Low energy building

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History

First generations of conceptual low energy buildings were built during 60's and 70's when the West, thanks to the generation of Hippies, has started to remind itself of the human connection to nature. New demands for living have looked for inspiration deep in history using the terrain, natural powers and local resources.

But the first low energy buildings have had many failures and many things have been overlooked. Among the common mistakes were too big glass walls in order to get as much passive solar gain as possible but it often led to overheating in summer. Also the thermal bridges and uncontrolled air change.

The low energy house with good energy performance has many advantages such as low energy demand and consumption, good indoor environment during the summer and winter, low air pollution.

National Standards and design guidelines

Main article: Low Energy Buildings Design Codes and Guidelines

This section deals mostly with codes for European buildings, although some principles, values and calculation are common also outside the Europe. There is the need of more study for instance for US buildings.

The development of low-energy buildings is highly dependent on evolving Standards and Directives; therefore the European Committee for Standardization (CEN) was founded in 1961 and set under Belgian Law. CEN produces a number of different publications: EN ISO (European Standards), prEN (Drafts of Standards) and other approved documents CEN TS (Technical Specifications). The European countries together work, develop and asses the Drafts of Standards where they specify and develop the new Standards based on their knowledge, information and existing international Standards and guidelines. ASHRAE organization is dealing with Standards related to heating, ventilation and air-conditioning systems HVAC.

Design: Building construction, technology, materials

There is wide range of materials available on the market, but some countries (especially Northern ones) still needs to be stimulated by importing for example good double windows. Important is the coefficient of heat penetration and avoiding of thermal bridges, less important is thermal-storage characteristic of constructions. Building construction are usually multi-layered, previous single-layer brick walls are not effective for Low Energy buildings.

Massive walls/constructions - with high surface weight. Load bearing construction with thickness: 1.thickness < 240 mm: burnt ceramic brick, special shaped brick from expanded concrete and 2.thickness from 120 to 180 mm: monolithic reinforced concrete and prefabricated walls, concrete shutter shaped pieces, with reinforcement and concrete. On the load bearing construction is attached thermal insulation with external rendering or grid system with thermal insulation and ventilated exterior skin. Less appropriate and used is sandwich system (from outside to inside: exterior brick wall, air cavity, insulation, interior load bearing brick wall).

Light walls/constructions - mostly wooden construction. Wood is nature material which people choose and has large potential with placement of insulation in between and at the same time avoiding the larger total thickness of wall.

Typical materials

• OSB board - wood chip board, OSB stands for Oriented strand board
• gypsum board - finish construction of interior walls and ceilings, Gypsum Board
• gypsum fibred boards
• engineering wood - profiles, joints, plywood, boards, Engineering wood
• thermal insulations - for achieving thermal comfort, reduce of heat loss or gain, Thermal insulation, building insulation
• vapour barrier and retarders - resistant layer to prevent moisture in the building Vapour barrier

Building constructions and example of construction compositions

Wooden construction - For timber structure building is traditional system of plank revetment [www.isofach.de] which is use worldwide and the widest usage is in North America. The system utilizes a wooden post-and-beam framing system with a prefabricated insulated panel system, in which the panels are applied to the exterior surface of the frame. Vertical wooden elements have statical counterwork and cooperate with large format board from OSB wood chip board (earlier usage of plywood). Vertical elements are most often wooden plank from solid timber; it is possible to use combined I-girder profile (flange made of wood, stalk of OSB). This system is known as "two-by-four" (2 x 4) because of original dimensions of planks in inches. The structure is made upon on built-up flat surface (concrete slab).

Example of construction composition (from outside to inside):

• exterior plastering, thermal insulation, diffusion foil layer, OSB boards with vertical timber planks and in between thermal insulation, vapour barrier, thermal insulation in insulated space, gypsum board (or another interior coating)
• exterior wall-covering placed on the system of wooden molding, thermal insulation, OSB boards with vertical timber planks and in between thermal insulation, vapour barrier, thermal insulation in insulated space, gypsum board (or another interior coating).

Note: first outside layer of insulation should be approximately 2/5 of total insulation thickness which should be designed and caculated based on total U-value of wall (U-value for low energy buildings) and climate conditions. Second layer should be approximately 3/5 of total insulation thickness (layer in between OSB boards and timber planks). Third inside insulation layer should be approximately 1/5 of total insulation thickness.

Prefabricated wooden construction - Becoming popular, made in factory in friendly climate conditions, fast assemblage on building site. The prefabricated elements can be equipped with ventilation or electrical installation right in factory which makes the building process on building site very fast and can takes few days only.

