mDhT Aeration Controllers are available for easy control of silo fans. mDhT Controllers are the easiest and most cost effective way of getting your nuts drying in the silo without the guesswork! |
The mDhT Controller is capable of controlling fans in up to 4 silos. It is fully automatic and once set will continue to do its job until the aeration targets are met whereupon it will maintain those targets. Aeration can be applied to dry or cool durable commodities such as grains and nuts. Lowering the temperature and/or moisture content of these commodities will reduce their rate of deterioration during storage by reducing the likelihood of mould development and infestation by insects. Aeration of grain will not kill insects but, applied effectively, will reduce the rate at which insect populations increase.
Effective ambient-air aeration is not just a matter of turning fans on. |
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It requires careful selection of the ambient air in a way that will achieve the desired result in the shortest possible time.To do this, it is essential that a suitable controller is used to control the operation of the fans. Such a controller will sense the conditions of the ambient air, evaluate these in the context of the conditions in the commodity and then on the basis of the strategy you have selected, decide wether the fans should be ON or OFF. |
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The mDhT Aeration Controller , developed and patented by WRC Technology achieves these objectives. It is a fully automatic controller that, once set, will continue to do its job until aeration targets are met whereupon it will maintain those targets. It offers two drying strategies and four cooling strategies.
The drying modes include modes based on:
• Differential RH (relative humidity) plus air moisture content,
• Differential RH only.
The cooling modes include control based on:
• Continuously variable differential wet-bulb temperature,
• Wet-bulb set point control with automatic switching to differential control after preset period
• Selected fixed differential between ambient wet-bulb temperature and grain temperature,
• Continuously variable differential dry-bulb temperature. |
The mDhT Aeration Controller is capable of independently controlling the operation of fans in up to 4 silos or 4 zones of a shed.
Limit values may be set in each mode, e.g. in drying mode a minimum RH and a maximum temperature may be set, while in cooling mode a maximum RH limit on ambient air and a minimum commodity temperature may be set.
In the event of a power failure the Controller will automatically restart when power resumes and all user selected values and data will be restored. |
A time delay function is provided in the Controller. This time delay is the period before the unit will recycle. That is, having made a decision to switch ON or OFF the delay period must elapse before the unit can make a further decision. This function is to eliminate rapid switching of fans.
The unit also provides a staggered start-up of fans to prevent large current surges. The Controller provides a readout of the Mode in which it is operating, wet-bulb and dry-bulb temperatures, RH and time ON for each fan and total time since the controller was switched on. Password control of selection of functions and parameters is also provided and the Controller has provision to activate an external alarm in the event of e.g. a sensor failure. In addition, an RS232 output is provided and an optional data logger may be attached, which will record all sensor outputs at hourly intervals together with the run-time of each fan.
Remote monitoring is also available via a suitable modem. |
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COOLING
An mDhT Controller, in differential dry-bulb mode, achieved a reduction in temperature in 1000 tonnes of Canola from 22.3ºC to about 16ºC from February to early June 1998, through one of the hottest periods on record in Australia. In the process of this it lowered the moisture content of the Canola from over 8% to 6.3% which further improved its keeping quality.
DRYING
During the 1997 and 1998 Macadamia nut harvests, nut-in-shell was stored in a silo in which the ambient-air fan was controlled by an mDhT Aeration Controller in differential RH mode. From harvest moisture contents ranging from 15 to 20% different batches of nuts achieved moisture contents of 7.3, 5.2 and 6.7%.
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