abstract
With the improvement of people's living quality and living conditions, many families have installed one or even two room air conditioners. In recent years, with the rapid popularization of large-sized multi-bedroom houses and villas, some families are using or considering installing and using household central air-conditioning systems to create a pleasant home environment.
At present, according to the investigation of domestic market, there are three main types of domestic central air conditioners that have been installed and used: small water chillers, duct air conditioners and (variable frequency) one-to-many air conditioners. This paper mainly introduces the application scheme of duct air conditioning.
As a small central air conditioning system, duct air conditioning is widely used in developed countries and regions such as the United States and Europe, and its market share in small and medium-sized air conditioning exceeds 50%. It is the leading air-conditioning model in these countries. Compared with the other two kinds of household central air conditioning systems, duct air conditioning has the advantages of low initial investment, high reliability, convenient maintenance and replacement of fresh air. However, there are also some obstacles in the current domestic application process. Because houses in developed countries such as the United States and Europe are relatively spacious, it is more convenient to install and use duct air conditioners. However, in China, due to the influence of the height of ordinary multi-storey or high-rise buildings, the installation space of air ducts is not enough, and some users are prone to excessive operating noise due to improper selection and installation. At the same time, with the current domestic per capita economic affordability and consumption awareness, it is still unacceptable to open all rooms in the whole house.
Based on the practical experience of previous installation, this paper tries to put forward the following solutions for the problems existing in the application of the above-mentioned air duct machines and referring to the popular apartment types at present.
Introduction of apartment type
As shown in figure 1, it is a typical family unit with a total area of120m2 (building area) and a clear height of 2.7m, of which the usable area is about 89m2. The function and area of each district in the residents' planning are shown as follows:
Figure 1?
Consider using duct air conditioning to meet the needs of household air conditioning and refrigeration in summer.
1 Determine the number and location of air supply outlets of air conditioners.
The independent area of this apartment includes bedroom, study, living room, dining room, kitchen and bathroom. * * * 1 1, considering the actual air conditioning effect requirements and the possible independent refrigeration requirements of each region. There is an air outlet in the study, master bedroom and bedroom; Although the living room and dining room share a hall, they are functionally partitioned and have a large area. The two air outlets face the living room and dining room respectively. For the sake of simplicity and economy, there is no separate air supply outlet in the bathroom and kitchen. On the one hand, it can prevent the odor from reaching other rooms through the return air pipe, causing secondary pollution; There is no need to set air supply outlets for passages and balconies. ?
2 Selection of installation mode and location of host computer
Pipeline air conditioning can be divided into floor-standing and ceiling-mounted from the installation mode.
Because the refrigeration capacity and volume of household air conditioners are not very large, it is advisable to install ceiling air conditioners from the perspectives of saving space, reducing noise, keeping the room clean and beautiful, and reducing the length of air ducts. The selection of indoor host location is very important, and its main basis is as follows:
(1) The location of the host should keep a certain distance from the bedroom, study and other places that need to be quiet;
⑵ It is convenient to connect the air duct to each room, and try to keep the distance roughly equal, so that the pressure of each branch pipe is close to balance;
(3) The ceiling should be allowed to conceal the indoor unit in this position to make the room clean and beautiful and reduce noise;
(4) Sufficient installation and maintenance space shall be reserved to facilitate maintenance;
5] can ensure smooth return air, can easily lead outdoor fresh air;
[6] It is convenient to connect with the refrigerant pipeline of the outdoor unit, and the pipeline should be as short as possible;
Once, due to the high static pressure of the air duct machine, you should choose a place that is not sensitive to noise.
Based on the above principles, the location of the indoor unit should be the bathroom, kitchen, restaurant and other places on the north side. Considering the influence of floor height and the convenience of ventilation, restaurants are not selected. When decorating, both the bathroom and the kitchen have suspended ceilings, and indoor units can be installed. Considering that the kitchen is in the middle position, the layout at this time can shorten the length of the pipeline and reduce the elbows, which is conducive to the balance of the pressure of each branch pipe, and finally choose to install it at the top of the kitchen. The outdoor unit is placed outside the kitchen, which is convenient for installation and maintenance and close to the indoor unit, which improves the refrigeration efficiency and reliability of use.
