Overview of district heat supply systems

Overview of district heat supply systems

A district heating and cooling system is a system in which heat supply sources are centralized in one location and managed centrally, thereby improving energy efficiency and contributing to the control of air pollution, rather than individual buildings installing their own heat source units. This system has been used in Japan since early times, and in 1972 the Ministry of International Trade and Industry (MITI) established a preferential system in terms of project approval and tariffs for district heating and cooling systems with a capacity of 5 gigacalories per hour or more. As of the end of 1999, the system was in operation in 135 districts nationwide.

Utilization of Unused Energy

Many district heat supply systems use gas or oil boilers as the heat source. Recently, however, the use of unused energy has been attracting attention as a way to address environmental issues such as energy resource depletion and air pollution. For example, low-temperature water heat from sewage treatment plants and waste heat from waste incineration plants, which were previously released directly into the atmosphere, rivers, sewage, etc., are now recovered and used in heat pumps for heat exchange and heating/cooling and hot water supply.

Status of Unutilized Energy in Japan

About 60% of primary energy in Japan is released into the atmosphere, rivers, and sewage as waste heat, and the Tokyo metropolitan area has about 43 trillion kilocalories of unused energy annually. This is about the same amount as the annual demand for heat used for heating, cooling, hot water supply, and other consumer uses in Tokyo. The Japan District Heating and Cooling Association estimates that combining district heating and cooling systems with unused energy would reduce energy consumption by about 30%, CO2 by 40-60%, and NOx by 60-80%.

Specific Installation Examples

Koraku 1-chome district (Bunkyo-ku, Tokyo)
Heat source: Untreated sewage
Operator: Tokyo Sewage Energy Co.
Since July 1994, the company has been supplying hot and cold water to an approximately 21.6-hectare business/commercial district that includes the Tokyo Dome. The heat supply system consists of an electric heat pump and a thermal storage layer, and is the first heat supply project in Japan to use untreated sewage as a heat source.

Takasaki Central District (Takasaki City, Gunma Prefecture)
Heat source: Groundwater
Operator: Tokyo Electric Power Co.
This project employs a system that combines a heat-recovery heat pump using groundwater pumped from a groundwater vein 60 meters or deeper and a heat storage tank to supply hot and cold water to 18.1 hectares of office buildings and public facilities in the central district, the heart of the city.

Toyama Station North District (Toyama City)
Heat source: River water
Operator: Hokuriku Urban
Hokuriku Urban is supplying heat using river water to the 15.3-hectare area north of Toyama Station, which is being redeveloped by Toyama City. The heat supply system is an electric heat pump that uses late-night electricity for thermal storage.

Atsubetsu District (Sapporo City)
Heat source: Waste heat from a waste incineration plant
Operator: Hokkaido District Heating
Hokkaido District Heating supplies heat mainly from waste heat from waste incineration plants in the 139.5-hectare Momijidai and Fukutoshin complexes developed by the City of Sapporo in 1971. The heat supply plant is attached to the Atsubetsu Garbage Disposal Plant, which started supplying heat in 1971. The plant relies on waste heat from waste incineration for 80% of its heat source.

These efforts have contributed greatly to improving energy efficiency and reducing environmental impact, and are a model case for the future development of district heat supply systems.