Two kinds of heat in every airstream Any heated or cooled air carries energy in two forms. Sensible heat changes the dry-bulb temperature of the air without changing its moisture content. Latent heat is the energy tied up in water vapour: it moves when moisture condenses or evaporates, and it can change without any temperature […]
Psychrometrics Basics: Reading Air Before You Recover Its Heat
Air is a mixture, not a single number Sizing any heat recovery system starts with the state of the air. Four properties define it: Dry-bulb temperature (DB): the ordinary thermometer reading. Wet-bulb temperature (WB): thermometer with a wet wick; tracks the cooling effect of evaporation. Humidity ratio (W): mass of water vapour per mass of […]
Psychrometric Processes in Heat Recovery: What Happens on the Chart
Four basic processes On the psychrometric chart, ventilation air moves along predictable lines: Heating: horizontal line to the right (dry-bulb up, moisture constant). Sensible cooling: horizontal line to the left (dry-bulb down, moisture constant). Humidification: line upward (more moisture). Dehumidification: line downward (condensation, latent heat released). Sensible recovery = a move along the constant-humidity line […]
Air Changes per Hour (ACH): The Ventilation Rate Behind Recovery Load
Definition Air changes per hour is the volumetric airflow divided by the room volume, expressed per hour: ACH = (volumetric_flow_rate / room_volume) x 3600 An ACH of 6 means the room air is theoretically replaced six times in an hour. Typical values Classrooms: about 4-6 ACH (see school ventilation) Laboratories and fume hoods: 6-12 ACH […]
Specific Heat & Density of Air in Recovery Math
The two numbers you reuse constantly Specific heat of air, cp: about 1.006 kJ/kg.K (or 1006 J/kg.K). Density of air, rho: about 1.2 kg/m3 at 20 degC and 1 atm. Together they give a volumetric heat capacity of roughly 1200 J/m3.K – the energy stored in each cubic metre of air per degree of temperature. […]
Seasonal Efficiency: Beyond Nameplate Ratings
Rated vs real A core may be rated at 75% effectiveness, but the energy saved over a year is lower, because recovery is most valuable in extreme weather and can even hurt in mild weather (it reheats supply you wanted cool). The seasonal efficiency weights effectiveness by the hours and temperature lifts actually seen. What […]
U-Value: The Building-Side Recovery Metric
Definition The U-value is the rate of heat transfer through a building element per square metre per degree of temperature difference, in W/m2.K. A low-U wall or window loses little heat; a high-U one loses a lot. U-value vs the exchanger k-value Do not confuse them. The exchanger overall conductance (UxA in the epsilon-NTU method) […]
Fan Static Pressure Class: Matching the Fan to the Recovery Core
Static vs total pressure Total pressure is the full energy of the moving air; static pressure is the usable pushing force after velocity energy is set aside. Fans are classed by the static pressure they can develop against a system – and the recovery core is one of the biggest resistances in that system. Core […]
Airport HVAC & Energy Recovery: Cutting Terminal Energy Use
Why terminals are energy hotspots Airports are among the most energy-intensive buildings in the commercial sector. Vast terminals run 24/7 with high fresh-air requirements, large glass facades, and constantly moving passenger loads. Heating and cooling the ventilation air alone can account for 40-60% of a terminal’s HVAC energy. Air-to-air heat recovery is the single highest-return […]
Plate Heat Exchanger: Working Principle, Types and Applications
A plate heat exchanger is one of the most efficient ways to recover thermal energy from exhaust air, process gas, or ventilation streams. It consists of multiple thin metal plates separated by gaskets or formed air gaps, creating alternating channels for the hot and cold streams. Heat moves through the plate material without the two […]