Inverters in server room

[AbsoluteWDJ]

I have recently gained a new customer with an issue that their server room sometimes maintains a room temp of around 24c (set point 21c) and just recently the room temp reached 29c. I believe from reading various other posts on the forums, that I might have an issue with the humidity/wet bulb temps, here is the information I've taken from the server room and air conditioning units. I'm thinking of adding humidifiers.....but thought I put it out there first for a more experienced point of view.

Server heat load and room - around 11.5kw.
We have two Mitsubishi power inverters, Indoor m/n: PKA-RP4FAL Outdoor m/n: PUHZ-RP4FAL
Ambient temp = 5c
Suction pressure = 100psi then would raise 105psi
Suction actual temp = 1c to 8c
Indoor return air temp = 26c
Wet bulb temp = 12c
R/H = 25%

If there is any recommendations out there it would be much apprieciated. Mitsubishi tech said to add more units.

[frank]

R/H = 25%
There's your answer. It's not a case of insufficient cooling capacity, it's a lack of latent cooling.

Add some fresh air ventilation or humidity.

[brunstar]

well looking at the unit, if it is trying to maintain 21 degrees and it has a return temp of 26 degrees you may find that they have added more heat load to the room, how many kw of cooling capacity do you have there at the moment with the two 4kw units, you will probably find that with the low ambients and the low humidity they are finding it hard to control and cutting out on freeze protection. by the looks of it they would be running continuously as your load is mkuch greater than the output of those machines, i think you need another 5 or 6 kw in that room to do the job, or put a larger unit in to do the majority of the load and have the two exisiting splits as back up.

[Gary]

Pressures don't tell us anything if we don't know what refrigerant is in the system.

[AbsoluteWDJ]

I believe the RP4FAL's have a nominal cooling of 10kw each. I haven't exact details of heat load from servers but I have asked their IT to see if they can give me that info, in the meantime I used AC Calc with room size, lighting load and around 70 servers at 350watts which totalled about 11.5kw. The room is enclosed with no windows or ventilation.

[AbsoluteWDJ]

Sorry Gary! There both R410a

[Gary]

The first thing I would do is maximize the evaporator airflow. The more air you can get through those coils, the better.

[AbsoluteWDJ]

Hi Gary, the fan speed is set on the highest level

[Gary]

Hi Gary, the fan speed is set on the highest level

Then the next step would be to add more evaporators... to the max the manufacturer will allow for those condensing units.

And if the mfg would allow it, I would add EPR valves to control the humidity.

[Gary]

And if the mfg would allow it, I would add EPR valves to control the humidity.

Hmmm... on second thought, this might conflict with the inverter controls. The alternative would be to adjust the inverter to provide a higher suction pressure (higher anti-frost setting)... along with the max evaps. The colder the coil, the more dehumidification and vice versa. You want to avoid dehumidification.

The ideal for this application would be to limit the evap leaving air temp to no less than 10C/50F.

[AbsoluteWDJ]

Mitsubishi do not manufacture this indoor model anymore. If they did are you suggesting to twin split the condenser on two 5 kw evaporators?

[Gary]

Mitsubishi do not manufacture this indoor model anymore. If they did are you suggesting to twin split the condenser on two 5 kw evaporators?

I am suggesting more evap capacity... as much as the condensing units can take without overloading.

[AbsoluteWDJ]

I did speak to Mitsubishi tech to see like Daikin whether there is a low humidity setting on the control settings but to no avail.

[AbsoluteWDJ]

Gary, do you believe i would get improved performance if i could bring the humidity up inside the server room....even if the ambient temperature is low? I can hear the inverter compressors build up speed and then drop after a while to partial load. This was when I measure the suction pipe temp at 8c.

