LIFE-CYCLE ENERGY ANALYSIS: COMPARISON OF LOW-ENERGY HOUSE, PASSIVE HOUSE, SELF-SUFFICIENT HOUSE

 LIFE-CYCLE ENERGY ANALYSIS: COMPARISON OF LOW-ENERGY HOUSE, PASSIVE HOUSE, SELF-SUFFICIENT HOUSE

Dr. Wolfgang Feist, Passive House Institut, 1997

Introduction

This paper is an analytic comparison of life cycle energy of three types of energy aware houses. The study looks at low energy housing, passive housing and self sufficient housing over an 80 year period. The study takes six construction standards with a mid-terrace house (156 m2 floor space) complying with the 1984 German Thermal Insulation Ordinance (WschVO 84) as a reference house.

The study analyses the cumulative primary energy input (CEI) which is the energy required in the construction of the houses and the embodied energy of materials along with continual energy consumed over the life time of the house, which in this case is 80 years. The energy is measured in kWh/m². The house types analysed are a low energy house (LEH), a low energy house with electrical efficiencies, a passive house, a future passive house and a self sufficient house. 

House types

• A low energy house has annual heat requirement of least than 70kWh/(m²a) which is 50% lower than required by the 1984 German Ordinance and it utilises good thermal insulation, reduced thermal bridges, airtightness, low energy glazing and mechanical ventilation to achieve this.
• A passive house (PH) is a building in which the heat requirement is so low that a separate heating system is not necessary and there is no loss of comfort.  PH only requires 15kWh/(m²a) for annual heating.
• A self-sufficient house (SSH) by definition needs no end-use energy deliveries - apart from the incident energy flows from natural sources (solar radiation, wind).

Method

The study analyses the life cycle energy of the chosen houses. The production energy input was calculated through life cycle analysis for the different standards as a starting point to compare the life cycle energy consumption.

Development of cumulative primary energy input over 80a service life

The cumulative primary energy inputs of the houses are also calculated and are compared against each other to establish the total energy consumption over the 80 yr period. The findings were graphed to illustrate to the differences in the life cycle energy used in each house type. The primary energy inputs of the houses are all relatively close with the exception of the self sufficient house which has a much higher PEI (primary energy input) which is largely due to the necessary extensive technology such as solar panels and photovoltaic’s which have a high embodied energy which increases its Primary energy input beyond the other house types. You would expect that the self sufficient solar house would have the lowest overall energy input but this is contrary to the truth as the renewable energy technologies used in a self sufficient hous have quite a high embodied energy and over an 80 year life period they have to replaced quite a few times thus increasing the energy input of the house maintaining a higher energy input than the Passive house and future Passive house over the 80yr life cycle.

Conclusion

Energy Comparison (http://www.passivhaustagung.de)

The passive house remains to be the most efficient house with the lowest energy input over the 80yr life cycle. The German 1984 Ordinance reference house has by far the largest energy input over the life cycle as expected followed by the low energy house. I can’t help but feel that there is some bias towards passive house in this paper. Analysing the houses energy input over an 80 year period seems to reflect passive house in a good light compared to the self-sufficient house. This means the replacement of the renewable technologies in the SSH several times over the life cycle thus increasing the energy input compared to if the analysis was carried out over a 25 year period, the replacements might not occur and therefore the energy input might not be as high. I guess the integrity of the results of this paper is reliant on the life expectancy of the houses which is dependent on the standard of construction and materials chosen for the build which varies from region to region.

                       

Passive House Case Study Hannover-Kronsberg, Germany

Passive House Case Study Hannover-Kronsberg, Germany

This case study looks at the 32 terraced passive housing project in Hanover Kronsberg built in 1998 by the developer Rasch & Partner in cooperation with the Stadtwerke Hannover. For the first time a heating system using exclusively post heating of the fresh air necessary was used. This very simple and cost efficient house technology concept is possible thanks to extremely high building envelope efficiency with very good insulation, thermal-bridge free construction, airtight building element junctions and windows of a quality not previously available. Together with the heat recovery system, this leads to a space heating requirement in the houses of less than 15 kWh/(m²a), a figure which is roughly a seventh of that used in typical new German housing.

The houses are arranged in four rows with eight houses in each row. This arrangement offers the advantage of reduced envelope surface area to volume ratio. This project was unique at the time and the main intention of this project was to show, that heat supply in passive houses can be realized by warming up the supply air of the balanced ventilation system. These houses have no conventional heating system with radiators, except one in the bathroom.

Passive solar

The main windows are directed to south, so daylighting is provided by direct solar radiation for the duration of the day. In winter, solar gains through windows cover about one third of space heating energy demand. In summer, a manual-driven shading system protects the rooms from too high temperatures. Besides this, the high quality thermal insulation in combination with the large internal masses (concrete) help to keep the temperatures in summer on a moderate level, if cross ventilation during the night is applied.

 Construction

The walls and roofs are made of light-weight wooden construction with Uvalues of Uwall= 0.13 W/(m²K) and Uroof = 0.10 W/(m²K). The core of the building, the cross-walls and end-walls are made of prefabricated concrete elements. In addition, triple-glazed windows with specially insulated window frames as well as a home ventilation system with a high efficiency heat exchanger were installed.

Thermal Image of Passive House

The roof is built from prefabricated lightweight wood elements with 400 mm high I-beams, which span from one partition wall to the next. An internal polyethylene foil forms the essential airtight layer. The outer wall elements for the north and south facades are also built using prefabricated lightweight wood elements. So-called half box beams are used as shafts. An internal polyethylene foil forms the airtight layer. The outer wall of the gable sides is, like the house partition walls, built from loadcarrying reinforced-concrete slabs. This is protected on the outside against heating losses by a 400 mm polystyrene external thermal insulation compound system. The

Thermal Bridge Free Eaves Junction

concrete itself forms the airtight layer for the gable wall. The floor slab consists of 240 mm prefabricated steel-reinforced slabs, which is insulated underneath by factory-made 300 mm polystyrene external thermal insulation. The concrete floor itself also forms the airtight layer. Only the exhaust and intake ducts in the gable area and the drainage pipe through the base plate penetrate the thermal envelope. The ventilation system and the supply pipes run to the building services container in the gable area of the houses.