HITACHI RAS Question

[mourgos]

Hi everyone.

I want to ask a question:

If I have a building with a VRV Hitachi RAS and lets say 10 indoor units, and suppose that one of them has a simple power cut off (maybe a fuse tripping), the whole VRV system of the building stops and goes out of service until someone restore the power to this particular indoor unit?

Thank you for your time.

[nike123]

Hi everyone.

I want to ask a question:

If I have a building with a VRV Hitachi RAS and lets say 10 indoor units, and suppose that one of them has a simple power cut off (maybe a fuse tripping), the whole VRV system of the building stops and goes out of service until someone restore the power to this particular indoor unit?

Thank you for your time.


They are not wired like that. Usually, all indoor units (with that small number of units) are on only one circuit breaker.

[mourgos]

Thank you for your answer nike123, but lets suppose that we have a lot of indoor units indepentetly wired and one of them doesn't have power.
What then?
We dont have operational the rest of the VRV system of the building?

[nike123]

Thank you for your answer nike123, but lets suppose that we have a lot of indoor units indepentetly wired and one of them doesn't have power.
What then?
We dont have operational the rest of the VRV system of the building?

No, you should have rest of system fully operational! Only indoor unit who is defective will show up in central control (if fitted), or in other wired controller when you perform error search at them as error announcement.

P.S. I speaking generally about VRV/VRF systems, I am not familiar with Hitachi that much.

[mourgos]

Thanks again nike!
I was told that with only one indoor unit out of power, nothing works and I found it difficult to believe (in fact unacceptable!).
Any other opinions from Hitachi experts?

[frank]

It's been a while since I've had to work on a Hitachi VRF but, generally speaking, losing power to one indoor unit will cause the whole system to shut down on most makes.

The reason is because at commissioning stage, each indoor unit is given a digital 'address' that the outdoor unit can 'see'

During normal operation, the outdoor unit looks electronically around the system at regular intervals, and 'talks' to each indoor unit it knows is attached to it, asking things like temp settings, suction temps, liquid line temps, etc, so that it can decide how fast to operate the compressor, among other things, etc.

Now, if one of the indoor units loses power, say, because someone switches it off at the isolator, or it blows a local fuse because the fan motor is cooked, then, during the routine 'look' around the system, the outdoor unit realises that one indoor unit is missing.

With a missing indoor unit, the outdoor cannot make any 'informed' decisions about compressor speed, etc, so it shuts down and gives an error message to alert someone that something is wrong.

Not only that, but if it continued to run with one or more indoor units 'missing' then it would be running unbalanced. In this situation, where do you draw a line about how far it can go operating unbalanced? does it just lose 1 indoor, 2 indoors, 3 indoors?? before it faults?

Better to stop when 1 is lost so as to require a 'fix' before any damage is done.

Hope this makes sense. I tried to make it simple. :D

[mourgos]

Hi Frank,
Thank you for your reply.
This is what I was told but then again why the outside unit cannot ignnore the missing indoor unit at all (remember that the communication between the unit controllers still exists ,only the power of one unit is missing).
Anyway if it is no way to overcome this problem,then when I have a real failure of one element I have to wait with a building whithout air- conditioning system for a day or days in August with 45 C until someone replace the failed element! (if it is available).
Not a good idea to me.
The traditional way with chiller water pipes and f.c.u's seems more attrative after that.
Am I missing something?

[frank]

I understand how you are thinking but, imagine that the outdoor unit is rated at say 100kW and all of the attached indoor units are rated at 100kW.

So far, so good - the system is in balance.

Now, if you lose 1 indoor, rated at, say, 12kW, you have an imbalance, 100kW outdoor, 88kW indoor.

As the system has a fixed refrigerant charge, where does the extra 12kW of heat transfer fluid go? It can't go into the 'switched off' indoor unit as this has the valve shut tight. Imbalance = shut down.

The comms with the controllers has nothing to do with the operation of the system as a whole. They are just a small 'window' into the system.

[frank]

Hi Frank,
The traditional way with chiller water pipes and f.c.u's seems more attrative after that.


I don't think so.

If you lose a compressor in the chiller, or a pump, then you also lose the whole building cooling/heating.

The basic difference between chiller and VRV/VRF is that if 1 fan coil requires cooling then you must energise the whole chiller and indoor water circuit to satisfy that 1 fan coil demand.
With VRV/VRF, you just run the compressor at minimum, and the rest of the system remains in standby state.
Much more energy efficient.

[Thermatech]

For Hitachi & most other 2 & 3 pipe VRV/ VRF systems that work with 5 to 12v dc communication network.

Every indoor unit at first power up does an electronic handshake with the outdoor unit. The indoor unit continually communicates information back to the outdoor unit so that the outdoor unit knows exactly what is happening in the system & then it can trim its operation to suit the indoor units requirments.
But then suddenly one indoor unit 240v is turned off.
The indoor unit needs 240v connected to the circuit board to be able to ramp open or ramp shut the LEV expansion valve.
The indoor unit in this case is not able to shut down the LEV expansion valve. As the outdoor unit is still running to supply refrigerant flow to the other indoor units this then would present a serious problem. The indoor unit with no 240v has wide open LEV valve but no fan operation. In cooling mode liquid refrigerant floods through the indoor unit & gets dumped back into the suction & liquid flood back to the compressor,,, not good.
So the Japs resolve this potential problem by shutting the complete system down & reporting a communication error for the unit which no longer has any 240v connected.