Example of construction composition (from outside to inside):

• thermal insulation system with exterior thin plastering (ETICS), gypsum boards, wooden I-profile with mineral thermal insulation, gypsum fibred boards, vapour barrier, wooden joist of bearing frame construction with mineral thermal insulation, gypsum fibred boards, gypsum boards.

Masonry - Burnt clay, shaped from expanded concrete

Reinforced concrete - Monolitic or prefabricated walls, walls from concrete shutter special shape

Example of construction composition (from outside to inside):

• exterior plastering, thermal insulation, masonry (ceramic masonry, shaped bricks from expanded concrete), interior coating or plastering
• exterior plastering, cork insulation boards, bricks, interior coating

Roof - minimal 300 - 400 mm of thermal insulation for flat roofs. Roof structure can be one-surface roof or two-surface roof with ventilated air layer, roof. For solar system (photo-termic,photo-voltaic) are nowadays usually made by systems. Manufactures and suppliers of roofage usually offer information about possibilities.

Windows, doors - Main and often very expensive part of building. The position, dimensions and connection to construction of windows and door have the main importance for an entire house - estetical, operational and energetic characteristics.

Resultant heat penetration through window depends on:

1. characteristics of glazing unit and characteristic of frame
2. rate of glazing unit and entire window
3. characteristic of distant frame on the edge of glazing units and its lenght
4. bond among window and wall
5. factual implementation

Glazing unit or insulated glazing should be at least double pane or triple pane unit. The roof windows are currently considered not sufficient for low energy or passive houses, but the view of Engineers differ. The visors (shading) should be part of the windows for instance blinds and rollets for common windows. The window wall facade and its shading should be very carefully designed and calculated with overall design of building.

Foundation, floor - Mostly are low energy houses without basement. Often mistake with designing low energy house is unsufficient thickness of thermal insulation under air channel on the ground floor. The good attention has to be put also on details and connection points (quoins).

Inside construction - Less importance then envelope construction. The partition/walls between spaces with different temperature have to be considered and fulfill the requirements of coefficient heat penetration.

Listed construction layers examples are taken from "Low Energy Building - Principles and examples" book and are usually used in middle Europe although the wooden structure are very popular in North America but the construction layers can differ little. The construction should be calculated and designed based on climate conditions of building site, local resources of materials and Engineer´s experiences.

Non-typical materials

Straw - Early use with clay and muld. For the last two decades the straw is again becoming sustainable material for building homes for walls (stacks of straw as insulation and load bearing construction) and roofs. Straw is natural material with very good thermal properties, especially insulation.

Earth - Earth sheltering is becoming more popular as the system is using the earth as insulation for walls and the building itself is covered with earth.

Snow - Snow has approximately the same R-value as wood or single pane glass and the snowhouse has been build by Inuits as a temporary house. The snow is a good insulation material although some problems with keeping the steady state and amount of snow at same place when the region is windy or sunny. And the problems occur when the snow melts around the house or on the roof by heat coming from inside of building.

Energy efficient features

Building envelope - protection for occupants and creating indoor environment. Walls, floor and roof create the enclosed space and separate inside from outside. The envelope has to balance ventilation and daylight requirements, provide thermal and moisture protection and determine the energy demand and life-cycle cost and impacts.

Daylight - illumination of interior space evenly by means of proper window placements and orientations, skylights, etc.

Direct gain - the sun rays enter the room and bring the heat which can be stored in room or distributed over the building.

Glazing and windows - performance the conductive heat losses and gains (U-value), visible light transmission and solar heat gains.

Overhang or shading devices - stationary or movable, protect usually south-wall from overheating the building.

Thermal mass - heat absorbed by walls and floors which can be absorb in day time and release in night time to heat up the space. Or cool down at night in summer depending on the year period.

Overall U-value < 0.15 W/m2.K

Windows and door U-value < 1.0 W/m2.K

Insulation thickness roof > 300 mm

Insulation thickness wall > 240 mm

Permeability < 0.6 h-1

Those values which should be considered as required design values are valid for European conditions. For Northern countries (for example Low Energy House in Sisimiut, Greenland) the wall insulation thickness is 300 mm and roof and floor 350 mm.

• Renewable energy
• Sustainable design

• Energy efficiency and consumption

Typical European house requires at least 250 kWh/m² per year and mostly they have been build when the resources of oil and electricity were still large and therefore the need of saving energy has not been primary target. Low energy buildings require 10 times less energy for running.

Heat loss and gain

Main article: Building heat loss and heat gain formulas

Building heat loss and heat gain calculations are important to determine energy bilation of the building. Heat loss can be through material surface, surrounding soil, unheated space, or in connection with air exchange. Heat gains are typically internal or passive solar gains.

