Sol-Air Temperature Calculator

Calculating the Sol-Air Temperature is a critical step in understanding the thermal environment of buildings and outdoor structures. This calculation helps in the design and analysis of heating, ventilation, and air conditioning (HVAC) systems, as well as in the assessment of thermal comfort and energy efficiency.

Historical Background

The concept of Sol-Air Temperature was developed as a method to incorporate the effects of solar radiation on the thermal performance of buildings and materials. It represents an effective outdoor temperature considering solar gain and is used in building simulations and environmental assessments.

Calculation Formula

The formula to calculate the Sol-Air Temperature (\(T_{sa}\)) is given by:

\[ T{sa} = T{o} + \frac{a \cdot I - Q}{h} \]

where:

• \(T_{sa}\) is the Sol-Air Temperature in °C,
• \(T_{o}\) is the outdoor temperature in °C,
• \(a\) is the solar radiation absorptivity,
• \(I\) is the global solar irradiance in W/m²,
• \(Q\) is the extra infrared radiation in W/m²,
• \(h\) is the heat transfer coefficient for radiation in W/m²-K.

Example Calculation

Suppose the outdoor temperature is 25°C, solar radiation absorptivity is 0.7, global solar irradiance is 800 W/m², extra infrared radiation is 100 W/m², and the heat transfer coefficient for radiation is 25 W/m²-K. The Sol-Air Temperature would be calculated as follows:

\[ T_{sa} = 25 + \frac{0.7 \cdot 800 - 100}{25} = 25 + \frac{560 - 100}{25} = 25 + 18.4 = 43.4 \text{ °C} \]

Importance and Usage Scenarios

The Sol-Air Temperature is used extensively in the field of building physics to determine the thermal load from the sun on building surfaces. It aids in the design of energy-efficient buildings by accounting for passive solar gain and the need for shading devices. It is also crucial in

the development of thermal comfort models and in the calculation of cooling loads for air conditioning systems.

Common FAQs

1. What is solar radiation absorptivity?

   • It is the fraction of incident solar radiation that is absorbed by a surface. Different materials and colors have different absorptivities.

2. How does global solar irradiance affect Sol-Air Temperature?

   • Higher global solar irradiance increases the Sol-Air Temperature, indicating more heat gain from solar radiation.

3. What role does the heat transfer coefficient play?

   • The heat transfer coefficient for radiation quantifies how effectively a surface exchanges heat with its surroundings due to radiation. A higher coefficient means more efficient heat exchange.

This calculator simplifies the process of estimating the Sol-Air Temperature, facilitating more accurate and efficient designs and analyses in the fields of architecture, environmental engineering, and urban planning.