Server Room A/C!

[sinewave]

After the much debated problems associated with low R/H problems in Server rooms I thought I'd run this by 'the collective'! :p



We have a client who's R407C 14kW Fujitsu Cooling only cassette has died. They want a quote for replacement.


We tend to fit Mitsi Electric nowadays due to the excellent local backup etc.


Would their Power Inverter units perform any better than their standard Inverter units in a Server room situation?

The old unit I feel was a tadge on the large side as the room is only 2.5M by 3.0M with three 2M racks in it so I am looking at maybe a PUHZ-RP100VHA3 unit?


Cheers in advance! :D

[The Viking]

Ideally you would fit something like THIS (http://www.airedale.com/v2portal/page/portal/airedale_int/airedale_intProductDefault/airedale_int_com/products/level_3_airedale_content_015.htm).

(Obviously choosing that range you would have to fit 2)

[sinewave]

Ah, well there lies the rub!

Obviously we may be competing against other contractors and 99% of them will not be quoting for specialist gear such as the Airedale units.

I bet they cost a bomb to?

The Mitsi kit will come in at around £1700 for a 10kW unit.

[superswill]

what about going mitsubishi heavy industry to bring the cost down?

[Karl Hofmann]

Sadly we are all at the mercy of the accountants who are ruled by the bottom line... So as long as it gets to the end of the warranty.

I have fitted numerous units to server rooms.. over the last few years used Daikin, Tosh and Sanyo, all inverters and no problems....

[Slim R410a]

I take it the R407c system is only 4/5 years old, comp died from short-cycling maybe?

Just quoted a server tonight, 2.5m x 3.5m, client give me a total of 6.0kW from server information. Have quoted a Daikin RZQ100C with FAQ100B wall mount, 9.1kW UK, 6.2kW sensible, which has a low humidity setting for computer rooms available as standard. Not sure if this is available on the Mitsubishi? However, I've not yet used this function on the RZQ, has anyone any experience with this? (says in my tech book it changes parameters & comp frequency control to avoid freeze-up)
I've installed and maintained plenty of Daikin RKS35, 50 & 60 cooling only inverters in servers over the last 4 years and not had a single problem, it seems to be fixed speeds and undersized kit that suffer!

The existing kit in there is an old R22 Daikin, R45? which just can't cope, cuts out on hp, also visited two years ago and was struggling then, recommended replacement.

[sinewave]

Not sure how the Mitsi gear stands on that, not had time to ring them tonight so will be on the phone sharpish Tom.

Just wanted some feedback here first as any manuf' will 'big up' their gear if there's a sniff of a sale!

:eek:

[Thermatech]

Almost without exception sales engineers will tell you that there kit is ok for server room application.

But look just test them out.

Get them to show you in the design technical data where it says the system will opererate without fault below 15 deg C wet bulb.

Almost without exception standard comfort cooling systems have a lower limit for humidity below which the system is not rated.
There is no published performance for sensible cooling duty below that quoted lower limit wet bulb temperature.
For most comfort cooling split systems & VRF systems the lower limit is quoted as 14 or 15 deg C wet bulb.

Look on any psychrometric chart & you will see what that means.

Walk into any server / comms room which has no fresh air ventilation or no humidifiers with a RH meter & see what RH & wet bulb temp you measure.
It will be much lower than 14 deg C wet bulb.

I would like a pint of beer for every time I have been to site & sat arround a table with the consultant, installation contractor & enduser manager & they all want to know why the kit has premature failure.
All I do is show them the room RH & wet bulb data & then had them the manufacturers data book & ask them to show me where in the book is indicates that the unit can work at the low wet bulb temperatures found in the room.
It work every time, without fail.
Then I just show them in the manufacturers data book what the actual lowest limit for room wet bulb temperature is.
Job done.
The consultant & installation contractor go back to the sales engineer who then does a deal to buy them off.

The fact is that when the room wet bulb temperature goes below the lowest operating limit quoted for the equipment by the manufacturer then there is NO DATA for what the sensible cooling capacity will be.

But when the wet bulb temperature does fall below that lower limit then the cooling capacity will be dramatically reduced by coil frost prevention mode or reduced compressor speed on inverter models to maintain aceptable evaporating temp / super heat at the indoor unit.

So who is going to accurately calculate what the actual sensible cooling capacity for the system will be.
This will I suspect be beyond the ability of most contractors. Perhaps some university graduate consulting engineer would have a go.

Therfore most engineers make an estimate & hope for the best.
Sometimes its ok & the system work long enough to get paid.
Sometimes it does not work well enough & the end user does not pay.

Ether way the system wont work for very long before its stuffed & the end user is looking for another contractor to install new units.

And so the never ending cycle begins again.

[Thermatech]

Just take a look at the thread by R1976 Sensible cooling in a school computer class room & you will see what I mean.
I would like another pint of beer for every school computer room disaster I've seen.

[The Viking]

TT,

You will get drunk.
(Alcohol poisoning is dangerous business is dangerous you know)

[sinewave]

:rolleyes:


That's cheered me up no end! :eek:


I hear what you're saying Thermatech & The Viking and appreciate your time & comments.


