Energy consumption in large scale data centers (LSDCs) doubled from 2000 to 2006 reaching 61 TerraWatt-hour (TWh) per year. Nearly all of the energy consumed by IT equipment dissipates as heat from the servers, creating a real problem of efficiently cooling LSDCs. Reducing the Power Usage Effectiveness (PUE) of a data center by even small fractions significantly reduces greenhouse gas emissions. We propose a novel Pulsed Variable Flow Rate (PVFR) dynamic cooling control strategy for liquid cooled LSDCs, based on the principle of pulsed power delivery instead of continuous power supply. We built a proprietary simulation software called DynaCool using model-driven design to evaluate the effectiveness of PVFR approach. An early evaluation shows that DynaCool achieves a PUE reduction of at least 15.4% over existing static and variable flow rate cooling control strategies. Assuming an adoption rate of 10%, PVFR would yield power savings of 1.88 TWh or greenhouse gas emission savings of 284,000 tons per year.