Eight Quality Problems in HVAC Installation Construction and Corrective Measures

◆ Regarding the Fabrication and Installation of Air Ducts
◆ Regarding the Installation of the Air Conditioning Water System
◆ Regarding Vibration Damping and Noise Reduction
◆ Regarding the Thermal Insulation of the Air Conditioning System
◆ Regarding the Installation of HVAC Equipment
◆ Regarding the Condensation of Pools and SAP
◆ Regarding the Layout of Comprehensive Pipelines in the Underground Garage
◆ Regarding the Laying of Outdoor Air Conditioning (or Thermal) Water Pipes

People who have dealt with the construction party know that they are very "sly". Every time a quality problem is found, they verbally claim that the problem is not serious and there is no need to panic, but it often ultimately affects the actual use and even the delivery.

Regarding the Fabrication and Installation of Air Ducts
Problem 1: No protective sleeve is installed or the protective sleeve is too thin when the air duct is set in the fireproof and explosion-proof wall or floor.
Cause Analysis: It is considered that the thickness of the sleeve does not matter much, and in order to reduce costs, leftover materials between 0.75-1.2MM are used.
Corrective Measures: Strictly implement the provisions of the mandatory article 6.2.1 of GB50243. When the air duct passes through a fireproof or explosion-proof wall or floor that needs to be closed, a pre-embedded pipe or protective sleeve should be set, and the thickness of the steel plate should not be less than 1.6MM. The space between the air duct and the protective sleeve should be sealed with a non-combustible and harmless flexible material to the human body. Before construction, combine the installation and civil engineering drawings to determine which walls and floors in the project have fire protection requirements and need to set protective sleeves, and cooperate with the pre-embedding during the construction of the civil engineering structure.
The method of passing through the fireproof wall
The method of passing through the floor
The method of going out of the roof
Problem 2: The side length of the air duct or the single-side area is greater than the specified value in the code, and no reinforcement measures are taken, resulting in vibration and noise during operation.
Cause Analysis: It is considered that the side length or the cross-sectional area of the air duct has no direct impact on the operation, and the construction unit considers saving costs and cuts corners.
Corrective Measures: According to the provisions of Article 4.2.10 of GB50243-2002: When the rectangular side length is greater than 630MM, the side length of the insulated air duct is greater than 800MM, the pipe section is greater than 1250mm, or the area of the low-pressure air duct is greater than 1.2M2, and the area of the medium and high-pressure air duct is greater than 1.0M2, reinforcement measures should be taken.
When the diagonal length of the air duct is < 1500mm, 2 angle steels and 2 tie rods are used for fixation, and the air duct is fixed on the angle steels with bolts, solid rivets or self-tapping screws; when the diagonal length of the air duct is ≥ 1500mm, angle steels are used for fixation around the air duct, and the air duct is fixed on the angle steels corresponding to the long side of the air duct with bolts, solid rivets or self-tapping screws.
The spacing of the brackets is 4.56m, which is greater than 3m (required by the code).
Problem 3: The quality of the installation of the flexible connection of the air duct.
Cause Analysis: The applicable conditions of the flexible connection materials used in the general ventilation system and the fire protection smoke exhaust system are confused, and the on-site management is not in place.
Corrective Measures: The manufacturing material of the flexible short pipe of the smoke exhaust system must be a non-combustible material; it shall not be of ordinary canvas material, and a silicone-titanium or glass fiber flexible connection (a non-combustibility test is required) should be used.

