April 6, 2021

Heating, ventilating, and air conditioning systems (HVAC) present businesses with an opportunity to realize considerable energy, emissions, and cost savings. This is especially true for business owners who take the time to calculate the optimal commercial HVAC size. While calculating may take time, the payoff is greater comfort at a low operating cost.

The Basics of HVAC Sizing

HVAC sizing is usually calculated in tons. While one may assume that it is the actual size of the air conditioner or heater, it is not the case. Instead, the sizing involves the number of British Thermal Units (BTU) that the system is able to produce. To clarify, a BTU is the amount of energy required to either raise or lower the temperature of one pound of water by one degree Fahrenheit.

One ton of heating or cooling equals 12,000 BTU. Most residential HVAC units range between 1.5 to 5 tons, while commercial buildings may range between 6 tons to 50 tons.

Apart from the HVAC size, another important aspect is the heating and cooling load. The term load expresses the amount of heating or cooling requirements of the building in real figures. The load of a building varies from room to room and is affected by the weather or season. The building design is also another factor that may affect the heating and cooling load.

Like for Like Estimation

Estimating the sizing of a commercial HVAC system is not an easy task, but if you are replacing your old system with a new one, you can apply this estimation. This method entails replacing the existing equipment with a similar one. For instance, you can replace a 7.5-ton gas pack with a new 7.5-ton gas pack.

While this is an easy way out, it is by no means the most accurate as many assumptions have been made.

Assumptions here include:
  • The previous load size was accurate
  • The building requirements have not changed
  • During extreme weather conditions, the heating and cooling requirements are not increased

The Ideal Estimation Method

To estimate the size of an HVAC unit correctly, there are a number of factors to consider, including:
  • The difference between outdoor temperature and desired indoor temperature range
  • The building design as well as the amount of insulation in the walls and ceiling
  • The average room size and the total number of occupants
  • The position of the building relative to the sun
  • The type and amount of indoor lighting (halogen vs LED)
  • The activities in the room
Now for the formula, you can take the following steps:
  1. Calculate the total square footage of spaces that will receive cooling. Here, you will be required to make some assumptions regarding the standard ceiling heights as well as other variations that may affect the real values.
  2. Multiply the square footage by 25 to get the total number of BTUs that will be required to heat or cool the space adequately.
  3. Adjust the figures as you see fit. To the value you got, add about 600 BTU per employee working in the building daily because people release a lot of body heat, and the system will have to compensate for it.

If you encounter units that are expressed in tons, convert them to BTUs by simply dividing by 12,000 BTUs to find the tonnage. With the value that you get, you can now start the procurement process. You can share your calculations with HVAC professionals who will conduct a more accurate assessment using a manual.

Accurate Estimation by Using a Manual

The Air Conditioning Contractors of America (ACCA) have published dozens of manuals with details on sizing an HVAC unit. Some of these manuals are Manual Q for commercial duct design and Manual N for commercial load sizing.

In Manual N, there are four main factors to consider when determining the right size HVAC equipment.

These factors include:
  • Application – What is the space used for – restaurant, grocery store, or office.
  • Building type – Is the building a warehouse or a multi-story building?
  • Square footage – What is the size of the space that requires air conditioning?
  • HVAC equipment type – Is the HVAC powered by gas heat or electric heat?
Apart from these factors, the manual also considers the building construction materials such as:
  • The building material used for the outside walls
  • The building material used for the inside walls
  • The level of insulation between walls (measured in R value)
  • The building material for the floors
  • The type of windows
  • The type of roofing
  • The number of occupants
  • The number and type of lights, electronics, and plants present in the space

After all these factors are determined, they are fed to the Manual N calculator, and the calculation is conducted. The resulting figure will determine the heating and cooling BTU requirement for the commercial building.

Of all the estimation methods, this is the most accurate and labor-intensive as well. However, thanks to technology, the calculation is not as tedious as it used to be previously as the calculations were done manually. With an HVAC technician in place, this evaluation will be done effectively.

Why Does HVAC System Size Matters?

Calculations may not be your forte, but when it comes to an HVAC system for your commercial building, it is a must. If you disregard these calculations and decide to wing it instead, then you are in for a rude shock. This is because an improperly sized system will raise numerous concerns, including:

Inadequate Heating or Cooling Capabilities

If you purchase an HVAC unit that offers low heating or cooling load, it will struggle to maintain a comfortable indoor environment during extreme weather conditions. This will affect not only your employees’ working conditions but also the viability of your products in the case of restaurants or warehouses where perishable products are stored.

Persistent Maintenance Needs

This goes without saying, if your HVAC unit is struggling to keep up with the heating and cooling demands of your commercial building, it will face wear and tear pretty fast. And if this happens, you will always have a technician coming over to fix one thing or the other.

If you consider the cost of these constant maintenance requirements, it is better to invest in the right size of HVAC unit that serves you hassle-free for longer.

High Energy Expenditure

For business owners who overestimate their HVAC sizing, high energy expenditure is something they will have to deal with. And to make matters worse, the performance of this system will also be inadequate. This goes to show that the correct HVAC sizing is very important to your daily business operations.

Contact the Pros

After reading through, you must have realized the importance of correct HVAC sizing. Since you can’t do it all by yourself, it is better to call in professionals. At Beyer Mechanical, we offer replacement, repairs, maintenance, energy management services, and design-build for all residential and commercial HVAC and plumbing systems in San Antonio, Corpus Christi, and Austin, TX. Contact us for all the above services, and if you want to get the accurate HVAC unit sizing for your commercial building, we are the guys for the job. Call us today!

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