by angib » Tue Oct 31, 2006 6:31 am
A heating old fart adds his thoughts:
'Hydronic' sounds really space-age compared to 'pumped hot water'! This is the standard heating system for houses here, so I would add one simplification - the air fan probably isn't required.
If the radiator core is fitted where it can have clear airflow above and below, the air that it heats will rise by convection and create its own circulation. Of course that means it will take a little longer to get the teardrop up to temperature from a cold start - it could be, oh, two or three minutes slower than with a fan!
As an alternative to using the thermostat on the water heater to control the cabin temperature, a domestic thermostat wired in to the water pump would provide better control - that's how my house works. It could even be used to switch the water heater on and off, to save gas when heating is not required, though this probably wouldn't save much as the heater would have to run for longer to get its water up to temperature.
One final simplification is to eliminate the circulating pump by carefully designing the water circuit so that it will thermo-syphon. Like hot air, hot water rises so if the piping rises from the water heater to the radiator core, drops inside the core (as the cabin air cools the water) and then drops back to the water heater, the water will flow itself.
Thermo-syphoning will further slow the response time, but eliminate the water pump (and its noise). This system was used here for domestic hot water production from heating boilers until a few decades ago. It has the one problem that the radiator core has to be turned vertical (like in a car) so that there is a drop from the inlet to the outlet to make the water thermo-syphon - for fan-less convection of the cabin air, the radiator core wants to be horizontal so that air can rise vertically through it easily.
Andrew
(currently being warmed by the hydronic system he installed himself)