In order to meet the standard of a low-energy house, the heating must be many times more effective than in average houses – up to 30kW per square meter. In addition to intelligent heating solutions, building an energy-efficient building requires above average materials and high-quality construction work.

Heiki Jürissaar, one of the founding members of Natural House OÜ, a company that produces energy-efficient prefabricated houses, says that a low-energy house is one step lower than a passive house. While the annual energy consumption of a passive house can be up to a maximum of 15 kW per square meter, in the case of a low-energy house, this figure can officially reach up to 30 kW per square meter. It is the efficiency of heating and energy-saving maintenance of the building, that is the first criteria from which the concept of a low energy house begins.

Heiki Jürissaar has been dealing with energy efficient houses for more than a decade.

“We have designed a low-energy apartment building in Norway. There we have floor heating, which draws energy from the seawater. For a low energy house, it is very important that the construction is of the highest quality. And for this apartment building, we used more special construction methods and materials. I is so much easier to reach the required low-energy kW/m2 in a private house than in public buildings. ”

Various sustainable heating options

High-quality insulation materials used in the interior and exterior of the building are not the only energy saving aspects of building a low-energy house, Heiki Jürissaar says. One must always look at the house as a whole. If we look at saving heat, for example, by ordering the best heat-resistant windows would be step 1.

Another important feature of building a low-energy house is that a ventilation system with a heat exchanger is used, which can be supplied with energy from nearby water, for example. In other words, the geothermal pipe is placed in a water body, the heating system draws heat from the water body and transfers it to the incoming fresh air.

Low-energy houses often use fireplace for heating. It is important that this is not just a beauty item – decorating the room. The fireplace is not efficient enough, even though it’s nice to look at. The fireplace only heats the air as long as the fire inside it is lit, because there is nothing in these fireplaces that can keep the warmth.

There is a possibility that a “hot water jacket” may be added to the fireplace – this way the fireplace heats the liquid that circulates in the floor heating system. “So during the time the fireplace heats up, the fire heats up the floor heating accumulation tank, and after the fire goes out, the storage tank has enough water circulating in the floor heating piping and warming the entire house.”

The advantage of low energy houses and passive houses, as the name implies, is that their constructions are of maximum thermal insulation – so these houses need little heating.

The first step – creating the right project

Jürissaar: “If you have an architectural sketch, the next step is to feed the sketched data into a computer program that will calculate under which conditions the house would meet the requirements of a low-energy house. The program also indicates whether the house with this project could be energy efficient at all. ”

According to Jürissaar, it is useful for each client to clearly set out what they want before starting to design a house. Confirm the starting point: whether the house has to be cheap, whether the house has to be energy efficient, with good design, or make compromises on important aspects.

“If you want an energy efficient house, it is important to know this before the project is created so that the architect can take that into account. By creating a calculation using a specific modeling program for the project, it shows how exactly the house fits into the section of low-energy houses and, if not, how to change a technical parameter or the design. ”

But at the same time, the criteria for a low-energy house are not at all cosmic. In fact, the only official criteria is the annual heating requirement per square meter (30 kW). But how do you get such a house in the end? According to the specialist, an architect should be used who can create an appropriate architectural project from the first sketch.

Different energy saving factors

An important factor in the design and the project of an energy efficient house is how the house is positioned relative to the north, south, east and west. The most favorable position to consider when designing a low-energy house is the south. In the south should be the side where the house has the most glass and window space, that is due to the heat and light that emits throughout the day.

Secondly, the house should be of high quality insulation, ie floors, walls and ceilings are well insulated. Third, in every quality living environment, there is a need for fresh, clean air. The ventilation of a low-energy house is usually solved by a balanced ventilation system that changes the air in the house and, at the same time, the energy loss of the exchanged air is minimal.

To maintain this quality, a heat exchanger is installed in the ventilation system, which takes the warmth of the outgoing air and returns it to the room with fresh air. This will save the energy. The heat exchanger does not produce any additional energy but helps to save it. The air leaving the building heats the incoming air. There are devices that are placed as additional heaters in the ventilation system.

“If it is frosty minus 30 degrees outside and 25 degrees Celsius is needed indoors, it is imperative that you have additional heaters in the ventilation system in addition to the heat exchanger. Which, for example, receive energy from geothermal heating. In the event of a severe coldness, the low-energy house should definitely have floor or radiator heating as an auxiliary heating, which could preferably be supplied with primary energy from the ground. A decent fireplace also gives you enough extra heat. ”

Building quality is important in building an energy efficient house. And although there is generally little talk about it, the quality of construction work is even the most important, says Jürissaar. “Because if you model a house with a computer program and, as a result, you get a house that meets low-energy specifications, then – if it is built poorly, the house may not meet low-energy requirements at all.

The first factor: wind resistance. If this is well done, then the heating costs will be lower. The second factor: moisture resistance. The flow of warm air through the house structures should be minimal. “In most cases, the pressure inside the house is higher than in the open air, the room’s air pressure is higher than in the open air, and if the house lets in too much air, a situation arises where the warmth inside moves outside with the air.

Houseś pressure test indicates the heating requirement

According to Jürissaar, the structures of the low-energy house and the ordinary house are not very different from the construction aspect in general. “Of course, there is more insulation in a low-energy house than in a conventional house (fewer cold bridges), but the question is how to make the structures moisture and windproof. Here we go back to the building quality. When a low-energy house is ready, in many cases it is checked whether it is well-built or not, whether it is vapor-tight or not. Pressure test is done, which were already the norm in Germany for example in the 1990s, “

However, if the construction quality of the house is poor, this test may indicate that when calculated, the air permeability was twice as good as planned before the house was built, but the quality of the construction work is poor, and so the heating requirements arise.

The structure of the test is similar to the effect of a balloon being inflated and then looking at how quickly it empties. The pressure inside the house is raised to a specific level and then the rate at which the pressure drops is measured. Then it is clear whether the pressure drop per unit time corresponds to the initial calculation. Depressurization can be used to calculate how much the house needs for heating.

When modeling a house, the u-values ​​of the exterior walls or structures are set, which is how good the insulation should be for these materials. Different materials have different u-values ​​at the same thickness. The task of the designer is to propose the best solution for different materials, to combine the structures of the house so that the cold bridges are also cut and the structures do not become very thick. And that the materials you use are reasonably priced. So you can make the same u-value wall at different cost.

“That’s art. But often the people who set the materials for the house have some preferences that are not due to the price of the material but to some third factor, ”Jürissaar states. “There are situations where the architecture is done, the structures are in place and then they say,“ Make this house, ”but it turns out that construction is expensive. Because complicated designs, expensive materials, unreasonable solutions have been used, that is, the people who created or designed this project have not thought at all about the cost of this house. This applies to both low-energy houses and all other buildings.

The cost of all buildings, including the low-energy house, is fixed during the design process. ”