The Science Behind Heat Recovery in Compressed Air Systems

Cost savings from your air compressor could be vanishing into thin air- literally.

Compressed air systems generate heat as a byproduct of air compression. Typically, excess heat is dissipated or rejected, but with heat recovery technology, businesses can harness and reuse this energy.

In this blog post, we’ll discuss the science behind heat recovery systems and how they can make a difference in your daily operations.

 

Types of Heat Recovery Systems

We can retrofit air-cooled or water-cooled heat recovery units with most air compressors. 

Several heat recovery technologies apply to compressed air systems, new and old. Your system choice depends on the compressor type and the intended use of the recovered heat.

 

The Science Behind Air-Cooled Heat Recovery Systems

An air-cooled compressor’s heat recovery system repurposes the hot air produced during the compression process. Here’s a brief step-by-step breakdown of the process:

1. Heat Generation: When an air compressor draws in and compresses ambient air, it significantly increases the air’s temperature. The potential for heat recovery begins in this stage.
2. Heat Capture: Hot air produced from compression is typically cooled by ambient air blown across the compressor’s heat exchanger. A heat exchanger transfers hot air from the heat source to a heat sink using methods like fins or plates, capturing heat for additional use rather than expelling or losing it. 
3. Heat Reuse: Once captured, the hot air can be directed where needed. Many applications route it through ducts to spaces requiring heating, such as warehouses, workshops, or garages. It can also be used to preheat air for other processes in your operations. 
4. Control and Regulation: Temperature controls and thermostats ensure the system operates effectively without overheating or underheating spaces. Temperature controls regulate heat based on current needs, ensuring that heated applications maintain a comfortable and consistent temperature.

 

The Science Behind Water-Cooled Heat Recovery Systems

Water-cooled heat recovery systems conserve energy and reduce operational costs by utilizing heat that would otherwise be rejected during the cooling process. Here’s a brief step-by-step breakdown of the process:

1. Heat Generation: Heat is usually absorbed by cooling water in a water-cooled compressor, transferring the heat from the air to the water.

   Heat Generation in Chillers: In the refrigeration cycle of a chiller, a refrigerant absorbs and compresses heat, raising its temperature further. The heated, compressed refrigerant gas circulates through a condenser coil, releasing heat to the cooling water around the coil.

2. Heat Capture: The heated water, now carrying the energy absorbed from the compressed air, is circulated through a heat exchanger. Heat exchangers transfer thermal energy in the water without direct contact between the water and the secondary fluid (or air if the goal is space heating).
3. Heat Transfer: Once captured, hot water flows through pipes or plates, depending on the type of heat exchanger used. A secondary fluid, which could be water or another medium, passes in the opposite or cross-direction to the flow of the hot water. The thermal energy from the hot water is transferred to the cooler secondary fluid, raising its temperature. The effectiveness of this heat transfer depends on several factors, including the temperature difference between the two fluids, the surface area of the heat exchanger, and the flow characteristics.
4. Heat Utilization: The heated secondary fluid circulates where needed, delivering hot water or low-pressure steam to various applications like process heating, domestic hot water heating, space heating, or preheating. 

 

Air Compressors Designed for Heat Recovery

We know wasted heat equals wasted energy, so we partner with industry-leading manufacturers to provide cost and energy-saving solutions to our customers. In 2019, Gardner Denver introduced the Ultima Series of Air Compressors as the first and only air-cooled oil-free compressors on the market. Ultima Series models offer both air and water cooling capabilities, and we work with businesses across the Central, Midwestern, and Southern Ohio Markets and Northern Kentucky Markets.

According to the Gardner Denver website, the air-cooled Ultima utilizes heat recovery for process water heating and “allows for the collection and recovery of up to 98% of the heat generated by the compression process.”

 

Additional Heat Exchangers 

Compressed air systems are customizable to the unique needs of your facilities. Some systems require additional parts or processes other than air or water-cooled units. These include, but are not limited to:

• Rotary Screw Oil-to-Water Heat Exchanger: Facilitates the transfer of heat from the hot compressor oil to the cooler water.
• HRV-Based Heat Exchangers: Custom-designed or adapted to transfer heat from the hot compressor exhaust air to preheat incoming fresh or processed air.
• ERV-Based Heat Exchangers: Operate on a principle similar to HRVs but with the added capability of moisture transfer, allowing for effective use in processes requiring humidity control and temperature management.
• Phase-Change Material Heat Exchangers: Use materials that absorb or release heat as they change phase (solid to liquid or vice versa), which can be incorporated around air compressor systems to capture and later release heat.

 

We Help Customers Save on Heating Costs

Heat recovery benefits businesses looking to improve their energy conservation and cut down on costs. Instead of using separate heating equipment that requires additional energy, heat recovery systems utilize heat produced by a system you already use. 

In fact, businesses can significantly cut their heating costs by as much as 60% to 90%, depending on system efficiency and the specific application. Additionally, reducing the energy load on cooling systems during the compression process can extend the life of the machinery. 

At Air Handling Equipment, we specialize in equipping businesses with advanced compressed air systems and cutting-edge heat recovery technologies. Contact us today to learn how your business can benefit from fitting current or new compressed air systems with heat recovery units.