【 Weak current College 】 Central air conditioner terminal equipment selection

With the rapid development of China's economy and people's living standards, built a lot throughout the shopping malls, office buildings, hotels and other public facilities, many of these high-class buildings are equipped with central air conditioning, the air conditioning system form primarily wind full air system and fresh air + fan-coil system.

These two systems are used in the central air conditioner terminal equipment in air handling unit (air supply unit, VAV boxes, air box) and fan-coil. Thus the two products in the market demand increased year by year, thereby promoting the domestic many manufacturers have started manufacturing, product quality and varied. This gives design and product selection has brought a lot of difficulties, this article in accordance with industry journalists work experience for the majority of peer reference.

A, central air conditioning Terminal:

Air handling unit to select notes in the air handling unit selection first according to the central air conditioning system load to determine the air handling unit required air flow, pressure, heat and air outlet noise and air filtration requirements. However, due to design or manufacture, the reasons being used we often found that the selection of air handling unit exists in one way or another, there are not enough wind cold, cold enough, box appearance of condensation, condensing coil overtopping, table coolers with water after paragraph. This requires that we in equipment selection strictly the quality well before they happen. About their experience with the following points:

1, box insulation; to prevent condensation tank shell, national standard specifies case insulation thermal resistance should be not less than 0.68m-2/kW while also preventing body paragraphs join Department produces cold bridges. Insulation currently use PEF or polyurethane foam.

2, Windward surface wind speed: at present, some manufacturers in order to narrow the product dimension, and often will air conditioning Chamber scored Windward surface wind speed, the larger causing air handling unit with cooling water after the consequences; such as stall water board design, then this problem is more serious. So when we should be in the selection will be cooler Windward surface wind speed control in 2 ~ 2.5m/s.

3. the provisions of air leakage indicator: national standards, air-box in box at static pressure for 700Pa, built-in air leakage rate shall not exceed 3 per cent in actual use, we found on-site air conditioning tank air leakage rate was as high as 10%. The analysis of this mainly consists of the following reasons.

(1) sealing material performance is not good

(2) of the unit structure design of unreasonable

(3) poor quality on-site installation

(4) large air box body rigidity, when start and stop running when deformation.

4, hot and cold enough: domestic manufacturers of cooling coil design selection by lot to sample test results of empirical formula Zoom calculation is in itself a certain error margin, and some enterprises have no test conditions and copying other manufacturers of related samples; this is caused by many manufacturers of such products and cold enough. So we're on the manufacturers site visits to personally know their product testing means.

5, condensing coil overtopping: this issue is currently the air handling unit with the most widespread in the event of a phenomenon, the user's response was most strongly. This problem is this:

(1) excessive Windward surface wind speed

(2) table coolers is negative, the unit is factory-no set seal

(3) the length of the condensate tray and depth. On the Windward face velocity too much problem as already said, the unit is set to the height of the water and condensate tray length and depth value determination, we should be in the order under the cooling section with negative pressure values in consultation with the manufacturer.

In addition to the main issue, we review the central air conditioning terminal when you should be aware of several "mini" issue.

1. adopt double fan blower air box back to the wind should be greater than the pressure blower, otherwise occur does not come in fresh air suction.

2. air handling unit Panel materials should give priority to the use of steel (surface spray) such as the use of FRP materials do Panel should be aware of the fire problem.

3, big air volume unit should be set up by the wind Board to ensure that air can flow through the filter and increasing even cooler.

4, large wind turbine to consider some features of merge (if the table is cold and heated section merge) to reduce the unit length.

5, big air volume unit should consider fan motor settings in case of external to save energy.

Second, central air conditioning Terminal:

Air blower plate Tube considerations when choosing our fan-coil units index in the following projects: air flow and cooling volume, quantity of heat, the cooling fan power units, water resistance, A sound level noise, dew, condensate, motor winding temperature, thermal insulation resistance and voltage-frequency, leakage current, and resistance to these indicators. But we in project evaluation a blower coil quality is good or bad for a standard primary or see its air, cold, noise, consumption of these indicators.

Usually in the choice of fan coil when many people think the coil technique has long passed, each manufacturer's product are very similar, and often considered only from the price. From the above table we can see that different manufacturers of products in the refrigeration capacity, power consumption, noise, there is quite a difference. But only from power, the same product maximum power and minimal power consumption between 23W, if an Office coil 10 hours per day to run, run 200 days per year (year use coefficient of 0.6), annual savings 27.6 unit, per unit of $ 1.1 per year operating cost $ 30. If the difference between the price of $ 400, that the initial investment will increase in three years time to recover. This is just the economic account does not include low noise coil to improve productivity and staffThe benefits of physical and mental health. The following will talk about the specific selection of some attention.

1. coil cooling capacity is not enough: this is the maximum number of user complaints. The main cause of the problem is that many companies do not have their own test methods, sample parameters from other manufacturers of samples on plagiarism and own production of coil thermal performance and poor (mainly by the fin forms, expanding quality, production process and so on). Therefore proposed in project review when the manufacturer's test facilities and methods, it is hard to imagine a does not have its own test equipment manufacturers can produce a good product.

2. air flow: at present we carry out specific engineering design are often based on calculated the cooling load through access to the relevant manufacturers for the samples to select air blower plate Tube. How to consider coil air flow is an issue. The domestic market, most manufacturers of coil is only one of three pipes, but also manufacturers provide second line pipe coil. I think for most civil buildings air conditioning system, select the second row of pipe coil more favorable (except in high humidity applications). This is because the second row of the product under the same cold air is large, this will increase the number of ventilation air conditioned room, increase accuracy and comfort air conditioning. The same cold, the use of small temperature difference, big air volume and air, will make a small difference, big air volume and air better air conditioning effect.

3. outside the machine Yu ya: as China's current coil national standards require fan-coil air volume, cold and noise, and other parameters of the test are in the machine outside the conditions of static pressure is o. But in the actual use of distributors pipe outlet often received before a short air ducts and ventilation louvers, another of the project also has back to bellows, so in actual use will find the actual air coil is less than the nominal air flow to, such a consequence is the room air flow reducing the temperature, ventilation, air conditioning comfort increase. Some designers to avoid this situation in selection while pressing the coil mid-range air volume selection, to avoid air volume, but increased the initial investment project. Thus I propose in national testing standards have not changed, we in the coil selection should be preferred to spare voltage (typically should be 10 ~ 15Pa) unit.

4. noise problem: it is products and a big gap between foreign products to a place that is also presently coil because of quality problems and a point being complained against. This problem causes lie in the coil of motor and blower configuration and matching of unreasonable. Another reason is the manufacturer of quality management is not strict, assemblers of responsibility is not strong, resulting in product quality is stable. So we visit a factory products should consult their authority by the national quality inspection departments to produce that product (Note must be we are prepared to order the product) noise detection reports. For selection of bulk larger projects should onsite sampling sent the quality inspection departments.

In addition to the above a few speakers, the coil selection you should be aware of when it is a quality inspection departments to produce qualified reports of dew test. The condensate tray insulation should adopt the overall thermal insulation, water dish should give priority to select the long drive. In addition, other things equal priority overall small light weight products. On the electrical aspects of the vast majority of parameters of the current domestic manufacturers of products can be achieved and may not be the focus of the investigation.

In short, in the actual operation of the central air-conditioning system, should make specific case-by-case basis, I think that all of central air conditioning terminal product suppliers and engineering are understood.