economizer capabilities for server room
The economizer is a little confusing. I am looking for any information to clarify the purpose and capabilities of these units. I am an Hvac tech from the residential installer upbringing but have since become more and more involved with troubleshooting and controls in the comercial side of hvac. I have done one year of hvacr tech school and am EPA universal. I am into my 10th year now.
My goal is to cool the server room with the economizer when the outside tempurature drops below 20* F while simultaniously shuting the 1st and 2nd stage of mechanical cooling off. I think I would like it to work as a stage of cooling but with exceptions.
I have a trane voyager 7 ton package unit 2 stage cooling with economizer and power exhaust as the primary mode of cooling this space. With three mitsubishi mini splits as backup. But with server room expansion the mini splits are curently runing 70% - 100% depending on outdoor temperatures. And the 7 ton is runing 90% - 100% 24/7. There is also an emergency back up from a 40 ton Trane intellipak that is ducted into the existing duct work of the 7 ton unit and is controlled by a DMS system, as is the 7 ton unit.
Thank you for your time.
Be very careful with this - I agree with your basic logic however further considerations must be made and I am no expert in server rooms.
What is controlling the humidity in this room?
What is your 'average' outdoor humidity during the months/weeks of 20 degree weather? You must realize humidity levels are very important in server rooms and with an economizer in use you can really adversely effect the humidity control.
If the 7 ton has an economizer on it already does it work or has it ever been used in the past?
I have had numerous server type rooms that the occupants/owners hate economizers and have forced us to disable them. They don't like the extra dirt infiltration that happens with economizer mode, basically the economizer gets used as the emergency cooling if the mechanical fails and the outdoor air temperature is adequate, and that is only in a couple of the DDC systems I have dealt with it happens automatically, otherwise its manual.
Next with the lack of available capacity due to growth, I would not recommend completely locking out the mechanical cooling, it needs to be available at all times. If they allow/want the economizer I would use it as 1st stage cooling any time the outdoor air conditions temp & humidity are adequate to cool the space, 2nd stage brings on compressor with the economizer operating to supply air temp, that way if the MAT is 55 the SAT won't get too low and cause the indoor coil to freeze and then 3rd stage the economizer goes back to min position/closed and the 2nd compressor comes on.
Do the units have some kind of low ambient kits for cooling?
Do the compressors have crankcase heaters?
I have one mountain top system where the only time the economizers are allowed to run is after Nov. 15th and before April 15th. Generally there is snow on the ground during that time frame so they figured it would minimize dirt intake. The first year the original design didn't account for the snow and wind levels - the economizer would suck in snow sometimes and that would leak down onto the transmitters - not good. Anyway a redesign of the intake hood and some different screens 'fixed' the problem for the most part. Sometimes the screens would just get clogged with snow and nothing that could be done but to bring on mechanical cooling.
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If free cooling was sufficient for the primary stages of computer room cooling, it would have been done before our time. There, now that I've established myself as argumentative, I'll try to be of assistance to you.
I have worked on a good number of computer room, server room, clean room, phone room, POP sites, and the like. I can't think of one that is currently using economiser.
Most outfits were abandoning economisers due to dust and/or humidity issues. You will also create a static pressure situation, although it may not be a "problem". Is the room sealed, as most server rooms are?
It's great to be alive and pumping oxygen!
An off the shelf package unit is misapplied here. You've said they basically have two other backup systems so I'm guessing this room is critical to the people that own it.
I would introduce the idea that they need to call this room what it is and and install a system that is designed for what they are doing in the room. Further retrofits and or adjustments to the existing unit is just going to get you in trouble. Sell them what they need first, if they don't want to buy it. Then agree to some modifications for what they have, this way you were always right when they have problems down the road, which they will and then you won't look stupid. Forget the economizer , you really don't want to bring in any more fresh air than you have to in order to meet the general ventilation requirements of the space.
I've never seen economizers used on server rooms for two reasons. First is humidity levels need to be maintained between 48% and 52%. Second is they need to be sealed from the outside and the rest of the space if they use a halon type fire suppresion system.
