VRV vs Digital control

[2007eng]

Hi experts,
I'm asking about the power consumption issue.
inverter vs digital control(time period on/off)

[K.R.Iyer]

What are you refering to - controlling pumps, fans and compressors (or) about the VRF Air conditioning systems?

[2007eng]

What are you refering to - controlling pumps, fans and compressors (or) about the VRF Air conditioning systems?

Hi K.R.Iyer,
I'm talking about the compressors mainly.Scroll compressors specially.
If I have a space needs 300TR as example and say my system is water cooled (same Cooling Towers) what is best system uses less energy VRV(40 water cooled units-inverter scroll comp) or Digital scroll comps in chiller(on /off for 4 compressor-3 way valve each AHU)

[thmech]

I am not sure for the actual energy consumption between VRV and Chiller with digital scroll however, if we compare just only compressor, VRV is using DC inverter scroll and, of course, digital scroll is basically from Copeland scroll so I think we can say that it is equal. But if you look in to the way its modulated capacity, VRV is just a name of Daikin product that using inverter technology as same as Mitsubishi, Fujitsu, LG so it is an inverter system ans as we know that inverter is playing with frequency and speed so it creates lots of problem such as EMC, oil return, etc. Efficiency losses due to inverter loss, oil return management, hot gas by-pass and high oil circulation rate are also being an issue when running inverter system. But those problems is not occur in digital scroll system because it is not playing with frequency and speed. So, for me, I prefer digital scroll system.

[Pyr0Beast]

Efficiency is pretty much the same in both situations. For same amount of cooling capacity you'll require the same amount of energy ...

[2007eng]

I am not sure for the actual energy consumption between VRV and Chiller with digital scroll however, if we compare just only compressor, VRV is using DC inverter scroll and, of course, digital scroll is basically from Copeland scroll so I think we can say that it is equal. But if you look in to the way its modulated capacity, VRV is just a name of Daikin product that using inverter technology as same as Mitsubishi, Fujitsu, LG so it is an inverter system ans as we know that inverter is playing with frequency and speed so it creates lots of problem such as EMC, oil return, etc. Efficiency losses due to inverter loss, oil return management, hot gas by-pass and high oil circulation rate are also being an issue when running inverter system. But those problems is not occur in digital scroll system because it is not playing with frequency and speed. So, for me, I prefer digital scroll system.


Thank you very much thmech for this good answer.
I'm with you the digital scroll system is very simple not complicated like the VRV, But the VRV capacity control technology is very sufficient I mean the compressure capacity is moduled with the demand of the AC speace(more than 20 steps). For this I think the VRV is very sufficient in the systems which its demand is variable (Big differences in load at the same place).I prefer digital scroll system when the load is stable relatively.
Thanks again.

[2007eng]

Efficiency is pretty much the same in both situations. For same amount of cooling capacity you'll require the same amount of energy ...

Hi Pyr0Beast,
I will be very glad if there is any document contain a comperison like this.
Thanks.

[abbasi]

Hi Pyr0Beast,
I will be very glad if there is any document contain a comperison like this.
Thanks.

Email me at

engineerali@gmail.com

i will give you the whole data u need;)

[mekaniko5]

the VRV capacity control technology is very sufficient I mean the compressure capacity is moduled with the demand of the AC speace(more than 20 steps). For this I think the VRV is very sufficient in the systems which its demand is variable (Big differences in load at the same place).I prefer digital scroll system when the load is stable relatively.
Hello 2007eng. I think you have a misconception about the Digital Scroll. Digital Scroll systems are also Variable capacity system which allows capacity modulation. I had the chance to see a presentation and learned that the inverter can modulate its capacity to provide 40-100% (or maybe 20 steps) whereas the Digital Scroll can provide 10-100% capacity. This is byfar the widest any variable capacity system can provide which translates to a lot of advantages which thmech has pointed out nicely.

And it makes sense that the inverter can only provide limited capacity, if you go too slow, you'll bump into oil issues.

