Let’s see what we can do to make a building energy efficient.
Energy efficiency measures for buildings are approaches through which the energy consumption of a building can be reduced while maintaining or improving the level of comfort in the building. They can typically be categorized into:
- Reducing heating demand;
- Reducing cooling demand;
- Reducing the energy requirements for ventilation;
- Reducing energy use for lighting;
- Reducing energy used for heating water;
- Reducing electricity consumption of office equipment and appliances;
- Good housekeeping and people solutions.
In addition, these measures can be divided according to the level of investment they require, i.e., their cost-effectiveness.
Simple measures for increasing energy efficiency without additional costs, resulting in immediate savings are the following:
- turning off the heating or cooling during the night and when nobody is at home,
- pulling down roller shutters and drawing curtains at night so that no heat is lost,
- avoiding obstructing and covering heaters with curtains, masks, etc.
- optimizing, in terms of time, heating, and preparation of domestic heated water,
- reducing the room temperature by 1°C during the heating season,
- setting the cooling to a minimum of 26°C during the cooling season
- using natural light as much as possible
- turning off the light in the room when it is not needed
- starting up washing machines and dishwashers only when they are fully loaded, preferably at night.
The measures for increasing energy efficiency at a low cost and quick return on investment (up to 3 years) are:
- sealing the windows and exterior doors
- checking and repairing fittings on windows and doors
- insulating radiator niches and roller shutters boxes
- thermally insulating the existing sloped roof or the ceiling adjacent to an unconditioned attic
- reducing heat losses through windows by placing roller shutters, curtains, etc.
- fitting thermostatic valves to radiators
- regularly servicing and setting the heating and cooling system
- installing automatic energy control and monitoring system in houses
- using energy-saving light bulbs in lighting bodies
- replacing home appliances with the ones that are more energy efficient – i.e., of energy class A.
The measures for increasing energy efficiency at slightly higher costs and a more extended period of return on investment (more than 3 years) are the following:
- replacing windows and exterior doors with the ones that have better thermal quality
- thermally insulating the whole exterior façade of the house, i.e., walls, floors, roof, and panels adjacent to unconditioned spaces
- building a windbreak at the entrance to the house
- repairing and renovating the chimney
- insulating hot water pipes and tank
- analyzing the heating and cooling system in the house and, if necessary, replacing it with an energy-efficient system and combining it with renewable energy sources.
It is best if these measures are implemented together with the necessary renovation measures. It is essential to plan for energy efficiency measures and possibilities for rational energy use as early as preliminary design development when constructing new buildings.
Thermal insulation of the external wall is one of the most critical measures because improving the thermal insulation characteristics can reduce its total thermal loss by 30%-80% on average. All parts of the building envelope play a vital role in this, including:
- external wall
- the wall between unconditioned spaces belonging to different users
- the wall adjacent to an unconditioned space
- the outer side of the external wall
- the ground floor
- the floor structure that separates the spaces belonging to different users
- the ceiling adjacent to an unconditioned basement
- the ceiling adjacent to an unconditioned attic
- the flat and sloping roof above a conditioned space
- the ceiling above an outer space
- windows and external door
However, it should be noted that the most significant heat losses occur through windows and external walls and that significant savings can be achieved just by renovating these elements. Heat losses can also be significantly reduced by renovating the roof above a conditioned space, i.e., the top floor ceiling adjacent to an unconditioned attic. Renovation of the ground floor usually is not economically justified because of a relatively small reduction in total heat losses concerning a significant investment needed for such an intervention.
Thermal insulation of the external wall should be carried out, as a rule, by applying a new thermal insulation layer on the outer side of the wall, and only in exceptional cases on the inner side of the wall. Using thermal insulation on the inside of the wall is not suitable for many reasons, and it is often more expensive because of the need to additionally solve the problem of water vapor diffusion, stricter fire safety requirements, the loss of functional space, etc. In addition, it’s not good to apply thermal insulation on the inside of the wall because, although the insulation value of the wall is improved, the heat flow in the wall significantly changes, and the main load-bearing wall becomes colder. To be more precise, the wall’s mass is lost, which could be used as heat storage should the thermal insulation be applied on the outside. Therefore, special attention should be paid to installing a vapor barrier to avoid condensation formation and mold appearance.
