Prevention and Treatment of Common Quality Problems in HVAC Installation

2025-05-09

Section 1 Common Quality Problems in the Installation Project of Air Conditioning Water Equipment and Pipelines
I. Installation of Packaged Air Conditioning Unit

The surface is uneven, there are gaps in the connection of each air handling section, and there are obvious gaps between the air handling components and the wall panels
Analysis of the causes:

The coordinate position deviation of the air conditioner is too large, failing to meet the requirements of the "Construction and Acceptance Specification" for the allowable deviation of the plane position and elevation of the equipment installation datum line;
Some products of each air handling section of the air conditioner are loose parts assembled on-site, resulting in an uneven surface of the wall panels, and even an excessive deviation in geometric dimensions;
The thickness of the sealing gasket at the connection between each air handling section of the air conditioner is insufficient;
The gaps in the connection between the air filter, surface cooler, heater inside the air conditioner and the air conditioner box are not sealed;
The pitch of the water baffle plates is unequal, the fold angle does not conform to the design requirements, and the installation is reversed;

Poor vibration damping effect
Analysis of the causes:

The air conditioner has no vibration damping measures;

Air leakage from the drain pipe
Analysis of the causes:

There is no water seal device in the drain pipe; the height of the water seal should be determined according to the air pressure of the air conditioning system. The height of the water seal is not set according to the height required by the air conditioning box. Generally, the net height should be 150mm.

Condensation on the outer surface of the air conditioning box in the suspended ceiling
Analysis of the causes:

When ordering the equipment, a separate requirement should be made for the air conditioning box in the suspended ceiling regarding the condensation on its outer surface. It is required to thicken the thermal insulation of the air conditioning box. Condensation on the air conditioning box in the suspended ceiling is not allowed.

Poor cooling effect and very good heating effect of the air conditioning box
Analysis of the causes:

The connections of the cold and hot pipes are wrong.
II. Installation of Fan Coil Units

Water leakage at the connection of the cold (or hot) water branch pipe of the fan coil unit
Analysis of the causes:

The fan coil unit is rigidly connected to the cold and hot water branch pipes. If the threaded sleeve is slightly skewed, it will cause damage to the coil interface and water leakage;
The quality of the metal flexible joint of the fan coil unit is poor, and cracks are likely to occur. Or the rubber gasket of the flexible joint of the fan coil unit is unqualified, and the sealing will be poor if the pipeline is slightly eccentric.

The condensed water in the condensed water pan cannot be discharged and overflows, and the fan coil unit is not easy to maintain.
Analysis of the causes:

The slope of the condensed water pipe is reversed or the slope is too small, and the condensed water cannot be drained, but overflows from the condensed water pan.
After the installation of the condensed water pipe, the water passing test was not carried out as required.
The condensed water pipe was not temporarily plugged, and garbage entered the water accumulation pan during construction, and then blocked the pipeline.
III. Poor Cooling Effect of the Cooling Tower

The cooling water temperature is on the high side, and the condensation temperature and condensation pressure of the air conditioning refrigeration system rise.
Analysis of the causes:

The axial flow exhaust fan on the cooling tower does not rotate or rotates in reverse; before the cooling tower runs, the motor monomer must be tested to confirm the correct rotation direction of the motor;
The holes of the water distributor are blocked. During the water passing test or commissioning operation, it should be checked and processed to make the water distributor unobstructed;
The rotation speed of the rotating water distributor is abnormal.
The flow rate of the cooling water pump is insufficient, and too little heat is carried away.
The make-up water volume is insufficient, resulting in an insufficient cooling water system.
If there is often a lack of water in the system, carefully check whether there are any wrongly connected pipelines, resulting in water loss.
IV. Common Quality Problems in the Installation of Valves

During the operation of the system, the valve is not flexible to open and close, does not close tightly, and there is a phenomenon of water (steam) leakage, resulting in rework and repair, and even affecting the normal water (steam) supply.
Analysis of the causes:

The valve is installed without a pressure test before installation.

The valve installation method is wrong.
The flange of the butterfly valve uses a common valve flange.
V. Common Quality Problems in Pipeline Installation
The width and height of the weld do not meet the requirements of the construction specification
Analysis of the causes:

The misalignment of the pipes is not on the same center line, which directly affects the welding quality and the appearance quality. If there is no gap left for the butt joint, the thick-walled pipe is not beveled, and when the width and height of the weld do not meet the requirements, the welding cannot meet the strength requirements.

The weld cracks or the pipeline twists, and the pipeline support loosens during the operation of the pipeline
Analysis of the causes:

The installation of the expansion joint does not meet the design requirements.
The temperature rises too quickly when the steam system is first put into operation.
The material of the expansion bolts for fixing the pipeline support is of poor quality, the aperture of the installed expansion bolts is too large, or the expansion bolts are installed on a brick wall or even a lightweight wall.

The operation effect of the system is not ideal during the operation of the system, and there is air blockage in the pipeline.
Analysis of the causes:

No air release device is installed at the highest point of the pipeline or where air may accumulate, and no water drain device is installed at the lowest point or where water may accumulate.

Leakage occurs during the use of the pipeline
Analysis of the causes:

The strength of the flange and gasket of the pipeline connection is insufficient, and the connecting bolts are short or have a small diameter. Rubber gaskets are used for thermal pipelines, asbestos gaskets are used for cold water pipelines, and double-layer gaskets or bevel gaskets are used, and the flange gasket protrudes into the pipe.
During the hydraulic strength test and tightness test of the pipeline system, only the pressure value and water level change are observed, and the inspection for leakage is insufficient.
The condensate pipe is concealed without a water tightness test.

