Foundation Slab Heat Storage Condition and Air Conditioner Power Consumption During Crawl Space Heating by Air Conditioner in a Highly Insulated House

<p>The energy-saving performance of a highly insulated house was evaluated based on the difference in temperature settings for crawl space heating with a single air conditioner. This heating system does not use dedicated ducts or fans for transporting warm air indoors. Air conveyance from under the floor to indoors is realized using ventilation fans. The temperature of the air conditioner was set to 22°C and 25°C, and the comparison results showed a 0.3°C difference in the room temperature of the living room. Also, comparing the difference between the living room temperature and the outside temperature was 0.7°C. The air conditioner power consumption differed by approximately 30% under the two settings, despite the fact that the average temperature difference was almost negligible. The conditions for indoor heat generation and heat gain by solar radiation were not significantly different between the two, and the difference was mainly due to the state of heat loss from the foundation slab under the floor. The following findings were noted. When the temperature setting of the air conditioner is lowered, heating stops even though the air conditioner is running, and the system enters a low-power consumption mode. Despite not being heated, the room temperature drops very slowly. For example, from 1:20 p.m. on February 8 to 0:20a.m. on February 9, the underfloor northeast corner air temperature decreased by 3.2°C, while the room temperature in the living room decreased by 1.3°C and the room temperature in 2F Room B increased by 0.5°C. The thermal image at this time showed that the wall and floor surface temperatures were the same or higher than the room temperature. In addition, it was confirmed that under the floor, the temperature drop was suppressed by the effect of heat stored in the foundation slab. When the air conditioner was operated at a high temperature setting, the heating ran continuously due to insufficient capacity. In this case heat continued to flow out of the foundation slab, resulting in higher power consumption. This indicates that heat loss from the foundation slab should be considered in heating load design and that moderate intermittent heating is necessary to achieve the energy-saving effect of heat storage.</p>