Can somebody explain the refrigerant cycle for VRV and city multi

[jbomba]

Hi im struggling how to get my head around the vrv refrigerant cycle i understand the refrigeration cycle fine but im puzzled how it can simultaneously heat & cool. Doesnt make sense to me someone enlighten me!

[lana]

Hi,

You mean the heat pump cycle?

[marc5180]

Why don't you download the vrv training manual and the city multi PURY manual and have a read through them, it's all explained in there.

[cool runings]

Hi im struggling how to get my head around the vrv refrigerant cycle i understand the refrigeration cycle fine but im puzzled how it can simultaneously heat & cool. Doesnt make sense to me someone enlighten me!

If you understand how the refrigeration cycle works then the VRV is only a varient from that.

On any system you have 4 main components

Compressor
Condenser
Metering device and
Evaporator

If the comp is running and the condenser is condensing vapour to liquid you then just expand that liquid
and boil it off in the evaps.

It does not matter where the evaps or condensers are in the system, to do this heat exchange.
The only thing that is important is the temp / pressure differances within the system needs to be set to allow correct flow of refrigerant around the system.

If you know how evaps and conds work the only differance between a cond and an evap is whether
they are absorbing or rejecting the heat.

Liquid flows from the outside cond and through the evaporators absobing heat and boiling off, then the
vapour returns along the suction back to the comp.

Evaps are simple, but for a evap to work as a cond and reject the heat, the hot gas (supplied by a 3rd pipe) moves through a series of valves and as the hot gas flows through the evap the the hot gas
condenses into liquid..

The only complication is the liquid needs to be put back into the liquid line, but if the liquid line is at the
same pressure then the gas will stop flowing, so a pressure differance needs to be lower in the liquid
line so the liquid from the heating evap (cond) can flow and the system can maintain working pressures
and a tempreature differances.

Quite simple in a very complicated way.....

All the best

coolrunnings

.

[JoeAT50A]

CityMulti VRF Variable Refrigerant Flow (m3/sec)
VRV Variable Refrigerant Volume (m3)
Basically both are same technology afterall.
coolrunnings is correct, air conditioning system are based on 4 main components and they tweak the units.
They used inverter compressor to vary the speed of the compressor.
Also metering device so called linear expansion valve (LEV) will control linearly based on speed of compressors.
Program and processes are as follow:-
1) Read data such as room/return temperature, set temperature, and liquid/gas pipes' temperature from indoor unit. Then report to outdoor units main controller (Micor-processor).
2) Outdoor unit's Micro-P will received all the data from connected multiple indoor units.
3) Then Micro-P will decide the speed of compressor and LEV opening pulses for all the connected indoor units.

That processes are not real time, may be every 3mins or 5mins (not so sure exactly interval).

Airconditioing system have many temperature sensors which are normally Ohm resistance based sensors.
That's why 3mins or 5mins scanning time is more than enough I beleived personally.

Aside from refrigerant controls, refrigeration circuit or cycle remain unchanged as CARNOT cycle with 4 major conponents and processes (compression, condense, expansion and evaporation).

Hope that will help.

[r.bartlett]

Hi im struggling how to get my head around the vrv refrigerant cycle i understand the refrigeration cycle fine but im puzzled how it can simultaneously heat & cool. Doesnt make sense to me someone enlighten me!

Think of it as the Koolgas defrost system but adapted for air conditioning

[JoeAT50A]

i understand the refrigeration cycle fine but im puzzled how it can simultaneously heat & cool. Doesnt make sense to me someone enlighten me!

In Citymulti R2 series, they used BC controller to make an arrangement of GAS (heating) and LIQUID (cooling).
BC controller has intelligent enough to recover between requirements of Gas and Liquid.

Some they do it with 3 pipings to recover. But mitsubishi used 2 pipings with BC controller to arrange seemlessly.
It is beautiful indeed.

[Peter_1]

Cool runnings, it's a little bit more complicated then you explain in the Mitsubishi system with the gas separator in the BC controller

[JoeAT50A]

Hi Peter,
Not so complicated.... BC controller have many solenoid valves and as well as expansion valve (LEVs).
Hardware machanism may conplicate but really seemless processes via program software.
Best combination of Mechnical and Electronic.

It's time to keep my mouth shut.........................j/k

6525

[cool runings]

Cool runnings, it's a little bit more complicated then you explain in the Mitsubishi system with the gas separator in the BC controller

Hello Peter.

You are correct when you say it is more complicated than I described.
The system can be extremely complicated, but the idea is a simple one
and I pitched the explanation at a basic level to give the original poster
a brief description of the system.

But I understand your point when you say the controllers can be complicated :)

All the best

coolrunnings

.

[soleowner]

I think everyone has done their very best to help out jbomba. I believe the complexity lies in the software programming. The mechanical components are not, themselves, complex.

The components are readily available such as a Compressor, HEX, solenoids, liquid gas separator, tube in tube HEX, thermistors, DC and AC fan motors, Inverters, Noise Filters, Reactors, Diodes, Stepper LEV's, valve blocks with various voltages from 12VDC~400VDC and 100~480 VAC. It's the software.

The big difference with VRF systems compared to typical high temperature refrigeration for comfort is the efficiency in maximizing the use refrigerant phases. Low and high pressure saturated gas, low and high pressure liquid, separating liquid from gas and vice versa.

As to the question of how does the refrigerant cycle work to get simultaneous heating and cooling within the the same refrigerant circuit. Just think about a typical heat pump and how it rejects the hot air absorbed in the space during cool mode. The hot air is rejected into the atmosphere at the ODU. What VRF "heat recovery" systems do is take that high pressure saturated gas and recycle it to the indoor coils that are calling for heat. It is possible that if fifty percent of the IDU's are calling for both heating and cooling that the outdoor coil will not have any refrigerant at all.

Here is a link to download a flash presentation of an older CITY MULTI R2 series.

http://www.mylinkdrive.com/CityMulti/Software/CM_Refrigerant_Flow/

NOTE: All current CITY MULTI models since 2008 are single inverter compressor systems.

I have also attached a word document to accompany the flash presentation.