POWERING INTERNET HOTELS & MODERN OFFICE BUILDINGS (PART III)

POWERING INTERNET HOTELS & MODERN OFFICE BUILDINGS
(Third of a Series)

II) THE MODERN OFFICE BUILDING

Let us now look at modern office buildings. Although not so power hungry as the Internet Hotels, the new computer age has also brought along the much needed transformation in the power system landscape that the design of office building wants to achieve. Computer loads are special as they require special treatment, too. They also generate harmonics that makes power systems not only dirty but also cause to reflect more loads into the system. As they themselves are vulnerable to system disturbances they help create, they therefore need to be isolated. These special pieces of office equipment even have special plugs thus needing special outlets. But then in the past and even in the present time, these special loads are not getting the attention they deserve from electrical designs.

Traditionally, computers & peripherals are not recognized as loads with “new identity”. They are just considered as part of the general purpose receptacles usually provided by traditional designs. But then, recent experiences show that computers and electronics equipment in offices now eat up more power than the traditional “plug-in” & appliance loads.

Using load densities intended for GPR’s (general purpose receptacles) with the thinking that computer and IT loads are part of it; is ‘highly argueable’ for reasons that the load densities recommended by the Electrical Code for GPR’s were established long before the advent of computers. Moreover, IEEE recommends that these loads shall have dedicated 3-wire single phase circuits, home-running to dedicated 3-phase, 5-wire panelboards, to be fed by the so-called PDU’s (Power Distribution Units) and to be served by dedicated delta-wye isolating transformer with a minimum factor of 173% in sizing system components to address harmonics.

THE OFFICE COMPUTER LOAD DENSITY*

Modern corporate offices today are expected to be replete with office computers and peripherals that would fill up 85% to 90% of the entire office desks of the building. But alas, the most recent PEC or NEC hasn’t established yet load densities for office computers & peripherals.

It has been learned that today, authorities & experts in the USA are still in the process of surveying or making census on usages of computers in offices. But then, even though load densities for computer loads in offices are not yet available in the present Electrical Code, power allocation for office IT equipments has to be inputted in any office building design. Otherwise then, will be the frantic call for additional power centers.

Researches made in the internet resulted in a number of internationally published technical papers that revealed that for corporate office buildings, an average density of 9 to 10 computer units per 1,000 sq. ft. These translate to about one unit per 100 sq ft or, say “one unit per 9.3 sq. m”. The same surveys say that in addition to the computer unit, about 1.3 peripheral units (printers, scanners, multi-function electronic devices, etc) are also seen as typical installations on a 9.0 sq. m office area. (*See Reference Paper: Energy Analysis Department, Environmental Energy Technologies Division, Ernest Orlando Lawrence Berkeley National Laboratory, University of California, Berkeley CA 94720, USA).

If a 400 va load density is assigned per 9.0 sq m, a 30 - 40 va load density per sq m is a reasonable assumption. For Call Centers, a load density of some 50 to 60 va per square meter is seen reasonable for operation areas. These are on top of the traditional building loads.

In other words, by general estimation, new Office Buildings must have about 25% to 35% additional loads for computers & electronic devices on top of traditional building load; that is, depending on the behavior of building clientele’s loads. Or a shift in load densities: from 110–120 va/sq m to 140-150 va/sq m. But these are just approximations, there’s no substitute to focused design computations.

POWERING COMPUTERS & GROUNDING METHODS

The last subject that I would like to share is how IT loads are fitted into the power system of the building– and grounding is the number one concern.

Ninety percent (90%) of the problems with ITE (Information Technology Equipments) installations are internal to the facility; only 10% are related to conditions on the utility electric service. Importantly, 75% of the problems arising within a facility are related to grounding - making proper and adequate grounding the single most important factor in reliable ITE system performance. In powering IT environments, the most recommended system configuration is the Three-Phase Five Wire System which could either be TN-S or TT 5-Wire schemes by choice as seen in Figures on screen. And there’s no way that the delta-delta or the wye-delta ungrounded systems are recommended installations.

On the other hand, the increasing population of non-linear loads in buildings such as UPS’s, controlled rectifiers, variable frequency drives (typical for elevators), computers and PLC’s are producing harmonics that distort the sinusoidal waveform of the power system. Ironically, these Information Technology Equipment or ITE’s are the ones that are fragile to these disturbances they themselves help create. But note that the Computer & Business Equipment Manufacturers Association of America (CBEMA) in a paper on power quality states, that 75% of the problems with perceived power quality problems are actually grounding problems. According to Messrs: Warren Lewis and Frederic Hartwell of Electrical Construction & Maintenance magazine in its February 1996 issue, they wrote: “a proper grounding system is the essential foundation for any other refinements that enhance power quality through reduction of harmonics. Without such a foundation, any sophisticated attempts to improve power quality will likely prove to be temporary, perhaps lasting only until the next thunderstorm.” Would the popular TVSS (Transient Voltage Surge Suppressor) work in ungrounded systems?

(To be concluded...)