Energy Accumulated in Heated Water - kWh
Water is often used to store thermal energy. Energy stored - or available - in hot water can be calculated
E = cp dt m (1)
where
E = energy (kJ, Btu)
cp = specific heat of water (kJ/kgoC, Btu/lb oF) (4.2 kJ/kgoC, 1 Btu/lbmoF for water)
dt = temperature difference between the hot water and the surroundings (oC, oF))
m = mass of water (kg, lbm)
Example - Energy stored in a 1000 liter water tank
Water is heated to 90oC. The surrounding temperature (where the energy can be transferred to) is 20oC.
The energy stored in the water tank can be calculated as
E = (4.2 kJ/kgoC) ((90 oC) - (20 oC)) (1000 liter) (1 kg/liter)
= 294000 kJ
= (294000 kWs) (1/3600 h/s)
= 81.7 kWh
- 1 J (Joule) = 0,1020 kpm = 2.778x10-7 kWh = 2.389x10-4 kcal = 0.7376 ft lbf = 1 (kg m2)/s2 = 1 watt second = 1 Nm = 1 ft lb = 9.478x10-4 Btu
- 1 Btu (British thermal unit) = 1055.06 J = 107.6 kpm = 2.92875x10-4 kWh = 251.996 calorie (IT - International Table calorie) = 0.252 kcal = 777.649
Example - Solar Energy stored in a 200 US gallons Water Tank
A solar energy water buffer tank with 200 US gallons is heated 200oF.
The solar energy stored can be calculated as
E = (1 Btu/lbmoF) (200 oF) (200 US gallons) (8.3 lbm/US gallon)
= 332000 Btu
Hot Water Energy Calculator
Energy Stored in Water - Liters/kWh
Energy Stored in Water - US gallons/Btu's
Related Topics
• Thermodynamics
Work, heat and energy systems.
Related Documents
Biomasses - Energy Content when Used as Fuel
Biomass fuels and their energy content.
Energy Conversion Factors
Convert between energy units
Energy Storage Density
Energy density - by weight and volume - for some ways to store energy
Energy Transfer Equation
Fluid energy transfer.
Fixtures - Hot Water Content
Content of hot water in some common used fixtures - basins, sinks and baths.
Heat Capacity
The amount of heat required to change the temperature of a substance by one degree.
Heat, Work and Energy
Heat vs. work vs. energy.
Hot Water Circulation System - Return Pipes
Hot water can be circulated through a return pipe if it's instantly required at the fixtures.
Hot Water Heating System Temperatures vs. Outdoor Temperatures
Hot water heating temperatures adapts to outdoor temperatures.
Hydropower
Power potential vs. head and flow rate.
Pressure Energy
Calculate the potential of pressure energy in a incompressible fluid.
Salt Hydrates - Melting points and Latent Melting Energy
Melting points and latent energy of salt hydrates.
Steam and Vapor Enthalpy
Vapor and steam enthalpy, specific enthalpy of saturated liquid, saturated vapor and superheated vapor.
Storing Thermal Heat in Materials
Energy stored as sensible heat in materials.