"Energy Harnessing Heat Pumps."

"Energy Harnessing Heat Pumps."

A heat pump is a system that extracts thermal energy from a low-temperature heat source and gives heat to air or water at a higher temperature. Compression heat pumps, which are most widely used in air conditioners, utilize a phase change in which the refrigerant absorbs vaporization heat when it evaporates by taking heat from the outside air, and conversely releases condensation heat when it is condensed. The condensed and liquefied refrigerant is then depressurized and heated back to the evaporator. This cycle is repeated for heating and hot water supply. It can also be used for cooling by reversing the flow of refrigerant and transporting the heat inside the building to the outside.

On the other hand, a heat pump that uses unused energy as its heat source is called an absorption type. Using water as the refrigerant and lithium bromide or similar material as the absorbent, heat is absorbed from the heat source in the evaporator, and the evaporated water is absorbed by the adsorbent to recover the heat absorbed. As the adsorbent is gradually diluted by absorbing water vapor and its absorbing capacity decreases, it is heated in the regenerator and only the water is released. The evaporated water also releases condensation heat when it is converted back to water in the condenser.

About 60% of primary energy in Japan is discarded as waste heat and steam. Furthermore, rivers, sewage, and groundwater are warmer than the outside air in winter and conversely cooler in summer, so the energy requirements can be reduced by using them as heat sources for heat pumps. In particular, in the case of gas-based heat pumps, city gas demand peaks in the summer months, so there is also the effect of reducing peak electricity demand.

The use of heat pumps that utilize unused energy is increasing in district heat supply projects, an important element in urban planning, and has been introduced in 34 cities and wards across Japan. In metropolitan areas, sewage systems with high-temperature domestic and industrial wastewater, such as leftover hot water, are especially expected to be used. The New Energy and Industrial Technology Development Organization (NEDO) estimates that the amount of heat contained in water discharged as treated sewage amounts to 47 trillion kilocalories per year, enough to provide heating and cooling for 2 million ordinary homes.

In the case of heat pumps that obtain their heat source from outside air, in regions where the outside temperature falls below minus 15 degrees Celsius, reverse cycle operation is required to remove frost from the heat exchanger, but this problem does not occur with unused energy because the temperature is almost constant throughout the year.

Geothermal heat pump systems."

Recently, geothermal heat pumps (GeoHP), which utilize geothermal energy, have been attracting attention. In this system proposed by Geothermal Engineering, a heat exchanger is buried about 10 meters underground and circulates a cooling solution such as water, brine, or ethanol to extract heat from the ground or, conversely, to release heat for heating and cooling. Since the heat is transferred underground, there is no need for an outdoor unit to dissipate the heat, and the system has the advantage of being extremely quiet during operation.

Geothermal heat is not used at high temperatures, as in geothermal power generation, but rather at low temperatures, so it can be used anywhere, not just in special geothermal areas. In addition, while it is difficult for individuals to obtain heat from sewage or rivers as in the case of district heat supply, geothermal systems can be introduced even in ordinary households.

However, while there are already numerous examples of geothermal heat pumps in the U.S., there are only a few in Japan, and NEDO is conducting international joint research on promoting the use of geothermal heat pumps, making this an area that is attracting worldwide attention. Road heating is considered to be a particularly effective use of geothermal heat. In winter, in regions with deep snowfall, hot water and other liquids were conventionally sprayed on roads to melt the snow that had accumulated on them, but the water cooled and the roads froze, causing accidents involving slips. In response, snow-melting pipes have been developed to melt snow on road surfaces by burying snow-melting pipes under the road surface and applying heat from heat pumps. Kubota is working on the development of heat pumps exclusively for snow-melting, and has proposed three types of heat pumps: water heat source, ground heat source, and air heat source.

There are various ways to use ground heat sources, including direct, heat pump, and heat pump with heat source. Although measures such as the installation of foreign object removal equipment are required, the geothermal heat utilization type can be an effective means from the viewpoint of energy conservation.