[BritCit_Juve]

Fit a humidifier and the unit will have better control as the rh is increased.
To test the situation stick a boiling kettle into the room to raise the rh.
alternatively leave the door open
Brit

[Gary]

Fit a humidifier and the unit will have better control as the rh is increased.
To test the situation stick a boiling kettle into the room to raise the rh.
alternatively leave the door open
Brit

I do not disagree with this. The ideal is to either add humidity or to not remove humidity... or both. From an efficiency standpoint, not removing the humidity is the better solution.

[Thermatech]

The suction pressure tells us that the indoor unit is operating at coil frost prevention conditions.
You are able to confirm the indoor coil temperatures at the temperature sensors by using the engineers mode at the remote controller to live monitor the data.
Because the unit is operating with lowsuction pressure / temperature the outdoor unit is slowing down the compressor to increase the indoor coil temp back to above coil frost prevention condition which is usually about +1 deg C on ME systems.
Then after the indoor coil has been more then +1 for a few mins then the compressor will try to ramp up again.
But as the indoor coil drops staight into coil frost prevention again the outdoor unit has to reduce compressor speed again.

Again you can monitor the live compressor speed data at the remote controller.

The single cause of the coil frost prevention with resulting slow compressor speed & reduced cooling performance is the low humidity which you have measured in the room.

25% RH & 12 deg C WB is normal for this application if the room is sealed with no freash air.
In this case the units dehumidify the room air until the WB falls below 15 deg C WB at this point the indoor unit will be in coil frost prevention conditions.

No body can give you any data for the sensible cooling of this system at any on coil condition below 15 deg C WB because Mitsubishi technical data book quote 15 deg C WB as the lowest allowable operating condition.

That operating condition is set by the manufacturer for a reason.
The design engineers know that is the lowest limit the system can operate at without continual coil frost prevention opertation.

This is why contractors have to oversize standard split systems for computer room application & then often resort to putting even more units in when the units do not cool enough.

You need to be aiming for 50% RH minimum & then you will see the outdoor unit ramp up the compressor & you will get much improved cooling performance.

If you monitor the RH & WB you will also note while monitoring the live coil temp data at the remote controller that at 50 to 60% RH the coil temp will be higher than coil frost prevention & you will also notice that the suction pressure will improve to 7 to 8 bar depending on the interconnect pipe length.

BTW
also make sure that the outdoor units cannot be exposed to any cold wind as this will make the fans free wheel & the system will overcondense & this will also make lower evaporating temperature at indoor unit & coil frost prevention.
If you can do anything at the outdoor unit to make higher discharge pressure that will also help.
Max air flow at indoor units & make sure supply air does not bounce off the server cabinets & short circuit straigh back to the indoor unit.

[AbsoluteWDJ]

Thanks for the post Thermatech... The controllers are hard wired PAR-20MAAT-E. If I operate in test mode the coil temp sensor is shown where the return air temp is normally. It shows either 3c and 6c. Can you monitor compressor operation on these controls and if so would you know where I could find how to?

[TRASH101]

Use caution if you are going to add humidifiers because unless they are adabiatic they will add a considerable heat load into the room.

[Thermatech]

The items of data available at the remote controller 'request code list' run up to about 150 seperate items.
You need the service manual for the list of data & how to use the engineers mode to access the data.

Then
from the remote controller you can monitor all the live data like compressor speed, compressor amps, outdoor fan speed all outdoor & indoor temp sensors LEV valves open possition ect ect ect.
The system records the operating data when it stops on a fault so you can recall all that data to see operating conditions of the unit when it last stoped on a fault.
You can view the run hrs of the compressor & how many times it has started.
You can confirm the dip switch settings at the outdoor & indoor unit from the remote controller.

Just go on the Mitsubishi uk web site & resister
after they give you a password you can down load any manuals you want.

The last time I was trouble shooting these units I printed off the pages of request code list & used the pages to record the data. Then you can build up a picture of how the system is operating.

