Daikin VRVII

[Cool100]

A question for those regular working on the VRVII's.
Suppose a REYQ14 and a REYQ16, master/slave combination, Heat Recovery, 14 indoor units.

Is following statement true?
When one of the indoor units - let's say a 4 kW - is switching into cooling mode, will then the total outdoor combination divided in 2 equal pieces, 50% available for cooling and 50% for heating?

Or in other words to make sure that my question is clear; let's say we have a total of 120 kW cooling or heating capacity, 1 indoor unit of 4 kW is switching for 2 hours into cooling mode and we need for all the remaining indoor units a total of 90 kW heating, then the outdoor unit can't handle this any longer because there's only 60 kW available that moment (50/50 split)

Or is it another combination?

If this statement isn't true, was it then perhaps true for the very first VRV generation (fabricated before 2005)?

I have for the moment the Service manual VRVII, Heat Recoevry 410a, SI39-306 in front of me on page 68, section 2.5.: Heat Exchange Mode in Heating Operation or
Simultaneous Cooling / Heating Operation.
But they don't give figures in this explanation to understand if this explanation is true.

Also, they give certain steps from A1 till C3 which aren't that clear for me.

Can someone explain this for me please and/or direct me perhaps to a paper where I can find this?

[The Viking]

Ehermm.......

Sorry to say but your reasoning is flawed.

I assume from your question(s) that you are looking at a Daikin 3 Pipe system, in other words a heat recovery system.

Say that your outdoor unit has a capacity of 80 kW cooling. (This will mean that it got about 120 kW heating capacity.)

Now, as you put units in cooling mode, there is a need to get rid of the heat generated by this process, if no indoor units calling for heating the outdoor unit's fan will start and the outdoor coil act as a condenser but if there are indoor units in heating mode, the outdoor unit will only be a compressor pumping the gas between the evaporators (indoor units in cooling mode) and the condensors (indoor units in heating mode).

If the heating demand is greater than the heat generated by the cooling load, then the outdoor coil will be utilised as an evaporator.

So, as you can see, your question about "split capacity" doesn't come in to it.

(Sorry)

[cool#9]

Hi Cool100
To understand it see the pdf about VRV K series from a training course, i thank the author for this explanation.
The system just have to keep the pressure targets with 2 outdoor exchangers, outdoor fan control, capacity control, etc.
In new series (P) this will change a lot...
Rgds
cool#9

[Peter_1]

I have a similar case. Interested in the answers.

[Cool100]

As mentioned in my first line, it's indeed a 3 pipe system or a heat recovery
This explanation is perhaps flawed reason why I posted it in this forum.
Here are a lot of experienced techs with expertise on Daikin VRV's and I know that you're one of them.

If this let I call it 50/50 story is true, then this is a serious disadvantage compared to the Mitsubishi's 2 pipe heat recovery system.

I've taken 80 kW cooling and 80 kW heating to make it simple. 80 kW hetaing is also true if you take low ambient (around -7°C)

It has something to do - according to Daikin- with the main and sub HE in the outdoor units.

[Cool100]

Hi Cool100
To understand it see the pdf about VRV K series from a training course, i thank the author for this explanation.
The system just have to keep the pressure targets with 2 outdoor exchangers, outdoor fan control, capacity control, etc.
In new series (P) this will change a lot...
Rgds
cool#9

Thanks for your info.
In this training course extract, you can't figure out if the statement of 50/50 is true for a heat recovery.
As far as I read it, you can have 10% running on cooling and the remaining indoor units can still run in heating mode.
You're speaking about the new series (P), are these available yet and if so, since when?

[Cool100]

The Viking, can you send me once a PM with your email if you want?

[Cool100]

Cool9,

It seems that this explanation handles the old K series.
Is this so?

It says something about the compressor control but nothing about the 4way valve, switching from heating to cooling.

What exactly is the trigger to use the outdoor heat exchanger as a condensor or as an evaporator?

Is it still so that as soon as one indoor unit 'calls' for heating, one of teh 4way valves in the outdoor unit switches so that one of the heat exchangers then acts as an evaporator?

