 # Law of conservation of Energy

In physics, the law of conservation of energy states that the total energy of an isolated system remains constant.

### Calculation of Kcal

kcal=1L water heating up 1°C
Ex：
• 100L of 30°C water heating up to 32°C，need 200kcal
(32°C -30°C) * 100L=200kcal
• 100L of 50°C water chilling to 40°C，need –1000kcal
(50°C-40°C)* 100L = 1000 kcal
It needs 80 kcal to make phase change of water and ice.
0°C water → 0°C ice = -80 kcal
0°C ice → 0°C water = 80 kcal
Ex：
How much cal. do 1 1°C water become to -2°C ice
(1°C-0°C) *1 kcal=1 kcal
(0°C-(-2°C))*0.5 kcal=1 kcal (When the water change into ice, it needs 0.5 kcal every 1°C of cooling)
Water→Ice = 80kcal
C Water → -2°C Ice = 1+1+80=82kcal
Phace change of water and steam
100°C Water 100°C Steam594 kcal
Heating efficiency of steam is great. If we heating up 100L water by 1L steam, the temp. will rise 5.9°C.

### Other calculation of Kcal

1. 1RT=3024 kcal (Metric Units) = 12000BTU(Imperial units)
2. 1KW electricity = 860 kcal (860 in theory, the actual value is 650~700 kcal) →Lower efficiency of heating, higher cost.
3. 1kg gas(heavy oil)=12000 kcal