All new buildings a building permit application is submitted for after 31.12.2019 must comply with the nZEB requirements. The requirements relate to the required annual energy, and required primary energy, which must not exceed the maximum allowed values, and a minimum of 30% of energy must come through energy from renewable sources.
When building an object with nZEB properties, some parameters are predefined, such as location and purpose, while we can influence the others, such as architectural and construction characteristics and the selection of thermotechnical systems and energy sources. With high-quality combination of these elements, the nZEB standard can be met.
The following is a simplified presentation and requirements of the nZEB.
Introduction
Buildings are responsible for approximately 40% of total energy consumption in the European Union, including in the Republic of Croatia. For this reason, measures have been adopted, aimed at reducing energy consumption in buildings and encouraging the use of energy from renewable sources in order to reduce energy dependency and greenhouse gas emissions, all through a nearly zero-energy building (nZEB) model.
A nearly zero-energy (nZEB) building is a building with very high energy properties. This nearly zero, or very low amount of, energy should be covered to a very significant extent by renewable energy, including renewable energy produced on or near the building.
The basic nZEB standard requirements refer to the required energy for heating, primary energy and the share of renewable energy sources in the energy supplied.
The allowable energy required for heating and primary energy shall be determined by the building’s shape factor and its purpose.
Nearly zero-energy buildings are based on the sum of the renewable energy sources used and the efficiency measures taken.
The annual energy required for heating and annual primary energy shall not exceed the maximum allowable values set and a minimum of 30% of energy must be met by energy from renewable sources.
All new buildings for which a building permit application is submitted after 31.12.2019 must meet the nZEB requirements.
nZEB
In order to meet the nZEB standards, it is necessary to meet certain requirements depending on the building purpose, the building location and the building shape factor.
Building purpose – family house / multi-apartment building / office building / hospitals / shops (wholesale and retail) / hotels and restaurants / sports halls / education buildings / other non-residential buildings
Building location – on the continent or on the coast
Building shape factor – (building compactness) – relationship between the paving and the girth of the heated part of the building, fo=A/V (m-1)
Nearly zero-energy building requirements are set as follows:
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- Annual energy required for heating per unit of surface of the usable area of the heated part of the building,
- Annual primary energy per unit of surface of the usable area of the heated part of the building, which, depending on the purpose, includes energy for heating, cooling, ventilation, preparation of consumable hot water and lighting,
- Minimum share of energy delivered from renewable energy sources (RES),
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- By complying with the air tightness requirement proven by testing on the building prior to the technical inspection of the building.
The required energy for heating is the amount of heat that needs to be provided within the heated space in order to maintain the minimum desired temperature of Q”H, nd [kWh/(m2·a)].
The required energy for cooling is the amount of heat that needs to be taken from the cooled space in order to maintain the desired temperature in it.
The required energy for heating and cooling depends on the climatic conditions of the building location, the architectural and construction characteristics of the building, the ventilation method and the building purpose.
Architectural and construction characteristics of the building that affect the required energy for heating and cooling are the following: the quality of the building envelope (thermal insulation thickness, type of glazing and sealing), the building shape (compactness), the openings orientation to the sides of the world, and sun protection.
Heat is lost passing through the walls, windows, roof and floor of buildings. These heat losses are called transmission losses. They are reduced by sufficient thermal insulation thicknesses and multiple insulating glasses.
Heat is also lost due to airing, that is, by the release of warm air and the entry of cold air into the premises. These thermal losses are called ventilation losses.
Ventilation losses are inevitable due to the need of room ventilation – these are necessary ventilation losses, and there are also unwanted losses due to air infiltration caused by poor sealing of the sheath.
Ventilation can be natural and mechanical
Natural ventilation implies air exchange in the premises without the fan use (by opening windows and air entering through racks, ventilation holes or grilles).
Forced (mechanical) ventilation implies air exchange in the room by using a fan.
Natural ventilation in residential buildings accounts for about a third of heat loss
The required energy for the preparation of consumable hot water is the amount of energy that needs to be delivered to the sanitary water in order to achieve the required temperature.
The delivered energy is the amount of energy that needs to be delivered to the building for the operation of technical systems, that is, to put it simply, the energy delivered is that amount of energy that you consume and pay for.
The delivered energy is calculated for heating, cooling, hot water preparation, mechanical ventilation and lighting
The energy delivered depends on the energy needed and the efficiency of the system.
The efficiency of the thermotechnical system is the energy ratio that the system has successfully handed over to space and the energy supplied to the thermotechnical system.
Necessary energy can be viewed as the net energy we need to heat the space, and the energy delivered as the gross energy we must consume. The difference between gross and net energy arises due to losses.
If you use heat pumps, the energy supplied will be less than the one needed, unlike the example with a boiler (gas, oil, wood pellets…), meaning that the heat pump is more efficient regardless of the use of different energy sources.
