Cooling Coil Power Selection

Enter the required cooling temperature and air flow, and the program will calculate the cooling coil power based on default values of coil wall temperature and outdoor air parameters. Calculations are based on formulas contained in the "knowledge" tab.

For Poland, external temperature and humidity values for calculations are usually assumed as:

• Text 32 ÷ 35°C
• Relative humidity - 45 ÷ 55%

Coil wall temperature is typically assumed to be between 6-12°C. Cooling coils most commonly occur as:

• water-cooled - supplied from a system such as chilled water. In this case, the wall temperature depends on the system operating parameters.
• direct expansion - where the coil wall temperature is close to the refrigerant evaporation temperature

Calculation of Enthalpy and Dew Point of Moist Air

Enter the outdoor air parameters, i.e., temperature (°C) and relative humidity (%), and the program will calculate its basic enthalpy, dew point, and moisture content (absolute humidity).

You can add a second air state to compare calculations and parameter values. Just click the "Compare two air states?" button.

Calculations are based on formulas contained in the "knowledge" tab.

How to Calculate Cooling Coil Power

To calculate cooling coil power (Q), we need to know the enthalpy difference (Δh) and air mass flow rate (ṁ). The cooling coil power formula is as follows:

Q = Δh × ṁ

• Q - cooling coil power, expressed in kilowatts (kW)
• Δh - enthalpy difference between air at inlet and outlet of the coil, expressed in kilojoules per kilogram (kJ/kg)
• ṁ - air mass flow rate passing through the coil, expressed in kilograms per second (kg/s)

The Δh value can be calculated as the difference in air enthalpy at the inlet and outlet of the coil. The air mass flow rate (ṁ) depends on the ventilation system specifications and the air flow required for the cooling process.

How to Calculate Dew Point

Dew point can be calculated based on the current temperature and relative humidity of the air, using the following formula:

Td = (b × α) / (a - α)

where:

• α = (a × T) / (b + T) + ln(RH)
• T - current air temperature, expressed in degrees Celsius (°C)
• RH - relative humidity of air as a fraction (e.g., 0.45 for 45%)
• a = 17.27
• b = 237.7
• Td - dew point, expressed in degrees Celsius (°C)

This formula is based on Magnus's formula for calculating dew point and is sufficiently accurate for most meteorological and HVAC applications.

How to Calculate Moist Air Enthalpy

Moist air enthalpy can be calculated based on temperature and relative humidity, using the following formula:

h = cp × T + w × (2501 + 1.86 × T)

where:

• h - moist air enthalpy, expressed in kJ/kg
• cp - specific heat of dry air at constant pressure, approximately 1.005 kJ/(kg·K)
• T - air temperature in degrees Celsius (°C)
• w - moisture ratio in air (absolute humidity), expressed in kg water/kg dry air
• 2501 kJ/kg - heat of water evaporation at 0°C
• 1.86 kJ/(kg·K) - specific heat of water vapor

Absolute humidity (w) can be calculated based on relative humidity and temperature, using appropriate equations of state for water vapor in air.

Enthalpy is a key parameter in thermodynamic processes such as heating, cooling, and air conditioning, as it reflects the total energy content of air, including both thermal energy and energy associated with water evaporation.