Communication question

[Husky250]

Hello to all,

I had a major dis-agreement today with another engineer regarding communication wiring in large VRF equipment. We were discussing if one of the Indoor units were to lose power, the entire network ( all indoor units ) would not operate. His statement to me was this is not true in Mitsubishi equipment. During the conversation he instructed me that Mitsubishi equipment incorporated an oversized accumlator. This in theory would account for an Indoor EEV to have no power, but the entire system would still operate.

I totally dis-agree with his remarks. From what I have learned, all Indoor units would not operate. This is a protective function programmed into the system. In my opinion, an oversized accumlator would not copensate for cold outdoor ambient conditions. If the system were allowed to operate under those conditions, liquid refrigerant would return to the outdoor unit.

Can you guys please confirm who is right on this subject? We were discussing Mitsubishi, but I think this control logic applies to all VRF equipment with multiple Indoor units connected to one outdoor unit.

Please advise who is right. I would love to prove this jerk wrong.

Cheers
Husky

[Thermatech]

For many VRV / VRF systems the indoor units need 240v power to the circuit board to operate the LEV valve.
If the 240v power is turned off while the indoor unit is operating & the LEV valve is in an open possition then the complete system of units connected to the outdoor unit need to stop as a safety precaution. In this instance the indoor unit is unable to shut the LEV valve.
Otherwise if any other indoor units & the outdoor unit were to continue to operate then liquid refrigerant could flood through the indoor unit with 240v power turned off & this liquid could then flood back to the outdoor unit.

However unlike most VRF systems which operate with a 5 - 12v d/c control communication between outdoor & indoor units Mitsubishi Electric City Multi is different as it uses 30v d/c control communication between outdoor & indoor units.
Mitsubishi indoor units can cope with 240v power off situation because the indoor unit can use the 30v d/c communication voltage as a backup to shut down the LEV valve so there will be no risk of any liquid bypass & flood back to outdoor unit.
This 30v d/c is generated at the outdoor unit so you can turn off 240v power to any indoor units or multiple units & the rest will continue to operate normally.

Historically City Multi outdoor unit have always had large suction accumulators & this allows the system to operate even with only one size 20 indoor unit cooling or heating in which case the accumulator will have high liquid level. So the system can cope with long pipe runs & all units running flatout when there will be only a small volume of liquid in the suction accumulator or only one tiny indoor unit running in which case the suction accumulator will have high liquid level but still protect the compressor from liquid flood back.

[Husky250]

For many VRV / VRF systems the indoor units need 240v power to the circuit board to operate the LEV valve.
If the 240v power is turned off while the indoor unit is operating & the LEV valve is in an open possition then the complete system of units connected to the outdoor unit need to stop as a safety precaution. In this instance the indoor unit is unable to shut the LEV valve.
Otherwise if any other indoor units & the outdoor unit were to continue to operate then liquid refrigerant could flood through the indoor unit with 240v power turned off & this liquid could then flood back to the outdoor unit.

However unlike most VRF systems which operate with a 5 - 12v d/c control communication between outdoor & indoor units Mitsubishi Electric City Multi is different as it uses 30v d/c control communication between outdoor & indoor units.
Mitsubishi indoor units can cope with 240v power off situation because the indoor unit can use the 30v d/c communication voltage as a backup to shut down the LEV valve so there will be no risk of any liquid bypass & flood back to outdoor unit.
This 30v d/c is generated at the outdoor unit so you can turn off 240v power to any indoor units or multiple units & the rest will continue to operate normally.

Historically City Multi outdoor unit have always had large suction accumulators & this allows the system to operate even with only one size 20 indoor unit cooling or heating in which case the accumulator will have high liquid level. So the system can cope with long pipe runs & all units running flatout when there will be only a small volume of liquid in the suction accumulator or only one tiny indoor unit running in which case the suction accumulator will have high liquid level but still protect the compressor from liquid flood back.

Thanks so much ! It seems to be clear any VRF equipment using the 5-12v DC Contol voltage will turn off if an Indoor unit loses power.

That answers my question regarding Mitsubishi City Multi systems.

Can anyone else answer this question on similar equipment?

What about LG multi-v equipment?

Thanks for help with this!!!!!!!!!!!!!!

[Husky250]

For many VRV / VRF systems the indoor units need 240v power to the circuit board to operate the LEV valve.
If the 240v power is turned off while the indoor unit is operating & the LEV valve is in an open possition then the complete system of units connected to the outdoor unit need to stop as a safety precaution. In this instance the indoor unit is unable to shut the LEV valve.
Otherwise if any other indoor units & the outdoor unit were to continue to operate then liquid refrigerant could flood through the indoor unit with 240v power turned off & this liquid could then flood back to the outdoor unit.

