Piping for air conditioning: what materials and dimensions are best?

Nowadays, air conditioning systems are standard technical equipment in modern households and commercial premises, especially during the summer months when temperatures are well above comfort levels. However, the efficient operation of air conditioning depends on a number of technical parameters. One of the key elements that fundamentally influences cooling efficiency is the air conditioning ductwork.

In this article, we will focus on the specifics of the ductwork that provides the connection between the indoor and outdoor air conditioning units. We will explain what requirements quality copper piping must meet, the importance of proper sizing, and why professional installation is key to the flawless circulation of refrigerant, the system’s working medium. We will also discuss the selection of suitable accessories and fittings that ensure a mechanically strong and tight connection between the individual components of the air conditioning circuit.

Air conditioning performance and its technical significance

Before we look at the issue of air conditioning ductwork in more detail, it is essential to understand the importance of the performance of the air conditioner itself. The power of an air conditioner, stated in kilowatts (kW), represents the amount of heat energy that the unit can efficiently remove from the interior.

Air conditioners with a nominal output of 5 kW are designed for cooling medium to large rooms, usually in the range of 40 to 60 m². However, several variables affect the actual cooling performance, such as the quality of thermal insulation, the orientation of the building to the sunlight, the height of the ceilings, the number and size of windows or the internal heat sources.

The correct choice of air conditioning performance is an essential prerequisite for efficient and energy-efficient operation, and is directly related to the requirements for the sizing of the ductwork.

Types of ducts for air conditioning

When designing and installing air conditioning systems, the selection of the right air conditioning ductwork is a crucial step that affects not only the cooling efficiency, but also the reliability and durability of the entire system. In practice, a variety of materials are used, each with its own advantages and limitations:

Copper piping: represents the standard in air conditioning technology. It is characterized by excellent thermal conductivity, high mechanical resistance and long service life. These properties make copper air conditioning piping the preferred choice for professional installations.

Plastic pipe: can be a more cost-effective alternative, but has significantly lower thermal conductivity and limited resistance to high temperatures and mechanical stresses. Its use is recommended only in specific cases where high demands are not placed on the performance and durability of the system.

Aluminium pipe: this type of pipe is hardly used as it has a lower thermal conductivity and a lower corrosion resistance compared to copper pipe. Nevertheless, it may be a suitable choice for some low-cost installations where maximum heat transfer efficiency is not required.

Pipe diameter for air conditioning

One of the crucial parameters that affects the efficiency and stability of an air conditioning system is the correct choice of the diameter of the air conditioning ductwork. Inadequate sizing, especially in the form of too narrow ductwork, can lead to increased dynamic resistance and restricted refrigerant flow, resulting in reduced equipment performance and inefficient cooling.

When designing duct routes, it is therefore essential to follow the recommended dimensions depending on the duct type and the performance of the air conditioning unit. For commonly used systems, the following technical recommendations apply:

Copper piping for air conditioning: the optimum outer diameter of copper pipes ranges from 06 to 15 mm, depending on the specific system configuration and the length of the piping route.

Plastic ducting for air conditioning: due to the different physical properties of plastic materials, such as lower strength and thermal conductivity, it is advisable to choose a larger diameter in the range of 20 to 25 mm to compensate for the reduced efficiency in transporting the refrigerant.

The exact sizing of the air conditioning ductwork should always be carried out by a specialist based on the project documentation, the technical parameters of the equipment and the conditions of the specific installation.

Effect of duct length on air conditioning performance

In addition to the correct diameter, the length of the air conditioning ductwork also has a major impact on the system’s functionality. As the pipe route lengthens, the pressure and heat energy transferred by the refrigerant is lost, which can adversely affect the cooling performance of the equipment.

In the case of excessively long air conditioning ducts, the efficiency of refrigerant transfer between the indoor and outdoor units can be reduced, resulting not only in reduced performance but also in increased energy consumption and faster compressor wear and tear.

For this reason, when designing the installation, it is advisable to design the pipework to be as short as possible and to follow as direct a route as possible. Minimising bends, elbows and height differences is important to maintain optimum operating conditions.

Pipe insulation for air conditioning

Effective insulation is an integral part of a quality installation and is essential to ensure the energy efficiency and operational reliability of the entire system. The air-conditioning piping through which the refrigerant flows must be thoroughly insulated to eliminate heat loss and prevent condensation from forming on its surface.

