ELECTRICAL ENERGY BASICS:

 

Electricity Tariff:

 

Calculation of electric bill for a company

Electrical utility or power supplying companies charge industrial customers not only based on the amount of energy used (kWh) but also on the peak demand (kVA) for each month.

Contract Demand

Contract demand is the amount of electric power that a customer demands from utility in a specified interval. Unit used is kVA or kW. It is the amount of electric power that the consumer agreed upon with the utility. This would mean that utility has to plan for the specified capacity.

Maximum demand

Maximum demand is the highest average kVA recorded during any one-demand interval within the month. The demand interval is normally 30 minutes, but may vary from utility to utility from 15 minutes to 60 minutes. The demand is measured using a tri-vector meter / digital energy meter.

Prediction of Load

While considering the methods of load prediction, some of the terms used in connection with power supply must be appreciated.

Connected Load - is the nameplate rating (in kW or kVA) of the apparatus installed on a consumer's premises.

Demand Factor - is the ratio of maximum demand to the connected load.

Load Factor - The ratio of average load to maximum load.

The load factor can also be defined as the ratio of the energy consumed during a given period to the energy, which would have been used if the maximum load had been maintained throughout that period. For example, load factor for a day (24 hours) will be given by:

HoursxrecordedloadMaximumhoursduringconsumedEnergyFactorLoad2424=

PF Measurement

A power analyzer can measure PF directly, or alternately kWh, kVAh or kVArh readings are recorded from the billing meter installed at the incoming point of supply. The relation kWh / kVAh gives the power factor. Load Maximum Load Average Factor Load =

Bureau of Energy Efficiency 43 2. Basics of Energy and its Various Forms

 

 

Time Of Day (TOD) Tariff

Many electrical utilities like to have flat demand curve to achieve high plant efficiency. They encourage user to draw more power during off-peak hours (say during night time) and less power during peak hours. As per their plan, they offer TOD Tariff, which may be incentives or disincentives. Energy meter will record peak and non-peak consumption separately by timer control. TOD tariff gives opportunity for the user to reduce their billing, as off peak hour tariff charged are quite low in comparison to peak hour tariff.

 

Three phase AC power measurement

Most of the motive drives such as pumps, compressors, machines etc. operate with 3 phase AC Induction motor. Power consumption can be determined by using the relation.

Power = √3 x V x I x CosΦ

Portable power analysers /instruments are available for measuring all electrical parameters.

THERMAL ENERGY BASICS:

 

Temperature

To change temperature given in Fahrenheit (oF) to Celsius (oC)

Start with (oF); subtract 32; multiply by 5; divide by 9; the answer is (oC)

 

To change temperature given in Celsius (oC) to Fahrenheit (oF)

Start with (oC); multiply by 9; divide by 5; add on 32; the answer is (oF)

 

Heat

Heat is a form of energy, a distinct and measurable property of all matter

 

Unit of Heat

Calorie is the unit for measuring the quantity of heat. It is the quantity of heat, which can raise the temperature of 1 g of water by 1oC.

1 Calorie = 4.187 J

 

Specific Heat

If the same amount of heat energy is supplied to equal quantities of water and milk, their temperature goes up by different amounts. This property is called the specific heat of a substance and is defined as the quantity of heat required to raise the temperature of 1kg of a substance through 1oC.

 

 

TABLE 2.1 SPECIFIC HEAT OF SOME COMMON

SUBSTANCES

Substance

Specific Heat (Joules / kg oC)

Lead

130

Mercury

140

Brass

380

Copper

390

Iron

470

Glass

670

Aluminium

910

Rubber

1890

Ice

2100

Alcohol

2400

Water

4200

 

Sensible heat

It is that heat which when added or subtracted results in a change of temperature.

 

The quantity of heat is given by:

Q = mass x specific heat x increase in temperature

Q = m x Cp x Δt

 

Phase Change

The change of state from the solid state to a liquid state is called fusion. The fixed temperature at which a solid changes into a liquid is called its melting point.

The change of a state from a liquid state to a gas is called vaporization.

 

Latent heat of fusion

The latent heat of fusion of a substance is the quantity of heat required to convert 1kg solid to liquid state without change of temperature. It is represented by the symbol L. Its unit is Joule per kilogram (J/Kg)

Thus, L (ice) = 336000 J/kg

 

Latent Heat of Vaporization

The latent heat of vaporization of a substance is the quantity of heat required to change 1kg of the substance from liquid to vapour state without change of temperature. It is also denoted by the symbol L and its unit is also J/kg. The latent heat of vaporization of water is 22,60,000 J/kg.

When 1 kg of steam at 100oC condenses to form water at 100oC, it gives out 2260 kJ (540 kCals) of heat.

 

Super Heat

The heating of vapour, particularly saturated steam to a temperature much higher than the boiling point at the existing pressure. This is done in power plants to improve efficiency and to avoid condensation in the turbine.

 

Humidity

The moisture content of air is referred to as humidity and may be expressed in two ways: specific humidity and relative humidity.

Specific Humidity

It is the actual weight of water vapour mixed in a kg of dry air.

Humidity Factor

Humidity factor = kg of water per kg of dry air (kg/kg).

 

Relative Humidity (RH): [As the name suggests…..relative value….actual value of water in air to total water if fully saturated air].

It is the measure of degree of saturation of the air at any dry-bulb (DB) temperature. Relative humidity given as a percentage is the actual water content of the air divided by the moisture content of fully saturated air at the existing temperature.

 

Dew Point

It is the temperature at which condensation of water vapour from the air begins as the temperature of the air-water vapour mixture falls.

Dry bulb Temperature

It is an indication of the sensible heat content of air-water vapour mixtures.

Wet bulb Temperature

It is a measure of total heat content or enthalpy. It is the temperature approached by the dry bulb and the dew point as saturation occurs.

 

Dew Point Temperature

It is a measure of the latent heat content of air-water vapour mixtures and since latent heat is a function of moisture content, the dew point temperature is determined by the moisture content.

 

Calorific Value

Energy content in an organic matter (Calorific Value) can be measured by burning it and measuring the heat released. This is done by placing a sample of known mass in a bomb calorimeter, a device that is completely sealed and insulated to prevent heat loss. A thermometer is placed inside (but it can be read from the outside) and the increase in temperature after the sample is burnt completely is measured. From this data, energy content in the organic matter can be found out.

The heating value of fuel is the measure of the heat released during the complete combustion of unit weight of fuel. It is expressed as Gross Calorific Value (GCV) or Net Calorific Value (NCV). The difference between GCV and NCV is the heat of vaporization of the moisture and atomic hydrogen (conversion to water vapour) in the fuel. Typical GCV and NCV for heavy fuel oil are 10,500 kcal/kg and 9,800 kcal/kg.

 

Heat Transfer

Heat will always be transferred from higher temperature to lower temperature independent of the mode. The energy transferred is measured in Joules (kcal or Btu). The rate of energy transfer, more commonly called heat transfer, is measured in J