The one exception is Mitsubishi Electric City Multi VRF.
This system uses 30v dc communication network & each indoor unit can use the 30v dc to shut down the LEV valve if the 240v power is turned off.
The higher communication voltage is needed for this emergency operation & it also has the benifit that the outdoor unit continues to communicate with the indoor unit even though 240v has been turned off at the indoor unit. All other indoor units continue to operate normally.
There is no risk of liquid bypass to suction because the indoor unit LEV valve has been able to shut using the 30v dc which is produced at the outdoor unit.

Also for 2 pipe heat pump systems in heating mode any indoor units switched off at remote controller or thermostat off.
In this case the indoor units at off have the LEV valve just a tiny little bit open to prevent any collection of condensed liquid & oil at the indoor unit coil.
If the indoor unit then has 240v turned off for most 5 to 12v dc control network systems this would be a problem as hot gas would cool in the indoor unit coil. Liquid & oil could then collect at the indoor coil which would make the system run short of gas & could potentialy trap enough oil to cause compressor damage if operating like this for long enough.
So the Jap designers overcome this potential problem by stopping the complete system with a communication error & the system cannot start again untill 240v power back on to the indoor unit.
Again this is not a problem for ME CM because each indoor unit can use 30v dc communication vltage to operate the LEV valve even when 240v turned off.

[mourgos]

Guys thank you very much for your inputs.
Now I have a clear picture of the problem.
Thanks again!

[nike123]

I understand how you are thinking but, imagine that the outdoor unit is rated at say 100kW and all of the attached indoor units are rated at 100kW.

So far, so good - the system is in balance.

Now, if you lose 1 indoor, rated at, say, 12kW, you have an imbalance, 100kW outdoor, 88kW indoor.

As the system has a fixed refrigerant charge, where does the extra 12kW of heat transfer fluid go? It can't go into the 'switched off' indoor unit as this has the valve shut tight. Imbalance = shut down.



Frank, isn't that the way how vrv/vrf work. If you have 1 or many indoor units switched of on remote, refrigerant doesn't go thru them either, same as if the indoor unit is unplugged. There is no imbalance because compressor speed is adjusted and less refrigerant is in circulation.

[nike123]

Mourgos, sorry for my mislead!
I was thinking that 1 unit without power should not be a problem but I stand corrected from more experienced guys with VRV/VRF things.:o
My experience with VRV/VRF things is low because I mostly work with chillers but I was worked on few Fujitsu VRF systems and I newer have got this sort of problem.

In hotels in which I fitted AC systems we always fit at least 2 chillers with 2 independent refrigerant circuits.
That give us (and customer) needed system redundancy.
We never put or advice fitting VRV/VRF systems in objects of that type.

[Thermatech]

Mourgos

In the UK VRF systems have been extensively used in hotels for many years.
The largest hotel chains have VRF systems on the standard specification. The most expensive / exclusive hotels in central london have every room air conditioned with VRF systems.

The larger hotels tend to have a dedicated maintenance engineer full time on site for instant response. They also tend to keep some spare parts on site for instant repair.
Otherwise there are many specialist contractors who have experenced VRF service engineers who have been on all the manufacturers training courses & are very good at resolving any problem.

Hotel facility managers have found over the years that overall including service & maintenance VRF saves so much money with heat recovery energy saving that chillers are no longer cost effective.
So in the UK VRF is standard air conditioning system for hotel applications.

[mourgos]

O.K. guys,
thanks again for your very useful replies.
I learned a lot because of you.
You are doing a wonderful job here.

[ACM]

Hello my friends

let reply what will happen for sure.

If the Setfree system you have looses power to just one indoor unit when in operation the whole sytem will shut down with alarm code 32.
the unit with out power will have an 03 alarm, no communication to out door unit.

you can not run the system with an indoor unit piped but not communication to the outdoor as it will fllood refrigerant and cause another problem.

If you want to isolate this unit then fit ball valves to the connecting pipes and power the condensing unit off and on again with the said indoor powered off.The condenser will not see the indoor this time and think its not fitted and will run ok.
Hitachi tech help line 01628 585393
or down load the manuals FREE at hitachiaircon.com

[frank]

Frank, isn't that the way how vrv/vrf work. If you have 1 or many indoor units switched of on remote, refrigerant doesn't go thru them either, same as if the indoor unit is unplugged. There is no imbalance because compressor speed is adjusted and less refrigerant is in circulation.

That's true Nike but, at least when it's switched off at the controller, the outdoor unit can still communicate with it and adjust the compressor speed to suit.

When it's switched off by local isolator or in fault the outdoor cannot communicate so it doesn't know what to do with the excess fluid.