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Understanding Electricity Units

One of the most common units of electrical power for appliances is the watt (W). Other common units of power include kilowatts (kW), British thermal units (BTU), horsepower (hp), and tons.

Watts, kilowatts and kilowatt-hours:

Watts (W) is a unit of power used to quantify the rate of energy transfer. It is defined as 1 joule per second. A kilowatt is a multiple of a watt. One kilowatt (kW) is equal to 1,000 watts. Both watts and kilowatts are SI units of power and are the most common units of power used.

Kilowatt-hours (kWh) are a unit of energy. One kilowatt-hour is equal to the energy used to maintain one kilowatt of power for one hour. Generally, when discussing the cost of electricity, we talk in terms of energy. Energy (E) and power (P) are related to each other through time (t):

Electricity is most often measured and paid for based on the number of kilowatt-hours used. The reason that kilowatt-hours are typically used as a measurement of energy rather than watt-hours is simply because of scale: the amount of energy a typical household in the United States uses in a year is on the order of millions of watts, so it is easier to discuss in terms of kilowatt-hours instead.

BTU and BTU/h

British thermal units (BTU) are a measurement of heat used as part of the Imperial and US customary units of measurement. It is defined as the amount of heat that is required to increase the temperature of 1 pound of water by 1 degree Fahrenheit. Heat is a type of energy, so BTU can be directly compared to other measurements of energy such as joules (SI unit of energy), calories (metric unit), and kilowatt-hours (kWh).

BTU/h, BTU per hour, is a unit of power that represents the energy transfer rate of BTU per hour. BTU/h is often abbreviated to just BTU to represent the power of appliances. For example, an AC marked with a label of 12,000 BTU actually has a energy transfer rate of 12,000 BTU per hour.

Horsepower:

Horsepower (hp) is a unit of power most commonly used to reference the output of engines or motors. There are a number of different definitions of horsepower. Two of them are mechanical horsepower and metric horsepower.

The term "horsepower" was developed by James Watt, who compared the output of steam engines to the power of draft horses based on how many times a horse could turn a mill wheel in an hour.

Ton:

There are many different definitions of a ton that are related to the measurement of weight. In the context of power, the "ton" refers to the ton of refrigeration. The ton of refrigeration is defined as the rate of heat transfer necessary to melt 2,000 pounds (1 short ton) of pure ice at 0°C in 24 hours. It is used mainly in the United States to describe how well refrigerators and air conditioners extract heat.

Electricity Calculation Formulas

1. Power (Watts)

Where:

• P = Power (Watts)
• V = Voltage (Volts)
• I = Current (Amps)

2. Energy (kWh)

Where:

• E = Energy (kilowatt-hours)
• P = Power (kilowatts)
• t = Time (hours)

3. Electricity Cost

Where:

• Rate = Electricity tariff per kWh

Save on Electricity – Tips for Lower Bills

Frequently Asked Questions (FAQ)

What is kWh and how is it calculated?

kWh (kilowatt-hour) is a unit of energy equal to one kilowatt of power expended for one hour. It's calculated by multiplying the power in kilowatts by the time in hours.

How much does it cost to run a 1000W device for 5 hours?

At an electricity rate of $0.15/kWh, running a 1000W device for 5 hours would cost $0.75 per day (1000W ÷ 1000 × 5 hours × $0.15).

What's the difference between watts and kilowatt-hours?

Watts measure power (the rate at which energy is used), while kilowatt-hours measure energy (the total amount of power used over time).

How can I check how much power my appliances use?

You can use a power meter or energy monitor to measure the actual power consumption of your appliances. Alternatively, you can check the appliance's label or manual for its power rating.

Is it cheaper to run appliances at night?

It depends on your electricity provider's rate structure. Some providers offer lower rates during off-peak hours, which are typically at night.