Climate control & energy > Condensor
Retrieving energy from hot flue gases
Burners used for greenhouse heating loose energy in the form of hot smoke leaving the chimney (or stack). This wastage can be prevented in a gas-fired central heater (boiler) by using a flue gas condensor. This is a device installed between the boiler and the stack that recovers heat (thermal energy) from the hot smoke before it leaves the stack. A flue gas condensor also recovers energy (so-called latent energy) from condensation of water vapour in the flue gases. There are no costs or disadvantages of operating a flue gas condensor, apart from the initial investment and servicing twice a year.
Types of condensors
There are three types of condensors: pipe condensor, lamella condensor and combi condensor. The lamella condensor is cheaper to install and smaller in size than the pipe condensor. A combi condensor consists of two condensors in one system: the first one cools the flue gases down for instance from 160 to 70 °C, and the second takes care of further cooling from 70 down to 40 °C. In this second condensor also condensation takes place.
CO2 enrichment
The flue gases have a certain temperature, volume, water vapour content and CO2 content. These characteristics are important if the flue gases are used for CO2 enrichment. If the flue gases go through a condensor, the temperature drops (which is good) while the CO2 content remains high. Moreover, the flue gases are stripped of water vapour, which is also desirable.
Efficiency
A condensor can transfer heat only to water that is colder than the flue gases. So the lower the temperature of the water, the more the flue gases can be cooled down, and the more energy is recovered. Condensation and recovery of latent heat occurs only if the temperature is below the so-called dewpoint temperature of the flue gases. This requires very good engineering of the water flows in the heating system. It become more complicated when also a heat buffer is present that also requires a low-temperature water flow to be effective.
Further reading
A flue gas condensor for energy saving (2003)
Energy saving in the boiler house (2005)
