Greenhouse heating systems are used by growers and nurseries to extend the growing season in their glasshouses. Where the number of months in the year is either too low for a profitable crop or insufficient for more than one harvest, these systems warm the air, control humidity, and provide an optimum environment for plants to mature.
Heating doesn't just warm the plants, however. It also raises soil temperatures. When the ground is cold, the roots don’t take up the nutrients as easily. This then slows the growth of the plants. It’s one reason why farmers cover their fields in black plastic. It’s to warm up the soil prior to sowing.
Glass alone, however, is seldom enough to warm the ground. Interior supplementary heat and insulation in some form is usually necessary.
What greenhouse heating systems do you use?
Supplemental greenhouse heating systems
Greenhouse heating systems come in two forms: Indirect heat or via hot water pipes. Both use either oil or gas.
Indirect heat comes from so-called CO2 burners – jet engine-shaped cylinders that heat the air as it passes over a naked flame contained within it.
With this design comes an added bonus. Carbon dioxide is released as the energy burns. This enhances the concentration of that gas within the greenhouse. Fans inside these heaters also circulate the warmed air.
Hot water pipes
Hot water pipes do what they say on the tin.
A boiler heats water which circulates through the pipes that line the interior of the greenhouse. In this greenhouse heating system, the water, when it cools, returns to the boiler where it is re-warmed and then re-circulated in a never ending cycle.
Although CO2 burners have built-in fans, external ones must be used to circulate the warm air that comes from these pipes. This is true the year round. That’s because anytime the air keeps moving, you reduce the chances of cold or hot spots, and plant disease.
Insulation is made possible by affixing bubble wrap to the inside of the greenhouse.
The challenge with using any type of lining is to avoid light loss in the process.
Is this technology effective? The jury is still out.
Some growers use bubble wrap to insulate the lower, colder part of their greenhouses, while others remove it because, in their experience, it stunts the growth of their plants. Where bubble wrap is used, it is secured to the inside walls with plastic fasteners affectionately known as Mickey Mouse Ears.
There is another side to bubble wrap. It can act as a form of diffused glass, which is known to produce higher yields than even artificial lighting. Wrap with larger bubbles lets in more light, too.
It's probably counter intuitive, however, to put bubble wrap on the ceiling because arm air rises anyway. You'd think that no insulation would be needed. But since that is also where the light needs to be most diffuse, one can’t help but wonder if doing so would yield unforeseen benefits.
Regulating greenhouse heat
Although heat needs to be added to the interior of greenhouses, a balance has to be found between enough and too much. This is why it makes sense to use thermostats. They can regulate the introduction of heat as well as the mechanics behind a ventilation system.
Thermometers should also be used with thermostats, not least so that hot and cold spots can be identified and rectified. Both should be located at plant level so that the readings will be accurate and heating systems will be activated when they’re needed most.
That said, they should be kept out of direct sunlight. One way to do this is to put them on the cooler side of the structure or to have them face to the north.
What other ways are there to control heat in your greenhouse? Tell us below.