Common problems and elimination of the hottest air

2022-10-23
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Common problems and troubleshooting of air HVAC design

I. Problems in implementing HVAC design specifications and standards

1.1 indoor and outdoor air calculation parameters do not meet the requirements of the specification

the design specification stipulates that the indoor air calculation parameters in winter should not be less than 12 ℃ in lavatories and toilets, and not less than 25 ℃ in bathrooms. However, some toilets in public buildings, lavatories (with external windows and walls) and toilets in residential buildings (with hot water supply in winter, which should be regarded as bathrooms) are not equipped with radiators, so it is difficult to meet the requirements that the room temperature is not lower than 12 ℃ and 25 ℃. Some residential buildings do not have radiators in their kitchens, which the author thinks is inappropriate. The indoor temperature of residential kitchens should also be set with radiators not lower than 12 ℃

the Design Code stipulates that the outdoor meteorological parameters of some major cities should be adopted according to Appendix II of the code. According to the Appendix II, the outdoor calculated temperature of winter heating in Beijing should be -9 ℃ except Yanqing and Miyun. Some projects are located in the suburbs of Beijing, but it is obviously inappropriate to use -12 ℃

1.2 there are omissions and errors in the calculation of heating heat load

the Design Code stipulates that the heat load of the heating system in winter should include the heat consumption of heating the cold air that seeps into the room from the consumption of 8.3 billion packaging bags in the year of the door and window gap. However, some projects do not calculate this part of the heat consumption when calculating the heating heat load, resulting in a large difference in the heating heat load; The "design code" clearly stipulates the correction rate of each direction in the calculation of heat consumption of enclosure structure, which is 0 ~ 10% in the north, -5% in the East and West, and -15 ~ 30% in the south. However, some projects change the correction rate of each direction to 20% in the north, 15% in the East and West, and -5% in the south, which is contrary to the requirements of the code

1.3 improper selection of radiator type in toilet

Design Code stipulates that cast iron radiator should be used in rooms with high relative humidity. However, steel radiators are used in toilets of many projects, and anti-corrosion measures have not been strengthened, which is inappropriate. The author once saw that the toilets of some office buildings used steel closed radiators, but after a few years of use, the string pieces of the radiators were corroded, and the remaining two light pipes were seriously rusted. Practice has proved that cast iron radiator or aluminum radiator is best used in such places

1.4 the vertical and branch pipes of the radiator in the stairwell are not separately configured.

the Design Code stipulates that the radiator in the stairwell or other places with freezing danger should be heated by separate vertical and branch pipes under the tension mode, and the regulating valve should not be installed. However, some projects share a riser with the radiator in the heating room of the adjacent room, which is connected on both sides. One side is connected to the radiator in the staircase, and the other side is connected to the radiator in the adjacent room, and a valve is set on the radiator branch pipe. In this way, because it is difficult to ensure the tightness of the staircase, once the heating fails, it may affect the heating effect of the adjacent room, and even freeze the radiator

1.5 the laying slope of heating pipes does not meet the requirements of the specification

the Design Code stipulates that the laying of heating pipes should have a certain slope, and the slope of hot water pipes should be 0.003, which should not be less than 0.002. However, the gradient of heating supply and return pipes in some projects is only 0.001 ~ 0.001 5. Of course, if the conditions are really limited, the hot water pipe can even be laid without slope, but at this time, it should be ensured that the water velocity in the pipe should not be less than 0.25 m/s

1.6 there are problems in the ventilation of the kitchen operation room

the code for design of catering buildings (JGJ) clearly stipulates the ventilation of the kitchen operation room: (1) 65% of the calculated exhaust volume is discharged to the outside through the exhaust hood, and 35% is discharged by the overall ventilation of the room; (2) Generally, the suction speed at the outlet of the exhaust hood shall not be less than 0.5 m/s, and the speed in the exhaust duct shall not be less than 10 m/S; (3) The make-up air volume of the thermal processing room should be about 70% of the exhaust air volume, and the negative pressure value of the room should not be greater than 5 PA. However, some engineering kitchens are not equipped with exhaust hoods, and only a few exhaust fans are set on the outer wall; Although some are equipped with exhaust hoods, the suction speed at the hood opening is far less than 0.5 m/s, and the air volume of the optional exhaust fan is insufficient. Most projects are not equipped with comprehensive ventilation devices, and air supplement devices are not considered, so it is difficult to meet the requirements of indoor sanitary environment and negative pressure value

