23 September 2011

DOAS HEAT PUMP WITH VARIABLE REFRIGERANT FLOW (VRF)


The paper is analyzing the concept of variable refrigerant flow Dedicated Outdoor Air System (DOAS) with Heat Pump function for summer cooling and winter heating. In recent years the air quality requested by implementing ASHRAE Standard 62.1 norms for fresh air led to large applications for DOAS. The implementation of DOAS comes with an increase of energy consumption and high cost of operation. Keeping in mind the reduction in energy consumption, one of the first premises is to recover the energy from the cold air or the hot air exhausted from the space served by the DOAS. Recognizing this fact the paper goes further to investigate other solutions in reducing the energy consumption. The climate characteristics for different locations are the base parameter for DOAS sizing. As a result the equipment is sized for the most unfavorable situation resulting in an operation of the equipment at 99% below its size. The application is for a region in the Eastern coast of the USA.
The new technology of variable refrigerant flow is a perfect fit to follow the outdoor conditions for that specific location. The paper is analizing refrigerant schematics and the component selection for DOAS with VRF. The main reduction in energy consumption comes from the ompressor
running with variable flow. The paper analizes the two compressor schematic and practical results. Next, the selection of the expansion devices and air coils which shall adapt in corresponding
manner to VRF. In conclusion, the paper advocates for a preferred selection of Variable Refrigerant Flow technology, heat recovery and water source Heat Pump for most of the DOAS.