Recently, passive houses have been gaining more and more popularity among private developers, their idea is being actively promoted. In many construction magazines and websites dedicated to construction, a large number of articles appear that describe the undeniable advantages and prospects for the development of building new houses of this particular type. Let’s analyze all the “minuses” and “pluses” of such houses together with you, pay special attention to the nuances of its construction and subsequent operation.
Of course, it is difficult not to succumb to the temptation when a large number of people speak of passive houses with genuine admiration. “A warm, healthy, environmentally friendly, “smart” home without the need for heating, which is also able to provide its residents with an optimal microclimate” – this is how the happy owners characterize these houses. For many readers, especially those who are directly related to the construction industry, passive houses can cause a lot of questions. In this article we will try to present this type of houses in a more real light, without unnecessary embellishments and exaggerations. The material presented by us in this article, our comments and doubts can cause dissatisfaction and criticism of ardent supporters of the idea of building passive houses. We do not want to “blindly” offer you advertising material, we want to present real facts, opinions and arguments of qualified specialists in the field of construction.
Why passive? The name “passive house” came to us from Germany. It was there, more than 20 years ago, that specialists from the Institute of Housing and the Environment began to develop concepts for building houses in which heat consumption would be so low that it would not be necessary to use “active” heating devices in it. In other words, to heat such a house, there should be enough solar energy, thermal energy generated by various household electrical appliances, as well as energy emitted by the residents of the house. Houses, which later came to be called “passive”, must consume a minimum amount of thermal energy, in no case exceeding 15 kWh/(m²•year).
A little later, in the 90s of the twentieth century, the PassiveHouse Institute (Passivhaus Institut) was created in Germany, which came to grips with the development and popularization of this type of construction. In the same years, the passive house standard was created and approved. According to this standard, the energy consumption of a house that can be considered passive should be no more than 15 kW•h/(m²•year), which is 7-8 times less than the energy consumption of an ordinary average house. In other words, for heating 1 m2 of living space of such a house, theoretically, no more than 4 kg of firewood, 2 kg of coal or 1.5 m3 of natural gas should be spent per year. In monetary terms, the annual costs associated with heating a passive house with a total area of 150 m² range from 163 hryvnia (when heating with natural gas) to 270 hryvnia (when using firewood).
Among other things, most propagandists who advocate the construction of passive houses pay special attention to the fact that, due to their low energy consumption, such houses do not require the installation of heating systems in them. For additional heating of the indoor air, it is enough just to install electric heating elements of small power in the forced ventilation system of the house. In order to ensure optimal indoor temperature conditions throughout the winter, it is sufficient that the power of the heating element is no more than 10 W for each m2 of heated area. In other words, in order to heat a house with an area of 150 m², it is necessary to install heating elements with a power of no more than 1.5 kW. Doesn’t that sound tempting.
Not always passive. It should be immediately noted that, unlike Germany, it is very difficult for us to achieve the German standard in the construction of passive houses, since this is due to at least two main circumstances.
First of all, the amount of heat energy required for heating a particular house depends on the difference between the outdoor temperature and the indoor temperature. In the predominant territory of Germany, especially in its southwestern part, the climate is an order of magnitude milder than in Ukraine, and the average outdoor temperature in winter is a couple of degrees higher than ours. In this situation, it becomes obvious that a passive house, the energy consumption of which is not more than 15 kW•h/(m²•year) in German conditions, when it is built on the territory of Ukraine (with the exception of its southern regions) will need additional heating, and, therefore , and in greater quantities.
Secondly, the estimated energy consumption of a house, which is laid down at the design stage, does not always correspond to the amount of energy that will be needed in practice. This parameter can only be calculated theoretically and approximately. In addition, the accepted method of calculation in Ukraine differs significantly from that used for settlements in Germany. So, according to Ukrainian standards, it is considered that the average daily temperature inside a room intended for permanent residence (residence) of people should be + 20 ° C, and according to German standards – only + 19 ° C, and then in the daytime. In addition, in Ukraine, nighttime temperature drops are included in the calculation. As you can see, when calculating the thermal energy of the same house, the need for thermal energy in a house in Germany is an order of magnitude less than in Ukraine.
In other words, a passive house built in Ukraine, but using German standards, will require more than 15 kW•h/(m²•year) for heating, that is, but will not be passive according to German standards. In order for it to become such, it will be necessary to invest a significant amount of funds for its additional insulation.
How can one try to reach the passive house standard? In order for your house to have minimal energy consumption, it is necessary to take into account many of its individual features at the design stage, namely the design of the house, the type and size of the walls, its location on the site, etc.
When designing and building passive houses, it is necessary to adhere to the following recommendations: • if possible, completely eliminate the formation of cold bridges in the wall structure;
• choose such building materials that are able to provide resistance to heat transfer of the roof, walls and floor on the ground more than 7.7 (m²•K)/W (according to the current Ukrainian building codes (DBN V.2.6–31:2006) this figure for the roof is 4.95 (m²•K)/W, and for walls 2.8 (m²•K)/W);
• install windows with a heat transfer resistance of 1.25 (m²•K)/W or less, and external doors with even lower resistance (according to Ukrainian standards, the heat transfer resistance of windows should be 0.6 (m²•K)/W)) ;
• window panes must be selected with a light transmission coefficient g of more than 50%;
• try to provide the house with high tightness. The air exchange coefficient of the house should be less than 0.6 h-1. Simply put, the volume of air that can pass through the existing gaps in the house structure within an hour should not be more than 0.6 of its total volume;
• install an efficient mechanical ventilation system in the house with the possibility of heat recovery;
• Where possible, use solar energy for space heating.
Floor, roof, walls. Floors, exterior walls, ceilings, roof structure must be effectively protected from heat leakage. For a house to be energy efficient, its average heat transfer coefficient must be less than 0.2 W/(m2•K). In order to achieve the required heat transfer resistance of the roof and exterior walls, the layer of thermal insulation materials must be at least 30 cm. •h/(m²•year) You will need a heat-insulating material with a thickness of about 40 cm. Such heat-insulating material has a high cost, it cannot be fixed to the wall structure with ordinary standard dowels – installation is done in two layers. It should be noted that it is much easier to mount the heat-insulating material in the frame. This wall construction technology will allow you not only to get a lighter structure with high thermal insulation characteristics, but also to reduce their thickness (as a rule, with the same thermal characteristics, they are 20 cm thinner than brick ones). Along with this, the walls built using frame technology are not able to accumulate heat, which almost completely excludes the possibility of passive use of solar energy. In addition, at present, Ukrainian customers do not trust this type of construction much, since frame walls, unlike brick ones, are not associated with strength, durability and reliability.
Brick walls can also be effectively insulated, but this will be a rather costly undertaking. In this case, there are doubts about whether this type of construction will pay off at all.
In addition, it is necessary to take care of effective thermal insulation of the floor of the building located on the ground in order to ensure its proper isolation from the ground and avoid unnecessary heat losses.
The heat-insulating layer of the roof must be at least 30 cm. This is primarily due to the fact that it is through the roof that significant heat leaks occur.
Good luck with your construction.