Single family House - Bern, Switzerland

Luisenstrasse 30

3005

Bern, Switzerland

Architect

Beat Wermuth und Partner Architekten GmbH
Bonstettenstrasse 6b, 3012 Bern
office@wup-architekten.ch
+41 31 305 02 01

Owner

Familie Hutterli Röthlisberger
Luisenstrasse 30, 3005 Bern
mhutterli@gmail.com
+41 31 352 82 12

Contact Details

Dr Arch. Cristina S. Polo López
SUPSI - University of applied sciences and arts of southern Switzerland
cristina.polo@supsi.ch
+41 58 666 63 14

Other Information

Related publications
Swiss Solar Price 2014 (German and French)
Top view © C. Martig
The neo-baroque style house of the Hutterli Röthlisberger family from Bern/BE, dated 1898, has been extensively renovated and thermally refurbished between 2011 and 2015. The intervention concerns the thermal improvement of the envelope, intervening on walls, roof and windows. It also concerns the installation of a photovoltaic system and a solar thermal system, as well as the replacement of the gas heating system with a heat pump, geothermal probes and a stove. The intervention also involved the installation of a comfort ventilation system with heat recovery. This renovation deserved the Swiss Solar Prize 2014.
Energy performance
35,22 kWh/m2.y

Climate Zone Cfb

Altitude 542 m a.s.l.

HDD 198

CDD 0

Protection level Listed

Conservation Area:
Yes

Level of Protection:
High

Building age 1850-1899

Year of last renovation:
2015

Building use Residential (urban)

Secondary use:
NA

Building occupancy:
Permanently occupied

Number of occupants/users:
5

Building area Net floor area [m²]: 215,0

Building typology:
Detached house

Number of floors:
2

Basement yes/no:
Yes

Number of heated floors:
3

Gross floor area [m²]:
258,0

Thermal envelope area [m²]:
570,0

Volume [m³]:
1250,0

NFA calculation method:
SIA 416

Construction type
Stone masonry wall

External finish:
Rendered

Internal finish:
Plastered (on hard)

Roof type:
Pitched roof

+ MORE - LESS
Top view © C. Martig
Top view © C. Martig
View of the corner house, road fork © M. Hutterli
View of the corner house, road fork © M. Hutterli
View of the corner house © M. Hutterli
View of the corner house © M. Hutterli
South front © M. Hutterli
South front © M. Hutterli
Top view © C. Martig
Top view © C. Martig
Top view © C. Martig
Top view © C. Martig
View of the corner house, road fork © M. Hutterli
View of the corner house, road fork © M. Hutterli
West view before interventions © M. Hutterli
West view before interventions © M. Hutterli
South-east view before interventions © M. Hutterli
South-east view before interventions © M. Hutterli
East view before interventions © M. Hutterli
East view before interventions © M. Hutterli
High aesthetic preservation © M. Hutterli
High aesthetic preservation © M. Hutterli
South view before interventions © M. Hutterli
South view before interventions © M. Hutterli

RENOVATION PROCESS

Architecture

BUILDING DESCRIPTION

The building is a detached single-family house, a two-floors neo-baroque construction with a mansard rooftop and is dated 1898. The general situation of degradation and the need to minimize energy demand collide with the important aspect of historic buildings preservation. The challenge is to achieve maximum results in both fields, opting for several high efficiency interventions, but at the same time with minimum aesthetic impact.
Urban context
As usual at road forks and corner houses in the Kirchenfeld district, according to the Kirchenfeld-Brunnadern building inventory, the house was designed with special care: the south-east corner of the house is characterized by a corner risalite, which is covered with the mansard roof. The house is listed in the cantonal building inventory and classified as worthy of protection (highest protection level). For this reason, any changes must obtain the approval of the Department of Historic Monuments.

HERITAGE SIGNIFICANCE

ELEMENTS WORTHY OF PRESERVATION
Due to the high protection level of the building, the goal is to achieve the highest aesthetic demand. Because of this, it was initially difficult to receive approval from the authorities. This led to the search for the best possible solution.
Heritage Value Assesment
The building is part of a protected area where the two street-side facade are well cared for and are part of the historical context of the district.
Heritage Assessment Files

State of repair

Conditions of the envelope
The existing building presents a general poor condition of the envelope and needs an energy upgrade. It also needs a replacement of the existing gas heating system. A total renovation was indicated.
Description of pre-intervention building services
The single family house was equipped with a gas heating system and no precautions has been taken for heat losses.