1.7 the connection between the expansion tank and the hot (cold) water system does not meet the specification requirements

the code for design of boiler rooms (GB) stipulates that valves should not be installed on the connecting pipes between the high-level expansion tank and the hot water system. The connecting pipe mentioned here refers to the expansion pipe and circulating pipe. This article is also applicable to the chilled water system of air conditioning. However, the expansion pipe of the high-level expansion tank of some air-conditioning chilled water systems is connected to the water collector in the refrigerator room and installed with valves, which is not allowed. Once the operation is wrong, it will endanger the safety of the system

1.8 the setting of the fire damper of the ventilation and air conditioning system does not meet the requirements of the specification

the high standard stipulates that the air duct should not pass through the firewall or deformation joint. If it is necessary to pass through, a fire damper should be set at the place where it passes through the firewall; When passing through the deformation joint, fire dampers shall be set on both sides. However, in some high-rise buildings, there is no fire damper at the place where the air duct passes through the firewall, and when some air ducts pass through the deformation joint, there is only a fire damper on one side, while there is no fire damper on the other side. In addition, the position of fire dampers in some projects is set improperly. As required, the fire damper should be set close to the firewall, and the thickness of the through wall air duct connecting the fire damper is 1.6 mm. The air duct within 2 m on both sides of the firewall should be insulated with non combustible materials. However, in some projects, the fire dampers on the ventilation and air conditioning air ducts are set at will, far away from the firewall, and the air ducts between them are neither thickened nor taken any protective measures, so there are hidden dangers

1.9 there is a problem in determining the air volume of the air supply outlet in the front room of the smoke proof staircase

the high standard stipulates the pressurized air volume of the front room of the smoke proof staircase of high-rise buildings, and gives the specific air volume value according to the situation. The note states that the wind speed through the door should not be less than 0.7 m/s when the door is opened; The number of doors opened is specified in the article description, which is 2 below the 20th floor and 3 above the 20th floor. The high regulation also stipulates that one pressurized air supply outlet should be set at each floor of the front room of the smoke proof staircase. According to these regulations, it can be calculated that the air volume of the air supply outlet of the front room on each floor should be l/2 (below the 20th floor) or l/3 (above the 20th floor, l is the total pressurized air volume of the front room). However, in some projects, the air volume of the air supply outlet in the front room of the smoke proof staircase is marked as l/n (n is the number of floors of the building), which is obviously much smaller. For example, in a 12 story building, the total pressurized air supply volume of the front room of the smoke proof staircase is set at 16000 m3/h, but the air supply volume of the front room on each floor is marked as 16000/121300 (m3/h), which is obviously smaller. The correct mark should be 16000/2=8000 (m3/h), and the size of the air outlet should be configured according to this

1.10 mistakenly mixing the calculation of exhaust air volume of smoke control zones with the calculation of exhaust fan air volume

"high standard" clearly stipulates the exhaust fan air volume: when undertaking the smoke exhaust of a smoke control zone, it should be calculated according to the area of the smoke control zone of not less than 60 M3/h per m2, and when undertaking the smoke exhaust of two or more smoke control zones, it should be calculated according to the maximum smoke control zone area of not less than 120 m3/h per m2. Please note that this refers to the selection of the air volume of the smoke exhaust fan, which does not mean that the exhaust air volume of the smoke prevention zone is doubled (the exhaust air volume of each smoke prevention zone is still calculated according to the smoke prevention zone area of not less than 60 m3/h per m2), but when the smoke exhaust fan is responsible for the smoke exhaust of two or more smoke prevention zones in either the horizontal or vertical direction, only the air volume of the smoke exhaust fan is determined according to the smoke exhaust of two smoke prevention zones at the same time. However, in some projects, the smoke exhaust fan in the horizontal direction is responsible for the smoke exhaust of 2-3 smoke control zones with different areas. In the design, the air volume of the smoke exhaust fan is incorrectly calculated according to the total area of the 2-3 smoke control zones it is responsible for is not less than 60 m3/h per m2, rather than according to the maximum smoke control zone area of not less than 120 m3/h per m2, resulting in the small air volume of the smoke exhaust fan, which is difficult to meet the fire protection requirements. Other exhaust fans (Systems) are responsible for the smoke exhaust of more than two smoke control zones (inner walkways) in the vertical direction. In the design, the exhaust air volume of smoke control zones (inner walkways) on each floor is calculated by mistake according to their respective area of not less than 120 m3/h per m2, rather than according to their respective area of not less than 60 m3/h per m2, which virtually doubles the exhaust air volume of smoke control zones (inner walkways) in the vertical direction, resulting in the larger configuration of air ducts and vents on each floor

