A sophisticated large scale hot water temperature monitoring and data storage system at the Port of Dover, designed to protect both the travelling public and harbour staff from the risk of Legionella, is claimed to be the most advanced of its kind in Europe. The electronic system monitors water temperatures at around 1000 taps and shower fittings throughout the 330 hectare Eastern and Western Dock sites, as well as hot water storage tanks. While ‘real-time’ temperature values can be monitored on line while the collected data can be stored for later investigation if a problem might occur.
To meet today’s regualtions, operators of hot water systems in workplaces, places of entertainment, and indeed any building or facility used by members of the public, now have to ensure that measures are taken to control the risk of exposure to the potentially lethal Legionella bacteria.
While a number of acceptable measures are available to facilities managers, such as instantaneous high temperature water heating, the most practical and cost-effective solution is to ensure that stored water temperatures always exceed 65°C, a temperature at which the bacteria is effectively killed off. This water temperature however, would result in user scalding at taps and showers, so in systems where this approach is taken, hot water for general use has to be cooled to below 45°C just before being delivered to tap outlets. For cooking and laundry purposes, slightly higher temperatures are permissible.
As one of the busiest ferry ports in the world, handling around 15 million passengers and 5 million vehicles annually, engineering staff at Dover realised some years ago that to meet legal health and safety obligations would require a significant investment in monitoring and control technology.
Apart from challenges of scale – the overall distance across both Eastern and Western parts of the docks exceeds 2km – there are around 150 separate small scale water heating and storage systems on the site, which have been installed over time in passenger facilities, customs and police offices, port operation areas and other buildings. The challenge was to engineer an easily managed localised monitoring solution with central monitoring, secure data transfer and verifiable long term archiving of data.
The chosen solution, reached after considerable research and system analysis, is a local area data monitoring network based on DAS data recorders and fibre optic data buses. This enables engineering staff to monitor temperatures accurately on line from around 1000 points around the site, with both visual and audible alarms for out of tolerance or faulty readings. The information gathered not only ensures high levels of protection against Legionella infection, but assists with other tasks such as routine maintenance, general water system diagnostics and precise location of system faults.
All hot water taps and shower heads within the Docks site are fixed temperature outlets designed to deliver hot water at 43° C +2° C. This is achieved by feeding hotter water (at about 60ºC), together with cold water, to a thermostatic mixer valve near to each tap outlet. The mixer valve only operates when the tap is opened and water is demanded by the user. The temperature of the hot water as it enters the valve, and the temperature of the water fed to the outlet are both monitored by independent thermocouple probes placed in the pipes, the signals being fed back to a DAS unit (Data Aquisition System Unit) in the vicinity.
The number of DAS units that are used depends on the number of temperature points being monitored at that location. The probes used in this type of location (Type T thermocouples) were specially designed to be easily inserted or removed using “EasyFit” push-fit plumbing fittings, and ensure that the probe is positioned centrally within the feed pipes. For monitoring the higher temperatures in cylinders and storage tanks, similar probes are fitted at the top and bottom of each tank. The probes in this case are PT100 resistance thermometers capable of measuring accurately up to 450°C.
Using an internal sampling rate of 5 seconds, the temperatures at each location are read and recorded. This collected data is then downloaded to the central monitoring station once every hour. The entire recording and transmission process is controlled using proprietary Eurotherm logging and archiving software that securely protects data from loss, corruption or tampering. Local communication is by FTP (File Transfer Protocol) via Ethernet 10BaseT links. Data from local groups of BAS units around the site are first fed into Ethernet to Optical Converters (EOCs), and then transferred via the optical fibre bus to the central monitoring point.
The central monitoring point at Dover consists of two FTP servers operating in a highly secure Raid 0 configuration and protected by uninterruptible power supplies. Two large scale hard disk drives mirror each other, allowing data to be restored from one to the other in the event of hardware failure, power outage or other system malfunction. System data is compressed using Eurotherm Review 5000 software, which also allows management reports to be compiled in Microsoft Excel format.
Colin Dobson, Building Manager for The Port of Dover, believes that this type of remote monitoring system will become an ‘industry standard’ for Legionella protection in the future. He comments: “Facing the challenge of meeting our legal obligations within such a geographically widespread and technically demanding site, meant that we had to come up with what is a pretty advanced solution. We now have what I consider to be an archetype system which will set the pattern for other Legionella monitoring solutions across a range of industries.”
