HVAC Psychrometry, Air Handling System and Duct Selection

Explore the three modes of heat transfer: conduction, convection, and radiation, along with factors like thermal conductivity and emissivity, plus practical examples such as insulation and thermal flasks.

Explore external heat gains driving building cooling loads, including solar radiation through glass, conduction through glass and envelope, and infiltration; consider climate, orientation, and envelope design for HVAC sizing.

Calculate solar heat gain using SHG values, window area, and 3 mm clear glass shading effects. Apply the cooling load factor and formulas to estimate peak cooling load.

Explore conduction heat gain through the building envelope, detailing U values, R values, CLTD adjustments, and the difference between window and wall thermal performance with a practical example.

Explore the four internal heat gains—occupants, lighting, equipment, and infiltration—and how they shape sensible and latent loads and air change per hour.

Describe air properties such as dry and wet bulb temperatures, dew point, humidity ratio, and relative humidity. Explore specific volume, specific enthalpy, and the difference between sensible and latent heat.

Learn to read the psychrometric chart to determine air properties from dry bulb and wet bulb readings, including dew point, humidity ratio, relative humidity, specific volume, and enthalpy.

Explore how sensible heating, cooling, humidification, and dehumidification move air on the psychrometric chart, altering dry bulb temperature, humidity ratio, enthalpy, and relative humidity in air handling systems.

Learn how air mixing in an air handling unit blends return and outdoor air using dampers and a BMS, and determine mixed air properties on the psychometric chart.

Explore how sensible and latent heat calculations drive air treatment in HVAC psychrometry, using Qs, Ql, QT, humidity ratio changes, and psychometric charts.

Compute sensible and latent air loads through a cooling coil using 0.2 kg/s at 28°C and 80% RH, deriving humidity ratios from the psychrometric chart.

Explore how the air handling unit supplies cold air, mixes return and outdoor air, dehumidifies through the coil, and is interpreted on a psychrometric chart by BMS to control loads.

Plot return and outdoor air points on the psychrometric chart, compute mixed and supply air conditions from sensible and latent loads, and determine the coil's sensible heat ratio.

Calculate mixed air from 80% return and 20% outdoor air, plot the points on the psychrometric chart, and compute the sensible, latent, total cooling loads and chilled water return temperature.

Analyze a worked example on the air conditioning process using a psychrometric chart to determine mixed air, enthalpy change, mass flow rate, and cooling coil load.

Compare round, oval, rectangular, and square ducting, including flexible ducts and fittings, and assess aspect ratio, space constraints, and ahu sizing to optimize cost, friction, and heat transfer.

Apply the equal friction method with a Pa/m loss, use the friction chart to derive round duct diameters from air quantity and velocity, then convert to rectangular ducts.

this worked example sizes an ahu’s ducts to three diffusers, computes 200–300 l/s airflows, applies 0.8 pa/m friction loss, and selects round and rectangular ducts with favorable aspect ratios.

Learn AHU selection fundamentals: sizing cooling coils and supply fan, balancing sensible and latent loads, managing mixed and supply air temperatures, and calculating static pressure losses through duct fittings.

Identify the largest pressure loss duct segment and sum seven losses: friction, junctions, fire damper, elbows, and diffuser to obtain 78 Pa external pressure for AHU catalog verification.

select an AHU fan and duct system by sizing ducts, calculating friction losses, and choosing rectangular and round ducts to meet 3600 l/s and 187.2 pa pressure rise.

Learn how precooling outdoor air in an AHU affects psychrometrics and coil load, comparing Q coil with Q room plus ventilation, and showing PCC, HRV, and ERV reducing enthalpy.