A local air-conditioning for occupied room is mainly used in Japan, thus individual cooling and heating units placed in each room of the house such as a stove, an air conditioner, and a kotatsu etc. By using these individual cooling and heating units, health risks have been occurred as a problem such as mold and tick caused by dew condensation or heat shock caused by temperature irregulation. The number of deaths due to heat shock is estimated to be 17,000 people per year in Japan, accounting for about 30% of 59, 416 deaths from annual accidents.
To solve this problem, the central cooling and heating system has been received attention to prevent the heat shock in residential buildings. The central cooling and heating system has been limited in Japan, because the space of mechanical equipment room and individual needs to adjust the thermal comfort have been increased. So, the whole-house air conditioning system is proposed and installed to residential buildings by several HVAC makers in Japan, because the system is only needing a small space for mechanical equipment room. However, the fans are CAV despite of the load changes from moment to moment that the room temperature difference and daily range occur. To improve this problem, it is effective to introduce VAV for the blower fans, and there is also a past study on the VAV system of the central air-conditioning, but there is no document which studied about the effect of environmental improvement. Therefore, in this study, evaluating the effect of improving indoor thermal environment by central air-conditioning system with VAV introduced in the residential house, using the actual measurement and the coupled calculation of the CFD and the ES, comparing the existing CAV system and the individual type air-conditioning generally used.
The indoor thermal environment improvement effect on introducing VAV to the blower fan of the central air-conditioning in the residential building is analyzed on following 4 aspects.
1. The percentage of the setpoint temperature ± 2 ºC for the whole house is 45 to 75% for the central air-conditioning CAV and about 60% for the individual air conditioner, whereas the central air-conditioning VAV is about 90%, and the proportion of comfortable areas is high.
2. Comprehensive central air-conditioning CAV, VAV increased PMV by 10 to 20% compared with individual air conditioning.
3. The temperature difference of up to 10 ºC is generated for individual air-conditioning, while central air-conditioning is 6 ºC, the temperature difference of 4 ºC is relaxed. The bathroom and undressing room, which are related to bathing activities, are also kept at 20 ºC or more, and the effect of suppressing heat shock is revealed.
4. By supplying the blowing temperature of the air-conditioner and the air flow rate obtained from the heat load, it is possible to set the indoor temperature roughly to the target setpoint temperature. Therefore, it is possible to equalize the indoor temperature by the VAV system by sensing the outdoor air condition and the air-conditioning blow temperature.