ABSTRACT
Labor and heating costs are the major costs of greenhouse operations particularly in mid- and high-latitude countries. Large energy costs are incurred to maintain the required thermal and radiant environments in greenhouses particularly during the winter season. While heating is mostly required at night, it may also be needed during the day. Annual labor costs typically range from 30% to 35% of the total cost of production, while heating costs typically range from 20% to 35% of the total production cost depending on the location and the local fuel prices. A number of heating and air circulation systems are commercially available today, and these systems include old steam heating, hot water heating, radiant heating, spaced unit heaters, central heating, underbench heating, floor heating, perforated tube air distribution, and horizontal air circulation.
This chapter goes over estimating heating loads in greenhouses first, and then moves to the passive and unheated greenhouse systems. The chapter then introduces the reverse return principle and covers in depth the spaced unit heaters and central hot water (hydronic) heating systems using step-by-step approach. Actual boiler room (including the boiler loops, manifolds, transport groups, expansion systems, vent stack, and fresh air inlets) and heat distribution system designs, the main supply and return lines, pipe rail heating, grow pipe heating, underbench heating, in-floor heating, sidewall and gable end heating, and snowmelt and overhead heating systems designs are included. Flue gas condensers and low grade heating systems, irrigation water pre-heating, combined heat and power system integration, carbon dioxide dosing systems, and heat buffer system designs are covered in depth using step-by-step design approaches. Real-world designs examples are provided for different parts of the world for each system in order to fully demonstrate and grasp the pertinent design concepts.