The operating conditions that you have described are classic low humidity high sensible cooling operation for comfort cooling split with SHF of around 0.7.
The system needs some latent heat to work normally.
Introduce some latent load / humidity will make the best improvement to system performance but also look out for any over condensing at the outdoor & the air flow in the computer room.

BTW
I looked at the performance data
The lowest indoor WB temp with cooling performance data is 16 deg C WB.
The manufacturer quotes the lowest operating WB at 15 deg C WB below which the operation cannot be garanteed.

So no one can provide you with any sensible cooling performance data for the system operating at 12 deg C WB.

This situation is just about the same for all standard mass produced comfort cooling split systems.

[AbsoluteWDJ]

I've never had to supply a humidifier before. So could anyone give me recommendations on good manufacture and application for server room at these sizes: width = 4m, length = 5m and height = 3m.

[nike123]

I've never had to supply a humidifier before. So could anyone give me recommendations on good manufacture and application for server room at these sizes: width = 4m, length = 5m and height = 3m.

You should size dehumidifier for required moisture removal rate of air conditioners, not by room size.

[AbsoluteWDJ]

You should size dehumidifier for required moisture removal rate of air conditioners, not by room size.

I have two Mitsubishi electric power inverters indoor m/n: PLA-RP4FAL, which are around 10kw nominal each. I would like to raise the server room R/H from 25% to 50%. Any recommendations?

[nike123]

I have two Mitsubishi electric power inverters indoor m/n: PLA-RP4FAL, which are around 10kw nominal each. I would like to raise the server room R/H from 25% to 50%. Any recommendations?

What is temperature of room?

[AbsoluteWDJ]

The items of data available at the remote controller 'request code list' run up to about 150 seperate items.
You need the service manual for the list of data & how to use the engineers mode to access the data.

Then
from the remote controller you can monitor all the live data like compressor speed, compressor amps, outdoor fan speed all outdoor & indoor temp sensors LEV valves open possition ect ect ect.
The system records the operating data when it stops on a fault so you can recall all that data to see operating conditions of the unit when it last stoped on a fault.
You can view the run hrs of the compressor & how many times it has started.
You can confirm the dip switch settings at the outdoor & indoor unit from the remote controller.

Just go on the Mitsubishi uk web site & resister
after they give you a password you can down load any manuals you want.

The last time I was trouble shooting these units I printed off the pages of request code list & used the pages to record the data. Then you can build up a picture of how the system is operating.

The operating conditions that you have described are classic low humidity high sensible cooling operation for comfort cooling split with SHF of around 0.7.
The system needs some latent heat to work normally.
Introduce some latent load / humidity will make the best improvement to system performance but also look out for any over condensing at the outdoor & the air flow in the computer room.

BTW
I looked at the performance data
The lowest indoor WB temp with cooling performance data is 16 deg C WB.
The manufacturer quotes the lowest operating WB at 15 deg C WB below which the operation cannot be garanteed.

So no one can provide you with any sensible cooling performance data for the system operating at 12 deg C WB.

This situation is just about the same for all standard mass produced comfort cooling split systems.

Thanks for the info... Am i'm right in thinking that the live monitoring data is of a PAR 21MA control and not the PAR 20MA. Cannot find the exact service manual for the outdoor model no but have found PUHZ-RP4VHA manual instead and in this you retrieve the data using a service tool. With which I don't own!

[AbsoluteWDJ]

What is temperature of room?

Lowest 24c and has been known to reach 29c

[nike123]

Lowest 24c and has been known to reach 29c
I see design temperature in first post 21°C.

I got about 15l/hr! I am not sure in my result so maybe someone else with HVAC system design knowledge could confirm.

[Thermatech]

Now I am confused

How old is this system ?
RP means R410a
and with R410a systems the system would normally have remote controller PAR-21MAA which you can use to get operating data.

