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HVAC School - For Techs, By Techs

Nov 27, 2017

Jamie Kitchen from Danfoss talks all about variable-speed motor technology. He discusses why those motors exist, what they do, and how to think differently about the future of HVAC/R.

Most techs think about variable-speed motors as the X13 and ECM blowers in residential applications. Those motors can adjust their performance based on ambient temperatures and moisture levels. So, variable performance may result in better comfort and efficiency.

ECM motors adjust airflow based on sensor inputs, especially dehumidification calls. The sensors may pick up both sensible and latent heat content. Sensible heat is what we can feel (dry-bulb temperature). Latent heat refers to moisture in the air (humidity, wet-bulb). ECM motors adjust their speed based on data from both, which is highly beneficial for greater comfort in the home. Human comfort is a lot more complex than feeling satisfied with a single number on the thermostat; ECM motors help control humidity and give you more leeway over selecting an acceptable dry-bulb temperature of a space.

Variable-speed motors exist on the commercial side of the HVAC industry as well. Commercial HVAC equipment brings in more fresh air and is overall less restrictive than residential. A variable-speed motor can help manage the latent heat of fresh air and work as a form of air treatment. Variable-speed motors compare indoor and outdoor conditions to treat the fresh air and maintain the indoor conditions. These motors account for sensible and latent heat loads, just like the residential ECM motors, and they adjust themselves constantly.

Jamie and Bryan also discuss:

  • Capacity and heat profiles
  • X13 motor controversy
  • Having multiple variable-speed components in a system (compressor, blower, etc.)
  • Sensible heat ratio (SHR) and heat load matching
  • Complex human comfort
  • Reheat coils
  • Air treatment requirements

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