[Greenbuilding] [BULK] Re: suspended slab

[Lawrence Lile]

All valid concerns.  However, the radiant floors I've worked with require 140F water, enough to sterilize them well.  Since this is above the safe temperature for a regular domestic system, you end up needing a mixing valve here with any radiant system at that temperature.  This is the same in a direct or an indirect system.  During the summer months, 50F incoming water would quickly cool the radiant heat pipes to below any temperature where salmonella would be a concern , and constantly flush them out, presumably with chlorinated water.    
 
As far as the extra valves to go direct, this consists of a single one-way valve. Doesn't take much extra planning, just download a schematic from your radiant heat supplier.   Compare the cost of that  one valve to the cost of a heat exchanger and extra pump, plus the efficiency of going direct versus the efficiency loss of a heat exchanger.  A heat exchanger is far more complex than the direct system, and would challenge a DIY'er even more.  THere are good reasons to go to a direct system.  
 
Since this comes up every 3-4 months, do a search on this forum and see what has been discussed about it before.  Direct radiant heat really is a standard way to connect the system, and is done safely quite often.  
 
I'm sure you're not convinced, and wouldn't put a direct system in your own house, but take a look at the info that is out there.  
 
Interesting info about the tankless water heaters coupled to a solar preheater.  I'm considering this very arrangement, and wonder whether it will not work so well.   Even if the tankless loses efficiency, if it is made up for by "free" solar energy it might still be worthwhile.   
 
--Lawrence Lile

________________________________

From: Shawna Henderson [mailto:shawna at abridesign.com] 
Sent: Tuesday, September 26, 2006 11:55 AM
To: Lawrence Lile
Cc: greenbuilding at listserv.repp.org
Subject: Re: [Greenbuilding] [BULK] Re: suspended slab


I think the health issue is not so easily shaken off. THe line feeding the water heater in a non-radiant floor house comes directly from the well or municipal line, at ±45*F. This is not salmonella-breeding condition in the line, nor in the water heater. Also, there is no recirculation from the end use back into the tank (ew, the thought of it!).