Hi, Geektimes!

Numerous publications on the topic of fresh air and the importance of this option in our homes prompted my modest person to describe his experience in equipping an apartment with a system of ventilation, air conditioning and reflections on the air humidification system.

Probably, each of us, especially after / before / in the process of purchasing a home, thinks about the issues of not only organizing the information space in the apartment, but also about more “prosaic things” such as comfort, air conditioning, fresh air, etc. My story began quite a long time ago (in 2010) and so there were circumstances that before / in the process of buying an apartment I had neither financial opportunity, nor time to think about what was happening, and all the technical solutions were already used during the operation.

I am not a rich man, so many of the necessary stages in the arrangement had to be done personally and in stages as funding proceeded. Some repair work in the rooms, the development of project documentation for construction, electrical, low voltage, ventilation, air conditioning, design and all other parts had to be combined with the main work and simultaneously save money. In this publication I will only touch on the organization of indoor microclimate.

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Studying a lot of forums, communicating with specialists, leafing through manufacturers' catalogs and visiting various sites, it was decided to use an inverter multi-split system with one outdoor and two indoor channel units as an air conditioning and ventilation system with the option of mixing outside air. I will not go into the details of the choice just describe the system. The outdoor unit is 7 kW, the internal channel unit is on the east side of an apartment with a power of 3.5 kW (serves the bedroom and children's room) and the channel unit is on the west side with a capacity of 5 kW (serves the living room-studio). The podmes is organized from outside by a single heat insulated air duct with a tee valve system and separation into each indoor unit with its duct fan with an air capacity of 100 m³ / h each. Fans receive power from the indoor units through the current relay, the indoor unit turns on — the supply fan turns on and the shutdown takes place simultaneously with the indoor unit's fan off. Natural exhaust through a combined bathroom and kitchen, for which door doors and lattices are installed in the doors of the bedroom / children's room and the bathroom.

Here is one of the sketches before installation, unfortunately a more detailed drawing has been lost, and I don’t want to redraw;) Forgive me for my laziness.

In the sketch there are no air mix fans, outdoor unit, freonovodnye communications, electrical connections and condensate drain system. Before that, we did more than one complex object with the person who did the installation work - he just had to have just such a sketch with oral explanations.

I also want to brag a bit about my experience that I haven’t met yet - using the aforementioned current relays, for starting / stopping the inlet fans together with the indoor units, and using “dry siphons” (a corrugated tube with a silicone cone inside) to drain the condensate from the canals to the sewer so that the smell in the tubes does not pass into the internal blocks and then into the rooms.

For two years, the whole system has been functioning regularly in the warm season (air conditioner operation for cooling + constant mixing) and in the offseason (air conditioning operation for heating + constant mixing), except for the constant air flow mode in the cold season (ventilation mode + constant mix). Due to the lack of heaters for heating the supply air, low temperature from the supply grilles and simply the senselessness of the event - only the fans + air mixing section (which is the channel indoor unit) work, it is easier from time to time to open the windows for ventilation.

In general, it is time to supplement the system with a mode of continuous inflow of treated (heated and filtered) air + add humidification and deeper cleaning. Those. try to ensure year-round full use of this system as ventilation. At this stage, the main priority for modernization is given to the bedroom and children's room, for this part I have a channel unit with a capacity of 3.5 kW in the cold and 300 m³ / h at a minimum speed over the air. In addition, while in the dressing room (where all the air ducts, adapters, etc. are installed and installed directly), there is no false ceiling and everything is accessible and visual, in order to test and test new system operating modes.

1. Heater for air heating

The minimum and inexpensive electric heater was found to be 1.2 kW with a minimum air flow through it of 90 m³ / h, which is noteworthy right away with a simple adjustment unit, a channel temperature sensor and automatic overheating protection.

2. System of cleaning and moistening

As I like to say, everything is invented before us. And the best natural humidifier / cleaner is rain or fog. As far as I understand a similar principle, the so-called "air washes" are used. And I myself have recommended these devices as proper humidifiers / cleaners for administrative and residential premises, well, sometimes electrostatic filters or installations with them for rooms where they smoke.

In a personal correspondence with eschava discussing the ventilation and air-conditioning systems, and suggesting that he use “air washes” to humidify, I got a crazy thought about using the channel indoor unit for other than its intended purpose. The intuitive solution was interesting and I decided to work it out in more detail and with a scientific approach.

