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Contenuto archiviato il 2022-12-27

USE OF SOLAR ENERGY TO HEAT LIQUID FEED FOR CALVES

Obiettivo

The objective of the project was to investigate the possibility of using solar energy for water heating in agriculture, using collectors forming an integral part of a roof.
In view of the situation on farms, where large roof areas with unobstructed exposure to solar radiation are common, and plenty of space is available for a storage system, it was desirable to seek a specific solution, suitable for agriculture. In this case the warm water was to have been used with milk powder as animal feed.
From a technical point of view the results of this project are quite encouraging. The solar collectors operated with an average performance of 33%; the power required by the air circulation fans was about 1 kw. From April through September 70% of the total energy was collected; the remaining 30% (41000 kWh) being collected during the Winter months.
Losses were found in the air circuit leading to a decrease in the heat transferred to the hot water tanks.
The net energy production of the 141 m2 solar roof amounted to 33000 kWh per year or 233 kWh/m2/yr. whilst energy received was 968 kWh/m2/yr. Energy delivered amounted to 115 kWh/m2/yr. This was one half of that expected; the losses being explained by air leaks. However energy savings of 15000 kWh were made (during a bad Summer ).
Economically the project was less of a success. Building and installation costs were higher than expected. Now that greater expertise is available it can be expected that these costs would be reduced. Simular comments can be made for the collectors which in this project were more expensive than liquid collectors.
Costs of the system amounted to 461 gulders/m2 and savings on propane gas at F 0. 9 per litre amounted to F 68 per m2.
This project has shown that for this type of application solar energy provides a technically viable solution and with costs at 200 to 250 gulders/m2 an attractive solution financially.
The solar installation comprises : the air collectors
: the air treatment system
: the solar boiler
: the hot water installation with the auxiliary heater.
Air collectors.
The collectors have a length of 10. 80 m and a width of 1. 03 m. Black aluminium plates (0. 9 mm) are used as absorbers, these having an absorption factor of 0. 94 (for radiation in the visible band of 0. 35 - 0. 79 mm) and an emission coefficient of 0. 96 (for rays of 8 - 14 mm). A 0. 6 mm box-section member is fixed to the underside of the absorber and acts as an air duct. This duct is insulated with 40 mm polyurethane.
The collector is covered with transparent double-walled polycarbonate panels having a light transmittancy of 84 %. The advantage of the panels is that they have an insulating effect and can be supplied in the lengths required thus reducing the chance of leakages.
The whole unit is sealed on the weather side by plywood.
The net surface area of the absorber is 0. 932 x 9 = 8. 389 m2.
The total surface area of the absorber is 16 x 8. 389 = 141. 42 m2.
Air treatment system.
The air treatment system consists of an air duct, a heat exchanger and two blowers.
The air ducts are rectangular and are connected to the collectors by hoses.
The ducts are of variable cross-section, so that the pressure therein is the same along the whole length. The air flow varies between 1600 and 5500 m3/h.
A differential temperature switch controls the blowers. As soon as the air temperature in the collector is 5 deg C higher than the water temperature in the solar boiler, fans are switched on.
Solar boilers.
Two solar boilers were used to store the solar energy received. One solar boiler has a capacity of 10000 lts and the other one 20000 lts. The latter was filled with about 17000 lts to leave room for the expansion of the water. The water in the tanks is not used as service water (closed circuit ). An oil film covers the water to prevent evaporation. Both tanks are insulated and provided with heat exchangers to extract the heat and to release it to the water in the hot water systems.
Hot water system with auxiliary heating
The hot water is under mains pressure. The water flows to the large solar boiler via two heat exchangers. It then passes via two heat exchangers into the small solar boiler.
Thence the water flows to a 2800 lit storage tank in which it is kept at a temperature of 60 - 70 deg C. At this temperature milk powder dissolves easily and the resulting solution is feed to calves

Argomento(i)

Invito a presentare proposte

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Meccanismo di finanziamento

DEM - Demonstration contracts

Coordinatore

IMAG-SCHIJNDEL
Contributo UE
Nessun dato
Indirizzo
MANSHOLTLAAN 10-12/POSTBUS 43
6700 Wageningen
Paesi Bassi

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Costo totale
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