We use different types of energy to start the devices for the heating/cooling process. In order to reduce everything to a common denominator, we calculate the so-called primary energy by which we correct the differences in the energy sources used. Each energy source has its own primary energy factor that takes into account the energy contained in the energy source, including the energy consumed to collect or excavate it, process, process and transport it to the user.
We designate primary energy with Eprim and calculate it as the product of the amount of energy supplied for the technical system and the primary energy factor.
Primary energy factors are determined by each Member State for itself. They are determined by their impact on the environment or according to the energy goals of the state. Renewable energy sources have low values, while non-renewable energy sources have high values of primary energy factors.
Primary heating energy consumption depending on the thermotechnical system applied
Eligibility for nearly zero-energy buildings (nZEB) can be achieved by different technical system combinations and different energy sources.
Nearly zero-energy buildings meet renewable energy requirements if at least 30% of the annual energy delivered comes from renewable energy sources.
Renewable energy sources (RES) are renewable non-fossil sources – the wind, solar, aerothermal, geothermal, hydrothermal and marine energy, hydropower, biomass, landfill gas, wastewater treatment plant gas and biogas.
In addition to renewables, we also have non-renewable energy sources – also called fossil fuels – which are energy sources that cannot be renewed, such as coal, oil and natural gas.
Thermotechnical systems
A properly selected thermotechnical system should aim for as low as possible delivered and primary energy, with as much renewable energy as possible, but all based on cost-optimal principles.
Heat generators are used for the thermal energy preparation (production) for space heating purposes, which are most often boilers (wall heaters), water heaters, heat pumps, solar hot water collectors, furnaces and heaters in buildings.
The most used energy sources are natural gas, electricity, remote heating (from the combined heat and power plant), wood biomass, extra light fuel oil and other petroleum products and, to a lesser extent, solar energy.
The energy sources used for boilers and water heaters are fossil fuels: natural gas, liquefied petroleum gas, fuel oils (most often extra light fuel oil), and renewable fuel: wood biomass (logs, pellets, chips).
Heating can be by hot water or airborne. It means that the medium supplied to the space we heat is warm water (by hot water) or warm air (airborne).
Heating/cooling devices are used to transfer energy to the space, and in the hot water system, there are radiators, floor (wall, ceiling) heating and fan coil units. In an air system, warm air comes out of the duct through grilles, ceiling diffusers, diffusers, air valves, etc.
Remote heating implies the preparation of heat energy (heated water or steam) in a central place for the needs of several users, and the prepared heat energy is distributed through insulated pipelines leading underground to thermal stations in each of the buildings connected to the system.
The heat pump’s operation is based on harnessing the heat from the ambient air, water or land, which are considered renewable energy sources. This means that heat pumps are not classified as heat generators because they do not produce thermal energy, but thermal energy is provided by transferring energy from a lower to a higher temperature level. Pumps can be used for heating only, for cooling only, or for heating and cooling (reversible pumps).
The heat pump system can be designed as direct or indirect.
The direct system is also called a direct expansion system, or air-to-air heat pump, widely known as split, multi split and VRV devices. The working substance between the internal and external units is freon.
In the indirect system, the refrigerant also circulates in a closed circuit, but transfers energy to the heating or cooling water, which then transfers energy to the room. Water is an energy carrier, and therefore we call this system indirect. Pumps used in indirect systems, divided according to the condenser waste heat removal method, are AIR-WATER, WATER-WATER or GEOTHERMAL pumps.
For the needs of domestic hot water (DHW) preparation we usually use a solution which is also used in the thermal energy preparation (boilers / water heaters, heat pump, remote heating), and increasingly with solar collectors, which are also renewable energy sources, thus reducing primary energy.
Venting or ventilation means the supply of fresh external air and a discharge of room exhaust air to ensure enough fresh air in the space. We determine the required amount of air based on the type and purpose of the space, and the usage regime. In family houses and apartments, it is customary to ventilate spaces that do not have access to fresh air through windows. The amount of fresh air depends on the purpose of the space and is expressed over the number of air volumes in the space that is replaced in one hour, or the amount of air per person.
Using a ventilation device without a recuperator causes large losses as it is necessary to heat the ambient air to room temperature. The recuperator uses heat from the exhaust air to heat the supply air and thus saves energy.
The reduction of the supplied energy to the building is achieved by the installation of high-quality lighting. Light technical requirements can be met using a different type of lighting, but LED lighting uses 6 times less energy than classic light bulbs (incandescent) and 2 times less than halogens (gas discharge).
For the purpose of electricity production, photovoltaic panels are also used, which, by directly converting energy from solar radiation, produce electricity using a photoelectric effect, also falling under renewable energy sources.
Below are some of the thermotechnical systems combinations that meet the family house nZEB standard, but with the remark that it is necessary to pay attention to the architectural and construction characteristics of the building.
