Shaping of the Architectural Detail in View of Energy Saving

Abstract

Global warming observed has provoked the tendencies to reduce the emission of CO2. In January 2014 Poland also introduced much stricter building-law regulations referring to how buildings should be designed in respect of heat insulation and a permissible value of EP coefficient (defining a yearly demand for primary energy). The changes introduced result from the general strategy included in the European EPBD (Energy Performance of Buildings Directive) which imposes (up to 2020) the reduction of greenhouse gases at least by 20 %. In December 2014 the European Union took up another obligation- to reduce greenhouse gases by 30 % by the end of 2030.

The consumption of energy in the building industry is vastly influenced by the thermal insulation of buildings, as well as by such things as: thermal Bridges, air tightness of a building.

When an architectural detail is not designed carefully enough or some other errors occur in the process of construction, one can observe a large energy loss which escapes through thermal bridges or other leaky places in the building. Energy loss may then reach even dozen or more per cent.

The European Union has changed legal regulations for the building industry, concerning mostly energy effectiveness. Those refer not only to the insulation capacity (passive protection from the heat loss) but also impose the obligation for new buildings to use renewable energy, which is understood as an active share of alternative energy. While doing their designer’s job, architects must now dedicate their time to the calculations how much heat is lost and to computer simulations of the energy balance, including the energy coming from solar panels, heat pumps, wind energy, etc.

The changes and limits to energy consumption introduced gradually influence the character of architect’s profession. The buildings designed as extensively segmented or glazed will become less economical than simple but carefully insulated blocks. Also, the role of an architect is about to be changed giving way to a new profession which could be dubbed as: a specialist in energy saving and the building physics.

1 Introduction

In local Polish publications one may come across faulty solutions referring to the process of shaping the so-called modern architectural detail. These can result in thermal bridges created, and consequently a large energy loss. Such a situation often occurs when foreign solutions designed for a different climatic zone have been applied directly, which should not be done in Poland where a former adaptation to the local climate conditions is fairly needed. In other cases, this may be an error in the designing or building process that matters. The growing costs of energy, as well as more and more strict legal regulations concerning energy saving make it necessary to design the architectural detail even more carefully.

The latest amendments to the Polish building regulations including the ordinance by the Minister of Infrastructure concerning technical conditions…., in force from 1 January, 2014, defines much stricter requirements to be applied to the building design in respect of thermal insulation [6]. This amendment refers to the original building, as well as its later alterations, including any changes in the way of using those buildings, both over and under the ground, which perform a usable function. In clauses: 148, 151 and 154, in individual passages, the Legislator has defined new requirements concerning the ventilation of buildings. In the ordinance of Chapter 10 on Energy saving and thermal insulation, in clauses: 328 and 329 the requirements defining the EP coefficient (yearly demand for non-renewable, primary energy) and the rules for its calculation were imposed. From now on the buildings must meet both requirements which concern:

• minimum thermal insulation of outer partitions in the building (walls, floors, roofs, ceilings, windows and doors)

• permissible value of EP coefficient influenced mostly by the central heating, hot water storage and electricity systems.

Up till now, it was enough to meet one of the requirements mentioned. Meeting both of them may be a real challenge for designers as the value of EP is defined by a combination of many different factors, such as: thermal insulation, method of ventilation, specific kind of fuel used for heating the building, etc. In the ordinance mentioned, clause 328, passage 1a, the requirements for alterated or reconstructed buildings were defined.

The changes introduced in the Polish building-law regulations result from the common strategy of the European Union (Energy Performance of Buildings Directive) aimed at the reduction of energy used by buildings, as well as the obligatory certificates defining the energy-effectiveness of buildings, which is specified in the directives issued by the European Parliament and Council [1]. The new EPBD directive no 2010/31/UE of 19 May 2010, point (3) says: Buildings account for 40 % of total energy consumption in the Union. The sector is expanding, which is bound to increase its energy consumption. Therefore, reduction of energy consumption and the use of energy from renewable sources in the buildings sector constitute important measures needed to reduce the Union’s energy dependency and greenhouse gas emissions. Together with an increased use of energy from renewable sources, measures taken to reduce energy consumption in the Union would allow the Union to comply with the Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC), and to honor both its long term commitment to maintain the global temperature rise below 2°C, and its commitment to reduce, by 2020, overall greenhouse gas emissions by at least 20 % below 1990 levels, and by 30 % in the event of an international agreement being reached. Reduced energy consumption and an increased use of energy from renewable sources also have an important part to play in promoting security of energy supply, technological developments and in creating opportunities for employment and regional development, in particular in rural areas. In December 2014 the European Union made another resolution - to increase the renewable energy sector up to 30 % by 2030.