Design Details and Examples

Insulation - three dimensional structural element plans, thermal insulation ISOVER: insulation and details, construction card and energy calculator, details in PDF

HVAC - HVAC shortcut for Heat, ventilation and air conditioning

Climate considerations

The local climate together with envelope materials and building design has great influence on building performance. The main tools for controlling the thermal indoor environment in buildings are shape of the building (massing), fenestration (shape, position and orientation of windows), solar control (shading and surface finishing), building fabric (insulation and thermal storage) and ventilation. The designer of building has to take those inputs into account and design well working building based on these inputs. For different climate types (typical meteorological year data and solar gain) are following considerations:

Hot/Dry Climates - Material with high thermal mass (thick walss such as adobe and masonry) should be used because of diurnal temperature swings with limited openings on the north and west facades, but with large opening on south facades to absorbe the direct sun in winter. The thermal mass materials will avoid the large temperature variations in building from outside to inside. Possibility of thermal stuck materials where the walls/floors collect and absorb the heat during the day and let out the heat during the nights. Large heat gain by windows can be reduced by closing shutters during day-time and the building could be ventilated in the night-time to cool down when it is need it.

Hot/Moist Climates - In climate with large moisture the low thermal capacity materials (light-weight walls) will perform in very good way, where the temperature drop during day/night is not significantly large. Common are masonry walls and it is possible to protect the walls with plants or overhangs. Possible use of reflective insulation to avoid letting the solar radiation in the building. The house can be elevated on stilts and fully cross-ventilated. Large openings protectd from the summer sun placed preffered on the north and south facades to catch breezes or encourage stack ventilation.

Temperate Climates - Good insulation for walls and openings should be shaded with overhangs during hot times and not shaded during cool months.

Cold Climates - The material used depends on local resources but the envelope should be air-tight (wind-tight) and well-insulated (very low U-value to reduce heat loss). Larger windows face south to increase the solar gains. The masssive construction should avoid overheating in winter at the same time. The construction should not be made from high thermal mass materials to avoid long time required to reheat the space and necessity of solar collectors usage or other renewable sources.

Integrated design process of low-energy building

In order to build a low-energy building an integrated design process should begin and be implemented in early stage of building even before the first drawing sketch from an architect is produced. The integrated design process enables all the team members to work together and look upon the main requirements, possible ways and solutions that will lead to design of best possible building regarding energy and needs .

Early in building process the design team will meet to ensure the cooperation and understanding of commitments between members. In the project a “key person” can be named to connect the members of team together and ensure that the integrated process will be continue. In Europe this person is usually called the business process manager. The owner will play the main and critical role and will be often join by a financial manager. The perfect strategy would be for the members of designer team (or head) to stay on the project to the very end of building process. The members of team must meet throughout the various design stages and periodically, during construction. Also the integrated design reguires many simulations and software to use in order to achieve the best possible solutions.

The integrated design process team:

1. Owner (or representative)
2. Architect
3. Designer (facilitator, business process manager)
4. Civil Engineer
5. Construction manager (contractor)
6. Structural, Mechanical and Electrical consulting Engineers
7. Specialized consultants (energy, finance)

The first step of the process preparation is for a developer (owner, or his representative) to identify the needs, criteria and commitments for high performance and energy efficiency of building. In this stage the main information should be also collected (space, number of people, budget, information about building site, type of soil, orientation, height of surrounding buildings, etc).

Second stage could be called a pre-design where the architect and teams of specialist will produce, based on information from stage one, the early graphic suggestions for the building. There should be more solutions available for the Engineers and specialists to analyze. The systems should be analyzed together such as: lightning (daylight and natural) with mechanical systems, daylight with envelope system, water and heating and cooling, ventilation and lightning. The team undertakes the whole building system analysis and must consider the interaction between systems.

The design development allows the number of solutions to be narrowed to few possible solutions with the best possible energy and indoor performance with respect to financial and architect value of the object. Greater details and plans should be considered for all aspects of the building. This phase should end with detailed design which will be agreed on by all members of team and owner. After detailed project documentation will be done, the contract stage can begin which are needed for proper pricing, permitting and construction.

The contractor and construction part of team should be at very large projects from early beginning but in small projects he can join the process in construction stage and together with the team should be fully involved in the process. The design team is fully responsible for assuring that the building and energy requirements will be met together with design and contract.

How the building meets the criteria is set in stage commissioning where all function and systems of building are assessed and evaluated by the design and construction team, and can be still changed before the final and closing stage of building. After the building has been fully built and open sometimes post-occupancy evaluation is done to assess how the building works and meets the criteria, energy and indoor performance set at the beginning by owner and team.