Central Oregon is not humid. but I really need a reliable source before I can start giving averages. Basically when I was in residential we installed humidifiers and they run quite often to maintain 30- 40% RH. I'll buy a few humidistats for the place. There is no humidifier in this server room and the economizer is set up for dry bulb setting and minimum outdoor damper intake. The enthalpy method is not enabled and requires additional sensors and proper comissioning. I believe the enthalpy is refering to the RH of the air but am not sure this will help me cool the server room when it gets too cold for the mechanical cooling. The 7 ton voyager has crankcase heaters and a cut-in/ cut-out switch set for 225 psi. I am satisfied with there set up until temps get down to 15* and below. Then I have to reset the minimum outside damper setting to maximum and turn off the mechanical cooling. This way the outside air is cooling the space. By the way isn't the economiser suposed to figure this out? Then I have to make sure I turn the mech. cooling back on before it gets too warn outside. and close the outside air damper back to minimum so that I don't get too cold of air going across the indoor coils. I've froze that up a few times already.
Maybe I should be looking at controling this with the controls system. Currently it only sees the space temp as a control point. It Knows the outdoor temp but it is not a control point. I don't have MAT or SAT sensors at this time.
Did you say 48% -52% RH? That is important to the circuit boards right? Well have you seen the size of those condensate pumps in the mini-splits? They don't look like they can handle that kind of humidity. I'd be pumping that out onto a sub-freezing roof top too. Oh this is getting time consuming.
Point well taken. I will propose a dedicated server room unit and at least they'll be aware of a more reliable solution. Although, What modifications were you thinking of?
Yes it is sealed. and all ducts have motorized dampers that close on a call for "halon".
The 40 ton unit is emer. backup only when the building is occupied otherwise the unit is in unoccupied mode and has no airflow to supply as backup. Another problem for the server room. Does any body Know how to set control points on a Invensis DMS system? Really, I'm willing to learn.
A reliable source is a Liebert system, when properly applied.
Whaddya got against the 400 pound gorilla?
It's great to be alive and pumping oxygen!
I have toyed with the idea of using a Glycol system using a water coil in the duct supplying the server room and a dry cooler outdoors to reject heat. This would isolate the room from unwanted humidity but would only work in the cold months for free cooling. What are your view?
3- Mitisubishi Mini Splits (1-Ton each)?
+ part of a 40-Ton Trane (lets say 5-Tons additional)
That’s 15-Tons of cooling + or –
Is this is a small server room?
The 7-Ton Trane is designed for commercial applications; all the economizer knows is that it’s getting cold enough out side to handle the load. Begin opening the outside dampers and closing the return’s. It is not designed to control RH.
All the Mitisubishis care about is achieving a set point. If these aren’t heat pumps they probably shut down when the OAT is below 40*. Again no RH control.
The 40-Ton Trane you said is emergency back up only. No RH control it just wants to get the room cool.
Stop trying to make this equipment do what they were never designed to do.
There is a reason that Liebert, APC and others charge a lot for there equipment. You’re paying for the fancy controls to handle the varying heat loads and ever changing RH that a server room gives. Along with a built in alarm notification system when something begins to go wrong. Its only job is to maintain temperature and humidity within a very tight window, protecting several Millions of $ of equipment and information.
Get the proper unit for the job.
This is the way to go. I can't comment on APC equipment due to site rule #6 http://hvac-talk.com/vbb/showthread.php?t=1241
Originally Posted by mtntom
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Originally Posted by Vampyreguy
My personal experience with my APC install has lets say Had Issues (Is that the PC term for Rule #6)
Although the installing contractor (we’ve all heard this before) could have been much better, APC’s tech support has been fabulous. Extending the warrantees, Getting back in a timely manor, (even @ 2AM) in general being there every step of the way. One by One the issues have been taken care of.
Thank You Charlotte. (You know who you are)
(BTW she is a member of H-Talk)