All those legislative decisions in EU countries will result in the situation that only energy-saving buildings are built and in the future these will be mainly passive or even zero-energy objects. Unfortunately, no definition of such objects has been defined yet. An energy-saving home is also a home in which energy is obtained from renewable sources (sun, air, wind, biomass, earth and water) and where energy-saving equipment has been installed. The transitional period from 2014 up to 2020 (until energy saving standards have been precisely defined) in EU countries will be used for a gradual adaptation of the building sector to the very strict requirements awaiting, as well as for education and propagation of the idea for energy-saving buildings. In Poland since the mid - 2013 the National Fund for Environmental Protection and Water Economy has activated the program of supplementing credits for the building and purchase of energy-saving homes. Individual investors who within the years 2013–2018 start the investment or purchase an energy-saving building may apply for extra money as high as 30 to 50 thousand PLN. The sum of supplementary money depends on a very strict energy-saving parameter - respectively: NF40 or NF15 (energy consumption lower than 40 or 15 kWh/m²/year).

The money invested in the construction of a new building or modernization of the existing object tends to grow steadily and can be easily lost due to a wrongly designed architectural detail. It may occur that the building which at a quick glance looks correct (in respect of insulation) is faulty in respect of solutions for the details applied that diminish energy effectiveness.

2 Thermal Bridges

The thermal bridge, also called the cold bridge is a commonly known phenomenon. Thermal bridges are created in places which are not sealed properly or remain not efficiently insulated, i.e. where the U-coefficient of heat transfer is significantly higher (worse) than the one for the adjacent building elements. Due to this along with a big difference in temperatures outside and inside the building in the winter time, one can observe the point or linear cooling of the partition. Through a thermal bridge the heat is lost beyond any control. The heat loss is proportional to the area of the bridge. In the place where the thermal bridge has been created the temperature of the building partition in the winter time lowers so much that the dew point is exceeded and steam is resolved into water. This phenomenon provokes a risk that the walls and ceilings in rooms become wet, as well as many other negative consequences, such as formation of fungi and molds. In extreme cases, in the places which are not properly thermally insulated, the process of freezing may occur, which consequently leads to biological corrosion of the building elements.

The standard definition of the thermal bridge is the following [5]: The cold bridge is a part of the building housing in which a usually equal heat resistance has been changed through:

• full or partial piercing of the building housing by a material of a different heat conductivity,

• changed layer thickness of the materials,

• difference between outer and inner surfaces of partitions, as in the connections: wall-floor-ceiling.

  Thermal bridges may have a point or line form.

In individual European countries fairly different standard regulations as to how to calculate thermal bridges are in a mandatory use. So far in Poland a simplified method to measure the heat loss due to thermal bridges has been applied [12]. It involves the correction of the U-coefficient depending on the question if:

• the outer wall has windows and doors - ΔU = 0,05 [W/(m²  × K)],

• the outer wall has windows and doors with balcony brackets -

  ΔU = 0,15[W/(m² × K)] (see Fig. 1).

  Fig. 1.

  

  Typical locations of linear thermal bridges: A – in a building of services and apartments, B – in industrial building (Source: Author’s drawing of December 2014)

There are no particular data which would define the energy loss provoked by thermal bridges. The correction coefficients ΔU, as well as some other sources of information make us think of the heat loss as big has even 20 % [8]. This happens mainly due to long linear bridges as a result of inefficient insulating of the cover wall in the place of connection with:

• the floor on the ground,

• the ceiling above unheated basement rooms,

• uncovered passages or drive-ins downward under the building,

• ring beams on subsequent stories,

• projections,

• cornices and attics,

• roof surfaces.

Thermal bridges may occur in any building objects, and the lack of tightness may result from a wrongly developed design or a careless execution of the investment.

An extensive energy loss in buildings may also result from windows, doors or balcony brackets that have been wrongly positioned in the cover wall. Then thermal bridges are created in specific locations (points) around those places. The more windows, doors or balconies are designed and then wrongly or carelessly installed and insulated, the bigger energy loss may occur–even as high as a dozen or more per cent. Presently, however, new technologies are available that make it possible to assemble balcony brackets tightly enough to prevent any thermal bridges. In this case, the warming layer is located between the cover wall and the balcony bracket through a specially shaped reinforcement of the balcony panel (see Fig. 2).

Fig. 2.

