The first speaker was Karin Adalberth and she shared her experience with building her own plus energy house in Sweden during our seminar in Tallinn on November 22, 2013, with topic on Modern and energy-saving concept in a small residential buildings. Karin talked about her own plus energy house and the importance of a good mechanical ventilation system.
On the ground floor, the air inlet are in bedrooms, living and dining room, and exhaust are located in a kitchen and bathroom and washing room (where heat exchanger is placed), and on the second floor are two bedrooms and with a bathroom in-between.
The mechanical balanced ventilation system with a counter-flow heat exchanger was installed in Karin´s plus energy house with high heat recovery >87% (temperature efficiency), so when it is 0°C outside and 21°C inside and the incoming air is preheated to 18°C, there is only 3°C which must be added. The system has two fans (2×35 W) with water-based heating battery (normally electricity).
In Swedish standard the normal ventilation rate to be secured equals to 0.35l/s m2, and in Karin´s small residential house this can be increased to 0.45 (when stove, kitchen fan and central vacuum cleaner are used) and/or decreased to 0.1 when the house is not occupied (manual switch by the entrance door). Also when the interior temperature Ti is above 25°C and TU< 22°C, the bypass is set up.
Karin talked about the necessity of internal solar radiation protection using fabric with metal threads to reflect outside. The external blinds are very important when designing an energy efficient house as when windows are oriented towards south and south-west in the evening it can get up to 25-30°C.
Karin´s plus energy house has several small next projects installed within: such as phase-changing material (gypsum wallboard with wax granulated which allows heat storage in walls) and special sewage system (from outgoing water from bath and kitchen which allows passing the heat to the incoming cold water). The incoming cold water is preheated in winter from 8°C to 15°C and in summer from 12°C to 20°C, which gives energy savings of 20-25%. The domestic hot water usage equals to 1,600-1,650 kWh/a for two adults and 10 years old daughter.
Karin said: “My 10 years daughter, who showers twice a week, does not consume that much of hot water and when she becomes a teenager, she will shower more and the water consumption will for sure increase.”
“Every year from November to half March we use the air heat distribution in the house, and sometimes we need to double supply air to 0,7 l/s m2 to give higher energy for fan power consumption as under floor heating would be too slow and so we have installed normal radiators where it is practical not under windows. In December in 2010 with outdoor temperature of -22°C and in 2011 with -11°C we have got radiator temperature of 25-28°C, resulting in indoor temperature of 20-22°C in winter. But it gets quite warm in summer, as 25-30°C and we are forced to use good solar radiation protection, bypass and airing of the house.”
Karin´s plus energy house is equipped with electricity energy-efficient domestic equipment, and for example during daytime the dishwasher is supplied from hot water storage (from pellets or photovoltaic), the lighting system consists of LED with 1 W a 7 W.
“The total household electricity is 1,750-1,850 kWh/a, annual ventilation consumption of 240-260 kWh/a (due to decrease of ventilation when leave house in order to save electricity for fans) and pumps (600 kWh/a), which leads to total consumption of 2,650 kWh/a compared to the calculated of 2,500 kWh/a. The energy production from PVs is 4,320 kWh/a, and estimated was 4,200 kWh/a.”
Karin said that at the time of built they got 60% of photovoltaic cost from government, and today she can proudly say that the return is already 35%.