How To Do A Heat Load Calculation On A House

Heat Load Equation:

\[ \text{Heat Load (BTU/hr)} = \sum (U \times A \times \Delta T) + \text{Internal Gains} + \text{Infiltration} \]

U-value (BTU/hr ft² °F):

BTU/hr ft² °F

Area (ft²):

ft²

Temperature Difference (°F):

°F

Internal Gains (BTU/hr):

BTU/hr

Infiltration (BTU/hr):

BTU/hr

Heat Load (BTU/hr):

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1. What Is Heat Load Calculation?

Heat load calculation is a method used to determine the heating and cooling requirements of a building. It considers various factors including building envelope properties, internal heat sources, and infiltration to calculate the total thermal energy needed to maintain comfortable indoor conditions.

2. How Does The Calculator Work?

The calculator uses the heat load equation:

\[ \text{Heat Load (BTU/hr)} = \sum (U \times A \times \Delta T) + \text{Internal Gains} + \text{Infiltration} \]

Where:

\( U \) — U-value (thermal transmittance) in BTU/hr ft² °F
\( A \) — Area in square feet (ft²)
\( \Delta T \) — Temperature difference between inside and outside in °F
\( \text{Internal Gains} \) — Heat generated from occupants, appliances, and lighting
\( \text{Infiltration} \) — Heat loss/gain from air leakage

Explanation: The equation calculates the total heat transfer through building components plus internal heat sources and air infiltration effects.

3. Importance Of Heat Load Calculation

Details: Accurate heat load calculation is essential for proper HVAC system sizing, energy efficiency optimization, and ensuring occupant comfort while minimizing energy costs.

4. Using The Calculator

Tips: Enter U-value in BTU/hr ft² °F, area in square feet, temperature difference in °F, internal gains in BTU/hr, and infiltration in BTU/hr. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is U-value and how is it determined?
A: U-value measures how well a building element conducts heat. Lower values indicate better insulation. It can be calculated from material properties or obtained from manufacturer specifications.

Q2: Why is temperature difference important?
A: Temperature difference drives heat transfer. Larger differences result in greater heat flow through building envelopes, requiring more heating or cooling capacity.

Q3: What are typical internal gains in a house?
A: Internal gains include heat from people (400 BTU/hr per person), appliances, lighting, and electronics. These can significantly affect the total heat load.

Q4: How is infiltration calculated?
A: Infiltration is estimated based on air changes per hour, building volume, and temperature difference. It accounts for heat loss through cracks and openings.

Q5: When should heat load calculations be performed?
A: For new construction, major renovations, HVAC system replacements, or when experiencing comfort issues. Professional calculations are recommended for complex projects.