In addition, part of partitions that are connected to the outer wall should be thermally insulated. Renovation of the existing external wall by applying insulation on its inner side is exceptionally done on protected buildings when it is necessary to avoid changes on the external façade of the building because of its historical value.
Thermal insulation of the roof or ceilings adjacent to an unconditioned attic can be carried out, although the roof is responsible for only about 10%-20% of the total heat losses in the building. The roof has a significant role in the quality and standard of living. It protects the house from rain, snow, cold, and heat. The most common type of roof on family and smaller residential buildings is a sloped roof. The space under a sloped roof is often intended for dwelling, although it is not adequately thermally insulated. In such cases, there is a great heat loss in winter and an even bigger problem of overheating in summer. If the roof is not thermally insulated, up to 30% of the heat can go out through it. Subsequent thermal insulation of the roof is simple and cost-effective because the return period of the investment is from 1 to 5 years. For thermal insulation of sloped roofs, non-flammable and vapor-permeable thermal insulation materials, such as stone wool, should be used. The connection between the thermal insulation of the outer wall and the roof should be achieved without thermal bridges. If the space under the sloped roof is not conditioned, i.e., if it is not intended for dwelling, thermal insulation should be applied on the top floor ceilings adjacent to an unconditioned attic.
It is recommended that the thermal insulation on a sloped roof be at least 16-20 cm thick. To prevent thermal bridges, the insulation should be placed in two layers, one between the rafters and the other under the rafters. Thermal insulation on the underside is usually closed with plasterboards or wood. Flat roofs are the most exposed to atmospheric influences of all the external elements of the building. That’s why it is important to insulate them well with thermal insulation and waterproofing and properly handle atmospheric water drainage. Flat roofs can be made as passable, non-passable, or the so-called landscaped roofs. The finish of the roof is created accordingly.
A terrace can be made with a green roof, with suitable waterproofing and thermal insulation on the underside adjacent to the dwelling area. In that case, the number of required layers and their total thickness increases. The required thickness of the soil is determined depending on the type of plants, and it is crucial to prevent the roots from penetrating to the waterproofing layer and moisture penetrating to thermal insulation. The green roof retains heat well, accumulates it in soil layers, achieving thus a constant temperature of the final layer, in both summer and winter.
Thermal insulation of the ground floor and the floor above an open or unconditioned space is not often applied to the already completed buildings. Here, it is necessary to distinguish ground floor structures from adjacent to an unconditioned space. Heat losses towards the ground make up to 10% of the total heat losses. In the case of newly constructed buildings, the ground floor should be thermally insulated with thermal insulation of the greatest possible thickness. In contrast, such a measure is generally not cost-effective in the case of existing buildings because it requires significant construction interventions. However, the thermal insulation measures of the ceiling structure adjacent to an unconditioned attic and the floor structure adjacent to an unconditioned basement are relatively cost-effective. In addition, it is necessary to thermally protect the floor structure above open passages. When applying thermal insulation, it is crucial to thermally insulate the whole external façade without interruptions in insulation to reduce the impact of thermal bridges to a minimum.
Although the losses through the ground floor are relatively small compared to those through other parts of the structure, the temperature of the ground slab, similar to the interior temperature, is much more comfortable for dwelling.
To avoid thermal bridges and unnecessary heat losses, it is necessary to insulate the whole outer envelope of the building, including parts of the structure adjacent to unconditioned spaces or spaces with different modes of use. A widespread mistake in practice is failing to isolate these elements completely or insulating them insufficiently.
A thermal bridge is a smaller area in the envelope of the conditioned part of a building through which the heat flow is increased because of changes in materials, thickness, or geometry of the building part. Because of the reduced thermal resistance compared to a typical cross-section of the structure, the inner surface of the thermal bridge partition has a lower temperature than the rest of the surface, which increases the risk of water vapor condensation. Depending on the cause of the increased thermal permeability, the two types of thermal bridges can occur:
- structural thermal bridges – occurring when there are combinations of different types of materials;
- geometric thermal bridges occur because of changes in the structure shape, e.g., the corners of a building.
