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Andrea Carvajal, Diego Carvallo, Angeles Hevia, Yasmina Taha

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Concept of the Design

Kushta Observatoriya

The circular form of the house was chosen for a couple of reasons. Because this shape had the least number of sides, it was assumed to have the least amount of exposed areas to the exterior. Therefore, heat loss would be at a minimum rate, when compared to any other shape. Energy consumption would be significantly lowered, while providing the thermal comfort required to the users of the building.

In the Balkans region, houses typically had a "chardak" or open terrace. "Chardaks" are defined as "tiny structures built for repose beside farmers’ fields" always maintaining its essential qualities of elevation, repose, sociability, and connection with nature.

The "chardak" is a place to view and as such can serve as a platform to the land and the sky providing a place of repose for those who work in the field and a place to watch over them to protect them from birds or animals that might steal the fruits of the fields. The "chardak" has served a number of uses including as a granary on the base level and a working and guest sleeping area on the upper level.

The importance of the "chardak" in Bulgarian houses was taken into consideration and emphasized in the layout of the house. It can be seen that a large semi-circular "chardak" is located facing the west facade, encompassed by the bedrooms and studio. The living room, which is designed to be the core of the house and designed to be the space which most activities were to be taken place in, is given a centralised location, in which all other rooms can overlook it. It is given much significance by also allowing it to be on a lower level than the other rooms. Several steps leading upwards to the bedrooms and study reinforced this concept. At the same time, the difference between public and private spaces was defined. The bedrooms and study were thought to be more private seeing as minimum guests would be allowed there.

The "chardak" is approached in the house ensuing the following principles:

1. The first way of accomplishing the "terrace", implementing the idea of "watching over something" is by generating different levels inside the house. Living and dining rooms as well as the kitchen are public spaces located in the underground level whereas the rooms are the private spaces on the ground level. The former is located in a lower level in order to make it visible from the latter generating a visual relationship between the different levels of the house.
The living and dining rooms are the space organisers, located in the centre of the house straightening up all the other spaces.

2. The concept of "chardak" is also considered as a terrace because different planes exist. The proposal is to generate different terraces that break a plane fragmenting the elements of the house. For this reason, according to their use, the facades are also in different planes. The main bedroom facade is in a different plane compared to the main bedroom and kitchen.

The idea of the design is to propose looking at the surroundings from different angles. This angled-way of looking is highlighted by the fragmentation generated on the facade, which intends to remark volumes that end in different planes to each other.

3. Green roofs are proposed, because they follow the "chardak" principles of elevated platforms to observe the surrounding lands, also connecting with nature and a sort of "granary" as food is grown and cultivated in these organic gardens.

Environmental Design and Approach

Designing an affordable Passive House in the village of Lozen, Bulgaria, was approached by first conducting a complete study of the climatic conditions in the area. It was found that Sofia, which is the closest city to the village of Lozen, has humid, continental weather conditions. It was assumed that both areas possess the same climate. According to the analysis made with the Weather Tool (Ecotect), the recommended strategies where mainly:

  • south orientation
  • thermal mass
  • night ventilation
  • evaporative cooling

Thermal Bridging

The house achieves a rate for thermal bridging of 0.01 W/mK because it considers the following strategies:

  • construction details based in the Passive House standards
  • uninterrupted insulation in the different building envelope assemblies
  • window connection to wall with exterior insulation
  • columns located in the exterior walls constructed in order to allow the external insulation layer to continue throughout the wall

Under the mantra "Build Tight Ventilate Right", the house achieves the 0.6 ACH@50 Pa considering that the windows inside the house will be opened in order to avoid condensation and mould growth problems, allowing humidity levels ranging from 40% to 70% as recommended by the UK's Chartered Institution of Building Services Engineers (CIBSE).

PHPP Calculations

The method used for calculating Space Heat Demand, the Specific Primary Energy Demand and the Specific Useful Cooling Energy Demand was Passive House Planning Package (PHPP).

It is important to state that the interior temperature inputted in PHPP was 19ºC because this is considered the minimum recommended for thermal comfort, according to the Intelligent Energy Europe programme.

Space Heat Demand

The Space Heat Demand of 14 kWh/m2a was achieved by considering the following strategies:

  • mud walls with two types of external insulation: vacuum and sheep's wool. The former considers a conductivity of 0.007 W/mK and the latter a value of 0.039 W/mK
  • green roofs in bedrooms, studio and kitchen enabling to reduce heat losses by using a minimum thickness of 0.80 mm with a thermal transmittance of 0.046 W/m2K
  • floor slabs with a thermal transmittance of 0.081 W/m2K including the use of EPS and sheep's insulation
  • double glazing windows with low-e coating and wooden frames accomplishing a thermal transmittance of 1.30 W/m2K

Specific Primary Energy Demand

The Specific Primary Energy Demand of the house is 78 kWh/m2a. This is achieved by considering the following strategies:

  • heating loads reduced
  • the cooling unit is provided by supply air cooling. However, using summer ventilation mainly in the west facade reduces its consumption
  • using a condensing gas boiler enables domestic hot water (DHW) and Space Heating to work. However, the latter has reduced its rely on the boiler considering an efficient building fabric with low thermal transmittance values
  • lamps used in the house are compact fluorescent lamps (CFL)
  • dishwashing machine is not considered to be used in the dwelling
  • clothes washing machine is used with a maximum temperature of 40ºC considering an electric use of 0.26 kWh per load (5 kg)
  • a combined unit is used for freezing and refrigerating with an electricity use of 0.80 kWh/d
  • the cooking is provided by a gas system considering 0.25 kWh/use
  • the use of electronics is considered as 80W taking into account it is residential use

Specific Useful Cooling Energy Demand

The Specific Useful Cooling Energy Demand of the house is 11 kWh/m2a. During summer, the excess heat is removed by cooling the supply air. However, considering the following strategies reduces the cooling loads:

  • summer ventilation during day time by opening the west wall windows
  • windows are opened in the bedroom with a fraction of opening duration of 60% and in the main bedroom of 40%. In both cases tilting windows were used with an opening width of 0.05 mt
  • a daily average air change rate of 0.39 is achieved when using this strategy


  • Passive House Planning Package (PHPP) software
  • Weather Tool (Ecotect) software
  • "Details for Passive Houses. A catalogue of the ecologically rated constructions", The Austrian Institute for Healthy and Ecologycal Building (IBO)
  • "Passive House Planning Package 2007", Passive House Insitute
  • "Ecohouse", Roaf, S.