A heat pump works by using a refrigeration cycle to transfer thermal energy from the outdoors to provide warmth for a building. It can also function in reverse by extracting heat from an enclosed space and releasing it outside to cool the area. Air conditioners are the type of units that solely provide cooling. In heating mode, a refrigerant is compressed at the outside temperature, causing it to become hot and transfer thermal energy to an indoor unit. When the refrigerant is then moved back outside, it is decompressed and evaporated, resulting in a loss of thermal energy, causing it to be colder than the surrounding environment. The refrigerant can then absorb energy from the air or ground before the process starts again. The operation of compressors, fans and pumps requires electric energy.
Air source heat pumps are the most prevalent models, although there are other variations, such as ground source heat pumps, water source heat pumps and exhaust air heat pumps. In district heating systems, large-scale heat pumps are also utilised. The efficiency of a heat pump is measured by its coefficient of performance or the seasonal coefficient of performance, with a higher number indicating greater efficiency and lower energy consumption. In terms of space heating, heat pumps are generally much more energy efficient than basic electrical resistance heaters.
The Important Types of Heat Pumps
A geothermal heat pump functions by utilising a heat exchange fluid (usually water mixed with antifreeze) to extract heat from either the soil or groundwater. The installation cost of geothermal heat pumps can be high. They can also be employed to cool structures by moving heat from warmer regions and channelling it into the soil through piping located underground. The water source heat pump functions in a similar way to the geothermal heat pump. However, it sources its heat from a body of water instead of the ground. The essential criterion is that the water body must be significant enough to endure the cooling effects of the unit and must not freeze or cause any negative impacts.
The fundamental function of air source heat pumps is to transfer heat between two heat exchangers. Typically, one of the heat exchangers is located outside the building and comes with fins to force air in using a fan. The other heat exchanger is used to heat the air or water inside the building directly. This heated air or water is then circulated through heat emitters, which release the heat around the building. Exhaust air heat pumps are utilised to extract heat from a building’s exhaust air. However, they necessitate mechanical ventilation. There are two types of exhaust air heat pumps available. The first one is used to transfer heat to intake air, while the second one transfers heat to a heating circuit, which includes a domestic hot water tank.
Solar-assisted heat pumps combine two systems, namely a heat pump and thermal solar panels, into a single integrated system. The solar thermal panel functions as the low-temperature heat source, while the heat generated is supplied to the heat pump’s evaporator. Absorption heat pumps, also known as gas-fired heat pumps, are a recently developed type of heat pump primarily used in residential systems. They rely on heat as their main energy source and can be paired with a diverse range of heat sources.
5 Important Applications of Heat Pumps
Heat pumps are typically utilised in regions where there is a moderate demand for heating, ventilation and air conditioning (HVAC) services; they can also serve as a source of domestic hot water and a means of tumble-drying clothes. Let us now examine the significant uses of heat pumps.
Space Heating and Cooling
Centralised heating systems use a single unit to produce heat which is then distributed throughout the entire interior of a home. These systems can employ various fuel sources, including oil, electricity, liquid petroleum gas and natural gas. Electric heating systems are deemed a safe and healthy option since they don’t produce any harmful by-products. Despite its benefits, electricity can be more costly than propane and oil. Additionally, electric HVAC systems may cease to operate during a power outage.
While oil and propane heating systems are efficient in converting fuel into heat, they necessitate homeowners to possess a sizable storage tank to contain the liquid fuel. On the other hand, natural gas heating systems can achieve up to 99% efficiency in fuel-to-heat conversion, but they require a properly functioning ventilation system to release carbon monoxide gas. Propane, oil and gas systems are typically less expensive than electricity but are not as eco-friendly. It is important to keep in mind that the prices of these fuel sources can be highly volatile, which can make it challenging for homeowners to estimate their heating expenses.
District Heating
In 2021, the production of district heat increased by approximately 3% when compared to 2020 and was able to cater to almost 8% of the global final heating requirements in both industrial and residential buildings. District heating networks have the potential to efficiently, affordably and flexibly incorporate low-carbon energy sources on a large scale into the heating energy mix. The production of district heat is primarily concentrated in China, Russia and Europe, which together account for over 90% of the global district heat production. Despite this, the capacity for decarbonisation of district heating remains largely unexplored as the majority of district network supplies globally (roughly 90% of total heat production), particularly in the two major markets of China and Russia, still rely on fossil fuels.
According to the Net Zero Scenario, district heating will continue to contribute a comparable proportion of global final heat consumption. However, advancements in energy efficiency within district heating networks and building structures will enable a reduction in district heat supplies by roughly 20% by 2030 in comparison to 2021. Meanwhile, renewable energy utilisation within district networks is expected to increase almost twofold from present levels during this period, with renewable energy sources (including renewable electricity) making up almost 20% of district heating supplies by 2030.
Industrial Heating
Utilising industrial heat pumps offers significant potential for lowering energy consumption and associated greenhouse gas emissions within the industry. A global collaborative project concluded in 2015 that gathered a total of 39 examples of research and development initiatives and 115 case studies from around the world. The results of the study demonstrate that high reductions in CO2 emissions (exceeding 50% in some instances) can be achieved with short payback periods of under two years. Industrial heat pumps have the ability to provide heating of up to 200°C, which can meet the heating demands of numerous light industries. In Europe alone, the installation of 15 GW of heat pumps could be implemented in approximately 3,000 facilities within the paper, food and chemicals industries.