Window.
Windows in passive houses should not only allow thermal solar radiation into the room, but also contribute to lower heat losses. In order to achieve the maximum effect, it is not enough to correctly position the windows in the project; it is also necessary to use special window profiles with increased thermal insulation characteristics.
Thermal losses.
Windows with a heat transfer resistance R of about 1.25 (m²•K)/W are still quite rare on the domestic market, but some companies are already successfully offering them. The frames of such windows are made of PVC profiles that are wider than the profile used in the production of standard windows. This profile has a larger number of chambers (usually from 5 to 7), some of which can be filled with special thermal inserts. Windows produced for passive houses have more seals in order to reduce air infiltration through various gaps as much as possible, as well as to significantly improve the overall thermal insulation of the window. These windows, although ideal for passive houses, are currently quite expensive.
The heat transfer resistance coefficient R is an average value, which is calculated on the basis of two main indicators: the heat transfer resistance of an insulating glass unit and a frame. Due to the fact that even the best window profiles have a heat transfer resistance R below 1.25 (m²•K)/W, windows for passive houses should have double-glazed windows with higher thermal insulation characteristics, that is, their heat transfer resistance coefficient should be over 1.25 (m²•K)/W. These requirements are met by windows that use double-glazed windows with two or three glasses assembled or glued at the factory, the space between which is filled with an inert gas or dry air, which helps to reduce heat losses.
It is worth noting that at present the production of windows, the heat transfer resistance R of which is much higher than 1.25(m²•K)/W, is rather complicated, time-consuming and unprofitable. That is why we have to put up with the fact that much more heat is lost through windows (at least 6 times) than through a wall of the same area. In this situation, one of the ideal solutions to reduce heat losses in a passive house would be a complete rejection of window openings, but such a solution would have a negative impact on the health of people living in the house. Based on current regulations, premises intended for permanent residence of people must have natural light, while the minimum area of windows must be calculated depending on the linear dimensions of the room. According to SNiP 31–02–2001, the window area must have a ratio to the floor area of at least 1:8. Light transmission. The large heat losses of windows can only be compensated by the heat of sunlight, which penetrates through them into the interior of the room. That is why in passive houses (in principle, as in all other houses), experts recommend adhering to the layout of the interior in such a way that, if possible, the largest number of windows is located on the southern facade. In order to ensure maximum use of the thermal energy of sunlight, it is necessary that the sun’s rays can freely penetrate into the building. In this case, the value of such a parameter as the coefficient of light transmission g of glass plays one of the main roles. For windows recommended for installation in passive houses, this coefficient is considered sufficient if its value is more than 50%. In this case, the only problem arises – how exactly to combine the high coefficient g of glass with its high heat transfer resistance R, because in order for the window to have high thermal insulation properties, it is necessary that the glass be as less transparent as possible.
Linear dimensions. In passive houses, it is extremely undesirable to install windows of a very large area. This is especially true for passive frame houses, since the walls of such a house are not able to accumulate heat. Large window openings, even if they are located on the south (sunny) side, can be the main cause of increased heat losses, which in most cases cannot be compensated by sunlight. In addition, in the summer period, these rooms will require additional cooling, since a very large amount of sunlight will penetrate through them.
Location. Particular attention in the construction of passive houses must be paid to its placement relative to the cardinal points, since this will help to avoid excessive heat losses. On the western and eastern facades, it is best to place window openings of a minimum area, since through them an order of magnitude less solar thermal energy will enter the house than through those located on the south side. On the north side of the house, which is always in the shade, there should be no window openings at all (with the exception of pantries, a garage or other unheated premises). If all unheated rooms are well isolated from heated rooms, then the window openings in them will not seriously affect the overall heat loss of the house.
Bridges of cold.
Cold bridges can form in the outer walls in places of protrusions, extensions, as well as in other structural elements that cannot be effectively insulated. One of the main problems is the various metal structures directly attached to the outer walls or emerging from them (railings, awnings, balconies). Since metal conducts heat very well, it is metal elements that are the main cause of high heat losses. Directly in contact with the warm layer of the wall (under the heat-insulating layer), they are able to remove heat from it to the outside. Experts are advised, if possible, to avoid fastening directly to the outer wall of any metal structures or elements.
In addition, a place on the roof, facade or floor, which for various reasons was insulated using a thinner layer of thermal insulation, in comparison with other elements of the enclosing structure, can become a place for the formation of a cold bridge. One of the most common mistakes is the failure to effectively insulate the balcony slab, which is a continuation of the ceiling.
Ventilation system. In a passive house, it is recommended to install a ventilation system with heat recovery, since it is with the air that a large amount of heat energy is removed from the room. This ventilation system, in comparison with the natural ventilation system installed in typical houses, will allow you to save a couple of thousand kW of electrical energy per year.
At the heart of a ventilation system with heat recovery is a heat exchanger. This device has two fans (one removes polluted air from the room, and the other blows fresh air), a heat exchanger (heat is transferred from the warm air exhausted from the room to cold fresh air), channels (for transporting air), ventilation grilles, as well as a special device for controlling the operation recuperator. The ventilation system with heat recovery costs more than 23 thousand hryvnias, but it is advisable to use it in passive houses, since it will allow you to get significant benefits during the operation of the house.
