#sizing

Tech Tips:

Size Matters — Industrial “Shortcomings”

This article was written by Jennifer Manzo, an HVAC technician and the founder of HVA-Chicks Coalition. You can find her on social media as @HVAChicksjennifer. Thanks, Jennifer! It’s no secret that the HVAC industry is in the throes of an oversizing epidemic. Instead of stating the obvious, I wanted to take a deep dive into […]

Homeowner’s Guide to Sizing an AC System (and who is responsible when you’re uncomfortable)

This tech tip was a collaborative effort between Matt Bruner, Adam Mufich, Ed Janowiak, and Genry Garcia. Thank you to everybody who gave their input! The next time you come across a homeowner who wants a bigger HVAC system, or you simply want to set expectations for a customer, share this tech tip with them. […]

Q&A – Sizing Heat Pumps for Heat Load – Short #213

In this short Q&A podcast, Bryan answers a listener-submitted question about sizing heat pumps for heat load in heating mode, something that we haven't talked much about in the past due to the greater need for cooling in our market. In most cases across the country, a heat pump's heating loads will be greater […]

Q&A – How to Deploy a Dehum – Short #211

In this short Q&A podcast episode, Bryan answers Howard's question about how to deploy a dehumidifier (dehum) in a sealed home. He addresses things like location and fresh air requirements in green-grass markets with high dew points. Before deploying a dehumidifier, you will need to know about the climate, the structure, and the client's […]

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Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this short episode, Bryan clears up the confusion behind pumping vs. compression.

Pumping is usually associated with liquid. Liquid, like vapor, is a fluid, but it’s a lot denser and is essentially incompressible because the molecules are close together. Liquid volume varies based on temperature and density, but we can’t squish the molecules together. That’s why compressors with very little axial and radial compliance fail when flooded; they can’t compress the liquid. A circulator pump in a hydronic system is an example of a pump that pushes liquid along, but the pressure difference across the pump is minimal compared to that of a compressor; the same is true of liquid vs. vapor CO2.

However, vapor molecules are far apart and can be squished together to take up a smaller volume. That’s why vapor can go through compressors, which take a fluid of one volume and apply pressure to shrink it to a smaller volume, raising the temperature in the process. Pneumatics, as opposed to hydraulics, utilize compression to move vapor around in a circuit. Recovery machines need to be able to compress vapor refrigerant and pump liquid into the recovery tank.

Compressors and pumps can either be positive displacement or non-positive displacement systems. A positive displacement system creates a trap and forces a fixed amount of fluid through a system, like a scroll compressor or a circulator pump. Refrigerant volumes may vary because vapor density varies with temperature and pressure (the volume flow is the same, but the mass flow varies). A condensing fan motor, on the other hand, is dynamic and varies the volume of air it moves in response to pressure, as the mechanism relies on velocity and kinetic energy to move air.

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