wrote:

A very small percentaqe of the heat you radiate goes in any
one particular direction, and the amount that falls on the 'receiving
/ absorbing surface' will thusly decrease as the square of the
distance from it.

Not if the surface completely encloses you. The MRT is solid angles weighted
by their temperatures. Multiply each area your body sees by its temp, add
the products, and divide by the total area of a reference sphere surrounding
you, containing the individual areas. You might radiate 50% to a large close
wall. As you walk away from a large wall, the near-field view factor might
still be about 50%.

And we don't need liquid helium. The MRT graph he

http://heatkit.com/html/guide2.htm#MasonryHeating

says we can be comfy in 90 F air with 40 F walls, in a bunny-free room.

Some buildings have chilled beams and ceilings for cooling. A chilled
floor would make more sense, since warm air rises. A slow ceiling fan
with an occupancy sensor and a room temp thermostat could stir up some
floor air as needed for comfort.

Nick