Air Flow and Ice – A Thought Experiment
Imagine a glass of ice sitting on a table. Now, imagine you place a lid on the glass so that all the water and ice are contained in the glass. If the ice and water are well mixed, the water and ice will both be at 32°F because the ice is slowly changing state from […]
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Underlying Problems That Get Missed
Today, I ran a service call with another tech where the previous tech had diagnosed an intermittent piston restriction. I read the history beforehand. For the past several years, there were many assorted comfort complaints and a lot of minor charge adjustments in both the summer and winter. It is worth noting here that the […]
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Static Pressure, Manometers, and Magnehelics
When you start talking airflow, it can get pretty in-depth pretty quickly. There is a big gap between what is useful for the average tech to apply every day and the whole story, so let's start with the simplest part to understand, static pressure. Static pressure is simply the force exerted in all directions within […]
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Impacts of Decreasing Evaporator Airflow
Airflow, airflow, airflow… When we set up and commission comfort cooling and heating systems, we need to pay more attention to airflow before worrying about the fancy controls or the refrigerant circuit. So, as a thought exercise, let's consider a typical 2-ton, straight cool, TXV residential system and think through what happens when we alter […]
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Low Airflow – Beyond the Obvious
One of our techs called me the other day and gave me a story of woe. He had been working on a system, and he had the following readings: Low superheat Low suction pressure Low head pressure He reassured me that the system airflow was correct and wondered what could have been wrong. I asked […]
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How to Determine the Friction Rate for Residential Duct Design
This article is written by one of the smartest guys I know online, Neil Comparetto. Thanks, Neil! Recently, I posted a question in the HVAC School Group on Facebook that went like this: “When designing a residential duct system, what friction rate do you use?” As of writing this, only one answer was correct according […]
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