Fan speed controllers

Ive been having issues recently with some danfoss optima condensers with high subcooling “over condensing”.

we are planning on fitting fan speed controllers to delay the fans running in low ambients but is there a rule of thumb when setting these?

Im after a quick reference to set them up quickly and then fine tune once running.

is there a temperature you lads are using so I can quickly check on a P-T chart and set accordingly depending on refrigerant.

Thanks

Howdy,
Saturation quivalent of +35 Celsius should be ok as a starting point
Cheers

Or, you can add a pressure control switch to start and stop one of the fans.

What's the problem with high subcooling?
What is for you overcondensing?

Would help if you clarify with any fault codes you are getting :)

The Optyma Meassures ambiant temperatures and controls the condenser fans as needed to maintain 8K subcooling.

Settings can be made in the controller, no need to add any extra regulators

Attachment 15326


http://files.danfoss.com/TechnicalIn...1/RS8GD302.pdf

I’m having problems with low head pressures due to the fan runing constantly when the comp runs during low ambient conditions.

This in turn is causing problems with my TEVs as I don’t believe they are receiving the refrigerate at the correct temp/pressure to operate correctly.

my idea was to fit a fan speed controller or a pressure control switch to increase my head pressure and therefore increase my liquid line temp/pressure at the TEVs.

hope this makes sense.

i use the term overcondensing meaning low head pressure during low ambiant conditions.

I’m only working on the small ompyma units with no front end controller

Quote:

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Originally Posted by Airconking

I’m having problems with low head pressures due to the fan runing constantly when the comp runs during low ambient conditions.

This in turn is causing problems with my TEVs as I don’t believe they are receiving the refrigerate at the correct temp/pressure to operate correctly.

my idea was to fit a fan speed controller or a pressure control switch to increase my head pressure and therefore increase my liquid line temp/pressure at the TEVs.

hope this makes sense.

i use the term overcondensing meaning low head pressure during low ambiant conditions.

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Is this a cold room or a freezing room?

What are ambiant temperatures in your area?

If you look at the picture I added in my previous post, the factory setting says that the Condenser fan should not run if ambient is below 10C, and you can adjust this temperature.

This is for the Optyma Plus with the EVO 3 controller.

Quote:

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Originally Posted by Tycho

Is this a cold room or a freezing room?

What are ambiant temperatures in your area?

If you look at the picture I added in my previous post, the factory setting says that the Condenser fan should not run if ambient is below 10C, and you can adjust this temperature.

This is for the Optyma Plus with the EVO 3 controller.

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These units are the optyma slimpacks, no front end controller like the optima plus models.

the fan runs when the comp runs, very basic system hence wanting to control the fan myself.

the system is feeding a freezer at -17’c and ambiants at the moment are between -5’c and +10’c depending on time of day.

Quote:

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Originally Posted by Airconking

These units are the optyma slimpacks, no front end controller like the optima plus models.

the fan runs when the comp runs, very basic system hence wanting to control the fan myself.

the system is feeding a freezer at -17’c and ambiants at the moment are between -5’c and +10’c depending on time of day.

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I see :)

Even with -5 to +10C ambient, I don't really see how it would interefere with -17 evap temp, but I'll take your word for it :)

The optyma slimpacks has connection points for fan speed controllers
See here to find your make https://assets.danfoss.com/documents...3723558119.pdf

If I had to set a default condensing pressure, I would have gone for 25 or 30°C for whatever refrigerant you are running on, that's always a safe bet :)

Quote:

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Originally Posted by Tycho

I see :)

Even with -5 to +10C ambient, I don't really see how it would interefere with -17 evap temp, but I'll take your word for it :)

The optyma slimpacks has connection points for fan speed controllers
See here to find your make https://assets.danfoss.com/documents...3723558119.pdf

If I had to set a default condensing pressure, I would have gone for 25 or 30°C for whatever refrigerant you are running on, that's always a safe bet :)

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Thanks tycho

I’ll have a play around next time I’m on site with it. just feel it was condensing to low hence not feeding to the TEV correctly and I was having issues with the coil freezing but only on the bottom half.
if I fit a pressure controll switch or speed controller I can control the head pressure a little better and hopefully solve the problem.
thanks again.

