Heating and CO2 System
The heating unit, one of the main components of a glasshouse, is usually a hot water boiler. The heating unit provides the desired growing temperature for crops under production to achieve the highest quality. A good alternative to the boiler is a combined heat and power unit if extra electricity is required. Usually, a CO2 dispenser is directly linked to the heating unit. The AVAG specialists have a great deal of experience with such cooling units as the pat and fan system (air) or hose system (floor).
In addition to their expertise in designing and installing heating and cooling units, Dutch firms possess a great deal of know-how on energy management. A variety of measures can be introduced to make the most economical use of energy; insulation, flue-gas condensers, heat storage tanks, measurement and control equipment and the use of waste heat. For example, a flue-gas condenser reduces the flue gasses produced by the boiler to 60°C.
A hot water boiler and a system of pipes
- A hot water boiler is the most common method of heating in a glasshouse. A gas or oil burner is used to heat the boiler. The boiler's capacity also depends on the amount of heat needed to achieve the desired maximum temperature in the glasshouse with respect to the outside minimum temperature.
- The system of pipes used to distribute the hot water and hence the heat throughout the glasshouse is usually a combination of several systems. The most common systems are:
- pipe rail heating: the pipes at floor level also serve as rails for bulkbins
- adjustable pipe heating: the pipes can be adjusted to the height of the crop as it grows
- monorail heating: the pipes at head height also serve as rails for bulkbins for hanging products
- hose heating: especially manufactured hose for heating purposes, often used to heat or cool the root environment.
- gutter heating: pipes placed immediately under the glasshouse gutters to melt any large quantities of snow on the glass surface.
- Pumps and mixer groups fitted to the boiler and elsewhere in the glasshouse can transport heat to where it is required.
- The hot water boiler can also be used to generate steam to disinfect the ground in the glasshouse. The boiler will need to be fitted with special devices.
A combined heat and power unit
- A heat and power unit is of particular interest to firms whose electricity (lighting) demands are high. Electricity is produced by a generator operated by a gas burning device. The cooling water from the gas engine can be used to heat the glasshouse.
- As the demand for electricity and heat is not always the same, a hot water storage tank is a good solution. The hot cooling water can be stored in a well-insulated tank and used when required.
- Flue gases from a heat and power unit should first be cleaned before being used as a source of CO2.
The closed glasshouse is a new development to enable a maximum energy efficiency. In a closed glasshouse in the summer, warmth is stored in an aquifer (underground water bubble), thus cooling down the climate in the glasshouse. In the winter this warmth can be used, in a system of heatpumps and air treatment, to heat the glasshouse.
- Hot-air heaters are falling into disuse and are only used if the crop under cultivation does not require much heat. Individual gas or oil heaters are suspended throughout the greenhouse. They were originally meant as extra CO2 dispensers.
- There are certain drawbacks to these heaters. Fresh air must be admitted (energy loss) to ventilate the glasshouse, while harmful gas residues present a risk.