Hay dryer

This is a simple idea and relatively cheap for a farmer who likes hay milk : a hay dryer with a greenhouse making it possible to make hay without thinking about  rain. With that method, we can make hay in Belgium begin May when the wheater is still very changing. We then become hay as rich as silage but without the drawbacks

Hay has more qualities than silage : it is lighter and more funny to handle than silage and there is no risk of listeriose nor butyric germs in the  cheese. Farmers make silage because the silage can be made when the grass is not totally dry.

Drying hay on the ground needs a long period without rain and that doesn't arrive when the grass is the most rich. Hay can be dryed in a barn but it needs then fossil energies or the biomethanization. What I will explain is better than a dryer with biomethanization of manure because it is not made at the expense of the soil humus. With the biomethanization, the soil becomes poorer. Presently there are dryers with a dehumidifier using a  heat pump : the humidity of the air is condensed  on the cold wall of the heat pump and is eliminated. This dry air will then heat on the warm wall of the heat pump, and becomes so still dryer. That heat pump needs energie, much more thant my dryer which has only fans. In France, farmers are drying with air which is heated under the roof of the barn warmed up with the sun. But it is not enough in Belgium and the roof is very expensive..

What we seek is to make hay without rain.  In Belgium,  2 days sunny weather are frequent. More than 2 days is doubtful. It is better to have the hay inside into 2 or 3 days.

After tedding on the ground, the hay is harvested with 40 % humidity, like silage. Then it is harvested in a greenhouse where the hay is safe from rain. If after that, the weather is variable, the greenhouse warms up enough during the sunny periods. Of course, it is not possible to ted when there is a long rain period. And if the rain arrives after 2 days drying in the greenhouse, when the hay is not completely dry, it will not rain continuously more than one day and then there are sunny periods again. We only  have to prolong the drying process one of two days and the sunny periods are then enough to dry totally the hay.

In a closed greenhouse full in the sun, the temperature reaches more than 50 °C. Hay must stay under 40 °C in order to not destroy its nutritive qualities. So it is necessary to use fans.

 The hay is placed along windrows on the ground of the greenhouse and will be periodically turned with a small windrow turner moved with a tiller The atelier Houssa at Hannut (Belgium) www.atelierhoussa.be is making that material. Two pictures of it :

The grass to be dryed will be placed along windrows in the greenhouse with a wheel loader. It requires a little work, but no more than to load 7 meters high cells with a telescopic gripper such as in the industrial dryers for hay.

The 4 meters high greenhouses are very expensive. The greenhouses with 2,70 m heigh are cheaper but a tractor is to large to go in it. With a tiller, we have not that problem and when the windrow is 1 meter wide and the speed 2 km/heure, a greenhouse of  8 * 30 meters is turned between 8 / 1,6 * 30 / 1.000 / 2  * 60 = 4,5minutes.The gras must be turned because the bottom layer stay always wet. The upper layer is always very dry

With one greenhouse of 30 m * 7, we can own one hectare at a time.One hectare at a time seems to be too little but with a greenhouse we have to work in another way : instead of one large harvest, we have to make numerous little harvests. Farmers who are drying in a barn with a dehumidifier and cells where the hay reachs 7 meters height are also obliged to make numerous little harvests because they are limited by the surface of the cells where they can put only 1 to 1,5 meter hay. If those farmers make 30 hectares in one year, they will not make more than 1 meter / 7 meter * 30 hectares, or 4 or 5 hectares each time. If we have 3 or 4 greenhouses of 30 m * 7 m, we can do even good but it kosts much less.

The farmer has to follow the weather broadcast to see if there will be two sunny days.

One hectare produces in one cut 4.000 kg dry hay. If the hay contained  40 % d'humidity when it was put in the greenhouse, 1 kg hay must evacuate  0,4 kg water. The psychrometric diagram indicates that, when the temperature 22 °C is and reaches 50 °C in the greenhouse, 1 kg dry air can absorb 7 kcal and 8,5 gr water. Actually, the temperature will reach more than 50 °C if the greenhouse is completely closed. But as the air absorbs water, its temperature will decrease. With a propeller, the temperature in the greenhouse will be 25 or 30 °C.

If the hay is put in the greenhouse  with 40 % d'humidity, 1,66 kg of that grass  contains 0,66 kg water, whereas 1,18 kg dry hay with 16 % humidity  contains 0,18 kg water.  1 kg dry hay contains 0,18 / 1,18 = 0,15 kg water.  To obtain 1,18 kg hay  we must extract 0,66 - 0,18 = 0,48 kg water. For 1 kg hay we must extract 0,48 / 1, 18 = 0, 40 kg water.

