Understanding KVA, DSM & Other Charges
Watts and Volt Amps – What’s a KVA and how is it calculated?
Have you ever wondered why some power ratings are expressed in WATTS, some in AMPERES or AMPS, some in VOLTS, and some in KVA? This page will explain in simple terms the difference between the power ratings and describe when each should be used in your data centre and network architecture planning.
A KVA is simply 1,000 volt amps. A volt is electrical pressure. An amp is electrical current. A term called apparent power (the absolute value of complex power, S) is equal to the product of the volts and amps.
On the other hand, a watt (W) is a measurement of real power. Real power is the amount of actual power that can be drawn from a circuit. When the voltage and current of a circuit coincide, the real power is equal to the apparent power. However, as waves of current and voltage coincide less, less real power is transferred, even though the circuit is still carrying current. Differences between real and apparent power, and thus watts and volt amps, arise because of inefficiencies in electrical transmission.
The resulting inefficiency of electrical transmission can be measured and expressed as a ratio called the power factor. The power factor is a ratio (a number from 0 to 1) of real power and apparent power. In the case of a 1.0 power factor, the real power equals the apparent power. In the case of a 0.5 power factor, real power is approximately half that of the apparent power.
Deploying systems that have higher power factors result in less electrical loss and can help improve your Power Usage Effectiveness (PUE). Most Universal Power Supply (UPS) units will list the average power factor and real-time load capacity of the UPS, in addition to the KVA.
Example: You own a 500 KVA UPS unit (apparent power) with a 0.9 power factor. The resulting real power is 450 kilowatts.
Additional services charged for electricity or any other charges such as DSM (Demand Site Management) must be divided equally amongst residents (tenants or owners).
Demand Side Management (DSM), is the modification of consumer demand for energy through various methods such as financial incentives and education. Usually, the goal of demand side management is to encourage the consumer to use less energy during peak hours, or to move the time of energy use to off-peak times such as night-time and weekends Peak demand management does not necessarily decrease total energy consumption, but could be expected to reduce the need for investments in networks and/or power plants for meeting peak demands.
A short example would be as follows:
A building has 100 residents and one municipal account. On the municipal account the Demand Site Management of City Power is R1,000. For the landlord to recover this correctly the charge of R1,000 must be divided by 100 residents. This means that each resident must paid a sum of R10 per month for this municipal charge. This would be the exact and correct amount charged for the recovery of services rendered by the municipality and according to the municipal charge; not more or less.
At the Tariff and Utility Management on the 12th of May 2014 we will be discussing electricity charges and tariffs in sub-metering. This will help you better understand the environment as well as manage your meters correctly.