Toshiba VRF

[kered]

Is anyone having any trouble with Toshiba 3-pipe VRF not maintaining temperature? I set the controller to cool 20 and watch the room temperature drop to 14C (with an air off of 2C) with the indoor unit still producing cooling after 20 minutes even though it has reached it's temperature after 10 minutes. Similarly on heating, set the controller to heat 20 and watch the room temperature rise to 35C with no sign of the indoor unit stopping after 15 minutes.

Indoor units are ducted type with passive return, I have re-located return sensors to underside of grid, I have de-rated indoor units, adjusted fan speeds to no avail. Original design has been checked by consultant and checks out ok. Rigid duct-work is approx 1M using swirl diffusers.

I've installed lots of Tosh VRF with no problems and would be interested to hear if anyone else has had similar experiences.

[DL A/C]

is this happening on only 1 unit or all of them??

[VRVIII]

is this happening on only 1 unit or all of them??

If the problem does only occur on 1 indoor I would check the electronic expansion valve drives ok on that unit. Could be the valve may failed in the fully open position, the valve should close when set point is reached.

[kered]

The fault is occurring on all of the indoor units - it's not confined to just one indoor unit. I'm aware of the PMV operating position and the fact that it should ramp closed as room temperature is achieved - on this system however it seems to have a mind of it's own.

[croc1774]

I dont suppose someone has set up the sensors on controls.

[Loops]

Hi Kered,

You don't say which Toshiba VRF system it is - R22 R407c or current R410a which would help us in the advice we could give.

But in principle I'd look at return air sensor location. You say the std one has been extended to the underside of the grille. In other words high level.

It will take time for the room to 'fill up' with cold air for the air sensor to shut down at set point, so the air at lower level will be much colder. The opposite is true in heating mode.

The effect of this is that at normal desk height there will be big fluctuations in temerature.

If you have a current R410a system and local controllers in the occupied space you could try setting the system to use the sensor built into the controller - set DN code32 to 0001.

If you have an older system try extending the retun air sensor to a height of about chest height. If you can't get the 'RBC-TA1 sensor kit' from Toshiba you can just cut and splice the sensor if you are careful but use a screened cable for this. About 0.5 or 0.75mm will be fine.

One other point is that if you have a current R410a system make sure that the indoor units aren't oversized for the rooms as this can cause big fluctuations due to 'minimum run time'.

I take it you have discussed this with the Eire distributor?? G T Phelans are very experienced with the VRF systems.

Cheers

Loops

PS if you need non-biased advice \ support on site for the Toshiba products and willing to pay expenses and time on site get in touch with me.