Moreover, the estimated solar power striking the Earth’s atmosphere is given as 174 PetaWatts (PW).īTUs (British Thermal Unit) measure the amount of energy, especially thermal energy transfer or heat. In addition to power, the electrical energy consumption is also referred in kWh that is, the electrical energy used by a 1 kW device within an hour. For example, in electricity generation, the capacity of a power plant is given in kiloWatts or GigaWatts. Here, C p is the specific heat of air (1.006 kJ/kgᵒC) ρ is the density of air (1.202 kg/m 3) q is air volume flow (m 3/s), and dt is the temperature difference in Celsius.Īpart from thermal applications, Watt is used for many other situations such as in electricity, light, audio and radio transmission, solar energy, etc. In terms of SI units, the sensible heat transfer rate ( h s) for a change of temperature can be calculated as follows in kW: For example, a 24000 BTU/hr air-conditioning system might consume 2400 W depending on the EER- Energy efficiency ratio (heat transfer rate to electrical power). Although the power of a heating or cooling system is represented in BTUs or BTU/hr, the input electrical power for the system to work should be given in Watts. In the form of the British unit, One Watt is equal to approximately 3.412 BTU/hr. 1 Watt is equivalent to 1 Joule per second. This measurement is named after the inventor of the steam engine, James Watt. The power should be also increased or decreased by 10% if the room is heavily shiny or shaded respectively. They also recommend that if the number of people who regularly use the room is more than 2, the BTU/he should be increased by 600 BTU/hr for each person adding. The certification organization, Energy Star recommends that when choosing an air conditioning system, it is a rule of thumb to use 20 BTU/hr per every square foot. Here, q is the volume of air in cubic feet transferred per minute to change the temperature by dt F. The transfer rate ( h s) of the sensible heat, which is added to or removed from an object to make its temperature change is calculated as follows in BTU/hr: But in most applications, this is misinterpreted as BTU itself. However, it is important to note that in terms of power, which is the rate of heat transfer, the unit should be presented as BTUs per hour. Since BTUs are often used in heating and air-conditioning, heating, ventilation and air-conditioning systems use BTU for the measurement of power. That is, one joule is the heat required to transfer to one gram of water to raise the temperature by one degree Celsius (C). Since lb and F are both conventional units, the BTU can be identified by its SI units’ counterpart, Joule (J). One BTU is defined as the amount of heat that should be transferred to one pound (lb) of water to raise its temperature by one degree of Fahrenheit (F). But it is often used as a measurement in heating and air-conditioning industry even at present. BTU is not a part of the International System of Units or SI units. The term thermal is often used for measuring thermal energy or the energy in the form of heat. Side by Side Comparison – BTU vs Watts in Tabular FormīTU is the abbreviated form for British Thermal Unit. Thus, the key difference between BTU and Watts is that BTU measures energy, which is a stand-alone physical property whereas Watts measures the rate of transfer of energy that is always associated with a time factor. BTU and Watt are two different types of measurement units to measure the energy transfer and power, respectively. The rate of work done or the rate of the heat transfer is defined as power. If there is a heat transfer from or to an object, an amount of energy is removed from or given to the said object. If an object is doing a work, the object is given an amount of energy to perform the task. It is first important to identify the concepts of energy and power in order to understand the difference between BTU and Watts.
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