Thermodynamic analysis of ultralow-temperature district heating system with shared power heat pumps and triple-pipes

Abstract

An ultralow-temperature district heating system that uses neighborhood-scale heat pumps was recently proposed and investigated. Although the system was found more efficient than any existing solution, there is still potential in this concept for achieving better efficiency and cost-effectiveness. One of the main origins of losses here is through the enlarged pipes. In this work, triple-pipes are proposed to be used instead of twin-pipes to have individual domestic hot water and space heating pipes, reducing the size of heat pumps and decreasing thermal loss rates. The proposed concept is designed, sized and thermodynamically analyzed for a case study in Denmark. The performance is compared with the previous version of this concept as well as the low-temperature district heating system, which is another important competitor to the proposed solution. The results prove that the proposed system outperforms both of the competitors in terms of energy efficiency. For three consecutive days in typical warm/moderate/cold weather in the case study, the proposed solution results in the rates of heat loss of 4.5/10.9/16.5%, respectively. The heat loss rates, for the conventional configuration and the low-temperature design, are 4.9/13.8/19.6% and 5.6/17.8/33.1%, respectively.