow, let the system run for a little while and stabilize.
We can check airflow via static pressure, but static pressure is just an INDICATOR of airflow; it isn't a direct airflow measurement. Static pressure is more like blood pressure; it refers to the pressure against the walls of the duct, which gives you an idea of how well air might be flowing. In our market, we try to hit 350 CFM per ton, and we must make sure we reach that airflow target before we measure the static pressure.
The data tag will list the target total external static pressure (TESP), and a typical TESP target is 0.5"wc. Going over 0.5"wc may result in reduced capacity, efficiency, and even airflow. Dirty blower wheels and other restrictions can adversely affect the static pressure, and those issues need to be taken care of. If we can't hit that 0.5"wc target without doing significant construction, the Kalos techs are supposed to tell the customer and ask them how they want to proceed.
After we confirm and optimize airflow, we have to do balancing. Anytime we make changes to the ductwork, the Kalos techs have to test the airflow before and after construction. Testing in and testing out will give us actual data to show the customer that their system airflow has improved. Adjusting dampers also requires us to test in and test out to make sure we maintain the proper airflow and static pressure. Balancing is an art and a science, and we need to do it well to make it address the customer's needs.
On installations, checking the charge requires us to WEIGH the charge, not just check the five pillars. Long line sets require additional charge, so we need to take that into account when we charge the system. Kalos techs must carry a scale (with extra batteries) on their trucks at all times to weigh the charge properly. After the unit runs for at least 20 minutes, we then have to check the superheat, subcooling, air temperature split, and saturation temperature (evaporating and condensing temperatures). On TXV systems, subcooling is typically the indicator that we need to use to set the charge.
After checking the charge, it's a good idea to check the electrical side. Checking voltage and amperage are important, but checking the voltage under load is perhaps the most important measurement you can gather.
On gas furnaces, we also have to check the combustion, which starts with checking the gas pressure. Then, we do combustion analysis.
Condensate is another "C" in the ABCs, ad we need to focus on if the system is draining and if the float switch works.
Remember: read the manual to get the best understanding of the system and tell the customer that you're being thorough if they think you're taking too long. Also, recovery machines are NOT acceptable substitutes for vacuum pumps!
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/
3 май 2019