Regarding the Installation Quality of the Air Conditioning Water System
Problem 1: Pipeline welding problems.
Cause Analysis: The pipelines are not aligned, there is no gap at the pipeline butt joint, the end face of the pipeline cut by gas cutting is uneven, resulting in an incorrect gap width or no beveling, making it difficult to weld the pipeline through. After the pipeline is welded, the welding slag is not cleaned up in time, and the antirust paint is directly applied.
Corrective Measures: Pipeline welding should be carried out in accordance with the provisions of Article 9.3.2 of GB50243: The assembly and bevel form of the pipeline butt weld joint should meet the provisions of the following table; the straightness of the butt joint is 1/100, and the full length is not greater than 10MM. The fixed weld joint of the pipeline should be far away from the equipment, and it is not appropriate to coincide with the center line of the equipment interface. The distance between the pipeline butt weld and the support and hanger should be greater than 50mm.
(Article 11.2.5.3 of GB50738-2011 "Code for Construction of Ventilation and Air Conditioning Engineering": The distance between the pipeline interface weld and the edge of the support and hanger is not less than 100mm).
Problem 2: The setting of the support and hanger for the equipment piping in the machine room is unreasonable.
Cause Analysis: The setting of the support and hanger for the equipment piping in the refrigeration machine room is unreasonable, and the support of the chilled water pipe does not have cold bridge prevention measures.
Corrective Measures: Generally, the civil installation design does not produce the processing and installation drawings of the load-bearing support and hanger. Preventive measures: Usually, the pipelines in the machine room are suspended by horizontal main pipes, and horizontal tees are opened to connect with the equipment on the ground.
The correct method: When DN150 ≤ the diameter of the vertical air conditioning water pipe
Problem 3: No water seal is set for the condensed water of the air conditioning unit, and there is a large amount of accumulated water in the machine room when the unit is shut down.
Cause Analysis: The water seal is not set according to the design requirements. The water accumulation tray is under negative pressure, and the height of the water seal should overcome the negative pressure height.
Corrective Measures: The height of the water seal of the condensed water discharge pipe of the air conditioning unit should meet the drainage requirements. For example, when the fan pressure is 800Pa and the diameter of the condensed water pipe is 50mm, H1 > 800/10 + 50 = 130mm, H2 > 800/10/2 + 50 = 90mm.
Problem 4: The selection of the thermometer setting is unreasonable, and the temperature test value is inaccurate.
Cause Analysis: The understanding of the drawings is not thorough, and the on-site construction is highly arbitrary.
Corrective Measures: Use a bimetallic dial thermometer and set the sampling point as close as possible.
Problem 5: Improper Selection of the Pressure-setting Point of the Air Conditioning Water System
The connection point between the expansion pipe on the expansion water tank and the system pipeline is not set near the suction port of the circulating water pump as required in the drawing during construction, and the water pump has the phenomenon of "cavitation".
Cause Analysis: The understanding of the drawings is not thorough, and the on-site construction is highly arbitrary.
Corrective Measures: The main principle for selecting the pressure-setting point is to ensure that there is no negative pressure or gasification at any point in the system. In the air conditioning water system, the determination of the pressure-setting point means that the lowest operating pressure at the pressure-setting point should ensure that the pressure at the highest point of the system is above 5kpa, and it is advisable to connect to the suction port of the water pump.
Problem 6: The Common Quality Problem of Improper Selection of the Filter Screen
The problem of improper selection of the filter screen aperture (4mm before the pump, 3-4mm before the chiller, 2.5-3mm before the air handling unit, 1.5-2mm before the fan coil unit)

Regarding the Common Quality Problems of Vibration Damping and Noise Reduction
Problem 1: The Inadequate Vibration Damping and Prevention in the Intermediate Floor Machine Room of High-rise Buildings
The vibration in the apartment or guest room areas above and below the intermediate floor or top floor machine room of high-rise buildings is relatively large.
Cause Analysis: The vibration damping and prevention measures are not in place, resulting in the equipment vibration being transmitted to the structure and causing resonance.
Preventive and Corrective Measures:
1. Select a floating floor, and adopt double-layer vibration damping measures for the foundations of equipment such as air handling units, fans, and water pumps.
2. Select low-noise water pumps and operate at the high-efficiency point.
3. Install hoses at the inlet and outlet of the circulating water pump.
4. Carry out sound absorption treatment on the four sides and under the top plate of the machine room. Use sound-insulating doors for the machine room doors, and fill the surroundings of the pipeline holes passing through the partition walls and floors of the machine room with sound absorption materials. Thoroughly reduce the impact of the noise in the machine room on the surrounding rooms.
Problem 2: The Common Quality Problems of the Vibration Damping Installation of Water Pumps
A. Parameters to be Considered in the Selection of Vibration Damping Devices
The material type of the vibration damping equipment, maximum deformation, allowable load, natural frequency, self-vibration frequency, damping ratio, and load-bearing range.
B. Precautions for the Installation of Vibration Damping Equipment
1. Precautions for the Installation of Vibration Damping Springs:
The installation of vibration damping springs must ensure that the springs are vertically stressed. When the horizontal disturbing force of the equipment is too large, it is necessary to consider setting a horizontal limit to avoid the spring from being twisted.
The installation position of the vibration damping springs must be suitable for the center of gravity of the vibration isolation system to avoid the eccentricity of the system and the generation of additional vibration.
The vibration damping springs with a limit device need to be pre-compressed first, and the limit device should be released after the equipment is installed.
2. Precautions for the Installation of Flexible Joints:
Considering that the flexible joint cannot bear lateral stress and torsional stress, the installation of the flexible joint must be straight.
Adjust the limit device of the flexible joint after the system installation is completed to ensure the vibration damping efficiency.