Let's compare a pair of the most advertised sinks for 45 m² and 300 m² with my 3.5 kW internal channel block:

	Contact area, m²	Productivity, m³ / h	Sizes, mm	Installation method	Noise level, dBA	Cost, $
Air wash 45	4.2	280	450x330x300	floor	25/37/42	550
Air wash 80	9.7	360/780	830x400x310	floor	37/48	4 340
Kanalik	≈9,6	300/400/550	700x615x200	suspended over false ceiling	32/39	435

Of course, the table is humorous, but, as they say - “in every joke ...”, because in each channel internal unit there are:

1. large area heat exchanger;
2. the fan is a lot of speed;
3. condensate drain pan to prevent water from escaping;
4. drainage pump with independent on / off from the water level in the pan;
5. coarse filter.

What else is needed for happiness? Oh yeah - to organize on the heat exchanger the methods of “air flushing” and “cold evaporation”, or in simple language, it is necessary to keep the heat exchanger louvers in a wet state when the indoor unit is working. By analogy with the "sink" - the air passing over wet surfaces will be saturated with moisture and small particles of debris soaring in the air will be captured by a film of water and run down the drain.

The first thing that came to mind was the use of something like a drip irrigation system over a heat exchanger, where water droplets would drain through it and keep the above mentioned methods of cleaning and moistening in operation. But Google drip irrigation system, faced with some problems, if you use ready-made solutions for my purposes. Strongly "collective farm" did not have to, because there was a more elegant solution in the form of low-pressure fogging systems. Yes, and the performance of one low-pressure fogger system (should work correctly at water pressure) is about 3 kg / hour, which is more than enough for my purposes. An additional advantage of low pressure systems is the larger size of the mist droplets than high pressure systems. Those. they are more suitable for wetting surfaces than for rapid evaporation in warm air.

If anyone is familiar with adiabatic humidification, of course, it will indicate to me that when I humidify, which I plan to exercise, the air temperature will decrease if I use cold tap water. I will give some calculations on the Id-diagram.

The table shows two calculations:

1. the outside air is heated to the desired temperature so that after mixing it with recirculation and humidification, up to +18% is fed into the room;
2. the outside air is heated to a temperature of +18 and moistened to 50%.

Firstly, we see that for different modes you need a different amount of heat for heating, and secondly, it turns out that I will need to evaporate a different amount of moisture. I think the truth is somewhere nearby. I also want to draw your attention to the fact that for heating the fresh air, I need 1.2 kW of power for the heater and +10 degrees for mixing with recirculation.

I didn’t specifically put into calculations the correct adiabatic humidification, in which the air temperature after humidification decreases. That is the reason - we can see the point of our air with a temperature of +18 and a humidity of 50% in the plate. It intersects with the curve of the partial pressure of water vapor at 35 degrees, so if we supply water for a temperature of +35 for adiabatic humidification, additional heating of the air after humidification is not required, and the air temperature at the entrance to our “sink” will be the same. Thus, I will need an additional heating boiler, which will warm the water to humidify up to +35. Why do this, because if you calculate the curve for adiabatic humidification for water temperature, for example, +7, then the air temperature for 300 m³ / h will drop by only 1 degree, and for 100 m³ / h it will generally remain at +18. The answer here is in the desire of the system to still work as an air purification, and even with a fogger performance of 3 liters, no one can guarantee me the moisture in the order I need (0.1-0.4 liters per hour) - most of the water will simply merge into sewer, not having time to evaporate.

And yet, I am very worried about the location of the fogger, the range of its mist jet and how the air from the air conditioner fan will distribute this mist-air mixture, whether the heat exchanger will work properly as a drop catcher or the mist will go into the air ducts and I will get large drips from the air distribution grilles and in the air ducts puddles will be formed, etc. etc.

Considering all these nuances, I made a decision about the natural tests in the cold season, when the outdoor temperature will be at least 0 - +5 degrees. Check how a cloud of mist spreads inside the duct unit, in air ducts and grilles, how the heat exchanger fins behave, the correctness of the water and outside air temperature calculations, how quickly the humidity rises and drops to an uncomfortable minimum. Only after processing all the information obtained experimentally, having developed the necessary work algorithms, it will be possible to proceed to the next item.

3. Arduino

Well, where without it to publish on this resource;) I think that it is more or less clear what I am going to do with this piece of iron and how everything should work. But more specifically, I will return to this point after the tests and in the process of implementation (with positive data obtained). Now I’ll just describe the component parts:

1. Humidity sensor on the intake air recirculation air, check the actual humidity in the rooms;
2. Temperature sensor for supply air at the canal outlet;
3. IR transmitters to control the start / stop of indoor units;
4. Valve normally closed with electric.

Maybe I will be looking in the direction of something with similar functionality, but with a web interface for implementing the “smart home” system, you should start once more to become more advanced, add light control, security and fire alarms, IP cameras and so on and so forth.

The publication is intended to discuss the decision, does not pretend to be correct and comprehensive, and I am ready and want to hear any constructive criticism, suggestions, comments, and the like.

To be continued…