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Thread: How much energy to heat 100 liters of water?

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10-14-15, 04:25 PM	#14
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	"DirecTV, I already told you." - john cleese

Both the 4 kWh and 5 kWh values are equivalent measures of energy. With the electric water heater, all 4 kWh spent goes into heating water. With the gas water heater, 4 kWh transfers into the water and 1 kWh is lost up the chimney. The end in theory.

In reality, the electric water heater is not 100% efficient. With every splice, every wire, and every component between the power source and the water, there are small losses. Thus, the water heater may only be 99.8% efficient. In this situation, to get 4 kWh worth of hot water, you would need an extra 8.016 watt-hours added to make up for the heat lost in transmission. Close, but not exactly lossless.

With a heat pump water heater, one can put more heat into the water than the electrical energy consumed. A heat exchange occurs in the evaporator with the outside environment. For every kWh the compressor draws from its power source to drive the process, 2 kWh of heat is drawn in by the evaporator. In the tank, all 3 kWh ends up in the water. The power source need not be electrical, there are belt-driven compressors in automotive a/c systems and gas-powered refrigerator units made for campers. A good many of these units have been engineered to move in excess of 4 or even 5 times as much heat as the operating energy.

Some common conversions taken from a university of Kentucky web page:

ENERGY UNITS
· 1 kBtu = 1,000 Btu
· 1 MMBtu = 1,000,000 Btu
· 1 therm = 100,000 Btu ~1 ccf of natural gas
· 1 quad = 1,000,000,000,000,000 Btu = 1015 Btu

POWER UNITS
· 1 watt/hour = 3.412 Btu/hour
· 1 kWh = 1,000 watt/hour = 3,412 Btu/hour
· 1 horsepower = 746 watts
· 1 ton of heating/cooling = 12,000 Btu/hour

FUEL UNITS
· 1 cubic foot of natural gas = 1,025 Btu (approximated by 1,000 Btu)
· 1 ccf of natural gas = 100 cubic feet ~100,000 Btu [c = Roman Numeral for 100]
· 1 mcf of natural gas = 1,000 cubic feet ~1,000,000 Btu [m = Roman Numeral for 1,000]
· 1 bbl fuel oil = 42 gallons
· 1 bbl fuel oil = 5.8 MMBtu
· 1 ton fuel oil = 6.8 bbl
· 1 gallon fuel oil = 136,000 Btu
· 1 gallon propane = 91,500 Btu
· 1 ton bituminous (Eastern) coal = 21-26 MMBtu
· 1 ton sub-bituminous (Western) coal = 14-18 MMBtu
· 1 cord wood = 128 cubic feet (4 ft x 4 ft x 8 ft)
· 1 cord dried oak = 23.9 MMBtu
· 1 cord dried pine = 14.2 MMBtu

Last edited by jeff5may; 01-18-16 at 07:11 AM.. Reason: subjective description and unit revision