Purpose <p>The air-cooled heat pump unit is widely used in the central air-conditioning system in large buildings such as shopping malls and hospitals. However, the noise emitted from the air-cooled heat pump units affects the life and work of the surrounding residents seriously. Therefore, it is of great importance to reduce the noise emission of the air-cooled heat pump units.</p> Method <p>In this study, the noise characteristics of a heat pump unit (type: YSPA0405HE) were measured. It was found that the sound pressure level reached 68&#xa0;dB at the residential buildings and most noise energy concentrated in the 250–1000&#xa0;Hz frequency band. To reduce the noise emission, we designed a semi-enclosed acoustic enclosure to isolate noise, in which labyrinth-style inlet and outlet channels were adopt to reduce noise spreading and ensure adequate air intake.</p> Results <p>The noise level at the residential buildings was measured with and without installation of the acoustic enclosure. Results shown that more than 10&#xa0;dB noise reduction is achieved at the residential buildings, which reached the national standard for the noise level of the second-class acoustic environment area.</p> Conclusion <p>This study provides a reference engineering example for the noise reduction of related heat pump units.</p>