[Greenbuilding] "Succesful" Open Hydroinic Heating System

[Speireag Alden]

On 2008, Jan 28, at 11:50, John E. Beeson wrote:

> I am intrigued here, but have some more questions.  So, does your  
> system
> - shown here again for everyone else - therefore run colder 'source'
> water throught the radiant floor loop whenever hot water tap is  
> called?

     Yup.  That's how the system gets flushed regularly.  Let's  
suppose that the circulating pump is on (I've twisted the timer  
switch).  Hot water flows from the tank through the loop and gets  
back to the tank considerably cooler.  Then I open a hot water tap in  
the bathtub.  The check valve in the circulating loop clamps shut as  
the pressure drops on its supply side.  Hot water runs out of the  
tank to the tap.  The pressure differential runs through the system  
to the only source of high pressure:  the cold water supply, just on  
the other side of the check valve.  Cold water flows through the heat  
pipe.  If I run five gallons into the bathtub, then the floor loop is  
flushed completely and the cold water hits the tank, there to be heated.

     The instant I turn off the tap, hot water flows out of the tank,  
driven by the pump, and through the loop.

     The occupants of the house are never aware that the floor bits  
which surround the pipe got a tiny bit cooler, because the pipe is  
embedded in a massive floor.  Things even out long before anyone  
would notice.

     To the extent that the floor is pre-heated, the cold water  
arrives in the tank a bit warmer than it would have.  You lose no  
energy, in the winter.

     In the summer, you gain energy, because your supply line to the  
water heater is running through a floor which never gets colder than  
about 20°C.  In my area, it's coming out of the ground at about 8°C.   
So that cold water warms as it runs through the floor, which warms  
from the warm air, which is supplied by the great outdoors.  The  
floor is sufficiently massive, and the through-put sufficiently  
small, that the floor never "sweats", even when you run all of your  
garden water through it.  But it does cool the house a bit.

     I suppose, in marginal conditions where it's very cold outside  
and very humid, the floor might conceivably sweat.  Certainly the PEX  
going into the floor does.  But that's not where it matters.

> And for posterity, I too am running a radiant floor.  And since this
> post to help inform and share info, I might as well disclose my  
> screwups
> (maybe).  Pretty different (I think) but with no insulation in the
> basement walls, I'm heating the earth - so the word is still out.  I
> plan on changing a lot of the system around but would love people's
> thoughts.

     Well, if you have an accessible basement, you can largely  
correct the problem.  Personally, I'd insulate around the outside of  
the house, to the extent feasible, and while I'm at it, ensure good  
drainage away from the house.  Then I'd put a layer of foam on the  
inside, floor and walls.  On the floor, I'd pour a concrete pad,  
sufficient to bear foot traffic plus whatever I might store down  
there, and on the walls I'd cover over with surface-bond cement.  Now  
you have an encapsulated layer of foam between your basement and the  
ground, which will almost make the basement into living space.

     Or, if your system is staple-up and you can get at the  
underside, you could put a layer of insulation across the rafters  
under your PEX, with reflective foil facing down as the bottom  
layer.  Your basement will then be cold, but the heat from the PEX  
will tend to travel upward as it builds up against the insulation layer.

-Speireag.