Is it since the VFRVII changed so that the software measures the actual evaporating and condensing conditions, compares this to nominal conditions and then 'decides' how a heat exchanger is switched?

[Cool100]

The Viking, can you send me once a PM with your email if you want?

Cool#9, if possible, can you send me also a PM with your email address?

[Cool100]

Say that your outdoor unit has a capacity of 80 kW cooling. (This will mean that it got about 120 kW heating capacity.)

Now, as you put units in cooling mode, there is a need to get rid of the heat generated by this process, if no indoor units calling for heating the outdoor unit's fan will start and the outdoor coil act as a condenser but if there are indoor units in heating mode, the outdoor unit will only be a compressor pumping the gas between the evaporators (indoor units in cooling mode) and the condensors (indoor units in heating mode).

If the heating demand is greater than the heat generated by the cooling load, then the outdoor coil will be utilised as an evaporator.

So, as you can see, your question about "split capacity" doesn't come in to it.

The Viking, I can follow your explanation of a heat Recovery system in general, but I think you start from the point of view there's only one HE in each outdoor unit but there are 2 and also 2 four-way-valves/outdoor unit

[cool#9]

You're speaking about the new series (P), are these available yet and if so, since when?

They're not available yet in France (REMQ_P) but i'll soon follow a training course to do the first commissioning on the French Riviera, i hope before december, and i think someone else on the forum could already explain the changes...
rgds
cool#9

[The Viking]

For more detailed description you better look out for the manufacturer's guys on the board.

BUT...

Say that you are looking at a system with 10 indoor units, all with a rating of 4 kW cooling/6 kW heating.

Various options:

Cooling only:
1 indoor unit calling for cooling - the compressors will run at 10% and the outdoor coils will be utilised as a condensor at 10%.

10 indoor units calling for cooling - the compressors will run at 100% and the outdoor coils will be utilised as a condensor at 100%.


Heating only:

1 indoor unit calling for heating - the compressors will run at 10% and the outdoor coils will be utilised as an evaporator at 10%.

10 indoor unit calling for heating - the compressors will run at 100% and the outdoor coils will be utilised as an evaporator at 100%.

I assume that we agree so far.

Mixed mode / Heat recovery:

1 indoor unit calling for cooling and 1 indoor unit calling for heating - the compressors will run at 10% and the outdoor coils WILL NOT BE UTILISED as the heating created by the cooling cycle will be supplied to the indoor unit in heating mode (and vice versa).

6 indoor units calling for cooling and 1 indoor unit calling for heating - the compressors will run at 60% and the outdoor coils will be utilised as a condensor at 50%.

5 indoor units calling for cooling and 5 indoor units calling for heating - the compressors will run at 50% and the outdoor coils WILL NOT BE UTILISED as the heating created by the cooling cycle will be supplied to the indoor units in heating mode (and vice versa).

1 indoor unit calling for cooling and 9 indoor units calling for heating - the compressors will run at 90% and the outdoor coil utilised as an evaporator at 80%.

I hope this has clarified things.

Exactly how it's controlled is something I normally don't bother trying to understand, its all in those little devilish Printed Circuit Boards.

But, the reversing valves are there to change the selection of main mode (Cooling only-mainly Cooling-mainly heat-heating only) in conjunction with these are several PMVs and solenoid valves to allow for seamless Heat recovery functions (as well as varying loads/oil recovery and so on)

Where more outdoor units are added and linked together, they will for all intent and purpose be working together as one.



PS. The above scenarios are for illustrative purposes and heavily simplified.

[puddleboy3]

Have a look at the following pictures. Hope this clears things up

[Cool100]

Puddleboy, some questions: were these pictures drawn by yourselves or were those taken out a manual or course of Daikin?
What with 2 units in master/slave? How's then the flow?

[Obi Wan]

Hello Cool 100,

This is a complicated question to answer, I see from some of the posts that some people have a fairly good understanding of the heat recovery concept.

As you know that on the VRV heat recovery outdoor units there are always 2 heat exchangers. On the G and K series there were the inner and outer heat exchangers each with its own 4way valve and electronic expansion valves. If you looked closely the outdoor heat exchanger had a double pass (inner and outer).