Aim of retrofit

Renovation
The energy renovation has a special focus on aesthetic preservation and in maintaining the character of the house. The goals for the renovation of this building are manifold: minimize energy demand (reach a Minergie level), use environmentally friendly building materials, maintaining the character of the house (preservation of historical monuments), consider urban environment, adhere to the cost framework (subsidies as Minergie and Bern renovated) and, where necessary, seek and implement new solutions.
Was the intervention planned following a step-by-step approach?
First step was a preliminary study some years before renovation. Second step was to define exactly the goals to achieve and at last every single intervention has been studied to fit with the overall renovation.
Lessons learned
The integrated solar system is the main element of this renovation. At the beginning it was difficult to obtain a licence to operate the building, but this solution demonstrate that it is possible not to affect the aesthetics of the element. This is a great example for the future renovations and for the building industry in general. In addition, it shows many different interventions that can well improve the whole.
Stakeholders Involvement
Public sector
Bauinspektorat der Stadt Bern
Bundesgasse 38, 3001 Bern
bauinspektorat@bern.ch
Tel.+41 31 321 65 45
Architect
Beat Wermuth und Partner Architekten GmbH
Bonstettenstrasse 6b, 3012 Bern
office@wup-architekten.ch
Tel.+41 31 305 02 01
Conservation Consultant
Manuel Hutterli
Luisenstrasse 30, 3005 Bern
mhutterli@gmail.com
Tel.+41 31 352 82 12
Energy Consultant
Manuel Hutterli
Luisenstrasse 30, 3005 Bern
mhutterli@gmail.com
Tel.+41 31 352 82 12
Other
Hans Dürig AG, Markus Dürig, Ing. HTL
Hintere Gasse 11, 3132 Riggisberg
info@hans-duerig.ch
Tel. 41 31 809 02 50
Other
Meyer Burger AG, PV Systems
Schorenstrasse 39, 3645 Gwatt
mbtinfo@meyerburger.com
Tel.+41 33 221 24 07
Other
INNOVAR, Christian Käsermann
Route des Genevrés 35, 1784 Courtepin
Tel.+41 26 684 10 87
Tools used
Was the renovation process done following a specific methodology? Minergie. This label corresponds
Energy calculation SIA 380/1
Hygrothermal assessment No
Life Cycle Analysis (LCA) No
Other No

RETROFIT SOLUTIONS

External Walls

Double-shell masonry wall

Double-shell masonry wall

The external wall was insulated with a double-shell blowing system with Isofloc H2Wall. This is the best possible insulation for an external wall, as reported in the cantonal buildings inventory. This was a premiere in Bern. In addition, it has been included on the inside a wall heating with 1cm aerogel insulation (corresponds to 3cm of conventional isolation).

The intervention maintains the original aesthetics of the wall and the the increase in wall thickness is minimal. This way, the interior space of the building remains practically unchanged.

U-value (pre-intervention) [W/m2K]: 0,68 W/m²K U-value (post-intervention) [W/m2K]: 0,44 W/m²K
More Details
Original wall build-up
Plaster - The external wall has a yellow finish:
20 mm
Stone - Double-shell masonry wall, external:
180 mm
Air gap - Double-shell masonry wall, air gap:
60 mm
Stone - Double-shell masonry wall, internal:
180 mm
Plaster - White:
15 mm
Retrofitted wall build-up
Plaster - The external wall has a yellow finish, reproducing the original one:
20mm
Stone - Original double-shell masonry wall, external:
180 mm
Insulation - Double-shell blowing system with Isofloc H2Wall (in existing air gap):
40 mm
Stone - Original double-shell masonry wall, internal:
180 mm
Other - Wall radiator behind plasterboard (insulation and wood beams):
50 mm
Plaster - Plasterboard with white finish:
25 mm


Windows

Wood windows

Wood windows

Most of the existing windows have been renovated and only a few have been replaced with a copy, due to the bad state of conservation.

The existing windows have been improved. The original single glazing was replaced with the thin, krypton filled double glazing and seals for airtightness. Where improvement was not possible, the windows have been replaced with a reproduction (west facade). The historical front windows have also been renovated.

Existing window U-value Glass [W/m2K]: 3,0 New window U-value Glass[W/m2K]: 0,7 Existing window U-value Frame [W/m2K]: 3,0 New window U-value Frame [W/m2K]: 1,3
More Details
Existing window type Casement window
Existing glazing type Single
Existing shading type Outer shutter
Approximate installation year 1898
New window type Casement window
New glazing type Double
New shading type NA
New window solar factor g [-] 45,0

Other interventions

ROOF

GROUND FLOOR

ROOF

The roof has been improved with cellulose insulation and also used to place a PVT and an hybrid system. The roof structure has been improved both statically and thermally. Originally the building had a U-value of 1.36 W/m2K for the roof, which was very high (as expected). The intervention made possible to reach a U-value of 0.19 W/m2K.

