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View Full Version : Misubishi City Multi Fan Coils will not achieve set point







CxIdaho
08-01-2013, 09:04 PM
Hoping someone else has seen this issue.

Newly installed VRF systems within the past year or so.

PURY-T-YJMU model outdoor units twinned
PEFY-NMAU/NMHU indoor fan coil units for the majority...

Each HP unit has approximately 6 to 10 indoor units connected.
There are a total of 5 HP units at this site and only 2 of the HP units are having issues with the indoor fan coils. Sizing, pipe lengths, charge and capacities have been verified several times.

BAS system is connected via BacNet and controlling set points, mode and night set back cycle commands etc. All Fan Coil parameters have been verified as correct several times. Misubishi GB-50 controls also connected to all VRF systems with standard mitsubishi zone controllers. System has been tested extensively both with BAS in control and without with the same exact results.

Of the 6 to 10 indoor units on each of the two problem HP units 3 or so will absolutely not achieve set point and based on trend data the units are cycling on and off well below set point with an intermittent range of temperature (cycle dead band) and inconsistent point of cycle as far as when they cycle on and off.

The specific problem indoor units always remain the same.

The remaining units in the building for the most part achive set point and cycle on and off based on the 3 Deg F dead band as expected. Many more consistently than some others.

Issue remains in effect regardless of building load and regardless of outdoor air temperatures or the number of units actively heating. It does not appear to be a capacity issue but appears to be control issue at the fan coils.

Any thoughts would be appreciated.

install monkey
08-01-2013, 09:36 PM
is the evap coil on the faulty indoor reaching 0ver 33deg when u put it in test on the local controller? does the faulty indoor reach setpoint if you turn a few units off on the same system, if so its diversity, usually 130% of indoor capacity over outdoor capacity, is the gas charge correct? as you say its been modified quite a bit. check drier to see if any temp difference, are coils clean?

CxIdaho
08-01-2013, 10:31 PM
install monkey

is the evap coil on the faulty indoor reaching 0ver 33deg when u put it in test on the local controller? Tested okay several times

does the faulty indoor reach setpoint if you turn a few units off on the same system, if so its diversity, usually 130% of indoor capacity over outdoor capacity, Nope, units do not achieve set point with others off or unloaded

is the gas charge correct? Double and Triple Checked, Yes

as you say its been modified quite a bit. Not really modified, all factory, BAS system simply controls via BacNet and has been tested with factory controls alone several times, auto mode, heat mode, what have you it makes no difference, same problems

check drier to see if any temp difference, are coils clean? Yes, strainer is reported as okay no pressure drop and coils are clean, filters clean and fan set up to run at maximum speed.

install monkey
08-01-2013, 10:53 PM
on the outdoor unit on sw1 - you can set the dipswitches to read indoor lev positions , have you checked to see if it is opening up- if it shows that it is then your gonna have to strip the unit to access the lev - using 2 open ended spanners, think its 17 and 21mm- don't use shifters!!!- unscrew the head off the lev- it will be tight- check it does open and close in your hand- then try running it with the head off- you should hear gas gurgling through quite loud- if not- try to refit the head- if you have to struggle to get the heads to bite then the pin is operating ok, could be a kinked pipe on that branch of the pipework, good luck

CxIdaho
08-01-2013, 10:57 PM
9894

Attaching trend data for 7 days of operation, all data in Deg F
Top data is outdoor air, bottom is space temperature
Set point is 72 for the entire duration of the 7 days shown
Space shows a few high spikes to 69, a couple to 70 and one to 71 - shows low spikes at 67, a few at 66 and one at 65 - typically operates from 67 to 68
Outdoor air upper range is about 37 and drops as low as 20

CxIdaho
08-01-2013, 11:02 PM
on the outdoor unit on sw1 - you can set the dipswitches to read indoor lev positions , have you checked to see if it is opening up- if it shows that it is then your gonna have to strip the unit to access the lev - using 2 open ended spanners, think its 17 and 21mm- don't use shifters!!!- unscrew the head off the lev- it will be tight- check it does open and close in your hand- then try running it with the head off- you should hear gas gurgling through quite loud- if not- try to refit the head- if you have to struggle to get the heads to bite then the pin is operating ok, could be a kinked pipe on that branch of the pipework, good luck


One unit showed a problem with the LEV while remaining 5 or so units appear to be okay - If they were not functioning and actually doinfg some heating of the spaces, the rooms would get very cold -

It appears they are cycling open and closed or on and off as can be seen from the trend data... the units are heating the spaces just not achieving set point, fans verified to be running continuously.

install monkey
08-01-2013, 11:06 PM
are the units operating on return air sensor or on the par f27? dipswitch no 1 switch to on, think its sw1 on the address board switch it on so you get the controller pic on the controller, this will cure any stratification problems or if theres fresh air to the unit that can affect the operation- see how it operates

CxIdaho
08-01-2013, 11:24 PM
are the units operating on return air sensor or on the par f27? dipswitch no 1 switch to on, think its sw1 on the address board switch it on so you get the controller pic on the controller, this will cure any stratification problems or if theres fresh air to the unit that can affect the operation- see how it operates

Going to have someone check this to make sure as I see factory default is off

stufus
08-01-2013, 11:41 PM
Going to have someone check this to make sure as I see factory default is off
As install says, should be sw1-1 on for controller sensor and sw1-9&10 on for power failure recovery
Also. Sw3-8 on to do away with 4c stratification
Cheers
Stu

install monkey
08-01-2013, 11:50 PM
yep its sw1 1 factory set is on off position, in on position it will control setpoint at occupancy level ,also check the static duct pressure switch is set the same as the others,also ensure all supply ducts are secure,check the office for draughts,staff leaving door open,or if the office is close to a cold corridor or foyer can affect performance

CxIdaho
09-01-2013, 12:39 AM
As install says, should be sw1-1 on for controller sensor and sw1-9&10 on for power failure recovery
Also. Sw3-8 on to do away with 4c stratification
Cheers
Stu

Verified with the installer that all of the above switches were set properly at start up exactly as described and double checked.

So what is next?

CxIdaho
09-01-2013, 12:46 AM
yep its sw1 1 factory set is on off position, in on position it will control setpoint at occupancy level ,also check the static duct pressure switch is set the same as the others,also ensure all supply ducts are secure,check the office for draughts,staff leaving door open,or if the office is close to a cold corridor or foyer can affect performance

Duct static switches checked
No drafts or open doors causing the issues as doors are closed, these are classrooms. Corridor is at temp and all supply ducts are secure and sealed with no leaks... building is well insulated in all areas and it is fairly tight construction.