Afternoon tea problems often exist in air conditioning design

The author of okmarts.com came into contact with the HVAC engineering design of some design institutes, and compared the "Code for Design of Heating, Ventilation and Air Conditioning" GBJ19-87 (hereinafter referred to as "Code for Design") and "Code for Fire Protection Design of High-Rise Civil Buildings" GB50045-95 ( Hereinafter referred to as "High Regulations"), "Heating, Ventilation and Air Conditioning Drawing Standards" GBJ114-88 (hereinafter referred to as "Drawing Standards"), "Provisions on the Depth of Construction Engineering Design Documents" (hereinafter referred to as "Design Depth Regulations"), etc. Specifications, regulations, standards, and found that the current HVAC designers have many problems in implementing the current specifications, regulations, and standards, as well as system design, equipment selection, and pipe network layout. The problems found and their cause analysis and solutions are summarized as follows.

1. Problems in implementing HVAC design codes and standards

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

The "Design Code" stipulates that in winter, indoor air calculation parameters, washrooms and toilets should not be lower than 12℃, and bathrooms should not be lower than 25℃. However, some public buildings' toilets, washrooms (with external windows and external walls), and residential buildings' toilets (hot water supply for bathing in winter, should be regarded as bathrooms) are not equipped with radiators, and it is difficult to reach room temperature not lower than 12°C and 25°C requirements. In some residential buildings, the kitchen does not have a radiator. The author thinks it is inappropriate. The indoor temperature of the residential kitchen should also be installed with a radiator not lower than 12℃.

   The "Design Code" stipulates that the outdoor meteorological parameters of some major cities should be adopted in accordance with Appendix II of the code. According to this appendix 2, the outdoor heating temperature in Beijing in winter should be -9°C except for Yanqing and Miyun. However, some projects are located in the suburbs of Beijing, but using -12°C is obviously inappropriate.

  1.2 There are missing and wrong items in the heating load calculation

   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 penetrates into the room through the gap between doors and windows. However, some projects did not calculate this part of the heat consumption when calculating the heating heat load, resulting in a large heating load. The "Design Code" clearly stipulates the correction rate of each orientation for the calculation of the heat consumption of the envelope, north 0~10 %, east and west -5%, south -15%~30%, but some projects have changed the correction rate of each orientation to 20% north, 15% east and west, and -5% south, which violates the requirements of the specification.

  1.3 Incorrect choice of toilet radiator type

   "Design Code" stipulates that the room with high relative humidity should adopt cast iron radiator. However, steel radiators are used in bathrooms in many projects, and anti-corrosion measures have not been strengthened, which is inappropriate. I have seen that some office buildings use closed steel radiators for toilets, but within a few years of use, the radiator fins were corroded, and the remaining two smooth tubes were also severely corroded. Practice has proved that it is best to use cast iron radiators or aluminum radiators in such places.

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

   The "Design Code" stipulates that for stairwells or other places where there is a risk of freezing, the radiator should be heated by separate vertical and branch pipes, and no regulating valve should be installed. However, some projects share the same riser pipe between the stairwell radiator and the adjacent room heating room radiator, using double-sided connection, one side is connected to the stairwell radiator, the other side is connected to the adjacent room radiator, and the radiator branch pipe The valve is set. In this way, since it is difficult to ensure the airtightness of the stairwell, once the heating fails, the heating effect of the adjacent room may be affected, and the radiator may even freeze.

  1.5 The slope of the heating pipe laying does not meet the specification requirements

   The "Design Code" stipulates that the laying of heating pipes should have a certain slope, and the slope of the hot water pipe should be 0.003, not less than 0.002. However, in some projects, the slope of the heating and return pipes is only 0.001~0.0015. Of course, if the conditions are restricted, the hot water pipeline can even be laid without slope, but at this time, it should be ensured that the water flow rate in the pipe should not be less than 0.25m/s.

   1.6 There are problems with ventilation in the kitchen operation room

The "Code for Design of Catering Buildings" (JGJ64-89) clearly stipulates the ventilation of the kitchen operating room: (1) 65% of the calculated exhaust air volume is exhausted to the outside through the exhaust hood, and 35% is exhausted by the full ventilation of the room; (2) Generally, the suction speed of the exhaust hood opening should not be less than 0.5m/s, and the speed in the exhaust duct should not be less than 10m/s; (3) The supplemental air volume in the thermal processing room should be about 70% of the exhaust air volume, and the room negative The pressure value should not be greater than 5Pa. However, some engineering kitchens are not equipped with exhaust hoods, but only a few exhaust fans are installed on the outer wall; although some are equipped with exhaust hoods, the suction speed of the hood is far less than 0.5m/s. The air volume of the fan is insufficient. Most of the projects do not have a comprehensive ventilation device, and no air supplement device is considered, so it is difficult to ensure the indoor sanitary environment and negative pressure requirements.

