View Full Version : Should freezer evaporator fan, run at all time??

11-04-2005, 07:55 PM
Hi guys,

I was commissioning a freezer 6M X 3m, -18c today,

While watching the temp dropping and adjusting the super heat and head pressure, a thought came to my little brain,
In a freezer room, if the unit is not in defrost mode, the fans work all the time.

When the unit have reached the set point, it stops.
The evaporator fans continue to run and circulate the air and slowly heating the room.

My issue is, why not let the fans run only when LSV is energised?

This will save money and the fans motors will last longer.

Your comments please.

Chemi :)

11-04-2005, 08:18 PM
The evaporator fans continue to run and circulate the air

Hi Chemi

This is exactly what happens with air conditioning so that the stat sensor can get a true reading. If you had a close control situation and the fans shut off with the compressor the control would be all over the place.

My thoughts are that evap fans on cold stores should only be off during defrost.

No doubt there will be differing opinions :)


I've taken your advice and I'm looking at hotels in Eilat - maybe for Xmas

11-04-2005, 08:33 PM
Hi Chemi,
The control sensor should be sensing the return air to the evaporator and not the air off. This controls the box temp. If the fans were allowed to cycle off with the lsv. then there is a possibility of hot and cold spots in dead areas which will effect the stock.

11-04-2005, 08:42 PM
I agree with chillymaster , if the fan goes off during the lsv is not energized may affect the stock . . .

11-04-2005, 09:22 PM
Thanks guys,

I agree on one thing only' there will be some very small temp differences in the room as it is closed most of the time.

Nothing will happened to the stock because the air will circulate just like in a fridge with a freezer at the top of the compartment and no fan is present :rolleyes:

Another solution for this minor problem is adding a very small fan behind the evaporator, blowing air at the sensor, starts when the evaporator fans stop.

I use this method at a cold storage for wine cellar, work like that for two years now and the owner said that he consumes less electricity.
In mini splits, in heating mode, the fan does not work when the
coil is below 30c.

I've taken your advice and I'm looking at hotels in Eilat - maybe for Xmas

Frank thats a good idea, I don't think you will regret it, needless to say that I might rive down to visit.

Chemi :)

12-04-2005, 01:44 AM
You need to leave the fans running, except in defrost mode. In a larger room you can get some statification of the air if you do not keep it stirred. Corners can get warmer as well as the upper prduct in a tall freezer and may take the product out of spec and damage the product. The small amount of energy used by the fan (and heat input to the room) is generally small compared to the external heat gain and infiltration load.

In large warehouses, that use a PLC control system, they are often controlled such that once the room is at temperature and the LLS (liquid solenoid valve) is closed, the fans will shut down after a period of satisfied time. BUT the fans are brought back on after a programed time to circulate the air and check the average room temperature. If during the fan run time, temperature is not met, the LLS is opened againand the cycle starts over.

So, in smaller spaces without PLC control, the fans are left to run to protect the product.


12-04-2005, 01:15 PM
Well Chemi, in most freezer rooms we install, we always shut off the fans when the LSV is shutted off for the reasons you mentioned.

The heatgain through the panels is +/- 500 W for the room Chemi mentioned (50 K over the 18 cm thick PU panels) so heat disipated by the fans is not that small at all compared to the heat gain.

The sensor is measuring air temperature with an extremely low specific mass compared to the stored product.
Result of this is when you open the freezer the air temperature raises very fast while the goods remain at the same temperature.
Most goods stored in a freezer have no latent heat or respiration heat anymore so temperature will stay relative stable.

We only let them run continuously in a blast freezer when the goods must be froozen very quickly. You then need many air changes per hour.

And we installed some times additional fans in a freezer to help stirring the air but this was in larger freezers.

So I'm not afraid for warmer corners in a freezer as long as everything well arranged in racks or boxes wit spacing between the goods. We did tests in the past in a storage freezer in a poultry factory and we measured differences smaller than 1C.

12-04-2005, 03:28 PM
Thanks Peter.

I will change the setting on the controller tomorow, RC - 43
and see how it goe's.

Chemi :)

26-05-2005, 11:19 AM
On the low temp Carel controller IR32COLBRO, from memory the default setting for the evaporator fans is to cycle off with the temp control.

The medium temp controllers the fans are set to run all the time.Another reason for not doing it on medium temp is because the air flow removes frost from the coil while the compressor is on an off cycle.

26-05-2005, 03:59 PM
I don't care of the manufacturer default.

I have set it so and it work less hours per day.

The three fans in this freezer, produce 0.8KW.

Chemi :)

26-05-2005, 08:21 PM
Another thing is, that if the motors are standing still for long periods, you should have motors with an internal heating element to prevent build up of ice in the motor.

27-05-2005, 04:36 AM
Ice weill build up only if there is moisture inside the motor which I doubt very much.

Chemi :)

27-05-2005, 12:09 PM
I don't care of the manufacturer default.

I have set it so and it work less hours per day.

The three fans in this freezer, produce 0.8KW.

Chemi :)


The reason I mentioned default settings was just to let you know that we have put these controllers on about 10 freezers in the last few years, the fans are running the way you have got them set now and we have had no problems at all by doing this.

I spoke to Technician from Carel about why they were set up this way and he said for energy saving. :)

27-05-2005, 04:57 PM
Yes , it saves a lot of energy.
I do not know how much but if customers feel the need to mention that the condensing unit run less time, it must be significant.

One more thing that I have noticed, is that the the defrost cycle is shorter, while fans are at rest, there is no ice build on the coil.

Chemi :)

29-05-2005, 07:02 PM
In my opinion freezer fan should not be Off.

1, If fan is off controller sensor could not give proper

PID action which in turn make the compressor run more

time and Entire cooling of the evaporator is not remov-


2, whole room temperater will not be homogenious,


21-06-2005, 04:55 PM
We always set it such away that the Fans cut-off when the temperature reaches set point - regardless whether the system cuts of the compressor on temperature OR with a LLSV and LP cut-out pumpdown system.

21-06-2005, 06:31 PM
Hi bersaga,

I am building at the moment a cold storage for a winery, its 50 sq/m by 3m high.

the evaporator is about 8 meters from where the heat is rejected, would you set the fans to stop on set point here?

Chemi :)

22-06-2005, 02:43 PM
Yes, I would. Once you have gone through the pulldown load and assuming you do not open the doors too often - the temperature inside will maintain to whatever set-point. Note that continous running of fans also adds heatload to the room - but not too much.

22-06-2005, 07:46 PM
Got your point.
Will give it a try in the next project. and post some pictures.

Chemi :)