3. Precautions for the Installation of Rubber Vibration Damping Pads:
Consider the influence of temperature during installation, and do not make the rubber vibration damping pads exceed the service temperature.
When the rubber vibration damping pads are used in series, a steel plate must be installed in the middle to separate them, and the number of layers should not exceed three.
Considering that the rubber vibration damping pads have a large friction force, there is no need to set a fixation between the rubber vibration damping pads and the foundation.
The concave patterns of the rubber vibration damping pads must be clean without sundries to avoid affecting the vibration damping effect.
C. Preventive and Corrective Measures:
Strictly implement the provisions of Article 7.3.1-3 of GB50243. The ground for installing the vibration isolator should be flat, the compression amount should be uniform, and the height error should be less than 2MM. Select vibration isolators with a matching weight, the height in the free state should be the same, and the stress center of the spring vibration isolators should be consistent.
Problem 3: The Phenomenon of Excessive Noise of Indoor Air Conditioners
The noise of indoor air conditioners exceeds the specified value in the code.
Cause Analysis:
(1) The selection of the air conditioner is unreasonable, the noise of the air conditioner itself is too large, or the normal working point of the fan deviates from its highest efficiency point.
(2) No noise reduction measures are taken for the total supply air duct, total return air duct, and centralized return air louver door of the air conditioning unit, or the noise reduction measures do not achieve effective results.
(3) No vibration damping measures are considered for the air conditioning equipment, no flexible hoses are installed at the inlet and outlet of the air conditioning fan, and the noise caused by vibration is transmitted into the room through the building structure and the air duct.
Preventive and Corrective Measures:
(1) Reasonably consider the installation position and residual pressure of the fan coil unit according to the level of the room. For those with high requirements, noise reduction treatment can be carried out in the air duct between the air outlet of the fan coil unit and the air supply outlet of the room, and a sound-absorbing static pressure box can be added to the return air.
(2) The maximum wind speed at the neck of the air supply outlet is 3-4m/s, the wind speed at the upper part of the return air room is 4m/s, and the wind speed is 2-3M/S when returning air in the corridor at the lower part of the room. In places with environmental noise requirements, carry out noise measurement according to the provisions of GB9068 to meet the requirements of the design specified value.
(3) Take vibration damping measures for the hoisting of the fan.

Regarding the Common Quality Problems of the Thermal Insulation of the Air Conditioning System
Problem 1: Due to improper construction, the thermal insulation effect of the air conditioning chilled water is not good, and condensation occurs.
Cause Analysis:
1. The specifications of the thermal insulation materials are too small, and the seams are forced to close, resulting in cracking over time.
2. The quality of the glue used is poor, and the drying time of the glue is too short.
Requirements:
Strictly implement the provisions of Article 10.3.10 of GB50243. The thermal insulation products should meet the design requirements. The pipe shells should be firmly pasted, laid flat, without sliding, looseness or fracture. It is necessary to prevent the pollution of dust and mortar at the construction site.
Regarding the Construction Key Points of the Thermal Insulation of the Pipes in the Air Conditioning Water System:
1. The thermal insulation structure of the pipeline valves, filters and flange parts should be able to be disassembled separately.
2. Before thermal insulation, it is necessary to confirm that the surfaces of the air ducts and pipelines are clean and free of foreign objects.
3. After applying glue to the rubber and plastic materials, they can be bonded only after the glue has dried. The glue is considered dry when there is no sticky feeling.

4. During the construction of the thermal insulation pipes, apply glue evenly on the two cut edges of the pipes. First, stick the two ends of the pipes, then bond from the two ends to the middle, and finally fasten along the cut edges with professional adhesive tape.
5. When connecting two pipe ends, apply glue to both ends of the connecting pipes. The connection part should be in an extruded shape, and then wrap the pipe ends with professional adhesive tape for at least two circles.
Problem 2: Common quality problems regarding the thermal insulation of air conditioning air ducts
Problem 3: Do the plate heat exchangers and the pump bodies of the chilled and hot water pumps need thermal insulation?
GB50736-2012 "Code for Heating, Ventilation and Air Conditioning Design of Civil Buildings"
Article 11.1.1 stipulates that the following equipment and pipelines (including pipe fittings, valves, etc.) should be thermally insulated:
1. The outer surface temperature of the equipment and pipelines is higher than 50°C (excluding indoor heating pipelines);
3. When there is no thermal insulation, the heat loss is large and it is uneconomical;
Article 11.1.2 stipulates that the following equipment and pipelines (including pipe fittings, valves, etc.) should be cold-insulated:
1. When the cold medium is lower than the normal temperature and it is necessary to reduce the cold loss of the equipment and pipelines;
2. When the cold medium is lower than the normal temperature and it is necessary to reduce the condensation on the surfaces of the equipment and pipelines;