  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 House" (GB50041-92) stipulates that no valve should be installed on the connecting pipe between the high-level expansion tank and the hot water system. The connecting pipe mentioned here refers to the expansion pipe and the circulation pipe. This article is also applicable to air conditioning chilled water systems. However, in some air-conditioning chilled water systems, the expansion pipe of the high-level expansion tank is connected to the water collector of the freezer room and a valve is installed, which is not allowed. Once the operation error, the system safety will be endangered.

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

   The "High Regulations" stipulates that the air pipe should not pass through the firewall or deformation joints. If it must pass through, fire dampers should be installed at the places passing through the firewall; when passing through the deformation joints, fire dampers should be installed on both sides. However, in some high-rise buildings, no fire dampers are installed where the air pipe passes through the firewall, and some air pipes are only equipped with fire dampers on one side when passing through the deformation joint, and not on the other side. In addition, the location of fire dampers in some projects is improperly set. According to the requirements, the fire damper should be set close to the firewall, and the thickness of the wall-through duct connected to the fire damper δ≥1.6mm, and the ducts within 2m 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 ducts are set up at will, far away from the firewall. The ducts in between are neither marked to be thick nor take any protective measures, and there are hidden dangers.

1.9 There is a problem in determining the air volume of the front room of the smoke-proof staircase

   The "High Regulations" stipulates the volume of pressurized air supply in the front room of the smoke-proof stairwell of high-rise buildings, and gives specific air volume values ​​according to the situation. The note to this article states that the wind speed through the door when opening the door should not be less than 0.7m/s; the article description specifies the number of doors to open, below 20 floors is 2, and above 20 floors is 3. The "High Regulations" also stipulates that the pressurized air outlet of the front room of the smoke-proof stairwell should be provided with one on each floor. According to these regulations, it can be calculated that the air volume of the front room air outlet of each floor should be L/2 (below 20 floors) or L/3 (above 20 floors, L is the total pressurized air volume of the front room). However, in some projects, the air volume of the air outlet in the front room of the smoke-proof stairwell is marked as L/n (n is the number of building floors), 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 stairwell is set to 16000m3/h, but the air volume of the front room of each floor is marked as 16000/12≈1300 (m3/h). Small. The correct label should be 16000/2=8000(m3/h), and the size of the tuyere should be configured accordingly.

  1.10 mistakenly confuse the calculation of the exhaust air volume of the smoke prevention zone with the calculation of the air volume of the smoke exhaust fan

The "High Regulations" clearly stipulates the air volume of the smoke exhaust fan: when a smoke control zone is responsible for exhausting smoke, it should be calculated based on the area of ​​the smoke control zone not less than 60m3/h per m2, and it should be responsible for two or more smoke control zones. When smoking, it should be calculated based on the area of ​​the largest smoke-proof zone per m2 not less than 120m3/h. Please note that this refers to the selection of the air volume of the smoke exhaust fan, and does not mean that the air volume of the smoke prevention zone is doubled (the exhaust volume of each smoke prevention zone is still not less than 60m3/m2 according to the smoke prevention zone area. h calculation), but when the exhaust fan is responsible for two or more smoke-proof partitions to exhaust smoke in the horizontal or vertical direction, the air volume of the smoke exhaust fan is determined based on the simultaneous exhaust of the two smoke-proof partitions.

However, some engineering exhaust fans are responsible for the exhaust of 2~3 smoke prevention zones with different areas in the horizontal direction, and the exhaust fan’s air volume is incorrectly designed according to the total area of ​​2~3 smoke prevention zones. Each m2 is not less than 60m3/h, rather than the largest smoke-proof zone area of ​​which is not less than 120m3/h, resulting in a small air volume of the exhaust fan, which is difficult to meet the requirements for fire protection. There are also exhaust fans (systems) that are responsible for the exhaust of more than two smoke-proof zones (inner walkways) in the vertical direction, and the exhaust air volume of each layer of smoke-proof zones (inner walkways) is not less than each m2 according to their respective areas. 120m3/h is calculated, instead of calculating based on the respective area per m2 not less than 60m3/h, the exhaust air volume of each smoke-proof zone (inner walkway) in the vertical direction is virtually doubled, resulting in the air ducts, The tuyere is configured too large.

