This demand can also be met by heat extraction from power stations, residual heat (e.g. from industry or from cooling) and renewable heat through heat supply. Demand for space heating in buildings and heat required for industrial processes accounts for more than half of the total energy demand in the Netherlands. Instead of converting fossil fuels or electricity into heat, it can also come from extracted heat from power stations, incinerators and industrial processes, cooling processes or renewable sources. Heat from renewable sources includes biomass, geothermal energy, ambient heat from water and air through the use of heat pumps (including aquathermal energy, thermal energy from mainly surface water and waste water), and solar thermal (extraction of solar heat). Recently, the attention for thermal energy from water has increased. According to the Unie van Waterschappen (the association of Dutch regional water authorities), it is estimated that aquathermal energy can potentially provide 25 to 40% of the heat demand in the Dutch household sector. To be able to use heat as an energy carrier, it is important to ensure that supply and demand are properly aligned in terms of capacity and location. We focus here on extracted heat, residual heat, renewable heat and heat as an energy carrier.
Heat from local heat networks can be used for heating buildings and for hot water, for processes in industry and in greenhouse horticulture. The vast majority of current heat networks are fed with extracted heat from gas-fired combined heat and power plants and waste incineration plants. Solid biomass (wood) is co-fired in some of the power plants. About half of the heat released from waste incineration plants is renewable, as roughly half of the waste is of biogenic origin. However, the supply of extracted heat is at the expense of electricity production, so it cannot be regarded as ‘pure’ residual heat.
Residual heat from industry, particularly when it comes from biogenic origin, prevents the use of fossil energy carriers for heat production and associated CO2 emissions. This also applies to combined heat and power that has a high combined efficiency in the production of electricity and heat. The use of heat and cold storage can save a lot of energy, for example, when summer heat is stored for the winter (that also happens with aquathermal energy) and cold for the summer. Various renewable heat sources are not weather dependent and can, therefore, offer a reliable potential for heat supply.
Heat as an energy carrier is now mainly used in production processes in industry (in view of the higher required temperatures, this usually involves steam) and in heat networks with a relatively high temperature (> 70 °C) for space heating and hot water in buildings. This often concerns residual heat that would otherwise be lost. Often, a great deal of heat is wasted due to poor insulation of industrial installations and buildings, so if energy saving measures are taken COHeat as an energy carrier is now mainly used in production processes in industry (in view of the higher required temperatures, this usually involves steam) and in heat networks with a relatively high temperature (> 70 °C) for space heating and hot water in buildings. This often concerns residual heat that would otherwise be lost. Often, a great deal of heat is wasted due to poor insulation of industrial installations and buildings, so if energy saving measures are taken CO2 emissions will be avoided in the case of fossil fuels used for heat production. In well-insulated new buildings, heat with a low temperature (+/- 40 °C) can be used that comes from residual heat that cannot be used effectively in other situations emissions will be avoided in the case of fossil fuels used for heat production. In well-insulated new buildings, heat with a low temperature (+/- 40 °C) can be used that comes from residual heat that cannot be used effectively in other situations.
The Dutch Climate Agreement (adopted in July 2019) aims to make heat supply to buildings more sustainable. Each district has its own characteristics and suitable sustainable heat source, i.e. high or low temperature heat networks with all kinds of different possible heat sources, renewable gas boilers or heat pumps (on renewable electricity). The aim is for the saved costs from natural gas to earn back the investment in the new heat supply. There is much to learn about how the market for heat networks can be organized from Denmark, where decades of experience with heat networks have existed. Transparency about the cost structure of heat from heat networks appears to be of great importance. Freedom of choice for consumers could also remain with heat networks.
According to the Royal Netherlands Meteorological Institute (KNMI) climate scenarios, by 2050 the average temperature will have risen by 1 to 2.3 ᵒC compared to the period 1981-2010. Due to the warming climate, there will be more summer days and more heat waves. Especially the extremely cold and hot days are getting warmer on average. On extremely hot days, this means that the risk of exceeding the indoor temperature (overheating of homes) will increase. The cooling requirement for offices and other buildings is also increasing.
The increasing insulation of existing and new buildings and the airtightness of buildings will further increase the effect on the cooling demand. If a rising indoor temperature is not prevented, for example with (natural) ventilation or sun blinds, the cooling requirement increases.
In dense urban areas there is also the urban heat island effect. Heat remains trapped between buildings and cannot be properly dissipated, so that the average temperature in the city is higher than outside.
There are various cooling options including air-conditioning (air-to-air heat pumps) and air-to-water heat pumps. There are also soil energy systems, including ground source heat pumps and heat and cold storage (UTES). There are also cooling networks that can be fed from various sources, including collective air-conditioning systems, heat and cold networks and aquathermal energy.
Recent figures indicate that around 6% of homes have an air conditioning system. This can be either a fixed or a mobile air conditioning system. The current electricity consumption of air-conditioning is estimated to be around 0.2 TWh per year (0.7 PJ). This results in a cooling demand of approximately 2.5 PJ. This is very limited compared to the current heat demand of around 300 PJ. This is a rough estimate, because the energy consumption of air conditioners depends on their use.
The 2018 WoON survey asked respondents with air conditioners how they use them. Over 70% indicated that they only turn the air conditioner on when it is too hot inside, compared to 6% who also turn the air conditioner on when it is not so hot inside. 1% almost always has the air conditioning on in the summer compared to 19% who almost never have it on.
About 1.5% of the homes have an air-water heat pump. To what extent air-water heat pumps are used for cooling (i.e. the energy consumption for cooling) is unknown. Furthermore, almost 1% of the homes have a connection to a ground source heat/cold source, but the energy consumption for cooling is also unknown. However, it is certain that the energy consumption for cooling with ground source energy will be limited, because no compressor (part of the heat pump) is needed, only a circulation pump to pump cold water around.
In the service sector there is more cooling than in homes. Current ATES systems and cooling networks mainly supply cold to the service sector. It is estimated that the entire service sector uses 7 PJ of electricity for space cooling.
Cooling options that use energy will contribute to the energy demand and, depending on the energy source, to CO2 emissions that we must avoid. It is therefore important to limit the energy demand for cooling as much as possible. This can be done with (natural) ventilation and sun blinds, but also with other ways to prevent heating up within the building. Think of the cooling effect of trees, water or green roofs. A problem that can occur on hot days is that the peak demand for cooling can cause capacity problems for the electricity grid. This problem can be exacerbated if demand is not sufficiently reduced in the future. Sustainability strategies in the built environment must consider the increasing demand for cooling on the one hand and the decreasing demand for space heating on the other. There are various ways of linking together a heating demand and a cooling demand, for example by using the residual heat from cooling processes (space or process cooling) to heat. This can also be done by using heat and cold storage or other low-temperature networks, such as aquathermy.