A lot is being made today of the need to “Be Green” and save energy consumption wherever possible.
Farm Electronics Ltd prides itself on promoting Energy Efficient Cooling Systems long before this became the buzz word it is now.
In the long term cooling of stored Potatoes the use of Ambient (Mother Natures) air is by far the most cost effective. In power terms it costs around 3 times as much to cool produce using Refrigerated air, than ambient air.
We have always championed the installation of Refrigeration with Combined Ambient cooling ventilation to allow the use of efficient fresh air cooling when it is available. Systems that use our well proven Cropscan 16mc3 electronic controller carry out very economic and close controlled ambient “air mixing” to achieve safe cooling temperatures even when it is well below freezing outside.
Some of our competitors have recently been promoting Fan Speed Control as the answer to dramatically cut your electricity bill. Unfortunately this is in reality a bit of a “Perpetual Motion Theory”. It’s too good to be true.
The Cooling Fans are at the heart of any well-designed ventilation system. In our systems they are very carefully selected to achieve two primary criteria. Firstly they must produce the air volume required to give satisfactory air movement, and air changes within the storage building. Secondly they must produce this air at the pressure required to ensure the crop is evenly ventilated.
By reducing the speed of these fans you can undoubtedly save considerably on your electricity consumption. However this is at the expense of reduced air volume and perhaps more critically in many storage systems loss of pressure. Consider this “Law of Physics”. (see notes at end of this article) Reducing the fan speed by 30% reduces the pressure capability by 50% and the volume by 30%. The reality is that the fans are no longer capable of doing “the job they were designed to do”. You would in effect be much better off by switching them “Off”, thereby making a 100% electricity saving. Either of these options would in reality of course lead to the deterioration of the stored crop! We suspect not the most economic outcome.
We have even come across Inverter Speed control being promoted for 2-Stage high pressure Grain Drying fans. It is impossible to dry Grain unless you have around 4″ to 6″ swg. pressure. Any reduction in the speed of this type of fan will cause the pressure produced to collapse. Buyer Beware!
In reality, just like insulating your loft at home, attention to the general storage building insulation and any unnecessary air leakage around the eaves line or doorways will reap far more efficiency benefits than the “magic bullet” route of Fan Speed control.
The fan laws:-
A) Air flow varies directly as the fan speed ratio:-
Initial Air Flow x (new motor speed) old motor speed) = New Air Flow
B) Pressure varies as (fan speed ratio) 2
Initial Pressure x (new motor speed) old motor speed 2 = New Pressure
C) Fan Absorbed Power Varies as (fan speed ratio) 3
Initial Absorbed Power x (new motor speed) old motor speed) 3 = New Power