Miscellaneous - My reference 

- 99.999 uptime may not give right picture. for example DC1 and DC2 down for 5 minutes. 

DC1 down once for 5 minute

DC2 down 10 times each with downtime of 30 second each. Total downtime is 5 minute here

Time to recover should be considered as well

- Total flooding fire extinguishing system - halon(ozon depeleter) not used, flourine based compounds and compound with inert gases.

water sprinklers get activated at 75 degree centigrade

- tmp 22-24 celcius with max approved by ashare 27.22 celcius. important frequent temperature variance can alter characteristics of chip. That is one among many reason why servers are not powered off even when it is not required for processing.

- Humidity 40-60% low humidity will increase the chances of static charges high humidity can cause droplets and corrosion.

-CRAC unit should not work in competition. one is cooling-dehumidifying and other heating-humidfying. use of dcim/bms can be used to check this condition.
CRAC units should be tested to ensure that measured temperatures(supply and return) and humidity readings are consistent with design values. Set points for temperature and humidity shuld be consistent on all CRAC units in the data center. Unequal set points will lead to demand fighting and fluctuations in the room.

CRAC computer room air condition self contained precision cooling.Good for small data center.

CRAH computer room air handlers work with big chillers. good for bigger dc and also cost less than CRAC for moderate or bigger dc(>500KW) 
spot cooler / floor mounted coolers 1KW to 5 KW
large floor mounted cooler - 20kw to 200kw
CRAC - 100KW to 400KW
CRAH - 500KW+
Air cooled DX system requires roof(3m)
Air cooled self contained system require duct
Glycol cooled system requires roof (3m)
Water cooled system requires roof(3m)
chilled water system requires roof (3m)
 

Increase in temperature requires more humidity to maintain relative humidity. Rise in temperature cause more vapors that can be trapped then it actually has hence vapors concentration decreases you need to use humidifier to maintain vapor concentration.

With cooling opposite is the case as temperature decrease ability to hold humidity decreases so density of vapors increases so you need to dehumidify to maintain relative humidity.