Project Date: 31 December 2009
Project Status: Complete
Research Organisation: OLEX
Project Number: CSE04
A Variable Speed Drive (VSD) installation on cooling towers has demonstrated reductions that can be achieved with industrial water and energy usage concurrently. Cable makers, Olex, fitted the VSD's to existing cooling towers at their Tottenham site. In conjunction with City West Water, Olex monitored the savings of their VSD retrofit, providing a template for other business looking to improve their cooling tower efficiency.
Cooling Towers have widely been acknowledged as huge water users. Throughout the recent drought the 4,500 cooling towers registered across the state of Victoria became a continual focus for water efficiency. What receives less attention was the costs savings that could be associated. The monitoring program established for this project aimed to demonstrate the business case for cooling tower efficiency.
The cooling system at Olex employs two towers, which both use two fans. The fans were run at 100 per cent capacity, regardless of the water temperature, consuming nearly 15 million litres of drinking water per year and a great deal of energy. To reduce plant potable water and energy consumption a new drive and associated controls where fitted to the cooling tower fan.
Before the projects implementation the cooling tower fans would run at 100 per cent capacity regardless of water temperature. This is known as an 'open looped' system. This creates a lot of water 'drift' through the tower and consumes a large amount of electricity. Creating a control system that the cooling requirements of the manufacturing plant with how hard the cooling towers are working creates a smarter 'closed loop' control system.
By retrofiiting variable speed drives and associated controls to the existing cooling towers such a 'closed loop' system was achieved. Production at the plant was able to continue uninterrupted throughout the installation. New drives and improved PLC controls contributed around two thirds of the $68,000 installation, with the remainder spent on an insulated room to house and protect the new controls.
Water meters (provided free to Olex, and all participants of City West Waters WaterMAP program) where used to monitor water usage at the site. The electrical current on drive feeds was measured before and after the installation. Careful monitoring enabled the site to quantify the savings resulting from the retrofit.
The project reduced water loss through cooling tower drift, saving 4.8 million litres of drinking water per year (nearly a third of the original 15 million litres consumed by the towers). Reduced fan operation resulted in savings of 78.1 megawatt hours per year of electricity - equivalent to greenhouse gas savings of 95.2 tonnes per year. At the time of completion (2009) these conservative saving estimates put the payback at 5.2 years; at 2012 prices the payback reduces to 3.5 years. Rising water and energy prices have seen the value of the project increase over time – in 2012 dollars the drive installation is saving $19,000. Continual price rises will see the attractiveness of cooling towers rise in the years ahead.
To determine if savings will be comparable in other business, a cooling tower efficiency calculator has been developed by the Australian Institute of Refrigeration and Air Handling. The calculator is freely available here. You may also view a case study by City West Water via this link.
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