subota, 10. ožujka 2012.

Wood or Pellet


Pellet, biomass and wood


Since 1980 the U.S. and Canada have produced wood pellet, in Austria and Scandinavia it appears on the market in 1990, since 2000 this fuel has spread in Germany and the United Kingdom, soon enjoying great popularity.
The pellet market is therefore a highly internationalized market, less than half of the Italian consumption is covered by domestic production, the majority of pellets consumed in Italy comes from Central Europe, Eastern Europe and North America. Last year 1.75 million tons of pellets arrived in Europe from North America. This situation is mainly due to greater availability of forest products and confirmed the robustness of the wood sector in countries close to us such as Austria, Germany, Slovenia, Bosnia, Romania, Poland, the Baltic countries.

Choosing a wood or pellet stove as a heating system for your home means to mediate between two important aspects: design and technology of the product. Without detracting from the importance of the aesthetic, that points to a model rather than another, and which has close ties to taste and personality, here we want to examine choices of a more technical nature, aiming to have a heating perfectly in line with needs.
In recent years, stoves have passed significant technological change. They have in fact witnessed the transition from old systems with manual to modern automatic control and digital devices, to get to thermo- stoves, which can, alone, meet the needs of an entire apartment. Modern wood stoves also ensure low emissions of greenhouse gases, energy content and greater cost savings compared to fossil fuels such as natural gas, diesel and LPG./p>
Wood stoves have cast iron firebox or refractory material to spread slowly accumulated heat. The air that powers combustion mainly enters through the grid at the sides of the stove or in lower areas. A pyrometer or automatic register allows you to automatically open or close, thus regulating the draft in the stove and then the intensity of the flame. Heat warms the air making it escape from the upper grid and is distributed in the environment by means of fans that regulate air flow. The ash produced is collected in the tray located under the stove easy to remove and clean.
"Air" products are great for small houses like two or three rooms in which, through an appropriate drainage system, heat generated can be broadcast in all rooms.
There are also "water" stoves that allow the production of hot water for radiators and domestic use. Compared to the type mentioned above, these stoves exchange heat with water generated by combustion of the heating systems easily integrating with traditional or low temperature systems (such as radiant floor or ceiling) allowing you to distribute heat in a more optimal and significantly way raising the efficiency of the generator or wood pellets.
The wood-fired generators are then listed on the basis of the material of which the boiler is built, stainless steel models are currently used, especially for the stoves in a modern style and have the advantage of being not only lighter but also of heating the rooms in a few minutes.
There are also models of stone or brick, widespread in rural and mountain areas. Their characteristic is to be internally made of refractory material and be free of elements in cast iron or steel, except the door for the supply of fuel.
For outer coverings, the choice is wide: classic ones are majolica hand made, ceramic or marble, while in other cases it may require customized designs. Stone tiled and oil stoves also heat by radiation: the walls of the oven get very hot, and continue to give off heat in the environment for several hours even after the flame has been extinguished.
Devices of this type have yields ranging from 83% to over 90% and all these values are written on the label serial number of the stove.
Let's see what information it must include:
1) if the product is CE marked or not (non-CE products may not be sold in the country). The indication EN 14785:2006, which is the European reference standard for pellet stoves and indicates test method adopted
2) the power of the stove (shown in kW)
3) its performance in% (the higher the yield, the lower the pellet / wood burned to heat)
4) the manufacturer
5) the value of CO (of course, the more this value is low less pollutant the product is).
This value must be less than 0.04% at the maximun operating speed and than 0.06% at the minimum (UNI EN 14785).
For proper installation of the stove it is necessary to provide for a certain distance on the sides and back, from both sides, also from flammable objects.
Depending on the product, between the walls and the heater there should be left a space of 15-35 cm and 30-60 cm at the rear sides.
If warm air comes out also from the back side of the generator, facing a wall, install an insulation and fireproof panel and before placing the stove on floors, carpets, rugs or flammable materials, prepare a medium fire resistant, like a steel plate or glass, which must extend at least 30 cm from each side of the stove.
For proper operation, please place the heater in a location where you can guarantee the flow of air needed for combustion and adequate smoke evacuation.
Equally important is the correct shape of the chimney. The air flow must go through permanent openings on the walls towards the outside. These must not be blocked nor inside or outside and must be protected with metal grids.
The chimney should be of a windproof and consisting of a number of elements such that the sum of their section, outgoing, always doubles that of the chimney.
The chimney must be positioned so as to exceed the height of the roof of about 500 mm, allowing the drag of smoke out the chimney even in the presence of strong horizontal winds.
Regarding the average cost of firewood, it has different prices depending on the area: in the mountains, where it is easy to find from local suppliers, it costs less than in the city or the sea. The costs vary between 10 and 17 euros per quintal. For the stove, wood consumption with a humidity of 20% and an average temperature is about 2-4 kg per hour. In mountain areas, in summer, you can also stock up on firewood in the woods. A pack of 20 kg of briquettes pressed costs about 3.5 euros, while pellets costs about 37 euros per quintal but the yield is higher than that of wood.

