Power factor improvement deviceTechnology outline:Electrical equipment such as induction motors, magnetic ballasts and transformers require two types of power to operate, namely active power and reactive power. Active power produces useful work while reactive power is used by inductive devices to generate magnetic fields. Total power is the vector sum of the two powers above. Power factor is the ratio of active power to total power. Good power factor indicates that the current is being effectively converted into useful work. A load with a power factor of 1.0 results in the most efficient loading of the supply. Poor power factor can be result from inductive loads or a distorted current waveform. When an electric load has a power factor of lower than 1, the apparent power delivered to the load is greater than the active power that the load consumes. The remedial methods for poor power factor are described as follows. Power factor correction is a technique of counteracting the undesirable effects of electric loads that create a power factor that is less than 1. Power factor improvement for inductive load can be achieved by reducing the inductive component of the current. This can be done by the addition of capacitors in parallel with the connected inductive load circuits. The inductive effects of the load can be cancelled out by the current generated by the capacitors. The figures below show two connection examples of power factor improvement by capacitors.
Poor power factor due to a distorted current waveform can be mitigated with a harmonic filter. The filter allows current only at the frequency of the voltage (e.g. 50 Hz) to pass through. The filter can eliminates harmonic current, which means that the non-linear loads are forced to become linear loads. After that, the power factor can be corrected using capacitors as required. How it can save energyImproving the power factor can enhance current-carrying capacity, increase the portion of useful electrical energy produced from the source, improve voltage to equipment, reduce power loss, and thus improve the efficiency of the power distribution system. Both power companies in Hong Kong require that the total power factor for any circuit should not be less than 0.85. Applicable Standards
Further sources of information:
Harmonics filterTechnology outline:Harmonics are currents produced by non-linear load such as the AC to DC power conversion circuits. They usually occur in multiples of the supply fundamental frequency. For example, on a 50 Hz supply, the 5th harmonic is 250 Hz, 7th harmonic is 350 Hz. Other sources of harmonics in buildings include computer equipment, VSDs, ACVV/VVVF lift drive systems and electronic ballasts etc. The presence of harmonics on the power distribution system will definitely reduce the efficiency of the system. Typical problems associated with harmonics include overheating distribution transformers, overloading neutral conductors, distorted supply voltage waveform and inefficient distribution of electrical power etc. The damages of harmonics can be eliminated by applying passive or active filters at appropriate location.
How it can save energyThe elimination of harmonics in power systems can reduce thermal stress due to harmonic currents and reduce phase to neutral voltage drop, thus enhance the power distribution efficiency. From the perspective of system operation, mitigating the harmonic problems in power systems can reduce the chance of abnormal failure of the systems such as false operation of protection equipment. Applicable Standards
Further sources of information:
Electrochromic glazingTechnology outline:Electrochromic glazing allows dynamic changes of a window's thermal, solar, and visible transmittances by applying small amounts of electric current to an electrochromic film affixed to the glass. The actions of changing the window's transmittance can be actuated through devices such as rheostats, thermostats, photocells etc.
Another switchable glazing technology, the liquid crystal suspended particle device (SPD), contains molecular particles suspended in a solution between plates of glass. In normal status, the particles move randomly and collide, blocking the direct passage of light. However, when energized, the particles align rapidly and the glazing becomes transparent. This type of switchable glazing can block up to about 90% of light. How it can save energyBy changing the window's thermal, solar and visible transmittances, the cooling load due to the solar heat from the windows can be reduced. At the same time, the daylight utilization can be maximized by proper control of the transmittance of the windows. Heat pump water heater (HPWH)Technology outline:Heat pumps have traditionally been used for space conditioning, but are now being used for water heating. HPWH are an efficient type of electric storage water heater that extracts heat from the environment to heat water. In a heat pump water heater cycle, heat from the air heat up and boils the refrigerant to become vapour at a low temperature in an evaporator. The temperature and pressure of the refrigerant vapour is then increased by the compressor. The refrigerant vapour with high temperature and pressure leaves the compressor and flows to the heat exchanger in water tank to heat up the water inside. The refrigerant condensed into liquid after releasing heat in the heat exchanger. The liquid refrigerant returns to the evaporator at low pressure and temperature after passing throttling valve to complete the cycle. The figure below illustrates the structure of a typical heat pump water heater. How it can save energyIn the operation of the heat pump water heater, energy is extracted from the air onto the evaporator. Energy is extracted from the "free source", and only a small amount of electricity is required to operate the compressor. Further, the HPWH removes heat from surrounding air to provide additional benefit of space cooling. How much energy can be savedSince the HPWH extracts heat from air, it delivers about twice the heat for the same electricity consumption as a conventional electric resistance water heater [1].
Reference:[1] Washington State University Extension Energy Program |
