Description
Energy-saving houses are manufactured with different characteristics and efficiency classes. Our goal was to create a house that can be operated energy-neutral over the years. The resulting house exceeds expectations both in the calculations and in the measurements of the first two years.
Here we present this idea of a house, fed from 100% renewable energy, to all building planners in order to contribute to a faster transition away from causes of global warming.
- Address: 82205 Gilching
- Construction year: 2018
- Building type: single-family house with separate apartment
- Living area: 210 m²
- Aditional usable area: 100 m²
- Rooms: 8
- Built to meet the following standards and guidelines:
- KfW 40 PLUS
- KfW 431 Energy-efficient construction and renovation - construction support
- 10,000 houses program EnergieBonusBayern with “TechnikBonus” for
- Energy-efficient new building as a 1-liter house (yearly requirement is 10 kWh per square meter living area)
- innovative heating and storage systems
- Heat pump
- Solar thermal system with heat storage
- Grid-serving photovoltaics
- Requirements of the EEWärmeG are surpassed by a factor of five!
- Total energy requirement: 7.6 kWh / (m²·a)
- CO2 emissions: 2.7 kg / (m²·a) approx. 13 t / y savings compared to the EnEV reference building
- Usable building area (AN): 334.6 m²
- Essential energy sources: mix of photovoltaics, electricity storage and power grid; heat pump and latent energy storage for heating and hot water
- Coverage according to EEWärmeG: 95% through renewable energy of the heating and cooling requirements from sun, rain, air and geothermal energy
The house has a floor area of 94.5 m² plus a 24 m² comfort room, built on a 656 m² plot. The complete building sits on a livable basement. A garage is attached to the northeast side of the building and gives the structure a symmetrical appearance.
Large floor-to-ceiling windows on the south and west sides invite the sun's warmth into the house. Smaller north and east windows offer brightness and good ventilation. The basement is surrounded by a light trench that offers the guest room a pleasant view from the outside and daylight.
A covered seating place connects seamlessly to the 25 m² open terrace. The ceiling of the patio at the same time is the balcony of the upper floor. From the house you look into the large south-facing garden and over a side street into the green. The distance to the neighboring house of 7 m to 10 m avoids a crowded feeling and gives space for a beautiful garden design.
Inside, the house is divided so that the upper floor can be used as a separate apartment with two rooms, a kitchen-living room and a bathroom. The entrance area is the vein of the entire house. Behind an apartment door on the ground floor resides a guest toilet, a cloakroom, as well as the spacious kitchen with its dining room and the adjoining living room, as well as a complete bedroom with walk-in closet and private bathroom. Thus, the ground floor can be used as an age-appropriate stairless apartment. In the basement there is the room for the technical equipment, an office workshop, as well as a hobby room with a separate daylight-flooded guest room and bathroom. The floor covering on all levels consists of light stone tiles with floor-heating.
The requirements for solid diffusion-open walls with good insulation, in-roof solar system, heat pump, latent heat storage, aesthetics and functional design, made it difficult to find a construction company and architect, willing to perform without horrific surcharges. Therefore, with my previous construction experience and my engineering knowledge, I designed the optimal combination myself.
In the following I present the innovative features of the house, grouped into an energy concept and the construction method. The ideas and findings can be adopted by other building planners in further projects in order to save effort and costs.
The energy source of the house is the sun - for both electricity and heat. There is a surplus in summer, but too little in winter. Excess electricity is fed and sold into the grid. Storing heat is only possible to a limited extent. In our latitudes, it is not possible to dimension the energy supply exclusively after winter with a proportionate investment. The chosen approach is therefore:
- The photovoltaic system is dimensioned according to the roof area and in such a way that an excess is produced in summer to cover the costs in winter. The usual system size is limited by the EEG surcharge-free systems to 10 KWh peak.
- Solar thermal system to supply the heat for the domestic water in summer.
- Thermal energy / ice-storage to carry the heat into the two coldest winter months; more on that below.
- Heat pump to harvest all the heat from the solar panels in the transitional and winter months (including rain and warmer winter days) and from the ice-storage.
