When investing in computer systems or upgrading existing systems the investment can easily run into the tens of thousands of dollars. This investment needs to be protected. Inadequate power, or improper cooling most likely will be damaging to the investment.

Cubix Corporation understands the ever-increasing demand businesses have for ever-more computer power in the form of PCs. This white paper discusses the problems of power and space, and why both elements are important considerations when planning a data center or computer network systems. This white paper will present solutions to the problems of power and space management.

Electrical power is expressed in watts and is a function of the voltage and the current. Most personal computers use a 230-watt power supply. 230 watts represents the maximum power that can be delivered by the supply. Normally, the PC will require about half the power that can be supplied (about 115 watts). From this we can derive the electrical current requirement as follows:

• Power (watts) = E (voltage) times I (current) or I=P/E therefore:115 watts divided by 115 volts = 1 amp average power required*

• 230 watts divided by 115 volts = 2 amps maximum power required*

• 1 Amp is about the current required to operate a 100-watt light bulb.

Now consider the standard 115-volt wall outlet. According to National Standards and local building codes either socket of a duplex wall outlet can deliver a maximum of 15 amps. If both outlets are connected together then, in total, they can deliver 15 amps. If they are connected to additional outlets, as is normally done, the total for all outlets combined is 15 amps. Remember this is the maximum.

Underwriters Laboratory (UL) recommends that no more than 12 amps be drawn from any single outlet. So why is there a limitation of 15 Amperes? If you look just behind the outlet, you will see it is connected to a set of wires. These wires are sized to allow them to carry 15 amps of current safely. More than 15 amps of current could cause the wire to heat up enough to cause a fire to ignite in the wall. If you follow the wire to the source of power you will find it terminates at a circuit breaker. It is the job of the circuit breaker to insure no more than 15 amps of current flows through the wire. If an overload is detected by the circuit breaker, power is automatically turned off.

This means the maximum number of computers that can be safely connected to a single wall outlet is 6 if they each draw maximum current of 2 amps or 12 if they each draw 1 amp. This assumes nothing else is plugged into any other wall outlet that may be connected to this circuit. Therefore, the minimum number of 15 amp circuits to operate 48 personal computers would be 4.

If you are attaching monitors, network hubs, printers, RAID sub-systems, etc. it could take 8 or more separate 15 amp circuits.

If the PCs need to be secured, an enclosed rack is required. An enclosed rack requires analysis of cooling efficiencies. Typically, computers are rated to run in an ambient (room) temperature of 40 degrees C. This is about 104 degree F. Some of the components within a computer will shutdown operation when the temperature reaches 50C. Therefore, no more than a 10-degree rise is allowed for worse case operation. In an open room this is normally not a problem, since very few business environments would allow room temperatures to reach 40C. However, in an enclosed cabinet the ambient temperature is the temperature of the air flowing into the computer. 40C and even higher temperatures can be reached if adequate airflow has not been allowed for in the design of the rack enclosure.

To insure no more than a 10C rise in temperature we use the following formula to calculate airflow:

Cubic Feet per Minute (CFM) = Watts / (0.5618 * 10C)

CFM=230/(0.5618*10C)=40.9 or about 41CFM

The small fan normally found in a PC is adequate for moving this amount of air. However, if you put 12 PCs in a rack you now need to move 12 times 41CFM or 492CFM of air. Each PC must be insured it receives at least 41CFM of fresh outside ambient air and the rack must be capable of expelling at least 492CFM. If both of these requirements are not met the potential for hot air build-up in one or more PCs can become a real problem.

.Solutions

Method 1. Using clones or individual brand name PCs.

1. Determine your power requirements by adding up the power required for each device.
2. Divide the required current by 12 for the number of individual 15 amp circuits "n" needed.
3. Identify "n" separate circuits. This may require the help of an electrician.
4. Divide the equipment up among the various circuits in such a way that no more than 12 amps are drawn from any one circuit.
5. While installing the equipment, insure that all extension cords and multi-drop outlets are rated for the appropriate amount of power.

Method 2. Use Cubix Density Series™ Computer Chassis and Precision Rack™ System.

The Precision Rack has been design to support Density Series chassis in a fault-tolerant power efficient manner. The racks are pre-wired to support 2, 3, 4, or 6 Density chassis. Each chassis can support up to 8 PCs. Therefore 48 PCs can fit in a single Precision 3000 rack with pre-wired solutions for power management. This means that any one power circuit can fail and all systems will remain operational.

If you are in a Data Center environment the racks are pre-wired for connection to 30-ampere power interconnects that will be found under the raised floor. An electrician may be needed to provide appropriate UL/CSA approved extension cords.

In other environments the rack has been design for easy connection to power sources that can deliver the required power. However, keep in mind that an electrician will probably be needed to provide the connections.

How to solve the cooling problem?

Method 1. Using clones or individual brand name PCs.

Insure that all PCs receive at least 41CFM of room temperature air.

If enclosed in a rack, insure the rack can expel 492CFM of air for 12 PCs. As a guideline a typical 120cm (4.7inch) box or muffin fan can pull 100CFM of air. Therefore, at least five such fans would be required. Keep in mind that the rack must be designed in such a way that all PCs receive intake air at 40C or lower temperature.

Method 2. Use Cubix Density Series Computer Chassis and Precision Racking System.

The Precision Rack is designed with two 10-inch fans; each fan can pull 550CFM of air. Even if one fan were to fail, the rack would remain cool. The front door is designed for security while allowing maximum airflow through each Density chassis. Also, each Density unit has at least six fans to direct airflow through the Chassis to maximize cooling efficiencies.

Computer investments need to be protected. Inadequate power, or improper cooling will most likely be damaging to the investment. Therefore, careful planning including total cost of ownership analysis should be done prior to any decision to purchase systems. Your analysis will show that Density systems in Precision Racks are a winning combination.

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