Arefeh Hesaraki

Demand-controlled ventilation in new residential buildings: consequences on indoor air quality and energy savings

The consequences on indoor air quality (IAQ) and potential of energy savings when using a variable air volume (VAV) ventilation system were studied in a newly built Swedish building. Computer simulations with IDA Indoor Climate and Energy 4 (ICE) and analytical models were used to study the IAQ and energy savings when switching the ventilation flow from 0.375 l·s−1·m−2 to 0.100 l·s−1·m−2 during unoccupancy. To investigate whether decreasing the ventilation rate to 0.1 l·s−1·m−2 during unoccupancy, based on Swedish building regulations, BBR, is acceptable and how long the reduction can last for an acceptable IAQ, four strategies with different VAV durations were proposed. This study revealed that decreasing the flow rate to 0.1 l·s−1·m−2 for more than 4 h in an unoccupied newly built building creates unacceptable IAQ in terms of volatile organic compounds concentration. Hence, if the duration of unoccupancy in the building is more than 4 h, it is recommended to increase the ventilation rate from 0.100 l·s−1·m−2 to 0.375 l·s−1·m−2 before the home is occupied. The study showed that when the investigated building was vacant for 10 h during weekdays, increasing the ventilation rate 2 h before occupants arrive home (low ventilation rate for 8 h) creates acceptable IAQ conditions. In this system, the heating requirements for ventilation air and electricity consumption for the ventilation fan were decreased by 20% and 30%, respectively.

An Investigation of Energy Efficient and Sustainable Heating Systems for Buildings: Combining Photovoltaics with Heat Pump

Renewable energy sources contribute considerable amounts of energy when natural phenomena are converted into useful forms of energy. Solar energy, i.e. renewable energy, is converted to electricity by photovoltaic systems (PV). This study was aimed at investigating the possibility of combining PV with heat pump (HP) (PV-HP system). HP uses direct electricity to produce heat. In order to increase the sustainability and efficiency of the system, the required electricity for the HP was supposed to be produced by solar energy via PV. For this purpose a newly-built semi-detached building equipped with exhaust air heat pump and low temperature-heating system was chosen in Stockholm, Sweden. The heat pump provides heat for domestic hot water (DHW) consumption and heating demand. Since selling the overproduction of PV to the grid is not yet an option in Sweden, the PV should be designed to avoid overproduction. During the summer, the HP uses electricity only to supply DHW. Hence, the PV should be designed to balance the production and consumption during the summer months. In this study two simulation programs were used: IDA Indoor Climate and Energy (ICE) as a building energy simulation tool to calculate the energy consumption of the building, and the simulation program WINSUN to estimate the output of the PV. Simulation showed that a 5.5 m 2 PV area with 15 % efficiency produces nearly the whole electricity demand of the HP for DHW during summer time. As a result, the contribution of free solar energy in producing heat through 5.5 m 2 fixed PV with 23o tilt is 15 % of the annual heat pump consumption. This energy supports 58 % of the total DHW demand.