Cooling Coil Size Selection Using ASHRAE Psychrometric Analysis | HVAC Tutorial

courses Detail https://www.udemy.com/course/advance-... https://www.udemy.com/course/revit-me... This video walks you step by step through sizing a cooling coil in an HVAC system using psychrometric analysis. Psychrometrics (the study of moist air properties) is one of the most powerful tools HVAC engineers have when they need to size coils correctly. In this tutorial, aimed at working HVAC professionals, fresh graduates, and students, we use an ASHRAE psychrometric chart and simple formulas to determine the coil capacity required to handle 6000 CFM of 100% outside air under extreme hot, dry conditions. We start by plotting the outdoor design point, then follow the complete air-conditioning process: cooling and dehumidifying hot air across the cooling coil, removing moisture (latent load), and then reheating the air back up to a comfortable supply temperature. Along the way, you’ll see how concepts like humidity ratio, relative humidity, dew point, enthalpy, sensible vs latent heat, sensible heat ratio, and coil bypass factor all come together on a single chart. Psychrometric Process Overview Our example starts with 6000 CFM of outside air at 110°F dry-bulb and 14.5% RH – a very hot, arid condition. On the psychrometric chart we locate this point and then draw the cooling and dehumidification line down toward the saturation curve. The air is cooled on the coil to around 50°F, which pushes it close to saturation and forces water vapor to condense out on the coil surface. This is where the latent cooling happens: we are physically removing moisture from the air stream. Because not every air molecule perfectly touches the coil surface, the leaving air is not exactly 100% RH. In practice, we get something like 90–95% RH at the coil outlet, described by the coil’s bypass factor. From here, a reheat coil (or another heat source) raises the air temperature from about 50°F up to a comfortable 75°F, without adding moisture. This is a pure sensible heating process, so the humidity ratio stays constant while the relative humidity drops to roughly 40%, which falls nicely in the typical indoor comfort band of 30–60% RH. Cooling & Reheat Capacity Using the psychrometric chart and standard HVAC equations, we calculate the total cooling capacity required for this process. For our design case, the cooling coil load comes out to roughly 34 tons of refrigeration (around 408,000 BTU/hr) to cool and dehumidify the 6000 CFM of 100% outdoor air from 110°F down to ~50°F and about 93% RH. This total includes both the sensible load (large drop in dry-bulb temperature) and the latent load (moisture removal). This is the number you would use when selecting the cooling coil or chiller capacity. Next, we size the reheat coil. Using Q = 1.08 × CFM × ΔT, reheating 6000 CFM from 50°F to 75°F (ΔT = 25°F) requires roughly 162,000 BTU/hr, or about 13.5 tons of sensible heating (≈47 kW). The result is supply air at 75°F and ~40% RH – dry enough to prevent condensation and mold issues, yet comfortable for occupants. Why This Matters This video is designed as a practical mini-workshop in psychrometric thinking. You will see how to: • Plot each process point (outdoor, coil entering, coil leaving, reheat outlet). • Read humidity ratio, enthalpy, and relative humidity from the chart. • Separate sensible and latent components of coil load. • Check that final room supply conditions fall inside the thermal comfort zone. • Use these results to select a real-world cooling coil and reheat coil. Whether you are preparing for design work, site troubleshooting, or HVAC exams, mastering psychrometric charts will make you more confident in coil selection and dehumidification strategies. Grab your psychrometric chart (or software) and follow along with the lecture to build a solid understanding of moisture, heat, and comfort in air-conditioning systems. #HVAC #HVACDesign #Psychrometrics #PsychrometricChart #CoolingCoil #HVACEngineering #MEPDesign #RevitMEP #ACCA #ASHRAE #CoolingLoad #LatentHeat #SensibleHeat #Dehumidification #VentilationDesign #BuildingServices #MechanicalEngineering #HVACTutorial #EngineeringStudents #HVACTraining #AirConditioning #IndoorAirQuality #ThermalComfort #EnergyEfficiency #BIM #EPICSSolution