Andrew Michler’s Passive House

During Enrico’s recent visit to Colorado, we finally had the chance to visit Andrew Michler’s passive house.

At about 2.000 m (6.400 ft), in the mountains near Fort Collins, Colorado, this building is capable of remaining comfortable even in case of a power outage, with an interior temperature of about 18°C (64°F) with no heating.

01 house
The southern front of the building.

The architectural design of the house follows the best practice of energy efficiency: the thermal envelope in compact and south-oriented. All main rooms (living room, bedroom) are aligned along the southern wall, while the services are located along the north side.

02 interior
An interior photo of the living room, before the installation of the furniture.

The building was designed to avoid any thermal bridge caused by structural elements or by the system distribution. This allows for more even internal surface temperatures, resulting in a higher comfort level. Furthermore, the airtightness of the envelope eliminates leaks of cold air, which would cause discomfort.

Andrew’s house is therefore very comfortable even if the interior temperature is lower than the average, at about 18°C (64°F) instead of 20°C (68°F).

04 wood finish
A detail of the end wall of the house, with interior cladding of rough wooden boards.

Reaching this high level of energy efficiency and comfort does not depend on the type of structure used (in this case, wooden frame). The key was the application of the passive house standard, and the good execution of the construction.

03 View
The view from inside the house, during the snow blizzard that blocked us there. With the heating that had been off for days, the building remained at about 18°C (64°F) even during the night.

The only system that was on during our visit was the mechanical ventilation, which includes a static heat recovery system. This kind of system is no novelty: it allows to bring fresh air to the main rooms of the house, by pre-heating it with the exhaust air extracted from the service rooms.

The indoor air quality of the house was monitored by Stefano Brunelli, under the direction of Prof. Shelly Miller of CU Boulder. Indoor air quality is a very important topic, and we’re going to cover it extensively in the future.

05 vent
The static heat recovery system inside the ventilation unit. The only “active” part of the system is represented by two fans to move the air.

The whole concept of the passive house standard is based on the primary importance of the thermal envelope over the building systems. If the building is compact, well insulated, with no thermal bridges and airtight, then the size and cost of the heating and cooling system can be greatly reduced.

06 insulation
A detail of the insulation of the house, with recycled cellulose.

Inside the interior middle wall, phase changing materials (PCMs) where installed to maximise the heat storage capability of the assembly. In case of a “lightweight” structure such as this one, these materials allow to increase the total thermal capacity of the building, with a resulting higher time constant. In case of a “heavyweight” structure, as in the case of a masonry house, the structure of the house itself work as a heat storage.

07 PCM
Phase changing materials (PCMs), used to increase the total thermal capacity of the building.

The cornerstone of a passive house envelope is represented by its windows, of course. These need to allow for passive heating in winter, and minimise heat losses.

Just like any other component of the thermal envelope, the energy performance of the windows depends on the local climate. Triple glazings are necessary in Colorado, for instance; double glazing is most likely fine for most of southern Italy. The goal is to guarantee comfort conditions, and avoid mold and condensation.

08 spacer
A photo of the windows: these are so efficient, to allow for ice to form on the outside!

We found our visit to Andrew’s house particularly interesting: we got stuck there under a snow blizzard, that left us under about 30 cm (11”) of snow.

Although the heating had not been on for days, however, the building remained perfectly comfortable even during such an extreme weather event.

09 monitor
The temperature inside the passive house remains around 18°C (64°F), while the temperature outside does not raise above -5°C (23°F). The heating system is not operational yet, so the inside temperature is maintained in a purely “passive” mode.

Our visit was a nice way to catch up with Andrew, and compare the current situation, in Emilia and Colorado, as far as energy efficiency, passive houses, and the construction industry in general.

We thank Andrew and his wife Jenny for the hospitality, and for the great time we had!

05 smoker
As for any good building, the most important part of a visit is good food and good company.

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