Thanks to the aesthetic integration of the PVT hybrid system, the compatibility is assured. The natural slate hides the collectors in the steeply sloping roof, making them invisible from the outside. The production of heat is therefore less efficient and more third-party energy is required, but it is a good compromise to maintain the original appearance of the building.

U-value (pre-intervention) [W/m2K] 1.36 U-value (post-intervention) [W/m2K] 0.19
More Details
Original roof build-up
Slate - Original black slate cover has been replaced by elements that maintain its original appearance:
10 mm
Other - Wood board (spruce):
22 mm
Other - Wooden carpentry:
160 mm
Other - Plasterboard:
60 mm
Retrofitted roof build-up
Slate - Integrated PVT system:
10 mm
Other - Pavatex-plus: roof layer with additional high thermic performance:
22 mm
Other - Insulation isofloc (in wooden carpentry 160+80mm):
240 mm
Other - Plasterboard (Fermacell):
12 mm
GROUND FLOOR

The intervention consists in the installation of thermal insulation under the ceiling of the cellar to keep the floor covering intact.

The intervention was carried out in the cellar where it was not necessary to pay particular attention to conservation.

U-value (pre-intervention) [W/m2K] 1 U-value (post-intervention) [W/m2K] 0.19
More Details
Original groundfloor build-up
Finish - Oak floor:
40 mm
Concrete slab - Concrete:
120 mm
Retrofitted groundfloor build-up
Finish - Oak floor:
40 mm
Concrete slab - Concrete:
120 mm
Insulation - Mineral wool:
140 mm

HVAC

HEATING

VENTILATION

DOMESTIC HOT WATER

HEATING

The original gas heating system has been replaced with a heat pump, a solar thermal system and a geothermal system. The main source is the water heat pump, which is supplied partly by geothermal probes and partly by the PVT and the natural slate collector systems. Both systems are used to support the heat pump by increasing the water temperature into the heat pump whenever possible and thus to improving the COP. The heat is distributed through radiators and through a stove. Historical radiators were not changed during the renovation (except newly painted). The solar thermal system is well implemented in the building.

The system has been designed to perfectly integrate with the construction. Wall radiators have been fitted to the wall with a minimal intervention in terms of space, while the PVT system (as well as the hybrid) has been built to adapt perfectly to the shape, colour and materials of the roof.

More Details
New primary heating system New secondary heating system
New system type Heat pump Stove
Fuel Electricity Biomass
Distribuition system Radiators and radiators wall Air
Nominal power 8 kW 10 kW
VENTILATION

A Zehnder comfort ventilation system with heat recovery has been introduced.

On the top floor, the supply air is routed via the screed into the built-in cupboards: apart from the inconspicuous supply air grilles in the cupboard walls (usually behind furniture), no architectural intervention in the rooms (pipes) is necessary. No audible ventilation noises.

More Details
Original roof build-up New ventilation system
Type ventilation system Centralized
Type flow regime Overflow
Heat recovery Yes
Humitidy recovery No
Nominal power NA kW
Electric power 0,0 kW
Control system Customized
DOMESTIC HOT WATER

The hot water preparation is carried out by the 2’840l tank, which is mainly supplied by the heat pump and the PVT system.

The system doesn't need conservation compatibility.

More Details
New DHW system
Type with heating system
Hot_water_tank Yes
With heat recovery Yes

RENEWABLE ENERGY SYSTEMS

SolarThermal

Photovoltaic

Biomass

Geothermal

SolarThermal

Two different types of STh have been used: special system on the lower part, PVT on the top of the roof (cfr. section PV)

Due to preservation orders, no conventional collectors were allowed. The collectors of the special system (lower part of the roof) are integrated in the underroof (layer battens and counter battens). External layer of the roof is natural stone plates, and the system is not visible at all.