So what you're saying is outside of a dedicated unit such as the Airedale etc neither of you would entertain the fitting of a top end inverter unit in this situation?

We have fitted around 5 inverter units in small server rooms now (all Fujitsu BTW) and like Karl none have failed yet and most are out of warranty now.

However I've always felt uneasy about the performance and reliabilty issues due to the working conditions these units endure.



Bottom line is we either quote on the same level (if wrong) playing field as other contrcators or walk away! :eek:

This is why I was looking at playing as safe as possible and specing one of the best main stream Inverter units on the market.

[Thermatech]

Sinewave

Back in the 70's & 80's Martair hi low's were available as mix match exactly for high sensible cooling applications.
Martair provided sensible cooling data for the system combinations. Larger indoor unit connected to smaller outdoor unit.
They also recomended some fresh air & provided FA spligot on the indoor unit exactly for that.
They still ran into problems with small rooms & supply air short circuiting which made compressor short cycle & cuased factured suction pipe at compressor.
But this was a cost effective solution for very small server rooms.

But for the last 2 decades the market is flooded with mass produced split systems which are made with sensible heat ratio of arround 0.75 & therefore need some humidity & latent heat load to work as specified in the performance data.
Any high sensible system with SHR of 0.95 or better will have a much larger indoor heat exchanger, a much larger fan & this will make the unit casing much larger & so the unit will cost more.

However we now live in a world when energy efficiency is important.
Look at the free cooling kit made for telecom cabins.
For a very large portion of the year free cooling with some fresh cool outside air will reduce the cooling needed by the dx system.
So use some fresh air for free cooling will also introduce some humidity into the room. The closer to 50% humidity in the room the better a standard split system will work.

If you select an inverter split system which 1/ has a control stratagy which controls compressor speed to maintain indoor coil evaporating temperature above coil frost prevention conditions & 2/ the indoor fan can be locked in high fan speed & 3/ the outdoor fan speed low ambient control stratagy is compatable, then in effect you have a high sensible cooling system as the outdoor unit will reduce the capacity but maintain appropriate discharge pressure with low ambient fan speed control.

But you have to estimate what the sensible cooling capacity for the unit might be becuse the manufactures dont provide that data below the minimum low limit wet bulb temp.

Dont make the common mistake of using a wall mount in a small server room because the cold supply air often just bounces back off the server cabinets & makes the unit cycle on/off/on.
Use a ducted unit & carefully distribute the supply air so that it has to pick up the heat from the cabinets before returning to the indoor unit.

So if the customer will not pay for a proper high sensible system i would fall back to a suitable specification oversized ducted inverter split system with fresh air.
This will save the customer energy cost & should last longer than the cheapest standard wall mount split solution & i would suspect most sales engineers could sell this option based on energy saving.

[sinewave]

Cheers Thermatech, I'll put it to the Client.

[Magoo]

Sinewave.
server rooms, data bank rooms all require exact operating conditions, all available from server supply companies. The RH is critical for static corruption possibilty of the server, data loss. So quote that to the accountant. data loss will make his wallet cringe [control, control ], so you have to have large coil surface area so as not to dry air, add fresh air just for moisture, considered humidification systems.
Now you can understand that the bob basic heat pump split system does not stand a chance, and will die after a short period. Purpose build systems become dollar efficient long term, mention that to the bean counter.
magoo

[BritCit_Juve]

For most of the year in the UK an inverter system will be running at part load so the compressor will be ramped back on its speed. This will result in higher sensible cooling as the evaporator coil and airflow are larger than the system cooling capacity requires
(larger indoor unit and smaller equivalent duty outdoor unit = high sensible).
In the uk the systems will usually be oversized as
1) consultant includes a fiddle factor
2) installer includes a fiddle factor
3 weather includes a factor as we never seem to get close to the room design conditions
4) system includes a factor as the condenser is sized to give the duty at 43°C
so for the first two years the system will work ok though not to the best advantage of the equipment in the room.
A domestic or industrial high wall or cassette will only give a lifetime of arround 4 years and has not got humidity control so can dry out the room resulting in high static conditions especially when the sealed buildings requirement is taken into account.
I agree that correctly tempered fresh air introduced into the room is the best engineering solution to the problem as in the uk you can have free cooling for approx 80% of the year but in winter you will still need to introduce humidity.
An IT suite rally requires 40% to 60%rh with a sensible heat ratio of 0.9 or better at the design conditions as not many computers actually perspire or breath. Most splits are rated at 0.78 to 0.86 at nominal with not all actually providing the sensible data.
The best solutiuon is currently the least energy efficient (fixed speed compressor resistance heaters electrode boiler humidifier) but if sized correctly for the sensible load using 2 or more stages of cooling there should be minimal difference between the unit capacity and room load during the year thereby bringing the efficiancy back into line (lowest efficiency being compressor start)
Unfortunatly within uk industry they still beleive the quality is the same whether a unit at £400. or 1400.00 if they do the same total duty:(.
Brit