Japans first passive house.

 
I decided that I wanted to do something a bit different for this blog post and thought that Asia would be an interesting case study for a passive house development. I chose the first ever Passive house built in Japan.

The house was built in Japan in 2009. Planned by local practice Key Architects, the first certified Passive House in Japan has been built in the city of Kamagura, Kamakura, approximately 50km southwest of Tokyo. The two-storey wooden building can be considered a prototype for the application of the German building standard even in humid, subtropical climates.

It was originally not the intention of this project to get the Passive House certification. The idea evolved from Miwa Mori’s (the owner of Key Architects) experience with developing a social housing prototype with Passive House standard for Ireland while working for MosArt Ltd. in Wicklow. The absolute must requirement by the client was that the house be driven solely by electricity, as the house mortgage was provided by the owner’s employer, the Tokyo Electric Power Company.

The design approach was to create a simple, two storey unit which would fit into a mature neighbourhood. Upon entering the house, a staircase with a double height space leads up to an open plan living-dining area at the first floor level, in order to access the space with the most daylight. The site does not have enough private open space at the ground floor level. To overcome this problem, the architects designed an access from the dining space to a roof garden. The building itself had to be constructed within a very limited budget due to the high site purchase price (ca. 2500euro/sqm).

In such a humid sub-tropical climate, reducing dehumidification and cooling demand during summer is more difficult than reducing heating demand in winter. Another competing issue was the strict earth quake requirements for Japan which require a rigid load bearing wall versus a diffusion open wall, in order to avoid condensation within the external walls during both summer and winter months. This building project was treated as a pilot project by the Passive House Institute in Darmstadt, Germany and the house will help improve the Passive House calculation methods for warmer regions.

This home is a great example of the Passive House standards building techniques - it features triple-pane windows, thick walls for insulation, and a minimum of exterior joints, which are prone to air leaks and thermal bridging. The core of the HVAC system is a HRV - or Heat Recovery Unit. This passive house has an energy profile a ¼ of what is considered the average kwh/sq ft.

This ultra-efficient house is a far cry from traditional Japanese housing, which use thin wall construction and single-pane windows, which even today is still quit typical. Japanese houses have a maximum life span of 30 years, at which point they are knocked down and rebuilt.

There is currently no minimum energy efficiency requirement for new residential buildings in Japan where one million new houses are built every year. A house with single glazed windows and no insulation is still acceptable.

Personally I find this project very interesting and am looking forward to the passive house concept expanding to more countries. I like the link between the architect and Ireland and the construction details are not too dissimilar to what I have constructed for our passive house project.

The Passive House standard is becoming an important measure of sustainable building, and in Japan’s climate these homes would save an enormous amount of energy.


Construction Details.

Timber construction, 78 m²

Exterior wall:

15 mm plasterboard and render finish
24 mm service cavity
140 mm wood fibre insulation
13 mm wood board (earthquake resistant)
12 mm wood board (fire proof)
100 mm wood fibre insulation
11 mm rain screen, Cedar panel

U-value = 0,16 W/(m²K)

For a very good thermal protection in passive houses the U-value for all exterior building elements in Central European Climate is recommended to be less than 0,15 W/(m²K).

Floor slab:

11 mm wood floor finish
165 mm reinforced concrete floor
155 mm XPS insulation

U-value = 0,217 W/(m²K)

For a very good thermal protection in passive houses the U-value for all exterior building elements in Central European Climate is recommended to be less than 0,15 W/(m²K).

Roof:

15 mm plasterboard and render finish
100 mm service cavity
286 mm wood fibre insulation
37 mm wood board
75 mm wood fibre insulation
Metal roofing system with timber deck.

U-value = 0,101 W/(m²K)

Glazing: 

Triple Argon double low-e
Ug-value = 0,64 W/(m²K)
g-value = 51 %

Air tightness:

n50 = 0,14/h which is well below the 0.6 needed.

Annual heating demand:15 kWh/(m²a) calculated according to PHPP

Heating load:18 W/(m²) calculated according to PHPP

Primary energy requirement:113 kWh/(m²a) total demand on heating installation, domestic hot water, household electricity and auxiliary electricity calculated according to PHPP.




