HVAC, psychrometric processes and thermal-energy models
Building thermal design starts with a boundary, an occupancy or process need and the actual environmental conditions. Sensible heat changes temperature, while latent effects involve moisture and phase change. A sensible heat ratio or factor uses sensible load divided by total load under a stated convention. A sensible-only calculation cannot establish the total cooling duty when moisture removal is significant.
Moist-air properties require consistent bases. Relative humidity is a ratio related to saturation at the same condition, not the mass of water per mass of dry air. Humidity ratio uses water-vapor mass relative to dry-air mass. Dry-bulb temperature, wet-bulb temperature, dew point and enthalpy describe different aspects of the state. A psychrometric chart is tied to a pressure basis; do not silently transfer its values to a substantially different altitude.
For a supplied air-flow model, heat transfer can be calculated from mass flow and the relevant enthalpy difference. Sensible-only calculations may use mass flow times heat capacity times temperature change. Track whether a stated flow is dry-air mass, moist-air mass or volume flow at defined conditions. Mixing streams requires compatible mass and energy balances rather than an unweighted average of every property. Cooling below a relevant dew point can cause condensation, changing both moisture content and latent load.
Refrigeration efficiency is a ratio with a stated boundary. Cooling COP uses useful cooling divided by input work, while heating COP counts the useful heating output. A higher COP is not a thermodynamic efficiency capped at one. Heat-pump performance depends on source and sink conditions, part-load behavior and auxiliaries. A Carnot expression provides an ideal bound using absolute temperatures; it is not an achievable equipment rating or an operating instruction.
Ventilation, comfort and energy objectives interact. More outdoor air can affect humidity, heating or cooling demand and contaminant dilution, but a universal airflow per person is not supplied here. Actual design criteria, controls, occupancy and applicable requirements must be known. Air distribution, filtration, condensate management, maintenance access and control stability matter alongside nominal plant capacity. Evaluate commissioning evidence and measured operating conditions before concluding that a nameplate or design drawing proves the installed system performs as intended.