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Understanding Heating and Cooling Load Calculations

14 March 2024

Whether you are looking to upgrade your commercial heating, ventilation or air conditioning (HVAC) system or are looking to install one in your commercial building, you will need to understand and know the load calculations. 

These are simply calculations that allow us to design the most suitable system at a size that will heat and cool your space efficiently. 

In most cases, when you are using an HVAC design and installation company, such as ourselves, they will work out the calculations before they start designing. However, it is helpful for you to understand what we are doing so that when we ask for information, you know what we need and why we need it.

In this blog, we run through the importance of each load calculation and how we work them out.

What Is HVAC Load Calculation?

Load calculation in HVAC design and installation refers to the mathematical process of working out the amount of heating or cooling a space requires to maintain a comfortable environment.  

Heating and cooling calculations estimate heat gain vs heat loss in a building.

If you are looking to heat your workspace, you will need to understand what the heat loss will be during the coldest climates.

Meanwhile, when looking to cool your space, you will need to understand the heat gain your building will experience during the hottest climates. Remember that factors such as occupants, activity and lighting will compensate for any heat loss, while they will also account for heat gain during hotter periods of the year. 

These calculations are a critical part of HVAC design because they determine the design and size of the solution provided. 

Why Is This Important?

As a business, you don’t want to be spending money where you don’t need to. Working out these load calculations when installing an HVAC system will ensure that you run an efficient system, meaning that you don’t use more energy than needed, therefore, you don’t waste money.

Both systems that are too small or too big will have this problem, which is why it is imperative that the solution designed fits your needs exactly as needed.

The size of the system will also impact the output of the system. If your system is too big, there is a chance that it will cause poor humidity in the space, making it an uncomfortable environment for those working in the space as well as risking the development of mould in the building.

Heat Load Calculations

Heat load calculations involve calculating the amount of heat energy needed to maintain a desired temperature within a building during the coldest parts of the day and year. 

Factors that influence this include:

  • Outdoor temperature 
  • Building orientation and insulation 
  • Window size, type, and orientation 
  • Occupancy and activity level 
  • Heat-generating equipment and appliances

Cooling Load Calculation

Cooling load calculations estimate the amount of heat that needs to be removed from the environment to keep it cool during the hottest periods of the day and year.

Affecting factors include: 

  • Outdoor temperature and humidity 
  • Building envelope characteristics (insulation, windows, doors) 
  • Solar heat gain through windows 
  • Internal heat gains from occupants, lighting, equipment and activity

Load Calculations

Below is the general calculation used to work out the size of the system needed for your building.

Before starting to calculate, you will need to understand some terminology. HVAC units are measured in tonnes, therefore, when determining the size, you will need to end the process with a measurement in tonnes. 

Throughout the process, you will refer to a Btu. This stands for a British Thermal Unit, which is the measurement of heat. 

The process of working out load calculations is the following:

  1. Determine the square footage of the space you are looking to heat or cool  
  2. Divide the footage by 500  
  3. Multiply that figure by 12,000 to get the space cooling load  
  4. Add around 380 Btu per person within the building and 1,200 Btu for every kitchen 
  5. Add 1000 Btu to account for solar radiation through windows 
  6. Convert the final number into tonnes by dividing it by 12,000

The final statistic will determine the size of the system you need. Once you have this statistic, you can work with commercial HVAC specialists to design a system that will provide an efficient heating and cooling solution for your workspace.  

Work With Our Specialists

Calmec are commercial HVAC specialists who design, manufacture and install air conditioning and ventilation systems for a range of industries. From care homes and medical facilities to schools and shops, we can work with you to provide a bespoke HVAC system that supplies efficient heating and cooling.

Our qualified team are able to complete all the necessary heating and cooling load calculations, which are used to produce thorough CAD designs to create a tailored system that meets your exact requirements and fits your space seamlessly.

With over 35 years of experience in the HVAC industry, you can trust us to provide quality solutions with faultless customer service.

Get in touch with our team to discuss your commercial HVAC requirements. Call us on 01202 070 280 or complete our contact form, and we will call you back as soon as possible. 

You can also view our previous projects to understand our work and how we might be able to help you.