If the greenhouse has as dimensions 30 m * 7 * 2,7 (then length of the greenhouse may not be greater the 30 m to have a good ventilation), it has a volume of 567 m³and as the weight of 1 m³ air is 1,2 kg at 20 °C,  the total weight of the air in the greenhouse is 680 kg.

For one m², it receives 5 kWh a day, but all that energie does not come in the greenhouse. Thermal solar panels have an efficiency of  40 %. We will suppose it is the same for the greenhouse.

In one summer day with sun, we have

5 kWh/m² * 40%  * (2,7 m + 7 m) * 30 m = 600 kWh

The greenhouse receives in one hour 600 kWh * 861 kcal/kWh /8 hours = 64575 kcal/hour

But we know that 7 kcal and 8,5 gr water are absorbed by1 kg dry air

Thus, 1 kcal is absorbed by 1 / 7 kg dry air

64575 kcal/hour need 1 / 7 * 64575 kg dry air sec to be absorbed or 9225 kg dry air

1 kg dry air absorbs 8,5 gr water

9225 kg dry air absorb 9225 * 8,5 / 1.000 = 78 kg water 

As the weight of the air in the greenhouse is 680 kg, the air in the greenhouse will be removed 9225 / 680 = 13 times per hour while the air absorbs 78 kg water.

In one day we can extract : 78 kg * 8 = 624 kg water        or, 624 kg water / 0,4 kg water/kg hay with 40 % humidity = 1560 kg hay / day. Between 4000 / 1560 = 2,5 days, we dry 4000 kg hay, more or less one hectare.

However, our Houssa windrow turner requires a strike without hay because the tiller must go there. The windrows placed in the greenhouse with a wheel loader, have 1 meter width and the tiller needs 60 cm. The weight of  hay in the greenhouse is then 4000 /1,6 = 2500 kg, more or less one cut of 62 ares. We can dry 2500 kg hay in windrows in the greenhouse between 2500 / 1560 = 1,5 days .

We supposed the hay was first dryed 2 days on the grassland. We can also place the grass directly in the greenhouse. We have then much less waste of broken leaves than with a tedder.

7 kcal are absorbed by 1 kg dry air. If the sun gives more calories, we have to blow more otherwise the temperature will increase. We can install two propellers : the first one is working continuously and the other one starts when the temperature reachs 35 °C.

The greenhouse has a volume of 567 m³ which are ejected 13 times a hour. The flow of the propellers is 567 m³ * 13 times / hour = 7400 m³/hour. A propeller with 7400 m³/hour often has a power of 1,5 kW. For on cut of 2500 kg hay, the propeller needs  1,5 kW * 8 hours * 1,5 days * 0.25 €/kWh electricity = 4,5 €. If we have to make 20 hectares in one year producing 10000 kg hay / hectare, the yearly cost to dry the hay is 4,5 € * 20 * 10000 / 2500 = 360 €, or  4,5 / 2500 = 0,0018 €/kg hay.

The working approach is different as usual. Presently, farmers work with large engines to harvest a large surface in one shot, when the weather is suitable during a long period. With my greenhouse dryer, you must make plenty of little harvests, but very often, because we are limited by the dimensions of the greenhouse. So, we will have a rich and very palatable hay. The only downside is that the hay is highly digestible and the fat percentage in the cow milk is lower. That hay is too rich for horses but we can cut the hay later to have a poorerr hay

I use such a dryer, but very small, because I have only 6 ewes. The dimensions of the greenhouse are 4 m * 3 m, and I have to move the hay with my hands. I am very pleased with it. My only difficulty is to move the hay. You can see it here :




You can see the propeller fan. The white engine above the fan is a dehumidifier De Longhi. It works with a heat pump. It absorbs ideally (at 30 °C)  25 liters water in 24 hours and  has a power of 400 W. As to make 1 kg hay from grass at 40 % humidity 0,4 kg water must be extract, that means that to dry 4.000 kg hay, thus the cut of one hectare, we have to pay for the electricity  :

25 liters / 24 hours * 0,4 kWh/liter water * 1.600 kg water to be extracted from 4.000 kg hay * 0,25 €/kWh = 166 € to dry one hectare with a cut of  4.000 kg dry hay. A dehumidifier is a good method to dry hay night and day, because it costs  4,15 €cent electricity/kg hay. It is not so much but if the farmer makes 10000 kg hay on 20 hectare each year, he will have to pay 8.300 €. In a Austrian farm of 30 hectares, the dehumidifier and the fan have, together, a power of 28 kW. The fan alone is 15 kW because it must cross 7 m hay, dry at the bottom but wet on the top.With a dehumidifier it is nevertheless more expensive than my greenhouse with two propeller fans with less power.

