Correct pump selection is of paramount importance, says Peter Nears, who is product manager for Biral Pumps at Hamworthy Heating, and has more than 25 years of experience in the commercial pump market place
'IN recent years there has been a tendency to treat the pump as a commodity item, not realising it is one of the most important items in the plant room. Old pumps are commonly replaced like-for-like or by one of a similar bore size, and usually higher head. In my opinion this is a recipe for future trouble as most pump failures can be attributed to over-sizing or poor selection.



Pumps for condensing boilers

Most modern circulators have a choice of manually selected speeds but invariably are left on site at maximum. This often results in over pumping, narrowing the differential temperature across the boiler, reducing operating efficiency. This is especially relevant today with the trend towards the use of condensing boilers, where a 20-degree differential temperature is the norm. Over pumping a condensing boiler will reduce differential temperature to the point where it may not condense at all, limiting potential energy savings.



Variable speed drives

In a recent independent experiment*, it was found that significant numbers of large commercial buildings were consuming large amounts of electrical energy via their heating pumps, despite having fitted variable speed drives.

A fundamental error was made; nobody checked the design and actual duty points before the variable speed pumps were installed. Put simply, new pumps were matched with old, which were already over-sized. If variable speed pumps are over-sized, then the computer chip in the pump cannot see small changes in system resistance when working at the end of their curve. Consequently they will always run at maximum capacity and maximum power consumption; a pump with maximum power consumption will always run excessively hot, eventually causing failure of the motor windings. Measurements were taken and most of these buildings were found to be over pumping. Considerably smaller pumps were then fitted, resulting in a significant reduction in power consumption. The popular message is that a variable speed drive on a pump will save energy ... but this is only applicable if the pump is correctly sized.



Variable speed pump selection



The chart below shows the operating range for achieving good selection for variable speed pumps.

The ideal design duty field is in band A which will provide maximum potential for variable flow rates and energy savings. A pump in band B would be better reselected as a smaller model because the energy savings in that area would be small against any volume changes. A product in band C should be reconsidered as a fixed speed pump because savings will be negligible and the capital cost can then be reduced. Pumps that are oversized appear in band D where the system curve is too flat to detect changes in system resistance and the pump will then run at maximum output with no potential for energy saving. Night set back or frost protection speed is shown on the chart as curve min 1.

Biral variable speed drive pumps are despatched from the factory with a default setting that limits the maximum power output from the pump, because we know that in many cases it will be over-sized. A switch in the terminal box will allow maximum performance to be employed if required.



Reducing system noise

Biral has a broad range of pumps with very flat curves, which give little change in head when zones or thermostatic radiator valves close down, thus preventing system noise that often occurs. Another important consideration is to remember that a circulating pump operating at low speed is significantly quieter than one operating at high speed.



Insulate the pump

Biral pumps are also currently the only product on the market that can be totally insulated up to flow temperatures of 100°C. This is possible because of the high quality motor windings used - class H, a grade higher than other products on the market which gives the pumps greater life expectancy as well as the capacity to handle heating water up to 140ºC, and chilled water for air conditioning systems.



Pump developments

Biral's new P range of pumps are particularly suited to modern building services, providing an energy saving ability of 30% at full load and up to 60% at partial load. The new pumps are suitable for any system that requires variable flow rates to match system heat demands. The built-in inverter linked to advanced permanent magnet motor technology gives total control and the ultimate in energy savings. This tried and tested technology has now been applied to pumps up to 65mm bore, giving flow rates suitable for boilers up to 1000kW at 20 degree differential temperature.

Precise pump selection, using multi-speed or variable speed drives, is a vital factor in determining the life expectancy of the product and it is clear that a one-size-fits-all approach will not give optimum performance or longevity. Working closely with the Hamworthy pump project team will result in improved pump reliability and, an opportunity to make significant energy savings with reduced running costs, during the life of the pump.



* Research courtesy of Walter Hertzog, Switzerland

For further information on Biral pumps email sales@hamworthy-heating.com, (0845 450 2865 or visit www.hamworthy-heating.com.