Accurate HVAC sizing is crucial for optimal system performance and energy efficiency. In addition to the rule of thumb formula, there are several important unit conversions used in the HVAC industry. In this blog post, we will explore the rule of thumb formula, along with key formulas and conversions that will help you accurately estimate HVAC system capacity and understand the relationships between different units.

The Rule of Thumb Formula:

The rule of thumb formula provides a rough approximation for HVAC system sizing based on the square footage of the space being conditioned. However, it's important to consult with an HVAC professional for precise sizing. Here's an overview of the rule of thumb formula, followed by important unit conversions:

Cooling Capacity:

The rule of thumb suggests a range of cooling capacity in British Thermal Units per hour (BTU/hr) per square foot of conditioned space. The following formula is commonly used:

Cooling Capacity (BTU/hr) = Area (sq. ft.) × Cooling Capacity per sq. ft.

Important Unit Conversions:

To facilitate accurate HVAC sizing, it's essential to understand and convert between different units. Here are some key conversions commonly used in the HVAC industry:

Tons of Refrigeration:

• 1 Ton = 12,000 BTU/hr

• 1 Ton = 3.516 kW

• 1 Ton = 12 MBH (thousand British Thermal Units per hour)

• 1 Ton = 3025.9 Kcal/min (kilocalories per minute)

• 1 Ton = 200 BTU/min

  Air Flow:

• 1 LPS (liters per second) = 2.119 CFM (cubic feet per minute)

• 1 CFM = 1.7 CMH (cubic meters per hour)

• 1 CMS (cubic meters per second) = 1000 LPS

• 1 CMS = 2119 CFM

Additional HVAC Conversions:

• 1 MPM (meters per minute) = 3.24 FPM (feet per minute)

• 1 CFM = 28.3168 LPM (liters per minute)

• 1 CFM = 0.4719 LPS (liters per second)

• 1 FPM = 0.00508 MPH (miles per hour)

• 1 CFM = 1.7 CMH

• 1 CMH = 4.4 GPM (gallons per minute)

• 1 GPM = 3.78 LPM

• 3.1 HP (horsepower) = 0.745 kW

• 1 HP = 9,550 BTU/hr

• 1 HP = 2,410 Kcal/hr

• 1 HP = 0.8 TR (ton of refrigeration)

• 1 TR = 1.25 HP

Understanding commonly used formulas and conversions is essential for accurate HVAC system sizing. The rule of thumb formula provides a rough estimation, but consulting with an HVAC professional is crucial for precise sizing. Additionally, being familiar with important unit conversions, such as ton-to-BTU, flow of air, and distance conversions, will help you navigate the HVAC industry more effectively. By incorporating these formulas and conversions into your HVAC sizing calculations, you can ensure optimal performance and energy efficiency in your HVAC system.