1. What is the CMH Formula?

The CMH (Cubic Meters per Hour) formula calculates air flow rate from power input, using the relationship between thermal energy and air properties. It's commonly used in HVAC and ventilation system design.

2. How Does the Calculator Work?

The calculator uses the CMH formula:

Where:

• \( kW \) — Power input in kilowatts
• \( \rho \) — Air density in kg/m³
• \( c \) — Specific heat capacity in J/kg·K
• \( \Delta T \) — Temperature difference in Kelvin
• 3600 — Conversion factor from seconds to hours

Explanation: The formula converts thermal power to volumetric flow rate based on the energy required to heat/cool air by a specific temperature difference.

3. Importance of CMH Calculation

Details: Accurate CMH calculation is essential for proper HVAC system design, ensuring adequate ventilation, maintaining indoor air quality, and optimizing energy efficiency in heating and cooling systems.

4. Using the Calculator

Tips: Enter power in kW, air density in kg/m³, specific heat capacity in J/kg·K, and temperature difference in K. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical value for air density?
A: At standard conditions (20°C, 101.325 kPa), air density is approximately 1.2 kg/m³.

Q2: What is the specific heat capacity of air?
A: The specific heat capacity of air at constant pressure is approximately 1005 J/kg·K.

Q3: How is temperature difference determined?
A: Temperature difference is the difference between supply air temperature and room air temperature in heating applications, or room air temperature and supply air temperature in cooling applications.

Q4: Can this formula be used for liquids?
A: While the same physical principles apply, different density and specific heat values would be needed for liquids other than air.

Q5: What are typical CMH values for residential systems?
A: Residential HVAC systems typically range from 500-2000 m³/h depending on the size of the space and ventilation requirements.