1.11 the smoke exhaust outlet of the smoke exhaust system of high-rise buildings is improperly selected.

the high standard stipulates that fire dampers should be set at the partition where the (ventilation and air conditioning) air duct passes through the fire compartment. The author believes that the smoke exhaust duct should not pass through the firewall. If it must pass through, a fire damper that can automatically close when the smoke temperature exceeds 280 ℃ should be set at the place where it passes through the firewall, and it should be interlocked with the smoke exhaust fan. However, some projects have neglected this in the design. For example, a smoke exhaust system in the basement of a project is responsible for the smoke exhaust of three rooms and one inner corridor (the doors between each room and the inner corridor are fire doors), a smoke exhaust fire damper is set on the smoke exhaust main pipe, and the smoke exhaust outlets of each room and corridor are single-layer louver vents, and there is no smoke exhaust fire damper at the place where the smoke exhaust pipe passes through each firewall. The problem caused by this is that the fire doors in each room are in vain. Once a fire breaks out in one room, it will affect other rooms through the smoke exhaust pipe. The correct approach is: add smoke exhaust fire damper behind the single-layer shutter smoke exhaust outlet (where the smoke exhaust duct passes through the firewall) (280 ℃ automatically closes) or change the single-layer shutter air outlet to a special smoke exhaust outlet (normally closed, automatically open the smoke exhaust when on fire, and re close at 280 ℃). 2、 Problems in engineering design

2.1 there are too many heating inlets

when setting heating inlets, we should consider the rationality of both the indoor heating system and the connection with outdoor pipelines. We should not only consider the convenience and convenience of the indoor system design, but also ignore the outdoor pipe system. However, there are too many heating inlets in some projects. For example, in a 7-story complex building, the indoor heating system is divided into 10 loops (4 on the first to second floors and 6 on the third to seventh floors), and the heating inlets are also set up as many as 10. There are too many connection points with the external line, and there are several directions, which not only causes trouble for the external line construction, but also brings inconvenience to the future indoor system adjustment

2.2 unreasonable design of heating system

unreasonable design of heating system: ① some heating systems are introduced by a main riser (trunk), divided into several loops, and there are no valves on the loops, which makes it inconvenient for system operation adjustment, maintenance and management. ② Some heating pipes are arranged unreasonably, which is difficult to coordinate with the construction profession, or the heating riser is directly erected on the window, which affects the use and is not elegant; Or the horizontal heating pipeline is laid on the ground of the channel, which not only affects walking, but also inconveniences the placement of goods. ③ Some high points of water supply and return mains are missing exhaust devices, which are difficult to eliminate once gas is collected, affecting the use of the system. ④ Some heating systems are of the same program, with a one-way loop length of 300 m, making it difficult for the gradient of the water supply and return mains to meet the requirements of not less than 0.002 specified in the specification. ⑤ Some heating systems are connected on both sides, and the heat load and the number of radiators on both sides differ greatly, while the two radiator supply and return branches use the same pipe diameter, and the hydraulic imbalance on both sides makes it difficult to distribute according to the design flow

2.3 the design of the exhaust system is unreasonable

for example, several living rooms and equipment rooms such as the concealed toilet (toilet) in the basement of a project are equipped with an exhaust system, the horizontal air duct is 60 m long, the section is only 200 mm 200 mm, and the wind resistance is large; It is incongruous to choose the roof fan for ventilation, but install the fan on the outer wall. In other projects, there are several private rooms (all darkrooms) in the basement, and each private room adopts

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