Fan speed controllers

[Airconking]

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

[HVACRsaurus]

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

[chemi-cool]

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

[Peter_1]

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

[Tycho]

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

optymacond.jpg


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

[Airconking]

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

[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.

[Tycho]

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.

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.

[Airconking]

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.

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.

[Tycho]

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.

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

[Airconking]

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

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.

[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 )

[Tycho]

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 )

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

Well said and information taken to heart (to remember)

Hope Airconking figures it out

[Airconking]

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 )

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

[Glenn Moore]

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

[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.

[Airconking]

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.

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