Cooling Load Inputs
Enter a consistent factor set. Corrected CLTD values must match the construction, time, orientation, and design conditions.
Example Data Table
These sample SI entries illustrate a moderate office zone. They are not universal design values.
| Input | Example | Reason |
|---|---|---|
| Room dimensions | 8 m × 6 m × 3 m | Defines zone volume and project context. |
| Wall U-value | 0.60 W/m²·K | Represents an insulated external wall. |
| Roof U-value | 0.35 W/m²·K | Represents an insulated roof assembly. |
| Glass solar factor | 500 W/m² | Must match orientation and design hour. |
| Ventilation airflow | 450 m³/h | Uses the project outdoor-air requirement. |
| Allowance | 10% | Provides a documented preliminary margin. |
Formula Used
This calculator uses the common CLTD/CLF calculation structure associated with the Rudoy and Duran method. Every factor should come from a compatible reference set.
Corrected cooling load temperature difference
The correction can account for the selected table assumptions. Use verified values for design hour, orientation, indoor condition, and local climate.
Envelope and glazing conduction
This equation is applied to walls, roofs, and conductive glass. Use matching units throughout the calculation.
Solar, internal, and outdoor-air loads
Total design load
The calculator reports sensible, latent, total, equivalent capacity, and a supply airflow guide.
How to Use This Calculator
1. Set units
Choose SI or Imperial first. Enter every linked value in that unit system.
2. Define conditions
Add indoor and outdoor dry-bulb temperatures, humidity, supply temperature difference, and allowance.
3. Enter envelope data
Use measured areas, verified U-values, and corrected CLTD factors for each exposed assembly.
4. Add solar and internal gains
Enter glass factors, people schedules, lighting, equipment, and realistic load factors.
5. Include outdoor air
Enter ventilation and infiltration separately. The calculator evaluates temperature and moisture effects.
6. Review before selection
Compare components, check high contributors, then confirm equipment with detailed mechanical design data.
Cooling Load Planning for Construction
Understanding the Method
The Rudoy and Duran approach is commonly recognized as the CLTD/CLF method. It gives designers a structured way to estimate peak room cooling demand. The method simplifies time-dependent heat transfer using published correction factors and tabulated values.
Start by separating envelope, solar, internal, and outdoor-air gains. Walls, roofs, and conductive glass use a cooling load temperature difference. This adjusted temperature difference represents weather, solar exposure, mass, and time effects.
Key Load Components
Windows need two separate checks. Conduction passes through the glass because indoor and outdoor temperatures differ. Solar radiation enters directly, then a cooling load factor accounts for delayed radiant release.
People add sensible heat and moisture. Lighting and plug loads add heat while equipment operates. Ventilation brings both sensible heat and latent moisture from outdoor air.
Good inputs matter more than complicated arithmetic. Use realistic areas, U-values, schedules, shading details, and outdoor design conditions. Use factors from a verified design reference for the selected location and construction.
Reading the Result
This calculator combines the main load categories into sensible, latent, and total cooling loads. It also applies a selectable design allowance. The allowance should cover documented uncertainty, not replace sound engineering judgment.
A sensible load changes air temperature. A latent load changes the moisture content of air. Both values are required when selecting coils, airflow, and dehumidification capacity.
Use the result as a preliminary room or zone estimate. Sum compatible zones only after checking diversity and operating schedules. System equipment also needs fan heat, duct gains, safety controls, and available capacity checks.
Design Limits and Checks
The original CLTD and CLF process remains useful for transparent hand calculations. However, complex buildings may require heat balance or radiant time series analysis. Dynamic simulation is often better for unusual schedules, heavy mass, or advanced façade systems.
Check every selected factor before issue. Different references use different assumptions for month, latitude, orientation, and construction. Never mix incompatible tables or change units without conversion.
Construction teams can use early results for equipment space, electrical planning, and budget studies. Mechanical designers should refine the estimate during detailed design. Field verification protects comfort, humidity control, and equipment reliability.
Clear Documentation
Record the inputs with drawings and calculations. This creates an auditable basis for revisions. It also helps reviewers identify missing shades, outdoor-air allowances, or internal loads.
Use the calculations with current local climate design data.
Frequently Asked Questions
What does this method calculate?
It estimates peak cooling load by combining conduction, solar gain, people, lighting, equipment, ventilation, infiltration, and latent moisture effects. It is intended for transparent preliminary design calculations.
Is this a full dynamic simulation?
No. It is a structured CLTD/CLF-style estimate. Complex buildings, unusual schedules, advanced façades, or detailed plant studies may need a heat balance, radiant time series, or simulation model.
What does CLTD mean?
CLTD means cooling load temperature difference. It is a tabulated or corrected temperature difference used to approximate delayed conduction loads through walls, roofs, and glass.
Why is glass solar gain separate?
Solar radiation through glazing behaves differently from conductive heat transfer. The calculator uses area, solar heat gain factor, shading coefficient, and cooling load factor for that solar portion.
How are people loads handled?
People contribute sensible heat and latent moisture. The sensible part uses a cooling load factor. The latent part is added directly because moisture removal is an immediate cooling requirement.
What is the difference between sensible and latent load?
Sensible load raises air temperature. Latent load adds moisture. Cooling equipment must handle both, especially where ventilation, occupancy, cooking, or humid outdoor conditions are significant.
Should ventilation always be included?
Yes, when outdoor air is supplied to the zone. Required ventilation can add large sensible and latent loads. Infiltration should also be included when leakage is expected.
Can I use SI and Imperial units?
Yes. Choose one unit system before entering data. The labels change with the selected system. Do not mix SI and Imperial input values in the same calculation.
How should I choose the allowance?
Use a documented project allowance. It should reflect known uncertainty, not correct missing inputs. Confirm final equipment sizing after checking loads, diversity, controls, and manufacturer performance.
Can this output select an air conditioner directly?
Use it as a preliminary selection guide only. Final selection requires coil performance, entering conditions, airflow, available static pressure, part-load behavior, and equipment manufacturer data.
What should I verify before issuing a design?
Verify construction areas, U-values, glazing details, shading, operating schedules, people activity, ventilation rates, climate data, and the compatibility of every CLTD, CLF, and solar factor.