1. What is the Heat Pump CFM Equation?

The CFM (Cubic Feet per Minute) equation calculates the airflow required for a heat pump system based on its heating/cooling capacity (BTU/hr) and the temperature difference across the system. This helps in proper system sizing and performance evaluation.

2. How Does the Calculator Work?

The calculator uses the CFM equation:

Where:

• \( BTU/hr \) — British Thermal Units per hour (heating/cooling capacity)
• \( \Delta T \) — Temperature difference across the system (°F)
• 1.08 — Constant that accounts for air density and specific heat

Explanation: The equation balances the heat transfer requirements with the airflow needed to achieve that transfer at a given temperature difference.

3. Importance of CFM Calculation

Details: Proper CFM calculation ensures efficient heat pump operation, prevents short cycling, maintains comfort, and extends equipment life. Incorrect airflow can lead to poor performance and higher energy costs.

4. Using the Calculator

Tips: Enter the heat pump's capacity in BTU/hr and the temperature difference in °F. Typical ΔT values are 15-20°F for cooling and 30-50°F for heating.

5. Frequently Asked Questions (FAQ)

Q1: Why is 1.08 used in the formula?
A: The constant 1.08 combines the specific heat of air (0.24 BTU/lb-°F) and air density (0.075 lb/ft³) with conversion factors for minutes to hours.

Q2: What are typical CFM values for residential systems?
A: Typically 350-400 CFM per ton (12,000 BTU/hr) of cooling capacity, but this varies based on system design.

Q3: How does ΔT affect CFM requirements?
A: Higher temperature differences require less airflow to transfer the same amount of heat, while lower ΔT requires more CFM.

Q4: Should this be used for both heating and cooling?
A: Yes, but remember that heating ΔT is typically higher than cooling ΔT for the same system.

Q5: What if my system uses metric units?
A: Convert BTU/hr to watts (1 BTU/hr ≈ 0.293 W) and °F to °C before using the formula, with a different constant.