I’ll be frank. District Councils are paying less than lip service to conditions of consent that are imposed on frost fan installations.
This is truer than ever in regards issues related to noise.
Why is this?
Two reasons.
(1) They need to impose conditions in order to ensure that the population is provided some protection from unreasonable noise (per the Resource Management Act) and nuisance (per the Health Act). So it’s not like they can just allow open slather for vineyards to install them wherever and whenever they want.
(2) They haven’t worked out how to do it.
“What?” I hear you say.
“They impose conditions and don’t check them?”
Yes.
Why do they not check for compliance?
Because they can’t figure out how to carry out a noise check on a fan quickly and without a large number of other factors affecting the measurement.
Let me introduce a short exchange from an Environment Court Hearing 16/05/2008 between myself and a Mr Heather from the Marlborough District Council;
MR MACLEAN: Do you know how the council enforces the standards in rule 1.4.2.3 for those frost fans, to make sure that they’re compliant?
MR HEATHER: You’re talking noise limits here?
MR MACLEAN: Yes.
MR HEATHER: Currently it’s my understanding – and again this is handled by our compliance section rather than our consent section – that we monitor by complaint. But I’m also aware that council is discussing a strategy to monitor frost fans, but I can’t say any more than that.
MR MACLEAN: No. So there’s nothing in place that you’re aware of?
MR HEATHER: No.
MR MACLEAN: They don’t test them before or after that you’re aware of?
MR HEATHER: No.
So then the Marlborough District Council (and by extension the residents in Marlborough) have a problem.
They have granted consents to operate frost fans under certain conditions and they can’t monitor those conditions.
If it’s one thing I’ve learned in life, it’s no good complaining that something’s broken unless you have a solution for fixing it.
So here is a tidy summary of the situation and in my next post I will provide several solutions to the problem.
What generates the noise from a frost fan?
There are two major components to the noise
(1) The motor.
(2) The rotation of the fan.
In all instances that I have encountered while researching frost fan noise issues, the major source of noise is always the fan.
Why?
Because the fan has to operate at a high speed in order to become aerodynamically efficient enough to do its job of drawing down the warmer air from the inversion layer to blow across the crop below.
When the fan operates at that high speed, a major side effect is noise as it thrashes the air.
A motor can always be silenced. An acoustic shroud installed, a muffler attached and/or the exhaust directed into a pit. But the blade will always have to turn quickly.
It’s that simple. The rotation of the fan creates the majority of the noise.
So if you know how much noise a frost fan makes at a certain value of revolutions per minute you can set that value as the limit that an individual fan can operate at.
For example;
(1) A common condition of consent is that a frost fan does not produce more than 55dBA L10 at 300 metres.
If the installer provides documentation that a fan produces 55dBA L10 while it is rotating at 2000rpm, then measure the rpm of the fan. Don’t bother trying to measure the noise.
(2) If a land owner has met the noise conditions that I outlined in my previous post on finding the ideal noise levels, then the amount of noise produced does not have to be re-measured to confirm compliance. Just the confirm the rpms of the fans when they were first installed and set.
So why is it easier to measure fan rpm rather than noise level?
Stay tuned for my next post.
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