Energy efficiency measures - Residential - Passive solar heating / Germany
Case study assignment
You are an architect participating in an international challenge to design and build an ultra-low energy house. To help achieve the project's energy design goals, you are asked to determine the cost effectiveness of using high performance windows as compared to windows typically used in new construction.
Site information
The project site is in Rottweil, 80 km southeast of Stuttgart, Germany, which is the nearest meteorological station. The house to be built is actually a duplex. Only the western half of the duplex will be designed as the ultra-low energy home.
The total floor area of the western half of the duplex is 224 m². The home is to be situated in a neighbourhood where waste heat from a nearby power plant is distributed through a district heating system. Assume the fuel is "Other" with a seasonal efficiency of 100% when defining the base case HVAC system. The design calls for a relatively low mass level and a high insulation level. Internal gains are expected to be about ½ that of typical homes.
The back of the building will face nearly due south (10° to the west of south) and feature an unheated solar "conservatory." The conservatory is essentially a sunspace that reaches from the ground floor to the roof. While some rooms will have windows that directly open to the outdoors, many of the windows will open into the conservatory. From the south to the west side of the house there will be overhangs that provide about 30% shading in summer and 15% shading in winter.
Double-glazed, vinyl frame windows are normally used in new home construction in Germany. For the ultra-low energy house, you decide to evaluate triple-glazed, xenon-filled windows with low-e glazing and wood frames.
A table has been provided to help you with this evaluation. It summarizes the orientations, sizes and performances of the windows in the conventional and ultra-low energy house. Only exterior windows are included, windows opening into the conservatory are not considered.
Case study assignment
You are an architect participating in an international challenge to design and build an ultra-low energy house. To help achieve the project's energy design goals, you are asked to determine the cost effectiveness of using high performance windows as compared to windows typically used in new construction.
Site information
The project site is in Rottweil, 80 km southeast of Stuttgart, Germany, which is the nearest meteorological station. The house to be built is actually a duplex. Only the western half of the duplex will be designed as the ultra-low energy home.
The total floor area of the western half of the duplex is 224 m². The home is to be situated in a neighbourhood where waste heat from a nearby power plant is distributed through a district heating system. Assume the fuel is "Other" with a seasonal efficiency of 100% when defining the base case HVAC system. The design calls for a relatively low mass level and a high insulation level. Internal gains are expected to be about ½ that of typical homes.
The back of the building will face nearly due south (10° to the west of south) and feature an unheated solar "conservatory." The conservatory is essentially a sunspace that reaches from the ground floor to the roof. While some rooms will have windows that directly open to the outdoors, many of the windows will open into the conservatory. From the south to the west side of the house there will be overhangs that provide about 30% shading in summer and 15% shading in winter.
Double-glazed, vinyl frame windows are normally used in new home construction in Germany. For the ultra-low energy house, you decide to evaluate triple-glazed, xenon-filled windows with low-e glazing and wood frames.
A table has been provided to help you with this evaluation. It summarizes the orientations, sizes and performances of the windows in the conventional and ultra-low energy house. Only exterior windows are included, windows opening into the conservatory are not considered.
Financial information
You can assume that the 80% of the purchase price of the home will be mortgaged by the buyer at an interest rate of 8% over 20 years. Energy prices are expected to rise at an annual rate of 2.5%, while general inflation is expected to be 2%. The discount rate used should be 9%. The windows are expected to last for at least 30 years.
The district heating system can supply hot water for heating at a price of €50/MWh and electricity is available at €0.10/kWh. The cost of the conventional double-glazed windows is roughly €210/m². You estimate the cost of the high performance windows to be about 35% higher.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
Results
The International Energy Agency (IEA) embarked on a project that challenged participants to design and build low energy housing. An ultra-low energy house or "Ultrahouse" was built in Rottweil, Germany as part of this initiative. The Ultrahouse is the western half of a 2-story semidetached house (duplex). The east side of the building was built to less stringent requirements for comparison purposes. All living areas are located to take advantage of the southern exposure and many are adjacent to a "conservatory" - a sunspace that extends the height of the house on its south side. Daylighting details allow sunlight to shine deeply into the building.
System description
In plan-view, the building is shaped like a trapezoid with the smaller and shorter side facing north to reduce window and envelope heat losses where solar heat cannot be utilized. Very high insulation levels are achieved in both the roof and walls of the building.
Due to the large areas of glazing on the southern sides, exceptionally high performance windows have been installed to limit nighttime thermal losses. The windows of the Ultrahouse are triple-glazed, xenon-filled, wood frame units that achieve U-values of 0.5 W/(m²-K) at the centre of glass and 0.86 W/(m²-K) overall. The solar heat gain coefficient is 0.48 at the centre of glass and 0.36 for the overall rated window.
The average annual energy use of the house was estimated to be 50 kWh/m². Actual measurements have indicated annual energy use of 18 kWh/m² during the 1994/95 heating period and 31 kWh/m² during the 1995/96 heating period.
