Two fans, one speed control???

[monkey spanners]

In an effort to save money on a quote i'm considering running two condenser fans off of one speed control, i don't much like the idea but other than a gut feeling of wrongness does anyone have any technical reasons why not to?

Other options are to put a baffle in the condenser and run one fan dol and the other on the speed controller.

Are those danfoss fsc any good? I've not been impressed by the alco ones which seem to fail for fun.

cheers Jon

[chemi-cool]

Hi Jon,
Check the ebmpapst fans, they come with built in speed controller.
www.ebmpapst.com

[monkey spanners]

Cheers Chemi,

This is for an existing system, we are quoting to fit a heat recovery system to it, so no opertunity to specify fans with built in speed controls.

[Quality]

Don`t tell me its for some poor farmers milk tank who happens to be skint:D.

I can see where your concerns lie but so long as the two motors combined don`t exeed the rating of the contoller there should be no problem

[chemi-cool]

Cheers Chemi,

This is for an existing system, we are quoting to fit a heat recovery system to it, so no opertunity to specify fans with built in speed controls.

In that case, one controller will do the job, check that its amp capacity is 20% more then the two existing fans.
Motor protection should be mounted on each line between the speed controller and each fan.
That is if you use motor protection.

[monkey spanners]

Don`t tell me its for some poor farmers milk tank who happens to be skint:D.

I can see where your concerns lie but so long as the two motors combined don`t exeed the rating of the contoller there should be no problem

I see you're no stranger to poor farmers, no money for the cooling equipment but 70k for a new jcb or tractor.
On one farm i was waiting for the tanker to empty the tank so i could fix the washing system and the customer came over and complained that he didn't expect to pay me for standing around so i took some money off the bill to keep him happy. Later i found out from his herdsman that he had a maserati in the garage :rolleyes::(

Thanks for the replies, anyone tried those danfoss fan speed controls? any problems with them?

Cheers Jon

[supra_84]

In theory it will work, but in principal there should be 2 one for each compressor. For isolation purposes more then anything, But i guess if its a Fabdec they dont normally bother with isolators and mount the control box next to the comps.
The Heat Recovery Units we have been fitting just have Head Pressure Valves but i guess thats more money again.

[Quality]

. Later i found out from his herdsman that he had a maserati in the garage :rolleyes::(

danfoss

Cheers Jon

Farmers :(

never used danfoss speed controlers so I couldn`t say but their gear is normaly not to bad

[old gas bottle]

i like the danfoss type with the capillary on as opposed to the aco or whatever with a sensor,2 mins to set up and not had a failure yet !, and yes i have run a pair of fans off one ,no probs either.:)

[monkey spanners]

Cheers OGB,

Danfoss it is then :D

[mad fridgie]

Hey Monkey, slightly off subject (sorry) its been 20years since doing milk vats in the UK, i believe now a days farms are bigger (more moo moos)
Do they used non refrigerated water for pre-cooling,
Do they use refrigerated fluid for pr-cooling.
What is a common size vat and what size refrig unit would they have
cheers
mad

[VRVIII]

In an effort to save money on a quote i'm considering running two condenser fans off of one speed control, i don't much like the idea but other than a gut feeling of wrongness does anyone have any technical reasons why not to?

Other options are to put a baffle in the condenser and run one fan dol and the other on the speed controller.

Are those danfoss fsc any good? I've not been impressed by the alco ones which seem to fail for fun.

cheers Jon

Hi Jon,
Have you considered the Johnson P215 range of fan speed controllers, I have been using these for years to control twin fan ac units and have never had any problems.
They are available with a range of 8~14 bar or 14~24 bar and use a pressure transducer rather than a sensors to provide much faster response time and far more accurate head pressure control.
They also have a wide range of adjustments possible, operating pressure with either fan cut out or min speed adjustment. When using min speed always check the max running current for the motor(s), then check current draw while setting min fan speed (I normally set this so that the min speed draws about 10% less than max current)
See below link for controller details:
http://webmanuals.lennoxeurope.com/Current%20Products/Controls/Varios%20controls/Johnson%20controls/Johnson%20P215LR_BR.pdf

[monkey spanners]

Hey Monkey, slightly off subject (sorry) its been 20years since doing milk vats in the UK, i believe now a days farms are bigger (more moo moos)
Do they used non refrigerated water for pre-cooling,
Do they use refrigerated fluid for pr-cooling.
What is a common size vat and what size refrig unit would they have
cheers
mad

Yeah the farms are getting bigger, got few with 2/300 cows sending 30,000L every other day.

Most have mains or bore hole water pre-cooling, some also have chilled water as well either with a two stage plate cooler or two seperate one.
Most vat sizes are between 7000L and 15000L though there are still quite a few old 600g and 750g fullwoods still working.
On the old icebank milk tanks it always 1hp per 200g of volume, but on the new dx and icebank tanks it varies depending on if they are on every day or alternate day milk pick up, if they have pre cooling, how quick the parlour is, etc.

I look after a 15000L dx tank with two 9hp scrolls on it that can cool the milk quicker than they can fill it!
And have recently installed a second hand 21000L chilled water tank with seperate ice builder that has two 7.5hp scrolls on it, this has bore hole water and chilled water to a two stage floor mounted plate cooler, and ice water to a plate in the tank, this setup drops the milk in the tank at 4.5c from 36c in the plate cooler and to 3.5c in the tank :)
I'll get some vids on youtube next time i get a chance.

Cheers VRVIII,

Those johnson P266 fsc look a good job, the one that does up to three aux fans would be just the job, if its not too much money.

Jon

[VRVIII]

Jon,

I think you will find the P266 to be quite expensive but the P215 are about £150 and available form most suppliers. Just wire the two fans in parallel providing the total current doesn’t exceed the 3 amp rating of the FSC. Done this loads of times and never had any problems.

[monkey spanners]

Jon,

I think you will find the P266 to be quite expensive but the P215 are about £150 and available form most suppliers. Just wire the two fans in parallel providing the total current doesn’t exceed the 3 amp rating of the FSC. Done this loads of times and never had any problems.


Cheers, i'll get some prices from the wholesalers tomorrow :)

[Scramjetman]

Hi Monkey,

I've been using Danfoss for a few years now and find their FSD's pretty robust. Not really good practice to run more than 1 fan per controller but have seen it done a few times (again in an effort to win the job that's being awarded on price - please note: the tender system sucks) and they seem to operate reasonably well. Bear in mind, they MUST be identical motors. There is a fair bit of trickiness with variable frequency control and out of balance currents that circulate in the systems due to differences in motor construction ( ie: no two sets of laminations are ever the same - even in two same sized motors) so even mixing up two same sized motors from different manufacturers can cause all sorts of expensive problems.

All the best with that.