1. Introduction

1.1    Engineering Problem

People are sensitive to humidity because the skin relies on air to get rid of moisture. When we sweat, water evaporates through the skin and cools us down. If the air is measured to be at 100% relative humidity, it cannot hold any more moisture. Therefore sweat will not be able to evaporate and air will feel warmer than it actually is and our skin will feel extremely sticky causing us to be hot and bothered.  However, if the relative humidity is low, sweat will evaporate very quickly and thus our body will stay cool. For example, if the air is 24º and has a relative humidity of 0% , the air will feel to you like it is 21º. If the relative humidity is at 100%, then the temperature will feel like it is 27º. We feel most comfortable when the relative humidity is around 45% (Discovery Communications, 2014).

Due its geographical location (1 degree north of the equator)  and maritime exposure, Singapore is characterised by a hot and humid climate. Instead of having clear-cut seasons like summer, spring, autumn and winter, the weather is warm and humid all year round causing the relative humidity to be in the range of 70% - 80%. It varies from 90% in the morning and falls to around 60% in mid-afternoon, when it is not raining. Often the humidity level touches a whooping 100% on rainy days (Janus Corporate Solutions, 2014). Due to the high relative humidity range, we often feel uncomfortable and hot despite the low temperatures. This often robs us of our sleep and prevents us from working to their fullest potential, a quality essential for success in a place like Singapore. Excessive humidity in the air not only causes mold and mildew to grow inside homes, it is also ideal condition for most pests, such as, clothes moths, fleas, cockroaches, dust mites and woodlice (Wikipedia, 2014). Also, the relative humidity fluctuates many times throughout the day but Singaporeans, known to having a hectic lifestyle, often find themselves time-bound and  unable to leave their work to switch on the dehumidifiers. This will not only make them feel uneasy, but the high humidity will also deviate their attention from their work and they will be unable to deliver the good quality work expected of them. All of these problems boil down to the high humidity rate in Singapore and the busy work lives of Singaporeans.

1.2    Engineering Goal

Our goal is to make dehumidifiers easier for people to use. Dehumidifiers are generally household appliances that are used to reduce the level of humidity in the air (Wikipedia, 2014). By using dehumidifiers, Singaporeans can easily get rid of problems stirred up by high humidity levels, namely deprivation of sleep and concentration towards our work and growth of pests and fungi.  It will be automatic and will turn on when the amount of humidity in the surrounding atmosphere is higher than a certain level (45% - 50%) and start decreasing the amount of humidity in the air. This way users do not have to lift a finger for the dehumidifier to do its job and this makes it more helpful and suited to the hustle and bustle of Singapore.

1.3    Specific Requirements

a) The dehumidifier should turn on when the amount of humidity in the surrounding atmosphere is higher than a certain level (45%).
b) Once the level of humidity has been brought down to a certain level (45%) the dehumidifier should automatically switch off.
c) The dehumidifier should decrease the amount of humidity in the surrounding atmosphere.
d) Build the structure of a dehumidifier.

1.4        Alternative solutions
The Different types of Dehumidifiers
  • The Chemical Absorbent Dehumidifiers / Desiccant Dehumidifiers
  • Homemade Dehumidifiers
  • Heat-pump Dehumidifiers

1.4.1 The Chemical Absorbent Dehumidifier

They are made of silica gel (desiccant), which is a desiccant-type of absorbent. The little packet of silica is situated inside the packaging of any kinds of goods that require the waterproof material against condensation and water damage. On a large scale basis, the silica material can be used to absorb the moisture from the air and dehumidify it. The gel is heated and placed on a wheel (separate loop that dries the gel) and removes damp air through a vent. This process does not need to cool air before removing moisture from it.  These dehumidifiers are particularly serviceable if the person's living conditions are extremely warm or humid which is similar to Singapore’s climate (Tsavo Media Inc, 2014).

A detailed description of how the chemical absorbent dehumidifier works:

Air inside the room flows over to the desiccant material (a hygroscopic substance used as a drying agent). This attracts the moisture from the air. The desiccant material is concurrently dried by air flowing the opposite way that exhausts the moisture towards to the exterior of the room. This describes the cyclical chemical absorbent dehumidifiers.

A wheel revolves the desiccant material. On one side of the wheel, the desiccant material extracts the moisture from the air. On the opposite side of the wheel, the material is dried through the air flow that extracts the moisture towards the air which is outside the room.