Two ways in which a ferro-concrete balcony panel can be fastened: A – traditional way with a thermal bridge, B – energy-saving way within the “Isocorb” system (Source: Author’s drawing of December 2014)

The heat loss in buildings, generated by windows and doors, results from their worse insulation from outer walls as well. The standard heat conductivity coefficient required for the outer wall, e.g. for a detached one-family home has now a minimum value of U = 0, 3 [W/(m² × K)], while its value for a window is U = 2 ÷ 2, 6 [W/(m² × K)]–depending on the climatic zone. In the market, there are three-pane windows available which are characterized by a much better coefficient reaching U = 0, 7 [W/(m²  × K)]. The heat conductivity coefficient for a triple-pane joint window, with a low-emission coat and an inter-pane void filled with argon may be as low as approx. U = 0, 55 ÷ 0, 6 [W/(m² × K)]. Yet, the heat loss may occur on the window profile whose insulation capacity does not usually exceed the coefficient value U = 1, 0 [W/(m² × K)]. As the share of window profiles in the whole middle-sized window area is about 15–20 %, the value of the heat conductivity coefficient for the whole window (profile + glass pane) does not usually exceed the coefficient value U = 0, 7 [W/(m² × K)].

The window insulation capacity and its proper assembling should be treated as two different problems. The largest heat loss occurs in the place of connection between the window and the cover wall, especially in the place where the window sill is fastened. A careless and not tight enough fitting-up may significantly lower the heat comfort of the room even if the best window is installed. Nowadays, a new method of window assembling has been developed in which windows are installed on the outside of the wall, even in the outer warming layer of the multi-layer cover wall. In this case, windows are fastened on special steel anchors (brackets) in the outer warming layer, not directly inside an opening in the brick wall. Recently, the sellers of window and door joinery have been offering various solutions for assembling windows at different prices, such as:

• commonly used the so-called traditional assemble method, i.e. inside the window opening, where a thermal bridge usually occurs (A - sealing made of polyurethane foam),

• energy-saving assembling inside the wall, in its outer part before the warming layer (B - sealing made of polyurethane foam + additional foil belts from the inside and outside of the polyurethane foam),

• energy-saving assembling on the outside of the window opening (C – within the thickness of the warming layer on the outside of the wall, on steel brackets + foil belts from the inside and outside of the window) (see Fig. 3).

  Fig. 3.

  

  Methods of window assembly: A–traditional with a thermal bridge, B and C –energy-saving methods (Source: Author’s drawing of December 2014)

Typically, thermal bridges that occur in industrial halls result from a wrongly designed warming layer applied to pad stones in the place where they contact the so-called foundation beam. Prefabricated foundation beams can now be manufactured in the warmed-up version, which means that they possess an inner Styrofoam (polystyrene foam) core. Nevertheless, designers often forget that the pad stones must also be warmed as this is where the foundation beam and the main bearing construction of the industrial hall are supported. In this case, thermal bridges occur locally, i.e. on the floor around the foundation.

3 Air Tightness of the Building

The standard definition of thermal bridge given above [5] is not precise as it does not clearly emphasize the lack of tightness of cover walls and roofs, which significantly influences the energy characteristics of the building. The building standard explains thermal bridges as: full or partial piercing of the building housing by the material of a different heat conductivity. In this case, thermal bridges are created for another reason, which is a lack of tightness or generally lack of any insulation material in the housing and, consequently, an air flow through any leaky places in cover walls and roofs. Not everybody knows that the heat loss in buildings may often result from the untight, leaky housing of the building through which due to the difference in pressure cold air penetrates into the building (infiltration) or warm air escapes outside (ex-filtration). In extreme cases the leakage may provoke the phenomenon of the so-called wind blowing (draught in the rooms), which extensively influences the using of the building in respect of comfort and ergonomics. Recently in Poland, there have appeared a lot of companies that deal with the measurement of the building tightness. The method of such air-tightness measurements is based on the Polish standard [4] and allows to measure the size of the air stream which flows through the gauge called the Blower Door. This device consists of a ventilating fan which is to pump the air into or out of the room in order to create a specific pressure, as well as measuring apparatus connected with a computer which measures the air flow at the specified difference of outside and inside pressures [7]. The measurement is done both for overpressure and under-pressure in the room, and the average value of the air stream flowing at the pressure difference equal to 50 Pa, is taken as a basis for defining the value of n50 coefficient. All the leaky places, located due to the pressure created by the Blower Door, can also be spotted by thermo-vision (a thermo-vision test by means of a camera makes it possible to observe the air flowing), as well as the using of an anemometer and smoke generator (See Fig. 4).

Fig. 4.

Pattern for testing the air tightness of the building (Source: Author’s drawing of December 2014)

In the attachment to the ordinance issued by the Minister of Infrastructure on the technical conditions… [6], in point 2.3.1. the Legislator writes: In residential buildings, blocks of flats, buildings of common use and industrial objects the outer non-transparent partitions, connections between the partitions themselves and between their parts (such as connections of flat roofs and roofs with the outer walls) all passages for the elements of installations (such as ventilation and fume ducts through outer partitions), as well as connections of windows with jambs, should be designed and performed so carefully that a full air tightness is achieved. Further on, in point 2.3.3., a recommended value of the building air tightness is given, depending on the kind of ventilation system designed (mechanical or gravitational). At the moment the testing of buildings in respect of their air tightness is not mandatory but fairly recommended, according to the attachment to the ordinance mentioned above, in point 2.3.4. which says: It is recommended that the executed residential buildings, blocks of flats, buildings of common use and industrial objects are tested in respect of tightness and that the test is done according to the Polish Standard on air penetration so that the required tightness is achieved as it was defined in point 2.3.3.