Fuel
Cost per unit (3)
Net calorific value
Average yield 87% (4)
Unit cost for 1 kWh
Wood (1)
0,15 €
4,0 kWh/kg
3,48 kWh/kg
0,043 €
Pellet
0,28 €
5,0 kWh/kg (2)
4,35 kWh/kg
0,064 €
Methane
0,85 €
9,5 kWh/m3
8,27 kWh/m3
0,103 €
Diesel
1,15 €
10,0 kWh/l
8,70 kWh/l
0,132 €
LPG
0,84 €
7,0 kWh/l
6,09 kWh/l
0,138 €
Notes:
(1) Wood beech type with 15% humidity;
(2) Per kg average calorific value reported by major manufacturers;
(3) The cost must be considered according to the unit of measurement expressed in equivalent calorific value;
(4) Methane generators of type condensation each year have a rate of return close to 95-98%.
To calculate the approximate need to heat an apartment with a stove between 10kW with an efficiency of 87% in its operation at the maximum power consumed in one hour: 10 / (5 * 0.87) = 2.29kg
To simulate the operation of the generator is estimated to a minimum the power reduced to one third, resulting in consumption was 765 grams of pellets per hour.
With regard to the maintenance of these generators, it must be done once a year maybe in the period in which the device is not used by a service center, authorized by the manufacturer of the product. On that occasion, the technicians must clean the fireplace insert, the gray scale combustion and eliminate blocking holes that may form. Finally, the service center must also verify the proper operation and calibration of automatic loading system if it were installed.
The domestic heating by wood stoves can facilitate not only from the standpoint of energy savings but also to the front "taxes", according to particular conditions.
Generators and wood pellets, if settled instead of a gas or oil boiler, can access the tax rebate of 55% (paragraph 344 of the 2007 Budget extended until 2010) if they follow the following conditions:
a) have an efficiency rating in accordance with the minimum Class 3 of the standard EN 303-5;
b) comply with emission limits set out in Annex IX to Part Five of the D. Decree No 3/4/06 152 and subsequent amendments and additions, or the most restrictive limits set by regional standards, if any (For generators with a power rating greater than 0.035 MW (35 kW);
c) use biomass fuels included between those eligible under Annex X Part Five of the same Decree. 152/2006 and subsequent amendments and additions.
d) ensure, to the only buildings located in climate zones C, D, E, F, that the values of the transmittance of closures and similar, such as doors, windows and shop windows shall comply with the limits given in Table 4 ° C to Annex Legislative Decree no. 192/05;
e) to declare compliance with the afore mentioned requirements in the declaration completed by a qualified technician and in the transmission of the necessary documentation to ENEA for access to facilities.
In this case the VAT rate of 10% applies both the supply of goods or services if the goods supplied are not considered "significant." If the good provided is "significant" (such as boilers) the VAT to be applied should be calculated as per Law 488/99, article 7.
Finally, in case of combined wood / gas or wood / diesel deduction must be required only for wood-burning generator.

Croatian Center of Renewable Energy Sources
 special thanks to
Andrea Bernardi
Consulente Energetico
Studio Tecnico Bernardi
www.studiobernardi.eu

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