[Thermatech]

Surprised that you think VRF inverter control is so poor.
But then a digital Scroll manufacturer will tend to 'talk up' there technology & put some 'spin' on facts to make any other manufactures kit look poor.

I would suggest you check out the facts.

for a number of years Mitsubishi Electric City Multi VRF has been 16% to 100% & controlled in 1% steps.

In practice you can be confident that any size outdoor unit will operate ok with only one size 20 indoor smallest size indoor unit running in heat or cool. Minimum capacity is in practice not an issue for ME CM systems & never has been.

Perhaps you can explain why 100% capacity in a 1 or 2 second burst every 20 seconds is a good idea & how that saves energy or gives better control ?

[mekaniko5]

1 or 2 second burst every 20 seconds is a good idea & how that saves energy or gives better control ?

2 seconds providing 100% capacity in a 20 second cycle basically is 10% capacity.
The rest of the time the compressor is not pumping refrigerant, the scrolls are separated by less than 1mm gap, the motor experiences less load and friction hence power consumption is minimal.
This is one of the main reasons why it is very efficient during part load conditions.

Both inverter and digital equally provides exeptional temperature control.

[thmech]

Email me at

engineerali@gmail.com

i will give you the whole data u need;)

May I also have that data? Please....I will mail you.:D

[Thermatech]

Please explain the typical operating pressures for R410a refrigerant digital scroll air conditioning system operating in cooling mode.
From your experiance commissioing this type of system at low load conditions when the compressor is off loaded for longer than it is loaded.

1/ Discharge pressure at load.
2/ Discharge pressure off load.
3/ Compressor Amps on load.
4/ Compressor Amps off load.
5/ Suction pressure on load
6/ Suction pressure off load.

How does the system maintain constant liquid line pressure to the indoor units ?
How does the system low ambient head pressure control work during low ambient cooling ?

[Pingo]

Surprised that you think VRF inverter control is so poor.
But then a digital Scroll manufacturer will tend to 'talk up' there technology & put some 'spin' on facts to make any other manufactures kit look poor.

I would suggest you check out the facts.

for a number of years Mitsubishi Electric City Multi VRF has been 16% to 100% & controlled in 1% steps.

In practice you can be confident that any size outdoor unit will operate ok with only one size 20 indoor smallest size indoor unit running in heat or cool. Minimum capacity is in practice not an issue for ME CM systems & never has been.

Perhaps you can explain why 100% capacity in a 1 or 2 second burst every 20 seconds is a good idea & how that saves energy or gives better control ?

Hi Thematech

I understand that Mitsu did/does have a problem with minimum capacity - from noise in pipework when running with only the smallest 20 unit running !

Noise is transmitted throught the pipe work from a valve in the outdoor unit which opens and closes quickly and this is being caused by low refrigerant velocity.



Regards pingo

[Thermatech]

Pingo

That could be a slight issue on some older models but not seen it yet on the newer ones.

The compressor was proteced by a discharge non return valve which could at minimum compressor speed rattle a bit due to low discharge gas velocity.

Did you find it is a problem on the latest R410a models ?

After they have done 30000 to 50000 hrs some discharge non return valve have been known to fail in closed possition & system locks out on HP.

If lots of contractors complained & claim warrantee about this the factory would make some 'counter measure' but if only 1 in 1000 has problem its not likely that the factory will make any change.

[Lc_shi]

How about the scroll digital controller?Any algorithm for it?

[Thermatech]

Pingo

I checked my notes & found that there is an alternative control stratagy on City Multi outdoor units which prevents the discharge check valve rattle.
This is activated with SW4 dip switch on the outdoor unit.

Personally I have never needed to use it as I have never had any complaint from an enduser about this issue.

Check with Mitsubishi Electric technical & they can provide futher details.

[Pingo]

Hi Thermatech

Noise problems from Mitsu systems !

I had heard about the problem in a general conversation i had with a Mitsubishi engineer some years ago.

Then on a site at Warwick on a new installation (now 2years old)
customer complained about intermittent noise from the system

On checking it was found that the noise was being transmitted through the pipe work from the outdoor valve chattering,

Mitsu responce was that the system was oversize and to fit some more wall units onto the Bs box !