During this process, the chemical absorbent material is contained on a bed. Two different stream, low humidity and high, are passed on to the sealed chambered sections, without mixing the two different humidified air, and hence the desiccant material may be removed and dried at intervals.
Screen Shot 2014-07-24 at 8.36.45 AM.png
Figure - Inside a chemical absorbent dehumidifier (bigclivedotcom, 2013).

Figure - Air flow occurring inside a chemical absorbent dehumidifier (Everything Ice, 2014).

1.4.2 The Homemade Dehumidifiers

As nowadays, the dehumidifiers sold are very expensive, people are able to build their own dehumidifiers called ''Homemade Dehumidifiers'' . However , these dehumidifiers are extremely labor intensive. They are also disparate from the controlled dehumidification processes.

The equipments needed to build this homemade dehumidifier is road salt [ caution: road salt can be detrimental to human skin and can rust off metals ], two buckets, a bit of chicken wire and a stand. A portable hygrometer can also be useful to conduct this experiment.
To create the homemade dehumidifier, firstly, make a hole in the bottom of one of the buckets. Cover this hole with netting or a wire to ensure that the salt doesn't fall out. Then, empty the bag of road salt into the container and place the bucket on a stand. After that, the other bucket goes underneath, it must be deep and wide enough to catch water that is captured and drained out of the bucket that has a hole in into bottom.

By going through a natural process, the road salt condenses moisture from the air in the surroundings. If you want to increase the rate of dehumidification, you can place a fan to blow air into the bucket.

To ensure that the effectiveness of the homemade dehumidifier is appropriate, all the windows and doors are supposed to be closed as the relative humidity is controlled by the temperature that is inside and outside (Tsavo Media Inc, 2014).
road salt dehumidifier.jpg
Figure - A homemade dehumidifier

1.4.3 The Heat-pump Dehumidifier
The technique used in this is similar to that of an air conditioner. A fan that draws indoor heat over a heat exchange coil that is reduced to near-freezing temperatures. The water vapour in the air condenses on the coils and is subsequently drained into a tank to be disposed of. Afterwhich, the air is reheated and distributed throughout the room again.

A more detailed explanation:

1. A liquid refrigerant is pumped through coils on the outside end of the heat pump dehumidifier.
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Figure - 1st process of a heat pump

2. A fan pulls the air outside over the coils. The water in the coils absorbs the heat in the surrounding and expands hot vapour.
 Screen Shot 2014-07-08 at 12.41.16 PM.png
Figure - 2nd process of a heat pump

3. The vapour is then put through a condenser, which increases its pressure and temperature, after which, it flows through the indoor coils.
Screen Shot 2014-07-08 at 12.41.27 PM.png
Figure - 3rd process of a heat pump

4. As it cools, the refrigerant condenses back into liquid and flows outside to collect more heat from the surroundings.
Screen Shot 2014-07-08 at 12.41.37 PM.png
Figure - 4th process of a heat pump

5. Meanwhile, the heat is pumped into air ducts to be distributed throughout the entire house.
Screen Shot 2014-07-08 at 12.41.50 PM.png
Figure - 5th process of a heat pump (Laura & Emilie, 2009).

1.4.4 Design 1

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Figure - Rough sketch of Design 1

This is the first design that we came up with. It is operated by Arduino and uses silica gel to dehumidify the air. A long pipe will lead from the bottom of the room to the top of the room. Silica gel will be place halfway inside the pipe. A fan will blow the humid air from the bottom of the room through the pipe such that it flows over the silica gel which will then absorb the moisture from the air.  Then the dehumidified air will be blown back into the room. This cycle will continue on until all the air in the room will be dehumidified. In order for the silica gel to not moisten itself and lose its absorption capacity, there will be a heater below it and an opening above it. When the fan is switched off, the heater will be switched on and the cap above it in the pipe will be opened. This will cause the silica gel to heat and the water vapour absorbed will be released. Therefore, the person will not need to keep changing the silica gel. The fan below is to blow the humid air towards the silica gel to dry.

Disadvantages: The pipes may have cracks in them which will cause the dehumidified and humid air to mix and thus the air will not be dehumidified as efficiently.

- Due to the heater, the silica gel can be dried and does not have to be changed again and again.
- The cap, when closed, will allow the dehumidified air to be blown back into the room since the air cannot escape from anywhere.
- The cap, when closed, allows the air, which is moist from the water vapour absorbed from the silica gel, to escape into the outside environment and thus, when the fan is switched on, moist air will not be blown back into the room.
- The arduino can be programmed in such a way that the fan will not be on at the same time as the heater thus only the dehumidified air will be blown into the room if the fan is on. And moist air will not be blown into the room since the fan will not be on when the silica gel is being heated.

