The importance of a water treatment regime
Martin Wilkinson, National Sales Manager at Spirotech UK, firmly believes that in the school environment, water conditioning and its control are vital to achieving efficient, reliable operation and longevity of plant.
In the past, school heating systems usually featured large, inefficient cast iron boilers. Up until about 20 years ago the plant was usually looked after by the caretaker and although maintenance was essentially low level the system was checked fairly regularly. Preventative maintenance measures were rare and a water treatment regime was usually overlooked.
Due to the low flow rates through these old cast iron boilers, they became the sacrificial sump of the whole system and the perfect place for corrosion particles to settle, resulting in a considerable build-up of sludge inside the heat exchanger.
Typically, these old boilers were very expensive to run and of course they also proved environmentally unfriendly when compared to their modern day counterparts. However they still worked; if the pumps were operational, they produced heat for the school. In addition they were often less sensitive to factors such as dirt and air, so this replacement of the old equipment needs careful consideration with regard to design and procurement of the plant.
Nowadays, within the school heating environment, the market trend is to replace these old style cast iron boilers with today’s low water content, high efficiency condensing, cascade type units where several boiler modules are linked together onto the same flow and return headers (collector pipes).
The modern boiler heat exchangers are highly sensitive to air and dirt so this needs to be taken into consideration if optimal system performance is to be ensured. Unless water quality is closely managed on a regular basis, the heat exchangers will always be the weak link and therefore can 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 even school closures can cause.
It’s years since caretakers had easy access to the boiler plant as the plant is often locked away without adequate periodic inspection regimes, so when the first boiler module goes down, it’s often not noticed until it’s too late. If nobody is tasked with checking the water quality, inevitably the plant may fail at some point.
The recent introduction of the British Standard BS8552 provides guidelines on system cleanliness and outlines the importance of each stage of water treatment, from pre-commissioning cleaning through to the correct use of corrosion inhibitor chemicals.
Addressing the particular issues that often arise within commercial heating and water systems and stressing the importance of a complete approach to water treatment- from bottom to top level system management – the new guidelines ensure that a range of issues from corrosion damage, system failure or even bacteriological contamination are avoided.
We all know that systems must be flushed and cleaned prior to installing new boilers but it’s also vital to ensure that action is taken to alter the system characteristics that caused the corrosion to occur in the first place. Dosing with chemicals alone isn’t the solution, as problems will recur, so we have to question what is at the root of these problems and then take incisive action.
It’s not necessarily a problem with the chemicals – it’s more commonly down to the method of application and appreciating the need for a regular maintenance regime to keep levels at the right concentration. This is particularly relevant in the school environment where funds are stretched and there’s no on-site personnel tasked with the development of a robust preventative maintenance regime for water conditioning.
In developing an effective water treatment regime, the effective and on-going removal of air and dirt need to be addressed. It’s essential to condition the water naturally to prevent corrosion. A deaerator (such as the SpiroVent Superior range) serves to remove air from the entire system through just one central point to achieve the lowest possible depth of dissolved gases. Apply vacuum deaeration to any system with a history of frequent faults and where possible use the de-aerator to control the refill water.
The removal of both dirt and air go hand in hand in establishing water treatment protocols and dirt separation is also viewed as vital to achieving long term protection. Even the most microscopic of dirt particles need to be removed from any circulating fluid and the dirt removal method needs to be capable of handling large volumes of dirt between maintenance periods, with minimal loss, so as not to result in the high pressure loss around the circuit that can be associated with traditional strainers.
Put simply we suggest a strainer approach can’t deal with the microscopic magnetite particles that typically make up sludge in the boiler. Strainers can only collect a relatively small volume of dirt and when they do, this means an increase in the pressure drop and more energy required to pump the water around the system as a result. Add to that the fact that the strainers need to be taken offline and cleaned out and it’s hardly surprising this is frequently overlooked or ignored.
Condensing boilers require low return temperatures to allow them to operate in condensing mode thus maximising efficiency. Typically this means a temperature difference across the boiler of 20°C or more. As radiator systems are required to operate at 11°C, there’s a mismatch to contend with. So boiler manufacturers will specify a Hydraulic Separator (low loss header) to be operational between the primary and secondary circuits. This results in the different flow rates and temperature differences around the boilers and the old radiator circuit.
The intention is to reduce velocities through the header. However secondary flow rates can sometimes be underestimated at design stage and this results in the over mixing of the primary and secondary circuits in the low loss header, producing a lower flow temperature to the school’s radiators.
Consequently the boiler flow temperature needs to be raised to compensate and an installation originally designed to operate at 80°C/60°C may have to run at 85°C/65°C thus impairing the boiler’s opportunity to condense.
Although efficiencies, the environment and operating costs are all important, it’s also vital that we avoid the downtime of the plant and the massive disruption if the school has to be closed due to heating problems.
So, undoubtedly the introduction of modern cascade systems installed onto the steel radiators and the issue of an inadequate maintenance regime for the system’s circulating fluid is a frequent problem in the UK’s schools. However, the industry has now opened its eyes to these problems and the solution is simple if the following steps are incorporated into a robust regime:
- Condition the water naturally to reduce oxygen and significantly prevent corrosion: a deaerator removes air content from the whole system through one central point.
- Protect the boilers by removing even microscopic dirt particles from the circulating fluid.
- Employ a method that can handle large volumes of dirt between maintenance periods yet still retain a continuously low pressure drop, irrespective of the amount of dirt removed.
- Introduce a dirt separator, removing the dirt from the system so that it takes just seconds with minimal water loss.
- Select a hydraulic separator with Spirotubes to provide deaeration, dirt separation and hydraulic balancing all at the optimum point in the system.
- An air free system means no ca
vitation of pumps so they can achieve their full design flow rates and no air pockets around the system especially at the top of radiators, which means maximum heat output achieved.
Spirotech’s SpiroCross is an effective solution for school installations. It is a deaerating dirt separating and hydraulic separator, in one compact unit. It is a passive device that looks after the system on a daily basis by removing the dissolved gases and also circulating microscopic dirt particles. It also ensures fast and efficient blow down of dirt, with no disruption to the continued operation of the system and results in less energy consumption by circulating pumps and significantly reduced corrosion. As there’s no mixing of primary and secondary fluid, this means there is no need to raise boiler temperatures, thus maximising the condensing opportunities. The installation of the SpiroCross solution helps to ensure increased longevity of all wet system components.