The water quality does not meet the operation requirements of the pipeline system, and it often causes a reduction in the pipeline cross-section or blockage.
Analysis of the causes:

The flushing before the completion of the pipeline system is not carried out carefully, and the flow rate and speed do not meet the requirements for pipeline flushing. Even the water discharge of the hydraulic strength test is used instead of flushing.

The pipe is frozen and damaged because the water in the pipe freezes quickly during the hydraulic test.
Analysis of the causes:

The hydraulic test is carried out at negative temperatures during winter construction.
After the pipeline is tested for water in cold regions, the accumulated water in the pipeline is not drained in time in winter.

The water pipes in the room are the same, but the construction methods are different, and the dimensions of the open ends are not uniform, resulting in rework.
Analysis of the causes:

A sample room is not made for the same type of rooms with the same pipelines.

The weight of the pipes and valves connected to the water pump is directly borne by the interface of the water pump, and the flexible short pipes connected to the inlet and outlet of the water pump are twisted and deformed.
Analysis of the causes:

Fixed supports are not installed for the pipes and valves at the inlet and outlet of the water pump.

Section 2 Common Quality Problems in the Installation Project of Air Conditioning Air Equipment and Pipelines
I. Installation of Fans

The fan burns out during operation
Analysis of the causes:

It is not clear how to connect the cooling fan of the variable frequency fan to the power supply, and it is omitted. When the variable frequency fan may operate below 30HZ, its cooling fan should be connected to the power supply separately.

Insufficient air volume of the fan
Analysis of the causes:

The resistance of the pipeline installation is too large, and the measures to reduce the pipeline resistance such as guide vanes are not in place.
The selection of the fan has not been reviewed, and the head of the selected grade is insufficient during the selection.

Relatively large noise of the fan
Analysis of the causes:

The muffler is not correctly selected and installed.
The sound insulation treatment of the air duct is not well done.
The wind speed is too high, and the wind speed is not reviewed during the design of the air duct.

Incorrect installation of the air valve, and different types of valves are mixed up
Analysis of the causes:

The installation positions and functions of the 70°C fire damper, 280°C fire damper, 70°C fire regulating damper, electric on-off air valve, and electric regulating air valve are not clear.
The valve label does not indicate clearly, and the workers do not understand the differences between these valves.

There is a large amount of accumulated water or oil at the lowest point of the exhaust oil fume duct
Analysis of the causes:

There are upward and downward elbows on the air duct, and the drainage measures are not taken as required.

Misalignment at the connection between the fan and the air duct
Analysis of the causes:

When installing the air duct, the cutting is not accurate, resulting in skewing.
The support of the air duct is not well done, resulting in the deformation of the air duct.

Air leakage in the installation of the air duct
Analysis of the causes:

The sealing filler of the air duct is not overlapped well.
The air duct flange is not flat when fabricated, resulting in poor sealing.
The lock seam of the air duct is not properly knocked, resulting in poor sealing.
The corner cover of the common plate flange air duct is not knocked in place.
The sealant at the flange corner is not well applied.

The installation of the air outlet is not aesthetically pleasing and the function cannot meet the requirements
Analysis of the causes:

The order size of the air outlet in the areas of the aluminum plate suspended ceiling and the mineral wool board suspended ceiling must be ordered according to the module.
The selection of the air outlet form should not only be determined according to the application occasion of the air outlet but also consider the fine decoration. The air outlet in the kitchen should use adjustable double-layer louvers.
When ordering the air outlet, the installation position, the installed system, and the size should be indicated.

Section 3 Common Quality Problems in the Thermal Insulation Project
The quality of thermal insulation seriously affects the impression of the entire project quality in the eyes of the owner, and once the phenomenon of condensate water leakage is found, it is very difficult to solve it through repair. Therefore, the analysis of the condensate water leakage caused by thermal insulation is specifically as follows:
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The loose materials contain too much moisture; due to the damage of the moisture-proof layer of the thermal insulation layer or random stacking, rainwater or moisture invades, resulting in poor thermal insulation performance of the thermal insulation layer;
The joints of the spliced plate-shaped or block-shaped materials are not tight;
Before construction, a detailed technical disclosure was not made to the workers, and the selection of thermal insulation materials was unclear, resulting in an uneven thickness of the thermal insulation structure, and even less than the specified thickness;
Improper protection of the finished product, the moisture-proof layer is damaged or the joints are not tight;
The thermal insulation structure is not firm and the thickness is uneven;
The protective shell is uneven and the surface is rough;
For the protective shell wrapped with aluminum plates or galvanized iron sheets, the joints are not straight;
The loose thermal insulation materials must be dried in the sun or baked before use to remove the moisture.
The rubber pads are not installed as required for the fixed supports in the main pipe well, resulting in cold bridges.
The specifications of the sleeves are not set according to the specifications, resulting in the thermal insulation materials unable to pass through.
The thermal insulation on the upper surface of the air duct is not fixed as required, but is directly fixed with transparent tape.
The thermal insulation has not been repaired after the filter is cleaned.
The air conditioning water drain pipe has not been thermally insulated.
All kinds of valves and pipeline accessories have not been wrapped as required.
There are gaps between the thermal insulation materials and the wooden supports of the pipeline.