recommend airway size function

[MWalford]

Hi,

The results of the recommend airway size function do appear to make sense. Could you help explain please

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Number Unique 342175 : , Length  108.2 m

Current life time cost for size:  4.5 m Diameter  =   15.9 m²
$ 917,089   Total Cost which consists of
   $ 825,559  Mining Capital Cost = $ 7,633 / m
   $ 15,112  Fan Capital Component
   $ 76,418  Power Cost (5 year) discounted : 16.8 kW

Recommended life time cost size:  4.3 m Diameter  =  14.2 m²
$ 911,374   Total Cost which consists of
   $ 791,025  Mining Capital Cost = $ 7,313 / m
   $ 19,870  Fan Capital Component
   $ 100,479  Power Cost (5 year) discounted : 22.1 kW

Potential Savings:  $ 5,715 
   $ 34,535  Mining Capital Cost
   $ -4,758  Fan Capital Component
   $ -24,061  Power Cost (-5.3 kW, 5 year) discounted

   $ -5,558  Annual Power Savings
 

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Mining capital cost – This is straight forward I have entered quotes from the same company for various different sizes to establish this (did not include cost of waste haulage)

 

Fan capital component – I can’t see where this comes from. Figures used in settings are $900/kw of installed fan power operating at 280kw.

 

Power cost – again I cant see where this comes from 280kw, $0.12/kwh..

[Martin Griffith]

Hi, 

The fan capital component accounts for the effect the proposed change in airway size will have on the type of fan you require . In your case, reducing the size from 4.5m to 4.3m, will increase the resistance in the airway, meaning that you will have to increase the fan power to acheive the same flow. Therefore the proposed change involves a loss on the fan purchase. This is worked out purely by the extra power lost in ventilating the airway at the same flow rate, adjusting for fan and fan motor efficiency and then multiplying by the fan purchase cost.

The friction power for a given airway can be seen in the Energy | Friction Power property.

The power cost is the cost of the electricity to run the fan which is ventilating the airway. This is also calculated from the Friction Power in the airway, multipliying this by the number of hours over 5 years to get the energy usage in kWh, multiplying by the power cost of 0.12 $/kWh and then adjusting for net present value. 

[MWalford]

Thanks Martin.

I think I understand now, the  costs and power from the airway optimizer are only for that one airway segment. The 'installed' fan accounts for all segments within the circuit.