When we get our electricity bills, it shows that we have used a certain number of units for the given period. When we go to buy appliances, most of them have watts mentioned on them. If you find it difficult to understand the relation between the two, then you are not alone. Electricity bill and its components are confusing to many and with this article we will try to explain what are watt, kilowatt and a unit of electricity. Power and Energy/Electricity are two words that are used so much for each other that many feel that they mean the same. Interestingly both of them have a very different meaning. Power is the rate at which electricity is used and energy/electricity is the actual consumption. To give an analogy, power is similar to speed but electricity/energy is the actual distance travelled. So        Power x Time = Electricity (or energy) Just like          Speed x Time = Distance Travelled. Power is always represented in watt (W) or kilowatt (kW).

A thousand (1000) watts make one kilowatt. So if any appliance is rated as 1.2 kW then it means that it consumes electricity at a rate of 1200 W. Now as we discussed earlier that power is the rate at which electricity is consumed and not the actual electricity consumed, Watt or Kilowatt just represent the rate at which electricity is consumed per hour. Which means that when you buy a 100 W bulb, it does not consume 100 units of electricity but consumes at a rate of 100 W. A unit (as mentioned on the electricity bills) is represented in kWH or Kilowatt Hour. This is the actual electricity or energy used. If you use 1000 Watts or 1 Kilowatt of power for 1 hour then you consume 1 unit or 1 Kilowatt-Hour (kWH) of electricity. So the reading on the electricity meter represents the actual electricity used. Just like the odometer on your vehicle that shows the actual distance travelled by the vehicle, electricity meter shows the amount of electricity that is used. So a 100-Watt bulb if kept on for 10 hours will consume:

100 x 10 = 1000 Watt-Hour = 1 Kilowatt-Hour (kWH) = 1 units (on your meter). Now with most of the concepts explained we would like to make it easy for you to calculate how much units does any appliance consume. goldstar ac unitMost appliances have wattage written on them (either on their container box or somewhere on the appliance). ac unit rustedOnce you have the wattage, next you need to figure out how many hours a day do you use it. camper hvac unitsAfter that you can use the formula below: Daily Units = (Wattage x Usage hours per day) ÷ 1000 Monthly Units = Units x 30 (or 28,29,31 based on month) Please note that this formula may not work always. For appliances like Air Conditioner, Water Heater, Cloth Iron (any heating or cooling device) and pumps, this will not work.

Also check this video that can help you understand how many units your appliances are consuming:Commercial refrigeration systems in the US are mostly rated in tons of refrigeration and this term is used widely in other parts of the world. However, outside the US, cooling systems may be normally specified in kW (or MW) or in Btu/h. The roots for refrigeration are in the ice making industry, and the ice manufacturers wanted an easy way of understanding the size of a refrigeration system in terms of the production of ice. If 288,000 Btu are required to make one ton of ice, divide this by 24 hours to get 12,000 Btu/h required to make one ton of ice in one day. This is the requirement for the phase change from liquid to solid — to convert water at 0°C (+32°F) into ice at 0°C (+32°F). As a practical matter, additional refrigeration is required to take water at room temperature and turn it into ice. To be specific, one ton of refrigeration capacity can freeze one short ton of water at 0°C (32°F) in 24 hours.

So, a ton of refrigeration is 3.517 kW. This is derived as follows: The latent heat of ice (also the heat of fusion) = 333.55 kJ/kg = 144 Btu/lb One short ton = 2000 lb Heat extracted = 2000 x 144/24 hr = 288000 Btu/24 hr = 12000 Btu/hr = 200 Btu/min 1 ton refrigeration = 200 Btu/min = 3.517 kJ/s = 3.517 kW = 4.713 HP A much less common definition is: 1 tonne of refrigeration is the rate of heat removal required to freeze a metric ton (1000 kg) of water at 0°C in 24 hours. Based on the heat of fusion being 333.55 kJ/kg, 1 tonne of refrigeration = 13,898 kJ/h = 3.861 kW. Thus, 1 tonne of refrigeration is 10% larger than 1 ton of refrigeration. Another unit of measure is the calorie which is the amount of heat removal required to raise or lower the temperature of one gram of water by one °C. A kilo-calorie is the amount of heat required to raise or lower 1 kg of water by 1°C. One ton of refrigeration is equal to 3024 kilo-calories per hour. This is 12,000 BTU/ h divided by 2.204 (pounds per kilogram) divided by 1.8 (°C to °F).

Most residential air conditioning units range in capacity from about 1 to 5 tons of refrigeration or 3.5 kW ~ 17.5 kW, or 12,000 Btu/h ~ 60,000 Btu/h. Large industrial chiller systems range up to 800 tons of refrigeration (2.8 MW or 9.6 million Btu/h).The ENERGY STAR Web page you are looking for cannot be found in this location. If you typed the page address (URL) in the address bar, make sure that you spelled it correctly. Return to our home page. Use our site map to locate specific topics. Use the Search box above to locate the information you need.Chiller efficiency depends on energy consumed. Absorption chillers are rated in fuel consumption per ton cooling. Electric motor driven chillers are rated in kilowatts per ton cooling. If a chillers efficiency is rated at 1 KW/ton, The term kW/ton is commonly used for larger commercial and industrial air-conditioning, heat pump and refrigeration systems. The term is defined as the ratio of energy consumption in kW to the rate of heat removal in tons at the rated condition.

The lower the kW/ton the more efficient the system. kW/ton = Pc / Er         (1) Pc = energy consumption (kW) The Coefficient of Performance - COP - is the basic parameter used to report efficiency of refrigerant based systems. The Coefficient of Performance - COP - is the ratio between useful energy acquired and energy applied and can be expressed as COP = Eu / Ea         (2) COP = coefficient of performance Eu = useful energy acquired (btu in imperial units) Ea = energy applied (btu in imperial units) COP can be used to define both cooling efficiency or heating efficiency as for a heat pump. COP can be used to define the efficiency at single standard or non-standard rated conditions, or as a weighted average of  seasonal conditions. The term may or may not include the energy consumption of auxiliary systems such as indoor or outdoor fans, chilled water pumps, or cooling tower systems. COP can be treated as an efficiency where COP of 2.0 = 200% efficiency. For unitary heat pumps, ratings at two standard outdoor temperatures of 47oF and 17oF (8.3oC and -8.3oC) are typically used.