VRV

[Manu68]

Hi Experts,

I have been into Chill based. There has some need into VRV.
Would some expert please throw light on below.

Do all VRV have indoor units having its electronic expansion valve? What are the options available?

I have heard people using AHU along with VRV. How does that help when compared to IDU? Any specific reasons for using AHU?

Do the pipes that run carry compressed refrigerant vapor? What is the limitation on the piping length?

Thanks in advance.

 

[EnergyProfessional]

Talk to manufacturer about limitations and options. Typically ~100 meters.
AHU addition depends on ventilation and other needs. Generally you need a DOAS.

AFAIK all the indoor nits have expansion valves.... they do have ducted units so you only supply air to a space.

 

[dbill74]

There are 3 main components of a VRV system;
1) The outdoor unit dumps or pulls heat from outdoors. All refrigerant goes from here to the IDU.
2) IDU (Indoor Distribution Unit) controls where refrigerant goes. It is basically a couple of headers with control valves and provides the refrigerant to the AHU's.
3) AHU's, usually one per room.

Herr is correct, because the AHU's will typically be "mini-split" style units, they are not generally designed to handle outside air requirements thus necessitating the need for a DOAS.
As for limitations, check with manufacturer and codes, i.e. ASHRAE 15.

 

[sprinkler1000]

Low air flow rates of the indoor units, no possibility to control humidity, propietary systems, are the main limitations of these systems compared to chilled wáter.

Máximum size of indoor unit is in the 100.000 btu/hr aproximate.

They are a good choice thou, when you need to centralize many individual split systems at a lower cost. High efficiency rates and long range refrigerant piping are some of the advantages.

 

[EnergyProfessional]

sprinkler1000: with longer refrigeration lines efficiency drops.

As long as you use DOAS for outside air, humidity is not a problem. They are equivalent to fan-coil units in that regard.

 

[sprinkler1000]

HerrKaLeun:

you are correct. I was making reference to some features that make these systems good in terms of efficiency (part load operation with variable flow for example).

Regarding humidity, you can not control how much latent or sensible load the system is going to handle, as you can do with fancoils or air handlers.

 

[EnergyProfessional]

sprinkler: I don't see the difference to a fan-coil unit regarding humidity. The VRV also varies airflow (=lower DAT) to dehumidify. Obvioulsy OA dehumdification needs to happen in DOAS... but that is also true in fan coil units.

 

[sprinkler1000]

Herr

What I mean is that if your latent load is higher than the usual you may not find an indoor unit that handles it. The VRV indoor units are more off the shelf than fancoils.

You can specify fancoil air flow, number of rows, etc, for some applications.