Water treatment
Make it a match W
Spirotech specification manager Ted Watson explains how matching the right deaerator/dirt separator to the flow rate will avoid a whirlpool of costly repairs
ithin commercial heating systems dirt separation can be a mucky business. But that’s okay as engineers and facility
managers are well aware that extracted magnetite drawn from the system is a sign that a carefully selected and installed dirt separator is performing as required. Similarly, the right deaerator will ensure that troublesome gases released from solution are arrested and then released to atmosphere. But get your flow rate wrong, or fit a ‘less expensive’ unit, and the dirt particles could stay put and air pockets could prevail resulting in corrosion, an inefficient system and higher energy bills with an increased risk of premature system failure. For most standard commercial heating systems
the average flow rate of circulating water is generally controlled between 1.0 and 1.5 metres per second. With a correctly sized deaerator/dirt separator installed in the correct location, and where all other components are running properly, this should see the system operating efficiently and effectively. As long as the plant or facilities manager carries out the simple task of draining off any gathering particles at regular intervals, then those working in that commercial setting should enjoy the benefits of a high performing system for years to come. However, if you get your calculations wrong, or substitute the so-called ‘expensive’ unit originally specified for a cheaper model just to save a few pounds, it could be risky for you and your customer. Not only in call-out and product replacement charges but also in major inconvenience and an unhappy workforce. Before we discuss how to get it wrong, let’s quickly remind ourselves what ‘right’ looks like.
Unhindered flow
A quality and properly sized dirt separator, installed correctly on a heating or cooling system’s return main, will allow the water to pass through the unit with the flow rate unhindered. Likewise with the deaerator on the system’s flow, where the temperature is at its highest. The dirt separator chamber must have sufficient depth so as to accommodate the turbulence created by the flow rate. The chamber must also encompass an environment or “laminar no flow zone” at the bottom in order to allow the settlement of dirt
SpiroVent deaerator including a cutaway view
particulate. If the dirt separator chamber is too shallow this water critical layering effect, and laminar flow, will not happen. In addition, the deaerator/dirt separator should
feature an appropriately constructed high quality, constant low pressure drop separator element within it. This will allow control of the flow to take place while also creating the environment for the dirt particles to be collected from the turbulent zone and then settle to the bottom of the no flow zone. All the dirt is collected and stored out of the water flow path until drained off at regular intervals. However, with a deaerator, the air is filtered up out of the top of the unit, to be released by an AAV.
Magnetic attraction
It’s worth mentioning at this point that the introduction of removable magnets has made first pass magnetite dirt collection even more effective. The magnets can be either internal, as in conventional separators, or external, as in newer products. The advantage of an external magnet lies in its easy removal and replacement. If fitted with a magnetic field booster the magnetic particle collection is accelerated.
Three-pronged approach
Of course, we mustn’t forget that chemical application has long been recognised as a go-to solution for managing system health. Its impact can go a long way to achieving improved efficiency. If applied and maintained correctly and in the right dosage, oxygen inhibitors can be effective, albeit this is not a permanent solution. We should bear in mind though that nitrate-based inhibitors can, in some circumstances, contribute to the development of microbiological growth at the expense of depleting inhibitor levels, and thus expose the system to corrosion attack. However, the introduction of a deaerator will significantly reduce the air content and improve system efficiency. So, let’s examine the impact of getting it wrong, although this may not be immediately apparent.
Turbulent times
With cost (a driving force) always a consideration, fitting a less expensive or ‘value engineered’ dirt separator or deaerator can be appealing, but this can turn out to be a short-sighted, short-term decision with long-term expensive consequences. A dirt separator where the depth of the chamber is insufficient to accommodate the turbulence and provide a correct environment, may appear initially to be operating successfully. But over time it will become apparent the dirt and air are both circulating
30 August 2017 with diminished efficiency. Suspended solids/debris and/or microbubbles will
remain in the turbulent zone where it will simply swirl around before being drawn back up in to the main flow again and out into the system. This scenario should be avoided as failure to do so will lead to the settlement of debris around the system. Consideration should also be given to the internal
separating element. Some dirt particles are so small it is not possible to see them with the human eye. A filter is often used to counteract this but this is not always ideal. Filters get blocked, due to poor maintenance, and must be regularly cleaned and replaced, causing additional work and cost. Spirotech separating elements (SpiroTube) are high efficiency, non-clogging, self-cleaning, virtually maintenance free and maximise performance.
High flow rate
As I’ve already said, the average flow rate of the water circulating in the majority of systems is controlled between 1.0 and 1.5 metres per second. However, in some systems, the prevailing flow rate could be three metres per second. Under these circumstances it is vitally important
to consider a “high flow” unit where a bigger chamber must be fitted. Standard sized units operating at high flow rates produce high pressure drops and can lose a significant level of efficiency. It is not the case that one size fits all, as the force of water travelling at three metres per second will simply power the dirt or air in a straight line through the separator. It is worth shopping around though, as not all manufacturers offer this higher-level and bespoke solution. There can be only one result of the ‘less expensive’ or poorly matched option. The dirt and air continue undiminished and contamination builds, resulting in corrosion in pipework or radiators, and premature system failure.
Cost-effective
When an installation is being designed a lot of attention is given to, on the face of it, ‘expensive’ components. But it is often forgotten that the water quality is a determining factor in the final efficiency, effectiveness and lifetime of the installed heating
system.The condition and conditioning of the water must be an essential and vital part of the designing phase, which is where the so-called ‘expensive’ components, with their higher performance levels and longevity, prove their worth. They are, ultimately, a more cost-effective solution. Having to replace poor performing components because they are inefficient or have a short lifespan is where the real cost comes in.
SpiroTrap dirt separator including a cutaway view
www.heatingandventilating.net
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