3 refrigeration area planning and return air problem
At present, air duct air conditioners abroad generally adopt centralized return air modes such as hall return air, channel return air or roof ceiling return air in home design, which has the advantages of simple installation, small static pressure loss of the unit and simple control. The temperature in the whole room is basically the same in every room. However, at present, there are great differences between domestic and foreign housing types. As shown in figure 1, this apartment has no obvious access (and cannot be closed into an access). Due to the limitation of floor height, it is impossible to completely suspend the ceiling, so we can only use the ceiling of the roof to return air. You can return air through the living room (after investigation, some users have adopted this scheme), but in this way, the living room becomes the public return air section of each room. Because the living room and dining room of this apartment have a relatively large combined area, it is bound to waste electricity if only air conditioning is turned on in the bedroom at night. According to the survey, most users hope that each room can be independently controlled and cooled to save energy and reduce the use cost. As can be seen from the above, we have designed five independent partitions for this room type: master bedroom, living room, dining room and study room. However, in order to realize the independent control of each area, the pipeline layout and control of the air duct machine are very complicated. According to practical application, the main places for our activities during the day are the living room, dining room and study, and we sleep in two bedrooms at night. Therefore, we can divide the family unit into living area (daytime) and rest area (night) according to the space and time of daily activities. The living room, dining room and study in the living area return air through the hall, and the two bedrooms in the rest area directly return to the bellows of the unit through pipes, which solves the problem of partition control and saves energy.
4 Pipeline design and layout
The biggest obstacle to pipeline layout in ordinary multi-storey buildings is height limitation. If the floor height is more than 3 meters, the pipeline can be easily placed on the top ceiling. But at present, the net height of commercial housing is generally around 2.7 meters. If the pipeline is placed on the ceiling and covered by a large ceiling, the indoor space after transformation is only 2.2 ~ 2.3 meters, which is obviously depressed. Therefore, it is easy to use the method of laying along the wall when arranging the pipeline, so that a concave-convex roof structure is formed in the final decoration, which not only keeps the indoor clear height, but also shields the air duct, which has a good decorative effect. At present, there are two main types of air ducts used: rectangular air ducts and circular air ducts. The material is generally steel plate, but also plastic or FRP. Recently, many units have begun to use flexible aluminum thin air ducts with thermal insulation glass wool felt, which can be easily bent and applied. The following points should be paid attention to in pipeline layout:
(1) The air duct shall be arranged as short as possible to reduce the pressure loss along the way;
⑵ It is not easy to have too many elbows and too small corner radius, and try to avoid sudden pipe diameter change to reduce local pressure loss;
(3) Don't destroy the original building structure, especially the load-bearing structure;
(4) Correct selection of thermal insulation materials, pay special attention to the thermal insulation materials that need to be flame retardant, and seal them with viscosity to prevent cold leakage.
As shown in Figure 2, the main air supply duct leads to the living room along the wall of the living room, the branch duct is above the passage between the two bedrooms (the whole ceiling of the passage), and the other duct passes through the living room and enters the study room. The living room and the dining room are naturally divided, which not only meets the air supply requirements of the study room, but also does not affect the overall decoration effect of the room. The return air duct consists of two parts, one is the return air from the dining room through the top of the kitchen, and the other is the same as the air supply from the bedroom. Fresh air is directly connected to the air return box from the outdoor through the air duct.
Figure 2?
5 design calculation
Select main technical parameters
Selection of (1) refrigeration capacity
The calculation of refrigeration capacity is mainly based on the following conditions:
(1) Heat introduced into the room through the wall;
(2) the heat introduced into the room through the window;
(3) Natural heat dissipation in the room, including the heat generated by personnel, lighting and equipment and the heat generated by catering processing.
The specific calculation is based on the cumulative calculation and superposition of various kinds of heat, which is complicated. Please refer to the relevant engineering design manual.
For ordinary brick-concrete houses, the recommended selection criteria are: the required cooling load index per square meter is 80W~90W, and the required cooling load per square meter for top-floor residents is increased by 15% ~ 20%.
According to the actual installation and operation in recent years, this index belongs to the economic index and can only meet the basic routine requirements of residents. Considering some unusual situations that may occur, such as high outdoor ambient temperature or good indoor refrigeration effect, the middle floor of general residential buildings should be 120 w/m2 ~ 150 w/m2, and the top floor should be 150 w/m2 ~ 65433.
