REVIT Calculation of Heat Gains in MagiCAD for Air Conditioning Systems / AutoCAD and Revit

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The calculation of heat gains is a critical stage in designing air conditioning (HVAC) systems, as it determines the required cooling capacity of equipment to maintain a comfortable indoor microclimate. In MagiCAD, a specialized BIM tool for MEP systems (mechanical, electrical, plumbing), this process is integrated into modules such as MagiCAD Room and MagiCAD Comfort & Energy. These tools operate within Revit and AutoCAD environments, providing automated calculations based on 3D building models. Let’s break down the heat gain calculation process step by step, considering the specifics of air conditioning systems.

1. Key Components of Heat Gain Calculation​

Heat gains include external sources (from solar radiation, outdoor air, and building envelope) and internal sources (from people, equipment, and lighting). MagiCAD accounts for both sensible heat, which affects temperature, and latent heat, related to humidity.

• MagiCAD Room: This module focuses on static heat gain calculations for individual rooms or entire buildings. It automatically analyzes space geometry, construction materials, window orientation, and climatic data (e.g., based on standards like EN 12831 or local norms such as Russia’s SP 50.13330.2012). The calculation includes:
  • Heat from solar radiation through windows and walls (considering shading coefficients and sun angle).
  • Heat gains from the building envelope (walls, roof, floor), with adjustments for thermal bridges (expanded in versions 2025 and later).
  • Internal sources: heat from occupants (based on occupancy), lighting, household appliances, and equipment (data from manufacturers’ BIM objects).
  • Results: Total cooling load in kW, with generated reports and specifications for selecting air conditioners, fan coils, or chillers.
• MagiCAD Comfort & Energy: This module is used for dynamic calculations, modeling hourly heat gains throughout the year. This is particularly important for air conditioning systems, where peak loads vary by time of day and season. Key features:
  • Consideration of variable factors: solar radiation, outdoor air temperature, humidity, and ventilation.
  • Simulation of indoor temperatures, climate stability, and energy consumption.
  • Integration with ventilation: Calculations include the impact of supply air on the thermal balance.
  • Standards: Compliance with ISO 52016 for energy efficiency, with data export capabilities for certifications (e.g., BREEAM or LEED).

Calculations are automated: MagiCAD extracts data from the BIM model, checks for clashes, and generates drawings with equipment placement. For air conditioning systems, this optimizes ductwork, diffusers, and cooling zones, minimizing energy overuse.

2. Calculation Process in Practice​

1. Model Preparation: Import the architectural model into Revit or AutoCAD. Define rooms and specify parameters (materials, occupancy, climatic zones).
2. Data Setup: Input climatic parameters (temperature, humidity, wind load). For air conditioning, specify target temperature (typically 22–24°C) and humidity (40–60%).
3. Run Calculation: Use MagiCAD Room or Comfort & Energy to perform the analysis. The program calculates heat gains by component and sums them for equipment selection.
4. Optimization: Based on results, adjust the design—add shading, improve insulation, or integrate heat recovery.
5. Reports: Automatically generate tables with a breakdown of heat gains, peak loads, and recommendations.

3. Calculation of Heat from Fresh Air in Mechanical Ventilation in New Versions​

Yes, in the latest versions of MagiCAD (2025 and UR-1), the calculation of heat introduced by fresh air through mechanical ventilation systems is supported and enhanced. This is critical for air conditioning systems, where supply air can contribute significant thermal loads during hot periods (sensible heat from temperature and latent heat from humidity).

• MagiCAD Ventilation: This module integrates calculations for ventilation systems, including sizing, balancing, and pressure drop. Heat from fresh air is factored into overall HVAC calculations, especially when integrated with Comfort & Energy.
• 2025 Updates: In UR-1 for Revit, a new feature sums heating/cooling power and supply/extract airflow from devices (including ventilation) and applies them to the space. This directly accounts for heat gains from supply air in the cooling load. For AutoCAD, new properties for heating and cooling volume in devices like climate beams and fan coils improve ventilation accounting.
• How It Works: In Comfort & Energy dynamic simulations, heat from fresh air is calculated based on airflow rate, temperature difference (outdoor vs. indoor), and enthalpy (for latent heat). The program models heat/cold recovery in ventilation units with HRV/ERV, reducing the load. Reports now include parameters like water temperature in pipes for heating/cooling balancing.

This feature is particularly relevant for energy-efficient buildings, where ventilation can account for 30–50% of the cooling load. Failure to account for fresh air can lead to undersized systems and overloading.