On the VRV II there were the upper and lower heat exchangers. In the service manuals they are referred to as the main heat exchanger (upper) which is about 2/3 of the outdoor heat exchanger assembly and the Sub heat exchanger (lower) which is the remaining 1/3 of the coil. There is also a third heat exchanger known as the sub cooling heat exchanger. These are 2 x 1m pipe within pipe type heat exchangers. All three heat exchangers have EEVs but only the upper and lower have there own 4 way valves. For this explanation we will ignore the sub cooling heat exchanger.
The heat exchangers are switched to balance the system and to achieve the target operating conditioning.

What is target operating condition?
Well, basically the outdoor unit calculates what the target condensing and evaporating temperatures which will be based on the number of indoor units in heating and cooling, ambient temp, indoor temp, pressure drop across the field pipe work plus more. It then compares this with the actual or current condensing and evaporation temperatures and decides what must be done to make the actual temperature the same as the target temperatures.
The outdoor unit has many options to choose from; it can increase or decrease the airflow rate, load the compressors up or down, switch the heat exchangers between evaporators or condensers or simply adjust the opening of the EEV’s.
The way the G and K series achieved this is remarkably different to the VRV II systems. G and K series relied heavily on the high and low pressure sensors, you had to go out of the high and low pressure control band before the system reacted and corrected the situation. On the VRV II the system tracks the operation of each indoor unit and will decide what it has to do to maintain target operation condition. E.g. say a 5kw indoor unit is operating in cooling and the room temperature is approaching the thermostat off point, the outdoor unit will be aware of the evaporator surface area it is about to loose, it has already worked out what it needs to do to compensate for this eventuality. So the moment the thermostat is switched off, the countermeasure is executed without any major deviation from the target operating conditioning.

You mentioned the steps A1 to C3 and the flow chart in the service manual. This basically shows when the upper and lower coils are switched as evaporators or condensers on the master, slave 1 and slave 2 units. (in a multi outdoor combination). The GR value is a result of a complex calculation the outdoor units has carried out to find the difference between the target evaporating and condensing temperatures and the actual evaporating and condensing temperatures. The GR value shown in the manual has no meaning if you don’t know what the actual calculation is, but at least you can see how the outdoor heat exchangers will switch between evaporators and condensers.

Back to basics!
When things get too complicated, I always like to go back to basics. The VRV II system is after all only an air conditioning system. It is important to remember that you can’t change the laws of physics.
Let me explain, If you were to remove all the heat exchangers from the indoor units and make them flat and join them up to make into one big heat exchanger. Hypothetically, when connected to the outdoor and put into cooling operation and the target operation condition is reached.

If you were to block off 50% of the indoor heat exchanger, what would the result be?
The low pressure will drop.

What must you do to get back to normal operation?
You will need to reduce the current load, say by loading down the inverter compressor and you need to reduce to condenser surface area to avoid over condensing.
If you now relate this thinking with the thermostats switching on and off on the indoor units or indeed the indoor unit changing mode between heating and cooling, as the actual size of the evaporator and condenser increasing or decreasing. In order to keep the correct capacity from the indoor units the outdoor unit is continuously sampling, calculating and adjusting the target operation condition. (every 20 sec)

On the VRV III the concept has changed again. Now we have the left and right hand heat exchangers, each with there own EEV’s, 4 way valves and now with there own inverter controlled fans. This means that the target evaporator and condensing temperature can be controlled more effectively in low ambients and can lower the operating range of the system.

Hope the above makes sense.

Regards

Obi Wan.

[Cool100]

ObiWan, can you PM me an email address of you where I can post something.

[Cool100]

ObiWan, can you PM me an email address of you where I can post something.

Forget to tell that I appreciate of course the long explanation you made for us all.

[Obi Wan]

ObiWan, can you PM me an email address of you where I can post something.

Got the following message wen sending the PM.

Cool100 has chosen not to receive private messages or may not be allowed to receive private messages. Therefore you may not send your message to him/her.