Dehumidifiers - CHOICE # 365

Dehumidifier manufacturers are urged to put their act together - by adopting the same standard which reflects more accurately the performances of dehumidifiers in use.

The call followed a comparative test of the Consumer Council on 10 models of dehumidifiers with claims of capacity ranging from 20L to 24L of moisture a day.

In the test, it was found that all manufacturers used test conditions heavily in their favour to measure the dehumidifying capacity of their products.

Among the 10 samples, 8 of them based their rating of capacity at conditions of 30℃ temperature and 80% relative humidity (RH). The other two models based their rating at temperature 32° C and same RH 80%.

In the view of the Council, this approach does not accurately reflect the indoor environment when the dehumidifier is operating with the windows closed.

The reason: dehumidifiers work best in warm, damp conditions. But in actual usage, the relative humidity will become progressively lower after the appliance has been in operation for a while. It stands to reason that the humidity does not stay consistently at a high level.

The Council has recommended that a more realistic measurement of dehumidifying capacity be adopted as laid down in the US Association of Home Appliance Manufacturers (ANSI/AHAM) standard which sets the test conditions at 26.7℃ and 60% RH.

The standard test environment (26.7℃ and 60% RH) stipulated in the Energy Efficiency Labelling Scheme of the Electrical and Mechanical Services Department is based also on the ANSI/AHAM standard.

In Japan and the mainland where many dehumidifiers are manufactured, the Japanese Industrial standard (JIS) and the Chinese National Standard (GB/T) adopt test conditions of 27℃ and 60% RH, similar to ANSI/AHAM. In fact, similar test conditions have been adopted in many regional / national standards, e.g. European standard, Taiwanese standard.

When tested against conditions set by ANSI/AHAM, the actual capacity ranged from to 5.61L to 13.24L per day.

The results contrasted sharply when the models were tested against their own criteria based on favourable conditions - the capacity rose to 13.83L and 23.38L per day. 

Half of the samples (5 out of 10) were, however, less than their own claims in dehumidifying capacity. Their measured capacities were 1% to 15%, or 0.3L to 3.1L, below the claims by the manufacturers.

At present, there are no mandatory standard test conditions for rating dehumidifying capacity of household portable dehumidifiers in Hong Kong.

To help consumers in shopping comparison and informed choice, the industry is urged to consider adopting the test conditions of regional / national standards which reflect more accurately the performance of dehumidifiers.

Substantial variations were revealed in the energy efficiency of dehumidifiers.

For instance, at conditions of 26.7℃ and 60% RH, 1 kWh of electricity can extract from 1L to 1.88L of moisture - a 47% difference in energy efficiency among the samples. For the energy conscious consumers, the savings on electricity cost could be significant.

The test also evaluated the safety of dehumidifiers: 3 samples were found to be less than totally satisfactory in all safety test items.

They should not pose safety hazards in normal use, but consumers are advised to use such appliances with due care - and don't forget to unplug the dehumidifier before cleaning it.

Besides dehumidifiers, there are also on the market different types of dehumidifying agents, namely, calcium chloride, calcium oxide, silica gel, activated charcoal, which are suitable for use in small enclosed environment such as storage cabinets, wardrobes, drawers.

Consumers are cautioned to use dehumidifying agents with anti-mold agents or insect repellents with care. Keep them away from food, drinks, toys, etc.