This study introduces a novel, ambient-temperature district energy system topology that enables bi-directional mass flow to booster heat pumps and includes distributed solarthermal generation. The ambient system topology is described, and a corresponding detailed model is developed in the MATLAB-Simulink® environment. An equivalent model is developed for a conventional, supply-return district system utilizing hot water (at 75°C) and chilled water (at 15°C), allowing for the direct comparison with the proposed topology—both with and without solar-thermal integration—in technical, environmental, and economic analyses. Technical performance is assessed using a system coefficient of performance and solar fraction, environmental performance is estimated using carbondioxide equivalent emissions, and economic performance is characterized using a levelized cost of energy approach. Annual simulations are conducted for the case study of an urban district energy system in Ottawa, Canada, connected to 12 commercial building clusters. The ambient-temperature system achieves an annual system coefficient of performance of 1.40 without solar assistance and 1.43 with solar assistance. The conventional system achieves annual coefficients of performance of 1.26 and 1.28, respectively. The solar fractions of the ambient and conventional systems are 5.5 and 4.0% for heating and 9.3 and 10.0% for cooling, respectively. Despite these noted improvements in performance with solar-thermal, the technical findings indicate that the rooftop solar collection fields are undersized relative to system loads due to rigid rooftop space constraints. Nonetheless, the ambient system (without solar) decreases annual carbon emissions by 32.16% relative to the conventional system, a significant improvement. Furthermore, while the ambient system’s levelized cost of energy is higher than the conventional both without solar (8.1 vs. 6.0¢/kWh) and with solar (11.0 vs. 9.2¢/kWh), the ambient system becomes the most economically attractive option if the social cost of carbon is considered at any price above $16/tCO2-e—a rate far below the existing Canadian price of $50/tCO2-e.