However unlike most VRF systems which operate with a 5 - 12v d/c control communication between outdoor & indoor units Mitsubishi Electric City Multi is different as it uses 30v d/c control communication between outdoor & indoor units.
Mitsubishi indoor units can cope with 240v power off situation because the indoor unit can use the 30v d/c communication voltage as a backup to shut down the LEV valve so there will be no risk of any liquid bypass & flood back to outdoor unit.
This 30v d/c is generated at the outdoor unit so you can turn off 240v power to any indoor units or multiple units & the rest will continue to operate normally.

Historically City Multi outdoor unit have always had large suction accumulators & this allows the system to operate even with only one size 20 indoor unit cooling or heating in which case the accumulator will have high liquid level. So the system can cope with long pipe runs & all units running flatout when there will be only a small volume of liquid in the suction accumulator or only one tiny indoor unit running in which case the suction accumulator will have high liquid level but still protect the compressor from liquid flood back.

Thermatech,
What happens if the the 30v DC control wiring is open. The metering device has no voltage to close at that point......Is that correct........?

I would be concerned about an Indoor unit being powered off and the system still operating. Imagine the piping on a large city multi being maxed out. You have a large amount of refrigerant in the pipnig network. From your fine remarks, this is an extreamly nice feature for the City Multi Series. I would like to study the system and others to learn more.

[Thermatech]

When the outdoor unit is first powered up it looks for all indoor units, remote controllers, B/C boxes. It will find & carry out an electronic hand shake with every unit which is connected on the 30v d/c daiy chain & which has an address.

If at any time the 30v d/c daisy chain is disconnected then the outdoor unit stops & reports a communication error for the unit address which it is no longer getting a reply from.

You are right the LEV valve default to shut possition using the control 30v d/c is a great feature but sales engineers are not cute enough to take advantage of it because most do not understand fully how the system actually works.

City Multi has always been like this since I first started commissioning them in 1992.

When you are more used to working with the other VRV ./ VRF system then turning the power off to any indoor unit is a problem.

But with City Multi you cannot do any damage to anything by turning 240v off to any indoor unit because the system is designed & engineered to cope with this.
Actually one way of time clock control is to set the dips on the indoor units for auto restart after power failure option. Then fit a time clock & contractor to the 240v ring main to the indoor units.

The outdoor unit can still communicate with all the indoor units as they are still connected to the outdoor unit on the Mnet 30v d/c daisy chain but the indoor units cannot operate as the 240v is off.

[Billy Ray]

Thermatech

thats good info, well explained, thankyou very much.

With regards the daisy chain wiring arrangement, is this necessary (or good practice).

or will spurs? chaotic arangements suffice.

Billy Ray

[Thermatech]

On Mitsubishi City Multi you can star wire out to all the units if you have too but most engineers will follow the Mitsubishi schematic diagram & daisy chain to all units.

At the end of the day provided all units & remote controllers are connected to M1 M2 at the outdoor unit then they can all communicate.
The important thing is what address each unit is given on the address dips & so long as it is connected to M1 M2 somewere on the system it will be able to communicate.

[Husky250]

When the outdoor unit is first powered up it looks for all indoor units, remote controllers, B/C boxes. It will find & carry out an electronic hand shake with every unit which is connected on the 30v d/c daiy chain & which has an address.

If at any time the 30v d/c daisy chain is disconnected then the outdoor unit stops & reports a communication error for the unit address which it is no longer getting a reply from.

You are right the LEV valve default to shut possition using the control 30v d/c is a great feature but sales engineers are not cute enough to take advantage of it because most do not understand fully how the system actually works.

City Multi has always been like this since I first started commissioning them in 1992.

When you are more used to working with the other VRV ./ VRF system then turning the power off to any indoor unit is a problem.

But with City Multi you cannot do any damage to anything by turning 240v off to any indoor unit because the system is designed & engineered to cope with this.
Actually one way of time clock control is to set the dips on the indoor units for auto restart after power failure option. Then fit a time clock & contractor to the 240v ring main to the indoor units.

The outdoor unit can still communicate with all the indoor units as they are still connected to the outdoor unit on the Mnet 30v d/c daisy chain but the indoor units cannot operate as the 240v is off.

What about the other popular units??? Daikin, LG, Sanyo......and the others?

[Thermatech]

Daikin & Hitachi stop on communication error when 240v power turned off at any indoor unit.

Not sure about all the other makes.

[Husky250]

Daikin & Hitachi stop on communication error when 240v power turned off at any indoor unit.

Not sure about all the other makes.

Thanks for your information.

I'm looking forward to learning more !

[Krondor]

Sanyo also stops on Error,
Toshiba has a dip switch on the outdoor to avoid this problem

[Husky250]

Sanyo also stops on Error,
Toshiba has a dip switch on the outdoor to avoid this problem

Thanks to all !

[hwtan]

guys, i have this mitsubishi fcu which keeps on blinking after resetting, waited for 3minutes and compressor didn't come on at all.

it is a system 3 and all the units are blinking, what could be the problem?

have read the above mentioned system and sounds familiar to my problems here, the signal is transmitted via 12volts.

any thoughts?