Demand controlled ventilation in a low-energy house: Preliminary results on energy conservation and health effects

In low energy dwellings the ventilation heat losses are significant. Reduction of these heat losses can be achieved by introducing demand controlled ventilation i.e. ventilation rates are set below normal level when rooms are no longer occupied. This paper outlines preliminary results on energy conservation and health effects in relation to demand controlled ventilation in a low-energy house. Simulations with the dynamic building performance simulation model TRNSYS 14.2 were run to evaluate the extra conservation of natural gas for space heating of a dwelling equipped with a demand controlled ventilation system. To simulate the ventilation demands, the simulation program used typical Dutch occupation schedules of a family with four members. Preliminary results indicate an extra energy conservation of 1520% with regard to the reference situation. Indoor climate parameters such as air and tap water temperature, relative humidity, dust and air exchange rate were adopted as indicators of human health risk. Experimental results indicate an elevated risk on overheating during the summer, odour nuisance in the sleeping room and kitchen, irritation of mucous membranes, including allergy, and Legionnaires disease. INTRODUCTION In order to reduce the CO2 exhaust from burning natural gas for space heating, the Dutch government has set limits to the energy consumption of new to build dwellings, offices and other utility buildings. According to Dutch building regulations a building permit will be refused if the energy consumption for space heating and hot tap water production exceeds certain limits depending on the size of de house; e.g. for a standard single family house the limit is 800 m of natural gas. At the ECN test location near Petten in the Netherlands, four typical Dutch dwellings were built to demonstrate the possibility of building houses of which the energy required for space heating can be reduced to 50% of this prescribed amount with low additional building costs. In addition, these buildings should offer its inhabitants a healthy indoor climate. Figure 1 gives a view of the project. The four buildings are equal in size but differ in the installations used for space heating and in building mass. Figure 1: Low-energy dwellings test site The facade of this complex is oriented North-South for a maximum heat gain from the sun in wintertime. Much attention is paid to reduce the heat losses from roofs, floors and facades. This is done by using 20 cm of isolation resulting in a heat resistance of 5 K mW. This paper deals with the residential building shown on the right hand side of figure 1, which is equipped with a demand controlled ventilation system. EXPERIMENTAL AND SIMULATION METHODS Test building and experimental setup The building on the near right is totally constructed from timber, with exception of the ground floor and the first floor on which a concrete layer has been laid because of the floor heating system. Beside the floor heating system heat to the rooms is supplied by radiator elements. A high efficiency gas boiler supplies the heat to these systems for space heating. Each room has its own room thermostat to control the room temperature and the flow of hot water for space heating is turned of by a thermostat valve All windows have double glazing wherby the total U-value is 1,1 W/m2.K. Element Construction U-value Ground Floor Cover layer, concrete, insulation 0.16 External walls Woodplates, Gipsum plate, insulation, gipsum plate 0.17 Internal walls Gipsum plate, insulation, gipsum plate 0.49 Roof Woodplate Isulation, woodplate, rooftiles 0.13 Windows Double glazing 1.1 Table 1: Fabric elements of building used in simulation All outside construction parts (groundfloor, roof, and facade have a U-value of 0,2 W/m. K resulting from the 20 cm of isolation. The total ground area of the dwelling is 42 m Ventilation systems The ventilation systems consists in fact of three subsystems: Mechanical supply and exhaust in winter time with 90% heat recovery. Natural supply and exhaust in summer time through windows in the facades at the southand north orientation. Natural supply and mechanical exhaust in times that the outside wind can not create sufficient air flow in the rooms. All ventilation system are controlled by the home network which is installed in the dwelling. For the balanced mechanical ventilation system in wintertime, ventilation rates are controlled by detection of movement in the rooms. If no movement is detected supply to and exhaust from rooms is kept at such a level that the air quality remains acceptable (temperature, air humidity). If movement in a room is detected ventilation valves are opened so that the prescribed levels are reached. The valves are situated in the outlets in the rooms. Powerline communication Signals are transported by power line communication, using the dwellings 230V system Ventilation rates are also switched to a higher level if air humidity in the room is in excess of 70% or if temperature exceed the comfort temperature .A webserver is used to transport data from a meteorological system to the power line system in the dwelling In summertime ventilation is established by open to windows based on outside windspeed, between 3 and 9 m/sec to avoid air velocities exceding 0,2 m/sec in the rooms Natural draught is created in p.e. the living room by the open (outside) window and a passage above the door between living room and corridor Demand controlled ventilation system Demand controlled ventilation in the heating season is implemented in the building by using movement detection in each room including the entrance of the building. If in a room movement is detected for a longer time than the room controller switches the room inlet/outlet ventilation valve in the ventilation system duct system from a minimum supply/exhaust rate to the rate required by the Dutch Building code Reducing the heat losses resulting from the necessary ventilation is implemented in two ways: • By using heat recovery on the exhaust ventilation flow is a major step to reduce the overall losses of these low energy houses. • Reducing the heat losses by demand controlled ventilation is a next step in rooms on presence. Normally building ventilation rates are 24 hours a day set at the prescribed level even if nobody is in the building. If the building or part of the building (living room or sleeping rooms) are not occupied the ventilation rate to that room can be reduced. At night time when everybody is asleep ventilation supply to the living room can be reduced and in daytime when nobody (normally) is present in the sleeping rooms the exhaust from that rooms can be reduced too. Supply rates can be reduced but room air humidity must be taken into account. Minimum supply rates should have a value so that air humidity in access of 70% is avoided. O W