Turning heat into energy

Monday, October 29, 2018

Heat is an inevitable by-product when producing compressed air.

Compressed air

However, while in the past this energy was simply lost to the atmosphere, today’s heat recovery technology allows this energy to be recovered and reused.


This may surprise some readers, but almost the entire energy consumption from the supply net of a standard compressor is converted into heat. Take, for example, an oil lubricated screw compressor: up to 94% of the electrical energy input to this equipment is available for heat recovery.


Being able to capture and reuse this energy for space heating, water heating or for other production duties offers real benefits for businesses and is in step with the view being taken across industry that a broader, more holistic view must be taken when it comes to energy efficiency.


Despite the powerful potential of heat recovery technology for enhanced efficiency, too few compressed air users are taking full advantage of it. This may be because too few of them have realised the inefficiency of using compressed air as a utility. However, if they stop to consider the cost of compressed air they may be more eager to look into the highly attractive efficiency savings that can be made by implementing heat recovery.


So, how do compressed air users take advantage of the potential to enhance efficiency using heat recovery? The best place to start is to look at the entire system and evaluate the parameters of each process; you can then identify the process that will make the best use of the heat produced by the compressor and thus make the maximum saving for the business.


The choice for a plant that has a constant demand for heat throughout the year can be very straightforward; regular processes that take place in paint shops and electroplating operations need a constant supply of heat, as do many temperature controlled processes in the manufacture of chemicals and foodstuffs, and so there is strong potential here to save energy through heat recovery.  


In a plant that does not require heat to carry out any process, the decision is also often a simple one: use the recovered energy to heat either hot water or the premises.  In fact, you can even switch with the seasons, using technology such as our DuoTherm system. In winter, recovered heat can be used for heating the premises; in summer, it can be used to heat hot water. By using this combined process to optimise the efficiency of heat recovery, businesses can save significant volumes of energy per year.


The next thing to do before investing in heat recovery is to calculate the potential energy and cost savings of implementing heat recovery by assessing the heat or hot water demand in areas where practical adjacent to the compressor installation. This assessment can then be compared to the average operating hours of the existing compressed air system, which will highlight the possible payback in terms of the immediate reductions in fuel, oil and gas costs.


As you might expect, the adoption of heat recovery for anyone purchasing a modern water-cooled compressor is a straightforward matter, as these new units are already well-prepared for easy integration of a heat recovery system into the cooling circuit.  However, there is now also an easy retrofit solution for plants running older compressor stations that are not prepared for heat recovery, allowing around 70-90% of heat to be recovered.


To learn more about heat recovery and the other methods of saving energy, please check out BOGE’s range of free white papers.