The following video is an interesting interview from the 15th International Passive House Conference Innsbruck, Austria, May 2011. It contains interviews with Wolfgang Feist (PHI), Ann-Marie Fallon (Ireland), Bjorn Kierulf (Slovakia), Miwa Mori (Japan). Miwa Mori talks about the first passive house in Japan.

Detailed energy saving performance analyses on thermal mass walls.

The paper Detailed energy saving performance analyses on thermal mass walls is a study carried out on the effect on energy of mass walls compared to conventional wood-framed construction. The location for this study was in Las Vegas, Nevada, for two identically sized houses with contrasting types of wall designs; one using conventional methods and one with thermal mass walls. The thermal mass walled house (massive house) was designed to be a zero energy house (ZEH). Real-time data logging has taken place for over 2 years using a wide array of thermocouples and heat flux sensors and has reflected the excellent energy saving performance of the ZEH.

Wall framing in the timber frame home is based upon 2 x 4 construction. With Blanket and batt insulation. The R-value for this normal wall was estimated to be 2.15 (m2 8C)/W. The walls of the ZEH are a pre- cast mass sandwich panel construction. The R-value of the mass wall construction was found to be 2.06 (m2 8C)/W. 

For the lightweight wall construction of the baseline house, it is obvious that the internal wall temperature varies significantly with the external wall temperature, which changes in relation to the climate conditions. Comparatively, the internal temperature of the mass walls in the ZEH remains more stable in both the heating or cooling season. The external temperatures of the massive walls did not reach as high as those for the conventional construction, particularly where the sun-exposed walls are concerned.


Data was collected from April and October in 2006, during which periods both the heating and cooling systems are shut off. Las Vegas has a typical desert climate, in April the ambient temperature reaches 35.8C at midday. During these times, the indoor temperature in the ZEH was found to be more stable and more comfortable than the baseline house.

In comparison with the traditional wood framing walls, the ability of storing heat during peak time of the mass walls is favourable for peak electricity saving but the remaining heat at nights is not beneficial for the total cooling energy usage. Obviously the heating energy consumption is reduced by the mass walls in winter, but unfortunately the cooling usage is somewhat higher than the conventional house.

In the massive house it was found that heat is continuously transferred into the indoor space, which means that the heat stored during daily time cannot be completely released back during night time. In other words, the massive systems of the type evaluated here actually are not energy conservative for cooling requirements and not suitable for the typical desert climate areas, like Las Vegas.

The internal wall temperature of massive systems changes more slowly than the conventional wall constructions, leading to a more stable indoor temperature. The simulated heating energy use was much lower for the massive walls while the cooling load was a little higher. Further investigation on the heat flux indicates that the heat actually is transferred inside all day and night, which results in a higher cooling energy consumption.


The thermal mass wall does have the ability to store heat during the daytime and release it back at night, but in desert climates with high 24-h ambient temperature and intense sunlight, more heat will be stored than can be transferred back outside at night. As a result, an increased cooling energy will be required.

 

Here is a short video on how to create a zero energy home:

A passive house in your region with your climate.

The Passive House Institute set up by Dr. Wolfgang Feist has developed several passive house building techniques to suit the central European climate.  However, it would be incorrect to copy details from the central European example to other parts of the world. Instead, the details should be found to suit the climate and geographic conditions to develop a passive house solution for each location. The local building traditions and specific climate conditions must be considered. Previously mistakes were made where Californian building techniques were copied to projects in Europe giving poor results.

The definition of a passive house is that the peak heating load should be projected to a lower level than 10W/m2. If the max load is lower than 10W/m2 the ventilation system can distribute all the heat needed throughout the building. There is almost no extra benefit gained by increasing efficiencies beyond this 10W/m2 threshold.

A passive house has a very low energy demand for maintaining interior comfort in the heating season. The heating demand is so low that the environmental impact is negligible even if fossil fuels such as oil, gas, or coal are the heating sources. There are also no problems with primary energy resources.


The basic principles of passive house design;