Toyo :: hygienic air handling units

HYGIENICE AIR HANDLING UNITS

Air-handling unit in hygienic design has following differences from standard design:

TOYO-AC MAHU Series air conditioners have been designed according to German Standard DIN 1946 part ISO 9001, Engineering Standard EN 1886 and Hygienic Standard VDI 6022.

TOYO-AC Modular type air handling units are built in double skin construction, with 40 or 60 mm thick rock wool insulated panels, within the capacity range of 1.000 – 125.000 m3/h. Outer surfaces of the units are made of PVC covered pre-painted sheet metal to RAL 9002 color, while the inner surfaces are of stainless steel.

CASING AND COMPONENTS:

Internal surface and walls are smooth and without open adsorption grooves
The inside surface and inside parts of AHU should be using the materials and skin of anti-corrosive of disinfection drugs, also should be clean.
Inside panel surface made of plastic coated galvanized steel sheet, stainless steel sheet or seawater resistant aluminum sheet (AlMg)

The AHU should be reliable air-tight. When the inside static pressure is kept by 1000pa, the cabinet’s air leakage rate should not more than 1%, for the system with class 1000 or higher; For the system with less 1000 class, the cabinet’s air leakage rate should not more than 2%
Seal and gap filling materials are non-porous and not moisture absorbing
All parts and components of the unit, such as fans, motors, filters, coils (together with droplet separator and drain pan), etc. are resistant to commonly used cleaning and disinfecting agents

For units height up to 1,3 m, components could be pulled out for cleaning and disinfection purposes. For higher units, both sides of components are accessible from service side through dismountable front panel or service door.
The inside structure should be convenient for clean and also easy to drain of waster water, and not easy to gather the dust and then produce the bacteria
When you open the door, you can see the area in red, there is no threshold, no any obstruction, so you can clean the inside very easy, then no dead angle. Please see below picture, if there is rubbish inside, you just need to open the door, and clean it.
The joints between the frame members and panels have unique double sealing strips. This provides an effective seal and contributes to excellent hygienic properties.

AIR INLETS AND OUTLETS

All units are equipped with airtight dampers according to DIN 1946Part 4
Inlets sections are equipped with drainage system
Dampers used in the air handling units and cabinet fans are made of aluminum profiles and aluminum damper blades with plastic driving gears. Gears are placed out of the air stream. To prevent leakage, plastic gaskets are used on the damper blades.

FILTERS

Bag filters are mounted at the 1st stage of filtration, i.e. the suction side for fresh air class G4 or F5 at least, and at the 2nd stage of filtration, i.e. the unit outlet - not less than air class F7. At each stage, the air humidity should be kept below 80% r.H.
In less demanding spaces, where return air is used, it is still necessary to maintain the maximum permissible pollutant concentration. It should be noted that filter class G3 and G4 are intended for the protection of coils and heat recovery devices rather than reduction of the dust load in a space. If the ambient air pollution is to be reduced, then filter class F7 or higher are to be installed.
Differential pressure gauges installed on each filter section
The section of units higher than 1,3 m is fitted with lighting and an 150 mm inspection glass
Air handling unit with standardized filter sizes according to DIN 24185. Filter classes according to EN 779 : G1-G2, G3-G4, F5-F9 and H10-H14. Execution : panel, bag, compact, HEPA or activated carbon filter.

AIR HUMIDIFIERS

Air humidifiers contain an inclined base pan for water drainage for prevention of a potential microbiological growth, depositions and corrosion. Water can be completely drained when the unit is not operating.
According to water hardness grade and air pollution, it is recommended to use a water-softening device or rather a device for germ elimination from water like for e.g. UV lamps
Drip tubes, condensate pans and water tanks are made of stainless steel
Drip tubes and condensate pans, water tanks, droplet separators and air deflectors are easily accessible for cleaning and disinfection purposes
Spray humidifiers (class A,B or C), evaporative humidifiers (class D) or steam humidifiers (class E) could be installed
Steam humidifiers are dimensioned and designed to prevent water condensation
The section of units higher than 1,3 m is fitted with lighting and an 150 mm inspection glass
It is better to use dry steam humidifier, and there should be no water drop during humidifying. The water for humidifier should be the same hygienic standard with living water. The humidifier material should be anticorrosive, and also easy for clean and check.
The air relative humidity, before the high efficiency filter for Ⅰ～Ⅲ class clean room in the air conditioning system, should not be more than 75%

HEAT EXCHANGERS

Droplet separators, drip tubes and condensate pans are easily accessible for cleaning and disinfection purposes
Heat exchanger surfaces are smooth and free from sharp edges. The fin spacing is minimum 2 mm for heaters a nd minimum 2.5 mm for coolers. In case of larger air-handling units heat exchangers consist of 2 parts interconnected by a heat exchange coil.
Differential pressure gauges installed on each heat exchanger section
Base pans below cooling coils are inclined and allow a free drainage of all condensed water, can be easily cleaned and disinfected and are made of stainless steel

Due to a very high relative humidity coolers are normally not installed upstream filters or a sound attenuator sections. Otherwise, re-heater should be installed in between.
Considering the pressures present, the siphon of the cooler base pan equipped with a return flow protection is dimensioned to enable the undisturbed water drainage
Heat exchanger for chilled water, glycol or as refrigerant DX-coil. Made of Cu/Al, Cu/Cu or Cu/Cu tinned coil or galvanized steel. Bottom integrated drain pan made of stainless steel 304L. Droplet eliminator made of PVC profiles in stainless steel 304L frame. Coil connections internally or straight to outside.
The outlet of the heat exchanger for condensate water should has the device to drain of the water successfully when negative pressure and automatically prevent suck-back. When dehumidifying, the water needs to be drained within 3 minutes after system working. The condensate pipe can not connect with the sewer directly.
AHU should not use water spray type heat exchanger. And face velocity trough the heat exchanger should not be more than 2m/s.

Condensate Trays

In order to drain the condensing water in cooling coils, humidifiers and heat recovery systems, double slope condensate trays in stainless steel are used. Condensate tray is big enough to accommodate the coil, collectors and droplet eliminators. Condensate tray is insulated with rock wool.

FANS

Fans are corrosion-protected. Fans with casing always contain a filter. For an easy cleaning the fans have backward curved blades and a condensate drainage on the bottom of the fan casing.
Fan casing for nominal diameters exceeding 400 mm contains an inspection opening. For hygienic reasons, fans without casings are preferred.
Differential pressure gauges installed on each fan section
The section of units higher than 1,3 m is fitted with lighting and an 150 mm inspection glass
Fans and motors are mounted on sliding frame which may be easily pulled out for cleaning and disinfection purposes

Heat recovery devices are used for exploitation of the exhaust air energy mainly in cases when fresh and ows do not mix like in e.g. plate-type recuperates
Droplet separators, drip tubes and pans may be pulled out for cleaning and disinfection purposes
Rotating regenerators may only be applied if, due to hygienic conditions, the return air may be used
For prevention of possible sound attenuator shutters pollution with dirt, they are normally preceded by a lter. The air humidity should be kept below 80% r.H.
For prevention of possible pollution during the transport, sound attenuators are packed separately before
Installation of sound attenuators downstream of the air humidifiers or coolers should be avoided. herwise, re-heater should be installed in between.
The shutter material is wear-resistant, easy for cleaning and
Sound attenu ators shutters are normally accessible on both sides or can be rather dismounted to facilitate cleaning and disinfection