Humidity Concern for a Closed Room

by

155W dehumidifier evaporator heat exchanger (with blue-colored hydrophilic coating) and PCB

Problem

When a storage room was kept open, humidity was not an issue as there was air circulation. However, dust accumulated quickly in the room. When the room was kept closed, dust accumulation was slow, but trapped humidity became an issue.

Troubleshooting

The hygrometer consistently showed relative humidity (RH) of more than 60%.

Solution taken

A compressor dehume (dehumidifier) was obtained. A machine is a cleaner option than quicklime (calcium oxide powder).

The impact of not solving the problem

The room was muggy. Rust and mold might start to develop on the items in the room.

Notes

  1. The primary purpose of having a compressor dehume is item preservation. While it can improve comfort by reducing humidity, it also releases heat into the room, so comfort depends on the room temperature and humidity. If the ambient temperature is already high, the low humidity may provide some comfort, provided there is ample space in the room for the heat to dissipate. If the ambient temperature is about 20°C, then the comfort benefit becomes an added bonus. Another way to achieve the comfort is to experiment with the RH level to get long off cycles. Initially, the room is warmed by the dehume, but when the RH stabilizes to the set level, the humidistat turns off the dehume automatically and the room starts to cool down.
  2. As the room is warmed by the compressor dehume, although warmer air can hold more moisture, the evaporator must remove more heat from the incoming air before it reaches its dew point and condensation occurs.
  3. Four machines can remove moisture from the air: compressor refrigerant dehume, desiccant dehume, Peltier thermoelectric dehume and air-conditioner. Compressor dehumes are generally much more energy-efficient than desiccant type and Peltier type.
  4. Compressor dehume energy efficiency is viewed from the amount of water that it can remove from the air. It does not lower the electricity bill and we should expect some increase in the bill. However it indeed gives a cheaper bill compared to using an air-conditioner as a dehumidifier.
  5. Compressor dehume moisture removal rate decreases if the room temperature is below 20°C. Desiccant dehume does better job at lower temperature. However, that is not an issue due to the high temperature in Malaysia.
  6. A compressor dehume is heavier than a desiccant dehume and Peltier dehume, but it now has four wheels as its standard.
  7. When the compressor dehume first arrives, do not turn it on yet. We do now know how it has been handled before arrival, so the compressor oil may get into the upper cooling loop. Leave it upright for 24 hours so that the oil can return to the compressor sump. Turning it on with insufficient oil in the compressor will permanently damage the compressor.
  8. There are two heat exchangers in the unit, one evaporator (cold coil) and one condenser (hot coil).
  9. The heat exchanger for the incoming air is the evaporator and is in blue. Here, the cold refrigerant liquid absorbs the latent heat from the air moisture and evaporates into a low pressure cold gas. The cold refrigerant gas goes through the compressor and becomes a high pressure hot gas. The heat exchanger for the outgoing air is the condenser and is in natural aluminum color. Here, the hot refrigerant gas releases the heat and condenses back into a high pressure warm liquid. The high pressure warm liquid goes through a capillary tube to become a low pressure cold liquid and enters evaporator again.
  10. The cold air from the evaporator absorbs the heat from the condenser and becomes warm before exiting the unit.
  11. The dehume will stop working when the built-in water bucket is full. For continuous operation, connect a discharge hose to the nearest drainage point.
  12. As it is a high power appliance, do not use a trailing socket.
  13. The warm dry air from the dehume can be directed at some items to speed up the drying such as clothes.
  14. The dehumidifier needs regular cleaning like an air-conditioner.
  15. Some points of consideration for getting a compressor dehume:
    1. Power in watt, starting from 100W. The higher the power, the faster it can remove moisture, but also the more heat it releases to the room. Using a high power machine in a small room will turn it into a hot room. A 155W dehumidifier generates about 155W of heat. For comparison, a resting adult releases about 100W (100 joules per second) of heat.
    2. Refrigerant type: R290 or R134a. R290 is more efficient. It is also an eco-friendly natural refrigerant as it is just propane. R290 has a GWP (Global Warming Potential) of 3 while R134a’s is 1430. Although propane is flammable, the dehumidifier is still safer than a cooking gas cylinder. If the manufacturer does not mention the refrigerant in the marketing material, then there is a high possibility that it uses R134a.
    3. The number of aluminum fins on the evaporator. The more fins there are, the larger the total surface area to capture the moisture.
    4. Dry air vent position: top outlet or side outlet. Theoretically top venting can give better air circulation in the room for better air drying.
    5. Access to the filter mesh. Snap-fit cover, magnetic cover or slide-out mesh. A snap-fit cover gives easy access to the net, but the snap-fit can wear out and loosen, causing vibrational noise. A slide-out mesh does not need a removable cover, but when sliding out, some dust may drop.
    6. Chassis width. With a larger width, the unit is more stable, the water bucket is not in an awkward deep C shape and the more spacious housing may improve internal airflow and ease of maintenance.
    7. Transparent or opaque water bucket for optional viewability.
    8. Optional lifting handle for the water bucket.
    9. WIFI connectivity for notification of full water bucket. This may be necessary only if the unit is to be put far away or there are a few units that need to be managed.
    10. UV-C (250-280nm wavelength) designed to prevent mold and odor within the dehume, with proper implementation as UV-C can degrade the plastic polymer of the dehume housing. If the UV-C is designed “to kill airborne germs”, then it should be a marketing feature and should be avoided. UV-C is effective only with sufficient exposure / dwell time. Achieving this would require a larger UV-C chamber or slower airflow, both of which compromise the unit’s size or dehumidification performance, making it largely impractical in a compact dehumidifier.
    11. Air filtration: Additional filtration may help remove airborne particles, but it can also increase airflow resistance. Dense filters, such as HEPA (high efficiency particulate air), reduce dehumidification performance immediately, while the benefit of keeping the evaporator clean is only realized over the long term. For most users, moisture removal should remain the primary consideration.

Tools used

  1. Analog hygrometer

This is problem-first learning. The knowledge was learnt because there was a problem to solve.

Leave a Comment

Searching...
0%