- Central ventilation system with heat recovery.
In order for the whole thing to work, a well-insulated construction of the house is necessary. This resulted in a low-energy house that is better than qualified passive houses.
In order to increase self-sufficiency, an electric vehicle with bidirectional charging capability is planned. This enables the household to be completely self-sufficient from solar energy for up to 8 months of the year.
The following figure shows the complete scheme of the bivalent solar and heating system with all its components.
Following the regulated area development plan, the building has an east-west facing roof. For aesthetic reasons, we chose in-roof panels, which also replace the roof covering, and hybrid panels, which provide electricity and thermal output at the same time. An increase in power generation efficiency of 15% is achieved by cooling photovoltaic cells to 20°C. These PV hybrid modules together with a heat pump, harvest solar heat, as well as heat that is transferred from air and rain - which is energy-efficient even at temperatures around freezing point, i.e. also at night and in fog!
After research, the choice fell on PV hybrid modules from regenerative energietechnik und -systeme GmbH in Dinkelsbühl, a system provider with the required experience and a few reference systems. Fa. Res ge me good advise for the design and dimensioning of the system. The following figure shows the structure of these modules ^1.
- https://res-energie.de/res-produkte/pv-kombimodule-hybridkollektor-pvt/
- https://res-energie.de/wp-content/uploads/2016/03/PV-Kombimodul-Grafik.jpg
The photovoltaic elements are wired in series strings in two groups of 15 and 20 modules. The thermal elements are piped according to a Tichelmann pattern.
Using an east and west layout of the panels reduces peak generation values and extends the duration of the solar harvest throughout the day. Thanks to the panels on the east side, electricity production starts earlier in the morning and covers the house's early day's electricity needs. The west side covers the increased consumption in the evening hours.
Due to rising electricity prices and lower grid feed-in tariffs, it makes sense today to use as much of your own solar power as possible.
Electricity from a roof-top photovoltaic system can currently be obtained for 10-14 ct/kWh. With a grid connection, the kilowatt hour costs nearly 30 cents. Every self-generated kilowatt hour (kWh) saves around 14 cents. Since photovoltaics generate the most electricity at noon, but household electricity requirements reach peak values in the morning and evening hours, the entire consumption cannot be covered directly by the panels. Often, additional electricity has to be drawn from the grid in the morning and evening. The excess electricity generated at noon, however, is fed into the grid. With the installation of a battery storage system, enables an increase self-consumption.
We have chosen a VARTA element with 6.5 kWh capacity. Measurements from the first few years show that the battery increases self-consumption to around 60%.
The BARTL - ECO 2S ground-water heat pump used has an heating capacity of 8 KWh and an annual performance factor of over 4. It therefore draws three times as much energy for heating from the sources (solar system or underground storage) as it consumes electricity.
The integrated managment system controls the pumps for the thermal solar system and for the floor-heating. It meausres and compensates outside tempeeratures and offers an interface for remote monitoring. The hot-gas side in the heat pump supplies the necessary temperature for the domestic hot water in the house.
The heat gained is brought into a 1500 liter buffer storage tank. Inlets and outlets at different heights allow the heat to be supplied and extracted efficiently by the heat pump and heating control.
The insulation of the buffer storage tanks on the market was too low to meet the requirements of the Bavarian 10,000 roofs program. The simplest and most cost-effective solution was to pack the storage tank on site with mineral wool (WLG 032) of 18 cm thickness. The tank itself stands on a 12 cm thick foam glass insulation (WLG 041) and 22 mm waterproof multiplex panel.
Another large heat store is located outside the house and is described in the following section.
How can thermal energy be stored efficiently? The most cost-effective solution for a family home is a water tank. Water has a very good heat capacity, additionally the latent-heat transition into solid ice is also usable, multipying the avaialble heat capacity by more than a factor of four!
