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In this part 22nd of full HVAC course, we will learn about Absorption Chillers.
Absorption Chillers
1. Absorption chillers are mechanical refrigeration units that use either ammonium nitrate or urea as an absorbent material (absorbent being a substance that can hold onto water vapor). These chillers have been around for many years, although they were once considered inefficient compared to their evaporative counterparts. There are a few different types of absorption chiller available in the market today depending on what size system you need. The best way to figure out what type of absorber will work best for you is to first determine how much cooling power you require. A typical home-sized unit may not be able to effectively cool a whole house, but one designed for commercial applications could easily handle tens of thousands of square feet. You should consider both the number of people who live in your residence and the hours they spend indoors. If you don't know exactly how much space you'll need to accommodate these factors, you should contact a licensed heating and air conditioning professional before purchasing any equipment.
2. Absorption chillier systems are comprised of two basic parts -- the compressor and the absorber. An absorption chiller works by turning the compressor on and off based on a set temperature requirement. When the compressor turns on, it forces cold gas into the absorber via a tube connected to the compressor's suction line. As the cold gas passes through the absorber, it absorbs moisture from the air surrounding the compressor, causing the air to become saturated with liquid ammonia. Once the air containing ammonia reaches its saturation point, the absorption process stops and the air is forced back into the room. Because the compressor keeps running continuously at a constant speed, it does not produce noise, making absorption chillers great for homes with families and pets.
3. In order to prevent overheating, absorption chillers employ a desiccant dryer. Desiccants remove the excess moisture from the air stream prior to entering the room. The dried air then enters the room where it cools down as the compressor runs. An example of a desiccant dryers uses silica gel as a drying agent. Silica gel is highly porous and can absorb up to 90 percent of its own weight in dew. That means if you place five pounds of silica gel inside a container, after 24 hours the remaining 10 pounds would weigh approximately one pound. As long as the absorber continues to operate, the desiccant will remain effective since it never loses its capacity to absorb moisture. Silica gel contains trace amounts of copper, aluminum, and sodium chloride, however, so it is recommended that you replace the desiccant every three months.
4. One major drawback to absorption chillers is the high cost associated with them. This is primarily due to their high initial purchase prices as well as ongoing operational costs. Additionally, absorbers tend to be massive machines that require plenty of space and proper ventilation in order to function properly. However, these drawbacks do not outweigh the advantages of absorption chillers.
An absorption chiller (also known as water chiller) works by passing a constant flow of chilled water over cooling coils inside a chamber. Chilling water produces ice, which then melts back into the flowing water. Heat is transferred from the incoming warm water to the outgoing cold water, decreasing the temperature of the incoming water. The process repeats continuously, maintaining a steady drop in the temperature of the incoming fluid. An absorption chiller does not have moving parts, making it ideal for use in a greenhouse environment where mechanical components may break down due to exposure to extreme temperatures or humidity fluctuations.
The function of the absorption chiller is to maintain a given temperature of the incoming fluid that passes through the chiller's cooling coils. If the temperature of the incoming hot fluid is higher than the desired output temperature, the absorption chiller will add additional ice to its cooling coils to lower the temperature of the incoming stream. As the temperature drops, fewer ice crystals are formed, leaving less mass of ice in the chiller. When the temperature of the incoming liquid reaches the desired output temperature, no ice crystals remain in the chiller, and the cooled water exits the chiller at the same temperature as the inflow temperature.
In the case of an absorption chiller, the amount of ice added to the cooling coil determines the ultimate rate of cooling the incoming water. In order to achieve maximum efficiency, a chiller requires a specific range of ice content at any time. Too much ice in the cooling coil means that the chiller will take longer to cool the incoming liquid. Conversely, if there is little ice in the cooling coil, the chiller will work faster, but the output temperature may diverge from the input.
There are two types of absorption chillers commonly used in greenhouses: open-loop and closed-loop absorption chillers. Open-loop systems do not have a feedback loop; they operate according to a fixed algorithm to determine how much ice should be produced based only on the quantity of water entering the chiller. Closed-loop systems use a feedback loop to regulate the amount of ice produced. These systems measure the actual temperature outside of the chiller and adjust the amount of ice produced accordingly. A typical application for an open-loop system would be to provide a constant supply of cool air throughout the day, while a closed-loop system could be used to keep a constant temperature in the greenhouse, regardless of external weather conditions.
Absorption chillers are widely used in commercial agricultural settings to control ambient temperatures. More specifically, these devices are used to ensure that livestock, crops, and fruits stay at certain temperatures. One example of a closed-loop absorption chiller is the Greenhouse Air System. As the name implies, this type of device circulates cool air around the interior of a structure, providing passive heating. Other examples of closed-loop absorption chiller applications include greenhouses and industrial facilities, such as data centers.
1. What is the purpose of an Absorption Chiller?
An Absorption Chiller works best for cooling warm air, but does not work well for cooling cold air. If the temperature of the air is above 55 degrees Fahrenheit, then the chiller's performance decreases. If the temperature of air is below 55 degrees, then the chiller performs at its peak efficiency. An Absorption Chiller uses the same basic principles as a refrigerator and operates in the same way. Cold air enters the unit via a fan and the water evaporates into the warmer air. A fan blows the cooled air out of the unit back into the room. There are two types of Absorption Chill units - vertical and horizontal. Vertical chillers are typically placed in the ceiling of a house and pull cool air down to the floor where the people live. Horizontal chillers are put inside of a building and pull air up towards the roof. The chiller pulls the cool air (from 55 degree F) down to 40 degrees F where the heat exchange takes place. A good quality Absorption Chiller should have a thermostat to regulate the temperature. You need to make sure the thermostat is set correctly. Too high of a setting and the cooler may have trouble operating properly. Too low of a setting and the unit may overheat.
2. How do Absorption Chillers work?
The first step in the working of an Absorption chiller is to get some cold air into the unit. First the fan pushes the warm air out of the unit into the outside environment. Next, the fan pushes the warm humid air into the interior space. Once the air reaches the hot side of the unit, the moisture begins to evaporate. As the air passes through the coils, the moisture moves away from the coils. When the air exits the unit, it is now cooled to about 55 degrees F. Cooler air is then pulled back into the room by the fan.
3. Benefits of Absorption Chiller Units
There are many benefits associated with using Absorption Chillers. One benefit is that they keep homes cooler. Another benefit is that they reduce humidity levels and decrease mold and mildew. Because the chiller removes moisture from the air, less moisture collects on furniture and carpeting.
4. Drawbacks of Absorption Chiller Units
Absorption Chillers do have their drawbacks though. The first drawback is that they use a lot of electricity. Also, if the unit fails and stops functioning, the entire house could become stuffy and hot. In addition, Absorption Chillers are noisy. Most units run between 50-60 dB. If someone is sleeping in a room with one, it could disturb them. Another problem with Absorption Chillers is that they sometimes leak. If the lid leaks, the unit loses its effectiveness.
Access Previous parts of this course, if you have missed them, by clicking Below...
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