District heating from a nearby power plant supplies heat during the winter months. No air-conditioning is used other than a ground-source heat exchange system for pre-cooling the ventilation air. In the winter months, the same ground-source system is used for pre-heating the ventilation air.
Lessons learned
Through a number of demonstration buildings, the IEA has successfully demonstrated the feasibility and effectiveness of using passive solar heating (PSH) design to significantly reduce heating energy use in residential housing, often to less than half of that of conventional homes. Increasingly, it is being recognized that many PSH features can often be implemented at no or low incremental cost to the project. For example, lower heating and cooling loads can lead to smaller, less expensive mechanical equipment or do away with the need for air-conditioning altogether. Advanced glazing systems are increasingly being integrated in mainstream new construction. The demand for PSH design is particularly strong in Germany and other European countries which have high fuel costs and high levels of environmental consciousness.
Photo
Ultra-Low Energy House, Rottwell, Baden-Württemberg, Germany
References
You can assume that the 80% of the purchase price of the home will be mortgaged by the buyer at an interest rate of 8% over 20 years. Energy prices are expected to rise at an annual rate of 2.5%, while general inflation is expected to be 2%. The discount rate used should be 9%. The windows are expected to last for at least 30 years.
The district heating system can supply hot water for heating at a price of €50/MWh and electricity is available at €0.10/kWh. The cost of the conventional double-glazed windows is roughly €210/m². You estimate the cost of the high performance windows to be about 35% higher.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
- The unheated "conservatory" sunspace acts like a buffer for heat loss and solar gain into the house. The windows of the conservatory therefore generally experience a lower temperature differential than windows that lead directly from the house to the exterior. This will likely have an effect of reducing the energy savings that are projected by RETScreen from the improvement of the conservatory windows. The thermal and solar interactions of a sunspace are complex and a significantly more detailed analysis would be required to model these effects.
- Heating system credits are not applicable to this case since the home uses district heating.
Results
The International Energy Agency (IEA) embarked on a project that challenged participants to design and build low energy housing. An ultra-low energy house or "Ultrahouse" was built in Rottweil, Germany as part of this initiative. The Ultrahouse is the western half of a 2-story semidetached house (duplex). The east side of the building was built to less stringent requirements for comparison purposes. All living areas are located to take advantage of the southern exposure and many are adjacent to a "conservatory" - a sunspace that extends the height of the house on its south side. Daylighting details allow sunlight to shine deeply into the building.
System description
In plan-view, the building is shaped like a trapezoid with the smaller and shorter side facing north to reduce window and envelope heat losses where solar heat cannot be utilized. Very high insulation levels are achieved in both the roof and walls of the building.
Due to the large areas of glazing on the southern sides, exceptionally high performance windows have been installed to limit nighttime thermal losses. The windows of the Ultrahouse are triple-glazed, xenon-filled, wood frame units that achieve U-values of 0.5 W/(m²-K) at the centre of glass and 0.86 W/(m²-K) overall. The solar heat gain coefficient is 0.48 at the centre of glass and 0.36 for the overall rated window.
The average annual energy use of the house was estimated to be 50 kWh/m². Actual measurements have indicated annual energy use of 18 kWh/m² during the 1994/95 heating period and 31 kWh/m² during the 1995/96 heating period.
District heating from a nearby power plant supplies heat during the winter months. No air-conditioning is used other than a ground-source heat exchange system for pre-cooling the ventilation air. In the winter months, the same ground-source system is used for pre-heating the ventilation air.
Lessons learned
- Passive solar heating (PSH) can significantly reduce space-heating costs.
- High performance windows are a key component of PSH design and even very advanced window systems can be cost effective in new construction when compared to windows typically installed using conventional building practices.
- The incorporation of a "conservatory" sunspace into the building shortens the heating season.
Through a number of demonstration buildings, the IEA has successfully demonstrated the feasibility and effectiveness of using passive solar heating (PSH) design to significantly reduce heating energy use in residential housing, often to less than half of that of conventional homes. Increasingly, it is being recognized that many PSH features can often be implemented at no or low incremental cost to the project. For example, lower heating and cooling loads can lead to smaller, less expensive mechanical equipment or do away with the need for air-conditioning altogether. Advanced glazing systems are increasingly being integrated in mainstream new construction. The demand for PSH design is particularly strong in Germany and other European countries which have high fuel costs and high levels of environmental consciousness.
Photo
Ultra-Low Energy House, Rottwell, Baden-Württemberg, Germany
References
- Beckert, Micheal, "Personal communication," Fraunhofer Institute for Building Physics, February 2002.
- International Energy Agency, Solar Low Energy Houses of IEA Task 13, James & James (Science Publishers) Ltd., London, Canada, 1995.
- Kemp, Steve, "Personal communication," Enermodal Engineering Ltd., 2002.
