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AutoVent 2t with advanced PC control
Venting The AutoVent 2t will control up to three fan banks (or variable speed fans) together with air inlet vent and water evaporative cooling The venting/heating algorithm will try to control both temperature AND relative humidity. If heating is available then this too will be used to try to control humidity in addition to temperature. Intelligent use is made of the fans and pad water to achieve the desired temperature and humidity. In addition, if the fans and pad are unable to control the temperature satisfactorily, the shading will try to assist and if this is still not successful the system will automatically switch over to air conditioning control(if fitted) Air Conditioner As an option, an air conditioner may be installed. This is only used after every attempt has been made to control temperature by fans and/or evaporative cooling Heating Air heating can be by either proportional control or ON/OFF control. Proportional control is normally used in conjunction with a boiler heating water pipes. This provides a very gentle heat and the heating pipes can be positioned either under the grow beds or between the rows of plants. In this way less heat need be supplied as compared with general warm-air heating. Water pipe heating is gentle, economical and avoids sudden drying of the air. The heating is used to control both the temperature and the relative humidity. Fogging Fogging may be used to assist with cooling or to increase humidity in dry weather. Five outputs are used; one that comes on constantly while fogging is called for and the remaining four that pulse on for short periods to inject puffs of fog to each zone in turn. The size of the puffs of fog is automatically varied depending on the size of the error that it is trying to correct. For example, if the humidity is just a little too low, then small puffs of fog will be generated whilst if the humidity is a lot too low then larger puffs will result. Stirring fans A single stage of stirring is provided as standard but this is increased to two zones if the output expander is fitted. Stirring fans are normally set to come on whenever the exhaust fans are off, when humidity is excessive, when injecting CO2 or when fogging. Shading Two stages of shading are available together with a thermal screen. Often one shade will be external and the second internal. The external one is usually of heavy duty material and does not introduce any heat into the greenhouse. Wind and rain overrides may be set to automatically retract this shade. Normally the shades operate to maintain the light level below a user set maximum. If the maximum light level is exceeded the appropriate shade (or both) will start to close immediately but once closed requires the light to remain below the setpoint for at least the time specified by the user. When changing from one shade to the other the rule followed is always "close before opening" in order to protect delicate plants. The thermal screen may be used to trap the heat in the lower part of the greenhouse and effectively provides "double glazing" but only when cold or when set to close for a particular time zone. The shades can be set to "crack" if high humidity is encountered. Purging In the event of very high humidity, the controller can be programmed to go into a purging mode. In this mode it increases the heating temperature by a few degrees (user set) to try to dry the air. Eventually the humidity will creep up again due to plant transpiration and the controller will switch on an exhaust fan for a few seconds (user set) to exhaust the warm humid air. Then the fan will then stop and the heater will again warm and dry the fresh air. This purging cycle will continue until the humidity is brought under control. If a dehumidifier is installed then purging is not normally used Dehumidifier An alternative strategy to reduce humidity is to use a dehumidifier. This is particularly useful when CO2 injection is used as it avoids venting to remove humidity. Optional CO2 CO2 is measured and injected providing 1) there is sufficient light, 2) the fans are off or 3) the fans are below a set limit. The user may specify any desired level of CO2 from 0 to 2000ppm and the system will try to provide this when the above conditions are satisfied. PC interface The optional PC interface allows the settings to be viewed and set from the user-friendly Compugrow software. It also facilitates the collection of measured data and events from the controller for logging to the hard drive whence it may be displayed graphically for ease of interpretation. The computer interface also allows for alarms to sound at the PC (via the PC sound card) or even be auto-dialled out to a telephone or pager (via the PC MODEM). If remote access software is installed (eg PCAnywhere) the PC and hence the controller may be accessed from anywhere in the world (password protected of-course) |
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