In practice, very common are combinations of these types of thermal bridges. They often occur in situations where there is:
- complete or partial penetration of the building envelope with materials that have different thermal conductivity properties
- change in the thickness of the structure or an element in the envelope,
- difference between the inner and outer surface, which happens at walls, floor, and ceiling connections.
The consequences of thermal bridges are changes in heat losses and in inner surface temperature.
If thermal bridges appear, the inner surface temperature of the thermal bridge partition is lower than on the remaining surface, which increases the potential danger of water vapor condensation at these places.
The best way to avoid thermal bridges is to apply thermal insulation on the outer side of the whole external envelope without interruptions in insulation and seal the connections well. By using thermographic surveying of the building, it is possible to spot typical thermal bridges.
It is almost impossible to build a building without thermal bridges, but with the thermal protection details adequately designed, the negative impact of thermal bridges can be reduced to a minimum. Potential places for thermal bridges are cantilevered balconies and roof eaves, structural connections, connections between the wall and windows, roller shutter boxes, radiator niches, foundations, etc. That’s why special attention should be paid to these elements when planning for construction details.
Windows should be placed at least partly at the level of thermal insulation; roller shutter boxes must be thermally insulated; thermal insulation of the wall should be applied all the way to the foundations and, if necessary, foundations should be insulated, as well. When construction is completed, thermographic surveying can also check the quality of construction and thermal protection.
A window is the most active part of the building’s external envelope, acting simultaneously as a receiver that lets solar energy in and protects against external influences and heat losses. Losses through windows are divided into transmission and ventilation losses. If the transmission and ventilation heat losses are calculated, the total heat losses through windows make more than 50% of the building’s heat losses. Losses through windows are usually ten or more times greater than those through the walls, so it is clear how important the energy efficiency of windows is in the overall energy needs of buildings.
For example, European legislation prescribes lower and lower U-values, and today they usually range between 1.40 and 1.80 W/m2K. In modern low-energy and passive houses, that coefficient ranges between 0.80 and 1.40 W/m2K. When constructing a modern energy-efficient building, the recommendation is to use the windows with a coefficient U <1.40 W/m2K. U-value or thermal transmittance is the heat transfer rate through a structure (a single material or a composite). We will be dealing with U-value in detail in the next module because it is one of the most important parameters you should know when energy efficiency in buildings is concerned.
Let’s go back to windows. Both glazing and window frames participate in the total heat loss through windows. No matter what material they are made from, window frames must ensure good sealing, a broken thermal bridge in the structure, easy opening, and a low heat transfer coefficient. Today, the glazing is made of insulating, two-layer or three-layer glasses, with different gas fillings or coatings to improve thermal characteristics.
The following factors influence the low U-factor of glazing:
The thickness and number of spaces between the panes, so it’s better if the number of spaces and the width between them is greater.
The type of filling also influences, so if the spaces between the panes are filled with a gas (such as argon, krypton, etc.), the window will have better characteristics.
The selection of glass thickness is also significant; although glass thickness has a minor influence on the characteristics, low-emission glass (Low-e glass) significantly reduces the U-factor. The Low-E glass is coated on the inside with a particular metal film that transmits short-wave radiation (sunlight) and reflects long-wave radiation (IR radiation).
The frame thickness and the possibility for installing insulating and soundproof glass depend on the type of frame material. Different window frame materials are used: wood, steel, aluminum, PVC, and a combination of materials, such as wood and aluminum, while the frame cavities can be filled with thermal insulation. The thicknesses of a good-quality window frame range between 68 and 93 mm, when PVC and wood are used, while the aluminum frames can even be thicker.
It is necessary to ensure the tightness of the glass and window frame, and the window frame and window sills, by using triple (or quintuple, depending on the number of glass panes) glazing as the protection against wind and rain so that no moisture enters from the outside. The connection between the window and the wall must be made so that no air leakage occurs. This ensures against penetration of moisture and warm indoor air into the joint, which would cool down and cause condensation and fungi.
Improving the thermal characteristics of windows and other glass surfaces can be achieved in the following ways: ensuring good sealing of windows and exterior doors; checking and repairing fittings on windows and doors, insulating radiator niches and roller shutter boxes, reducing heat losses through windows by installing roller shutters, placing curtains, etc., replacing windows and exterior doors with the ones of better thermal quality (recommendation U <1.40 W/m2K).
