Impact of ageing on the energy efficiency of refrigerating household appliances

In a recent article ⁽¹⁾, German researchers highlighted the time dependence of the energy consumption of refrigerating household appliances, i.e. refrigerators, freezers and their combinations. 

 

Energy efficiency in refrigerators and freezers has been constantly increasing for several decades, as highlighted by the constant qualitative evolution of energy labels. For example, in the USA, the average annual electricity consumption was divided by 4 between 1974 and 2015, while the equivalent volume increased by 20% (2). However, with about 2 billion units in service worldwide, the IIR estimates in a recent Informatory Note that domestic refrigerators and freezers consume almost 4% of global electricity ⁽²⁾. It is therefore crucial to assess the additional electricity consumption that the ageing of these appliances may generate. 

 

With 45-55% of the total energy consumption of refrigerating household appliances, the heat flow through the cabinet walls makes up the largest contribution of the components of these applications to their total electrical energy consumption. Since the 1990s, the cabinet walls of household refrigeration appliances essentially consisted of polyurethane (PUR) foam with cyclopentane as blowing agent. PUR foams have good initial thermal insulation properties but an increase of up to 15% of their thermal conductivity over a period of one year has been determined.  

 

Because of the usual material composition of polyvinyl chloride with a plasticiser, the effects of ageing are also significant regarding the door gasket, which is the second largest source of energy consumption (25-30%). 

 

Eleven new appliances were examined by the researchers under standard measurement conditions. After only two years of operation, an additional energy consumption of up to 11% was measured.  

 

Furthermore, 21 older appliances that had been measured i when new were tested again after 21 years of operation. For these older appliances, an average increase in energy consumption of 28% was found. For certain individual appliances, the maximum increase was 36%.  

 

Based on these measurement results, an aging model was developed that can help predict the increase in energy consumption of household refrigeration appliances due to ageing. This model shows an average increase in energy consumption of 27% for an appliance age of 16 years, which corresponds to the average operating time of these units. 

Supplemental performance tests of eight reciprocating compressors used by these appliances showed no  significant effects of ageing after two years of operation. Furthermore, measurements of the thermal conductivity of polyurethane foam test samples were carried out over time and an increase in thermal conductivity of 26% over a period of about three years was determined. 

 

These findings should sensitise the stakeholders (manufacturers, consumer organisations, standardisation bodies and legislators) to the ageing processes related to household refrigeration appliances. This makes it easier to determine the replacement period of appliances according to economic and energy criteria and the overall economic impact caused by the ageing of domestic refrigeration appliances. 

 

Sources:

⁽¹⁾ Paul A. et al. Impact of aging on the energy efficiency of household refrigerating appliances, Applied Thermal Engineering 205 (2022) 117992, https://www.sciencedirect.com/science/article/abs/pii/S1359431121014125  

⁽²⁾  IIR Informatory Note,  The Role of Refrigeration in the Global Economy (2019)  https://iifiir.org/en/fridoc/the-role-of-refrigeration-in-the-global-economy-2019-142028