Calculating Total Power Requirements Transcript

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Calculating Total Power Requirements

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Slide 1

Welcome to the Data Center University course on Calculating Total Power Requirements.

Slide 2: Welcome

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Click the Notes tab to read a transcript of the narration.

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Slide 3: Learning Objectives

At the completion of this course, you will be able to:

Calculate total power requirements for a data center.

Understand the components of the data centers electrical capacity calculation:

Critical and non-critical loads

Electrical Service via the utility

Generator Standby Power Systems

Recognize the benefits to right sizing your power needs.

Discuss the power evolution in the data center as well as the impact of multi-core processor

technology and new dynamic loads.

Slide 4: Introduction

An essential part of data center planning and design is to align the power requirements of the IT equipment

with the capacity of the supporting infrastructure.



Over the years, the architecture of data center physical infrastructure which includes cooling, power,

security, fire suppression, racks and cabling, has evolved from fixed, hard-wired, centralized components to

mobile, modular components that employ standardized technologies.

These innovations simplify the process of calculating power needs and allow for a much higher degree of

flexibility in data center design. With the adoption of scalable pay as you grow UPS architectures, its

becoming easier and less costly to install and grow these back-up systems.

Slide 5: Introduction

Despite these new technology innovations, data center designers still need an organized methodology for

calculating future electrical needs of the data center or server room.

Confronted with the challenge of determining both current and future power requirements, data center

managers often over size their power requirements by as much as 70%.

This leads to both the drastic under utilization of the infrastructure and the commitment of financial

resources to fund unrealized investments. Accurately determining power requirements is one of the most

important pieces of the overall data center project process.

This course will provide you with the working knowledge needed to determine current, and future, total

power requirements for your data center.

Lets begin by identifying availability requirements.

Slide 6: Identifying Availability Requirements

Successful design initiatives begin with a needs assessment that includes the identification of availability

requirements for the data center.



This assessment essentially establishes the availability needs of the business applications being processed

by IT equipment.

Some popular availability configurations, from a power and cooling perspective, include N, N+1, and 2N.

Slide 7: Identifying Availability Requirements

Its important to remember that the redundancy architecture deployed will impact the amount of power

consumed in the data center.

No matter what the actual physical infrastructure system design configuration is, the core issue will be to

provide sufficient power to the critical load while keeping that critical load cool enough to operate without

experiencing downtime. It is important to address this carefully, because underestimating the required

capacity may result in future power disruptions. Over estimation can lead to excessive upfront installation

costs and higher ongoing maintenance expenses.

Once availability requirements have been identified, the next phase of the design process includes the

identification of load components and their power requirements.

Slide 8: Determining Load Requirements

Determining the load requirements is critical because most data centers are part of a larger building.

Data centers and network rooms draw a total load, which is the sum of the power consumed by the installed

IT and physical infrastructure equipment.

Before we explore each of the components which contribute to the total load requirements, lets establish

our data center assumptions.



Slide 9: Data Center Assumptions

This pie chart illustrates a breakdown of how the electrical capacity is divided among the various loads in a

data center.

For purposes of this course, our breakdown assumes a 50 square foot, (4.64 square meters) data center

with an initial steady state critical load of 50kW, plus a future steady state load of 50kW. The cooling system

is assumed to be 50% direct expansion (DX) and 50% chilled water. The utility voltage is 480 volts AC.

Now lets use this information to determine the load components for the data center.

Slide 10: Critical Load Requirements

Regardless of whether the data center consists of a single rack environment or a full scale data center, the

first step in calculating total power requirements is to determine the size of the critical load that must be

served and protected.

The critical load includes all of the IT hardware components that make up the IT business architecture:

servers, routers, computers, storage devices, telecommunications equipment, etc., as well as the security

systems, fire and monitoring systems that protect them.




This process begins by compiling a list of all such devices, with their nameplate power rating, their voltage

requirements, and whether they are single phase or three phase devices.

It is important to note that the nameplate power requirements are the worst-case power consumption

numbers required by Underwriters Laboratory (UL) and in almost all cases, the nameplate power

requirements are well above the expected operating power level.