When it comes to tips for improving domestic electrical appliances’ efficiency, we will mention some of the most essential electricity consumers.
The first advice is that the so-called stand-by losses should be avoided whenever possible in all electrical appliances. Contrary to popular belief, these losses are by no means negligible because most home appliances are constantly plugged in all days of the year. At the level of the European Union, the so-called Stand-by initiative has been launched to reduce these losses.
First, we will talk about refrigerators and freezers as large domestic consumers of electricity. A refrigerator is a home appliance that maintains an inside temperature lower than its external environment temperature. It achieves this by transferring heat from the inside of the device to its environment. Although there are several principles of refrigerator operation, the most common way is to use a compressor. Consider its size when buying a new appliance because bigger appliances will undoubtedly consume more energy and cost more.
When placing a refrigerator in the room, care should be taken not to put it too close to the heat source or expose it directly to the sun because that will increase the compressor’s operating time or the time needed to reach the set temperature. If placing is unfavorable, an increase in external environment temperature by one degree will also mean an increase in electricity consumption by about 5% compared to the reference value. It is also essential to avoid placing refrigerators in tight spaces. A refrigerator must be placed in an area according to the manufacturer’s instructions, i.e., often, it must be at least 5 cm apart from the walls or other appliances. This reduces the accumulation of dust behind the appliance and the temperature around it. It is highly desirable to clean the refrigerator every two months. Behind and under the fridge, there is metal, usually black, pipes. Their role is to transfer heat from the inside of the appliance to the environment. Very often, the pipes are covered with dust that acts as an insulator, so the refrigerator must work much longer to maintain the required temperature, and thus its consumption of electricity increases. Rational use will increase the lifespan of the fridge, which is approximately 15-20 years.
If the refrigerator has an energy-saving mode, it is advisable to use it; otherwise, the thermostat should be set at approximately 4-5°C in the fridge and -18°C in the freezer. During more extended absences from home, it is good, if possible, to empty the refrigerator/freezer and turn it off.
A kitchen stove is the next essential appliance we use every day. It basically consists of a hotplate and an oven. Today, there is a growing trend towards buying hotplates and ovens separately, then separately installed in kitchen furniture. Especially popular is the glass-ceramic cooktop, which has about 20% to 25% lower electricity consumption than classic hotplates. However, it must be noted that the utilization of input energy (up to 92%) is the highest in gas stoves. If the losses in production, transmission and distribution of electricity are added, gas stoves are much more cost-effective than electric ones. Among other things, gas stoves can be used during power outages, making them more suitable for the areas where power outages are expected. However, it should be emphasized that electric stoves are generally easier to maintain and clean than conventional gas stoves. In addition, there is no danger of gas leakage in electric stoves, and thus no risk of explosion must not be neglected.
The main requirements about modern cooktops and ovens, i.e., stoves, are that they:
- need the shortest possible time to reach the maximum temperature
- accumulate as little heat as possible after they are switched off
- have the most delicate possible regulation
- are energy efficient and
- are as much reliable as possible (with as few failures as possible).
Although induction cooktops are very similar in appearance to traditional glass-ceramic cooktops, these two should be distinguished. Induction heating is the future of cooking from the point of view of electricity use and has attracted many followers from the very beginning. A unique way of operation allows very rapid temperature increases to be achieved, allowing quick reactions to any changes in power level. Namely, in an induction cooktop, heat is developed at the bottom of a cooking vessel and not on the cooktop itself, resulting in much faster healing of the vessel contents. It should be noted that induction cooktops require unique cooking vessels to close a magnetic circuit. It is elementary to test whether the existing cookware can be used on induction tops. Namely, if a small magnet attaches to the vessel’s bottom, that vessel is safe to use on induction tops. Because of this characteristic of the cookware and cooktop, i.e., their ability to close the magnetic circuit and generate heat at the bottom of the vessel and not on the cooktop, the cooling time after cooking is concise. That’s why induction cooking is also called cold cooking.
The positive habit of turning off the cooktop and oven immediately after use saves some energy. However, it is essential to note that the cooktops or ovens can be switched off even before the end of cooking, and in that case, their accumulated heat can be used.
