This article is targeted at the user who will become involved with development of the power systems plan for a call center of greater than 50-production seats and addresses only new construction. In a retrofit, the basics are nearly the same however there are additional parameters to work through with the local Power Company modifying the existing building to suit and the building owner(s) requirements. It should be noted that high rise building do not make good call centers since they create structural, power and mechanical challenges with placement of support systems. The basics are the same for the smaller call centers, but there are other power support options that are less expensive but not addressed in this article.
There are really two power systems within a call center. The first power system deals with the commercial power which is defined and controlled by the National Electrical Code (NEC). The other power system is the Isolated Ground (IG) – Uninterruptible Power System (UPS). The IG-UPS system is the basic support for production seats and communications.
Power Needs:
The first and most important step is to identify a Professional Electrical Engineer (PE-E Electrical) to assist in the building power design. This becomes very important if you are contemplating the use of a low-rise raised floor. The PE-E must have experience with the specific raised floor product selected for the project. There are specific design consideration with low-rise floors from both a power and communications perspective. The use of raised floor, coupled with a zone wiring system, will provide maximum flexibility in the future reconfiguration of the operating area floor space. Plug and play technology makes reconfiguration of workstations possible.
The next step is to resolve the total number of production seats and any other critical operational floor locations that must be protected by the UPS system. Experience has proven that in call center environments that due to floor space costs, workstation levels can max out at 100 square feet of space per person. This space includes isles, and is calculated based on all space which is not required (i.e. Restrooms, Lunch Room, etc.) to support the employee. If you have working with a raised floor environment with zone wiring, the one person per 100 square feet of space method should be applied. This will generate a higher power requirement, but it will allow you more flexibility in future growth and reconfiguration options as the call center environment matures.
Now that we have the number of locations to be supported, we can move on to the next step. It is important to assist the PE-E by providing the required information about the equipment deployment for each production seat location. You can look at the back of the equipment and find the power supply information that is on the information tag attached to the electronics. This estimate will, in most cases, be on the high side, because the numbers are stated in the theoretical maximum load. This maximum will only be reached if the machine is fully loaded. Normally this not the case with a piece of equipment used in a production seat environment.
The PE will perform calculations to help estimate the Volt*Amp/1000 load (KVA) for each seat location and the total requirement for the power load. The next recommendation will be the number of workstations per power circuit. History has proven that no more than four workstations per circuit should be used due to the possibility of additional equipment requirements in workstations where specific work-related responsibilities require a personal fax machine, printer, etc. Equipment suppliers will provide the volt and amp loads and the BTU/Hour information for the Communication Rooms. This information is needed by both the Mechanical Engineer and Electrical Engineer to complete the calculation required for the power and air conditioning requirements.
The PE-E is now in a position to size electrical system for supporting equipment. You will be tasked with determining how long the UPS is to support the load and if power conditioning is required. Why do you need power conditioning? Power conditioning removes all the power fluctuations. This is as much a financial consideration as it is functional performance issue. The longer the time the system needs to perform the higher the cost. If you have a generator as part of the supporting equipment you can reduce the time required. In a 24/7 environment, the recommended minimum time that a UPS runs should be 18 minutes which is the estimated safe shut down time for all equipment with a walking time allowance from the farthest point in the building to the server room even when a generator is available. Generators don’t always start on demand so allow some trouble shooting time to resolve any unforeseen issues. It is essential for the generator to continuously be tested and operational.
To size the generator requires identifying the additional equipment that will need to be supported. In most cases this will include air conditioner(s) for the operating floor and the communication room(s), emergency lighting, and other functions that support your production seats. Based on the current condition of the commercial power grid and the possibility for “rolling blackouts”, it is strongly recommend that all call centers have local generating systems.
The decisions that are made in the early phase of construction will directly effect the operational cost as the call center expands, or modifies in configuration. Power changes can be the most traumatic because they may require a shut down of the support equipment. Therefore, it is best to consider some form of raised flooring with an under floor zone wiring system developed for both power and communications as the operation emerges.
Mechanical Needs: of Call Centers
A call center is consists of four types of mechanical requirements. They are divided into the general office area, consisting of the conference rooms, single office spaces, and similar spaces. The open call center area with tens of cubicles is the second type of area. The main computer equipment room is the third type of space. And fourth is the communication room, which normally has limited computers and only voice and data switching equipment. Each is thermodynamically different and must be treated different.
Mechanical air conditioning and cooling of space is calculated based on the amount of heat generated within space or penetrating through the outer skin of the building. The interior component of the space is usually the same regardless of the geographical location of the building or the orientation of the building or the type of structural or architectural esthetics of the building. In addition, the call center type buildings are no longer considered to have many architectural elements (glasses, etc.). The exterior skin of the building and the orientation or the location of the building effects the air conditioning load requirements.