The Outdoor unit is a PURY 300YGMA year 2006 working on R410A

3 Wall PKFY P50 indoor fan coils
2 Wall PKFY P32 indoor fan coils

Regards Pingo

[Thermatech]

Pingo

I think if you double check with Mitsubishi Electric Technical engineers that you can resolve that with the alternative control 'counter measure' which was an option for that model.

The product is constantly being improved & refined & so ME have moved on to develop the YHMA which is a re design of the outdoor unit & I would suspect that any slight problems with the YGMA model has been addressed & designed out.

A retro fit solution would be to replace the discharge non return valve with a solenoid valve which is energized open only when the compressor runs.
But personally I have never visited a site yet where the enduser has complained so for me its never been an issue.

[Sridhar1312]

As i know the VRV system piping is crucial and when it almost entire indoor units will have impact, and is not suitable exclusively for Cooling alone as the power saving is not that effective.
flexibility of chilled water system is more rugged and is cost effective when compared to VRV

[Thermatech]

I was talking to a doctor from India & he is currently working in the uk.

He explained that it would be pointless importing a new European car like Jaguar or BMW ect because there is no specialist car repair mechanics in India who would know how to trouble shoot or make any repair. The technology on these cars is much too advanced.

He carried on to explain that in India the air conditioning systems are very simple & that there are no complicated systems from Japan because there are no air conditioning engineers who would be able to trouble shoot the electronic controls.

He explained that air conditioning manufacturers like LG have done very well in India because the LG systems are still simple straight forward & not too complicated for the local air conditioning engineers.

I personally have never been to India so I was wondering if this is accurate description ?

Perhaps engineers in India like digital scroll systems because they do not have complicated inverters.

[nike123]

Perhaps engineers in India like digital scroll systems because they do not have complicated inverters.

Every engineer from construction to maintenance should love more any system which is less complicated and with same or better performance.

[mekaniko5]

I understand that Mitsu did/does have a problem with minimum capacity - from noise in pipework when running with only the smallest 20 unit running !

Noise is transmitted throught the pipe work from a valve in the outdoor unit which opens and closes quickly and this is being caused by low refrigerant velocity.


I would think that the noise is a result of resonant frequency.
Frequency variations emitted by the system from low capacity requiremetns result in a resonant frequency which may amplify the sound and vibration.

[K.R.Iyer]

I was talking to a doctor from India & he is currently working in the uk.

He explained that it would be pointless importing a new European car like Jaguar or BMW ect because there is no specialist car repair mechanics in India who would know how to trouble shoot or make any repair. The technology on these cars is much too advanced.

He carried on to explain that in India the air conditioning systems are very simple & that there are no complicated systems from Japan because there are no air conditioning engineers who would be able to trouble shoot the electronic controls.

He explained that air conditioning manufacturers like LG have done very well in India because the LG systems are still simple straight forward & not too complicated for the local air conditioning engineers.

I personally have never been to India so I was wondering if this is accurate description ?

Perhaps engineers in India like digital scroll systems because they do not have complicated inverters.

Well, a quick update on India scenario for you:-
LG is a leading player only in window and wall mounted splits. USP is price. Not known in above 2TR capacity as a serious player. Inverters are known to India since 2000 through Daikin, though in last 2-3 years the VRF sales are zooming after Blue Star introduced Digital scroll VRF. Very recently Samsung, Mitsubishi and LG also have launched VRF products. Though every OEM takes consultants on an abroad trip, there are no serious trainings offered on installation and trouble shooting by any OEM to contractors. May be they may do it, when the market volume increases and more units start breaking down needing attention, this will happen

[mekaniko5]

How about the scroll digital controller?Any algorithm for it?

Digital Scroll uses proportional integral or PI logic. PI logic determines two things; 1. How much demand is needed by the indoor unit to condition the room and 2. The fastest way this demand can be delivered. By constantly measuring the difference between actual room temp and the set point, the PI logic intelligently determines the fastest response to the required computed demand.