In fact, studies conducted by reputable consulting engineering firms and power supply manufacturers

indicate that the nameplate rating of most IT devices is well in excess of the actual running load by a factor

of at least 33%.

The U.S. National Electrical Code (NEC) and similar worldwide regulatory bodies also recognize this fact

and allow electrical system planners to add up nameplate data for anticipated loads and multiply by a

diversity factor, anticipating that not all devices are running at full load 100% of the time.

Therefore, the nameplate information should be adjusted to reflect the true anticipated load.

Lets take a moment and practice manually calculating load requirements.



Slide 13: Calculating Critical Loads

We can use this table as a simple example of how to string together a workable calculation worksheet.

For the purposes of this example, we are making the assumption that one rack of equipment will represent

the entire critical load component in our imaginary data center. In reality, a typical 5,000 square foot (465

square meter) data center could consist of 100 to 200 of these racks with various types of servers and other

installed components.



In this example, Server #1, the first component in our rack, does have a nameplate that reveals a rating of

300 watts.

For simplicitys sake all of our component power readings should be converted to Kilowatts which is the

easiest measurement to calculate power requirements. 1 Kilowatt is equivalent to 1000 Watts. Therefore,

we have converted our 300 watt nameplate rating for Server #1 to .3 kilowatts.




For Disk Array #1, the second component in our rack, we have a nameplate rating of 500 Watts. Again, we

convert to Kilowatts and our conversion comes out to .5 kW.

Both Server #2 and Disk Array #2 are a bit more problematic because, in our example, neither has a visible

nameplate rating. Although this is unusual, it can happen. However, we can use a formula that will allow us

to calculate a kW rating for these two devices.

If the wattage is not listed on the device, it can be determined by multiplying the incoming current in amps

by the voltage of the device, which is typically 120 or 208V in North America and 220V outside of North

America, to get the VA or volt-amps.


If you dont know the voltage information off hand, you will need to contact your electrician or facilities

manager. If you dont have power consumption of the individual component in amps, consult either the

product manual or the vendors website. Then, multiply the anticipated VA number by 0.67 to estimate the



actual power, in watts, that the critical load will represent. Finally, divide the number by 1000 to establish

the Kilowatt (kW) load level of the anticipated critical load.

In our example, we have determined the voltage for Server #2 to be 120 V and the amps coming in to be at

5 amps. Therefore, 120V x 5 amps = 600 VA. To covert to watts we need to multiple the VA by .67. That

gives us a total of approximately 400 Watts. We convert this figure to .4 Kilowatts.

We follow the same procedure for determining our kilowatt rating for Disk Array #2. (310 watts / 1000 =.31

kW)

The sum of our four components is equal to 1.51 kW.


This figure will represent the first line item in our worksheet which is the critical load (the power

requirements of all our servers, storage, network equipment etc).




Its critical to consider the future load requirements because data center loads are not static. Once built or

established, the IT equipment will be under an almost constant state of change during the lifetime of the

data center.

IT refreshes will, at a minimum, have a 3 year cycle where new, more powerful and efficient devices will be

installed. These new devices will replace the original devices that are the current basis for calculating the

bulk of the power requirements.


A realistic assessment of the scope and timing of future changes and upgrades should be developed by the

IT organization to allow proper planning for the initial determination of power requirements.

The downstream elements of the electrical power and distribution system can be scaled, or adjusted to

known loads and future loading, but the utility input service supplying the NCPI (Network Critical Physical

Infrastructure) components either has to be sufficiently sized to carry the known load at start-up and future

loads, or a provision has to be made for installation of additional capacity without incurring excessive

downtime that would adversely affect the availability expected by the IT end user.

Once an estimate is made for the amount of future loading, it is added to the base loading information, to

establish the electrical critical load number in kW.



Slide 19: Calculating Peak Power Draw

Our worksheet will also assist in calculating future loads. For purposes of this exercise, well list our best

estimate of what the additional future critical load will be over the next three years.

Lets assume that our server base in the data center will grow by 20% over the next 3 years to reflect an

anticipated growth in business.