Since originally no conventional solar system was possible due to monument preservation regulations, a collector that is not visible from the outside has been developed, with which the heat can be efficiently extracted from the natural slate roofing. 13m2 of natural slate collectors were installed, which corresponds to an output of about ~5kWp. The collector consists of copper lamellas, which are clamped between the slate plates. The heat is conducted via the fins into a soldered copper tube, through which it is dissipated via a glycol solution, as in conventional collectors. Due to possible condensation moisture and to increase efficiency, a 1 cm aerogel insulation, covered by a sub-roof foil, was placed between the roof battens and the slate. PVT and the natural slate collector systems are used to support the heat pump by increasing the water temperature into the heat pump improving the COP. The PVT and natural slate collector systems are also used to regenerate the geothermal probes/ground temperatures with excess heat available from the PVT and the slate collectors on multi-day to seasonal time scale (on diurnal time scale the solar tank is the heat storage). The regeneration thus increases the net solar electricity production and at the same time prevents the ground to cool down over time, assuring a constantly high COP over the lifetime of the geothermal probes. In addition, the cooled roof helps the rooms of the top floor to remain cooler in summer. This renovation deserved the Swiss Solar Prize 2014.

More Details
SolarThermal System
Type Natural slate collectors
Collector area 13,0 m²
Elevation angle 80,0
Azimuth 5,0
Overall yearly production 10000,0 kWh
Heating_contribuition 6242,0 kWh
DHW contribuition 1330,0 kWh
Cooling contribuition 0,0 kWh
Photovoltaic

Roof-integrated PVT (13 m2) + roof integrated PV (5.5 m2) + STh natural slate collectors (13 m2)

Due to the high level of protection, solar panels are slightly visible from the street, leaving part of the original slate roof intact. During the refurbishment, the requirements of the preservation of historic monuments were somewhat softened, so that both PV+PVT system was possible on the flat (upper) part of the roof.

The arrangement of solar panels on triangular pitched roofs approaches solves the critical points with tailored solar modules with attention to detail and fixing systems. First 'optical' roof-integrated system with 3S Hybrid 900/240 modules. Optically' integrated into the roof, because the installation is integrated into the roof and flush with the eaves, but the solar system is not a completely tight roof skin. The actual dense and back-ventilated roof skin lies underneath, i.e. the installation is hybrid roof-integrated and 'on roof'. - Eight hybrid collector modules (13 m2) and 12 purely photovoltaic special modules (5.5 m2) on the southern, 25° inclined roof surface. - Electrical output: 2,728 kWp. Active cooling of the modules increases the annual electrical yield by up to 10%. - The thermal output of the hybrid collectors is at least 7.2 kWp (manufacturer's specifications).

More Details
Photovoltaic System
Type Monocrystaline
Collector area 18,5 m²
Total nominal power 2,7 kW
Elevation angle 28,0
Azimuth 170,0
Overall yearly production 3207,0 kWh
Heating contribuition 0,0 kW
DHW contribuition 0,0 kW
Cooling contribuition 0,0 kW
Lighting contribuition 3537,0 kW
Biomass

Stove

In the building there was already a fireplace/stove whose only element visible from the outside was a chimney that came out in the north-west part of the roof. This chimneypot remained intact, while the gas boiler chimneypot was removed. The new stove is located in the living room and is connected to the central heating system.

The new heating system includes several interventions. The main source is the water heat pump, which is supplied partly by geothermal probes and partly by the PVT and the natural slate collector systems. Both systems are used to support the heat pump by increasing the water temperature into the heat pump whenever possible and thus to improving the COP. The water is stored in a 2840 L tank. It also works thanks to the stove. In addition, a 'Frischwasserstation' which contains a small heat exchanger to provide warm water (Brauchwasser) on demand have been installed which prevents the formation of legionella. The hot water of the solar tank is used to heat up the 'Brauchwasser' in the Frischwasserstation when required. From the tank the water is then distributed to the radiators and wall radiators.

More Details
Biomass System
Type Logs
Storage size Normal cellar in the basement
Origin of biomass Kanton Bern
Overall yearly production 2798,0 kWh
Geothermal

Heat pump with bore holes

The execution in a geothermal heat pump is not very invasive for any building, in fact all the pipes coming out of the building are underground, while inside the building there will be a presence of greater pipes due, in this case, to the complexity of the system that combines several energy carriers. The use of more vectors allows a better management because it gives priority to the vector that has production potential at any specific moment.

