UNIFLAIR AHU Minimal Fanspeed Change

Do what?

lower the minimum fanspeed below 40%... (factory settings)

Why, if shutting down one of the units works?

every AHU must stay on to complete the test. in my testroom i have only 3 AHU's and the external pressure management system must need at least 3 units to work correctly

Could you furnish all info. printed on the name plate of the equipment? You can locate it on all the units.

"i can't lower the fan speed below 40%"

What does the spec. sheet say for this model. You can't make it to perform out side of its design parameters.

we've got several AHU's from different manufacturers and only with the uniflair AHU we have this problem. i know that it's possible because i've seen it in the past at other datacentres but nobody can't or won't give me an answer how to do it.

"because I've seen it in the past at other data centres "

Simple! Get in touch with your buddies/pals at other data centres & get it from the horse's mouth.

as it was that easy.... former boss and no info from the engineers who performed it

See if you can download the user's manual from their site. Or beg, borrow, or steal. Could you give complete details i.e. type, capacity etc, etc,...

http://cr4.globalspec.com/announcement/581/Belden-Inc-Intelligent-Power-and-Cooling-Strategies-to-Optimize-Data-Center-Energy-Efficiency-September-13-2012

Lowering the speed below 40% may result in insufficient air flow to cool the fan motors.

Good point, and it may even say that in the manuals. If so, then the original poster is out on a limb, so to speak.

Why this arrangement needs to take place is still abstruse.

Would obstructing the inlet work?

Possibly the same problem with low air flow for cooling the motors.

OK then, how about spilling some of the air out of the duct to lower the pressure?

Not too sure I have no idea what the test arrangement is or what the test objective is with the OPs description.

Can you re-articulate your question please jimstrabag?

we are constantly trying to lower the PUE (power usage effectiveness)of our datacenters for "colt technologies" in belgium

we have 6 big datarooms which are cooled by big air handling units what runs on chilled water. to lower the PUE of these machines we must control the fanspeed of all the fans to run all at the same speed depending on the differential pressure between the measurement points (under false floor and roof of cold hallway) inside that room. each dataroom should have it's own system in the future. i'm working with a partner who works in the farming industry where they use this systems for controlling everything humidity/ temperature/ pressure,... we have a test room where only 3 AHU (9 fans) stands but the pressure is to high when these 3 AHU's are running so i stopped one of the machines. the main thing we want to now right now is the Power with good pressure of these 3 machines running at a lower fanspeed. i know that there will be problems with cooling of the motors and the cooling capacity of the machines. just keep in mind that it's a test and if succesfully that it will be implemented in a dataroom with 10 machines (30 fans) where constantly people are going in out the room and the speed of the fans constantly changes.

Instead of turning of 1 complete, 3 fan machine could you not just turn turn off individual fans on each machine?

From all you have explained, First we must understand that if the pressure is on the high side even at 40% reduced fan speed, then the total fan capacity is kinder too big for the systm.

The possibility of reducing the air flow below 40% is not feasible, because it will leed to other problems associated with the cooling coil of the AHUs. Hence, i would rather advice that you punture the system by supplying other spaces to reduce the pressure within the proposed space if the cooling required would still be met. or simply resize the AHUs and replace if necessary. But minding the fact that we are trying to reduce PUE, you can just deside to resize and replace the cooling fan and coil of each of the AHUs. but you must also reduce the flow rate of the chilled water by resizing the pipe to be able to supply the adequate volume of chilled water required for the new system.

Install a narrow duct- say 24" x 8" immediately next to unit on each side. Turn a 1" flange inward on bottom end and install a butterfly damper along the long axis. Cut a 22" x 6" inch hole in floor panel 1" from the edge of the tile and seal with silicone on the inward-turned flanges.

Extend the ducts up the sides of the AHU and turn down into the inlet filter with a 180 degree ELL.

The pressure in the plenum will drive air up an into the unit- allowing it to maintain airflow that is at least equal to the 40% speed even though the ACTUAL air feed to the room under-floor plenum will be less.

Adjust the damper to maintain the pressure you are trying to maintain.

Kindly clarify where the pressure is developed, whether in a duct or ???

It is very likely less than 0.25 inches water column (in IP terms). Just enough to push the supply air through a mildly congested under-floor plenum and out the perforated tiles that act as supply grilles where the cold supply is fed up near the intakes of the various DP equipment boxes.

OK so one big question. Is it the room that is over pressurized or the duct?

If it is the duct it was probably Undersized from the get go and the best recommendation is to put a bypass in it.

If it is the room -- why is it over pressurized?

For proper humidity and temperature control, most Data rooms are sealed there for you would simply be circulating the air to control the environment, with no pressure increase, via no OSA entering a room with no relief. You would just have to deal with humidity issues from infiltration due to the pressure drop from the low temp in the data room.

If it is an occupied and working data room that needs OSA in it due to personnel working in it then it must and is required to have a relief or exhaust fan in it to remove/control CO2. If the OSA is fixed or proportional coming into the room then the relief/exhaust fan should be on a drive to regulate the rooms static pressure.

The Biggest issue with slowing the supply fan to slow is an extreme drop in humidity and an increase in static electricity, since the slower you move air over the evaporator coil the more water it will remove from the air.

So the real problem is not to slow the fan down but to find out why there is a pressure problem. With no relief the slowest fan will still build pressure.