![]() Now we need to determine if the calculated value for can be delivered by the fan. Substituting in the known parameters gives: So, what is the RPM of the fan required to be to deliver this flow rate increase?īy re-arranging the above formula (Eq. V 2, calculated by multiplying the space by the new air change requirements, is simply 37500m 3 x 6.1 which give a new requirement of 228750 m 3/hr. From the manufacturer’s data sheet we know that to deliver this performance, the RPM (U 1) of the fan is 1160 r/min. 8 number 1000mm 4 pole long cased axial fans were used. The original air flow rate, V 1 is 187500 m 3/hr at a pressure loss of 185Pa due to ductwork, louvres and other system elements. Later additional machines are added to the factory and the required number of air changes per hour increases to 6.1 to maintain the desired maximum air temperature within the factory. Volumetric flow rate (, m³/hr) varies directly proportional to the ratio of the rotational speed ( U, r/min) of the impeller.Įxample – Industrial Warehouse, a change in air volume.Ī Factory of 37500m 3 space currently requires five air changes an hour to remove waste heat generated by industrial process machinery. The first law of fans is a useful tool when working out the volumetric flow rate supplied by a fan under speed control or conversely working out what the RPM would be to deliver a required volume of air and hence what frequency to set a variable speed drive (VSD) to. That there is no change in the diameter of the fan.Ignoring special applications, the upper limit for the RPM will be approximately 3600 (60hz supply frequency) You will not be looking at situations beyond the design speed of the impeller. However, it is unlikely that this would be a problem. That there is not an extreme difference in the change of rotational speed of the impeller in question and as such creating significant differences in the density of the air.The first three derivations of the Fan Laws are predicated on a couple of assumptions: We will assume that the fan size and air density are to remain constant. To start we will consider only the effect of a change in the speed of the fan on the flow rate, pressure and power consumption. So, in short, the basic fan laws are used to express the relationship between fan performance and power. They are most useful for determining the impact of extrapolating from a known fan performance to a desired performance. The Fan Laws are a group of useful equations for determining the effects of a change in the speed, the diameter of the fan and the density of air in the system. Geoff Edwards, the technical product engineer at Axair Fans UK Limited, explains the three basic fan laws when applied to warehouse ventilation studies.
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