When cooking, it is good to plan in advance and choose the right size cooking pot. Namely, significantly more energy is used to prepare a small amount of food in an inappropriately large than a correspondingly smaller pot. In addition, it is wise to use as little water as possible because the food will be cooked the same in a little or a large amount of water. Less water in the pan also means a shorter cooking time and reduced energy consumption. Furthermore, it is valuable and desirable to use pot lids because, in that way, heat leaves the pot more slowly, and the food is cooked faster, increasing the utilization of produced heat by up to four times compared to cooking without a lid. When the water in the pot boils, it is wise to reduce the power to an appropriate level to continue cooking. It is advisable to open the oven or lift the pot lid as little as possible during cooking because, in that way, energy is unnecessarily wasted.
Cooktops and ovens should be cleaned regularly to maintain hygiene and reduce heat transfer losses. Modern ovens have self-cleaning programs, whereby food soiling is removed at very high temperatures. Less energy will be consumed if the self-cleaning program is started while the oven is still hot, i.e., immediately after baking. So, in addition to the right choice of a stove, i.e., cooktop or oven, responsible behavior during their use is crucial.
Today, a microwave oven is an increasingly common appliance in many households. It is used for defrosting, heating, or even cooking smaller amounts of food. Food can even be baked in the so-called combination microwave ovens (with a built-in infrared heater). The main advantage of using microwave ovens lies in the speed of food preparation and the related reduction of energy consumption. When installing a microwave oven, care should be taken to leave enough space around it for air circulation. Microwave ovens that can choose the temperature, i.e., the power, are more energy-saving and valuable than ordinary ones, as we don’t always need the maximum power the oven can reach.
For washing machines and clothes dryers, the same rule applies to all other electrical appliances, i.e., the proper choice from the point of view of energy efficiency and rational use are the essential preconditions for achieving energy savings during their use. Most of the energy, even up to 90%, is used by a washing machine to heat the water needed for washing.
An average washing machine consumes about 100 liters of water, while larger washing machines consume 160 liters per washing cycle. From the above stated, it is clear that the washing machine costs are high and that it is essential to use the appliance rationally. Namely, most of the used clothes can be washed in cold or warm washing and cold rinsing. This saving operation mode of the washing machine saves up to 65% of the energy consumed during hot rinsing. Washing machines should be kept clean both inside and outside. It is essential to clean the appliance, protect it against cale, change filters, and regularly check the drain hose and electrical installations.
During each washing/drying of the laundry, the washing machine/clothes dryer should be suitably loaded (according to the manufacturer’s recommendations). An empty or overloaded washing machine/clothes dryer cannot perform its function because of the need to re-wash/dry.
Dishwashers are handy domestic appliances that are becoming almost unavoidable, especially in younger households. With the right and rational use, the dishware washed in a dishwasher is hygienically cleaner than in manual dishwashing, while the washing process uses less energy and water.
Like with the washing machines, it is essential that the dishwasher is adequately loaded and that the dishware is correctly placed in it. In that way, the dishwasher will perform its task in the best possible way. Economy dishwasher programs should be used whenever possible. In principle, before loading the dishwasher, the dishware need not be rinsed, and water is unnecessarily wasted. It is imperative to regularly clean the filter, and drainage channel from food remains because otherwise, energy consumption can be significantly higher due to poorer washing results.
Electric appliances for domestic hot water preparation in most households consume a large amount of electricity. This segment of consumption has a great potential for energy savings, and the basic principle is that, if possible, instead of electricity, other available energy sources, such as natural gas, liquefied petroleum gas, or solar energy, are used for the preparation of domestic hot 1water.
Small domestic appliances are all those small, utility devices that are found in almost every household. The most commonly used small domestic appliances are a vacuum cleaner, an iron, a hairdryer, etc. Given that these appliances are not marked with an energy efficiency label on the market, when purchasing them, additional care should be taken that the selected appliance meets the set goals. By rational behavior and proper use, e.g., by regularly replacing full bags in a vacuum cleaner or by cleaning the lower surface of the iron, significant energy savings can be achieved, and the appliance’s lifecycle extended.
It was certainly the aspiration towards improving the quality of life that has been the main idea guiding the progress of mankind. It seems quite natural that one tries to provide maximum comfort and security for themselves and their family. One of the ways to achieve the above goals is to use the so-called smart control system. In jargon, the buildings in which such systems are used are often called smart homes.
