Digital V/s Inverter Technology

[munesh]

What is the difference in digital and inverter technology?
Which is better and why?
How do these operate?

[Lowrider]

Do you mean a digital scroll and a normal scroll on an inverter?

If so, I do know the difference. A normal scroll uses an inverter or frequency drive to adjust the compressor performence according to the load.

A digital scroll, to my understanding, is the same type of scroll, but the scroll keeps turning at the same speed but the static part of the scroll is moved up and down to match performance to load.

For the advantage and disadvantage of either one, there is something to say for each. I never used the digital scrolls but worked on a lot of scroll's with or without inverter and in my opinion they work fine.

[EngFBN_BR]

The frequency inverter drive controls the voltage and AC frequency supplied to the compressor motor. By that way, the motor's speed and the mass flow are reduced according to the heat load.
The digital scroll has a kind of clutching system piloted by a solenoid valve. The capacity reduction is achieved by modulating this solenoid with a PWM controller. If 70% of capacity is required, 70% of the time the compressor will be in full load and 30% it will be stopped.

I believe some of the advantages of the digital scroll comparing to the inverter drive are:


No mass flow reduction. The system operates only with full flow or no flow. Don't have to deal with oil return issues,
Simpler system. The inverter is a power device subject to electrical noise, heating, overtension, high current, etc... It has huges rectifying capacitors, IGBTs and sensitives control boards that can fail.

I don't know if the modulation of the mass flow has effect with the refrigeration accessories, mainly in the TXV. I never used this kind of compressor, but the idea looks great.

[Jadeair]

I install alot of digital scroll ducted units made by an Australian company. Nice and simple without all the multiple pc boards, etc involved with inverter systems. Load is varied via an unloading solenoid on the compressor so in the worst case if need be it can be disconnected to run at 100%.

[munesh]

Here in India Blue Star is using Digital Scroll in their VRF Systems. So by definition of VRF (Variable Refrigerant Flow) the equipment cannot be called so as digital scroll works on different principle.

[Diegogto]

Here in India Blue Star is using Digital Scroll in their VRF Systems. So by definition of VRF (Variable Refrigerant Flow) the equipment cannot be called so as digital scroll works on different principle.

it can be discussed if Digital Scroll systems are not VRF systems, but the discusion may come on fundamentals of VRF (or VRV) systems. For me, VRF are systems that can regulate the indoor units' capacity. As digital scroll regulates the amount of refrigerant toward inner units, it is actually a VRF system.

I have a question: I've read that digital scrolls regulate flow with a returning valve and that the scroll elevates, regulating the flow... i'm kind of lost here... could someone explain extensively how does digital scrolls work? Thanks!

PS: sory my english... Spanish is my first language and sometimes i write in english using direct translation... (hola tu -> hello you):confused:

[TRASH101]

I've read that digital scrolls regulate flow with a returning valve and that the scroll elevates, regulating the flow... i'm kind of lost here... could someone explain extensively how does digital scrolls work? Thanks!



I believe the concept is that while the solenoid is closed (loaded) the discharge pressure exerts force downwards causing the scroll to "mesh" thereby compression is regained. When the solenoid is open (unloaded) the drop in discharge pressure allows the scrolls to separate. The volume within the scroll itself would probabley be enough to cause separation but it may well be aided with a spring. The outcome is that the motor runs at a fixed speed while unloaded the volume is drastically reduced which drops the run current.

Thats just my thoughts on it (I may be talking bol*0x);)

[Chunk]

Digital scroll

The beauty of this technology is its inherent simplicity. The standard Copeland® Scroll™ has a unique feature called axial compliance. This allows the fixed Scroll™ to move in the axial direction, by very small amounts, to ensure that the fixed and orbiting scrolls are always loaded together with the optimal force.
This optimal force holding the 2 scrolls together at all operating conditions ensure the high efficiency of Copeland® scrolls. The Digital Scroll™ operation builds on this principle.

The Digital Scroll™ operates in two stages - the "loaded state", when the solenoid valve is normally closed and "unloaded state", when the solenoid valve is open. During the loaded state the compressor operates like a standard Scroll™ and delivers full capacity and mass flow. However, during the unloaded state, there is no capacity and no mass flow through the compressor.

[munesh]

Thanks Everybody! It was nice getting all the replies. It is quite useful.

[mohan]

Advantage inverter based compressor is its capacity variations on variable load conditions.

For example if your peak load is 10TR and average load is 7TR, you can use 7TR compressor @60Hz same compressor can deliver 10TR @90Hz.


Incase of digital if your peak load is 10TR you are left with no choice than 10TR.

In digital you can only handle reduced loads.

[nike123]

Advantage inverter based compressor is its capacity variations on variable load conditions.

For example if your peak load is 10TR and average load is 7TR, you can use 7TR compressor @60Hz same compressor can deliver 10TR @90Hz.


Incase of digital if your peak load is 10TR you are left with no choice than 10TR.

In digital you can only handle reduced loads.

It is not exactly like that.
Every compressor has motor that need to overcame the reaction force of compression.
So, if inverter compressor could deliver 10TR at 90 Hz and 7 TR at 60Hz than his motor must be of same power as one of digital scroll of 10 TR at fixed speed (60Hz).

Also, capacity variations on inverter is from 30% (very inefficient - low COP) to 130% of nominal capacity at 60Hz (again, with lower efficiency than at 100% load).

Digital scroll can vary his capacity from 10% to 100% of nominal capacity.

Converted in refrigeration capacity, Inverter of 10TR maximum capacity, can vary his delivery from 2.1 TR to 10TR. Digital Scroll of 10TR can vary his delivery from 1TR to 10TR.

It is obvious from above that Digital scroll has broader range of capacity variation.

Now question is how efficient is one in comparison to other at various loads.

The most efficient is compressor whose motor is optimized for one condition. That is fixed speed compressor at full load and design conditions.

Every move from that point mean, that motor is over-sized or under-sized, and that his efficiency is not any more at maximum.

[Sridhar1312]

Here in India Blue Star is using Digital Scroll in their VRF Systems. So by definition of VRF (Variable Refrigerant Flow) the equipment cannot be called so as digital scroll works on different principle.

Recent product launch in Chennai Blue star claimed that they are able to control both Temperature and Relative Humidity with Electronic Expansion Valve. To the best of my knowledge it is not feasible. Can any one explain how the control of RH and Temperature is achieved.

[Ashutosh Kumar]

Here in India Blue Star is using Digital Scroll in their VRF Systems. So by definition of VRF (Variable Refrigerant Flow) the equipment cannot be called so as digital scroll works on different principle.
Exactly sir. Digital Scroll machines should be called as VRF...
Also I would one thing... failure rates are very high in digital scroll as moving parts are much more nos. unlike inverter in which only one scrolls keeps on rotating.

[desA]

... failure rates are very high in digital scroll as moving parts are much more nos. unlike inverter in which only one scrolls keeps on rotating.

Can you please substantiate this statement with suitable reference information, or case studies?

It is a very broad statement & could be very misleading.