Testing buildings in respect of air tightness is not yet obligatory in EU countries, except for United Kingdom, while in Germany and Denmark it is required only for buildings equipped with mechanical ventilation [2].

The studies done in Poland in which a few passive or energy-saving buildings (those were designed and performed very carefully when it comes to air tightness) were tested in respect of tightness show that the improvement in tightness made it possible to save up to 40 % of energy [2]. In industrial buildings a typical place where air leaking occurs is the connection of multi-layer panels used for the so-called light building structures:

• with the foundation beam,

• with the roof,

• internally between the panels in the place of connection by means of special locks,

• where the roof ridge is covered with tinware,

• where skylights and smoke vent flaps are situated.

Any leakage may result not only from a careless execution of the project but also from some inner faults of building elements designed for the so-called light structures (e.g. untight locks between the panels, which should tightly connect them one to another). The leading manufacturers of multi-layer panels have introduced a new generation of protective panels which make it possible to save up to 20 % of energy needed for heating homes [11].

4 Conclusion

The beginning of 2014 brought in a lot of changes as to the requirements concerning the energy effectiveness of buildings. Among those, there is an obligation for the building to meet simultaneously both conditions of heat conductivity through partitions U and the permissible value of the coefficient defining the demand for non-renewable original energy EP. As for the required values of the U coefficient, compared with those of the late 2013, one may say that they are still kept on a safe level and will not make the architects change their attitude to partition designing dramatically. More controversy among architects is raised by the newly introduced values of EP coefficient (original energy). Those are much more difficult to respect, especially in some categories of buildings, as they refer to the energy balance of the whole building, including the method of heat delivery (heating, cooling, electricity) to the building, as well as the source of energy used. Therefore, to meet the EP demands the designers may need to apply solutions that so far have not been popular with those categories of buildings, which will consequently increase the cost of investment.

To achieve the standard EP coefficient (of primary energy), first both the EU coefficient (of usable energy) and the EF (final energy) must be calculated according to the rule defined by the following formula: EU > EF > EP [3]. The architect may influence only the EU coefficient through a proper designing of the function and body of the building, as well as the kind of outer partitions (of adequate U coefficients). An excessive segmentation of the building body leads to a higher energy loss. This is defined in Clause 329: on technical conditions… [6] giving permissible factors of the building segmentation A/V (coefficient of the building shape), where:

• A - is the sum of surfaces of all building partitions separating the heated part of the building from the outside air, ground and the adjacent unheated rooms, calculated on the outline,

• V - is the cubature of the heated part of the building minus arcades, balconies, loggias, galleries, etc. calculated on the outline.

What also provokes energy loss is an excessive glazing and therefore the current legal regulations define the permissible glazing quotient A0max, for specified types of buildings.

The theories, commonly used only few years ago, which stated that windows should be a little leaky as the inflow of fresh air prevents the dampness in rooms, as well as molds and fungi, now belong to the past. So do the gravitational ventilation systems in favor of mechanical ventilation with recuperation. Within a few years from now on, recuperative ventilation will probably become the only legally admitted solution, even for detached one-family homes.

One of significant factors of a modern building, along with energy effectiveness, is its air tightness. The designer should pay a special attention to it by choosing an adequate sealing for windows and doors. What also matters is how the steam-proof foil is connected and any piercing in installations insulated.

While designing architectural details, one should aim at the maximum air tightness.

The new architectural detail has been introduced for common use. As an example one can mention the assembling of:

• balcony brackets to prevent thermal bridges,

• windows and doors installed within the warming layer of the outer wall and sealed with belts.

In the near future, due to much stricter regulations concerning energy saving, new building technologies focusing on saving energy are going to be developed. Among others, a more and more common system of building certificates, based on energy effectiveness (energy-effectiveness certificate) as merely one of many factors, will play its role. The most prestigious buildings have to meet many other (more than a dozen) demands to be granted a prestigious certificate LEED [9] or BREEM [10].

All in all, the circle of Polish architects is deeply concerned about the changes introduced. They ask a question if the coefficients: A/V and A0max., included in the building law regulations, will put an end to segmented, sculptured and glazed buildings? Will the European Union after 2030 allow only simple blocks with eye-sockets (small windows) and those more spectacular objects can be done only at a great cost? The question arises if the changes implemented may diminish the role of an architect giving way to a new profession called for instance: the building physicist. The newly introduced building-law regulations may also make it necessary to modify the methods of educating future architects.