Monday, April 18, 2011

Go Green - Journey towards Green IT

To get an understanding of the power saving with virtualization, one needs to start with measuring the power consumed in the current datacenter. The simplest way is to connect an energy meter to the powerline and measure the power being consumed - but that does not help much in planning for a greener data center. Isolating the power supply to data center and connecting an energy meter to the power line is a good step for measuring the power being consumed.

A typical data center

A typical non-virtualized data center usually consists several Industry Standard Servers(ISS) - x32 or x64. These individual servers are so powerful that very few applications can fully utilize the server resources. Most often, only 5-10% of the server capacity will be utilized. So when new applications are brought in, new servers were added - leading to uncontrolled server sprawl.

Measure the power consumed

The first real step is document how much power each of the devices in the datacenter is consuming. This includes servers, networking, storage, lighting, power converters, UPS, & cooling. The power consumed by these devices can be easily found in the product manuals. If you are not able to find the power information in the manuals - or if you do not have time t go through all the manuals, the faster solution will be to use HP Power Calculator or HP Power Advisor Even if you have non-HP servers, you can use HP power calculator to estimate the power consumed by choosing an equivalent HP server. Similar to HP power calculator or HP Power Advisor, other vendors - such as Dell, IBM, Cisco, EMC, Oracle also provide power calculating utilties.

Table below shows a sample of server power & cooling power requirement.

Power calculations

Power consumed by the computer equipment is computed in Watts and in British Thermal Units (BTU) equivalents.

Watt = current x voltage

BTU/hr = Watts x 3.14

Power consumed by the device is dissiapated as heat, which in turn requires cooling. One also needs to determin the cooling power needed for the data center.

Cooling power required is dependent on the total power consumed by all the devices + lighting + the data center room charateristics. As a rule of thumb, 12,000 BTU/hr requires one ton of cooling.

Providing sufficient cooling is essential for running the datacenters reliably. If the cooling systems fail, over heating of servers/devices can cause fires and complete damage to the data center equipment. Therefore early warning systems are usually installed in the data center, and the actual cooling system deployed will be greater than the theoritical requirement. In addition, the local city fire departments also have several guidelines for datacenter cooling & insulation standards.

It is therefore not possible in this article to give an exact calculation of the cooling requirements, however the calculations given below can be used as a rough guide to estimate the cooling needs. For complete accuracy you should consult qualified air conditioning equipment specialist or installer.

Calculating Heat Load
The amount of heat generated is known as the heat gain or heat load. Heat is measured in either British Thermal Units (BTU) or Kilowatts (KW). 1KW is equivalent to 3,412BTUs.

The heat load depends on a number of factors:

  • The floor area of the room
  • The size and position of windows, and whether they have blinds or shades
  • The number of room occupants (if any)
  • The heat generated by equipment
  • The heat generated by lighting
Floor Area of Room

You must take into account those factors that apply in your circumstances and adding them together a reasonably accurate measure of the total heat can be calculated.

Room Area
The amount of cooling required depends on the area of the room. To calculate the area in square metres:

Room Area BTU = Length (m) x Width (m) x 337

Window Size and Position
If, as is quite common, your Server Room has no windows, you can ignore this part of the calculation. If, however there are windows you need to take the size and orientation into account.

South facing Window BTU = South Facing window Length (m) x Width (m) x 870
North facing Window BTU = North Facing windows Length (m) x Width (m) x 165
If there are no blinds on the windows multiply the result(s) by 1.5.

Reverse the constant multiplier - if you are living in the southern hemisphere.

Add together all the BTUs for the windows.

Windows BTU = South Window(s) BTU + North Window(s) BTU


Purpose built Server Rooms don't normally have people working in them, but if people do regularly work in your Server Room you will have to take that into account. The heat output is around 400 BTU per person.

Total Occupant BTU = Number of occupants x 400

Clearly most heat in a Server Room is generated by the equipment. This is trickier to calculate that you might think. The wattage on equipment is the maximum power consumption rating, the actual power consumed may be less. However it is probably safer to overestimate the wattage than underestimate it.

Add together all the wattages for Servers, Switches, Routers and multiply by 3.5.

Equipment BTU = Total wattage for all equipment x 3.5

In our example above - the datacenter will need ~37 tons of cooling capacity - i.e,.442,897 BTUs


Take the total wattage of the lighting and multiply by 4.25.
Lighting BTU = Total wattage for all lighting x 4.25

Total Cooling Required = Sum of all BTUs.

Total Heat Load = Room Area BTU + Windows BTU + Total Occupant BTU + Equipment BTU + Lighting BTU

This is the amount of cooling required so you need one or more air conditioning units to handle that amount of heat.

AC capacity is marked in tons - 1 ton of cooling = 12,000 BTUs. So depending on the total BTU of your data center, you can choose the cooling systems.


Nilay Shrivastava said...

thank you for such an informative and article

Saras said...

Very informative..

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Unknown said...

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