Sharing Return Air Sensors?

[C_Henderson]

I am currently working on 3 Lieber Hiross units in a server room.

Number 1 runs every 20 mins or so to get the return air down to 20 degrees (all the 3 units have a 20 degree setpoint on return air) There isnt much heat load in this area of the room...

Number 2 runs consistantly 24-7 as there is a lot of heat coming from this area near the return air vent.

Number 3 never runs due to equipment being moved and therefore no having no load to bring the return air temp up. it just basically acts as a fan.

1, 2 and 3 are all along one wall. Supply up about 7.5ft and return about 4ft high. I'm doing alot of work on these. and cutting out all the other stuff im doin, i'd like to give number 2 a hand so its not running balls out all the time n try to get number 3 to do some work...

what i figured is that as return air sensor no 2 is sensing 26 degrees and number 3 19 degrees. could i put the return air sensor in the same ducting as number 2 so it senses 26degreees and kicks in with some cooling as well, so basically the units act as one. cooling and shutting off at the same time. i will also change the supply ducting on number 3 so it blows towards the heat load that number 2 is dealing with...

will this create any problems or has anyone tried it before? the only problem i can thing of is that if number two fails. Number 3 will do too...

any suggestions on this please?

[NoNickName]

I don't see why three CCUs in the same room are sensing three different temperatures.

[C_Henderson]

I don't see why three CCUs in the same room are sensing three different temperatures.


because all the server equiptment has been moved around in the room...
theres is no load near unit 3 only a computer moniter.
near number 2 on the other hand is a LOT of computer/server equipment chucking loadsa heat out stright towards the return, therefore the return at 26degrees where as 3 is at 19... unit number one doesnt have a lot of heat around that area either, but enough to kick in and out to keep return around 20 degreees return...

[Jase]

I'm sure you can fit a remote sensor within the room and set up average settings within the Hiromatic controller. Is no.1 unit the master?
I would not bother altering/swapping sensors on units as this will cause you problems. Why not talk to Liebert Hiross and discuss your requirements.

Regards
Jase

[KayPoh]

Number 2 runs consistantly 24-7 as there is a lot of heat coming from this area near the return air vent.

Why not try putting a big floor standing fan at No. 2 area to direct the heat away so as to spread out the heat.

[NoNickName]

Yeah, I would just mix the air better. No need to bother with the sensors.

[alex1081]

Dear Henderson,
hiross units with microface control and same software version have a standard possibiity , with bus connection ,to work in different modes.
They can share the sensors and setpoints or not.
With Hitomatic control you can manage better because you can add some more features.

Could be better , if you are not familiar with this software , to contact the Hiross service in London.

Are you sure about the offset Value of the Return air sensor temperature are correct ?
This is what they are reading and what do you have really in the inlet of the units.

Ciao
Alex1081

[Tiesse]

Firstly, cards on the table, I work for Emerson (Liebert-Hiross).

Don't go moving sensors around, that will potentially add to your woes (if you move the sensor of a unit that has no load to a heavily loaded unit, you could end up with the unloaded unit icing up).

Depending on the version of Microface controller, there is a solution to your problems.

The issues you have are due to an uneven heat load (as your original post explains).

The units can be networked together to communicate with one another (by using our Hirobus cable).

If the units have Microface E controllers you are in luck (not just Microface, but the next generation which was the Microface E).

You network the units together then select teamwork mode 2. This controls to the average temperature across all units & then where the average dictates a colling stage requirement, before bringing on the next stage of cooling across the units (teamwork mode treats the system as one large unit) the system looks at each unit's local temperature & runs the cooling circuit that is currently in standby with the largest cooling demand.

The problems you are experiencing are exactly the reason this mode was designed (the original Microface only gave the option to have all units networked operate as a large units cycling the compressors on a hours run principle).