The cooling requirements of the interior depends on the heat contribution of the following: the human bodies (nominally 500 Btu/hr per person), the computers (nameplate rating of CPU computer 500 watts, the monitors range from 250 to 350 watts), the printers (idle mode nominally 400 watts to in use value of 720 watts (HP-IV)), the copiers (nominally 1200 watts when in use), and lighting (typically 1.5 to 2.0 watts per square feet). The above nominal values differ with equipment. In an unscientific study, the actual power consumption of a computer is less than the nameplate values given. Unfortunately, there are no technically published data for actual power consumption of a computer station, or a group of stations. Till, the technical publication is published, mechanical engineer must design for the maximum possible power consumption. Cooling requirements for specialty rooms such as computer facilities with tens of heat generating equipment or break room facilities with many vending machines is the summation of heat dissipation of all equipment.
One Watt is 3.4 Btu/hr (thermal British unit per hour). One air conditioning tonnage is 12,000 Btu/hr with 400 cfm (cubic feet per minute) of air.
The exterior shell of the building is divided into Conduction, and radiation. The convection contribution is mostly mixed with conduction calculations. The conduction is the amount of heat gradually penetrating through the skin (walls or roof or doors or windows). The “R” value of walls or roofs is the amount of resistance to this heat travel. The amount of heat passing through the skin is the product of the area of the skin and the temperature difference on two sides of the skin divided by the R- Value. The outer skin temperature is the worst ambient temperature generally at solar noon (12:00 noon adjusting for the daylight saving) on July 22nd (the longest day of the year) depending on the location (New York, Denver, Dallas, or Los Angeles). The inner skin (indoor) temperature is typically set at 75 degrees.
Radiation contribution (the amount of light passing through glazing) also depends on exact location of the building. However, building orientation is much larger factor. Typically, 200 Btu/hr per square feet for the west facing, 160 Btu/hr per square feet for south facing, the 100 Btu/hr per square feet for east facing, and 30 Btu/hr. per square feet for north facing glazing. East facing has been lowered intentionally, since the peak hours of east facing is 9:00 to 10:00 am and does not cause major comfort issues. Tinted glass, fins, overhangs, curtains, vertical blinds, and dual pane glazing reduce the radiation factors.
Within the computer rooms and the communication rooms or dedicated printer/copier rooms, the humidity control also becomes an important factor for proper operations. Many of the printer manufacturers or server suppliers will void the company warranty if the humidity within space is not controlled. Special dedicated computer air conditioning units facilitate all of the cooling and humidity requirements. Liebert, Compuair, Data aire are some of the examples of the manufacturers. Due to critical support conditions of the computer rooms, a secondary air conditioning unit is highly recommended as back-up unit.
There are many types of air conditioning units. Depending on the type of building, size of project, structural issues, and several other parameters, the mechanical engineer must select the best possible systems for the space. Controls of such space must be also well suited for the space given.
It is highly recommended that the building selected must provide the maximum flexibility for the mechanical engineer. High rises are nearly the worst selection for a call center and a one story building with strong roof structural support and high ceiling is the most ideal space for call center. It is very difficult to provide approximate tonnage for any call center. It must be calculated only on case by case basis.
For a given shell structure building, the cost of electrical and mechanical system can be near 60% of the tenant improvement cost and that includes the entire furniture system in the construction cost. Therefore the mechanical and electrical system of the building are the most significant component of the total budget.
Finally, the heating, ventilating, and air-conditioning unit designed and installed will be for a well coordinated building with very high heat load, sophisticated control system, high maintenance system, and a most essential component of maintaining healthy environment for the equipment and the human occupants.
Communications Room Needs:
The communications room will follow the same basic procedure. Yes, some environments require multiple communications room as in the case of a high rise building and large floor plate area’s. The number of communications rooms will be dictated by both Power and Digital Communications requirements.
Based on the digital communications requirements the recommendation of at least one Communications Room per floor; additional rooms are recommended when:
The usable floor area to be served is greater than 10,000 ft^2.
• There should be one Communications Room per 10,000 ft^2 of usable floor space.
• The rule-of-thumb estimates usable floor space at 75% of total floor space.
• The length of horizontal distribution cable required to reach the work area is greater than 328′ total cable feet. This is a measure of the cable required to go from the cube to the termination in the Communications Room. It is recommend that the maximum should be about 175 ft. This will allow you to run faster as speeds increase in the future.
When there are multiple Communications Rooms, it is recommend these closets be interconnected with at least one conduit (trade size 4) or equivalent for copper risers and one for fiber risers. The number and size of cables, which run between the rooms, will dictate the quantity of conduits. It is recommend that all digital communications be carried on fiber risers.
Assuming one work area per 100 ft^2 the Communications Rooms should be sized as follows:
Usable Closet
Floor Size
Area Feet
1,000 – 10,000 10 X 11
800 – 8,000 10 X 9
500 – 5,000 10 X 7
Note: Room size will finally be dictated by the communications cable design and the total amount of equipment installed.
In most cases the communications rooms should be centrally located in the floor plate area they support. You will need to start with the list of the equipment to be installed in each communications room. One or more communications room per floor given the square footage of the floor plate, the wire runs not exceeding 150 to 200 square feet, etc.
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