ceis: testing plastics to save energy, associated with BAYER, BASF and FIW MÜNCHEN
“In order to achieve the aim to reduce CO2 emissions by 50-85% by the year 2050, we must reduce the energy consumption in buildings.
The main CO2 emitters in Europe are:
- 2/3 of the energy consumption in buildings is used for heating and air conditioning
- 80% of energy consumption is used in buildings with < 1000 m2
Heating and air conditioning appliances are the main energy consumers, accounting for two thirds of the total energy consumption of a building. Nevertheless, most of this energy is wasted due to lack of insulation.
Some plastic materials play a very important role in energy efficiency of buildings reducing energy loss and, therefore, the energy demand of buildings. These materials, in their application as thermal insulators, are expanded polystyrene, extruded polystyrene or polyurethane foam, among other.
The cellular structure of these materials is what grants them their insulating capacity. The “cellularity” of these materials can be quantified using testing methods; in fact, the applicable testing standard is ISO 4590:2002. This method enables to determine its content as a closed cell volume percentage.
In order to know whether the new appliances were obtaining results that could be compared with those obtained in conformity to standard ISO 4590:2002,ceis arranged for an intercomparison during the period 2011-2012. In this intercomparison, in addition to ceis, companies such as BASF or BAYER took part, all of them using the new appliances and a laboratory, FIW München, which conducts tests in accordance with ISO 4590:2002 and is also accredited to do so.
The result obtained after comparing the results was that the data provided by FIW München and the rest of the laboratories were within the reproducibility limits established in ISO 4590:2002. For this reason, ceis has put forward a proposal for the inclusion within ISO 4590:2002, which is currently being reviewed by ISO/TC61 / SC10 / WG11, of these new testing appliances as an alternative method to those mentioned in said standard.
Well, we now know that, due to their structure, rigid cellular plastics such as polyurethane foam or extruded polystyrene make it difficult to transfer heat, i.e., they have low thermal conductivity so they are used as thermal insulators both in construction and in industrial equipment and installations.
Thermal conductivity of these materials can be determined using the following standards ISO 8301:1991 (heat flow meter method) and ISO 8302:1991 (guarded hot plate method). These two methods are also mentioned in UNE-EN 12667:2002.
The guarded hot plate technique and the heat flow meter technique are equally valid, the only difference between them being that the former is an absolute method (ISO 8302:1991) and the latter a relative method, i.e., it is based on previous equipment calibration carried out using a material with known and certified thermal conductivity.
The test itself is a very simple physical experiment and it involves the application of a temperature gradient, programming the plates at different temperatures for there to be a heat flow through the specimen. The difference in temperature is calculated as the difference between the measured temperatures and the centre of each plate.
In order to accurately determine the material thermal conductivity we must be at the steady state; i.e., a series of balance criteria such as the following have to be met:
- Temperature criterion: the plates have to be at a stable temperature
- Criterion relating to the output signal on heat flow meters: the signal of heat meters cannot vary
- Inflexibility criterion: The average signal of the heat flow meters in the different measurement blocks adopted by the equipment shall not vary monotonously, i.e., the difference between successive blocks must involve a change of sign or be equal to zero
This way, the material steady-state thermal conductivity can be determined.
Once again, ceis is in the forefront of TESTS.