Heating and Ventilating

Water conditioning within school heating systems is important because it makes a vital contribution towards achieving efficient and reliable operation and longevity of plant while avoiding the common problems that frequently occur as a result of inefficient boilers and poor preventative maintenance. Martin Wilkinson explains
Until some 20 years ago, schools generally operated with large, inefficient cast-iron boilers. In the 'old days' this plant would be checked by the school caretaker although maintenance was low and preventative maintenance measures were rare.

Due to low flow rates, these old style boilers are the perfect location for corrosion particles to accumulate, causing a large build-up of sludge inside the heat exchanger. The older boilers were comparatively expensive to run and less environmentally friendly than their modern day counterparts, but generally, they were less sensitive to factors such as air and dirt.

Nowadays, there's a trend to replace the old systems with modern boilers featuring low water content and high efficiency condensing cascade units, where a number of boiler modules are linked together onto the same flow and return collector pipes.

Sensitive to dirt
Although the new systems undoubtedly present many benefits, it is widely acknowledged that modern boiler heat exchangers are very sensitive to the presence of air and dirt, so this approach needs careful consideration with regard to design and procurement of the plant.

Unless water quality is adequately managed in the new systems, there's the potential for the heat exchangers to prove a weak link and compromise the integrity of the whole system. This is especially important within a school environment in view of the major disruption that system downtime and the ensuing school closures can cause.

It's years since school caretakers have had access to the boiler plant, so the plant is often locked away without adequate periodic inspection.
Within a modern cascade system if the first boiler module should go down, it can often go unnoticed, so further plant failure is almost inevitable at some point. With a modern cascade system, preventative maintenance and water conditioning are key to performance. It's a given that systems must be flushed and cleaned prior to installing new boilers but action also needs to be taken to rectify the system characteristics that cause corrosion to occur in the first place.

Simply dosing with chemicals alone isn't the long term solution as problems recur after a short space of time, so the root of the problem needs to be addressed and a regular water maintenance regime must be implemented.

Traditional strainers can have difficulties dealing with the microscopic magnetite particles contained within system sludge in the boiler. Strainers tend to collect a relatively small amount of dirt and when they do, it results in the pressure drop increasing; this means increased energy required to pump the water around the system. If strainers are to be cleaned out, it requires them to be taken offline and as this is a labour intensive job, it is often overlooked.

Modern cascade systems installed onto old steel radiators combined with an inadequate maintenance regime for the circulating fluid is a recurring problem in schools throughout the UK.

Fortunately, the industry is now addressing these problems and the long term solution is surprisingly straightforward.

A rigorous and effective preventative maintenance regime is vital and it's essential to condition the water naturally to prevent corrosion. A deaerator is a good way around this as it serves to remove air from the entire system through just one central point to achieve the lowest possible depth of dissolved gases. Apply vacuum deaearation to any system with a history of frequent make up and where possible use the de-aerator to control the refill water.

Dirt separation is the most important step in cleaning the system and achieving long-term protection. A dirt separator is a hassle free way to clean dirt from the system in just seconds, with minimal water loss.

These products help to remove magnetite, sand & grit build up within the system and cleaning of the unit can be carried out in a fraction of the time that it would take with traditional filters.

Maintain hydronic stability
Deaerators and dirt separators are also crucial to maintaining hydronic stability, the foundation for a healthy system, helping to ensure the highest standards of performance are achieved whilst preventing a build-up of lime scale, corrosion or bacterial growth.

The introduction of combined deaerating/dirt separating hydraulic separator units (Low Cross Header) is also particularly beneficial to modern cascade boiler systems - helping to eliminate any unnecessary cross mixing of the primary and secondary water flows, whilst allowing the system to operate with the lowest boiler temperatures. These units also offer 'temperature differential deaeration' and dirt separation at the optimum location on the system.

Chemicals can only work best when used in conjunction with the other aspects of the treatment listed above, as dealing with problems at their source is of vital importance.

Where possible, contacting a total solution supplier who can advise across all elements of water treatment, in order to achieve hydronic stability and help to ensure that systems run to optimal efficiency.

The author is of national sales manager at Spirotech UK