1. What is a Hot Water Heating Coil Sizing Calculator?

Definition: This calculator determines the required surface area of a hot water heating coil based on heat transfer requirements, overall heat transfer coefficient, and log mean temperature difference.

Purpose: It helps HVAC engineers and technicians properly size heating coils for optimal thermal performance in air handling systems.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( A \) — Coil surface area (m²)
• \( Q \) — Heat transfer rate (W)
• \( U \) — Overall heat transfer coefficient (W/m² K)
• \( \Delta T_{lm} \) — Log mean temperature difference (K)

Explanation: The heat transfer rate is divided by the product of the heat transfer coefficient and temperature difference to determine the required coil area.

3. Importance of Proper Coil Sizing

Details: Correct coil sizing ensures efficient heat transfer, proper system performance, and avoids issues like insufficient heating or excessive pressure drop.

4. Using the Calculator

Tips: Enter the heat transfer rate in watts, overall heat transfer coefficient (default 50 W/m² K), and log mean temperature difference (default 20 K). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical U value for hot water coils?
A: Typical values range from 30-60 W/m² K depending on coil construction, water velocity, and air velocity.

Q2: How do I calculate log mean temperature difference?
A: ΔT_lm = [(T_hw,in - T_air,out) - (T_hw,out - T_air,in)] / ln[(T_hw,in - T_air,out)/(T_hw,out - T_air,in)]

Q3: What affects the heat transfer coefficient?
A: Water velocity, air velocity, fin spacing, tube diameter, and material properties all affect U.

Q4: Should I include a safety factor?
A: Yes, typically add 10-20% to the calculated area to account for fouling and design uncertainties.

Q5: Can this be used for other coil types?
A: The same principle applies to chilled water coils, but U values and ΔT will differ.