HVAC Formulas and Equations by Tons of Concrete

HVAC Key Formulas:

\[ P_{kW} = \frac{A_{room} \times 44.6}{3412 \times EER} \] \[ Q_{cfm} = \frac{Q_{btu}}{1.08 \times \Delta T} \]

Room Area (A_room):

m²

Energy Efficiency Ratio (EER):

Cooling Capacity (Q_btu):

BTU/h

Temperature Difference (ΔT):

°F

Power Consumption (P_kW): kW

Air Flow Rate (Q_cfm): ft³/min

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1. What are HVAC Formulas and Equations?

Definition: These formulas calculate key HVAC parameters including power consumption and air flow rates.

Purpose: Essential for HVAC system design, energy efficiency analysis, and proper ventilation planning.

2. How Do the Formulas Work?

The calculator uses two main formulas:

\[ P_{kW} = \frac{A_{room} \times 44.6}{3412 \times EER} \] \[ Q_{cfm} = \frac{Q_{btu}}{1.08 \times \Delta T} \]

Where:

\( P_{kW} \) — Power consumption in kilowatts
\( A_{room} \) — Room area in square meters
\( EER \) — Energy Efficiency Ratio (dimensionless)
\( Q_{cfm} \) — Air flow rate in cubic feet per minute
\( Q_{btu} \) — Cooling capacity in BTU per hour
\( \Delta T \) — Temperature difference in °F

3. Importance of HVAC Calculations

Details: Proper calculations ensure energy-efficient operation, adequate cooling capacity, and proper air circulation in buildings.

4. Using the Calculator

Tips:

For power calculation: enter room area and EER
For air flow calculation: enter cooling capacity and temperature difference
Default EER is 3.5 (typical for residential units)
Default ΔT is 20°F (standard temperature difference)

5. Frequently Asked Questions (FAQ)

Q1: What is a typical EER value?
A: Residential units typically range 3.0-4.0, while high-efficiency units can reach 5.0+.

Q2: How do I determine ΔT?
A: ΔT is the difference between supply air temperature and room temperature (usually 15-25°F).

Q3: What's the 1.08 constant in the air flow formula?
A: It's the product of air density (0.075 lb/ft³) and specific heat (0.24 BTU/lb-°F) at standard conditions × 60 min/hr.

Q4: Can I use this for heating calculations?
A: The air flow formula works for heating if you use heating capacity instead of cooling capacity.

Q5: Why convert room area from m²?
A: The formula uses metric inputs for area but imperial for other units, reflecting common engineering practices.