(Although over the last five years, servers have consumed increasingly large amounts of power, this trend

may be reversed in the near future as multi-core processors begin to replace the traditional CMOS chip. We

will discuss more about multi-core processors later on in this course. For the purposes of this example, well

assume that the power consumption will be the same.)

Since our projected growth will be 20%, we will add 20% to our current critical load numbers to establish our

future load.

This equation illustrates the additional power requirement increase of our future load and shows how we

have taken our existing critical load of 1.51 kW and multiplied by 20% to determine how much in extra kW

we have to account for in our future critical load.

Slide 20: Calculating Future Critical Loads

In order to ensure that our electrical system is capable of supporting peak power draws (due to some

variations that might exist in the critical load) we will also add the critical load and future load kW amounts



and multiply by a factor of 1.05. This will give us a total of 1.90 kW (1.51 + .3 x 1.05). This would be the

peak power draw. In order to calculate the net amount of extra capacity needed to address this peak power

draw consideration, we simply take this peak power draw number (1.90) and subtract the sum of the existing

load. In this case, 1.90 -1.81 results in an extra .09 kW of power required.

Slide 21: UPS Load Requirements

Although the UPS will support the critical loads in the event of an outage or power anomaly, the UPS

equipment itself will also consume a portion of the available power. While UPS models will vary in terms of

their efficiency and some UPS architectures are less efficient at lower load levels than others, for purposes

of this particular course, lets assume a UPS efficiency rating of 88%.

UPS battery charging or external battery banks are a significant but intermittent power consumer. Under

normal operation with a charged battery the battery charging load is negligible. However, when a battery

has been partially or completely discharged the battery charging power can be on the order of 20% of the

rated UPS load.

Now lets take this information and calculate UPS loads.

Slide 22: Calculating UPS Loads

To derive the UPS load you need to know the existing load, future load and the inefficiency factor for the

UPS & UPS battery charging.

For purposes of this example, we assume the UPS inefficiency rating to be 12%, and the UPS battery

charging factor to be 20%. Adding these 2 together will result in an inefficiency factor of 32%.

Now, take the Existing Load of 1.51 kW and add it to the Future Load of .3 kW and multiply it by the UPS &

battery inefficiency of .32. This will result in the UPS Load of .58 kW (for this example).

(Image on next page)



Now that weve calculated the UPS load, lets move on to lighting loads.

Slide 23: Lighting Load Requirements

Lighting loads account for all the lighting in the data center portion of the building. To perform this

calculation, you will need to know:

The square footage of the data center: in this example of an imaginary one rack data center, we are

assuming the space to be 50 square feet (4.64 sq meters). A simple formula for average lighting

consumption is 2 watts per square foot or 21.5 watts per square meter. Again, for the purpose of producing

consistent numbers, we are converting watts to kilowatts. Therefore, 2 watts will be converted into .002

kilowatts, or if calculating in meters, 21.5 watts will be converted to .0215 kilowatts.

So, to calculate the lighting load:

Take the square footage and multiply by the average consumption to get the Total Lighting Load, in this

case: 50 x .002 = .1 kW or 4.64 x .0215 =.1kW for calculation in square meters

Cooling will comprise the largest draw on the data center requirements, so lets estimate that next.



Slide 24: Cooling Load Requirements

All electrical equipment produces heat, which must be removed to prevent the equipment temperature from

rising to an unacceptable level.

Most IT equipment and other equipment found in a data center or network room is air cooled.

As we learned previously, a significant portion of the power consumption in the data center is controlled by

the cooling load. While this particular course does not significantly address the specifics of calculating

cooling requirements, it is important to note that the size of a cooling system will have a direct impact on the

data center load requirements.

(For more information on calculating total cooling requirements, see the DCU course Calculating Total

Cooling Requirements)

Slide 25: Cooling Load Requirements

Cooling systems vary widely in efficiency but can be broken down into chilled water systems and direct

expansion systems.

Chilled water systems are somewhat more efficient, and a general guide for power consumption is 70% of

the total peak load being supported.

Direct expansion systems require about 100% of the total peak load being supported.

(Note that cooling loads have start-up peak loads that exceed the steady state values. We will account for

these in this calculation.)

Every kW of power must be compensated for with an equal amount in kW of cooling so that the heat

generated by power consuming equipment can be removed, and a consistent temperature is maintained in

the data center.



