Generally, the wallboard of air handling unit is made of double-layer colored steel plate or cold-rolled steel plate by powder spraying (the inner side plate of some bottom plates is stainless steel), and the insulation materials in the middle are mostly polyurethane foam or flame retardant centrifugal glass wool. Judging from the thermal conductivity, water absorption and density, both of them are good thermal insulation materials. However, due to the high-speed operation of the air handling unit, the vibration of the box is relatively large, while the glass wool is relatively light, and there is a large gap in the structure that is easy to fall off due to long-term vibration, resulting in a sharp increase in thermal conductivity and loss of thermal insulation performance, resulting in dew condensation on the wall of the air handling unit and high air supply temperature.
However, polyurethane foam may not have a good thermal insulation effect, such as inferior polyurethane foam thermal insulation materials will also affect the use effect. Therefore, when selecting air handling units, do not rashly choose wall insulation materials.
2 air leakage rate
The box structure of most air handling unit manufacturers consists of panels and aluminum alloy frames or angle steel welded frames. The sealing treatment of the box is also an aspect that should be paid great attention to when selecting the type, because if the air leakage rate is too high, there will be two consequences: first, too much air leakage leads to insufficient air supply; The other is to cause air leakage in the air treatment room under negative pressure. In summer, this will make untreated hot and humid air enter the air supply system, so that the dew point of the machine can not meet the design requirements and the air supply temperature parameters can not be guaranteed. The Code for Manufacturing Modular Air Conditioning Units (GB/T 14294-08) issued by the State Bureau of Technical Supervision stipulates: "When the static pressure in the unit is kept at 700Pa, the air leakage rate of the unit shall not be greater than 3%". Some manufacturers have dovetail-shaped sealing grooves on the frame of air handling units, and are equipped with corresponding rubber sealing strips. Under the rated working condition, the air leakage rate can be guaranteed to be less than 2%, which meets the specification requirements. This is a good way to solve the air leakage problem of the unit.
3 surface cooler selection calculation
Surface cooler is the core component of combined air handling unit, where air and refrigerant exchange heat. The usual coil structure of surface cooler is to expand aluminum fin and copper tube with expander. The wall thickness of copper tube and aluminum foil varies slightly from manufacturer to manufacturer. Generally, the wall thickness of copper tube is 0.2 ~ 0.6 mm, the diameter is 7 ~ 16 mm, and the thickness of aluminum foil is 0.15 ~ 0.20 mm. It is worth noting that the fin spacing selected by different manufacturers is quite different when calculating surface coolers. Taking a system as an example, the treated air volume is 79 000m3/h and the cooling capacity is 83 1kW. The scheme adopted by a factory is to reduce the fin spacing of surface coolers (about 1.8mm) and increase the heat exchange area. The scheme adopted by Factory B is to select the conventional fin spacing (about 2.5mm) and adopt the form of two-stage surface cooler sections in series to extend the heat exchange time. The two schemes have their own advantages and disadvantages in fan power consumption, water resistance and section size. The former may cause large wind resistance, thus increasing the power consumption of the fan, while the latter may increase the unit size and water flow resistance. After a comprehensive technical comparison and comprehensive consideration of cost factors, we decided to adopt the products of Factory B. This example shows that the rationality of surface cooler selection calculation is related to the performance and comprehensive cost of the whole air handling unit, which should be paid enough attention to.
4 fan selection
Fan is the only energy-consuming component in each functional section of air handling unit. Like ordinary fans, when ordering, we should choose the appropriate fan type according to the relationship between air volume and pressure head, such as forward multi-blade or backward curved blade, so as to ensure the best noise and efficiency of the fan. In recent years, the efficiency of wing fans imported from abroad is very high.
With the development of computer technology and the improvement of automatic control level, VAV systems are more and more widely used in office buildings, clean workshops, hospitals and other occasions, which puts forward new and higher requirements for the selection of air supply and return fans of air conditioning units. First of all, the characteristic curve of the fan should have gentle characteristics, so that when the air volume decreases, the system can avoid increasing unnecessary static pressure; Secondly, when selecting the fan, its working range should be in a relatively stable and efficient area; Thirdly, the return/exhaust fan should be of the same model or type as the blower and have the same or similar performance characteristics to ensure the effective matching of the whole system during operation.
5 filter selection
Filters are divided into: primary filter (usually called G class), intermediate filter (usually called F class) and high efficiency filter.
The primary filter is classified as G 1\ G2\ G3 \G4(G4 is the primary filter with the highest filtering effect, and others are arranged in order).
Intermediate filters are divided into: F5 (F8 is the intermediate filter with the highest filtering effect, and others are arranged in order).
High-efficiency filters are divided into: 300,000-level filter 65438+100,000-level filter100-level filter (100-level filter is the most efficient filter).
High, others in turn)
The mainstream filters in the market are: non-woven fabric filter, belt filter, metal filter, paper filter, nylon mesh filter and glass fiber filter.
Filter \3M filter (a low-resistance, high-efficiency and energy-saving filter introduced by 3M company in recent years)
Dust in the air has an impact on human health and product quality, especially in some special industries, such as precision instruments, electronics, medicine and hospitals. This requires the selection of combined air handling units according to the requirements of different industries.
The air used in comfortable air-conditioned environment has certain requirements for dust content. Generally, the indoor dust concentration is 0. 15 ~ 0.25mg/m3, and dust particles ≥ 10μm should be filtered out. The filter part of this air treatment unit only needs to be equipped with coarse and medium efficiency filters. For the above-mentioned special industries, it is necessary to configure high-efficiency filters to achieve ultra-clean purification, which requires higher standards. The dust concentration in indoor air is expressed by the particle count concentration (particle/liter).
6 convenient maintenance
As mentioned above, the combined air handling unit is usually used in occasions with large system air volume (usually above 10 000m3/h), so its overall size is often large. In modern buildings, due to the limited investment and functions of developers or owners, the size of the computer room is often compressed very small, which easily leads to the parts that need daily maintenance and cleaning, such as surface coolers and filters, which cannot be taken out or are difficult to take out because of the narrow space. After the completion of some buildings, the original reserved equipment maintenance passage is occupied, and it is impossible to pass when the equipment needs to be replaced or repaired. Therefore, in the construction, on the one hand, attention should be paid to reserving maintenance space and passages as much as possible; On the other hand, when ordering equipment, manufacturers can be required to improve the structure of air handling units according to the actual situation of the computer room, such as designing surface coolers without plugging in electricity on both sides.
Model parameter description of suspended ceiling air handling unit 020 030 040 050 060 080100120150 nominal air volume m/h2000 3000 4000 5000 6000 8000/kloc-0. The area of 5000 coils is m0.28 0.401.291.55 cold capacity. Four rows of standard working conditions kw1.4717.16 23.37 28./kloc-0. .3690.369086866 working condition: kw1171.09 204.72 259.44 mm10/990100. 000 1 4001510 630 630 725 725 Remarks:1. Standard working conditions: inlet air temperature is 27 C/19.5 C (DB/WB), inlet and outlet water temperatures are 7 C/12 C 2. Fresh air conditions: inlet air temperature is 35 C/28.5 C (DB/WB), and inlet and outlet water temperatures are 7. 4. The overall dimensions are respectively provided with data of A /B type length.