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Energy Conservation

What is the use of computers in energy management?


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February 27, 2010 6:53PM

Conventional personal computers are not of much value in conserving energy. Most computers for energy management are microprocessors used to operate HVAC equipment such as chillers, boilers, rooftops, and terminal equipment like VAV boxes. Usually a single microprocessor operates each item of equipment. Within a given building the microprocessors linked together over a simple network known as RS-485. This is a 2-wire communication bus operating as a master slave.

The most popular building automation protocols are BACnet (ASHRAE) and LonWorks (Echelon) running on RS-485. The key to conserving energy with microprocessors is to use their ability to inter-communicate for sharing operating information. The single most important energy conserving program is that of an operating clock running from a master controller, which can signal equipment to operate appropriately.

Buildings operate in either the occupied or unoccupied mode. Using the master controller (usually another microprocessor but sometimes a personal computer running Windows) various sections of a building can be placed into the occupied or unoccupied mode from a master calendar scheduler. Careful adjustment of the occupied start and stop times offers the single most important energy conserving opportunity for any building.

The second most important consideration is to reduce unnecessary reheating of the supply air. Reheating is a common practice in larger buildings where a single air handler supplies low temperature air (55 degrees typically) to terminal units like VAV boxes. When the boxes squeeze down to their minimum position, usually around 40%, the microprocessor of that VAV box can cause discharge air reheating to prevent abnormally low space temperatures.

Microprocessors, suitable connected over a dedicated network (i.e. BACnet, LonWorks....), can sample space temperatures from various rooms. These temperatures can be used in an optimization algorithm that causes the air handler discharge air temperature to be reset up or down, as determined by the warmest spaces, to minimize reheating.

These are the two most important building energy considerations:

  • Clock scheduling of occupied-unoccupied times
  • Discharge air reheat minimization