Boosting Efficiency and Sustainability in Manufacturing with Heat Recovery
Compressed air is known to be a heavy consumer of electricity, and there are several ways to increase efficiency. But even if a large air system is optimized to minimise electrical consumption, it still converts 96% of input power into heat. Generally, most of that heat is rejected into the cooling air flow (or cooling water) and not the compressed air.
In most installations the warm air heats up the compressor room or is ducted outside to prevent overheating the compressor room. In the relatively small percentage of cases where the compressors are water-cooled, the heated water is either recirculated through a closed-loop chiller system or, if cooling water is drawn from a natural source, the heated water is put back into that water source.
How much thermal energy (BTUs) do your compressors reject as waste heat?
BTUs available are directly in proportion to the input kW, and your compressor supplier should be able to provide the BTU information for your specific model.
Heat can be captured from either air-cooled or water-cooled compressors and used in a variety of ways.
- Space heating
- Makeup air heating
- Boiler makeup water processing
- Industrial process heating
- Heating process fluids
- Heating food and beverage products
- Heat-driven chillers
- Water heating for showers and bathrooms
Using the waste heat from water-cooled compressors presents the additional benefit of reducing the operating costs of closed-loop chiller systems since it reduces the work they must do.
Basic space heating
The simplest and most common form of heat recovery involves integrating HVAC ductwork and controls to harness warm air exhausted from air-cooled compressors to reduce space heating costs in colder months and to remove the warm air in warmer months. Thermostatically controlled fans and ventilation louvers regulate space heating and maintain optimal compressor operating conditions.
Exploring water/fluid heating options
To capture more waste heat, apply heat exchanges to tap into the compressor cooling fluid circuit to heat water or other fluids. Some air-cooled compressors have optional integrated heat recovery to heat fluids for a range of applications in electroplating, food processing and industrial laundry.
- Easy integration: HPC KAESER compressors are easily adapted for fluid heat exchangers. In fact, many models offer built-in fluid-to-fluid heat exchangers as an option to recover up to 76% of the original input energy. Water-cooled compressors offer even more heat recovery potential, enabling year-round energy savings for continuous process heating applications.
- Practical considerations: You have to calculate and compare the potential cost savings against the implementation costs, which include engineering, material and project management. You have to consider how much heat you can harness. This includes knowing how often the compressors are running and whether your use of the waste heat is continuous or intermittent. The engineering must address a variety of factors, including controls and heat loss between the compressor and the point of use.
Types of fluid-to-fluid heat exchangers
Plate type
Rotary screw compressors can be equipped with plate-type heat exchanger systems. They can be integrated within the unit or installed externally. Applications include:
- boiler heating systems
- industrial laundry
- electroplating
- general process heating
Shell and tube
In water-cooled systems, integrated shell and tube heat exchangers are available, depending on the water quality. Applications include:
- non-potable water heating system heating
- oil refineries
- large chemical processes
Fail-safe
Some compressors can be equipped with fail-safe heat exchangers for applications requiring absolute protection from contamination. These heat exchangers are always installed externally. Applications include:
- food processing
- tap water heating
- chemical and pharmaceutical industries
- commercial kitchens
Conclusion
As mentioned in the opening, you likely have several types and areas of energy use. There are likely ways to reduce all of them to some degree, but you have to assess which presents the most savings potential while considering the costs to get there.
Because compressed air is often a major power consumer, it may be an area to find savings. Of course the first approach should be to reduce demand for compressed air in the first place, but as long as you are running compressors, consider whether you have recycling opportunities. By implementing energy reduction strategies, you may achieve improved efficiency, lower operating costs, and a smaller carbon footprint.