The holistic approach to protect HVAC systems

HVAC systems require major capital investment, have long term operating costs and their energy consumption impacts significantly on the environment profit. To maximise the return on investment and minimise the impact for the wider environment it is crucial to protect and maintain structural integrity and design efficiency. The energy carrier within the majority of HVAC system is water. It has no COSHH (Certificate of Substances Hazardous to Health) requirements and is therefore extremely environmentally friendly but its inherent properties and consistently variable quality present major operational issues. The instant that water enters a HVAC system it will react physically, chemically and biologically, generating processes that are inter-related and will fuel each others development. In broad terms they include corrosion, scaling, bacterial contamination and general fouling.

Energy consumption

The consequences of corrosion can be disproportionate to the small amounts of metal destroyed by the process. Just 2mm of rust can reduce heat transfer by five percent across component surfaces. Scale has a more significant effect on the transfer efficiency with as little as 0.5 mm layer generating a four percent loss. In addition, scaled and corroded surfaces contribute to bacterial contamination. The insulating effect of biofilm growth is four times as resistant to heat transfer as calcium based scale.

Impact on HVAC system

The by-products of corrosion can block inline valves, strainers, and narrow bore pipes, reducing flow rates and increasing the rate of further sedimentation. The associated fouling will again increase the propensity for microbial growth. Impingement by particles causes excessive wear of pumps, impellers, mechanical seals and connective pipe work. Localised pitting can perforate vessels and pipes allowing system contents to escape. Inevitably plan fails constituting both a health risk and considerable replacement cost. The detrimental effects of scaling waters causes similar problems to corrosive waters and scale build up within components can be catastrophic. Biofilms are composed primarily of algal and bacterial microbial cells and the extra cellular polysaccharide slimes they produce. Rough or fouled surfaces provide a suitable substrate for attachment and the surrounding water bathes them in a nourishing soup encouraging colony growth. They are capable of producing basic corrosion cells and mineral acids that cause severe localised pitting. In addition, they can provide a breeding ground for harmful bacteria given favourable conditions for growth.

Chemical additives

Consideration when specifying a water treatment regime must be given to its efficacy, its whole life cycle cost, how easily it can be implemented and managed and what potential risk it presents to personnel and environment. The conventional approach to meeting these objectives has been predominantly to use chemical additives. Corrosion inhibitors can be directed at different parts of the electrochemical process. Anodic inhibitors protect the anodic site preventing metal ions going into solution. However, under-dosing an anodic inhibitor can generate localised pitting and conditions for accelerated corrosion. Cathodic inhibitors prevent electrons being removed from the metals surface through precipitation of a protective film at cathodic sites. Synergised inhibitors combine a mixture of anodic and cathodic inhibitors to give improved performance with reduced risk of localised pitting corrosion. Scale inhibitors work by restricting crystal germination and growth or, by shifting the pH to a more acidic solution and biofilm growth and microbial contamination are controlled using oxidizing and non oxidising additives. Chemical additives require COSHH compliance and labelling is mandatory due to their aggressive/toxic nature and the associated risks. They are dependent on a clean system to ensure their effective dosage and it is recommended that suitable mechanical filtration accompanies their use.

Filtration

The patented EnwaMatic® water treatment unit combines reproducible principles of water chemistry with standard water treatment technologies. The unit provides effective dirt and air separation with environmentally sound water conditioning. Processing <1% total flow rate and filtering to <5µm the unit has negligible impact on system efficiency unlike the associated pressure drop of inline filters. The EnwaMatic® creates changes in key water parameters pH, alkalinity and hardness to elicit corrosion inhibition, control of scale formation and a biocidal effect. The unit contains a calcite/dolomite media blend that dissolves into the system water to establish carbonate equilibrium. The equilibrium is dynamic relying on a saturation point. The analogy is the ability to dissolve sugar in hot tea. At saturation excess sugar remains within the cup but if more hot water is added the saturation point adjusts allowing the excess to be dissolved. The process is self regulating and continuously adjusts to achieve the design chemistry buffering against system «top up». In soft water applications, hardness is elevated to prevent corrosion. DNV (Det Norske Veritas) accredited the EnwaMatic® after undertaking a trial within their own property’s heating system. During the six months period, pH elevated for 5.71 and stabilises at 9.25 and the level of ferrous ions decreased significantly from 16mg/l to 0.01 mg/l and remained low. Data extrapolated from weight loss coupons immersed during the trial documented corrosion at 0 mm/year. DNV also documented after six months treatment that the particle content was within the limits set for potable water. In hard water applications, the excess hardness is actively precipitated within the filter bed as a fine sludge that is backwashed to waste. Elevation of pH to ≥9 provides a harsh environment for bacteria as cell wall replication is difficult at pH >8.5. Unlike conventional chemical additives the calcite/dolomite media will not contribute a nutrient source. In addition, the high level of filtration actively removes nutrient load and substrates that promote colony growth. In applications where the EnwaMatic® has replaced both the chemical inhibitors and biocide there has been no increase in total viable counts. Crystal Cruises installed EnwaMatic® on board Cyrstal Harmony on a 50qM chilled system. The results were 2-3000 kg mud removed within six months and 25% improvements in the compressor efficiency (2MW reduction in constant load; from 8 to 6MW).

Approval from Wärtsilä

EnwaMatic® is also the recommended water treatment system by Wärtsilä, the world number one in ship engines. The technology obtained approval from the engine manufacturer after several years approval period with the final test running for 16,378 engine hours. In connection with the intense testing period, the ship-owner Color Line, operating several cruise ferries, decided to change all closed loop water systems for engines and HVAC systems on their entire fleet to EnwaMatic® Maritime.

Svenn Lorentzen, Sales Manager at Enwa Water Treatment AS, says: “The EnwaMatic® technology is already in use in more than 5000 buildings in Europe alone. The recent move in to the maritime segment has already resulted in the delivery to more than 50 ships. We see that the market demand for our EnwaMatic® units is quite strong and promising, as more and more of both our existing and new customers order these environmentally friendly and energy effective water treatment systems. This technology is completely in line with the market trends and the future of both maritime and offshore related business, in addition to the land based market. We are very optimistic about the further development.”