Slide 26: Calculating Cooling Loads

This chart illustrates the power requirements for cooling. The power load needs to be supported by an equal

amount of cooling load, so take the total sum of all electrical loads that were calculated previously

throughout this course; (existing critical load, future critical load, peak power draw, UPS/battery and lighting).

This number is 2.58 kW.

Lets assume that half of the installed air cooling equipment consists of chilled water system and the other

half is a direct expansion architecture. So, dividing 2.58 in half give us 1.29 kWs for each of the two air

cooling architectures.

Finally, you will need to know the Cooling Efficiency Factor for these cooling architectures. DX is multiplied

by 1 which results in a factor of 1.29 and chilled water is multiplied by .7, resulting in a factor of .90. By

adding the DX load to the chilled water load, we can derive the total cooling load of 2.19 kW.

Slide 27: Total Power Requirements Summary Calculation

Now the total power requirements for the data center has been calculated. This chart is a summary of the 6

steps we have taken to arrive at our total power requirements sample number.




Slide 28: Finalizing Electrical Capacity Computation

Once the total electrical capacity (current, future, UPS, lighting and cooling) is estimated in Kilowatts, two

critical determinations can be made: the first is an estimate of the electrical service, or utility power needed

to supply the data center, and the second is the size of any standby power generator capacity that may be

needed to achieve the desired availability.

Slide 29: Finalizing Electrical Capacity Computation

Although operators will look at the steady-state power consumption of the loads within a data center when

determining electrical costs, designers should avoid sizing the power sources (Electrical Service and the

Generator) that power the data center to the steady state values.




These sources must be sized to the peak power consumption of the loads, plus any de-rating or oversizing

margins required by code or standard engineering practice.

Using the same percentage breakdown of the data center electrical requirements as discussed previously,

this illustration emphasizes the important distinction between peak power and steady state power by

comparing the electrical service requirements for both. (In practice, this difference between peak and steady

state requirement causes the electrical service and generator sizing to be substantially larger than might be

expected.)

Observe that the electrical service required at peak is almost 4 times the steady state critical load value.

(It also must be noted that this is only an estimate, and that the final determination of the service size is

highly dependent on accurate site specific information.)



Slide 30: Calculating Electrical Service

The electrical service, (the power coming in from the utility) can be calculated as follows:

Take the total electrical capacity required in Kilowatts (4.77) as well as the requirements of the National

Electrical Code and similar regulatory bodies,(1.25) and multiply to get the estimate for the total utility (5.96

kW).

Next, determine the three phase AC voltage of the service entrance to be supplied by the utility company.

Typically this is 480 Volts AC in the United States and 230 Volts AC in most other parts of the world.

Use the following formula to determine the electrical service size to supply the data center, in Amps:

Amps = (kW x 1000) / (Volts x 1.73)

To use our example, take the Total Adjusted Power Requirement (5.96) and multiply it by 1000 to get 5960.

Then take the Data Center AC voltage (480) and multiply it by 1.73 to get 830.4

Now, all you have to do is take 5960 and divide it by 830.4 to get 7.18 amps.

(This provides an estimate of the electrical service capacity required to support the critical load, cooling, and

the building functions for a data center. It is strongly recommended that the services of a qualified

professional consulting engineer be retained to verify the initial estimate and develop the final data center

electrical supply design.)

Slide 31: Generator Standby Power Systems

Once the size of the electrical service has been determined, consideration can be given to sizing an

appropriate standby power generator, which will provide power in the event of a utility failure and maintain

the availability of the data center.



A typical generator installation is illustrated here.

It is important to identify that the data center can be just one of many loads on the system, so this diagram

can be interpreted as a subset of a much larger electrical system.

Air conditioning loads, for example, require high starting currents and can impose harmonic currents on a

generator that may impact its ability to supply the power needed. The UPS itself may contribute to this

problem if it does not operate at a high input power factor, and may cause generator failure.

It is sufficient to note that the UPS must be chosen carefully to achieve end-to-end reliability. A UPS system

that exhibits poor efficiency characteristics under low load conditions is to be avoided.