But you have PAR 20MAA which would normally be fitted to older R407c models PKA P4FAL which does not have all the extra fuctions included on the PAR-21MAA

Perhaps you have a very early R410a model system & older PAR20MAA remote controller.
In this case you can access the operating data but need service monitor tool PAC-SK52 which you connect to the outdoor unit.

Please can you double check outdoor , indoor & remote control model numbers & manufacture date from unit model number labels.

[beagle]

Could well be a PAR20 controller, I'm almost certain when the R410a kit first started to trickle through they were supplied with PAR20's, then it went to either/or with little to no information on the differences from Mitsi between the two. I've been away from Mitsi kit for a good few years now so it's nice to finally find out exactly what the differences are :)

[AbsoluteWDJ]

Yeah it is a PAR20 MA and R410a. I've booked a course this friday with Kooltech on M Series and Mr Slims fault finding, I believe we'll receive the service tool then. Thanks for the info Thermatech.

[ateeq.baig]

I have recently gained a new customer with an issue that their server room sometimes maintains a room temp of around 24c (set point 21c) and just recently the room temp reached 29c. I believe from reading various other posts on the forums, that I might have an issue with the humidity/wet bulb temps, here is the information I've taken from the server room and air conditioning units. I'm thinking of adding humidifiers.....but thought I put it out there first for a more experienced point of view.

Server heat load and room - around 11.5kw.
We have two Mitsubishi power inverters, Indoor m/n: PKA-RP4FAL Outdoor m/n: PUHZ-RP4FAL
Ambient temp = 5c
Suction pressure = 100psi then would raise 105psi
Suction actual temp = 1c to 8c
Indoor return air temp = 26c
Wet bulb temp = 12c
R/H = 25%

If there is any recommendations out there it would be much apprieciated. Mitsubishi tech said to add more units.
dear
you have to set the differencial value 1 digree
so your unit will auto at 21c and restart at 22c

[nike123]

dear
you have to set the differencial value 1 digree
so your unit will auto at 21c and restart at 22c

These are inverters, my friend. They do not work on ON-OF principle, and in normal conditions, they keep temperature around 0,5K from set value.

[AbsoluteWDJ]

Thanks for the support people. I used the kettle method which brought the r/h to 45% and wet bulb to 16.5c, I install service monitor tool on outdoor unit. The Hz went from 54 to 68 the ambient temp was 4c. So I did see an improvement with the inverter however I do believe it counter balanced itself because I was adding extra heat into the room. I made a couple of adjustments to the indoor units 1. disconnected louver motors and fixed downwards 2. Set controller as thermastatic control. I've found this has helped alot and has given us a realistic room temp because the indoor height is about 3 meters and the units are opposite one another at a distance of around 5 meters. The customer would like backup for the existing equipment so we are considering to install a Daikin RZQ which has an EDP setting. Does anyone recommend these?

[laf100]

I have read a post warning that RZQ's have a high leak rate on the condenser coil, may be Daikin have addressed this, but best to do some homework on it!
Found it:
http://www.refrigeration-engineer.com/forums/showthread.php?t=17355&highlight=Daikin

[R1976]

Hi

I recently fited a Mitsubishi unit in a server room. The indoor unit had a larger coil size than normal on a split for the condensor capacity and I believe this is a specialist system for server rooms. Indoor PKA-RP50FAL2, outdoor PUHZ -RP50VHA3, the indoor size was that of a 10kW unit.

[AbsoluteWDJ]

I have read a post warning that RZQ's have a high leak rate on the condenser coil, may be Daikin have addressed this, but best to do some homework on it!
Found it:
http://www.refrigeration-engineer.com/forums/showthread.php?t=17355&highlight=Daikin

I've spoken to a friend of mine who mainly supplies Daikin. He has had four condensor coils to change on the RZQ's! In saying that he also believed they were 2007 manufacture year. So i've spoken to the supplier who has never heard of this problem! He did mention there on D series now and I'll receive 3 years warrenty. So i'll supply and install the RZQ's in the hope that the issue has been resolved.