Calculated according to the total effective living area of 89㎡, 150w/m2.
89? m2× 150？ Width/m2 =13350W
Then at least one 5-duct air conditioner (cooling capacity 12500W) is selected by the host. In fact, at present, it is rare to see the whole household fully open air conditioning in China. The most common situation is:
During the day:? Living room+dining room+kitchen+bathroom+passage? The total area is 40.5 square meters.
Or? Living room+dining room+study room+bathroom+passage? The total area is 47.7 square meters.
Evening:? Master bedroom+bedroom+bathroom+passage? The total area is 36.3 square meters.
If the maximum value is 47.7m2, the required cooling capacity is 47.7×150w/m2 = 7155w.
In addition, the refrigeration capacity of 7 155W can also meet the refrigeration demand of the whole family (7 155W/89? M2=80.4W/m2), so you can choose three air conditioning units with air ducts (cooling capacity of 7 100W), which not only meets the needs of the whole house's economic operation, but also meets the requirements of indoor local high-efficiency refrigeration. The initial investment cost is reduced and the operation cost is saved.
(2) Pipeline calculation
The refrigerating capacity of the main air conditioner is 7 100W, the air volume is 1450m3/h, and the static pressure at the outlet of the unit is 50Pa, 80Pa and 120Pa. Now calculate and confirm the required static pressure at the outlet. The selection of pipe diameter should be based on the premise of ensuring low noise, so as to save materials and facilitate installation. The recommended velocity of ordinary steel plate and plastic air duct in the main pipeline is 6? M/s ~ 14m/s, and the velocity in the branch pipe is 2? M/s ~ 8m/s. In order to reduce the noise as much as possible, the main wind speed is 6m/s, and the cross-sectional area of the required air duct is 1450m3/h÷3600÷6? m/s？ =0.067m2, rectangular steel pipe 320mm×320mm.
Each air supply outlet and air return outlet is equipped with an air valve to control the realization of regional refrigeration. All air supply outlets adopt side air supply mode, with side return air or top return air in the hall and top return air in the bedroom. Calculation of pipeline resistance (omitted). Confirm that the static air pressure required by the unit is 80Pa.
6 control mode
(1) Control requirements: simple, reliable and applicable control. The air conditioning unit can work under the following conditions:
(1) whole room comprehensive economic refrigeration;
② Refrigeration of living room, dining room, kitchen and bathroom;
(3) Refrigeration except master bedroom and bedroom;
④ The master bedroom and bedroom are cooled separately.
(2) Control principle
The line controller (main controller) is used to set the working mode and working temperature. In order to simplify the control, only one temperature sensor is set and placed on the return air side of the unit to control the start and stop of the compressor. Each controlled room is equipped with an air valve switch, which is used to control the air valve and send an on-off signal to the air conditioning host.
Figure 3?
In addition, you can also choose an air valve switch with a thermostat, supplemented by indoor three-speed air volume adjustment, to achieve local temperature control function.
7 conclusion
(1) The most important problem in installing duct air conditioning in ordinary multi-bedroom houses is the layout of ducts. Due to the limitation of storey height, it is necessary to use walls, doorways, kitchens and bathrooms to arrange pipes, and to cover and beautify them in the later decoration. ?
(2) Considering the living habits and economic ability of China people at present, from the point of view of energy saving, we should control the home intelligently in different areas, avoid the complexity and simplify it, and take convenience, practicality and simplicity as the principle.
(3) The air supply pipeline should be calculated accurately, so as not to cause the wind at the end not to be sent or the pipeline noise is too large.
(4) Due to the high floor and narrow space, hoses can be used in some areas, especially at the intersection of pipelines, so as to facilitate installation.
(5) Disadvantages of the scheme: Because the air circulation of the study room needs to return air from the restaurant through the crack of the door, the study room cannot provide refrigeration alone. In addition, because the air supply in the study and dining room is on the same pipe, it has certain influence on each other. In actual use, it is found that the air supply in the study room is obviously reduced when the restaurant is cooled, but the above situation is rare in actual use. It is suggested that the restaurant and the study should not open the air valve at the same time. ?
(6) For winter heating in the Yangtze River basin and its south area, in view of the small price difference between heat pump units and single cooling units, heat pump air duct units should be used with electric heating equipment to solve the problem.