Are Fresh-Air Air Conditioners That Require No Larger Wall Opening Reliable?

Both approaches appear to have advantages and disadvantages. Enlarging the opening is the obvious choice because the additional fresh-air duct needs enough space. A larger opening allows higher fresh-air volume and lower noise, although it can reduce the installation's visual appeal.

For this reason, many air-conditioning brands now offer installation solutions that require no larger opening. Their purpose is to keep the room looking attractive and avoid further damage to the wall. To some extent, this approach does meet users' needs.

However, avoiding enlargement inevitably reduces the cross-sectional area available for the fresh-air duct. A narrower duct delivers less air per unit of time. Maintaining adequate fresh-air volume therefore requires a higher air velocity, which in turn creates more noise.

China's national standard GB/T 18883-2002, Indoor Air Quality Standard, specifies that indoor fresh-air volume should be at least 30 m³/(h·person), or no less than 30 m³/h for each occupant. In a bedroom occupied by two people, for example, a fresh-air air conditioner installed without enlarging the opening should deliver at least 60 m³/h. A living room requires even more fresh air.

According to the Allowable Air Velocities for Different Noise Standards in Air-Conditioning Fresh-Air Ducts, a main-duct velocity of 9 m/s corresponds to a noise requirement of 45 dB, which is already far from quiet. If a wall-mounted unit uses the existing opening and allocates even half of its cross-sectional area to the fresh-air duct, the air must travel at 11 m/s to provide suitable fresh-air volume, making the noise still higher.

The actual user experience of a so-called no-enlargement fresh-air air conditioner may therefore fall short of expectations. Its principal drawback is the difficulty of balancing fresh-air volume with noise.