h a l f b a k e r yMake mine a double.
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All portable dehumidifters simultanelously reduce the latent of the air in the room (i.e., reduce the humidity) while increasing the sensible heat in the room (i.e., increased temperature).
This design removes latent heat from the air inside the building, turning it into sensible heat in the air outside
the building. Plus, depending on how the device is used, it can double as an air conditioner.
Start with a (slightly cool; I'll explain why it's cool later) concentrated liquid desiccant; pass it through the air handler, where it absorbs humidity from the air inside the building, and also heat (warming up as a result).
Without giving that warm, dilute desiccant any additional heat, move it through a hydraulic motor into the device's vapor-liquid seperator. The interior of the vapor-liquid seperator is at very low pressure. Because of this, some of the water in the desiccant boils off, cooling the desiccant.
The remaining desiccant, now cool and concentrated, is removed from the vapor-liquid seperator by a pump, and sent back to the air handler.
The cool, low pressure steam, is removed from the seperator by a multi-stage compressor, with intercooling between stages. The last stage of cooling, still below atmospheric pressure, condenses the steam, after which it is removed from the condensor by a pump. Naturally, all stages of cooling of the steam are done using air from outside the building... this is why the dehumidifyer needs to go through the wall or a window.
If the device is used purely for dehumdification, all of the condensate is sprayed onto the external coolers, where the evaporation of that condensate helps cool them.
To use the device purely to cool the room, without dehumidifing, one pumps the condensate back into the desiccant. This dilutes the desiccant without significantly warming it; thus, when evaporation/boiling occurs in the vapor/liquid seperator, it cools the desiccant to a temperature well below what it would have been if the condensate had not been added. In the air handler, the cold desiccant cools the air.
To use the device to simultaneously cool the room and dehumidify, one moves some of the condensate into the desiccant, and sprays some of it onto the external coolers.
As an added feature of this design, we can continue to dehumidify (or air condition) even at very low room temperatures, without frost forming in the air handler, simply by adding some antifreeze to the liquid desiccant.
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A completely reversed version, with the desiccant/air interface outside, and steam condensors inside, might also be a good form of air source heat pump, for heating a building. |
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It's advantage over regular ASHPs would be the resistance of the outside air handler to freezing up. Not to mention, in winter, we usually do want to humidify the inside of the building. |
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The AC in our lab sets the air at any desired temperature, and if the set temperature is lower than the normal temperature, it also desiccates the air by an adjustable amount (condensing water is captured, and depending on the setting either reintroduced into the air, or discarded into the sink) - is this process less efficient, or what makes your process better? |
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Ah, just read your anno - the possibiliy to add water to the room air would be a plus, that is right. although i guess a plain old dish of water would do the job rather good as well. |
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There are several advantages to the design, even excluding it's use as an air source heat pump. |
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(1) This is probably the most important: If the temperature of the room is at the desired temperature, but the humidity is higher than is desired, this device can dehumidify *much* more efficiently than your lab's air conditioner. And for improving comfort in summer weather, reducing the humidity is often more important / more effective than reducing the temperature. |
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(2) Your lab's AC discards unwanted condensate into the sink... this is a horribly inefficient use for liquid water, when spraying it onto the refrigerant condensor coils would vastly improve their efficiency. The energy savings you could get from doing this would vastly exceed the cost of running the pump for spraying the water. |
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(3) If you want to keep the room especially cold, frost may form on your lab's air conditioner's heat exchanger. This can block flow of room air through the heat exchanger, and it can insulate the heat exchanger. That can prevent it from removing more water from the air and prevent it from cooling the air. |
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In my design, frost is prevented from forming because the "heat exchanger" is the surface of a liquid... rather than undergoing desublimation (forming frost), water vapor from the air will enter the liquid desiccant. And since the desiccant is a mixture of water and lots of a salt, it's freezing point is lower than pure water. |
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(4) The device can work using only two chemicals -- water and a liquid desiccant. Neither of these needs to be replenished under ordinary circumstances, but if one does need to add more of either, water is cheap, and for a desiccant, calcium chloride is readily availble, inexpensive, and fairly harmless, both to people and the environment. |
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In contrast, your lab's air conditioner uses a refrigerant that's probably a gas at atmospheric pressure/temperature, which is kept within a hermetically sealed system. If the system is damaged (perhaps due to some hail hitting the condensor), the refrigerant will leak out, and the device will stop working. If it's an older air conditioner, the refrigerant might be a chlorofluorocarbon, which will result in depletion of the ozone layer. Either way, a leak is expensive to fix, and on top of the cost of mechanical repairs, it's costly to recharge the refrigerant. And did I mention, that you won't realize that a leak has occured until you notice that the room's not getting cooler? |
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If a leak occurs in my device, it will either occur in the atmospheric pressure portion, or the vacuum portion. |
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If the leak is in the atmospheric pressure portion, harmless liquid desiccant will leak out, and be easily spotted. After the repair of the leak, water from the tap can be used to refill the device, and calcium chloride can be gotten at any hardware store. For that matter, if the machine is refilled with just water, and no desiccant, it can still function as an air conditioner. |
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If the leak is in the vacuum portion, air will leak *in*, which doesn't do any real harm -- the machine will still work, through at slightly lowered efficiency. This kind of leak could probably even be fixed while the machine is running. |
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