HVAC Load Calculation Formulas

 

Introduction

Accurate HVAC load calculation is the first step in designing any air conditioning or heating system. It determines the amount of cooling or heating required to maintain a comfortable indoor environment.

Tip for Beginners: Always consider both sensible heat (temperature change) and latent heat (humidity/moisture load) in calculations.

---

Key Formulas

1. Sensible Heat Load:

$$Q_s = 1.1 \times CFM \times \Delta T$$

• Q_s: Sensible heat (Btu/hr)

• CFM: Airflow (cubic feet per minute)

• ΔT: Temperature difference (°F)

2. Latent Heat Load:

$$Q_l = 4840 \times CFM \times \Delta W$$

• ΔW: Difference in humidity ratio

3. Total Heat Load:

$$Q_t = 4.5 \times CFM \times \Delta h$$

• Δh: Change in enthalpy

---

Example Calculation

• Room: 20 × 15 ft, 9 ft ceiling

• Airflow: 800 CFM

• Temperature difference: 75°F indoor – 95°F outdoor = 20°F

• Sensible Heat:

  $Q_{}$$s_{}$$=$$1.1$$\times$$800$$\times$$20$$=$$17$$,$$600$$B$$t$$u$$\mathrm{/}$$h$$r$Qs​=1.1×800×20=17,600Btu/hr

(You can expand with latent heat example and total heat load calculation.)

---

Practical Tips

• Use psychrometric charts for accuracy.

• Always include safety margins (10–15%) for peak load.

• Document all assumptions for future reference.

---

Suggested Images

• Psychrometric chart example.

• Step-by-step calculation table.

Internal Linking:

• Link to Duct Design page for airflow considerations: Duct Design and Airflow Formulas

• Link back to Master Page: HVAC Formulas Master Guide

• Fan and Pump Horsepower Formulas for HVAC Systems

Tags:
HVAC load calculation, cooling load formula, heating load calculation, MEP HVAC formulas, air conditioning calculation