Key actions recommended ensuring successful integrated design process:

• Integrated process begins at earliest stage
• Name “key person” of integrated design process
• Simulation and interaction among building systems
• Analyzing costs (building cost, life-cycle, maintenance)
• Energy and indoor performance at the best level
• Evaluation of criteria
• Rewards for extra work

Results shows that the integrated design process benefits from cooperation of all team members and the process provides the necessary information and strategies to plan, design and build the high low-energy performance buildings. The building will have reasonable initial and life-cycle costs over entire existence cycle. The design objectives which will be achieved are: safe, secure, flexible, aesthetic, functional/operational and sustainable. A successful integrated design leads to the perfect whole building design.

An interesting newly developed part of the Integrated Design Process is the idea that the process should start on "room level". The whole design and energy calculation should be done on room level using the new software IDbuild Software created by Technical University of Denmark. The software analyzes one room using variation input data (orientation, geometry, window height and properties, thermal mass and insulation, ventilation and cooling, energy, etc.). First the reference room is designed and simulated and after that the two variation rooms can be calculated and compared. After the number of variation of the best possible room, the architect knows how the best performance room should look like and he uses these designed rooms to create the overall design of building. This approach is coming from Engineer´s point of view therefore the architects could feel limited but on the other hand this way of designing is very energy friendly.

Economy and costs

The extra cost for good and working low energy house in comparing to normal house will be around approximately 10 (15)% of acquisition price and the difference should return in 10-20 years thanks to energy savings. Most of these extra costs are paid for a good project (project and realisation stage) which is the base for well-working low energy house with all the aspects which need to be included in the project, such as building orientation and envelope, indoor climate, materials, etc. Other costs are for material (insulation, windows and doors with good performances. solar collectors, etc.).

Current developments

Nowadays with the shortage of natural energy resources most people look for possible savings and they often start with their own housing situation. For middle Europe it can be said that in next ten years more than half of the new dwelling buildings will be built according to passive or low energy Standards. With increasing knowledge of low energy designs Engineers and Architects are also getting more experiences and the housing situation for small investors is getting larger and larger. Technical Standards are getting more restrictive and therefore the environmental impact is also greater. Many Engineers and researchers are making bigger investigation and trying to set on the limits of low energy or passive design through for instance investigation of possibilities of building well performance passive house in northern extreme climate and with these researchs hope to stimulate and develope further the housing in other climates. Those investigations could also stimulate the large scale buildings which development is not so fast. Challenges are given by climate conditions of building site, building technologies at present time and place, engineer knowledge and experiences. The spreading of low energy design seems to be quiet fast in Europe although the third countries are not envolved in building or even research. To built an efficient and good-working low energy house require to have money from beginning (design) to the very end (house) but it pays of itself during the very years of building duration but also it pays of for the future energy savings for next generations.

Related Terms

• zero energy building - a general term applied to a building with a net energy consumption of zero over a typical year (heat demand lower than 5 kWh/(m².a)
• passive building Passive House
• almost passive building (building with very low heat demand) - the building performance is very close to passive house requirements, but some parameters were not reached)
• energy-plus building - a passive house with a large foto-voltaic system which products more energy then uses (energy excess can be supplied to supply network)
• Minergie® - low energy standard in Switzerland Minergie
• Minergie®-P- parallel to passive house, Minergie in Switzerland
• 5-liter-Haus (3-liter-Haus) - approximate furnace oil consumption of 1 m² of floor area, expression used in Germany (3-liter-Haus is approximately 30 kWh/(m².a) in an European climate
• energy independent building - in high-latitude and/or extreme highland regions, the house produces itself the necessary energy for running, no energy supply from outside, Solar Homes

Examples

• Low-Energy House in Sisimiut, Greenland

• Building Examples with the combination of integrated design strategy and the appropriate application of technology to achieve low energy buildings. Wide range of concepts. List of buildings: "Meletikiki" office building near Athens, Greece; "Avax" office building in Athens, Greece; "Ampelokipi" residential building in Athens, Greece; Residential settlement in Ljubljana, Slovenia; Office double façade building in Nova Gorica, Slovenia; Office atrium building in Ljubljana, Slovenia; Office and residential development in Berlin, Germany; University Engineering building, Leicester, UK; Office building with stack ventilation, Nottingham, UK.

• Existing Low Energy Houses in UK and their modernisations

• Europe´s first low-energy airport terminal in Zurich

Resources

• WBDG The whole building design

• EPBD Energy Performance Building Directive

• CEN European Committee for Standardization

• ASHRAE Advanced Energy Design Guides (AEDG). HVAC

• Low Energy building design

• Energy Star Green House Plans

• Low Energy Building - Solar Server

• Low Energy Building Concept

• Online Fabric Structure community joins over 800 low energy buildings manufacturers worldwide