Supplying heat to the building is one of the most important necessities, especially in our climate zone. The more that thermal energy is usually the largest part of the total energy consumed in a residential building.
The heat, which translates primarily into a sufficiently high level of temperature in the rooms, is responsible for the feeling of comfort in the building, which is why its delivery is so important.
The supply of heat to buildings takes place from a central point (local boiler room or heating plant or cogeneration plant), using a heating network or using its own generation within the building.
Regardless of which method of delivery is chosen, thermal energy can be produced using different methods and its various sources.
Central heat generation
As noted earlier, single-family homes can be supplied with heat using district heating networks of various sizes and complexity. It can be a small network, limited to one or several sets of buildings located in the area of the housing estate or urban district and fed by the housing boiler room, as well as a municipal public heating network of large size and complexity, covering the area of several urban districts or even the entire city, powered by the municipal heating plant or combined heat and power plant.
Regardless of the size of the network and the generating unit, heat in these cases can be generated using conventional methods based on the thermal extraction of energy from fossil sources, such as hard coal and lignite and natural gas, as well as using alternative methods, which include .in. obtaining thermal energy in the process of biomass and biogas combustion and the use of renewable energy sources (RES), such as: the sun and geothermal energy.
Heat from biomass
An alternative to combustion in conventional power plants and cogeneration plants of conventional fossil fuels (coal and gas) is the combustion of biomass, i.e. organic materials of mainly plant origin, which in practice means primarily the burning of wood and wood waste.
Biomass can be a good alternative to burning fossil fuels primarily due to their endless resources. Biomass resources are in fact renewable, at least because of the growing energy crops, dedicated to energy production in heating and cogeneration plants.
Biogas is a gaseous product of fermentation of organic materials, so it can be formed, among others from agricultural and forestry products and waste, from animal faeces, from sewage, from landfill waste, etc., and like biomass, is another alternative to conventional fossil fuel combustion at power plants and combined heat and power plants. Also, due to the end of fossil fuel resources, its use may be beneficial.
Warm from the sun
Not only due to depletion of resources, but also due to the environmental effect, solar energy can be a very beneficial alternative to conventional fossil fuels. The use of solar energy for heat production in a centralized system, i.e. power plants and combined heat and power plants, involves the use of a set of mirrors focusing solar radiation at one point, which results in obtaining a very high temperature at this point, used to heat the heat transfer medium.
It is also possible to use a set of so-called parabolic collectors, consisting of a mirror shaped like a gutter, in whose focus, i.e. the point where the sun rays intersect, there is a pipe through which the circulating heating medium flows. This pipe passes through the bonfire along the entire length of the gutter, and is also connected to the pipes of many identical collectors, usually placed in rows. Thanks to this combination, the heating medium is heated in turn by each collector, i.e. the heat energy transferred by the factor is the sum of the energy received at each of the collectors.
Fig. 1 and Fig. 2 show examples of solar energy devices in centralized systems described above.
Warmth from the ground
It happens that heating plants or cogeneration plants also use the heat of the Earth’s interior, and thus geothermal energy to produce heat supplied to users. This is done through wells, into which cool water is pumped, which is heated through the Earth’s interior. After heating, the water is pumped to the surface, and the heat transferred through it is used to heat buildings. High-temperature geothermal water is also used in heating plants and combined heat and power plants. The collection of heat from them involves drilling a well into a bed of such water and pumping it to the surface to use the heat that it transfers.
Independent heat generation
In many cases, single-family homes do not use a centralized heat supply system. Heat for heating and the preparation of domestic hot water (hot utility water) is obtained in such buildings on site, and it is delivered to the rooms using a central heating pipe system (central heating) or without it, generating heat locally.
In standard houses, devices using conventional energy sources are usually used, so the heat is obtained in the process of burning minerals, such as coal, natural gas, LPG (propane butane), crude oil or heating oil. However, the shrinking resources of these minerals and, consequently, their increasing price mean that many users of single-family homes are looking for other alternative methods of producing heat for their apartments. Such methods use alternative energy sources, which are primarily renewable energy sources (RES), such as: biomass and biogas, the Sun and Earth.
Heat from biomass
Biomass in home applications is basically the same as in centralized systems because they are still organic materials. Also in this case, it is primarily wood and its waste. The differences are mainly in the form of biomass ready for combustion and result from the size differentiation of power and home furnaces. It is clear that biomass adapted for home applications must have a different form than that adapted for combustion in large energy furnaces. In addition, in single-family buildings, biomass is used in central domestic heat production (stoves located in the home boiler room), as well as in local production, heating a single room (most often wood-burning fireplaces are used for this).
In home applications, biogas is most often used in rural farms where you have access to agricultural products and animal waste. Biogas production in such places is used not only to supply energy to the home, but also, and in many cases, primarily to supply energy to utility rooms related to agricultural production. For this reason, biogas can be an excellent alternative to traditional energy production.
Warm from the sun
Unlike devices used in large power industry, in household applications, mainly thermal solar collectors are used, i.e. devices used to obtain heat from solar radiation.
They differ from sets of focusing mirrors and parabolic collectors in that they do not concentrate sunlight at one point, but the element absorbing heat from sunlight is distributed over all or almost all of their surface.
Such collectors are connected to the heat removal installation and transferring them usually to the storage element, which is usually a water tank. The circulating medium that transfers heat in the system of thermal solar collectors can be gas (most often air) or liquid (most often aqueous polypropylene glycol solution).
Technical thermal solutions for solar collectors dedicated to, among others for home applications there is a lot, but in practice the most popular are flat thermal solar liquid collectors and thermal vacuum-tube solar liquid collectors.
Usually, the heat from solar collectors is used in practice to produce domestic hot water (DHW), but it can also be used to heat rooms (in the central heating system), as well as in other applications (e.g. swimming pool water heating).
As noted earlier, usually solar collectors transfer heat to the reservoir through a piping system in which the working medium circulates (usually an aqueous solution of polypropylene glycol). However, solar collectors without this part of the installation are often found with a water reservoir attached to them. Most often, this solution is used with pipe collectors. They are shown in Fig. 5.
Warmth from the ground
In domestic applications, you can also use the heat of the Earth’s interior. This is done similarly to heating and geothermal heat and power plants, as it is also necessary to introduce a heat transfer medium under the Earth’s surface. In home applications, so-called vertical or horizontal ground probes, drawing heat from the Earth’s interior or groundwater. Heat is most often recovered using compressor heat pumps powered by electricity.
Indirect heat generation methods
Examples of direct heat recovery from alternative sources are discussed above. However, it should be remembered that indirect heat generation is also possible, using the conversion of electricity from alternative sources into heat. Both in the case of electricity received from the public power grid, i.e. generated by power plants and combined heat and power plants, as well as in the case of independent (backyard) electricity generation, this can be done using alternative energy sources. Such electricity will be used to power heat generating devices, so in the end it can be said that this heat will come from alternative sources, although they will be sources of heat only indirectly.
Alternative sources of electricity generation in centralized as well as home systems may be:
Sun – sets of focusing mirrors and parabolic collectors as well as photovoltaic farms (PV) in power plants; photovoltaic systems for home applications,
- Wiatr- wind power in centralized systems as well as domestic,
- Water- hydropower plants in centralized systems as well as domestic,
- Geothermal energy – geothermal power plants in centralized systems,
- Biomass – biomass power plants in centralized systems,
- Biogas – biogas power plants in centralized systems.