December 20, 2021


Larger companies, like factories, restaurants, and office complexes, have commercial HVAC systems. These office heating and cooling systems provide comfort for the building and its occupants.

A commercial HVAC system is sized in tons. The size increases by increments of half a ton. Most small buildings will have a commercial HVAC system of between 2-30 tons. Calculating the HVAC size your commercial space will need is relatively simple.

How to Calculate What Size HVAC System You Need 

First, calculate the square footage of the area you would like to cool down or heat up. The equation used in this guide is for buildings with eight-foot ceilings. If you have taller ceilings, you will need to adjust your HVAC system size accordingly.

Divide the square footage by a volume of 500. Take the number you arrive at and multiply that by 12,000. For each person who works in the building eight hours a day, add 380 BTU. If the number of full-time building occupants varies, use an average.

For each kitchen, add 1,200 BTU. For each window in the space, add 1,000 BTU. Take your final total and divide that by 12,000. This will give you the approximate size of the HVAC system you will need.

Choosing the Right Type of Office Heating and Cooling Systems  

Society values options. This is no different when discussing HVAC systems. Split system air conditioners are the least expensive option and work best if you have a small commercial building. They provide individual rooms with heating and cooling as needed. They are a great solution for small offices, server rooms, stores, or cafés.

Multi-split air conditioning systems let you control several indoor units while just having one central outdoor unit. They can be used to keep a room with a large space or multiple smaller rooms comfortable. These are often used in restaurants, larger shops, and doctors’ offices.

Variable refrigerant flow (VRF) air conditioning or variant refrigerant volume (VRV) air conditioning systems work best in large spaces. These include larger offices, hotels, and bigger retail spaces. VRF and VRV systems are powerful. They are prized for their ease of operation, and they can quickly heat or cool large buildings.

How is HVAC Tonnage Calculated?

The two terms you will hear HVAC professionals use when discussing cooling and heating are “British Thermal Unit” (BTU) and “tonnage” BTU is a way of describing the amount of power needed to take one pound of freshwater that is at sea level and raise it from 58.5 degrees Fahrenheit to 59.5 degrees Fahrenheit.

One ton of air conditioning is the equivalent of the amount of power needed for 12,000 BTUs of heat per hour. Tonnage is usually more important because it lets you know how big of an air conditioning unit you’re going to need to adequately cool a commercial space. You can use the following steps to estimate HVAC tonnage.

First, measure the area that needs to be cooled in square footage. This means taking the room’s length and width and multiplying in those two numbers to get the square footage of the room. A room that is 100 feet long by 100 feet wide is 10,000 square feet. Do this for each room in the commercial space.

To get a base NTU value for the building, take the square footage and multiply it by 25. In the case of the room mentioned above, it would be 250,000. For each room’s occupants, add 400 BTUs. If there were 100 occupants in the space, you would add 40,000 more BTUs. Add another thousand BTUs for each window or door, If there were two windows and a door, that would be an additional 3,000.

In our scenario, we have 100,000 square feet multiplied by 25 + 4,000 (BTU per occupant) + 3,000 (BTU for doors and windows) for a total of 293,000. Now, we take our total and divide that by 12,000 to determine the tonnage capability needed for a commercial AC system. We wind up with a total of 24.4 tons.

How are Commercial and Residential HVAC Systems Different?

Office heating and cooling systems  can be divided into two types. They are residential and industrial. One primary difference between the two styles is size. Commercial HVAC systems are drastically larger than residential HVAC systems. The larger the building that needs to be cooled, the more significant the HVAC structure is. This increases the complexity of the system.

A second difference is location. Residential HVAC systems are typically installed outside the home. In some homes, you may see it in the garage or in a crawl room. However, a commercial HVAC system is mounted on the building.

Another difference is complexity. Residential HVAC systems come pre-built as a separate device that is installed. Commercial HVAC systems are composite devices. The parts are put together and installed on the rooftop building.

How Does a Commercial HVAC System Work?

Commercial HVAC systems are designed to carry out three processes. They are air conditioning, ventilation, and heating. Each process requires a specific module mounted on the roof. These modules are sized to work together and are operated or controlled by your central thermostat.

During the winter months, the thermostat is what ignites the heating cycle for the HVAC system. The thermostat sends signals to the furnace. The furnace activates a gas valve, which produces a flame. The burner produces heat.

The heat is transformed into the air in the exchanger and is then distributed to the furnace via an internal fan or motor. From there, the heat is distributed through the ductwork of the building.

The ventilation process works by expelling harmful contaminants through flues and vent pipes. This happens during the heating and cooling process. At the same time air is being expelled, your ventilation system facilitates a controlled entry of fresh air.

The cooling process uses refrigerants to absorb the heat. The refrigerant is put under pressure by a pump. The heated and pressurized gas moves to the condensation coil.

It releases heat and turns gas into a cooling liquid. A blower takes warm air from the room and pushes it over the evaporator. The compressed liquid transforms into an even colder source, removing the heat from the air and cooling it before it’s returned to the building.

How Professional Sizing Helps

Your commercial HVAC system needs to be precisely sized if it’s going to reach its maximum energy efficiency and peak performance level. If your system is undersized, it will not adequately cool, heat, or ventilate your building. This means that the system will be working overtime. This will lead to premature wear and tear and expensive repairs.

Conversely, if your HVAC system is oversized, it will frequently cycle off and on, leading to temperature swings, hot and cold spots, excessive humidity, and wasted energy. At Beyer Mechanical, we want to help you avoid the frustration that comes from an HVAC system that is not properly installed.

For more than two decades, Beyer Mechanical has led the field in construction, commercial service, and engineering. We are proud of our proven track record, professional team, trusted technicians, and exceptional results.

If your system is beyond repair and you want to replace it, we are the team that you can count on to help you design, maintain, and install a commercial hVAC system tailored to your property. We offer services along the I-35 corridor in New Braunfels, Austin, Pleasanton, and Corpus.  Contact us now. Let’s get started making your commercial space a comfortable place to work.

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