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The Nestwerk Pillnitz residential project was the result of a concept developed in 2000-2001 by 9 self-organised families consisting of a total of 39 persons who had decided to build their homes together in an environmentally compatible way and create a neighbourly atmosphere. The building plot was found on the sunny south-facing slope of the Elbe river, near Pillnitz Castle Park, in a rural area and yet close to the city.
Two Passive Houses with a total of 9 apartments were built using ecological building materials and technologies. The two buildings, consisting of three terraced houses with penthouses on top of each of them, were built around a peaceful courtyard shared by everyone. Each apartment also has a garden for personal use. The useable floor area of each apartment ranges from 52 m² to 144 m². The building follows the course of the slope by means of storeys that are staggered. On the ground floor, a kitchen and a large living room are situated on two levels, with ample room height for the living area. On the upper floor there are single bedrooms and a bathroom. The apartments on the top floor extend across one level and are connected to a separate covered staircase on the outside. All decisions were made in consultation with the home owners’ association, architects and engineers, both during the planning phase and during the construction of the buildings. The creation of an ecological and healthy living environment was a major concern for the home owners’ association.
In order to combine minimal energy consumption with maximum living quality, an advanced form of the Passive House concept was developed.
The timber frame buildings were exclusivley made of materials that do not pose a health risk. The wall construction consists of DOKA formwork girders (wooden I-beam profiles, centre distance 1.28 m) with OSB boards placed in between the beams to provide reinforcement and wind-tightness. The external wall was erected in one piece covering three storeys before adding the interior walls and ceilings made of solid construction timber, in order to avoid non-windproof wall-to-ceiling connections. A total of 37cm of cellulose insulation from recycled newspapers was inserted in the walls, resulting in a U-value of 0.11 W/m²K. The rear-ventilated green roof was constructed in a similar way with 34 centimetres of cellulose insulation (U-value 0.12 W/m²K). The rigid roof battens form the roof overhang.
Counter lathing with a 30cm insulation layer provides the necessary thermal protection for the partial basement and floor slab (U-value 0.15 W/m²K). The window areas are limited to 30% in order to prevent overheating in the summer. The wooden windows have triple low-e glazing and 23 insulated profiles with a U-value of 0.85 W/m²K and a g-value of 44% in total.
The finishing materials have been selected according to stringent ecological principles. No chemical wood protection was applied, only the oak-wood threshold was impregnated with boron salt. Natural paint was used for the inside and the outside. Joints were sealed using cotton wool and flax fibre. In some areas, clay bricks complement the timber construction appropriately. The concept was rounded off by an entirely green roof and rainwater collection.
The basic components of the energy supply concept are ventilation units with fan heaters for each apartment, a solar system for each building (12m²) with a buffer storage tank (1000 litres) and a central condensing boiler. The proprietry separation of the apartments and the individual layouts were a decisive factor for the use of ventilation units in each apartment (with the respective sub-soil heat exchangers). An additional heater was installed in the bathroom as well as a 3m² wall heating surface in the living room. These heaters were added purely for reasons of comfort so that the users can enjoy their warmth on cold and unpleasant days.
The heat is distributed mainly via pre-insulated double tubes which are commonly used in solar technology. A flow-through system is used for domestic hot water. The 36 kW condensing boiler is designed for hot water production taking into account the heating-up times. The total remaining heating demand for both buildings is 8kW, based on the PHPP calculation. The post-heating demand for the apartments is between 650W and 1,600W. All rooms can be heated via the supply air with reserves for higher room temperatures. The air distribution system consists mainly of round and oval folded spiral-seam pipes. In accordance with the wishes of some of the residents, the main bedroom was decoupled from the main ventilation network by sealing the bedroom doors on all four sides. The supply air duct can be shut separately and the sound-proof air transfer opening can be sealed. This way, the room temperature can be adjusted, and opening the bedroom windows at night doesn’t automatically cool down the entire apartment.
