Air on a shoe string
Estimated to account for more than 80 Tera (1012) Watt hours of electricity consumption, and 55 million tonnes of CO2 per year across the EU, compressed air is equivalent to around ten per cent of total industrial electricity consumption. PNEUROP, the European Committee of Compressors, Vaccum Pumps and Pneumatic Tools, surveyed its members on the relevance of energy efficiency to them. Dave Welch, Ingersoll-Rand, on the results.The PNEUROP study provides an explanation for why energy efficiency has been a low priority with compressed air users. Since compressed air is an essential part of thhe production process for most industrial compressed air users, system reliability is the absolute primary performance criterion and has been seen by many users as more important than potential energy savings.
According to the PNEUROP survey, the cost of compressed air is the least important performance criterion for users. This represents an important finding for the survey, since the basic tool that must be used to encourage energy efficiency is cost reduction. Several reasons seem to explain the low priority which users give to compressed air costs, even in highly cost-competitive industries.
The first is the absence in most businesses of compressed air accounting - in many cases, users are simply not aware of compressed air costs. Neither the compressed air operating costs, nor the energy for compressed air appear as distinct items in corporate cost accounting. Compressed air energy costs are most often included in general overhead costs.
Because of the nature of compressed air energy costs, responsibility for cost reduction measures is often divided between managers for maintenance, production, purchasing and finance. Co-ordination between these functions is a problem in all enterprises. It generally requires very high level decisions to cut across the conflicting priorities of these functions and this type of decision is rare for compressed air, which is not viewed as a strategic business issue for users.
Experience has shown that industrial enterprises are loath to allocate precious capital resources to energy saving investments, even when they show high rates of return on investment. The advent of the Climate Change Levy, however, has raised the profile of energy efficiency in processes that are heavy users of electricity. Companies should now be examining their compressed air systems to see whether they can apply one or more of the following changes to optimise energy consumption:
- improvement of drives - use of high efficiency motors and integration of variable speed drives into compressors;
- optimal choice of the type of compressor, as a function of specific end-use applications;
- advanced compressor technology, particularly multi-stage compressors;
- use of sophisticated control systems;
- recuperating waste heat for use in other functions;
- improved air treatment - reducing pressure and energy losses in cooling, drying and filtering; optimising filtering and drying as a function of users' needs and of temperature conditions;
- overall system design, including multi-pressue systems;
- reducing frictional pressure losses in networks;
- reducing air leaks;
- optimising certain end use devices;
- measuring and tracking system performance.
Work undertaken during the PNEUROP study has confirmed that all of these technical measures can improve energy efficiency in many installations.
In the UK, the government is providing an incentive for adopting energy-saving equipment through the Enhanced Capital Allowance scheme, allowing companies to write off 100 per cent of the cost of certain types of equipment in the year that they buy the equipment.
In most cases, ECAs are available for individual energy saving components within the system, plus the cost of installation and optimisation.
If a variable speed drive is fitted, the full cost of the purchase and fitting of the drive will be specified on the ECA list. For a compressed air system, however, only one compressor fitted with an eligible VSD per system will attract the enhanced allowance. You will not be able to claim for more than one VSD per system. A compressed air system is specified as being one or more compressors on a branch or ring main system.
Integration of speed controllers can be very cost effective in compressed air
installations. With most variable speed drives on the market, their use is restricted
to the sale of new compressors, since retrofitting them to existing machines
is too problematic.