Cascade systems are a popular solution for light commercial environments, but to maintain performance it’s important to consider the benefits of dirt separation and deaeration – Roger Williams, Commercial Support Manager at Spirotech UK, explains more.
Certain pieces of legislation, introduced over the past decade, have changed the face of the industry we operate in. The minimum efficiency standards set for domestic boilers in 2005 was a watershed moment, and one that sounded the death knell for non-condensing boilers.
This drive towards greater efficiency has propelled the UK from being the dirty man of Europe to one of the most forward thinking in terms of its energy reduction aspirations. One positive result of this has been the steep decline in large cast iron boilers that once dominated the market – models which have since been replaced with advanced condensing units.
In the commercial and light commercial arena, or for large domestic properties or office buildings, the move towards the same high efficiency boiler model has been no less prominent, yet boiler size and greater output requirement are factors that ultimately affect future maintenance.
This desire to marry high output demand with energy efficiency has led the semi commercial market down the cascade boilers route, offering a practical alternative to changeable output demands.
Team work
In a cascade (otherwise known as master and slave) system, boilers are connected together hydraulically with sequence or step controls to more accurately monitor energy demand. Most importantly perhaps, a cascade will also improve the efficiency of the system, as individual boilers can be turned on and off according to demand.
On the one hand, the combined power capabilities of cascade systems are a godsend where accurate usage management is concerned, but in terms of ongoing management and maintenance, the system is open to many (if not more) of the same potential pitfalls as its domestic counterparts, and if correct maintenance practices are not met, trouble will be afoot.
The old cast iron boilers may have been supreme energy wasters, but they were robust and would rarely breakdown or malfunction. To the contrary, modern boilers are energy efficient but highly sensitive to contamination and rely on clean water running through them to maximise performance. Water quality can be compromised by a number of factors, the biggest of which is dirt, which will flourish if air is not being constantly removed from the system.
Fully protected
Cascade systems can be designed with as few as two or as many as six boilers as part of the set up, but research has shown that reliability is optimised for systems with four to six boilers within a cascade. In terms of efficiency, there is no appreciable difference between several small, or one or two larger boilers.
Regardless of the number or size of boilers installed, it is important to be aware that each one is at risk of the same contaminant problems, so each needs to be fitted with the appropriate safeguards, which in the case of dirt removal means a dirt separator should be fitted on all units to ensure adequate protection.
Whilst cascade systems are beneficial for more accurate heat control and output management, there is a greater overall risk of faults occurring in a system made up of several boilers, which makes the need for full protection all the more pertinent.
Depending on the demand and size of the building, individual deaerators should be used in conjunction with an appropriate dirt separator, such as the Spirotech MB3 unit.
Air removal
Deaeration can sometimes take a backseat to dirt separation in terms of installer priorities, but for new installations, where cascade systems are installed, it’s advised that dirt separation and deaeration be installed. A deaerator works by continually removing the air, including microbubbles, from a system, which, if left, will speed up the growth of magnetite. This approach should always be taken in accordance with the correct system set-up, which should also include appropriate chemicals treatment.
If the building is large or multi storey, installers should also consider system pressure requirements, as it may be necessary to install a vacuum degasser, rather than individual deaeration units. The vacuum degasser would be set up to work alongside the boiler cascade and would work in accordance with the output of one or multiple units, depending on demand.
Where a cascade system is replacing an older boiler, it’s advisable that both deaeration and dirt separation be installed, as historic dirt will likely be circulating the system and will damage sensitive components if not removed.
Corrosion issues
The issue of good water quality is especially pertinent when we consider that many of the components included within a modern boiler are made of aluminium, such as the heat exchanger, and are particularly sensitive to corrosion through sustained contact with system dirt.
Whilst the sophistication of control and volume output is greater for cascade systems when compared to standalone installations, the same principles of good maintenance must apply.
The traditional split between a commercial and domestic installer has meant that crossover between disciplines has, until now, been limited, but with the rise of the master and slave model, there is now less separation between the product groups for domestic and commercial engineers.
A thorough understanding of air and dirt, and an acknowledgment of the greater impact they have as the pipe network gets larger, is the key to enhancing efficiencies, and installers should therefore make sure that they scale up the dirt separation and deaeration requirements in line with the size and output of the particular cascade system they’re installing.
