Daikin VRV electric heater control

[mchild]

I have attached a page from the VRV training manual where they speak of controlling a separate heater using an adapter board. Would that be the KRP1B board or is there another board for this? The KRP1B has a power connection to be connected at the main power connection terminal of the indoor unit. Here in the U.S. the wiring diagrams never shows this board connected to the main power. Is it necessary to connect for the heater control function to work and will it work on our 60Hz power (the board specs show it is as 230v 50Hz where our electric is 240v 60Hz)?

As shown in the attachment certain conditions have to be present for the heater to be switch on and off. It looks like the temp of the liquid pipe would be the final controlling parameter with a change of 4*C at the liquid pipe. What does this translate to in change of temp in the room? How much should I expect the room temp to fall before the heater is switch on and then how much would the room temp increase before it is switch back off?

Thanks for some clarification on this.

[mchild]

I thought this would be an easy one for the many resident Daikin experts. No?

[Yuri B.]

Hello!

It looks like the temp of the liquid pipe would be the final controlling parameter with a change of 4*C at the liquid pipe
It seems to monitor subcooling - if the SC is more than 7K (too big load as room temp is too low) - heater on.

[mchild]

Hello!

It seems to monitor subcooling - if the SC is more than 7K (too big load as room temp is too low) - heater on.


Yuri B,

Thank you for your thoughts. Do you know if the KRP1B board is the one they reference in the attachment? So there the heater is not controlled by the set point of the room temp on the controller?

Is there any way to determine how far the room temp will drop before the heater is turned on using the SC as the trigger to turn it on?

[Yuri B.]

Seems indirect control of the heater - room temp set point has no direct bearing on it - a control through monitoring the temp of the pipe and the temp corresponding to the condens. sat. pressure.


Is there any way to determine how far the room temp will drop before the heater is turned on using the SC as the trigger to turn it on?

I dont think you would get precise numbers. Many factors are to be taken into consideration. Filters, for instance, may be partially blocked and the heater wont be turned on because the pipe sensor is sensing low subcooling (cond sat temp 49 but pipe temp 44, for instance, instead of 42)

[mchild]

Seems indirect control of the heater - room temp set point has no direct bearing on it - a control through monitoring the temp of the pipe and the temp corresponding to the condens. sat. pressure.


I dont think you would get precise numbers. Many factors are to be taken into consideration. Filters, for instance, may be partially blocked and the heater wont be turned on because the pipe sensor is sensing low subcooling (cond sat temp 49 but pipe temp 44, for instance, instead of 42)


Yuri B,

Thank you again.

I am assume the add on board they refer to is the KRP1B which has a power connection. Do you know this board? Would the power connection be required for controlling an electric heater? In the U.S. they never show this board connected to the main power.

[Yuri B.]

Honestly I am not familiar with Daikin VRV at all. What is the indoor unit's model? (then I would download a manual and look up at shematics)

[mchild]

Honestly I am not familiar with Daikin VRV at all. What is the indoor unit's model? (then I would download a manual and look up at shematics)


I have the schematics for my indoor FXSQ units, they do not show the add on PC boards. Plus, it really would not answer the question as to how switching the electric heat on by reading the SC would impact the room temp. If the liquid pipe temp drops to less than 43*C and the target room is 21*C, how far below that would the room temp be? I think someone familiar with the Daikin VRV and the control of electric heat will be the only one to really know the answer. But, thank you for trying to help.

[VRVIII]

I think you are misunderstanding what this type of heater control is used for; some indoor units have a heater kit option that is mounted in the unit. The heater would only be used to assist the ac, normally to bring the room up to temperature and the ac would then hold the room temp. This is why the KRP1B heater thermostat control is on at 4 oC below set point / off at 2 oC below. However the ac thermostat control is on at 1 oC below set point (0.5 for FXS units) / off at 1oC above set point (0.5 for FXS)

The Tc value in question is measured by the outdoor press transducer and converted to temp valve, the Th2 indoor liquid/coil thermistor is used to measure the indoor subcool. Both of these are checked by the indoor PCB which in turn will send a signal to the KRP1B to de-energise the heater if any of the sensor values are greater than those mentioned. This is used as safety and nothing to do with thermostat control.