To create a really comfortable church requires having the floor and wall temperatures controllable and set to about 72°F. This is impossible to do with standard heating systems, because they heat the air within the room and if the outdoor temperature is cold, say 20°F, then the walls are cold. Even with good insulation the walls must be colder than the air temperature inside, because it is the air that heats the walls. This makes a real difference to the comfort of the people in the room because our skin is sensitive to the infrared temperature of the surroundings. Here in Bend, Oregon, the ground temperature is 55°F, which means the floor temperature will be 55°F until heated by the air above it. A typical forced air system will blow air into the room at a temperature considerably higher than the preferred temperature of 72°F, and so it is impossible to be truly comfortable in a room here with outside walls and a floor laid directly onto the ground.

The obvious solution to this problem is to heat the floors and walls to approximately 72°F, and the usual method of doing this is running copper pipes into a slab of concrete poured over the ground and then pumping hot water through the pipes. That requires considerable expense during construction, plus expense heating the fluid, and expense operating and maintaining the system, and risk of failure. Locally this isn’t very efficient in the long run because the subsurface ground temperature is cold, and it would take years to overcome the slow transfer of heat from the one-hundred foot depths. It could never stabilize completely.

What would work would be to create a totally passive system which automatically communicated 72°F heat to the floor and walls. That can be done by creating a large heat sink and that can be created under a new building with a clear view of the sun. The verbal description is a bit wordy, but the actual construction is simple and the final operation is almost totally passive. After clearing the ground to a solid construction level, begin by laying down a layer of insulating material over the entire ground that will be under the building’s floor. That will make it easier to control the thermal mass at an ideal temperature. Then begin to construct the large thermal mass above the insulation by laying down some pipes, perhaps 6″ PVC. These will be used to conduct heat from the air heated in the solar collector to the two foot thick layer of local dirt or sand which will be placed over the pipes. The thermal conductivity from the pipes or from the under-floor thermal mass need not be great because the rate of heat flow through the system will be modest but continuous over the course of several months. It will be heated for months for 24 hours per day by a totally passive solar-heat-sink, which is designed with a thermal mass which will exhaust heat  to the under-floor-thermal mass 24 hours per day. The solar mass heats for several hours during the day and transfers heat to the the under-floor-thermal mass will reach its operating temperature and the interior of the building’s thermal mass will be72°F all the time. After several months of doing this the building’s thermal mass will reach an ideal operating temperature. This under-floor-thermal mass will have a large crawl space above it but below the buildings floor, and this air space will be controlled to always be 72°F, and thus the floor above it will also be 72°F. If it is required to ventilate the crawl space this could be done with a standard blow-air-through heat exchanger. The temperature of the system would be done by blinds controlling how much sun light is allowed to shine on the solar-mass.

Of course the details must be dealt with, but the basic idea is simple enough. It is to heat a very large mass passively, using solar energy, and then to transfer the accumulated heat very slowly over the course of a year into a well insulated room via conduction of the heat to the floor and walls.