Heating pipes

Heating pipes are commonly used in temperate greenhouses (typically located at latitudes above 45°). Hot water runs through the pipes, releasing heat to the greenhouse through convection and radiation – hotter the water temperature, more the greenhouse is heated.

The heating power of the heating pipe system depends on the characteristic maximum temperature the pipes can handle, the pipe diameter, and the number of pipes per area. The arrangement of the pipe system determines the temperature distribution inside the greenhouse.

Greenhouses can have multiple (2 or even 3) heating pipe systems at different heights in the crop (bottom, middle and top).

Contribution to energy balance and resource use of greenhouses:

When the temperature of the greenhouse drops below an optimal temperature setpoint, energy is added to the greenhouse via the heating pipes.

The heating of the water for the pipes is typically done using a boiler or a co-generator (CHP), both of which run on fossil fuels.

Possible steps towards sustainable, fossil-free greenhouses

Depending on the possibilities available locally, sustainable sources of energy – such as geothermal, solar or wind energy, industrial heat, or heat pumps – could be used to heat the water in the pipes. However, unlike a CHP, which additionally provides CO₂ supply for the greenhouse, using more sustainable sources of energy require separate sourcing of CO₂.

Decreasing the heating pipe temperature can reduce the energy consumption due to increased conversion efficiency of heat pumps. However, in order to meet the heating demand with the lower pipe temperature, either the heat-exchanging surface needs to be enlarged (for e.g. increasing the number of heating pipes per unit area of the greenhouse, or using pipes with a larger surface area) or the heat transfer needs to be improved (e.g. using pipes made of high conductivity materials such as aluminium, or increasing convective heat transfer through forced ventilation instead of free air movement).