Feb 26, 2017 7:08 pm
I am writing this post hoping to find some advice from someone knowledgeable about ceiling fans – specifically about the power of ceiling fans, and about ceiling fan installation.
My electrician has recently installed a ceiling fan for me. I supplied the fan (bought from bunnings) and he did the installation.
Arlec 120cm 4 Blade White Ceiling Fan With Oyster Light And LCD Remote Control
https://www.bunnings.com.au/arlec-120cm ... l_p4370744
The fan was installed, however the performance of the fan is very poor. I am very disappointed. At full speed, I can barely feel air movement when standing underneath the fan. It's very poor.
I am unsure whether there is a fault with my fan, or whether this particular model is just very poor.
My initial thoughts were to assume that the model that I purchased is just poor, and I need to buy a more expensive fan, however I am having second thoughts.
1) Is it possible that the electrician has made an error when doing the installation, somehow with the wiring, somehow resulting in less current being supplied to the fan, causing the fan to be underpowered? Or conversely, is it binary in the sense that the fan either turns on and runs at full power, or it doesn't turn on at all?
2) Or, is it just this particular model which is pathetic?
In order to quantify what I mean by "disappointing and underpowered", I did an RPM test. I put a piece of coloured sticky tape on one of the fan blades and visually counted how many rotations that fan did over a period of one minute. On the maximum speed setting, the result was 146 RPM.
3) Does anyone know what RPM this particular fan should perform at?
Note: If anyone suggests that I speak directly to my electrician, please don't. I am aware that this is an option, but I want to seek opinions from this forum (hence the post).
Re: Ceiling Fan - underpowered2
Feb 26, 2017 7:19 pm
I have since found out that the specifications for that model say 200 RPM (as specified in the link). That means that my fan is performing under the the design specification.
The big question now is:
4) Is it possible that the electrician has made an error when doing the installation, somehow with the wiring, somehow resulting in less current being supplied to the fan, causing the fan to be underpowered? Or is this just not possible, and instead the problem is due to the fan itself being faulty?
5) What could the cause of this problem be? I am trying to make sure that I don't order to fan to be uninstalled on the assumption that the fan itself is faulty, when in fact the problem may be due to incorrect wiring installation by the electrician.
Re: Ceiling Fan - underpowered3
Feb 26, 2017 8:27 pm
At full speed, I can barely feel air movement when standing underneath the fan. It's very poor.
Have you checked to make sure it is not on the winter setting?
EDIT: There is some information about ceiling fans in the link below but most of my posts about ceiling fans have been on another forum.
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Re: Ceiling Fan - underpowered5
Feb 26, 2017 9:40 pm
Is there 300mm space between the blades and the ceiling?
The rake should be correct out of the box but have you checked it?
Re: Ceiling Fan - underpowered6
Feb 26, 2017 10:11 pm
Is there 300mm space between the blades and the ceiling?
This distance (the distance between the blades and the ceiling) is determined by the physical length of the down rod. The downrod and ceiling mount makes up part of the product itself - it's not something that can be altered (intentionally or mistakenly).
To answer your question, the distance between the blades and the ceiling is 200mm.
But again, it's not something that can be altered - I don't believe this is the cause of the problem.
Re: Ceiling Fan - underpowered7
Feb 26, 2017 10:12 pm
A few facts to re-cap:
F1) According to the product specifications, the Arlec fan should spin at 200 RPM.
F2) The Arlec fan is only spinning at 145RPM (at the maximum speed setting)
So that key question I have here is:
6) Is it possible that the power being supplied to the fan (ie: the house wiring/circuit, the installation wiring that was installed by the electrician) is causing the fan to be under powered, and thus spinning at an RPM less than the product specification?
7) Or conversely, is the problem (lack of power / lack of RPM's) within the fan itself?
Re: Ceiling Fan - underpowered8
Feb 27, 2017 12:54 am
I cannot comment about whether or not the electrician has made an error when doing the installation, I can only comment on airfoil characteristics and what may affect the efficacy of yours.
It is 'possible' that the speed control is faulty.
The optimum efficacy from the blades to the floor with an accessible boundary swept layer is 2.5 m.
The optimum distance from the blades to the ceiling is 300mm. 200mm is restrictive for a decent fan.
The optimum rake is 6 degrees.
The blade's pitch needs to match the motor's power for peak efficiency. If the pitch is too steep, the motor will struggle, too shallow and it won't move much air. Your fan has a small 45W motor and the foil pitch will almost certainly be shallow.
Most fans cannot perform at peak efficiency if the above conditions are not met and this is the case in most Australian houses. There are some very good fans available that have aerofoils engineered to aeronautic principles. If you are able, try to find a link to the BigAss fans design and testing department and see how a good fan is designed.
The Arlec fan is very basic in that it has flat blades that generate high drag wingtip vortices and bleed, the efficacy losses compounded by the close airfoil/ceiling separation zone. Increasing the revs from 146 rpm to 200 rpm may not give you the incremental improvement that you might be expecting.
Re: Ceiling Fan - underpowered9
Feb 27, 2017 7:01 am
thanks for your response, there was some very good details/analysis about the Arlec fan.
How about this HPM fan? Based on the same analysis that you did on the Arlec fan, how do you think this one would perform?
https://www.bunnings.com.au/hpm-1200mm- ... n_p4441507
Re: Ceiling Fan - underpowered11
Feb 27, 2017 7:34 pm
Link is no good.
What is your ceiling height?
A good house ceiling fan needs about 300mm space between the ceiling and the blades. The Arlec would have 200 mm because the small motor and the blade design does not require more. The short down rod would have sent a very BIG signal to me and the electrician should have known that and questioned your product choice.
Beware of people telling you to choose a fan with longer blades, bigger fans require a greater space between the blades and ceiling and are more suited to higher ceilings. Longer blades also generate more noise due to the blade's higher tip speed.
Fans also need an open lower swept boundary layer for peak circulation cooling efficiency because that is where the coldest air is. Having a fan sitting over furniture is less efficient than having it sit over an open area. Always give any fan its best opportunity to perform well.
BigAss fans are superbly designed to aeronautic principles and are highly efficient and economical. The large BigAss fans in Bunnings incorporate numerous aerodynamic narrow blades that add to the swept solidity ratio without increasing drag whereas wide blades have greater surface air flow separation (pressure drag).
The winglets that you will also see at the end of the aerofoils are there to reduce bleed and parasitic vortex drag. I am sure that you have seen passenger jets also fitted with winglets, they are fitted for the same reason.
If you see a fan with multiple narrow blades and winglets, it has been designed for engineered excellence rather than point of sale appeal like fans with wooden rattan blades are.
Fans are bought to serve a purpose and if you want good function, you have to be prepared to invest more to buy engineered quality. I personally like the BigAss Haiku range, not only for their efficiency but also because they are a modern stylish feature, not just an attachment.
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