Boosting Efficiency and Sustainability in Manufacturing with Heat Recovery

Energy reduction strategies are part of keeping costs low and staying competitive. In manufacturing and process industries, as well as light industrial and even commercial business, the main consumers of electricity and gas (and sometimes oil) are HVAC, lighting, production equipment, process heating and cooling and compressed air. Energy reduction strategies should start with identifying the biggest consumers and then assessing the scale of potential reduction opportunities within each area. This will help prioritize where to put your time and money to achieve cost reduction and sustainability goals.

Compressed air is known to be a heavy consumer of electricity, and there are several ways to increase efficiency through proper sizing, pressure reduction, compressor controls, leak reduction, etc. But even if a large air system is optimized to minimize 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? The 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

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.