Impressive results ! Comparison study of geothermal system Vs variable refrigerant flow (VRF)


Impressive results ! Comparison study of geothermal system Vs variable refrigerant flow (VRF)

The case of the office headquarters of ASHRAE organization.

The organization ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), founded in 1894 and headquartered in Atlanta. Is a leading global scientific institution dealing with energy efficiency, heating, cooling, indoor air quality and sustainable building design. In 2008 the organization started a renovation in the building by installing geothermal heat pumps and VRF systems (Variable Refrigerant Flow). Upon completion of the renovation, they carried a two-year study comparing these two systems. The results were impressive! Geothermal heat pump surpassed with a big difference in energy efficiency the VRF system.

The VRF systems serve the first floor and geothermal heat pumps the 2nd floor. The building includes 1,600 sensors that monitor the functions of air conditioning systems and conditions in each area and enable taking measurements constantly. The premises served by the geothermal heat pumps and the VRF don’t have exactly the same cooling and heating loads, so the researchers calculated the actual loads based on the functioning of each terminal unit and related sensors. They focused their research on identifying the actual cooling performance - heating, data analysis and calculations based on measurements from both systems. They collected data on the operation (on-off / heating / cooling), the zone temperature and air outlet temperature at each fan coil or heat pump. The study also included measurements from the geothermal heat exchanger, such as water supply and return temperature. Thus, although the energy consumed by each system is influenced by several factors, for example the exact area of ​​space, the occupancy of each office, cooling and thermal loads, control & operating condition strategies, the researchers reached a comparable size, making perfectly clear the actual effectiveness of each system.

The efficiencies calculated include all the energy used by both systems. For the period studied the VRF systems used 41% more energy for cooling during the summer period (May to September) and 172% more energy for heating in winter (October to April).

Monthly energy consumption per sqm diagram :

The main difference between the geothermal system and the VRF system lies in the heat exchange medium: soil instead of ambient air. It is clear that the temperature of the ground was more favourable than the temperatures of the ambient air to the heat pump. This allows the geothermal heat pump to operate at higher efficiencies. Due to the thermodynamic heat elimination advantages and exchange with the ground and not with the air, the system of the geothermal heat pump has far better operational efficiency, especially when the weather is cold and hot.

The President and CEO Doug Dougherty said: "The study of the cooling and heating performance in the ASHRAE office building shows that the geothermal system consumed 44% less energy on average than the VRF system for the period of two years, all variables calculated."

The conclusion of very significant study, the more detailed and reliable which has occurred in recent years, is that in every new building constructed, designers, engineers and owners are to consider geothermal energy as the preferred solution for heating & air conditioning. In no case VRV-VRF systems can be considered an adequate solution from modern buildings, lagging by far in energy consumption.


Related Links:

Full text of the study ASHRAE: here 

Learn how it works geothermal energy: here