This system, along with the effective air exchange of the interior, also plays the role of a heating system. A heating element is placed in the air channel of this system, which heats the air entering the room. It is the heating element of low power (with a power of 10 W / m2 of the heated area) that is the traditional source of thermal energy in passive houses.
It should also be noted that when discussing the issue of savings, along with the possibility of reducing heating costs, the fact that the operation of the fans in the system also requires a significant amount of electrical energy is omitted.
In order to reduce to some extent the need to use a heating element, and, consequently, to reduce bills for the consumption of electrical energy, experts recommend installing a so-called ground heat exchanger. It will heat the air entering the room with the heat accumulated in the soil, since even in winter the temperature of the soil at a depth of only 1.5 m is within 5 ° C, and in autumn (at the very beginning of the heating season) even higher .
Home tightness. It is of great importance, since all the efforts (financial and physical) that were aimed at reducing the heat loss of a passive house will not make much sense if cold air flows freely through the walls into the room. All existing technological openings in the winter period of time must be closed, all cracks (for example, at the junction of doors and windows to walls) are carefully sealed using sealing tapes. The only leaky place in the passive house is the outside air inlet of the ventilation system.
It should be especially noted that due to the fact that in a passive house there is no inflow of fresh air, it is strongly not recommended to arrange fireplaces in it.
In order to check whether your house meets the necessary tightness requirements, you must order a special test, the so-called Blower-Door Test. This test can be carried out by employees of the company, who specialize in performing various building measurements, using special equipment. During the test, a special fan is mounted on the outer entrance door, which creates a difference between the pressures of the outdoor and indoor air of 50 Pa, and under these conditions, the passing air volume is measured.
solar energy. In addition to the thermal energy that we receive from the sun directly through the windows, the use of this type of energy in passive houses is the use of solar collectors as a heating element for heating water for heating and water consumption throughout the year. Since the efficiency in the winter period in the Ukrainian operating conditions of this system is low, it cannot be taken as the main source of heat in the house. In our conditions, it will not be possible to do without traditional heating devices and heating elements in the hot water water treatment system.
Of course, solar collectors are an excellent free source of thermal energy (even if we take into account its high dependence on the various vagaries of nature), the only problem at present is its cost. Currently, not every owner can afford to pay more than 30 thousand hryvnias for this system.
House shape. One of the essential, but at the same time little covered in the literature promoting passive construction, is the aspect concerning the shape of the house. We will try to fill this niche. It is much easier to achieve low energy consumption in houses that have a compact form. These houses have a minimum ratio of the area of the outer walls (enclosing structures) to the total volume of the entire house. This is most typical for large multi-apartment passive houses of panel or block construction.
In order to achieve the desired effect, it is necessary that a single-family house has much better thermal insulation of the exterior walls than a large apartment building. In other words, building a passive house for one family is not always economically justified and cost-effective.
Expenses. Based on various publications on the Internet and construction magazines on the topic of passive houses, it can be concluded that in a number of Western European countries the construction of passive houses usually costs 8–15% more than the construction of a similar standard house. In Ukraine, this difference is about 20-35%. It is enough to simply calculate this difference in monetary terms. So, for example, a typical construction of a fairly modest house without finishing is about 350 thousand hryvnia. In order for this house to become a passive type, the owner will have to additionally “fork out” for another 70-122 thousand hryvnias
What will you get in return for the “overpaid” money? In addition to the fact that such a house causes much less harm to the environment, you also get serious savings in the fuel and energy resources needed to heat it. The size of this savings will directly depend on the type of fuel used to heat the house. If you use relatively cheap wood, coal or natural gas as fuel, then the return on investment in this project will now be doubtful, since the money spent can be returned in savings only after a couple of decades. If you heat the house with the help of electric energy, then in this case it is worth considering: it is better to spend money initially during construction and invest several tens of thousands of hryvnias, but at the same time receive significant annual savings on heating in the future.
Many may have doubts about the profitability of building a passive house. Yes, these houses require individual design, the use of three times as many heat-insulating materials during construction, they provide for the use of expensive doors and windows, an expensive ventilation system, the installation of solar collectors, etc. But we should not forget that the house passive type there is no standard heating system, the installation of which also requires significant investment.
Summing up, it should be noted that the average developer, who is forced to calculate every hryvnia spent, is best to pre-perform a detailed economic calculation, since not all currently available solutions are economically justified and cost-effective in Ukraine. We advise you to approach the issue of designing a passive house with particular care and scrupulousness. One of the best construction options may be the construction of an energy-saving house, which, compared to a passive house, has higher energy consumption rates (from 50 to 70 kW•h/(m²•year)), but at the same time is a simpler and cheaper solution (to for example, from aerated concrete, porous ceramics, etc.). Of course, if you have money and you are thinking how to spend it wisely, then it is best to build a passive house or even a house with zero energy consumption. The choice depends solely on your needs and financial capabilities.
We wish our clients successful construction.