(1-2)Air conditioning in the house using ground heat

The layer of the earth 8m below the ground surface retains the average temperature on the surface, given usual thermal conductivity. We can use this fact to cool the house in summer and warm it in winter. Pipes imbedded in the ground for this purpose are called cool tubes. We have two sets of three cool tubes 3.2m below the surface which run 10m to the basement from different sides. They are very useful for a climate which has a very hot summer and very cold winter such as Japan, though we can not neglect the heat island effect there.

There is a solar room on top of the experimental house to obtain buoyant or lifting power. The windows facing outside are double glazed and the walls between the room and the house are thermally insulated with 60cm of fleece. There is a chimney on the roof to lift the air in the solar room which is sucked through four ventilation holes in the floor and two in the wall. When it is very hot and the air in the solar room is warmed, more cool air from the basement can be brought into the house.

This relationship can be described by the calculation linking three equations, firstly Bernoulli's, describing air flow, secondly that of thermal transfer, and thirdly that of heat balance in a room.

This system must be used during two extreme seasons. Else, heat will be stored or taken in the ground. Dehydration of the air might be necessary in the basement in summer.

The equation of thermal transfer

The equation of heat balance in a room

�@�@�@ Bernoulli's equation, describing air flow

In the case of calculating the air flow between rooms, the velocities in Bernoulli's equation are all squared, so we have to ascertain whether their signs are negative or positive. In our numerical calculation, we solve the simultaneous equations by giving the sign for each velocity and finding the proper combination of the air velocities. For a layered wall we replace the total thermal conductivity to the convolution of each layer's thermal conductivity to have the calculation time reduced. An equivalent temperature on an outside wall from the solar radiation was obtained by eliminating the shadow area of the wall. Wind pressure on an outside wall was found from the experimental equations1).

There are six water tanks in the solar room which are expected to have lifting power from sunset until sunrise. The air temperature change in a living room on one day in summer and one in winter are shown in the next figures along with calculated results(not given yet.

1)M.V.Swami and S.Chandra;"Correlations for pressure distribution on buildings and calculation of natural-ventilation airflow", ASHRAE Transaction, 243-266, 4th tech. session, 1988.

Air temperature in a living room on a summer day and a winter day with 
calculated results of dotted lines(not given yet).

In winter the room temperature is around 9�Ž even when it is below zero outside and its average temperature is a few degrees higher than that of the average outside temperature. It means that the air was warmed by the ground heat. However, high temperatures outside in the daytime are not well utilized. One way would be to shorten the overhang to to increase the solar energy available.