With grass at 40 % humidity, 1.000 kg hay give 400 kg water and as to extract 25 kg water during 24 heures we need a power of 0,4 kW, we use 9,6 kWh, or 9,6 / 25 = 0,384 kWh / kg water. So, 1 ton hay requests 400 * 0.384 = 153 kWh.

It is funny to note that the little home dehumidifiers have het same performance as the big industrial dehumidifiers : 25 liter water extracted between 24 hours with a power of 400 W.

Those figures are valid when the conditions are ideal : temperature 30 °C and humidity 70 %. A factory gives the absorption capacity for different tempeératures, for a dehumidifier of 20 kW :

30 °C    60 % humidity   760 kg captured in 24 hours.

27 °C    60 % humidity   680 kg captured in 24 hours.

20 °C    60 % humidity   501 kg captured in 24 hours.

We see that, if the temperature is  lower than 30 °C, the dehumidifier is less efficient. We must know that, if the temperature goes  above 32 °C, the dehumidifier stops working because the air temperature is higher than the plate delivering the heath. The heath goes from a warm surface to a cold surface, not the contrary.

Let us still dream about dehumidifiers. Suppose a farmer installs several dehumidifiers in a barn completely closed and thermical insulated to keep night and day a temperature between 25 et 30 °C. This room can be first warmed up till 25 °C so that the dehumidifier has then its most efficiency.  It must not exceed 30 °C because the warm panel of the heat pump cannot yet deliver its heat to the air of the room which has to refresh it. For 4.000 kg dry hay,  1.600 kg water have to be extracted, during 3 days, night and day, or 500 kg water in on day. As the dehumidifiers extract 25 kg a day, 20 dehumidifier for one hectare are necessay and 60 for 3 hectares. My own dehumidifier costs included VAT 400 € for one piece from a dealer. Exclusive VAT and for many pieces, it cost no more than 250 €, or 15.000 € for 60 dehumidifiers while I read in the farmer press that a dehumidifier for a little farm costs minimum 65.000 € . Where is the mistake ?

Farmers who likes a dehumidifier have to keep in mind that electricity price increases very much when the grass is very wet.We can calculate it :

This are some rates of humidity in grass and the corresponding wheight of water each time for 1 kg dry matter, and the price of electricity for one hectare in a year when 40 % costs 400 € for on hectare, as explained above :

16 % wet :       0,19 kg water 1 kg dry matter        price 1 ha

20                             0.25                                        151 €

30                             0,43                                        260

40                            0,66                                        400

50                            1                                             606

60                            1,5                                         909

70                            2,33                                      1.412

80                             4                                         2..424

90                              9                                        5.454

If the grass is cut without any tedding, it contains 80 % humidity and using a dehumidifier costs 2.424 € for one hectare in a year.

If the farmer harvests 30 ha such grass, it costs 72.720 €. It is absolutely uneconomic.

If it rained on the grass, it costs then 5.454 € for one hectare during one year.

We explained that a greenhouse of 7 * 30 meter can extract 512 kg water a sunny day. A dehumidifier with a heat pump extracts 25 kg water a day with an electric power of 0,4 kW. To extract 512 kg water between 24 hours, it needs as power 512 / 25 * 0,4 = 8 kW. The Austrian farm had a dehumidifier of about 13 kW. Thus, 1,6 greenhouses extracts the same as a dehumidifier of 13 kW which is in service in a 28 hectare farm.

With the greenhouse, the grass may be wet : the dry process has only to be  prolonged one or two days. The sun is free. I already had that case with my greenhouse of 3 meters on 4. It rained on the grass just after I cut it but with the greenhouse it was dry without any problem..

The harvest on the grass-land is easier with a greenhouse than with a deshumidifier because the dehumidifier must start with a hay at 40 % wet, 2 days tedding, while we can put hay in the greenhouse which stayed on the grass-land not so long. The hay is earlier save against the rain and will dry in the greenhouse instead of on the grass-land. So, we have more time to harvest and we can do it more relaxed.

A dryer with a greenhouse is more or less similar to a dryer where the air is heated under the roof of the barn. However, the greenhouse warms up more quickly when there is a a rift in the sky because with a barn, the sun must first warm up the roof..