Common Quality Problems in the Installation of HVAC Equipment
Problem 1: Common quality problems in the installation of cooling towers
(1) The installation of the cooling tower brackets is incorrect.
(2) The horizontal distance between the cooling tower and the exhaust outlet of the fume exhaust fan is less than 6 meters, and the arrangement of the water pipes affects the air inlet of the cooling tower.
Problem 2: Common quality problems in the installation of water pumps (fans)
A. Problems with the configuration of the foundation and inertia block: The dimensions were not checked before the foundation casting and the production of the inertia block, and the setting is unreasonable.
Problems and solutions: The length of the straight pipe section at the suction port should not be less than 2 times the pipe diameter.
Article 10.8.5.2 of GB50738-2011 "Code for Construction of Ventilation and Air Conditioning Engineering"
C. Problems in the installation of the flexible connection of the water pump
Phenomena:
1. When installing the rubber flexible connection of the water pump, it is stretched and twisted, and the pipe bursts when the pump is started.
2. Selection and use of the metal flexible joint and the rubber flexible joint.
Installation instructions for the flexible rubber joint:
1. When installing the rubber flexible joint, it is strictly prohibited to install it beyond the displacement limit.
2. The pipeline must have a fixed support or a fixed bracket. Otherwise, an anti-pulling-off device should be installed to prevent it from being pulled off under pressure during operation.
3. Tighten the installation bolts symmetrically and gradually to prevent local leakage.

Common Quality Problems Regarding the Condensation in the Pool and SAP Spaces
Phenomena: In some hotel projects, there is a large amount of condensation in the air outlets and suspended ceilings of the pool and SAP, affecting the comfort of use.
Cause analysis: During the construction process, the design requirements of the installation drawings, the dew point temperature, and the selection of decorative materials were not checked. Under the premise of meeting the functional requirements, aesthetics should also be taken into account.
Prevention or solution ideas:
1. Use a heat pump for dehumidification to reduce humidity;
2. Optimize the air distribution to dry the condensation;
3. Increase the exhaust air volume to reduce humidity.
4. Use materials with better thermal resistance performance for the suspended ceiling, such as aluminum-plastic panels, and use materials with good thermal conductivity inertia for the air outlets (materials include wood, plastic-sprayed aluminum, plastic, etc.)
5. Increase the thermal insulation performance of the external envelope structure, etc.;
6. Drain the condensed water.
Article 12.5.4 The installation of the smoke exhaust pipe (duct) shall meet the following requirements:
1. The slope should be greater than 0.5%, and the drain valve should be set at the lowest point;
2. The blocking plate of the cleaning hole should have a heat-resistant cushion layer and be fixed tightly;
3. When the smoke exhaust pipe passes through the partition wall, the surrounding gaps should be filled densely with asbestos rope;
4. At the connection between the smoke exhaust pipe and the smoke exhaust duct, a closed short pipe passing through the wall with a flange and a closed wing ring should be pre-embedded.
Article 12.5.5 The ground outlet end of the smoke exhaust pipe should be equipped with a rain cap; at the position 150～200mm above the ground, measures should be taken to prevent the smoke exhaust pipe from being blocked.

Common Quality Problems Regarding the Pipelines in the Underground Garage and on the Roof
Phenomena: The spacing of the pipeline layout in the basement is unreasonable and messy, and the identification is not clear.
Cause analysis: During the integration of the pipelines, the identification, pipelines, and moving lines were not comprehensively considered, and the unity of function and aesthetics was not planned.
Phenomena of the integration of the pipelines on the roof: The spacing of the pipeline layout on the roof is unreasonable and messy, and the space utilization rate is low.
Corrective measures and preventive corrective measures for the integration of the pipelines on the roof: When deepening the integration of the pipelines, consider the division of the functional areas in the underground garage and the key points of the pipeline deepening
1. The main moving line
2. The general passage
3. The guiding signs. Then, the integrated pipeline layout should comply with the following principles:
Correct cases
Common quality problems of the outdoor pipeline air conditioning water system
Phenomena: The outdoor pipeline network was not backfilled according to the design requirements, and there is no compensation for the long straight hot water pipeline.
Cause analysis:
1. Ignore the compensation for the thermal expansion and contraction of the long straight pipeline.
2. The design generally requires construction in accordance with the installation acceptance specifications in the preparation instructions of the construction drawings.
Preventive corrective measures: Strictly follow the construction requirements of Article 6.2.2 of GB50242, and install compensators for the pipelines with excessive straight lengths in the hot water system. For example, if the straight length of the hot water pipeline is 30M, the temperature is 80 degrees, and the ambient temperature during installation is 20 degrees, its thermal elongation should be 0.012*(80 - 20)*30 = 21.6 (mm). Therefore, the installation of the compensators for the heat medium pipelines should be calculated according to the code requirements, process requirements, and pipeline layout, and installed at the required parts. And pay attention to the clearance requirements for the inspection of the inspection wells to facilitate the inspection.