REQUIREMENT OF HEAT PUMP SYSTEM PERFORMANCE FOR AN ENERGY EFFICIENT SEAWATER-SOURCE HEAT PUMP DISTRICT HEATING SYSTEM

As renewable energy utilization technology, whether a seawater-source heat pump district heating system (SSHPDHS) is really energy efficient has great significance on the popularization of the system along the seaside area in cold climate. The paper makes an comparative study between the SSHPDHS and China's traditional boiler-house district heating system (TBHDHS) by calculating the primary energy consumption of the two systems for supplying the same amount of heat load to end users. Not only the lower limits of comprehensive coefficient of performance for the heat pump unit and seawater pump (named as COPI) are derived and calculated under the four typical heating district radii: 0.90km, 2.80km, 4.75km and 6.70km which correspond to the four different values of EHR' (i.e., the primary energy consumption ratio of transportation to the heat supplied: 5%, 10%, 15% and 20%), but also the definite COP requirement of the heat pump unit (i.e., CON can be ultimately calculated given the power of the seawater pump. The calculations show that the COPI values of a SSHPDHS with supply and return hot water temperature difference of 10 degrees C should reach 2.69, 2.75, 2.82 and 2.90 when the index of EHR' is set as 5%, 10%, 15% and 20% respectively with the coal-firing boiler's heating efficiency of 78% (The heating efficiency is in accordance with China's national design standard) and the hot water temperature difference of the TBHDHS being 25 degrees C. The study confirms that a smaller heating district scale and lower power consumption of the seawater pump facilitate designing a more energy efficient SSHPDHS. It is suggested that a careful calculation should be done to judge whether a SSHPDHS is more energy efficient than a TBHDHS instead of a rough estimation for a given project.