# How much free energy have we got?

• technicalm

#### technicalm

Hey all.

Our heating equipment draws air through it at 5000m^3 per hour.

Lets say it's 20degC outside.

The fan pulls the air through and the exhaust air is 6deg cooler.

So we have scavenged that 6degC for our use.

Excellent. So let's pretend there are not any system inefficiencies or losses after that...

As a heating engineer, not a physicist, can anyone please calculate how much heat energy we are harvesting from the 6 degrees out of 5000m^3 of air?

Thank you,

new member, Matt

I guess it would be...
Energy=mass*specific heat capacity*change of Temperature
air density at 20C 1.2 kg/m^3
specific heat capacity at 20C 1.005 kJ/kg*K

mass = 5000 * 1.2 = 6000kg

Energy = 6000 * 1.005 * 6 = 36180 kJ or of energy per hour, which is equal to...
36180kJ/3600s = 10.05kW of power

wow. quite a lot from thin air!

So that's where the increase in energy comes from in a heat pump, it may only consume 1kw of electricity but mysteriously gives out 3 or 4.

thanks.