Relative Humidity
> 45%
< or equal to 45%
Figure - Requirments for Design 1

1.4.5 Design 2
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Figure - Front view and side view of Design 2 and requirement table.

This is the second design we came up with. As the air gets sucked in by the fan attached in the front of the box, the air will travel through the pipe and enter the wheel. The wheel is divided into two sections.

One of them carries the air with low humidity rate and the other big portion carries the air with high humidity. On one side of the wheel, the desiccant material extracts the moisture from the air. On the opposite side of the wheel, the material is dried through the air flow that extracts the moisture towards the air which is outside the room.

There is an extra pipe attached to the wheel which pumps in hot air. The air from the atmosphere enters that extra pipe and the air is heated up with the help of the heater. This heated air is to ensure that the silica gel in the wheel will stay heated up for it to function properly.

There is another outlet from the wheel that pumps out the moisture extracted from the air. The water now can also be used for other uses. The low humidity rate, which is the dry air from the wheel will then get pumped out of the wheel through another outlet pipe. This dry, processed air will leave the dehumidifier and lessen the humidity in the room.

- There might be cracks in the pipe which will cause the air with different humidity levels to escape into the room and the air cannot be dehumidified efficiently.

- The heat pump will heats the desiccant so it can pass through the wheel to remove moist .
- Since the desiccant wheel is rotating slowly, the entire wheel can be warmed eventually .
- Through the pipe, the moist air can be blown out of the room and it will not be mixed with the dehumidified air.
- Due to the fan, the humid air can be blown into the desiccant wheel and the dehumidified air can be blown out of the wheel and into the room.

1.4.6    Final Solution

We have chosen to build Design 2 (1.4.5), which is a simplified version of a chemical absorbent dehumidifier. It mainly consists of a desiccant wheel that rotates slowly and absorbs moisture from the air which is blown in through a fan. The desiccant will be simultaneously dried because hot air will be blown into it by a hair dryer at the same time.
The desiccant wheel will be made of a round tin box filled with silica gel. There will be cross-shaped partitioning inside the box so the silica gel does not get collected to one side as the wheel turns.  A motor will be connected to the tin box to allow it to revolve. Mesh from a flour sieve will replace the cover of the tin box.
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Figure - Round tin box

The desiccant wheel will be placed inside another square tin box. The back and the front of this tin box will have identical holes cut on them, with cross-shaped metal rods placed in front of the holes. Two pipes will be attached to two different sections of the rod, both at the back and the front of the box. One pipe will be attached to a hair dryer while the other pipe will be attached to a fan at the front of the box. The two pipes at the back of the box will serve as exhaust pipes as the humid air from the hairdryer will be blown out of the desiccant wheel into the outside environment to prevent it from mixing with the dehumidified air in the room. The other pipe will allow the fan to blow dehumidified air back into the room.Screen Shot 2014-08-07 at 9.12.28 AM.png
Figure - Front view, side view and back view of desiccant wheel (from left to right)

A basic description of how the entire dehumidifier will function: The fan will blow humid air through the silica gel which will extract the moisture from the air and the dehumidified air is blown out back to the room through the opposite side of the wheel. In the meantime, the hair dryer blows the hot air into a section of the wheel and this warms up the desiccant as it travels along to maximize its absorption capacity since the warm air allows the moisture to evaporate from the desiccant as water vapour. The moist air is then being blown out of the room, with the aid of a pipe, which leads it to the environment outside. This way the air is dehumidified and the desiccant is dried again so that it will not be repeatedly changed.

A hygrometer is an equipment used to measure the water vapour in the atmosphere or the relative humidity.  They usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed. There are a variety of hygrometers such as, simple psychrometers and hair hygrometers or even more complex ones such as a cooled mirror dew point hygrometer.

An Arduino, which consists of two parts, the hardware and software, allows users to build close to anything. It is made to be connected to sensors which in turn feed it physical information to act upon.

The hygrometer will measure the relative humidity in the air and when it goes above 50% , the Arduino, which is connected to the hygrometer and humidifier, will be given instructions to switch the dehumidifier on automatically. Similarly, when the dehumidifier decreases the relative humidity back to 45%, the hygrometer, measuring the relative humidity, will instruct the dehumidifier to turn off and thus the relative humidity will not go below the necessary percentage. This will reduce hands-on work required to minimal and thus make the lives of the busy Singaporeans much easier. Another advantage of attaching a hygrometer is that users can also read off it to know the relative humidity in the atmosphere.

Relative Humidity
Switch Dehumidifier
> 45 %
< or equals to 45 %

Figure - Requirements for final solution

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