Daikin indoor fan control logic

[mchild]

I have a Daikin VRV-S system with ducted FXSQ indoor units. I am curious how the fan control logic works with these units.

From what I can tell from observing the operation, if the unit is set at the controller for High fan, the system will change the fan speed between the Low and High setting. If the unit is set at the controller for Low fan there is no changing of the fan speed. Thus, the controller setting of the fan speed determines the maximum speed not the constant speed.

So my question is, when set to High fan, what determines whether an indoor unit is operating in Low or High fan? Rate of change in Delta T?

Is the control logic the same for cooling and heating?

Thank you for your help.

[El Padre]

Hi,

Is the fan set on auto mode? The control logic differs slightly from cooling and heating because the fan will not start immediately in heating mode untill the coil reaches a predetermined temperature. Has somebody changed the static pressure settings on the fan coils?

Cheers

[nicolacozma]

Cooling Mode
thermostat ON - fan speed could be H or L as selected from BRC
thermostat OFF - fan keep the speed as for thermostat ON

Heating Mode
thermostat ON -hot start control - fan speed became H or L as selected from BRC
thermostat OFF - LL speed as standard (or SET or OFF depending by field settings on BRC)

Hot start control start conditions: after defrost ending or oil return ending or thermostat ON

Hot start control ending conditions:
gas thermistor on indoor HEX >34degree
OR
saturated condensing temperature > 52degree
OR
lapse of 3 minutes

Hot start control
step1
indoor fan OFF till Tc>35degree OR lapse 300sec
step2
indoor fan LL till Tc>35degree AND step2>60 sec OR Tc>50degree OR lapse 120sec
step3
indoor fan L till Tc>35degree AND step3>60 sec OR Tc>50degree OR lapse 60sec
step4
indoor fan SET speed H or L


Maybe in your case, putting the fan in H speed, will cooldown the indoor heat-exchanger, this fact is sensed by gas thermistor and the unit take the decision to reduce the speed of the fan in order to increase the temperature of the hex.

Normally the unit have to be capable to maintain stable operation condition for the fan.

If this stable operation condition are not reached the reason could be: shortage of refrigerent, indoor air temperature too low, decalibrated gas thermistor.

Hope this could be usefull for you.

[mchild]

Hi,

Is the fan set on auto mode? The control logic differs slightly from cooling and heating because the fan will not start immediately in heating mode untill the coil reaches a predetermined temperature. Has somebody changed the static pressure settings on the fan coils?

Cheers

El Padre,

Thanks for replying. Let me explain a little more how my system is set up to operate.

The system has one wire remote controller. I have set the fan with each indoor unit to go off in both heating and cooling mode when there is not a call for heat or cool. Also, I do not have Auto for fan available on my controller. After my system was installed a couple of months ago I asked on this board how to get the Auto Fan. I never did get a response. I was told how to set the controller for Auto changeover from heat to cool and back, but not the Auto fan.

Static pressure setting is the factory set at medium.

I understand the fan delay on heating as to not have a rush of cold air. What I am trying to understand is what determines when the fan will be in Low and when it will be in High during the operation of the indoor unit in either heating or cooling. Even though I do not have Auto showing on the controller the fan speed of the indoor units does seem to operate in an Auto mode moving from Low to High and back on a regular basis.

[mchild]

Cooling Mode
thermostat ON - fan speed could be H or L as selected from BRC
thermostat OFF - fan keep the speed as for thermostat ON

Heating Mode
thermostat ON -hot start control - fan speed became H or L as selected from BRC
thermostat OFF - LL speed as standard (or SET or OFF depending by field settings on BRC)

Hot start control start conditions: after defrost ending or oil return ending or thermostat ON

Hot start control ending conditions:
gas thermistor on indoor HEX >34degree
OR
saturated condensing temperature > 52degree
OR
lapse of 3 minutes

Hot start control
step1
indoor fan OFF till Tc>35degree OR lapse 300sec
step2
indoor fan LL till Tc>35degree AND step2>60 sec OR Tc>50degree OR lapse 120sec
step3
indoor fan L till Tc>35degree AND step3>60 sec OR Tc>50degree OR lapse 60sec
step4
indoor fan SET speed H or L


Maybe in your case, putting the fan in H speed, will cooldown the indoor heat-exchanger, this fact is sensed by gas thermistor and the unit take the decision to reduce the speed of the fan in order to increase the temperature of the hex.

