What is the Proper Tons Per Square Foot for Commercial HVAC Systems?

Calculating tons per square foot in commercial hvac

You’ve been asked to design a new commercial building and you need to calculate its heating and cooling needs.

How?

By calculating the correct HVAC tons per square foot.

In commercial and residential buildings alike, there is no single rule of thumb to follow.

Rather, your HVAC tons per square foot requirement will depend on the building’s size, design, weather, the stated thermal comfort needs, and other factors.

Below, we offer a summary for finding the correct HVAC tons per square foot in commercial and residential buildings. We use British Thermal Units (BTU) as a reference point for identifying the heat removal requirements of the building.

What Does it Take to Remove Heat?

Your calculations should start with understanding how much heat typical AC units can remove.

Today’s industry standard is that it takes 1 ton of AC to remove 12,000 BTU of heat per hour.

Most single unit houses require 1 or 2 tons of AC, but in commercial buildings, you will require far greater AC infrastructure.

Determining how much is the tricky part.

If your AC system is too small, then it will take longer for it to remove heat from your building. In practical terms, this means that the AC will run longer and consume more energy. As a result, it will drive up your building’s operating costs.

However, if the AC system is too large, then it will never run at full efficiency and, as a result, will consume more energy than necessary. This too will raise your building’s operating costs.

As noted above, your specific AC needs will depend on multiple factors, such as the building’s design and its location’s weather. This is because buildings retain and lose the amount of heat and cold air at different levels (i.e., some more rapidly than others). Furthermore, you must also factor in how occupants will use the AC system throughout the year.

These are both complex calculations that will result in a peak heating load figure and a peak cooling load figure. You need these figures to ensure your HVAC system runs efficiently.


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How to Calculate HVAC Tons Per Square Foot in Commercial Buildings

You should not use average figures to determine the final size of your air conditioner and heating system, but rather, to get a rough idea of the scope.

Some HVAC designers will calculate the AC requirement by measuring the space they want to cool in square feet. They will then calculate the BTU by dividing the space (in square feet) by 500 and then multiplying its answer by 12,000. They will also add approximately 380 BTU for each person in the space, 1,000 BTU for each window, and 1,200 BTU for each kitchen.

Thus, a 2,000 square foot area with two windows, four regular occupants, and one kitchen would have a BTU of 52,720. This would require 4.39 tons of AC or 455 square feet per ton.

This is close to the 400 square feet per ton sizing of the HVAC industry in Chicago and Orlando, but you will notice the variance due to us adding a kitchen and windows.


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Conclusion: Don’t Restrict Yourself to a General Rule

The industry standard is a benchmark, but not a firm rule. You will have variances in your final calculation based on the building’s unique attributes.

In fact, even the thermal challenges buildings face differ.

For example, buildings in hot climates will get hotter (i.e., the peak heating load), so you might have to focus on removing more than 12,000 BTU an hour to keep it cool. However, buildings in cold environments have a different issue, which is to retain heat, not remove it.

Moreover, as noted earlier, failing to calculate the right size of your HVAC units can cause major operational issues. These include costlier operating costs and, potentially, more frequent HVAC maintenance and repair work.

Additional variables affecting your calculations include the type of HVAC system. For example, with an Underfloor Air Distribution (UFAD) system, you can diffuse cool air closer to people and, as a result, use less energy and require less time to cool the space.

AirFixture helps architects, engineers, and building owners design and implement UFAD HVAC systems to lower their long-term costs and increase their building’s value.

Use our FREE guide to see how UFAD systems will help you propose an HVAC system that meets your budget and timelines.