Condensation forming on uninsulated or inadequately insulated ductwork can lead to wet building structures, mould growth or even damage to the air conditioner’s electronic components over time.

Flexible insulation materials with low thermal conductivity and high resistance to moisture and mechanical stress are most commonly used to insulate air conditioning ducts. Polyethylene foam, gel foam or closed cell elastomeric foam are considered standard materials that effectively prevent both heat and moisture penetration.

The correct insulation thickness is determined by the diameter of the pipe, the operating temperature of the refrigerant and the environment in which the pipe is routed, for example, the exterior requires an even higher level of protection.

Fittings for air conditioning piping

When installing air-conditioning piping, especially in the case of copper piping, suitable fittings are essential to ensure quality and tight joints at branches, bends or transitions between different pipe diameters. The most commonly used fittings are copper or brass fittings which, thanks to their technical properties, can cope with operating temperatures of up to +150 °C and pressures of up to 40 bar.

Advantages of copper fittings:

• excellent corrosion resistance,

• stability of the material even when exposed to UV radiation,

• long service life,

• reliable joint tightness without refrigerant leaks,

• compactness and a wide range of shapes and sizes.

There are two main ways of connecting ducts for air conditioning. By detachable (e.g. threaded) and inseparable (capillary soldering or press connections). Detachable joints allow quick assembly and easy disassembly, but their long-term reliability can be affected by thermal expansion and material fatigue.

In professional installation, the choice of fittings is therefore tailored to the specific technical conditions, service requirements and life expectancy of the system.

Types of pipe fittings for air conditioning

For proper installation and maintenance of the air conditioning ductwork, it is essential to use the appropriate types of fittings. The selection of specific components depends on the method of connection (soldering, crimping, threading), the pipe dimension and the operational requirements.

The most commonly used fittings:

90° elbow – allows pipe routing at right angles, available in both soldered and threaded versions.

Coupling – for direct connection of two pipe sections of the same diameter.

T-piece – divides the pipe into two branches, it is used for refrigerant discharges.

Adapter – used to connect pipes of different diameters, e.g. 1/4″-3/8″.

Reducer – a component for connecting pipes with different threaded ends.

Threaded fittings are preferred where future disassembly is required. Their disadvantage is their lower resistance to mechanical and thermal stresses compared to permanent (soldered and pressed) joints.

Special components:

Schrader valve – service valve for connection of pressure gauges, evacuation and refilling of refrigerant.

Plug – used to close off the pipe in inactive sections or during maintenance.

Filling adapters – a set of connectors for connection to both the high and low pressure branches of the system when refilling refrigerant.

Each type of fitting performs a specific function, so it is essential to choose them with regard to the technical requirements of the specific air conditioning installation.

Influence of environment and climatic conditions on air conditioning piping

When designing and installing ductwork for air conditioning, it is essential to take into account external factors such as climatic conditions and the location of the system. The outdoor environment, especially high humidity, extreme temperatures or dustiness, can significantly affect both the duct’s lifetime and its reliability.

In areas with permanently humid climates or frequent rainfall, it is necessary to consider additional corrosion protection (e.g. special coatings or protective covers), an increased level of insulation to prevent condensation on the pipe surface and thus prevent damage to the building elements. Prior consideration should also be given to the selection of a material with a higher resistance to external influences. Typically, copper piping with UV stabilised insulation is recommended.

When installing in indoor areas with fluctuating temperatures or in heated technical rooms, it is important to address the thermal expansion of the pipe and the correct anchoring to prevent mechanical stress on the joints.

Taking the environment into account is a key prerequisite for the long-term functionality and maintenance-free operation of the air conditioning system.

Final recommendations on the selection of ductwork for air conditioning

Choosing the right ductwork for your air conditioning system is one of the key factors that affect the overall performance and reliability of your air conditioning system. In the case of conventional units, it is not only important to choose the correct diameter and duct material, but also to pay attention to the quality of insulation, the installation method and the adaptation of the system to the specific environmental conditions.

Careful planning of the pipe routing, the use of quality fittings and professional installation are prerequisites for efficient, economical and long-term trouble-free cooling. Consultation with experts is recommended to help you design the optimum solution tailored to your space.

Remember that efficient cooling is not only the result of technical components, but also of precise installation and regular maintenance of the entire system. Make sure you have quality components and take the first step towards reliable cooling of your space with the experts from Slovklima.sk.