Waste Heat from a Compressor: What Can You Do with It?

During the compression process, a compressor generates more than just compressed air. One of the by-products is heat. Even the most efficient compressors convert a large portion of the electrical energy into heat:  

Approximately 94% of a compressor’s electrical input (shaft power) is converted into heat, which must be removed by its cooling system. The huge amount of heat produced raises an interesting question: can this heat be reused elsewhere in the company? 

Yes. When a company requires heat for space heating, domestic hot water, or industrial processes, waste heat from the compressor can be put to productive use. By recovering this energy, companies can reduce their reliance on conventional fossil fuel-based energy sources, such as gas boilers, while lowering energy costs and CO₂ emissions.

Where Does the Heat Come From?

Compressing air generates heat, which the compressor must remove to continue operating reliably. This is done through oil, water, air cooling, or a combination of these methods, depending on the type of compressor. Without reuse, this heat is usually discharged into the environment. With heat recovery system, part of this heat is captured and put to productive use. 

Depending on the installation and application, a significant portion of the released heat can be reused. Technical documentation often refers to recovering approximately 75% to 90% of the available compression heat. The exact percentage depends on the compressor type, operating hours, heat demand, and the method used to transfer heat. 

Two Practical Forms of Heat Recovery

There are generally two ways to reuse heat from a compressor:

1. Using warm cooling air for space heating.
2. Transferring cooling water through a heat exchanger.

Both solutions have their own benefits and applications. 

In this setup, warm cooling air from the compressor room is redirected through air ducts to another area. For example, a workshop, warehouse, production hall, or technical room. During summer, the heat is discharged outside. During winter, the warm air can be redirected indoors, to help reduce the need for conventional heating. 

This solution is particularly attractive when:

• The compressor operates for many hours
• The heat demand is located close to the compressor room
• The heat is mainly required during the colder months
• Air ducts can be installed practically and efficiently
• The space is suitable for warm air heating

One of the main advantages is that this application can be relatively simple. The concept is straightforward: warm air that would otherwise be discharged outside is directed to a location where heat is needed. 

There are, however, some considerations. Warm air is less suitable for transportation over long distances than hot water. The system must also be properly controlled so that the compressor can always dissipate its heat, and the heated room does not become too warm. 

With a heat exchanger, the heat from the compression process is transferred to water. Cold water flows through a heat exchanger located in the compressor or in the Energy recovery unit. The released heat is absorbed by the water, which can then be used in the customer heating or process installation. To give an example of heat exchange’s working principle, the cold water flows past the heat exchanger and absorbs the heat. 

Possible applications include:

• Supporting a central heating system
• Underfloor heating
• Domestic hot water
• Process heating
• Preheating
• Degreasing baths
• Cleaning processes
• Drying or air treatments

One of the key advantages of water-based heat recovery is that heat can be stored, controlled, and transported more effectively than warm air. As a result, this solution is often more attractive when heat is not required directly next to the compressor room, or when there is a specific process application. However, this approach requires a more thorough technical assessment. The right solution depends on factors such as:

• Available compression heat
• Compressor operating hours
• Compressor size greater than 15 kW
• Required water temperature
• Distance to the heat demand
• Pipe losses
• Existing heating installation
• Payback period

Heat recovery through a heat exchanger is therefore not a one-size-fits-all solution. It is typically is a customized solution. 

Heat recovery is not only about reusing energy. It can also have a positive influence on the conditions inside the compressor room. When compression heat is removed more effectively, the temperature within the compressor room can decrease. This is beneficial because an excessively warm compressor room increases the risk of failures and can negatively affect compressor efficiency. Cooler intake air helps compressors perform better. Warm air requires more energy to compress. A well-ventilated compressor room and an effective heat removal strategy can therefore improve reliability, efficiency, and the service life of your installation. 

For this reason, heat recovery is not only a sustainability issue. It also impacts on maintenance, operational reliability, and total cost of ownership.

Heat recovery becomes particularly attractive when three conditions come together: 

1. Sufficient heat is available: a compressor that runs for many hours generates substantially more usable heat than a compressor that only operates occasionally. 
2. There is a clear heat demand: the heat must be used in a meaningful way. For example, in a building, production process, or heating system. 
3. The technical integration makes sense: distance, required temperature, piping, and control systems must be compatible. The shorter and simpler the path between the heat source and the heat demand, the greater the likelihood of a cost-effective solution. That is why it is wise to evaluate heat recovery at natural decision points. For example, when replacing a compressor, renovating a compressor room, upgrading offices, expanding production, or modifying a heating system. At these moments, the integration can often be implemented more intelligently and cost-effectively.