💡 Internal Gains Share
📊 Load Per Unit Area
Load Breakdown
Full Calculation Table
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How to Use the Commercial Load Calculator
Choose the closest match for default lighting, plug load, and occupancy density, or select Other / Custom to enter your own project values.
Enter conditioned floor area and ceiling height. These drive both internal gains and room volume for the load calculation.
Choose the closest Canadian city for summer and winter design temperatures, and enter window-to-wall ratio for solar and envelope load estimation.
Click Calculate Commercial Load to see total cooling load, heating load, and a full breakdown between internal gains and envelope components.
Understanding Commercial Building Loads
Commercial load calculations differ fundamentally from residential ones because internal gains, not envelope heat loss or gain, usually dominate the total. An office full of computers, LED lighting, and people generates a steady stream of heat that has nothing to do with outdoor temperature, and that heat has to be removed by the cooling system regardless of season.
Why Internal Gains Dominate Commercial Cooling Load
A residential home might have one occupant per 40 or 50 square metres and modest plug loads from household appliances used intermittently. A commercial office can pack one occupant per 8 to 12 square metres, running a computer and monitor continuously for eight hours, under LED lighting sized for task visibility rather than ambiance. Multiply that density across an entire floor and internal gains alone can exceed 40 to 60 watts per square metre, often larger than the envelope load contribution except on the most extreme summer or winter design days, a pattern reflected in Natural Resources Canada's building energy use surveys of the commercial and institutional sector.
Cooling Load in Winter: A Real Commercial Phenomenon
Interior zones with no exterior walls have no envelope heat loss to offset internal gains at all, which means they can require cooling on a day when the building's perimeter zones need heating. This simultaneous heating and cooling requirement is why many Canadian commercial buildings use four-pipe systems or heat recovery chillers that move heat from interior zones to perimeter zones rather than rejecting and generating heat independently, an approach covered in the systems chapters of the ASHRAE Handbook, HVAC Systems and Equipment.
Envelope and Solar Load Still Matter at the Perimeter
While interior zones are internal-gain dominated, perimeter zones with significant glazing still see meaningful solar heat gain, especially on south and west orientations during summer afternoons. A building with a high window-to-wall ratio needs more perimeter zone cooling capacity even in a cold Canadian climate, since solar gain through glass does not care what the outdoor air temperature is. This calculator applies a simplified envelope and solar estimate scaled by window-to-wall ratio and your selected city's summer design temperature; the solar gain calculator breaks that piece out in more detail by orientation if the perimeter zone needs a closer look.
Using This Load for Equipment Selection
Once you have a cooling and heating load estimate from this tool, the next step is usually sizing the air handling equipment and, for larger buildings, the central plant. Feed the cooling load into the AHU sizing calculator to get supply airflow and coil sizing, or into the chiller plant calculator if the building uses a central chilled water plant. This tool gives a preliminary estimate suitable for early design and budgeting; a full ASHRAE-compliant load calculation, checked against the ASHRAE 90.1 compliance calculator for envelope and system requirements, should be performed by a mechanical engineer before finalizing equipment selection.
Building-Type-Specific Considerations
Retail spaces often carry higher lighting density than offices due to display and accent lighting, while restaurants add kitchen equipment heat gain that this general tool does not fully capture. For food service or retail-specific sizing, see the restaurant HVAC calculator or retail HVAC calculator, which include occupancy and equipment profiles specific to those building types.
Frequently Asked Questions
Commercial buildings pack more people, lighting, and equipment into a given floor area than residential buildings. An open-plan office might have one occupant per 10 square metres generating both metabolic heat and computer equipment heat, compared to a house with far fewer people per square metre and far less plug load. This is why internal gains, not envelope loss, typically dominate commercial cooling loads.
Yes. In a well-insulated commercial building with high occupant density and significant equipment heat, internal gains alone can exceed the building's heat loss through the envelope even at outdoor temperatures well below freezing. Interior zones with no exterior walls are especially prone to this, since they have no envelope heat loss to offset the internal gains at all.
Modern LED lighting in Canadian commercial buildings commonly runs 6 to 10 watts per square metre for open office space, lower than older fluorescent-era buildings that could exceed 15 watts per square metre. Retail spaces with accent and display lighting often run higher, sometimes 12 to 20 watts per square metre depending on merchandising design.
A higher window-to-wall ratio increases solar heat gain on sun-exposed facades, which can significantly raise peak cooling load on south and west orientations even in a cold Canadian climate. Buildings with extensive glazing often need stronger perimeter zone cooling capacity even when the interior zones are load-dominated by occupancy and equipment rather than solar gain.
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