Introduction

掌握需量就如掌握方向盤
  1. Not knowing the current demand is like driving a car without an odometer in a highway.
  2. A demand meter with an early warning system is like having an over speeding limit detector.
  3. Having an over demand warning system is not enough, better yet is to have an automated load shedding control system. This is like having a braking system in place. When the demand is close to exceeding, the demand controller should automatically issue load shedding instructions to selected equipment to have them reduce consumption or cut power altogether, it is only when the demand during the next cycle is in the safe zone that power is restored to the equipment. This is what demand control is all about.
  4. The larger the scale of the power user with institutions such as schools, universities, shopping centers, factories, large restaurants, corporate HQ, then the more complex the demand control and the greater the need.

Significance

When the power consumer uses power based on a time-of-use system from the power utility, then they are required to have contract demand as well.

  1. The utility company will use 15 minute blocks for determining the average demand. The maximum demand within one month will be used as the basis for comparing with the contract demand to determine if it has been exceeded.
  2. The greater the difference, the greater the penalty (within 10% the penalty is 100%; greater than 10%, the penalty is 200%).
  3. Out of the total utility bill, the demand fee portion can take up from 30 to 45%, smart usage will greatly influence the outcome and total electricity cost.
  4. Among the many energy saving approaches, the foremost is demand control.

Alarm

快超過需量得警報
  1. Without any demand indicator, the user wouldn't know if their power usage has exceeded the contract demand, and they are in the dark all of the time and can only wait until the bill comes to pay the bill without knowing how they stand with regards to the contract demand. So the least that is needed is to install a demand meter with an over use alarm, much like a car with a over speeding radar detector so that they could keep track of their consumption and avoid exceeding the contract demand and be penalized.
  2. For small scale power users such as a marketplace, restaurant, school, office, small factory, public building, the least that they should have is an early warning system, so that they could at the very least manually shed the loads or the air conditioner.

Appropriate Demand

A utility company have different ways in dealing with a large scale power user as compared to a residential user, a residential user only needs to compute their bill directly from their kWh energy usage. But for large users, aside from the kWh, they also need to account for their own designated contract demand (kW); if usage is within the contract demand, then regular billing is applied; but if the contract demand is exceeded, then additional penalties apply.

  1. The larger the contracted demand, the larger the basic fee that needs to be paid every month, doing so is like throwing good money away, but the right amount of contracted demand can save the user a great deal.
  2. The demand meter can show the maximum demand for the month and can be used as the basis for determining the appropriate contracted demand.
  3. Article from Department of Education: How to Determine the Contracted Demand to Lessen the Energy Bill

Reducing Max Demand

需量控制須即時資訊

DEMS Controller

  1. Demand Controller for the small scale user (from 75 to 600kW).
  2. Features include demand display, warning alarm and simple load shedding.

Load Shedding