A couple of questions

[marc5180]

Hi all,
I've been set a task of preparing a powerpoint presentation and reading it out in front of the class at college. This is the task;
"Describe system layout and operating principles for multi evaporator systems with independant control for each evaporator"

I've decided to explain about a VRF, however i have a few questions.

Firstly, how does heat recovery work? I know that it uses the heat from one room and transfers it to another room but this can be done with out the compressor running, or so i have heard. Is this true? and if so how?

What type of VRV/VRF's are there, i.e 2pipe (that heat or cool) 3 pipe (that can heat and cool simultaneously) and supposedly Mitsubishi have brought out a 2pipe that can do what daikins 3 pipe does, how true is this and again how does this work.

Lastly do the indoor units on VRV/VRFs have evaporator pressure regulators on or are these not needed?

Lots of questions, sorry

[Brian_UK]

Good luck Marc... EPRs are not required on these AC units because you have EEV on the inlet.

Personally I would have gone for a multi evaporator cold room system as it should be easier to explain.

{edit} Have a look at the Sporlan EPR document here..
http://www.parker.com/literature/Sporlan/Sporlan%20pdf%20files/Sporlan%20pdf%20090/90-20.pdf

[Thermatech]

Mitsubishi City Multi VRF R2 heat recovery operation example.

One indoor unit in heating mode ( condenser )
One indoor unit in cooling mode ( evaporator )
Outdoor unit compressor sends hot gas to B/C distributon box which in turn sends the hot gas to the indoor unit asking for heat.
The indoor unit heating condenses the hot gas to a warm liquid which returns to the B/C distrubution box & through a subcooler to get rid of bubbles in liquid.
The B/C disribution box sends cool liquid to unit asking for cooling.
The cooling unit flashed off the liquid through the LEV valve & vapor returns to the B/C distributon box.
From B/C distributon box vapor returns on suction pipe back to outdoor units.

Full heat recovery from room cooling to room heating.
Only 2 pipes needed.
Been doing it like this since 2001 in the UK & longer in japan.

The refrigeration is simple basic stuff its all the electrinic control thats complicated.

[marc5180]

Good luck Marc... EPRs are not required on these AC units because you have EEV on the inlet.

Personally I would have gone for a multi evaporator cold room system as it should be easier to explain.

{edit} Have a look at the Sporlan EPR document here..
http://www.parker.com/literature/Sporlan/Sporlan%20pdf%20files/Sporlan%20pdf%20090/90-20.pdf
I would like to talk about a cold room but i dont know enough about them because i don't work on them often.
The problem that i am having with using a VRF system is how far do i go? Do i talk about 2 pipers or 3 pipers, bc boxes or bs boxes, fixed speed compressors or inverter compressors and the list goes on... meaning my presentation will go on for a long time and everyone will probably be asleep by then:confused:.

[marc5180]

One indoor unit in heating mode ( condenser )
One indoor unit in cooling mode ( evaporator )
Outdoor unit compressor sends hot gas to B/C distributon box which in turn sends the hot gas to the indoor unit asking for heat.
The indoor unit heating condenses the hot gas to a warm liquid which returns to the B/C distrubution box & through a subcooler to get rid of bubbles in liquid.
The B/C disribution box sends cool liquid to unit asking for cooling.
The cooling unit flashed off the liquid through the LEV valve & vapor returns to the B/C distributon box.
From B/C distributon box vapor returns on suction pipe back to outdoor units.
So what you have explained is how a 2 piper works? So discharge is sent to BC box and superheated vapour is returned on the suction line.
I heard that heat recovery can be done when the outdoor unit has stopped running and the heat from one room can be used and transferred to another room that requires heating. Not sure if its Mitsuibishi or Daikin systems that do this, or both.

[frank]

Hi Marc

The compressor is needed in both 2 pipe and 3 pipe systems (Mitsi and Daikin) to produce the circulation. Without the compressor you cannot achieve any heating or cooling.

With Daikin 3 pipe, if the indoor units are balanced, i.e. 5 cooling and 5 heating, then the outdoor coil is not needed and the outdoor condenser fans do not run, but the compressor does.

As soon as one of the indoor units is satisfied on thermostat or changes mode then the indoor circuit become unbalanced and the outdoor coil acts as either condenser or evaporator to make up the imbalance.

Does this make sense to you?

[marc5180]

Hi Frank,
yes that makes sense. I wondered how it could work without the compressor running but i was assured it did.
Thanks.

[marc5180]

I need a picture of inside a BC for my presentation but can't find one anywhere. Does anyone know where i could get one?

[Thermatech]

You might find something usefull on the Mitsubishi Electric USA or Austrailia web sites.

BTW
in full heat recovery the compressor runs to circuulate refrigerant but outdoor coil & fan are not needed or used.

All the best for your presentation.

[icecube51]

I would like to talk about a cold room but i dont know enough about them because i don't work on them often.
The problem that i am having with using a VRF system is how far do i go? Do i talk about 2 pipers or 3 pipers, bc boxes or bs boxes, fixed speed compressors or inverter compressors and the list goes on... meaning my presentation will go on for a long time and everyone will probably be asleep by then:confused:.
don't worry, when i went for mi presentation or final script, it was 364 pages. i designed an indoor ice rink of 1800m². they were happy. the other guys had 10 or 15 pages. i heard last year it was still there as model for newcomers.

Ice