Performance of Household Dehumidifying Agents Vary Vastly Moisture Removal Capacity Could Differ by Over 85% Virtually Non-existent Moisture Absorption Efficacy for Bamboo Charcoal/Activated Charcoal Models

15 April 2021
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家用吸湿剂表现极悬殊  吸湿量最多相差逾8成半   竹炭╱活性炭样本吸湿效能近乎零

Hong Kong weather is particularly humid during the transitional season between spring and summer. Many people like to place dehumidifying agents inside their wardrobes, shoe cupboards and storage boxes to prevent mould and mildew. The Consumer Council tested 20 models of household dehumidifying agents and found drastic variation in their performance, including the moisture removal capacity (MRC), moisture removal rate and reverse-permeability of moisture. Taking 80 days as the test period, the MRC of 10 tank-type models saw a variation of over 85%. The 3 reusable bamboo charcoal/activated charcoal models had an average daily MRC of close to zero, while the 2 models of silica gel were almost fully saturated after around 14 days. Besides, despite the large hanging wardrobe dehumidifying bags’ claim of an MRC of up to 1,000ml, their accumulated MRC was recorded at around 150ml in 80 days (15% of the claimed capacity), indicating a slow moisture removal rate. For the 3 models of small dehumidifying pouches with calcium chloride, 19.9% to 23.2% of the absorbed moisture permeated back into the exterior, reflecting a higher reverse-permeability of moisture. The Council reminds consumers to regularly check and replace dehumidifying agents to achieve the best moisture removal effect.

Consumers should also attend to the leakage and compression resistance of the dehumidifying agents. Many of the tested models featured calcium chloride as the key ingredient. Once calcium chloride absorbs moisture in the air, it will deliquesce into an irritating solution. Should this solution leak while in use, not only would it contaminate items in storage, but it might also cause skin allergic reactions if in contact. Consumers should pay extra heed while using.

The test was conducted according to the test method of moisture absorption efficacy and quality inspection of dehumidifying agents as laid down in the Japanese industrial standard JIS S3106. 20 models of household dehumidifying agents were included in the test, most of which had calcium chloride as the main ingredient and half were tank-type products with claimed MRCs ranging from 400ml to 750ml and average price from $6 to $42.3 per tank. The 3 highest-priced models had reusable containers and only required a dehumidifying agent refill. 3 tested models were small dehumidifying pouches with claimed MRCs from 50g to 70g and their average price ranged from $2.4 to $7.1 per pouch. 2 models were large hanging dehumidifying bags with claimed MRCs of up to 1,000ml (the lower compartment of the bag holds the absorbed moisture) and priced at around $24 per bag. 5 tested models were silica gel or bamboo charcoal/activated charcoal which claimed to be reusable after being sun-dried or bake-dried in an oven or microwave oven, with average price from $4 to $12 per bag. The Council also reviewed the labelling information of all models with reference to the JIS standard.

The first and foremost function of dehumidifying agents is its moisture absorption efficacy. The tested samples were placed in a conditioning chamber with the temperature at 25°C and relative humidity 80% for a total of 80 days while the weight increase (i.e. MRC) of the samples were measured regularly. The results revealed that the 80-day accumulative MRC of the 10 tank-type dehumidifying agents ranged from 227.4ml to 424.9ml, a variation of around 87%. Amongst these, 1 model with a higher claimed MRC (750ml) only had an accumulative MRC of less than 230ml, the lowest amongst all tank-type models. Its MRC was approximately the same as another model without a labelled MRC. 2 models of large hanging dehumidifying bags, despite claiming to have a higher MRC than tank-type models, only recorded accumulative MRCs of 152.9ml and 155.4ml respectively, reflecting that dehumidifying products with a higher labelled MRC do not necessarily have a faster moisture removal rate. The desiccant in tank-type and large hanging bag models may require an extended period to fully saturate. Hence, the MRC measured in the test should not be directly compared to the claimed MRC of the products.

As the 3 models of small dehumidifying pouches contained less calcium chloride content of dehumidifying agent than tank-type dehumidifiers, the desiccant in these samples were already saturated by day 58 of the test period and could no longer absorb moisture. However, their accumulative MRCs ranged from 55ml to 85.2ml, all higher than claimed. The 5 models of dehumidifying agents that claimed to be reusable also stopped increasing in weight by day 58 of the test, amongst which the 2 models of silica gel had measured MRCs of 22.4ml and 34.8ml respectively, while those of the 3 bamboo charcoal/activated charcoal models ranged from 0.33ml to 1.44ml only, showing an exceedingly weak moisture absorption efficacy.

