- The type of crops that are to be stored.
- Headroom for tipping trailers.
- Whether the building structure is suitable for the side loads transmitted by the stored crop or whether you need internal thrust walls.
- Vehicular and pedestrian access into the building.
- The availability of the electrical power supply.
- If you are currently using the building as a store, where you will store the equipment when you have completed the conversion.
- Whether you have a choice of locating the main air duct centrally or down one side of the building.
- Where you intend to site the fans – internal or external fan house
- Whether your existing concrete floor is suitable to accept a drive-on floor.
- How you will make the building vermin and bird proof.
We work closely with our distributors many of whom can offer not only advice on planning issues enhanced by local knowledge but also a full design and planning application service.
Whether your building is new or a converted grain store we can design, build and supply a drive-on floor or box store system to fit your needs.
We have converted a wide variety of farm buildings into efficient and effective bulk drying and storage facilities
- The capital cost of a bulk drying system is lower.
- Bulk-drying is suitable for a wider variety of crops such as beans, peas, herbage seeds, potatoes, onions, garlic, woodchip etc.
- Bulk-drying has a faster loading rate.
- Bulk-drying has lower running costs – best use of latent heat.
- Bulk-drying has low maintenance costs.
- There are fewer moving parts to go wrong.
- Bulk-drying enables ease of loading.
- The bulk-drying ventilation system provides both drying and ventilation for long-term conditioning
- The storage height depends on the design height of the store – don’t overload!
- For grain drying, storage height is normally 10’ or 12’ deep.
- The size of the fan dictates the drying capacity of the store.
- Generally work on 100 cubic feet per minute (cfm) per ton of crop e.g. a 30kw fan producing 30,000 cfm at 4.0” standard water gauge pressure will dry 300 tons of grain at one time at 10’ deep). The pressure that the fan has to work against to force the air through the crop is dictated by crop type, storage depth and ventilation rate.
- The optimal ventilation rate for grain is 20 ft/min through the crop at 8’ to 10’ deep and 24 ft/min at 12’ deep.
We have had the experience of stores loaded to 12’ deep with grain at over 24% moisture content dried without the use of stirrers. This has been achieved in correctly designed and operated stores with large capacity fans installed, ventilation of the whole store and running the fans for 24 hrs a day with NO HEAT until the crop is below 18%.
Note:
When the ambient relative humidity (RH) is high the airflow will do no harm to the crop but it will prevent deterioration until the ambient RH falls when drying will then continue to occur.
Stirrers are beneficial when the speed of drying is the primary requirement, or where the site is low on power availability.
They are good for fluffing up the crop to reduce resistance to airflow so increasing the airspeed through the crop.
They reduce the risk of capping by breaking up the drying front working its way up through the depth of crop.
They are advantageous for crops such as grass seeds which tend to compact down and so reduce the airflow through the crop.
If you are going to increase the size of your fans (probable) then you need to calculate whether the main air duct can handle the increased airflow. Consider the cost of removing the front/rear gable end of the building (it may be more cost effective to build another store next door).
We offer a self-install package, including one-day’s on-site instruction and an installation manual, for both ducts and floors.
Generally, the rate of floor installation is about 20 to 25 square metres per man/day so an 18 m x 18 m floor area should take around 16 man-days.
A 20 m long x 3.0 m high duct will take around 10 man days to erect.
- Traditionally a 1.22 m x 1.22 m cord operated flap or fixed blade louvre was placed at each gable end of the building to vent the air.
- New buildings, however, are well sealed and much more airtight than older buildings so that with the increases in drying capacity and fan sizes consideration needs to be given as to how to remove the air from the building.
- In many instances, cowls are now being employed rather than fixed blade louvres as they have a much higher “free area”. Airspeed through exhaust openings (and intake into the fan house) should be kept below 1000 ft/min.
We design an air distribution system to work on an air speed of 1800 to 2000 ft/min inside the main air duct and under the floor. From this we calculate the cross sectional area required in both instances and therefore identify the required duct size and the floor bearer depth.
