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It is cheaper to save 1 kWh then to produce it!
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September 21, 2020

It is cheaper to save 1 kWh then to produce it!

All about the passive house: Insulation, airtightness and ventilation!

The passive house works on the principle of coverage of the peak heat demand per 1 m2. If one wants to heat a room of 20 m2, one would either need two light bulbs with a total of 200 W or one can invite two neighbours. This would give a new interpretation of hospitality in a passive house.

Small passive houses require about 300-400 mm of insulation and 200-300 mm of insulation in larger buildings, and all installation without thermal bridges. Note that thermal bridges in old buildings renovated into passive house levels cannot be entirely avoided. Passive house windows are crucial elements, and it is necessary to install them correctly and connect to an airtight layer in the building envelope. And passive house windows must have a spacer between glazings made of non-conductive materials.

Mario said many exciting things, but the most important thing about airtightness: No one feels responsible for airtightness in buildings.”

German building requirements ask for n50< 3 h-1 and passive house requirements are n50 < 0.6h-1. In fact, it is usually around 0.3 h-1, meaning that is ten times more airtight than building legislation requires. One example of good airtightness practice is a bundle of cables penetrating an airtight wall, and each cable being must be installed separately and made airtight, and this requires proper planning.

The passive house must be equipped with an air handling unit with heat recovery of 75-80% or better, closer to 90%, and with low-energy fans. Therefore, in passive houses, it is customary to heat and cool by just volume of the air and supply temperature that is required.

EPBD, nZEB and renewables!

Mario talked about the European Union’s EPBD target of achieving nZEB (nearly zero energy buildings) by 2020, as some Member States, such as Germany, have been even more ambitious, setting their target date for 2018. New buildings will be built to a passive house standard with additional renewable energy sources. According to Mario, an energy-plus house can generate three times more energy than it requires, for example, using photovoltaics on roofs and other technologies.

Mario stated: „Traditional resources are limited and nuclear power is not the answer for Germans. The answer to energy savings is the passive house standard, which offers a factor of 10 energy savings in Germany, and there are even more savings still possible in many other countries.

Because oil is more expensive, Mario talked about the possibility of using renewable energy sources, but there is still not enough to cover the current energy demand in the world.

Mario said: The biggest and cheapest energy resource is energy efficiency. It is cheaper to save 1 kWh then to produce it!”

Renovation of a concrete apartment building in a warm climate!

The concrete apartment building (24 apartments from 1974 with a total floor area 2 000 m2) with a single oil-based heating system for the entire building had many problems with a leaking roof and mould growth. Some time ago, several windows in the building were already replaced to 1.4W/(m2.K), which was a challenge for Mario´s team. Nevertheless, the older windows were exchanged for new windows with U-value of 0.75-0.9 W/(m2.K). The thick windows´ frames were partially covered with insulation from the outside. And one layer of bricks under the window sill was replaced by insulation. Basement walls were also insulated with vertical insulation in the length of 700 mm.

After fixing the roof structure and replacing the damaged insulation with cellulose insulation, a new additional structure was installed on top of the existing structure to change the inward slope to outward. An exhaust ventilation system with a heat pump for extract air was installed on the roof, and the ventilation ducts were placed on the exterior of the existing façade and covered in a total of 140 mm of insulation. The exhaust system is self-regulating and set to the minimum required amount of air (15-25 m3/h), and the windows can be opened if the occupants wish so.

The renovation costs came to €475/m2, not including the cost for renovation of balconies. After a complete renovation, the heating consumption (now with pellets) is down from 116 kWh/(m2.a) to 27 kWh/(m2.a), resulting in 87% savings; and the primary energy is 183 kWh/(m2.a). The renovation was financed by a loan from the bank with 20% discount.

Ventilation in a passive house in a warm climate!

In warm climates, natural cooling should be used if possible, and according to Mario, there is no need to use active cooling in Poland and Germany if free night cooling can be used. Free cooling should be considered at the beginning of the project. For example, in a passive house school, where Mario changed the fire protection areas in order to use the same air volume in the classrooms opposite the corridors, i.e. outdoor air was supplied to the classrooms on one side of the building and transferred through the corridors to the other rooms. This offers a cheaper solution, as the night cooling concept works well with the thermal energy and air movement. In addition, the windows in school are used for ventilation and have three parts: one is fixed, the other is openable, and the third part consists of protection against rain & burglar so it can be ventilated at nights.

New passive house in a cold climate!

One of Mario´s presented projects was a new residential house with a floor area of 180 m2 located close to St. Petersburg in Russia, as an example of a passive house in a cold climate.  A fairly large family house sits on insulation and does not touch the ground directly to reduce thermal bridges. In his design, Mario creates a compact structure that is more suitable for cold climate regions, and he plays architecturally with parts of the garage because it does not have to be insulated and is cheaper to build.

The passive house in St. Petersburg has 400 mm insulation and TGI (Truss Joist I-beam) structural wooden beams, windows with four glazings with 0.5 W/(m2.K) and a small number of north-facing windows with 0.3 W/(m2.K).

And Mario spoke significantly about renewable energy sources, such as pellets as a source for heating and domestic hot water supply. He showed a picture of a stove in this residential house, and next to the stove was standing a small bottle with a very small amount of pellets, which is necessary for heating this home for a week. And only 2 m3 of pellets are used for heating every year, which ensures an indoor temperature of 24°C in the living room.

Payback on a passive house!

The question of investing in existing or new apartment buildings is difficult to answer. Still, if the existing building is in good condition (i.e. bricks or concrete structure) and the layout of the apartments is right, then it is worth keeping.

Mario stated that the impact value on a building after renovation is enormous, as long as a specific approach is maintained: We do not renovate to save energy, we renovate when it is necessary. If a building needs renovation, the difference between excellent and average renovation can be calculated. And the goal is to achieve the payback time of less than ten years. In this case, it is possible to save money on energy, but also renovated apartments can achieve higher rents.

According to Mario, a more extreme efficient renovation would be about 30% more expensive than a normal renovation. However, some energy-efficient renovation projects could also receive 20% of government subsidies. Government institution will also receive actual consumption values from a building for the next three years to see the real effectiveness of a renovation.

Mario said: „For now, everything in the buildings is based on calculated energy analysis, but a good approach to demonstrate the effectiveness of renovation is to get real data for future analysis. Passive house monitoring should be done to prove that the passive house standard (and any other certified buildings) can be achieved in reality, not just on paper.”

About Mario Bodem

Mario Bodem is an architect (Diploma Architect DPLG), and he studied architecture in Paris and Moscow. He has worked as an energy consultant at TAE /BAFA and since 1992 has been working independently on various projects.

Since 2007 Mario is a partner at ING+ARCH Company in Germany and has many years of experience in the construction and renovation of energy-efficient and passive houses around the world. Mario is an expert in energy-efficient renovations, passive house design, engineering and energy consulting.

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