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Tech Tips:

Why the Sauna Feels Hotter When You Throw Water on the Rocks

I admit it, I'm a sauna guy now. The ones at the gym are pretty gross, so I got a small one at home because I guess I’ve missed sitting in attics or something. If you’ve ever sat in a traditional sauna, you know the drill: the heat’s already intense, and then you or someone […]

A Tale of Two Latents

When the quiz or the teacher asks what “latent” heat is, there is generally some reference to it being hidden heat, which is what the word “latent” means. We then learn that it is heat energy transferred that results in a change of state rather than a temperature change. Later on, we hear a lot […]

Coil SHR, Ventilation, and Bypass Factor – Advanced Psychrometrics Part 2

This is the second article in a three-part series where we explore advanced psychrometrics. The source material for each of the articles in this series is ACCA Manual P Sections 3, 4, and 5. This article is based on information found in Section 4. If you followed the previous advanced psychrometrics article, you now know […]

Sensible Heat Ratio (SHR)

Every piece of air conditioning equipment can move a certain amount of heat BTUs (British Thermal Units) at set conditions. In most cases, during the cooling mode, a portion of those BTUs will go toward changing the temperature of the air, and a part will go toward changing vapor water in the air into water […]

Psychrometrics and the Magic Line – Short #265

In this short podcast episode, Bryan talks about psychrometrics and the magic line inside a messy-looking chart. The psychrometric chart is a key tool for understanding the relationship between air and water. “Psychrometric” comes from the Greek roots for “cold” and “measurement.” As such, a tool called the psychrometer (with paired wet-bulb and dry-bulb […]

Psychrometrics Basics w/ Jamie Kitchen Podcast

In this episode of the podcast, Jamie Kitchen from Danfoss talks about wet-bulb, dry-bulb, relative humidity, dew point, enthalpy, and latent heat. These are the building blocks of psychrometrics, which deals with human comfort as it relates to temperature, humidity, and heat loads. Humidity is water vapor in the air. As the air's dry-bulb temperature […]

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HVAC School – For Techs, By Techs

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 comprehensive episode, Bryan and Roman dive deep into one of the most challenging topics in modern HVAC: making VRF (Variable Refrigerant Flow) and ductless systems perform effectively in humid climates like Florida. The conversation tackles a common misconception that inverter-driven equipment automatically handles humidity well simply because it can “turn down.” Roman emphasizes that successful application of VRF technology in humid environments requires skilled professionals who understand building science, envelope integrity, and proper system sizing. The biggest takeaway? If you’re going to err on sizing, undersize rather than oversize – these systems will run longer and maintain better humidity control when properly sized.

The hosts explore the three critical factors for dehumidification: runtime, coil temperature, and surface condensation. They explain how traditional inverter systems were programmed for energy efficiency by allowing coils to warm up as they approached the set point, which unfortunately sacrifices latent capacity. Modern systems with active dehumidification capabilities use expansion valve control to “starve” the coil, lowering saturation temperature to around 35-37 degrees while extending runtime. Roman shares his personal experience with a 7,000 BTU unit serving his 700 square foot master bedroom suite, demonstrating how proper application and understanding of equipment capabilities can deliver excellent humidity control without oversizing.

The discussion takes a practical turn as Bryan presents a comprehensive troubleshooting checklist for humidity problems, starting with bulk water leaks and progressing through envelope integrity, duct sealing, equipment selection, and pressure balancing. They debunk common “solutions” that actually make problems worse, like adding attic insulation or solar attic fans without addressing root causes. The conversation reveals a counterintuitive truth: reducing sensible load through excessive insulation can worsen humidity problems by reducing equipment runtime. They explain why “active dehumidification” through overcooling isn’t true dehumidification, and why another solution – reheat – requires adding sensible heat back to spaces to maintain longer equipment runtime.

Topics Covered:

VRF and inverter sizing misconceptions – Why undersizing is often better than oversizing in humid climates
Three factors of dehumidification – Runtime, coil temperature, and surface condensation explained
Active dehumidification technology – How expansion valve control creates longer runtime and colder coils
Equipment capacity ratings – Understanding that a “12K” unit may actually perform at 18,000 BTU
Latent vs. sensible capacity – Why checking engineering specifications is critical for humid climate applications
VRT (Variable Refrigerant Temperature) – When this energy-saving feature should be disabled in humid climates
Fan operation strategies – Why continuous fan operation can worsen humidity problems
Duct and envelope leakage – How pressure imbalances drive moisture problems
Surface condensation – Why vents and ducts sweat and how to prevent it
The overcooling trap – Why lowering the set point creates interstitial space moisture problems
Humidity sensors in thermostats – Understanding what they do (and don’t do)
Load diversity and zone control – How multiple smaller units can outperform single large systems
Reheat strategies – From electric resistance to passive solar gain
Common mistakes – Why attic insulation and solar fans often worsen humidity issues
Troubleshooting checklist – A systematic approach from bulk water to equipment selection

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Search Episodes

VRF, Ductless and Humidity Control w/ Roman

11/27/2025

Bryan Orr

The History of the Thermostat – Short #267

11/25/2025

Bryan Orr