Quote:

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Originally Posted by Airconking

Thanks tycho

I’ll have a play around next time I’m on site with it. just feel it was condensing to low hence not feeding to the TEV correctly and I was having issues with the coil freezing but only on the bottom half.
if I fit a pressure controll switch or speed controller I can control the head pressure a little better and hopefully solve the problem.
thanks again.

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Is the evaporator superheat set by a electronic valve or a thermostatic expansion valve?

Just asking, because any subcooling you have on the high side is a bonus once it gets to the expansion valve.

If the bottom half of the evaporator is icing over, I am more inclined to think it has something to do with the defrost timer or placement of a deforst sensor.

if it's a pump down system, with electrical defrost, it could be that the defrost temperature sensor is placed at a bad location so it gets warm too fast, and/or the defrost timer is set to short and stops the defrost before the coil is fully defrosted.

Or

in one absurd case I had, that the solenoid feeding the evaporator has a slight leak, so the compressor kept running during the defrost cycle.

and another case, the evaporator was directly above the door to the room, so every time they went in or out, the warm humid air from outside went straight up into the evaporator and turned it into an icecube :)

Had I been you, I would have first checked the placement of the evaporator, that it is not above or close to any doors, second, observed the evaporator during a full defrost cycle to make sure it was fully defrosted, and that it wasn't just partially de-iced, made sure that the compressor properly pumped down when a defrost cycle started (it might start or stop a few times) but it should'nt start and stop continously during defrost.

I'm assuming this because you say you were having issues with the bottom half of the coil freezing, I understood this as the bottom half of the coil is icing over <--- if this is the case, then check the defrost

if by bottom half freezing, you mean only the bottom half of the coil is getting cold, then check the superheat across the evaporator, because either it is to high, or there is not enough liquid in the system. most optyma Units have a liquid sight glass, but it's placed close to the condensing unit so if the evaporator is some ways away, you can't tell if you have clean liquid all the way to the TEV)

your last post provided the last piece of the puzzle, and I can tell you that the problem is not the subcooling of the liquid from the condenser, it's either the defrost timer, defrost sensor placement (icing over), leaking solenoid, TEV setting or not enough refrigerant (only icing on lower half and icing over). pretty sure this has nothing to do with the subcooling of the liquid leaving the condenser.

I'm guessing the system only has a sight glass on the liquid leaving the condensing unit (if at all), so you don't really know if there is pure liquid coming to the TEV.

I'd have started by checking the defrost amd that it was properly deiced before a new freezing cycle started, boring and time consuming, I know, but it has to be done :)

Quote:

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Originally Posted by Tycho

Is the evaporator superheat set by a electronic valve or a thermostatic expansion valve?

Just asking, because any subcooling you have on the high side is a bonus once it gets to the expansion valve.

If the bottom half of the evaporator is icing over, I am more inclined to think it has something to do with the defrost timer or placement of a deforst sensor.

if it's a pump down system, with electrical defrost, it could be that the defrost temperature sensor is placed at a bad location so it gets warm too fast, and/or the defrost timer is set to short and stops the defrost before the coil is fully defrosted.

Or

in one absurd case I had, that the solenoid feeding the evaporator has a slight leak, so the compressor kept running during the defrost cycle.

and another case, the evaporator was directly above the door to the room, so every time they went in or out, the warm humid air from outside went straight up into the evaporator and turned it into an icecube :)

Had I been you, I would have first checked the placement of the evaporator, that it is not above or close to any doors, second, observed the evaporator during a full defrost cycle to make sure it was fully defrosted, and that it wasn't just partially de-iced, made sure that the compressor properly pumped down when a defrost cycle started (it might start or stop a few times) but it should'nt start and stop continously during defrost.