1.11 Improper selection of smoke outlets for smoke exhaust systems in high-rise buildings

   "High Regulations" stipulates that (ventilation and air conditioning) ducts pass through the partition wall of the fire compartment

   Fire dampers should be installed. The author believes that the exhaust duct should not pass through the firewall. If it must pass through, a fire damper that can automatically shut off when the flue gas temperature exceeds 280°C should be installed at the place where it passes through the firewall and interlocked with the exhaust fan. However, some projects are negligent in the design. For example, a smoke exhaust system in the basement of a project is responsible for the exhaust of 3 rooms and 1 inner aisle (the doors between each room and the inner aisle are fire doors), and a smoke exhaust fire damper is installed on the exhaust main pipe, and each The exhaust vents of the rooms and walkways are all single-layer louvered vents, and there is no smoke exhaust fire damper where the exhaust pipe passes through each firewall. The problem that this brings about is that the fire doors in each room are the same. Once a fire occurs in one room, it will hit other rooms through the smoke exhaust pipe. The correct approach is to add a smoke exhaust fire damper (automatically closed at 280°C) behind the single-layer louver exhaust vent (where the exhaust duct passes through the firewall) or change the single-layer louver air vent to a special exhaust vent (usually closed, When it catches fire, it will automatically turn on the smoke exhaust and turn it off again at 280℃).

  2. Problems in engineering design

  2.1 Excessive heating entrance

   When setting up the heating entrance, it is necessary to consider the rationality of the indoor heating system as well as the rationality of the connection with the outdoor pipelines. It is not only convenient and labor-saving to design the indoor system without taking into account the outdoor pipe network system. However, some projects have too many heating entrances. For example, in a 7-story comprehensive building, the indoor heating system is divided into 10 loops (4 on 1st to 2nd floors and 6 on 3rd to 7th floors), and there are as many as 10 heating entrances. There are too many connection points with the outside line. There are all directions, which will not only cause troubles to the construction of external lines, but also inconvenience the adjustment of the indoor system in the future.

  2.2 Unreasonable heating system design

   The heating system design is unreasonable: ①Some heating systems are introduced by a main (main) pipe, divided into several loops, and there are no valves on the sub-rings, which causes inconvenience to system operation adjustment and maintenance management. ②Some 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 unsightly; or the heating horizontal pipe is laid on the ground of the passage, which affects walking and is inconvenient Item placement. ③Some supply and return water mains are leaky with exhaust devices at high points. Once the gas is collected, it is difficult to eliminate them and affect the use of the system. ④Some heating systems are of the same program, and a loop is 300m long, which makes it difficult for the slope of the mains supply and return water to reach the requirement of not less than 0.002 specified in the code. ⑤Some heating systems are connected on both sides, and the heat load and the number of radiators on both sides are very different, but the two radiator supply and return branch pipes use the same pipe diameter, and the hydraulic power on both sides is unbalanced, which makes it difficult to distribute according to the design flow. .

  2.3 The exhaust system design is unreasonable

For example, there is an air exhaust system in several living rooms and equipment rooms such as the dark toilet (toilet) in the basement of a project. The horizontal air duct is 60m long, and the cross-section is only 200mm×200mm. The wind resistance is relatively large; The fan is installed on the external wall, which is very uncoordinated. In some projects, there are several private rooms (all darkrooms) in the basement of the project. Ceiling exhaust fans are used in each of the private rooms. The exhaust air is discharged to the outside through a horizontal duct of tens of meters long. The section of the duct is only 150mm×150mm, which has high resistance. , The exhaust effect is poor.

  2.4 The choice of air conditioning system is unreasonable

If a project has a command hall, conference hall, computer room, etc., the ideal air-conditioning system should be a low-speed air duct system for rooms of this nature, but the design uses a fan coil system and does not have a fresh air supply system. Obviously it is unreasonable. Another example is that the interior design parameters of some rooms are required by Party A of a project: winter tn=18~22℃, φ=55%±5%, summer tn=25~26℃, φ=60%±5%; another part of the room tn =22±2℃, φ=40%~60%, cleanliness level is less than 10000, fresh air 40~60m3/(h·person). For these two types of houses, fan coil systems are all adopted in the design, and no fresh air supply system is provided. Such a system cannot meet the requirements of Party A.

  2.5 No fresh air is added when the toilet uses fan coil

   The temperature in the toilet must not only meet the temperature requirements, but also eliminate the odor and ensure the hygiene requirements. However, the toilets of some projects have neither exhaust air nor fresh air supply. It is inappropriate to simply use horizontal concealed fan coils for cooling and heating, causing the odor to circulate by itself.

  2.6 There is a problem with the setting and caliber selection of the balance valve

   The air conditioning chilled water system should be equipped with a balance valve, which should generally be installed on the return pipe. In some engineering fresh air units, the chilled water supply and return pipes are equipped with balance valves with the same diameter as the pipe diameter. The author believes that there is no need to install a balance valve on the water supply pipe, but only on the return pipe. The balance valve diameter should be determined by checking calculations.