Cooling Coil Calculation

When selecting a cooling coil, many engineers jump straight to software... but understanding the fundamentals is what makes the difference on-site.

1. Cooling Load (Q) Start with the basic equation:

Q = m × Cp × ΔΤ

Where:

m = air mass flow rate (kg/s)
Cp = specific heat (~1.02 kJ/kg.K)
ΔT = temperature difference (°C)

2. Airflow Method (Most Practical) In real projects, we usually use airflow:

Q1.2 x CFM × ΔT

(or in SI)

Q = p x V x Cp × ΔT

Example:

Airflow = 5000 CFM
Entering air = 30°C
Leaving air = 15°C

ΔT = 15°C

Q1.2 x 5000 × 15 = 90,000 Btu/hr (~7.5 TR)

3. Coil Selection Parameters

Don't stop at load calculation. Always verify:

Entering air DB/WB (important for latent load)
Chilled water temperature (e.g., 7/12°C)
Face velocity (recommended: 2-2.5 m/s)
Number of rows & fins spacing

4. Key Field Insight

A common mistake is oversizing the coil:

Leads to low humidity control
Causes short cycling
Reduces system efficiency

5. Pro Tip from Site

If your supply air temperature is too high:

Check coil fouling
Verify water flow rate
Measure △T across coil (air & water side)

Good engineering is not just calculation... it's verification on site.

Comments

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