I'm assuming this because you say you were having issues with the bottom half of the coil freezing, I understood this as the bottom half of the coil is icing over <--- if this is the case, then check the defrost

if by bottom half freezing, you mean only the bottom half of the coil is getting cold, then check the superheat across the evaporator, because either it is to high, or there is not enough liquid in the system. most optyma Units have a liquid sight glass, but it's placed close to the condensing unit so if the evaporator is some ways away, you can't tell if you have clean liquid all the way to the TEV)

your last post provided the last piece of the puzzle, and I can tell you that the problem is not the subcooling of the liquid from the condenser, it's either the defrost timer, defrost sensor placement (icing over), leaking solenoid, TEV setting or not enough refrigerant (only icing on lower half and icing over). pretty sure this has nothing to do with the subcooling of the liquid leaving the condenser.

I'm guessing the system only has a sight glass on the liquid leaving the condensing unit (if at all), so you don't really know if there is pure liquid coming to the TEV.

I'd have started by checking the defrost amd that it was properly deiced before a new freezing cycle started, boring and time consuming, I know, but it has to be done :)

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signt glass located at the condenser and it’s running with a TEV.... defrost probe located in a good position at the top end of the coil away from the heaters.
Evaporators located at the back of the freezer away from the door.
Ill Check afew things suggested next time I visit and hopefully get to the bottom of the problem

This situation happens every cold winters day when condenser fans are not controlled correctly. When the TEV is selected for the job the valve is capacity sized for summer conditions . But when winter comes the air over the condenser reduces the condensing pressure to a point where the valves rated capacity is reduced due to the lower pressure drop across the valve ( condenser pressure / evaporator pressure) the force to push the refrigerant through its orifice has been reduce, this causes a lower evaporator temperature causing the evaporator to ice up and often cut out on low pressure. The unit can no longer achieve design temperature.
TEV’s have a limited capacity band and when the condensing pressure can vary so much ie Summer 30 deg C (13.5Bar)/ Winter -5 deg C (4.2Bar)on R404A Evaporating at minus 17 degC (2.4Bar) so summer conditions 13.5 Bar - 2.4Bar = 11.1Bar delta p across the TEV , winter conditions 4.2 Bar - 2.4Bar = 1.8 Bar delta p across the TEV . So if the condensing condition is allowed to fall with the ambient then the pressure drop across the Tev will drop and the evaporator will be starved of refrigerant. THIS IS WHY FAN SPEED CONTROLLERS AND HEAD PRESSURE CONTROL SYSTEMS are available to overcome major variances in condensing conditions summer to winter. T
This is why split a/c units have fan speed controllers to maintain a decent pressure difference across the cap tube or bullet to maintain a good evaporator pressure summer and winter. If you can’t fit a fan speed controller get a piece of cardboard and blank of a small piece of the condenser to raise the discharge pressure but not to high to cause HP trips ( Tight arse solution )

Quote:

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Originally Posted by Glenn Moore

This situation happens every cold winters day when condenser fans are not controlled correctly. When the TEV is selected for the job the valve is capacity sized for summer conditions . But when winter comes the air over the condenser reduces the condensing pressure to a point where the valves rated capacity is reduced due to the lower pressure drop across the valve ( condenser pressure / evaporator pressure) the force to push the refrigerant through its orifice has been reduce, this causes a lower evaporator temperature causing the evaporator to ice up and often cut out on low pressure. The unit can no longer achieve design temperature.
TEV’s have a limited capacity band and when the condensing pressure can vary so much ie Summer 30 deg C (13.5Bar)/ Winter -5 deg C (4.2Bar)on R404A Evaporating at minus 17 degC (2.4Bar) so summer conditions 13.5 Bar - 2.4Bar = 11.1Bar delta p across the TEV , winter conditions 4.2 Bar - 2.4Bar = 1.8 Bar delta p across the TEV . So if the condensing condition is allowed to fall with the ambient then the pressure drop across the Tev will drop and the evaporator will be starved of refrigerant. THIS IS WHY FAN SPEED CONTROLLERS AND HEAD PRESSURE CONTROL SYSTEMS are available to overcome major variances in condensing conditions summer to winter. T
This is why split a/c units have fan speed controllers to maintain a decent pressure difference across the cap tube or bullet to maintain a good evaporator pressure summer and winter. If you can’t fit a fan speed controller get a piece of cardboard and blank of a small piece of the condenser to raise the discharge pressure but not to high to cause HP trips ( Tight arse solution )

