Abstract The increased generation of renewable power is challenging in terms of the power balance and reliability of power grids due to the intermittent nature of renewable sources. Heating, ventilation, and air-conditioning (HVAC) systems in buildings, at demand side, are promising candidates for providing frequency regulation. In this study, we systematically assessed the use of variable-speed pumps in HVAC systems for frequency regulation. The dynamic characteristics of the pump were investigated. The results show that the power of the pump can response to the frequency change rapidly (returning stable within 1s), while the response of flow rate is slightly slower. A frequency regulation control strategy is proposed and implemented on a test rig. From the viewpoint of power grids, the experimental results show that the pump can provide high-quality frequency regulation (performance scores of 0.989 and 0.968). From the viewpoint of buildings, the experimental results indicate that the fluctuation magnitude of the air-handling unit outlet air temperature increases (from 3.3 K to 7.1 K) with increasing automatic generation control (AGC) signal frequency, whereas the fluctuation magnitude of the indoor air temperature increases to some extent and then decreases when the frequency of the AGC signal is above a certain level.