The existing PC-based desktop environment is being changed to a server-based virtual desktop environment due to various advantages such as security, mobility, and upgrade cost reduction. In this paper, a virtual computing lab service system which is applicable to the existing computer lab is designed and implemented using both an open source-based cloud computing platform and hypervisor. In addition, a node power scheduler is proposed in order to reduce power consumption in a server farm. The experimental results show that the power scheduler reduces power consumption considerably over the server farm without the power scheduler.