Normally the unit have to be capable to maintain stable operation condition for the fan.

If this stable operation condition are not reached the reason could be: shortage of refrigerent, indoor air temperature too low, decalibrated gas thermistor.

Hope this could be usefull for you.

nicola,

Your description of the hot start control looks like what may be happening when I am hearing the fan run at different speeds. Since my system is set to have the fan off when thermostat is off how would that change the sequence of steps shown in your hot start description.

I take this to mean that in cooling mode the fan would not perform as it is now doing in heat mode which is based on the hot start control. In cooling the fan will run at the one speed set on controller. If I get my controller to show Auto fan, will that change how the fan is controlled in cooling?

[nicolacozma]

mchild,

Since my system is set to have the fan off when thermostat is off how would that change the sequence of steps shown in your hot start description.
Hot start control procedure became active only during thermostat ON.


I take this to mean that in cooling mode the fan would not perform as it is now doing in heat mode which is based on the hot start control. In cooling the fan will run at the one speed set on controller.
Hot start control is available only in heating mode. In cooling your statement is correct.


If I get my controller to show Auto fan, will that change how the fan is controlled in cooling?
There isn`t Auto Fan mode on Daikin VRV indoor units.

For the units with auto fan mode the fan operate as follows: bigger difference between setpoint temp and return air temp higher speed will be set on fan, and lower differente on temperature will decrease the speed of the fan.

[back2space]

I understand what your asking for. My system does the same if you set high fan speed in cooling, it will operate in high fan speed until set point is reached then it will default back to low to continue air circulation, speeding back upto high when the temperutre has increased and cooling has started again.

In heating its the same again it will continue in high speed until set point reached and then it will continue in low and if temp reaches another 1C over the set point outdoor unit will switch off.


El Padre,

Thanks for replying. Let me explain a little more how my system is set up to operate.

The system has one wire remote controller. I have set the fan with each indoor unit to go off in both heating and cooling mode when there is not a call for heat or cool. Also, I do not have Auto for fan available on my controller. After my system was installed a couple of months ago I asked on this board how to get the Auto Fan. I never did get a response. I was told how to set the controller for Auto changeover from heat to cool and back, but not the Auto fan.

Static pressure setting is the factory set at medium.

I understand the fan delay on heating as to not have a rush of cold air. What I am trying to understand is what determines when the fan will be in Low and when it will be in High during the operation of the indoor unit in either heating or cooling. Even though I do not have Auto showing on the controller the fan speed of the indoor units does seem to operate in an Auto mode moving from Low to High and back on a regular basis.

[mchild]

mchild,

Hot start control procedure became active only during thermostat ON.


Hot start control is available only in heating mode. In cooling your statement is correct.


There isn`t Auto Fan mode on Daikin VRV indoor units.

For the units with auto fan mode the fan operate as follows: bigger difference between setpoint temp and return air temp higher speed will be set on fan, and lower differente on temperature will decrease the speed of the fan.

Thank you.

Why would Auto fan NOT be used with VRV? Not using it makes no sense as these are supposed to be the most advance systems for comfort.

[mchild]

I understand what your asking for. My system does the same if you set high fan speed in cooling, it will operate in high fan speed until set point is reached then it will default back to low to continue air circulation, speeding back upto high when the temperutre has increased and cooling has started again.

In heating its the same again it will continue in high speed until set point reached and then it will continue in low and if temp reaches another 1C over the set point outdoor unit will switch off.


back2space,

Do you have VRV-S?

I think what you say for heating is similar to what my system is doing. I have not used it in cooling mode but since I have mine programed for fan off when thermostat is off then I don't think mine will go to Low in cooling but will either be on High when unit is on or off when unit is off. There will not be any Low speed operation in cooling as there is now in heating. I think the reason there is in heating has to do with the hot start feature nicola was describing when in heat mode which does control the fan speed.

[brunstar]

they are sophisticated systems and the auto fan is not avaliable to select on your controller. it will select it automatically as stated in previous posts on coil temp and DT. you will be best to leave it at the default so that it runs on low low fan speed on heating and fixed on cooling to give you truer temperatures and to also dry the coil out on cooling once the unit has cycled off, running it fan off on cooling will make your fan coils smell after a season or two.
I don't see why you want to stop the fan?, on heating the hot air may stratify in the duct work and lag the system coming back on on heating..up to you though.

