The Consumer Council has questioned the basis on which manufacturers of dehumidifiers used to measure the capacity of their products.
The concern is that, in an actual operation, they do not remove the moisture in the air as fast and effective as the manufacturers claimed.
This was borne out in a test of the Consumer Council on 10 models of dehumidifiers with capacity claimed to range from 14 L to 18 L a day.
As household dehumidifiers work best in warm, damp conditions, manufacturers have adopted, in their favour, a set of ambient conditions at high temperature and relative humidity (RH), to measure the capacity rating of their products.
In the test, nine of the models based their rating of dehumidifying capacity at 30℃ and 80% RH. The remainder one used an even higher temperature of 32℃ and the same 80% RH.
This approach, however, does not accurately reflect the indoor environment when the dehumidifier is operating with the windows closed.
In actual operation, the relative humidity will become progressively lower after the dehumidifier has been in operation for a while. The RH will not be maintained consistently at a high level.
A more realistic measurement of dehumidifying capacity is laid down in the Association of Home Appliance Manufacturers (AHAM), an American standard which sets the conditions at 26.7℃ and 60% RH.
In Japan where many dehumidifiers are manufactured, the Japanese Industrial Standard (JIS) adopts similar test conditions of 27℃ and 60% RH. No standardization bodies have been found to set standard test conditions at 30℃ and 80% RH.
The test found that when tested at AHAM conditions, the actual dehumidifying capacities of the test samples ranged from 6.42 L to 9.66 L per day, falling well short of the claimed capacities (based on the manufacturers' favourable conditions) by 40% to 54%.
Even when tested against their own criteria at conditions of 30℃ and 80% RH, though the samples fared evidently better rising to 11.14 L and 15.44 L, they were still 4% to 27% below their claimed values.
One sample, however, did manage to exceed its claimed capacity by some 4%.
There are currently no unified standard test conditions for rating dehumidifying capacity of household portable dehumidifiers in Hong Kong.
To help consumers make informed choices, the industry is urged to consider standardizing the test conditions which reflect more accurately the performance of dehumidifiers in use.
The standard test environment (at 26.7℃ and 60% of RH) stipulated in the EMSD "Energy Efficiency Labelling Scheme" which is based on the AHAM standard, is recommended for their consideration.
Consumers are reminded that when comparing the capacity among different dehumidifiers, the temperature and relative humidity on which the claimed capacity values are based should be identical.
Furthermore, the test revealed substantial variations in the energy efficiency of dehumidifiers. For the energy conscious consumers, the savings on electricity costs could be significant.
At conditions of 26.7℃ and 60% of RH, 1.01 L to 1.49 L of moisture can be extracted using 1 kWh of electricity - a difference of 32% in energy consumption among the samples.
In addition to performance and energy efficiency, the test also evaluated the safety of dehumidifiers. With two exceptions, the samples were found to be less than totally satisfactory in all safety test items.
Although they do not pose imminent hazards, consumers are advised to use such appliances with due care. And do not forget to unplug the dehumidifier before cleaning the appliance.
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