Mitsubishi City Multi - Stand by

[Contactor]

Hello, I have the following symptoms-

PURYP500 (2x250 twinned) 17 cassettes
PURYP300 11 cassettes

Both of the above systems are in the same new build, not yet comissioned. Additional charge correct. Pressure tested at 36 bar 24 hours, strength test 41 bar 10 mins.

Seem to be heating very well (not yet run on cooling), however, would anyone like to comment on the following:

1. Bottom of receiver covered in thick ice.
2. Suction pressure occasionally dropping way below 0 deg C.
3. PAR27 controllers go into standby, then units run up to set point in temp, then intermittantly back to standby.Occasionally some fan coils stop, even if others in same group are still running.

Am I normal?

Thanks!;)

[nike123]

Am I normal?

Thanks!;)

In relation to what?

Just kidding!:D

[nike123]

1. Bottom of receiver covered in thick ice.

That mean that receiver saturation temperature is below 0°C. Are you sure that "receiver" is not accumulator.


2. Suction pressure occasionally dropping way below 0 deg C.What is outdoor temperature.


3. PAR27 controllers go into standby, then units run up to set point in temp, then intermittantly back to standby.Occasionally some fan coils stop, even if others in same group are still running. Did you checked your voltages against what they suppose to be, and did you checked that remote control wiring is according to instalation manual (length, type, cross section, shielding, distance from power cables, etc...)?

[Thermatech]

Yes normal for commissioning heat mode in winter low temp conditions.

The room temperature on coil temp is very low.
The index of indoor unit capacity may be more than the outdoor capacity.

In cooling mode the outdoor unit use fan speed control to control the head pressure. Target about 24 bar discharge.

But

In heating mode the indoor units are the condenser & so no head pressure control because fan speed set at remote controllers. Target about 28 bar discharge.

For example if the total capacity of the indoor units is 130% & the capacity of the outdoor unit is 100% then with all indoor units running flat out the system is overcondensing.
Low discharge = low suction pressure / temp & frosted suction acumulator due to low suction pressure / temp.

Consultants tend to design the system for max cooling load & dont think about the implications of the system heating the building up from very cold with indoor units in excess 100% system capacity.

The system will try to cope with this extreem operating condition by switching off some indoor units.

Try running only 50% of the indoor units.
You should find that the system will operate at better suction & discharge pressure / temp.
When those rooms are finally up to reasonable room temp then 1 by 1 turn on indoor units untill all rooms are up to temp.

The system will run better when the building is all up to temp.
But at the moment the builing is cold & the complete structure is cold so it will take time for the building fabric to warm up.

[Contactor]

Many thanks Thermatech, I can get some sleep now!

Regards