- This depends on several factors including (1) the crop type, (2) the initial moisture content (it is much quicker to dry from 20 to 17 than 17 to 14% moisture content (MC) due to it being more difficult to get the moisture out of drier grain), (3) the crop depth, (4) the ambient temperature & relative humidity.
- A general rule of thumb is ½% per 24 hours ventilating with the correct airflow at the correct humidity.
- Ambient temperature, however, is an influencing factor, i.e. the cooler the air the lower its “moisture carrying capacity”, so that air at 5 deg C and at 65% RH will have one quarter of the drying effect of air at 20 deg C at 65% RH! Therefore it pays to get the crop dry before the ambient temperature falls in the autumn.
- The introduction of a gas heater once moisture content is below 18% will increase the potential drying rate by a factor of three.
- Without heat the ambient RH may be suitable for drying for only 8 hrs a day whereas with heat (or dehumidification) the RH can be maintained at the required level 24hrs/day.
- Estimated safe storage periods can be identified through Krager tables and these estimates are dependent on the crop in question, its moisture level and its temperature.
- If the crop is dried and cooled to optimum levels then all year round storage can be achieved.
- Many overseas farms still rely on organo-phosphate chemicals to enable them to store the crops for long periods at high crop temperatures.
- However, it has been shown that the chemicals can be virtually eliminated by the introduction of a simple controlled ventilation system to cool the crop.
- Regular monitoring and record keeping both during and after drying is essential. The Home Grown Cereals Authority online Knowledge Centre is a good place to consult on grain storage.
- A crop airflow meter and a manometer are essential tools for monitoring the drying performance.
- Yes, spare heat from your renewable heat system is passed through a heat exchanger to warm the air feeding your fans in your drive on floor installation. The demand on the supplied heat is controlled by the drive on floor electronic control system.
- Yes, woodchip can be dried on your drive on floor. Typically a 200kw boiler supports a 40 tonne store with woodchip stacked at 1.5m high – this stack is reduced in moisture content from 40% to 25% over a 2 to 3 day period.
- You can also dry logs on the drive on floor by employing a slightly different drying technique.
- An axial fan compresses the air along the fans axis whereas a centrifugal fan turns the airflow through 90 degrees.
- Axial fans have always been considered noisier than centrifugals but with modern attenuation technology this can easily be overcome.
- For high pressure applications such as grain and seed stores the choice is between multi-stage axial fans or centrifugal fans. The choice is often set by site parameters such as power availability dictating motor size – in which case multi-stage axial fans would be the primary choice.
- For lower pressure or mixed pressure applications such as bulb or potato stores and multi-use crop stores the versatility of a carefully selected axial fan is hard to beat.
- We recommend annual cleaning and disinfecting removing dust, insects, mites etc.
- We recommend checking RH sensors annually.
- We recommend servicing gas heaters annually.
- We advise that control panels remain on at all times – the small amount of heat generated will help reduce condensation and therefore reduce any potential for corrosion.
- Our standard panels include a thermostatically controlled anti-corrosion heater.
- Check your fan greasing schedule.
1. Assuming 8’ to 10’ storage depth the required airspeed through the crop in a grain store is 20ft/min and the fan working at 4.0”swg pressure:
i. A 30kw fan will produce 30,000 cfm at 4.0” swg.
ii. 30,000 divided by 20 ft/min airspeed through the crop means that the fan is capable of ventilating a floor area of 30,000/20 = 1500 sq ft.
iii. If the floor width is 30’, then the length of duct outlets which should be open is 1500 / 30 = 50’ run.
iv. If the duct outlets are every 16” then 50 x 12 / 16 = 37 outlets open.
2. Assuming 12’ storage depth the required airspeed through the crop is 24ft/min and the fan working at 6.0” swg pressure.
i. A 30kw fan will produce 26,000 cfm at 6.0” swg.
ii. 26,000 divided by 24 ft/min airspeed through the crop means that the fan is capable of ventilating a floor area of 26,000/24 = 1080 sq ft.
iii. If the floor width is 30’, then the length of duct outlets which should be open is 1080 / 30 = 36’ run.
iv. If the duct outlets are every 16” then 36 x 12 / 16 = 27 outlets open.