When the thermal collectors no longer supply enough energy, the heat pump extracts the energy from the water in the outside storage tank until the water freezes. During the phase change from liquid (water) to solid (ice), considerable amounts of latent energy (92 Wh/kg) are released. During the phase change, the water temperature remains constant at 0 °C. [^2]
[^2]: Source: https://www.energie-solaire.com/wq_pages/de/site/page-273.php
The ice becomes water again through geothermal energy or when the sun shines again. When winter is over, the term "ice" storage is actually no longer suitable because the storage almost always contains 100% water.
In summer, the large latent heat storage system is barely heated above 20°C, which serves as cooling for the photovoltaic panels.
Instead of the currently usual 10m³ storage tanks made of concrete rings, we used a 24,000 liter storage tank made of steel - a former vinegar tank with a diameter of 2.4m and a length of 5.5m, with a wall thickness of 10mm enamelled on the inside agains corrosion. The tank was buried vertically in the ground without insulation. The volume is "increased" because the ground is warmer than the tank in winter.
Ten of these heat exchanger towers were installed vertically next to each other inside the steel tank. On the top, concrete rings with a manhole cover bridge the 1.5 m between the top of the tank and the ground surface. In this area, all the heat exchanger towers are connected in parallel. This enables a high volume flow with good heat distribution at the same time.
Underfloor heating enables a comfortable temperature control of the rooms with low heating flow temperatures. Room thermostats regulate each room individually.
Low-energy houses are characterized by an airtight shell. However, this means at the same time a lack of air exchange in the living areas, at the same time an accumulation of humidity in the house (cooking, breathing, showering, etc.) This is why a ventilation system with heat recovery is required for houses to meet the KFW 40 standard. Furhter advantage is fully automatic ventilation of the rooms (it does not have to be done several times a day by means of manual intermittent ventilation). The central system recovers approx. 80% of the heat in the exhaust air. Air filters reduce dust and pollen in the house. A good indoor climate also prevents the formation of moisture and prevents mold growth.
As a central ventilation system with heat recovery, we have installed a Stiebel Eltron LWZ 170 E-Plus and ventilation with a volume flow of 210 m³/h.
High-quality building materials were used and installed in accordance with the applicable regulations. The costs of good materials are justifiable with good choices and only make up a small proportion of the total construction costs.
The basement was built with impemeable concrete completely encapsulated with an outside insulation of 14cm Styrodur WLG 0.043 W/m²K. The soil in the property consists mainly of gravel from the terminal ice-age moraines which provides good water dissipation. Underground water is not expected and a long-life of this basement perimeter insulation can therefore be assumed.
The exterior walls of the house are built with the innovative Kellerer ZMK X-6.5 brick ^3. With the properties of this brick, multi-family and passive houses can be built and they avoid the disadvantages of the complex and damage-prone outer thermal insulation.
The calculation of the thermal conductivity of the exterior walls results in a U-value of 0.15 W/m²K, corresponding to the values required for passive houses.
The roof construction consists of 24cm wood rafters with insulation between the rafters WLG 032, above that a 5.2 cm wood fiber insulation board (WLG 045). Results in a total U-value of 0.12 W/m²K for the entire roof area.
The house demonstrates that future-oriented construction is possible through a careful combination of photovoltaic and solar thermal modules, a heat pump, a large latent heat storage system and the appropriate solid construction.
The measured solar generation (8160 kWh) is greater than the electricity demand for heating and hot water (3230 + 4000 kWh).
The primary energy requirement is extremely small for a 6 person household!
With an e-vehicle with power-to-home capability, the house can be self-sufficient for 8 months from self-generated solar energy.
The calculation according to the EEWaermeG results in an over-fulfillment of the EnEV requirement values by 300%. The building meets the requirements of the EEWärmeG to over 490%.
The extrapolation of the CO2 emissions of 2.7 kg / (m² · a) from the energy certificate results in a saving of approx. 13 tons of CO2 per year compared to the EnEV reference house!
The combination of ideas and product selection in this solar house with latent-heat storage are suitable for every new building. Passive houses are also possible in a solid construction.
New building projects can be based on this innovative energy concept using similar combinations of existing technologies.