Heater Coolers Ventilation Systems

Overview

Engineering reference data for Heater Coolers Ventilation Systems in HVAC systems.

Key Formulas

Sensible Heat

$Q = \dot{m} c_p \Delta T$

Heat causing temperature change.

Latent Heat

$Q = \dot{m} h_{fg} \Delta\omega$

Heat causing moisture change.

COP (Cooling)

$COP = Q_c / W$

Coefficient of performance.

Variables

Classification of Heaters and Coolers

Heaters and coolers are commonly classified by their operating medium:

• Heaters: Water Heated, Steam Heated, Electrical Heated
• Coolers: Water Cooled, Brine Cooled, Evaporation Medium Cooled

Additional Heating Equations

Steam Heater: When saturated steam is used, the heating process is: $H = q_s h_e$ where:

• $q_s$ = steam flow (kg/s)
• $h_e$ = evaporating enthalpy of water (J/kg)

The evaporating enthalpy depends on steam pressure:

• At 1 bar absolute (100°C): $h_e = 2258\ \text{kJ/kg}$
• At 10 bar absolute (180°C): $h_e = 2014\ \text{kJ/kg}$

Water (Fluid) Flow through Cooler: The water flow cooling process can be calculated with a formula similar to the water heater equation.

Cooling Equations

Dry Surface Cooling: For a cooler with a dry surface: $H_c = \rho c_p q_v (t_i - t_o)$ where:

• $H_c$ = heat removed from air (W)

Wet Surface Cooling: For coolers with wet surfaces, the enthalpy of moist air must be used: $H_c = \rho q_v (h_i - h_o)$ where:

• $h_i$ = enthalpy of moist air into the cooler (kJ/kg)
• $h_o$ = enthalpy of moist air out of the cooler (kJ/kg)

Selection Criteria

Water Heated Heaters:

• Air speed through heater (front area): 2 - 5 m/s
• Water speed: Copper pipes: 0.2 - 1.5 m/s; Steel pipes: 0.2 - 3 m/s

Steam Heated Heaters:

• Air speed through heater (front area): 2 - 5 m/s
• Note: Remember condensate drain.

Coolers:

• Air speed through cooler (front area): 2 - 3 m/s (install drop separators above 3 m/s)
• Water speed: Max 0.2 - 2.0 m/s in copper pipes
• Note: Wet surfaces must be drained.

References

• Original Source