[Greenbuilding] [BULK] Re: Controlling FLoor Heat

[Lawrence Lile]

>I have regularly used air temperature sensors for radiant floor heat.
This only works if you have a well insulated building that is not air
leaky. It is not possible to have a floor running at 90 F and not heat
the air to over 75 if you have a well insulated building. 

R60 roof, R30 walls, Everything caulked until the caulk runs out the
other side, 90F floor, 72F building air temperature - that's my
experience.  Yes, it is possible.  How? I dunno, that's what it does.
Don't ask me I just live here. 

>If you dont insulate well under the heated slab, all bets are off, as
the floor is heating the ground.

That's probably the major issue.  


>My current favourite approach, as I have had loads of challenges with
controls too, is to use a Thermostatic Radiator Valve with a remote air
sensor to control the flow of water into a manifold that serves several
loops (from 2 to dozens). 

Got a mfr/model number on that item?

>In small systems (say 2500 sf house), the pump is small and runs all
the time when it is cold, and the supply temp is kept at 95 to 105
depending on the quality of the insulation and the severity of the
climate. Return temps are always under 90 or so to ensure I get good
condensation from the boiler to get best efficiency.

One of the problems is my supply temperature is probably too high -
140F.  I'll have to do some more hacking to allow it to be colder than
the DHW temperature.  (yet another consequence of combining the floor
heat with the DHW.  Friends don't let friends use open loop radiant
floors.)


Now don't get me wrong, I am having a great time researching and
reworking this system.  Nothing more fun than getting a soldering iron
out and rewiring the inside of an electronic thermostat.  Giving an
engineer a system with bad controls is like wrestling with a greased pig
- you begin to realize that the pig likes it.  


--LL