[Thermatech]

So

Who are you gathering this information for ?

Korean manufacturer ?
or
China manufacturer ?

They would like copy all this stuff from the Japs also.

[mchild]

So

Who are you gathering this information for ?

Korean manufacturer ?
or
China manufacturer ?

They would like copy all this stuff from the Japs also.

Ha, nothing quite so exciting as international corporate espionage. Just trying to understand this sophisticated system. Here in the US we have little that offers the level of sophistication so understanding how our typical system functions is rather simple.

These systems though have so much more and since few companies install or work on them here there are not many people who understanding how they work. I am just trying to be better aware.

But, I will say that the most advanced communicating systems that we do have here in the US are transparent in how they operate with the manufacturer providing detailed written documentation as to the sequence of steps and the logic control behind the control system.

[mchild]

they are sophisticated systems and the auto fan is not avaliable to select on your controller. it will select it automatically as stated in previous posts on coil temp and DT. you will be best to leave it at the default so that it runs on low low fan speed on heating and fixed on cooling to give you truer temperatures and to also dry the coil out on cooling once the unit has cycled off, running it fan off on cooling will make your fan coils smell after a season or two.
I don't see why you want to stop the fan?, on heating the hot air may stratify in the duct work and lag the system coming back on on heating..up to you though.

brunstar,

While it does seem like the system does a good job of managing the fan speed in heating I do not understand the reason it does not change the fan speed in cooling.

There are many times when there is a low cooling load but the high fan speed will maintain a high sensible cooling capacity while the latent capacity is diminished. Often we have a low sensible load and high latent load. If the system were to set the fan speed based on DT in cooling then it would better manage that condition with out having to set the unit in Dry mode - it would be automatic.

Of course, I am talking theory here as I have not used my system in cooling. I bought this system because I am confident it will do a good job of managing the entire cooling load. I'm just trying to understand how it functions.

As to the fan off when thermostat is off. I have a two story home. With the default setting of fan in LL in heat when thermostat is off caused the second story of my home to over heat. Thus, even though the two units for the second story were not calling for heat, but since the EEV does not fully close for oil return purposes, the space significantly over heated. I am sure some of this occured as heat from the first story rose to the second story.

Since making the change to fan off each of the four units maintains the set temp very closely - there is no overheating at all. I am sure the remote sensors help with this.

The reason I want the fan off in cooling is to reduce the re-evaporation of the condensate from the coil and in the drip pan. There are studies that have shown a significant increase in humidity in the conditioned space when the fan is not off when the thermostat is off.

[brunstar]

fair enough but the reason the fan runs all the time is to give you good even air flow which will elliminate hot spots and dead areas, i just feel that the humidity added back into the air will be minimal as the unit should have adequate drainage.
i would leave the fan on but it is not my unit and if you are happy to do what you are doing that is ok.
if you are suffering from stratification on the upper level the setpoint may need to be varied depending on where the air is going. but on heat you really need to keep pushing the heat down to the occupants level. sounds like you have it under control.

[back2space]

back2space,

Do you have VRV-S?

I think what you say for heating is similar to what my system is doing. I have not used it in cooling mode but since I have mine programed for fan off when thermostat is off then I don't think mine will go to Low in cooling but will either be on High when unit is on or off when unit is off. There will not be any Low speed operation in cooling as there is now in heating. I think the reason there is in heating has to do with the hot start feature nicola was describing when in heat mode which does control the fan speed.

Nope but its an energy saving feature. If its reached its set point then whats the need to blow air at higher speed than low when temp is already achieved.

[brunstar]

you already staed that you have the fan off on setpoint so it is not running on low low fan speed.
I was talking about on cooling you can select the low fan speed and leave it on that so that you don't get the hot spots and dead areas. the low low is designed to give you true air temperature readings keeping the air mixed.

[mchild]

you already staed that you have the fan off on setpoint so it is not running on low low fan speed.
I was talking about on cooling you can select the low fan speed and leave it on that so that you don't get the hot spots and dead areas. the low low is designed to give you true air temperature readings keeping the air mixed.

I am aware on setting the fan speed when t-stat is off in heat mode using field code 12(22)-3. But how do you set the fan speed in cooling when t-stat is off? From what I understand it stays at the same speed as t-stat on. If, as you say, I can set the fan to low when t-stat is off in cooling then I may try that instead of the fan off.