A “floating drum” storage offers a good, simple way of measuring gas production. You just record the change in height of the drum and volume of gas = area * height (area of a circle = pi Dsquared/4 or pi Rsquared and there are 1000 litres in a cubic metre). If you want more accuracy use a small diameter drum with greater height to get the necessary capacity. Pressure and volume of any gas are related by p1v1=p2v2, where p is pressure, v is volume and 1 represents the initial conditions and 2 is the final conditions. Mass and volume are related by density, where Density = Mass/Volume and the density of biogas is about 1.18 kg/m3. The easiest way to develop the pressure needed for burners etc is to add weight to the drum (bigger diameter – more weight, since Pressure = kg*9.8/sq.metres) and if you measure “pressure” in mm of water you need to know Pressure (Pa) = 9.8 *Height (mm). I think that should let you calculate anything you need and I hope you understand the “useful” metric units I have used.

I have set up a spreadsheet to do the hard work, which provides the example below for you to practice on.

## Pressure/Volume Calculations

A “floating drum” storage offers a good, simple way of measuring gas production. You just record the change in height of the drum and volume of gas = area * height (area of a circle = pi Dsquared/4 or pi Rsquared and there are 1000 litres in a cubic metre). If you want more accuracy use a small diameter drum with greater height to get the necessary capacity. Pressure and volume of any gas are related by p1v1=p2v2, where p is pressure, v is volume and 1 represents the initial conditions and 2 is the final conditions. Mass and volume are related by density, where Density = Mass/Volume and the density of biogas is about 1.18 kg/m3. The easiest way to develop the pressure needed for burners etc is to add weight to the drum (bigger diameter – more weight, since Pressure = kg*9.8/sq.metres) and if you measure “pressure” in mm of water you need to know Pressure (Pa) = 9.8 *Height (mm). I think that should let you calculate anything you need and I hope you understand the “useful” metric units I have used.I have set up a spreadsheet to do the hard work, which provides the example below for you to practice on.

## Calculations for gas volume

## Volume of gas

Volume Contained## Volume change with pressure

Final Volume## Mass of gas

Mass## Volume change with temperature

Final Temperature (C)