CPD Programme
‘blown down’ through the valve at the base of the separator. In operation a dirt separator would normally
be blown down at building handover and quarterly thereafter. Maintenance is typically then no more than five minutes in a year. Dirt separators can remove any dirt particle, not just magnetic dirt, provided that the particle is heavier than water. As with the deaerator, dirt separators require a still water zone to remove all dirt particles that are heavier than water. Fitting dirt separators into existing systems has reportedly shown impressive reductions in solid matter. One particular independent test saw the dirt content reduced from 620 g/m3 (sized 5 to 10μm) to less than 1 g/m3 of all particulates larger than 0.45μm following the installation of a dirt separator, over a seven-week period.
Figure 4: Inline dirt separator
piped water systems is to incorporate a filter or a strainer. There is always a compromise when using strainers – large mesh sizes allow larger particles to pass through, while a finer mesh will collect a large volume of particles rapidly, potentially leading to obstruction of the waterway. To prevent problems, and ensure that system performance does not suffer, strainers are provided with apertures that allow all the by-products of corrosion to pass through or they would block up. Specialised dirt separators (as shown in Figure 4 ) remove particles down to 0.5μm (compared to strainers that typically only remove down to 1,600μm). Manufacturer tests have shown that,
during the normal commissioning period, the separator will remove approximately 90% of all circulating material, which can then be
Combined deaeration and dirt separation
A combined deaerator and dirt separator (shown in Figure 5) reduces the cost and space requirements compared to separate devices.
Conclusion
By achieving an air and dirt-free system components will have an extended life and increased performance. By applying modern deaerator and dirt separator technology this can be achieved to a higher level without the need to clean strainers and without onerous maintenance requirements. Temperature differential deaerators need little or almost no maintenance, and dirt separators typically require blowing down for the first two to three months – then just a quarterly blow down lasting around 5-10 seconds. Thereafter, pressure differential deaerators require annual maintenance and solenoid valve diaphragm replacement. Hence wear on equipment will be reduced, and maintenance costs on heat exchangers, pump seal replacement and radiators will be lower, with consequent improvements in effectiveness and reduced operating costs.
Figure 5: Combined deaerator and dirt separator
Case study one: example of reduced maintenance through dirt and air removal – Holland
This was undertaken in an apartment block built in the 1970s using two-pipe heating systems. The boilers were replaced in 2005, and then in 2007 an investigation was undertaken comparing the use of air and dirt separators in three similar buildings – one fitted with a combined air and dirt separator; one with a dirt separator; and one with
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30 25 20 15 10 5 0
Maintenance cost reduction
Air and dirt separation
separation Dirt
Strainers only
Figure 6: Case study one – impact of deaerators and dirt separators on maintenance costs
standard strainers. The cost of maintenance in the three buildings was recorded and the normalised values are shown in Figure 6. The system with the combined dirt and air separator required far less maintenance to ensure effective operation of the systems by reducing the dissolved air as well reducing the amount of ‘dirt’ in the system by 27 per cent compared to the previous year. By comparison, the system that used dirt separators reduced maintenance by 17 per cent.
Case study two: Reduction of pump power through deaeration – Beijing, China
An existing heating system was designed to supply 103m3/hour (28.6 L/s). However when in operation large fluctuations in flowrate were observed, although the pump was maintained at constant speed. The system was monitored both before and after the fitting of a deaeration system. The effect of the deaeration may be clearly seen on the outline pump/system curves shown in Figure 7. Deaerating the system effectively reduced the system resistance so moving the operating point from one to two, employing a smaller impellor and reduced pump head. This reduced the power input to the pump by 31% compared to the original system without a deaerator.
Design flowrate
Pump head (m)
40 30 20 10 0
System before deaeration
System after deaeration
Pump Curves
160mm impellor
152mm impellor
0 20 40 60 80 100 120 140 160
Flowrate (m3
/hour)
Figure 7: Case study two – pump power reduction through deaeration
May 2010 CIBSE Journal
65
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