Air conditioning with fresh air: does it make sense?

  • Dec 24, 2019

The vast majority of domestic air-conditioning air cooled or heated, taking it only room, however, there are several models of air conditioners can take fresh air streets.


A few years ago I found in the bedroom air conditioner Hitachi RAS-D10EXR with fresh air function. Besides copper pipes connecting the indoor and outdoor unit, it has a tube with an inner diameter of 25 mm, through which air may be supplied from outside. He swings a separate pump and blown out through a narrow gap in the right side of the body.


Inside you can see the blow slot pump - its size is only 8x45 mm.


The compressor that supplies air of the street, very noisy. When it is included at maximum speed, the noise of the air conditioner at a distance of half a meter about 55 dBa, when the pump is turned off and the air conditioner is running at minimum speed, the noise does not exceed 35 dBa.

To approximate measure the amount of air supplied to the room, I leaned to the outer gap 60 millimeter impeller anemometer Tecman TM856, blocking residue slit. The size of the gap through which air is blown turned 8x60 mm, its area of ​​0.00048 m². Anemometer indicated air speed about 1.7 m / s when the maximum speed of the pump, air conditioning pumps respectively slightly less than the room 3 m³ air per hour. This is a very, very small: one person needs at least 30 cubic meters (as of health standards at least 60 cubic meters) of air per hour.

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I conducted an experiment. Ventilate the room, I closed the window, turned on the fresh air supply, air-conditioned for maximum speed and measured the change in carbon dioxide levels when in the room per person.


Total ten minutes CO2 level increased from 450 to 850 ppm (believed that the ideal air, carbon dioxide concentration of no more than 700 ppm for humans). Then I left the room and CO2 levels began to decline gradually. When I re-entered the room, CO2 level again began to rise sharply and after 15 minutes more than 1,000 ppm (the level considered unacceptable for a person). After another 15 minutes, CO2 levels went up to 1200 ppm, and the experiment was stopped. Thus, in less than an hour, in a room with "ventilation" air conditioning airflow becomes so stuffy that it can be harmful to health.

In addition to inefficiencies in the operation of the air conditioner with air inflow from the street identified and other shortcomings. First and foremost is the loud noise of the pump that supplies fresh air into the room (it is noticeably noisy and at a first speed when which comes into the room very little fresh air, and the third speed the noise drowns out the work itself air-conditioning). The second problem - street noise coming through the air pipe. When a strong wind outside, begins to howl and the air conditioner, and when it's loud passing car, is also heard. As a result, the tube had to cut and extra hole on the street, specifically made for it, wall up.


Unfortunately, the function of fresh air in my air conditioner was useless.

To effectively konditsioniroaniya and ventilation need two devices - air conditioning and installation of ventilation (breather). Without pritochki and can be dispensed with, leaving open the window or plastic box in a vertical position. Many konditsionerschiki argue that when the appliance box have to be tightly closed, but it is not. In the open window air conditioner will be less effective, and it will consume more energy, but in the room will be fresh air, not CO2 concentration when the air can "hang the ax."

P.S. Experiments and measurements I have done for the program "Miracle of Technology" NTV. Sam has not yet watched. :)

https://www.youtube.com/watch? v = 4eX_-6Z627c

© 2018 Alex Nadozhin

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