(Price per trade)
|Technical installations (€)||208,500|
|→ Heating, solar system (€)||52,900|
|→ Plumbing (€)||59,900|
|→ Ventilation (€)||59,300|
|→ Electrical installations (€)||27,100|
|→ Sub-soil heat exchanger (€)||9,300|
|Total construction costs (€)||1,258,800|
|Specific construction costs (€/m²)||1,345|
|Share for building services||17 %|
|Share for heating, solar system, ventilation||9 %|
Table 1: Construction costs
Including the cost for media connection and the sub-soil heat exchanger, the construction costs amounted to € 1,345/m². The share for the building services (plumbing, electrical installations, heating ventilation) amounts to about 17%. If only heating and ventilation are taken into account, this share is about 9 % (Table 1).
On the basis of these values, a comparative analysis for a low-energy house was carried out the results of which were used for a dynamic economic feasibility study. A similar level of user comfort was assumed for the analysis, i.e. with a solar system and simple exhaust air ventilation. The calculation of the running costs was based on a quotation from the building services company. Taking into consideration the different maintenance cycles, the costs of per year and apartment amount to € 316, 75 % of which are due to the ventilation system. The greatest single position of € 118 is due to the replacement of the filter for the external air filter box, for which a service life of one year was assumed.
The evaluation of the running costs (Table 2) shows that these amount to a total of € 1.60/m²a. The economic feasibility calculation takes into account the installation costs for the energy system as well as the additional construction costs incurred for achieving the Passive House Standard such as the timber structure, insulation, windows and doors. The extra costs for the building constitute less than 5 % of the total construction costs. For an observation period of 20 years and taking into account a capital growth of 10% p.a., the Passive House achieves an even balance of the costs in comparison with the low-energy house (Table 3).
|Annual costs per unit||Annual costs per m²|
|Operating costs for heating and solar system||78.37||0.75|
|Operating costs for ventilation||238||2.29|
|Dwelling unit of 100m²||464|
Table 2: Running costs
In our opinion, the future development of the Passive House has to lead to an integral ecological concept does not focus on energy savings alone. The objective is an ecological Passive House. Clients do not want to miss out on the design quality of their houses in order to achieve the Passive House Standard. Most home owners are looking to build a nice cosy house first, and low energy consumption as a second step. Design features such as roof overhangs, complex floor plans, large window areas in the living area, or even round building shapes can be realised successfully with some effort for planning. In this project, the planning effort was quite considerable, about 80 detail drawings were made. Particularly the non-visible ventilation ductwork required much conceptual work.
|Passive House||Low-energy house|
|Investment costs for energy (€)||116,200||124,800|
|Service life (years)||20||20|
|Additional construction costs (€)||69,000||0|
|Service life (years)||60||60|
|Total investment (€)||185,200||124,800|
|Actual cash value at beginning (€)||170,857||124,800|
|Capital expenditure (annuity) (€/yr)||14,896||10,881|
|Useful energy demand for heating (kWh/yr)||19,260||53,900|
|Initial prices for Electricity (kWh/yr)||2,600||3,000|
|Initial prices for Gas (kWh/yr)||23,851||63,041|
|Consumption related costs|
|Increase in energy prices 10 % /a|
|Initial prices Electricity (€/kWh)||0.158||0.158|
|Initial prices Gas (€/kWh)||0.0452||0.0452|
|Purchase Electricity (€/yr)||983||1.134|
|Purchase Gas (€/yr)||2.579||6.817|
|Energy costs (annuity) (€/yr)||3,562||7,951|
|Increase in costs 5 % /a|
|Running costs (annuity) (€/yr)||6,036||5,512|
|Total costs (€/yr)||24,495||24,344|
|Total annual costs (€/m³yr)||26.17||26.01|
Table 3: Comparison of the economic feasibility of the Passive House with a low-energy house
Hypothesis: period under consideration 20 years, interest rate 6%, annuity factor 0.087
After initial concerns, the clients were thrilled with the living quality in the Passive Houses. Joining together to construct the building proved to be a successful idea. Over the next two years, the energy consumption of the building will continue to be monitored because the actual energy consumption ultimately depends on the users.