We’re Fans of Efficiency - not carbon debits!

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To sustain a comfortable environment in a working space, we have to use energy in order to provide heating, cooling and ventilation. There is no excuse for unnecessarily wasting energy due to either bad equipment selection, or ducting that produces negative system effects.

Figure 1 - A very poor fan installation

The installation shown in Fig.1 is of an actual installation and we will now analyse what effect it will have on fan performance and the utilisation of the energy input.

There is a sharp bend immediately upstream of the fan inlet, which could starve about 20- 30% of the impeller sweep.

There is an abrupt expansion immediately prior to the fan, which will cause further serious starvation.

If fans had nightmares, this would be about as bad as it can get!

To accurately predict the output of such a fan installation is not possible. However, we can say that the performance will be below the tested fan curve. Our extensive knowledge of fan applications tells us that such an installation could be expected to deliver approximately 30% of its potential performance.

For the purpose of illustrating the harmful effects a bad installation can have on the environment, we will assume the fan to be driven by a 7.5kW output electric motor, running 8 hours a day, 200 days per year. The energy used to move the air is serving a useful purpose, however the 70%, which is wasted, only serves to produce needless greenhouse gases and carbon. The wasted energy is a large contributor to climate change and to demonstrate this, we will do the sums!

A 7.5kW output motor requires an input of approximately 8.5kw (pre MEPS2). If 70% of the energy is wasted, then the wasted power equals 8.5x0.7= 5.95Kw. For the operating times shown above, the wasted energy equals 9,520 kW hours or 9.4tons of greenhouse gas containing about 2.6tons of carbon. The cost of the wasted energy at $0.15 per kW per hour is $1,428 per annum.

However the bad news does not end there. The turbulence caused by these poor fan inlet and outlet conditions will give you 10-20dB more noise than expected. So at 30% flow, you may not be aware of the air movement, but you will be able to hear it.

Figure 2 - How a fan should be installed

For an axial fan to perform close to, or at, full potential, it must have reasonable inlet and outlet conditions. Fig 2 is an example of a more acceptable installation. For useful tips and recommended practice refer to the “C’mon give a fan a chance” section in the Fantech catalogue and website.

In conclusion, we have demonstrated that a poor installation is dangerous in many ways:

• It harms the environment
• It costs more to run
• It fails to achieve the air movement and;
• An impeller running in such turbulent air is liable to adverse stress and could suffer fatigue failure

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