The new heating system includes several interventions. The main source is the water heat pump, which is supplied partly by geothermal probes and partly by the PVT and the natural slate collector systems. Both systems are used to support the heat pump by increasing the water temperature into the heat pump whenever possible and thus to improving the COP. The PVT and natural slate collector systems are also used to regenerate the geothermal probes/ground temperatures with excess heat available from the PVT and the slate collectors on multi-day to seasonal time scale (on diurnal time scale the solar tank is the heat storage). This regeneration is a win-win situation: By cooling the PVT panels and transferring the excess heat (up to 12 kW) into the ground e.g. in summer, the PVT panels produce significantly more electricity (up to 500 W) than the pump required to transfer the heat into the ground (~50W). The regeneration thus increases the net solar electricity production and at the same time prevents the ground to cool down over time, assuring a constantly high COP over the lifetime of the geothermal probes. In addition, the cooled roof helps the rooms of the top floor to remain cooler in summer. The water is stored in a 2840 L tank. It also works thanks to the stove. In addition, a 'Frischwasserstation' which contains a small heat exchanger to provide warm water (Brauchwasser) on demand have been installed which prevents the formation of legionella. The hot water of the solar tank is used to heat up the 'Brauchwasser' in the Frischwasserstation when required. From the tank the water is then distributed to the radiators and wall radiators. The geothermal system includes two probes of 150 m each.

More Details
Geothermal System
Type Vertical loop
Exchange area 33,6 m²

Energy Efficiency

Energy Performance
Energy performance certificate: Before renovation: envelope G global G After renovation: envelope B global A
Voluntary certificates: In this case Minergie it corresponds to the EPC cathegory B
Energy Use
Heating
Consumption_estimation_Calculation_method: Steady state simulation (e.g. EPC, PHPP)
Documents:
Technische daten.JPG
Swiss solar price

Consumption_estimation_Before: 43312 kWh/y
Consumption_estimation_After: 35,22 kWh/m2.y

Primary Energy
Consumption_estimation_Calculation_method: Steady state simulation (e.g. EPC, PHPP)
Consumption_estimation_Including_DHW: Yes
Consumption_estimation_Before: 46867 kWh/y
Consumption_estimation_After: 11109 kWh/y
Measured Parameters
Internal Climate
Type_of_monitoring: Punctual
Description: Complexity of the plant requires performance and flexibility, which is not available in typical control systems of individual components. Temperature and flow rate data should not only be used for monitoring and control, but also be recorded as a basis for optimisation. The control system was put together and programmed from inexpensive components.

External Climate
Type_of_monitoring: Continuous
Description: The strategy of monitoring ist to follow the temperature of the solar systems (sloping, PV, PVT) according to the external air temperature. This is the link: https://grovestreams.com/singleDash.html?org=2776f02c-f718-3407-83e0-78bc4c61ecda&itemUid=10f024e4-0cf4-37df-a184-79853932b9d6&api_key=f66a4104-ad33-3159-90e6-10bd46a26c29
Documents:
Monitoring temperature esterne_1.JPG

Construction
Type_of_monitoring: Continuous
Description: The strategy of monitoring is to follow the temperature of the solar systems (sloping, PV, PVT) according to the external air temperature. Information available: https://grovestreams.com/singleDash.html?org=2776f02c-f718-3407-83e0-78bc4c61ecda&itemUid=10f024e4-0cf4-37df-a184-79853932b9d6&api_key=f66a4104-ad33-3159-90e6-10bd46a26c29
Documents:
Monitoring temperature esterne.JPG
Print screen of the overview of solar elements temperature


UserBehavior
Type_of_monitoring: Punctual
Description: Thanks to the ventilation control, the temparture is monitored, and the ownership wishes to have light reduced temperature. The automatically change of air doesn't require other minotoring.

Internal Climate

Temperature

The thermal comfort of the occupants improved thanks to the new walls and roof insulation and the new heating system.

Indoor Air Quality

Indoor air quality improved thanks to the new ventilation system. The automatically change of air guarantees the necessary hygienic exchange.

Daylight

Daylight does not change compared to pre-intervention due to the original size of the openings which was determined by the existing structure. In some rooms where the size of the windows are large in comparison to the surface of the room itself, the deepening has been done to avoid overheating in summer.

Acoustic Comfort

The change of glazing windows improved the acoustic comfort of the house. The introduction of a ventilation system has been well elaborated, in fact there are no audible noises.

Artifact Conservation

NA

Costs

Financial Aspects

The roof intervention cost is around CHF 45,000. The estimation costs were made on the basis of the annual CHF savings due to the renovation. An interesting aspect is that many of the interventions were carried out with the help of the owners. As well as being very involved and enthusiastic about the renovation, the owners were able to keep some costs down.

Investment Costs

Cost of energy related interventions:
about 200'000.- CHF (total)
Amount includes: Roof, walls, doors and windows, insulation cellar,
Running Costs
Lifecycle cost
No

Environment

Water Management

Inside the building there are water-saving taps/mixers.

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