​Specific heat capacity ​ 

is the amount of heat required to raise 1kg of a substance through 1°C.​ 

​All materials will have a different specific heat capacity, this means it will take different amounts of heat to heat different materials by the same temperature.

Below are some specific heat values of various materials.

​So it would take 4.186 kilojoules of energy to raise the temperature of 1kg of water by 1 ⁰C, but only 0.125 Kilojoules of energy to raise the temperature of 1kg of Lead by 1 ⁰C.

​The calculation would be: 4.186 x 1kg x 1⁰C = 4.186Kj

​A kilojoule is a unit of measure of energy, in the same way that kilometres measure distance.

​Whats a Kilojoule???

​As plumbers we more usually use Kilowatts when talking about energy.

A Kilowatt (or kilowatt/hour) is a unit of power.


A Kwh is how much energy we would need to do a task for 1 hour and is the basic measurement of for electricity, gas and power-tools.

​There are 3,600 kilojoules in a kilowatt-hour.

(3600 is the amount of seconds in an hour)

​For plumbers, it is important to work out how much heat is needed to heat a volume of water from one temperature to another. ​ 

Imagine we need to select a boiler that will heat a hot water cylinder.
 

The hot water cylinder holds 150 litres of water, and we need the water to be heated from 10°C to 60°C. 

​The calculation would be:
4.186 (the specific heat capacity of water) x 150 (the amount in litres of water in the cylinder) x 50 ( the °C difference between 10°C and 60°C)

so

4.186 x 150 x 50 = 31.395 Kj or 8.72 Kwh

​We also must take into consideration the time in which we want the job to be done.
The calculation from the previous slide was:

4.186 x 150 x 50 = 31.395 Kj
31.395 ÷ 3600 = 8.72 Kwh

So we would need a boiler with the power output of 8.72 Kw to heat our hot water cylinder by 50⁰c, but it would take 1 hour to do it, what if we need the water to heat quicker?

Well we just need to factor this time into the calculation.

If we wanted to heat the water in half an hour the calculation would start the same we would just change the conversion at the end:

31.395 ÷ 1800 (The amount of seconds in half hour) = 17.44 Kwh (Which of course is double)

We need to find a boiler that will heat 10 radiators and a hot water cylinder. 

With pipework the heating system holds 100 litres of water, and the hot water cylinder holds 125 litres of water a total of 225 litres. 

We need the water to be heated from 10°C to 80°C. 

We need to find a boiler that will heat 10 radiators and a hot water cylinder. 

With pipework the heating system holds 100 litres of water, and the hot water cylinder holds 125 litres of water a total of 225 litres. 

We need the water to be heated from 10°C to 80°C. 



Firstly lets calculate the kilojoules needed:

We need to find a boiler that will heat 10 radiators and a hot water cylinder. 

With pipework the heating system holds 100 litres of water, and the hot water cylinder holds 125 litres of water a total of 225 litres. 

We need the water to be heated from 10°C to 80°C. 



Firstly lets calculate the kilojoules needed:

4.186 x

We need to find a boiler that will heat 10 radiators and a hot water cylinder. 

With pipework the heating system holds 100 litres of water, and the hot water cylinder holds 125 litres of water a total of 225 litres. 

We need the water to be heated from 10°C to 80°C. 



Firstly lets calculate the kilojoules needed:

4.186 x 225 x

We need to find a boiler that will heat 10 radiators and a hot water cylinder. 

With pipework the heating system holds 100 litres of water, and the hot water cylinder holds 125 litres of water a total of 225 litres. 

We need the water to be heated from 10°C to 80°C. 



Firstly lets calculate the kilojoules needed:

4.186 x 225 x 70 =

We need to find a boiler that will heat 10 radiators and a hot water cylinder. 

With pipework the heating system holds 100 litres of water, and the hot water cylinder holds 125 litres of water a total of 225 litres. 

We need the water to be heated from 10°C to 80°C in 40 minutes.



Firstly lets calculate the kilojoules needed:

4.186 x 225 x 70 = 65.929.5 Kj

​Now we need to convert to Kwh's, to do this we divide the Kj by the time required (in this case 40 min) so how many seconds in 40 min?

​Now we need to convert to Kwh's, to do this we divide the Kj by the time required (in this case 40 min) so how many seconds in 40 min?

Well there are 60 seconds in a minute so 60 x 40 =

​Now we need to convert to Kwh's, to do this we divide the Kj by the time required (in this case 40 min) so how many seconds in 40 min?

Well there are 60 seconds in a minute so 60 x 40 = 2400 s

​Now we need to convert to Kwh's, to do this we divide the Kj by the time required (in this case 40 min) so how many seconds in 40 min?

Well there are 60 seconds in a minute so 60 x 40 = 2400 s

so
Now we can convert our Kj into Kwh:


65.929.5 Kj ÷ 2400 s = 27.47 Kwh

​
27.47 Kwh


Which boiler would be the most suitable?

​
27.47 Kwh


Which boiler would be the most suitable?

The only one that would meet our needs is


'F'