Within the context of smart buildings, smart electrical wiring systems are often mentioned, which will, given the further development of technology, almost certainly completely replace the traditional electrical wiring and make it possible for the users to adapt, in the best way, their dwelling to their needs. The new smart systems take over the care and control of all the functions in a flat, a family house, and any other building intended for dwelling. There are no technical limitations as to the size of a system or blocking of information flow, i.e., the limitations depend solely on the designer’s creativity and the user’s wishes.
Smart control systems can be more complex or simpler, larger or smaller, on which the number of components integrated into the system depends. The system functions as a set of several components placed in rooms, with each performing the function for which it is intended. All the components are interconnected by communication equipment and communicate with each other. Generally speaking, the system components can be roughly divided into two basic categories: components for collecting external information and sending it to the system, such as motion, smoke sensor, gas, water detectors, temperature sensors, thermostats, etc. and executive components which, based on the information gathered in the system, perform the functions for which they are intended, such as regulation and control of lighting, window and roller shutter actuators, fan coil unit controllers, etc.
Smart systems are programmed so that, based on the data collected in the system, they send an order to a component to perform its function.
The smart wiring system can be applied in all the buildings, regardless of their purpose. Smart wiring will primarily increase the comfort of the space it covers, the safety of people and material goods, and reduce electricity consumption and other fuels. Before designing a project of electrical wiring in a family house, it is necessary to define the functions placed under the control of a smart system. The most common functions of smart systems in buildings are:
- indoor lighting control,
- outdoor lighting control
- heating and cooling control (based on the set operation modes)
- roller shutter, curtain, window control
- opening and closing all types of doors
- protection against fire, flood, gas leakage, etc. (notifications on mobile phone, telephone)
- various alarms.
Of course, this is not a complete list of devices, but it is important to understand that in addition to information on how much electricity a device consumes, equally important is to use it correctly.
To accompany this lesson, we have prepared an Excel table showing the average consumption of the most common domestic appliances. You can adjust it to your data by entering the estimated time of use and the price of electricity, and thus obtain the information on how much money is spent on each of the appliances we use in homes.
In the end, we will mention another important measure that is not directly related to designing and construction but to the building’s use, and that is energy management or energy monitoring. Energy management is a procedure for containing and reducing an organization’s overall energy consumption and energy costs. Some typical objectives of energy management, which depend on the needs of each individual organization, include; lowering operating costs, increasing profitability, reducing environmental pollution, and improving working conditions.
Typical steps in energy management are: Establish team, Set goals and objectives, Gather historical database, Perform energy audits, Report findings, Prioritize and implement, Measure and verify performance, and Maintain measures.
In many buildings, the energy consumption is substantially higher than needed to maintain the desired comfort level. These buildings have a large energy savings potential. The energy consumption could be reduced by 20 – 40 % by energy efficiency measures like thermostatic radiator valves, sealing of windows, automatic controls, etc. By implementing such measures, the energy consumption will be reduced to the level calculated during the energy audit and remain constant for some time.
However, experience from many implemented projects has shown that energy consumption starts to increase again after some years. Three to five years later, the energy consumption sometimes has returned to the same level as before implementing the energy efficiency measures. Similar trends with increasing energy consumption over time have also been experienced in new buildings.
To avoid this, energy monitoring was introduced: Energy monitoring is a control tool aimed at keeping the energy consumption at the correct level permanently. Energy monitoring is based on periodic registration (weekly) of the energy consumption and the corresponding mean outdoor temperature measurements.
Energy monitoring proved to be a useful tool not only after implementing an energy efficiency project but also during the whole lifetime of a building. In addition, to discover and avoid excess use of energy and water, energy monitoring enables the building owner and the operation and maintenance personnel to get: more correct operation of technical installations; documentation of results from energy-saving measures; help to identify buildings with the highest energy efficiency improvement potential; quick feedback on the consequences of changes in operational routines; increased awareness on energy saving possibilities; better budgeting of energy and water costs.
International experiences from implementing energy monitoring as a separate measure show that achieved savings of energy and water consumption are between 5 and 15 %. This, of course, requires that actions are taken when deviations from the target value are registered.