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see, working on larger systems I don't have to think about stuff like this :D

Well said and information taken to heart (to remember) :)

Hope Airconking figures it out :)

Quote:

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Originally Posted by Glenn Moore

This situation happens every cold winters day when condenser fans are not controlled correctly. When the TEV is selected for the job the valve is capacity sized for summer conditions . But when winter comes the air over the condenser reduces the condensing pressure to a point where the valves rated capacity is reduced due to the lower pressure drop across the valve ( condenser pressure / evaporator pressure) the force to push the refrigerant through its orifice has been reduce, this causes a lower evaporator temperature causing the evaporator to ice up and often cut out on low pressure. The unit can no longer achieve design temperature.
TEV’s have a limited capacity band and when the condensing pressure can vary so much ie Summer 30 deg C (13.5Bar)/ Winter -5 deg C (4.2Bar)on R404A Evaporating at minus 17 degC (2.4Bar) so summer conditions 13.5 Bar - 2.4Bar = 11.1Bar delta p across the TEV , winter conditions 4.2 Bar - 2.4Bar = 1.8 Bar delta p across the TEV . So if the condensing condition is allowed to fall with the ambient then the pressure drop across the Tev will drop and the evaporator will be starved of refrigerant. THIS IS WHY FAN SPEED CONTROLLERS AND HEAD PRESSURE CONTROL SYSTEMS are available to overcome major variances in condensing conditions summer to winter. T
This is why split a/c units have fan speed controllers to maintain a decent pressure difference across the cap tube or bullet to maintain a good evaporator pressure summer and winter. If you can’t fit a fan speed controller get a piece of cardboard and blank of a small piece of the condenser to raise the discharge pressure but not to high to cause HP trips ( Tight arse solution )

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glenn
this is what I believe to be happening although you worded it much better.
my 1st plan will be to install some sort of fan controll and go from there.
thanks

This situation happens to many small systems due to low condensing temperatures during winter not being taken into account when the system is designed . Every small condensing unit that has to operate through summer and winter where the condenser is subject to the variances of ambient conditions must have some type of head pressure control fitted to maintain the summer design conditions throughout the year to maintain the correct system operation.
TEV’s can and do work with a reduced delta P but only to a point . The lower discharge pressure causes a lower refrigerant flow into the cooler causing major ice build up issues and often LP trips.
The term “over condensing “ in this scenario often crops up and “increased sub cooling “ is another term used.
Over condensing or “really” lower condensing condition is the result where no head pressure control have been installed . These could be either fan pressure switches , fan speed controllers or condenser liquid back up systems.
Pressure switch control is the worst due to the wide diff setting causing system and expansion valve instability
Liquid back up systems are ok but can be slow to control due to the size and volume of liquid required to function
Fan speed is by far the best method when set up correctly
Increased sub cooling is also a resultant condition of lower condensing temperatures. As the ambient drops and the colder air is drawn across the condenser the condenser pressure drops accordingly . The reduce delta P across the TEV causes liquid to back up in the condenser , the condensed liquid becomes colder “sub cooled” but where normally increasing the sub cooling enhances the system and TEV capacity due to the lower delta P in this scenario it is not the case . All that happens is the system doesn’t work properly anymore , with the resultant fed up customer all due to a lack of thought during the design and installation process

Danfoss make some nice little fan speed controllers that just screw onto a 1/4 flare fitting, they do two types, one has a minimum speed for the fan, and the other a cut off one where the fan stops when its really cold, i'd get the cut off version as even the minimum speed can be too high with some units.

Quote:

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Originally Posted by monkey spanners

Danfoss make some nice little fan speed controllers that just screw onto a 1/4 flare fitting, they do two types, one has a minimum speed for the fan, and the other a cut off one where the fan stops when its really cold, i'd get the cut off version as even the minimum speed can be too high with some units.

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Thanks monkey spanner’s.... I’ll take a look