A slower moisture removal rate might affect the dehumidifying efficacy of the product, especially when quick moisture removal is required for extremely damp environments. On the contrary, dehumidifying agents with a slower moisture removal rate could have a longer effective period in an environment with a relatively constant humidity. The test results revealed that the 3 bamboo charcoal/activated charcoal models had an average daily MRC of close to zero. The remaining 17 models showed a faster moisture removal rate in the initial phase (first 7 days) of the test period and gradually slowed down afterwards. The 10 tank-type models had an average daily MRC from 5ml to 8.8ml in the initial phase and dropped to an average of 1.4ml to 3ml per day in the later phase (day 69 to 80). On the other hand, the 2 models of large hanging dehumidifying bags had a relatively slow and stable moisture removal rate.

The average daily MRC of the 3 models of small dehumidifying pouches ranged from 3.7ml to 6.5ml during the initial phase. As their MRC was relatively low, their moisture removal rate had greatly slowed down by day 21, and recorded an average daily MRC of less than 0.5ml in the later phase as the samples were close to saturation. The 2 models of silica gel had an average daily MRC of only 2.5ml and 2.8ml respectively in the initial phase and were almost saturated in approximately 14 days, indicating a shorter effective period.

After use, the dehumidifying agents may have water or solution stored in the container or bag. Therefore, it is important to have good resistance against leakage, compression, and reverse permeation of moisture. After the moisture absorption efficacy test, 2 models of tank-type were found to have leaked after the samples were placed upside down for 24 hours, indicating that the quality of the membrane and the tank’s cover have room for improvement. 1 model of the large hanging dehumidifying bags was found with breakage and leakage of the solution after placing a 10kg weight on top of the sample for 1 minute to simulate compression by garments and items inside a wardrobe. The weight of 3 models of small dehumidifying pouches were found to have decreased by 19.9% to 23.2% when placed in a constant environmental chamber of 30°C for 24 hours, reflecting a higher reverse-permeability of the absorbed moisture. Dehumidifying agents should be replaced as soon as suggested by the replacement indicator, to prevent dampening of storage items resulting from the re-permeation of moisture.

There is obvious room for improvement for the product labelling information. For example, 5 models did not show the effective moisture removal period on their labelling, while 2 models did not display information of their ingredients and/or standard MRC, etc. The Council urges manufacturers to examine their labelling stringently in order to enhance the transparency and accuracy of information.

When purchasing and using dehumidifying agents, consumers should consider the applications and requirements of the environment where the dehumidifiers will be used, such as the humidity, size of the space, types of items in storage and their materials, in addition to the habit of use, etc. Consumers should also pay heed to the following:

- Before purchase and use, check for any defects on the product, including the plastic container, packaging and aluminium foil wrapper;
- For more humid days and environments, select dehumidifying products with a higher MRC and faster moisture removal rate for shoe cupboards and wardrobes storing garments and handbags. Also, replace the dehumidifiers frequently to achieve the best effect. When the humidity is not high, it is recommended to use products with a more constant moisture removal rate and to regularly check the status of the product;
- Tank-type dehumidifying agents have a higher capacity and are more suitable for larger spaces such as wardrobes, clothing storage boxes, shoe cupboards, etc. Dehumidifying pouches are generally smaller in size and are more appropriate for smaller drawers or storage boxes. Large hanging dehumidifying bags are best used for hanging in wardrobes or closets;
- If calcium chloride dehumidifying products include a replacement indicator, consumers should regularly check to see if replacement is required. Alternatively, once tank-type dehumidifying agents run out of white calcium chloride desiccant and the lower compartment is full, it is an indication to replace the product. The solution inside the tank should be handled according to the instructions. Avoid splashing the solution on skin or clothing, and never use it to water plants;
- Items that are more sensitive to moisture, such as cameras, camera lenses or collectibles, should be stored in an air-tight container with silica gel that will change colour to indicate saturation;
- Sustainable products, such as silica gel and bamboo charcoal/activated charcoal, should be dehydrated according to instructions before reuse. It should be noted that charcoal-type products have a lower moisture absorption efficacy, while that of silica gel products might decline with repeated recycling;
- Ensure the dehumidifying agents are placed in an enclosed environment for the best moisture removal performance. For example, keep the wardrobe door or container lid closed, open the door or lid less frequently and for shorter lengths of time.

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