[Greenbuilding] Simple Solar Radiant System

[dantonioli at earthlink.net]

I have a solar hot air system on my home that works only when there's enough
radiation to heat the inside of the panel to 74 degrees. The temperature
hits 74 degrees and a small, 24 watt fan turns on to brings fresh, warm air
into the house.
 
I want to design a simple solar radiant system that works on the same
principle I have two thermal panels on my roof that will eventually be
hooked up to a larger "master plan" system when time and money permit for
doing everything right.
 
In the meantime, I want to use them to heat a radiator in my cold, ground
floor office that's chilly even when it's warm outside.
 
The model is simple: one loop, filled with water/glycol, and pumped when the
temperature hits a set point. When the sun shines and it's cold inside, I'll
at least be able to partially heat the space with solar. 
 
Yes, I understand that a comprehensive system with storage and boilers makes
sense, but that's for later.
 
Does anyone have any experience with such a simplified system and/or know of
any Homepower-type articles online?
 
Dan Antonioli