Prokofiev P.S.

Volgograd State University of Architecture and Civil Engineering, Russia

High efficiency humidification
in ventilation and air conditioning

One of the main steps is temperature and moisture treatment of outside air for common and technological areas. Humidification units also play role of wash devices, because the water dissolves gases and smells, catches small parts of dust and freshens the processed air. Actually, humidification units are additional steps of cleaning the air. They are irreplaceable in air conditioning systems if you need to humid air with simultaneous heating. In this case the humidification units are supplied with coolant temperature is higher than wet bulb temperature of the air.

Adiabatic humidification is more economical then isothermic, at least in 1-2 times, whereas in this case the vaporization process is due to internal redistribution of energy and external energy consumption is due to implementation of various less costly works. In the most advanced systems of adiabatic humidification generation of 10 kg moisture takes about 40 Watt of energy consumption.

In this article a fundamentally different design of the adiabatic humidifier is described, called by the authors [1] as rotary plated heat exchanger (RPHE), construction is shown in Fig. 1.

Rotary plated heat exchanger works as follows. Treated air is drawn through the inlet tube into the case in radial toward the rotating disks and is held in slot channels between the disks to the outlet tube. When the disks rotate its bottom part is in the tray with water, when the disk goes up from the tray to air stream due to surface tension forces on surface of disk the skin of water are formed which blurs the air across the surface of the disk, and with this skin air processes. Obviously, the disks should be made of well-wettable material and the surface should be thoroughly degreased.

RPHE can be installed on the suction or discharge side of the network, as moisture section in the central conditioner or in hanging supply units, inside or outside the attended room. In recent years "Invent Ltd." had carried out investigations on design optimization of RPHE, and the mass production is founded in Volgograd.

Fig. 1 Construction of RPHE.

Analysis of most our projects made for dozens office buildings and malls shows that for most of them required humidifiers adiabatic efficiency ratio E_a is about 0,8. The value of E_a is calculated by the standard formula:

where t₁ – inlet temperature of the air dry bulb, °С;

t₂ – outlet temperature of the air dry bulb, °С;

t^w –temperature of the treated air wet bulb, °С.

In common the effectiveness of humidification RPHE depends on the diameter disks, clearance between its, depth to the water, rotor speed, air velocity and starting parameters of the air.

RPHE works without eliminator and air velocity is more than in air coolers, so device can be mounted in practically any air conditioner, e.g. now “York” firm applies in their central air conditioners and “Venta” firm in the air conditioners “NOVAIR”. An important feature of RPHE is the ability to stop humidification at a given point, it allows to avoid using the second heating.

Problems of humidification at residential buildings deserve a special consideration. According to most experts centralized humidification in air conditioning systems of residential buildings is inappropriate and to solve problems associated with low relative humidity indoors the most effective is using of individual home humidifiers.

To evaluate the situation in the SEC "Invent" conducted laboratory tests on domestic adiabatic humidifiers “VENTA” (Germany) and “AIR-O-SWISS” (Switzerland), that presented at fig. 3 and 4. At first sight, the design is same, but in fact both of the humidifier does not have anything in common with RPHE except appearance.

Fig. 2 Experimental sample of RPHE.

Fig. 3 Domestic humidifier “Venta”.

Fig. 4 Domestic humidifier “Air-O-Swiss”.

In both foreign devices wheels are made of plastic and nonwettable clearance between the disks is 4 and 5 mm. The frequency of the disk is in the range of 1 to 1.5 rpm. To get wetted surface of disks somehow, in the unit “AIR-O-SWISS” radial tabs are made on disks that are need for scooping water from the tray. The test results of humidifiers “VENTA”, “AIR-O-SWISS” and RPHE are presented in table below.

Humidifier	Inlet temperature		Outlet temperature		Frequency, rpm	Ea, %
	t1, °C	tм1, °C	t2, °C	tм2, °C
	28,8	16,8	18,1	16,9	9,5	90
	26,5	15,9	17,5	16,4	9,5	89
	Disks Æ160mm, clearance 1,35mm, diving 30mm. Total 80 disks.
	24,8	12,8	21,8	13,4	1,0	30
	24,8	12,8	22,2	13,4	1,0	26
	Disks Æ250mm, clearance 5,0mm, diving 30mm. Total 16 disks. (2 rotors each 8 disks)
	24,2	12,6	23,8	12,8	1,25	5
	24,2	12,6	24,0	12,8	1,5	6
	Disks Æ180mm, clearance 4,0mm, diving 108mm. Total 88 disks. (4 rotors each 22 disks)

As seen, the coefficient of efficiency in the adiabatic humidification RPHE is disproportionately higher than of foreign samples. Very low value of E_a of humidifiers “VENTA” explained not only by the fact that the disks are made of nonwettable material and fitted with a large clearance, but also by the fact that at the chosen layout the air is not moving in the clearances between the disks but across the disks.

Bibliography

1. Author's certificate №1216576 «A device for air heat and treatment».