wb8foz@nrk.COM (David Lesher) writes:

I'm less sure. IMHE, anything running will not promote condensation. It will be warmer than ambient.

The concern is greatest if you have any external doors opening directly into the co-locate area (no vestibule or 'air lock'). Since it is "Relative" humidity, what will happen when the warm, humid outside air enters a cold area? The supersaturated air will condense when it hits any relatively cool object, such as the supporting superstructure and rack rails. Water will then do what it does best, start dripping onto the equipment in the racks. I actually learned this lesson in high school when I opened a window in the school computer room on a hot, muggy summer day. The same thing will happen in the winter, if you let very, very cold air into a warm area with 40%-50% relative humidity. The real lesson is avoid external doors and windows opening directly into the controlled area. This tends to be a religious issue. To make matters worse, for a major data center you really need about four different environmental zones: people, magnetic media, paper, and electronic equipment. Most of the time you compromise and pick a happy medium set of environmental settings. One misconception is the idea of "Telco environment" being better. In fact, most times the telco environment is worse. The reason you need more robustly built telco equipment is C.O.'s have a harsh environment. So, with that in mind, here is one person's opinion on a good comprise set of environmental parameters for a data/telco/isp co-locate space. This assumes the space is used for mostly EDP/network equipment, and only incidental people, tapes, and paper are in the area. Donelan's Climate Settings: 8,500 BTU/hr heat dissipation per full rack Not all of it must be installed on day 1, but I want to see pre-planning how the HVAC will be expanded to meet the load (e.g. enough room reserved, aisles wide enough, to bring in additional units later, pre-plumbed for the outside heat exchangers, compressors, etc). Minimum 1 air change per hour This is actually a 'clue-check' question. How the co-locate operator answers it will tell you if they really know their HVAC systems. Unoccupied areas can get by with as little as 1 air change per 24 hours, but if you are doing an install or other work in the area, you'll appreciate more frequent air changes. Humidity: 35% to 50% R.H., non-condensing, max 2% change per hour Ideal: 40%-45% R.H., measured at three locations with max 5% variation. Humidity is expensive to control, so it is common to have R.H. at the high end of the range (e.g. 45% R.H.) in areas naturally more humid (e.g. northeast) and R.H. at the low end of the range (e.g. 40% R.H.) in areas naturally drier (e.g. southwest). Maximum (not to exceed 24 hours/annually): 20%-60% R.H., non-condensing Temperature: 59f to 77f (15c to 25c), max 4f (2c) change per hour Ideal: 72f (22c) at my rack, but since it is econmically infeasible to control the temperature at the rack level, I normally ask for 68f (20c) as a room average, measured at three different points, with a maximum of 4f(2c) variation. The assumption is at worst I'll end up with 72f(22c) at my rack. Anything much colder than 68f(20c) is a bit harsh on humans that need to work in the area. A tech thinking about how cold he is, isn't thinking carefully enough about the job he is supposed to be doing. Maximum (not to exceed 24 hours/annually): 49f(10c) to 85f(30c) You'll notice I tend to be metric-centric in my measurements. These are much stricter than your typical C.O. environments. Its more a practical matter of negotiating with the co-locate operator, and asking for more than you really need on the assumption even if they deliver just 50% of what they promise it won't be an immediate disaster. They may have no problem delivering 68f(20c) when the co-locate is 90% empty. But when it fills up, I'm betting with the lower the starting point, the less likely I'll run into my upper limit. I choose most of the values to give myself enough of a buffer before exceeding any equipment parameters, so I can try to negotiate a resolution with the co-locate operator before the levels start to causing equipment to shutdown. Otherwise if you set the limits at the maximum your equipment will tolerate, a co-locate operator may not do anything until after the temperature goes over 104f(40c), but by then its too late. Obviously the co-locate operator wants to write the contract with the largest acceptable environmental ranges possible, and the co-locate lessee wants the narrowest acceptable environmental ranges. Its a barginning point, how much do you really want to pay for +- 1 degree, or +- 10 degrees. In reality, most modern electronic equipment will operate well in a wide range of human-habitable enviroments, as long as the enviroment is stable. Its the oscillations that will kill your equipment every time. And in most cases, if the price is the same, I am willing to trade a particular value for tighter tolerances, e.g. 75f+-1f. But the price is rarely the same, so I generally choose the bigger range as shown above. -- Sean Donelan, Data Research Associates, Inc, St. Louis, MO Affiliation given for identification not representation