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Waste Heat Recovery Calculations

Large industrial and commercial productions use a lot of energy, that result in a high rate of exhausted waste heat. Rising energy prices let company reconsider their energy usage. Extracting the heat out of the exhausted air through a heat recovery system can reduce massively the energy spending costs, as well as the CO² emissions of a company.

Waste heat recovery systems can be easily installed on top of already existing systems, and thus are cheaper than replacing the whole heating system. However, waste heat recovery units have a payback period of around one to one and a half years. Therefore, when considering a waste heat recovery system, it should be calculated how much energy costs can be saved.

To calculate the potential savings, different factors must be considered. The following text describes the most important factors for calculating the heat energy costs that can be saved through a waste heat recovery unit.

Waste heat flow rate

Waste heat comes typically in the form of hot air, smoke or steam. An important factor is thus the flow rate of the exhausted air. The flow rate states the volume or the mass of air that gets exhausted and determents the potential value of the extracted heat. The flow rate also depends on the medium the heat is contained in.

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Steam or hot air contains a different amount of heat per volume. A medium with a higher temperature than the recovery medium (E.g. inflowing cold air) produce a higher energy saving outcome. Thus, the greater the difference between the incoming and outgoing medium is, the higher will be the energy saving through a waste heat recovery system.

Final temperature

The term “final temperature” represents the lowest temperature the medium can be cooled down too. If the medium is exhausted air with a temperature of about 190 °C, it can be cooled down to around 140°C. Thus, the final temperature depends on the medium, the cleanliness and the initial temperature of the exhausted air.

Type of heat recovery system

Another factor in calculating the potential savings in heat energy through a heat recovery system is the heat exchanger unit itself. It depends on the specific setting, the unit will be installed in, as well as the unit type and the way the heat is recovered. A direct heat recovery system is the cheapest option. However, a direct heat recovery system is heavily dependent on the location it will be installed in.

Through a direct heat recovery system, a heat exchanger is placed between the two inflowing airstreams and transfers the heat from one medium to the other one. Another distinction is between a passive or active heat exchanger. A passive heat exchanger does not require any energy input. An active heat exchanger, on the other hand, needs extra energy (E.g. Heat pump)

Heat recovery calculater

For the calculation of the saved energy costs through a waste heat recovery unit, multiple factors need to be considered and the calculation can become quite complex. The article gives you an overview of the most important factors that need to be examined and measured before a system can be installed. However, the best option is to let an expert measure the local conditions and calculate the cost savings.


exodraft has many years of experience in measuring potential heat savings and implementing heat recovery systems in various settings. For the specific purpose of giving you the most accurate overview of your current emissions and possible energy costs savings, exodraft developed the calculation software OptiCalcHR™.

Contact us now and get a free calculation without any obligations – we will find the best heat recovery system for your specific circumstances.

    Fill out this appraisal form to clarify your heat recovery potential:

    How do see your recovered heat being used (you can select multiple options)?
    Transferred to the district heating systemUsed in production processesHeating of factory, warehouse or office premisesUsed for apsorption chillers/refrigerationHot water for bathing facilitiesAir curtain & air heatning systemsHot warter for general cleaning/washing purposesOther