Certain UPS topologies, such as the delta conversion, are better suited for generator supplied systems.

They can produce less harmonic distortion and manage various load levels more efficiently.

When selecting a UPS, the choice between a typical double conversion UPS and a Delta Conversion UPS

can influence the required generator size greatly, frequently by a factor of 3 (meaning: the generator would

have to be 1.75 to 3 times larger for a typical double conversion UPS than a Delta Conversion UPS).

When selecting a generator, base the choice on the kW rating of the generator, but be aware that

generators are designed to operate loads at a lower power factor than 1.0, typically 0.8. This means that the

current and voltage will be slightly out of phase and that the generator must withstand that difference. A

1000 kW generator, designed to operate loads having a power factor of 0.8 will be rated at 1200 kVA.

It is important not to confuse the kVA rating with the true power capacity of the generator, which is always in

kW.

Slide 32: Calculating Estimated Generator Size

Now lets determine the generator size for the data center.

To calculate the correct generator size, you will first need:

The number of kilowatts of the existing power load requiring generator back-up. This is made up of

the critical load, plus the future load, plus the peak power draw, plus the UPS and battery plus the

light load. In our example, the number equates to 2.58 kW.

Next, you need to assess the status of the UPS. For this example the UPS is assumed to be a

fully power factor corrected UPS, so the existing load of 2.58 kW will be multiplied by 1.3, to result

in 3.35 kW.

(If your UPS consists of a traditional double conversion UPS with input from harmonic filters, the existing

load of 2.58 kW will be multiplied by 3.0 which calculate to 7.74 kW.)



Then, you need the number of kilowatts from the cooling load requiring generator back-up. This

was figured previously, when we calculated the cooling load. In this particular case, we will be

using the number 2.19 kW and multiplying it by a factor of 1.5 to get 3.28 kW.

Finally, add the 3.35 and 3.28 to result in 6.63 kW for the estimated generator size.

Slide 33: Planning for Future Changes

Now that we have reviewed all the elements involved in data center power capacity planning, lets look

ahead. New technologies will be introduced that will impact our power and cooling load calculations in

different ways.


The basic building block of computer architecture has, for many years, been the CMOS chip. This chip,

which is commonly found in todays servers, has dominated the desktop computer and server market since

the early 1970s.

Over the last three decades, the chip manufacturers have continually improved the CMOS chip, but are now

quickly reaching the theoretical limits of the design. Any further enhancements to the

CMOS chip are difficult to justify financially, because the cost of additional engineering is high and the

increases in horsepower and throughput are negligible.


This illustration depicts the evolution of the CMOS chip and demonstrates the architectural wall that has

been encountered.

Now, chip manufacturers are introducing new multi-core processor chips. These new chips consume power

in a different manner than the traditional CMOS chip. While CMOS generally consumed power at a steady

rate, multi-core processors power consumption will go up and down depending upon the level of processing

required.




When power varies with time, many new challenges occur for the design and management of data centers

and network rooms.

Fluctuations in power consumption can lead to unplanned and undesirable consequences in the data center

and network environment; including tripped circuit breakers, overheating, and loss of redundancy in

redundant power systems.

Because of this multi-core processor dynamic loading feature, power and cooling planning and monitoring

methodologies in the data center will have to be redefined to manage these new multi-core environments.

Slide 37: Summary

To summarize, lets review some of the information that we have covered throughout the course.

Assessing the electrical power required to support the critical loads within the data center is an essential

step to help ensure that the data center meets the end users requirements. Once business requirements

are defined, a proper availability needs assessment can help to better define the NCPI topologies required

to meet the business need. Automated tools exist that can help data center staff quickly identify and size

their data center loads. A power requirements worksheet should include proper measurement formulas for

key components such as UPS, generators, cooling and utility power. New technologies, such as the multi-

core processor chip will be introduced that will impact our power and cooling load calculations in different

ways.

By accurately calculating the total power requirements in a systematic and comprehensive manner, data

center personnel will be able to employ all the economic advantages of scalable, modular, NCPI

infrastructure components without sacrificing reliability or uptime.

Slide 38: Thank You!

Thank you for participating in this Data Center University course.

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