Commercial Greenhouse Equipment - Heater systems

Comparison of systems

Disadvantages of Unvented Direct-Fired Heaters

• Discharges combustion products into the greenhouse, damaging crops and leading to serious discomfort, injury and/or death if not properly ventilated. These risks far outweigh any benefit that may be sought from CO2 being released in the combustion process.
• Direct fired units, often advertised as 100% efficient, are in fact 92% efficient at most. The latent heat of vaporization consumes Btu's to maintain water vapor in its gaseous state, reducing efficiency to roughly 92%. Then, you must provide fresh air to meet safe air requirements. The energy required to heat this air can bring the overall system efficiency below 80%. And, the colder it gets, the less efficient the system is.
• Risk for increased condensation issues due to the water vapor produced from combustion. This vapor can condense within the greenhouse and cause mold and/or fungal diseases, as well as premature failure of metal objects (structures, conduit, wiring, etc).
• Short heat recovery time reduces temperature fluctuations, promoting a natural growing environment.
• Provides circulation to reduce dead spots in the greenhouse, reducing high moisture areas that promote mold

Disadvantages of infrared heat systems

• Claims that heat source is ‘like the sun’ are untrue because the sun provides light energy in wavelengths necessary for proper photosynthesis to occur.  Infrared heat is of a different wavelength.
• Infrared has uneven temperatures along the tube. The longer the tube, the greater the temperature differentiation, resulting in uneven plant growth.
• Can only heat what it can see; therefore, obstructed plants will not get necessary heat.
• Air becomes stagnant with lack of movement, leading to mold.
• Tubes that heat plants on cold, sunless days actually block light during warm sunny days.
• Recommended by loading docks and customer areas where the doors are constantly opening.

Advantages and Disadvantages of Hot Water under bench heating

• Provides good soil heating.
• Does not provide air movement, which could result in mold.
• Reacts slowly when called upon to heat.

Advantages and Disadvantages of Hydronic Unit heaters

• Short heat recovery time reduces temperature fluctuations, promoting a natural growing environment.
• Provides much needed air circulation to decrease dead spots in the greenhouse, reducing the high moisture areas that promote mold growth.
• Usually supplied by one boiler which does not give you redundancy.
• Fan may be used to circulate air in the warmer growing periods.
• Don’t have products of combustion to be vented.