South Korean researchers have developed a heat trading system that includes a ground source heat pump, solar heat collectors, a fuel cell system and two heat storage tanks for district heating during peak solar production hours.
District heating is a type of heating network that usually uses natural gas as a source of electricity for a central heating plant or energy center. The heat is distributed through a network of pipes that connect the energy center to the various buildings, creating a heat network commonly referred to as “urban central heating”.
The researchers configured a network of heating pipes in three KITC buildings located in Lsan, South Korea. The network uses a 310 kW geothermal heat pump, a pair of solar heat collectors and a 10 kW natural gas fuel cell system as a heating source. Two 994 square meter solar heating systems were installed on the parking lot and roof of one building, according to the KICT press release. The heat exchange system also includes two hot water storage tanks with volumes of 40 m3 and 10 m3.
“When there is enough sunlight, warm water for heating is fed by solar heat to the secondary pipe of the district heating through the heat exchanger,” says KICT in its statement. “When there is not enough sunlight, hot water can be supplied through a heat pump system and a fuel cell system.” The solution can be controlled both manually and automatically in an integrated control center, according to KICT.
Solar electricity in residential buildings combined with heat pump systems often produces excess heat, because the building’s usually higher heat demand at night and the stronger heat demand based on renewable energy sources during the day do not match each other. KICT’s solution is designed to minimize heating losses by allowing buildings to export excess heat to the heating network through a so-called secondary pipe.
“The system has the potential to increase the use of renewable thermal energy in cities and buildings, ultimately reducing their carbon dioxide emissions,” said researcher Yongki Kim.
The team first presented a computational fluid dynamics model to estimate the required pipe insulation of the system in the paper “Pipe Insulation Evaluation for Low-Temperature District Heating Implementation in South-Korea,” published Frontiers of energy research.
It now claims that the demonstration project shows that “a two-way (two-way) pipe is effective in a network of low-temperature heat pipes with a heat loss of around 10 percent”.