Thursday, November 11, 2010
Wednesday, November 3, 2010
- Companies whose system require care and feeding by a staff in a specific geographic location.
- Privacy laws that require the data be kept within certain boundaries.
- Disaster recovery and accessibility concerns.
- Physical latency which is the time that it takes to communicate with the facilities.
Friday, October 22, 2010
- Customers today consider moving a viable option - the move to virtualized environments and converged architecture make it easier for data center users to migrate to a new facility. This is amplified by the fact that many customers are currently implementing these solutions and require some type of migration - either in place or to a new facility.
- There is an efficient marketplace - the emergence of national/international databases, reporting, and competitive placement have made it very easy for customers to understand what market rates are and to obtain competing proposals.
- Capacity is not constrained in most markets - the facility expansions of recent years combined with improvements to many facilities mean that there is available capacity in most markets.
Monday, March 8, 2010
Understanding the difference between kVA and kW is critical to proper operation of a data center. The equation is simple – kW equals kVA multiplied by the power factor, but the implications can be a little more complex.
Power factor is the ratio of resistive to reactive power. In layman’s terms resistive power is burned on the spot whereas reactive power does not burn all of the power and “bounces” some back into the system. A lightbulb is an example of resistive power while an electric motor produces reactive power. Most electric systems and utility grade equipment are designed around a power factor of 80%. Most data centers, on the other hand, are almost completely resistive load and have power factors approaching unity (100%).
Since the data center power factor is high and, as such, kW is very close to kVA, some people discount the difference and use the two interchangeably. This is very dangerous and can lead to the creation of “phantom” capacity.
The fundamental limitation crops up in how much capacity critical equipment such as the generator and UPS have. Most of these systems are designed for a power factor of 80%, which means that they can only produce kW equivalent to 80% of kVA.
What does this mean. Let’s walk through a sample calculation. A data center is filled full of 120 V circuits where the customers are allowed to draw up to 16 Amps, which is equivalent to a kVA of 1.92. If we assume that this equipment has a power factor of 95%, this is equal to 1.82 kW. If we look at the other side, the 600 kVA UPS has a power factor of .8, so it produces 480 kW. So the capacity of the UPS is 480/1.82=263 circuits. If we had done “simple” division on the kVA side, we would have had a capacity of 600/1.92=312 circuits. So we actually have 49 fewer circuits than the “simple” math would have indicated, hence the reason that it is critical to convert all loads and capacities to kW!
Recently, manufacturers have begun to address this by designing systems with higher power factor ratings. A few companies are also marketing retrofit kits for existing UPS systems to increase the power factor rating.
Check back in a few weeks for the next installment – “Implications of Data Center Power Factor for the Utility Grid”.