Datacenter Chilled Water Crac performance
Datacenter Chilled Water Crac performance
(OP)
I have 6 downflow cracs that are being supplied with 45deg cw. I am seeing a varing delta T's across the coil averaging 12deg with one as high as 27deg. The total available name plate tonage is 140 Tons with an IT load of 150Kw. The cracs are all set with 67deg set point but the room has an ambient 76 deg. Based on available tonage and the electrical load I would have expected the room to be much closer to the set point.
I was wondering about the circuit setters on each crac because they are all wide open with one 10% closed, which is also the crac with the 27deg delta across the coil. Would slowing the cw flow across the coil allow me to get the space temp colder.
I was wondering about the circuit setters on each crac because they are all wide open with one 10% closed, which is also the crac with the 27deg delta across the coil. Would slowing the cw flow across the coil allow me to get the space temp colder.





RE: Datacenter Chilled Water Crac performance
RE: Datacenter Chilled Water Crac performance
RE: Datacenter Chilled Water Crac performance
The final result is loss of humidity control,what is the room humidity, and an increase in localized hot spots. The single biggest contributor to the inefficiency of CT is by-pass air. We define by-pass air as cooling that returns to the ACU without doing any work or air that does not pass through electronic equipment and gets warmer by extracting heat.
Consider that most computers and other electronics equipment use front to back air flow to dissipate the heat generated in the box and 100% of the power into the computer is turned into heat. A typical computer will elevate the air temperature between 30�F and 40�F from the intake to the exhaust.
If the return air is only 10�F to 20�F warmer than the supply, then a significant amount of the supply air is mixing with the hot air coming from the back of the cabinets. This will "dilute the hot air" before it returns the ACU and not do any work to extract heat. In a data center for every five ACUs, the by-pass airflow rate is an astounding 60%.
RE: Datacenter Chilled Water Crac performance
Imok2, are your units capable of a dehumidification mode? All you should need is for one of the units to be in that mode. There's not a lot of air exchange in these rooms; sometimes near zero. If one CRAC coil is cool enough to wring out the moisture, the ramaining ones can chug along at their 75° return set point, no worries. Just periodically rotate the CRAC unit set for dehumidification to equalize drainage, coil corrosion, etc. If they don't have a dehumidification feature, just set one unit for a return temp of 60° and the rest for whatever you want room dry bulb to be...
RE: Datacenter Chilled Water Crac performance
Will help in both normal power loss and dropping the plant.