Air-source heat pumps
Air source heat pumps are relatively easy (and inexpensive) to install and have therefore historically been the most widely used heat pump type. However, they suffer limitations due to their use of the outside air as a heat source or sink. The higher temperature differential during periods of extreme cold or heat leads to declining efficiency, as explained above. In mild weather, COP may be around 4.0, while at temperatures below around −8 °C (17 °F) an air-source heat pump can achieve a COP of 2.5 or better, which is considerably more than the COP that may be achieved by conventional heating systems. The average COP over seasonal variation is typically 2.5-2.8,with exceptional models able to exceed 6.0 (2.8 kW).
Ground source heat pumps
Ground source heat pumps, which are also referred to as Geothermal heat pumps, typically have higher efficiencies than air-source heat pumps. This is because they draw heat from the ground or groundwater which is at a relatively constant temperature all year round below a depth of about eight feet (2.5 m). This means that the temperature differential is lower, leading to higher efficiency. Ground-source heat pumps typically have COPs of 3.5-4.0 at the beginning of the heating season, with lower COPs as heat is drawn from the ground. The tradeoff for this improved performance is that a ground-source heat pump is more expensive to install due to the need for the digging of wells or trenches in which to place the pipes that carry the heat exchange fluid. When compared versus each other, groundwater heat pumps are generally more efficient than heat pumps using heat from the soil.
Solid state heat pumps
Main article: Magnetic refrigeration
In 1881, the German physicist Emil Warburg put a block of iron into a strong magnetic field and found that it increased very slightly in temperature. Some commercial ventures to implement this technology are underway, claiming to cut energy consumption by 40% compared to current domestic refrigerators. The process works as follows: Powdered gadolinium is moved into a magnetic field, heating the material by 2 to 5 °C (4 to 9 °F). The heat is removed by a circulating fluid. The material is then moved out of the magnetic field, reducing its temperature below its starting temperature.
The first system of DHC in Japan using untreated sewage as a source of heating and cooling water
DHC (district heating and cooling) system - first
system of centralized heating and cooling
For the first time in Japan, in the Koraku 1-chome, Tokyo, for the district heating system installed DHC, which uses the heat of raw sewage. As expected, the use of heat waste water will reduce energy consumption and greenhouse gas emissions. Application of this system reduces energy consumption by 20%, CO2 and NOx emissions by 40 and 37% respectively.
Wastewater has been used in other projects as a source of low-grade heat for heat pumps. However, the project in the Tokyo area Koraku 1-chome unique in that for the first time in Japan using untreated, raw sewage; using heat pumps not only at treatment plants, but also on the pumping stations and sewerage networks.
In the future, expects a significant increase in the use of wastewater as a source of low-grade heat.
The volume of sewage produced in huge quantities large cities, virtually unchanged during the year. The temperature of wastewater below the outside temperature in summer and higher in winter. This makes them an ideal source of low-grade heat for use in heat pumps. By some estimates, the city communications, together with sewage dumped about 40% of heat used. The project aims to use this huge source of heat for the District of DHC, working on a heat pump, saving a considerable amount of energy and significantly reducing emissions of NOx and CO2
Heat exchangers on DHC - station constructed below the pumping station of sewage. They are used to transfer heat pump heat of wastewater flowing through the pump station. The heat pump allows you to get chilled or heated water. This system reduces energy consumption (electricity) by 20% compared with the heat pump that uses air as a low-grade heat source. To remove the majority of suspended solids in the effluent applied automatically filter (Fig. 2). To protect against corrosion of pump parts used stainless steel tube heat exchanger – titanium
Cleaned pipe heat exchanger installed inside the brushes c
At DHC-mounted station 3 heat pump, 2 with a cooling capacity 10.5 MW and heating capacity 12.8 MW each and a heat pump with a cooling capacity 3.9 MW and heating - 5 MW. This pump is used periodically, when it comes to hot and cold water simultaneously. Flow of sewage passing through DHC-station, up to 129 600 m3 per day. Station cooling water to a +7 ° C and is heated to +47 ° C and ensures that water building with total area of 126,400 m2, giving it a thermal network performed on a 4-pipe scheme, laid under the ground at a depth of 7-8 m.
To equalize the heat load and use low-cost electricity at night stations were installed accumulator tanks totaling 1520 m3. From April 1995 to March 1996 the station provided DHC 37,741 GJ of thermal energy for cooling water and 9,151 GJ for hot water. In August 1995, heat pump installation conversion factor was 4,3. In February 1996, - 3,9.
Heat exchangers in the DHC-station constructed below the pumping station to pump sewage. They are used to transfer heat pump heat of wastewater flowing through the pump station. The heat pump allows you to get chilled or heated water (Fig. 1). This system reduces energy consumption (electricity) by 20% compared with the heat pump that uses air as a low-grade heat source.
To remove the majority of suspended solids in the effluent applied automatically filter (Fig. 2). To protect against corrosion of pump parts used stainless steel tube heat exchanger - titanium.