Wastewater heat pumps for building energy savings

Thread Content

Building energy consumption accounts for a large proportion of the total energy consumption in the country, and within building energy use, the energy consumed by HVAC systems plays a crucial role. It is predicted that by 2020, China’s HVAC energy consumption will reach 1 billion tons of standard coal, accounting for over 30% of the total energy consumption. Developing and utilizing low-grade renewable clean energy represents a new model for HVAC energy consumption. Renewable clean energy sources include solar energy, wind energy, hydroenergy, biomass energy, geothermal energy, as well as industrial waste heat and urban waste heat. Compared to other types of heat sources, urban wastewater has unique advantages and constitutes an ideal low-grade heat source. Urban wastewater is the combination of industrial wastewater and domestic sewage, and it represents a renewable clean energy source derived from urban waste heat. Using urban wastewater as a heat and cold source for heating and air conditioning in buildings can directly reduce the consumption of other scarce energy sources. It also serves to utilize waste, representing a form of resource recycling. It is an important measure for developing a circular economy, building a society that conserves resources, and creating a favorable environment. Wastewater source heat pump systems use wastewater as a heat source; in winter, they capture the low-grade thermal energy from the wastewater. With the help of a heat pump system, and by consuming some electrical energy, this captured energy is used to heat indoor spaces ； In summer, the heat inside the room is removed and released into the water, thereby achieving the purpose of air conditioning in summer. It has the following features: (1) Significant environmental benefits. A wastewater-source heat pump system is a heating and cooling system that utilizes urban wastewater as a heat source or sink for energy conversion. After passing through heat exchange equipment, the wastewater releases either cold or heat back into the main wastewater channel; it does not come into contact with other devices or systems, operating in a closed cycle that prevents pollution of the environment as well as other equipment or water systems. During heating, boiler room systems that use coal, gas, oil, etc., are unnecessary; there is no combustion process, thus avoiding smoke pollution ； It generates no waste residues, wastewater, exhaust gases, or dust, resulting in significant environmental benefits. The urban sewage heat pump heating system is a new type of green and environmentally friendly heating method that can provide heating in winter using only a small amount of electrical energy. Urban wastewater heat pump systems not only have the practical effect of improving the atmospheric environment, but can also serve as an iconic representation of \"green engineering\". China’s annual sewage discharge amounts to 46.4 billion m3; if this waste is fully utilized, it could save 33 million tons of coal. Based on the country’s total annual energy consumption of 3 billion tons of standard coal, this represents 1.1%, while if we consider the primary energy consumption for heating, ventilation, and air conditioning, which is 1 billion tons of standard coal, the figure rises to 3.3%. At the same time, emissions can be reduced by 2.62 billion tons per year. (2) High efficiency and energy saving. In winter, the temperature of wastewater is higher than that of the ambient air, so the evaporation temperature in the heat pump cycle increases, and the energy efficiency ratio also improves. Assuming a unit volume of wastewater is 100 m3 and the available sensible heat temperature difference is 5°C, the amount of heat that can be utilized is Q = 2.1×106 kJ. During heating, it is equivalent to 71.3 kg (26.38 yuan) of coal. Energy savings rate: The efficiency of coal-fired heating is 0.6, the power generation efficiency is 1/3, and the efficiency of water-source heat pumps is 4/3; the energy savings rate is 55%. (3) It operates stably and reliably. The temperature of water bodies remains relatively stable throughout the year, with fluctuations that are much smaller than those in the air. This makes them excellent heat sources for heat pumps and cooling sources for air conditioners. The constant temperature of water bodies ensures more reliable and stable operation of heat pump systems, as well as enhancing the efficiency and cost-effectiveness of these systems. There are no difficult issues such as winter defrosting for air-source heat pumps. (4) Multi-functional and widely applicable. This heat pump system can be used for heating and air conditioning, serving multiple purposes; one such system can replace the original boiler and air conditioning units or systems. Urban wastewater heat pump air conditioning systems utilize urban wastewater to generate heat for heating in winter and to remove heat for cooling in summer; they also use this wastewater to provide hot water for domestic use throughout the year. During the cooling season, partial free supply of hot water for domestic use is available. A set of systems for use in both winter and summer, fulfilling three functions. (5) Low initial investment and operating costs. Urban wastewater source heat pump systems offer significant economic advantages in terms of low initial investment and low operating costs, saving approximately 20% on both investment and operational expenses compared to other systems. The actual projects (Beijing Yuèdū Hotel, Beijing Honglìyuàn Building, Beijing Jingyàn Hotel, Beijing Xinfuli Residential Complex, Shanxi Guoruiyuàn, Shanxi Senior Citizens’ Apartment, etc.) have demonstrated good operational performance and significant economic benefits. The system adjusts automatically based on outdoor and indoor temperature requirements, allowing it to operate without supervision, while also enabling network-based monitoring. The wastewater heat pump system has a simple principle, high equipment reliability, and low maintenance requirements; there are no maintenance issues with the equipment on a regular basis.