Under pressure

Martin Willkinson, Commercial Manager at Spirotech, discusses the importance of installing the right pressurisation system to ensure a healthy and efficient heating and cooling system


The propensity to treat the symptoms and not the root cause of a problem is usually borne out of either not having the wherewithal to treat the cause or, more often than not, a lack of knowledge that means we perpetuate a reactive approach.
How our heating and cooling systems are installed and maintained is a prime case in point. For too long the industry has reacted only when system problems have become so severe that it begins to malfunction or grind to a halt all together.

The issue of dirt in the system and more specifically metallic dirt (sludge or magnetite) has been viewed as the prime culprit for system breakdown. This, of course, is inaccurate and the market is slowly starting to wake up to the damaging effects that air, and more accurately the incorrect management of it, has on a healthy system.

The real elephant in the room, though, and what the vast majority of system malfunctions stem from is problems with pressurisation and how the changes in system pressure can dramatically affect the efficiency of a building’s heating and cooling system. To not consider pressurisation, or to ignore it completely in the design phase, is akin to building on a floodplain – the devastating results of which will eventually show themselves.


Premature system failure


Often, very simple issues are overlooked during the design or installation process, and as a result, the quality of the fluid in the system is seriously compromised, the system efficiency is greatly reduced and effectively results in the premature failure of major system components. This causes higher long term operating costs and ongoing expenditure for those tasked with maintenance, let alone system disruption and discomfort for the user. The system must, as a result, be cleaned frequently and reliance on chemical applications to keep the problems at bay continues – a thoroughly ineffective solution.

A poorly designed, installed or maintained pressurisation system can lead to negative pressures around the circuit. Air can be drawn in through automatic air vents, gaskets and micro leaks. High pressure situations can lead to water being emitted through the safety valves and then the subsequent frequent addition of further raw refill water. The introduction of fresh oxygen rich water depletes any level of corrosion inhibitors that may be present. The onset of corrosion is then inevitable, and the cycle continues. Last but not least if common tap water is used for topping up the system it will most probably form lime scale in the heat exchanger.

In a nutshell, the corrosion problem starts when air is constantly introduced into the system, dirt and sludge begin to build up and the system is cleaned and treated with chemicals; the cycle goes on and the same issues recur time and time again.


Optimum conditions


A good pressurisation regime creates the optimum conditions for a system to operate effectively and reliably and ensures that the required minimum pressures are achieved. Of course, there’s no getting away from the fact that air will always be present in a system, so a good pressurisation system will by no means cure the problem. Nevertheless we should aim to achieve what’s known as ‘hydronic stability’.


Ensuring that heat is transferred to the right place at the right time is crucial to a properly functioning system. When heat does not come to the desired places then there will likely be a blockage in the system, caused by air, corrosion or limescale build-up. Such restrictions can seriously hinder the heat transfer capabilities and will mean either the pump or the boiler needs to work harder and is thus not running at optimum efficiency levels, which causes energy loss.


One of the biggest causes of a reduction in system pressure or malfunction is due to a system either not being installed properly in the first instance or design recommendations not being adhered to, or when extensions are made to existing buildings yet considerations regarding the appropriate pressurisation levels have not been considered.


Pressurisation units are also left open to problems if they are not maintained to the correct manufacturer recommendations. Corners should never be cut in this regard. When new buildings are added there’s often little thought given to the need to increase vessel size to accommodate a bigger heating and cooling system too, which will likely result in a reduction in pressure and reduced heat exchange capacity.


Latter extensions to existing heating and cooling system can be left open to malfunction if the initial design and installation requirements have not been considered. It is also common for a design recommendation to be made at the planning stage but not carried out in the final installation, usually as a result of cost cutting measures. This scenario is particularly common in large municipal installations like hospitals, which also suffer from many of the problems associated with open spill systems (commonplace in the UK market).


Re-filling should be avoided wherever possible, but adding new make-up water to a system is a necessary evil, as it introduces air, hardness (limescale), it dilutes any inhibitor and salt builds up in the system. If scaling is allowed to accumulate it will reduce the heat transfer capacity and requires the pump to work harder to function with pressure will drop as a result.


Vital system components


The quality of the system fluid is an important factor for efficient functioning and should be regarded as a vital system component and treated as such. Therefore, fluid should not only be carefully selected but also properly maintained. Next to that, chemicals should be used to flush systems to rid them of any impurities, or to close or prevent micro leaks. If excessive dirt is present, treatment and cleaning with chemicals must take place far more often.


If new water must be added, ensure it is softened water or free from dissolved air, which is easily achieved by installing a vacuum degasser combined with a pressurisation unit – the SpiroVent Superior would be an ideal choice here.


The SpiroPress Fill is primarily for use on smaller systems with relatively low pressures and volumes. The SpiroPress Fill range offers the choice of a simple mechanical auto fill unit or a wall hung pumped fill unit. Both systems are used to provide make-up water and are used in conjunction with an independent fixed gas cushion type expansion vessel.

The SpiroPress Control is designed for use on systems up to (but not limited to) 300,000 litres and the range offers the choice of four units available to cover the pressure range from 1 bar to 16 bar. All units are used to provide both full vacuum degassing of the system water and all make-up water is also degassed prior to entry into the system providing substantial long term protection.


For systems with very large volumes and pressures, Spirotech’s SpiroPress MultiControl is recommended, especially if space is limited and traditional fixed gas cushion type vessels are difficult to accommodate. The SpiroPress MultiControl range offers a multitude of units to cover all system volumes and pressures up to 16 bar. Special units are also available upon request for systems operating at higher pressures or when multiple pumps or valves are required.


These larger units can be used as a standalone complete pressurisation solutions, although to maximise longevity of system components and to offer optimum protection to the circulating fluid it is strongly advised that it is used in conjunction with a vacuum degasser to fully vacuum degass the system.

At the heart of a properly functioning system should always be good pressurisation and the bottom line remains that if a system is not designed, set up or installed problems, failure, inefficiency and ongoing costs will continue to be the order of the day.


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