[Greenbuilding] Distibution and radiant heat

[Corwyn]

On 1/7/2011 8:57 PM, Chris Koehn wrote:
> A timely discussion for me..
> I am currently planning and pricing an architect designed home to be built on one of the BC southern gulf islands that has no grid power. There will be wood burning heat- currently a cook stove and a fireplace are specified. The floor plan is rather longitudinal, with a bath&  mud room at one end of the home and somewhat isolated from the main space.
> I am wondering if it's advisable to consider picking up heat off of the ceiling and moving it beneath the floor (in insulated duct, through a crawl space) and dumping it in to the bathroom area? We'd presumably need some air handling equipment, but the energy used to move hot air must (?) be less than heating the space (with propane).

A FIREPLACE?  Seriously, a open fireplace?  And you are worried about 
moving a little bit of stratified heat?  With an elaborate, PV powered, 
high embodied energy device.

How much energy do you think there is in a say 8,000 cubic feet of air 
at 73° (68° + 5°)?  145 BTUs per °F.  If you are heating a 65°F bathroom 
with it, you get 1160 BTUs (assuming you lose none on the way).  And you 
are going to try to accomplish this with PV power? Let's guess that this 
requires a 130 CFM fan.  Running for one hour (that's all the heat there 
is) 24 watts seems a common rating for such a fan.
or 0.36 Amp-hours from the battery.

The same amount of heat from burning propane is 0.0126 gallons.  1 
gallon would amount to 79 days (how long is the heating season in BC?). 
  How long would it take to just pay back the cost of the fan and duct 
work?  Not to mention, batteries, PV panels, controllers, etc.  In terms 
of either money or embodied energy.

And how much would it warm the bathroom?  It didn't take long for me to 
add up 600 BTUs / °F of thermal mass is a bathroom what with heavy 
toilet, tub, sink, water, tiles etc.  Which means that heat would raise 
the temperature at MOST 2°F.

The same amount of heat vanishes up the chimney of the fireplace every 5 
minutes (just in room air being sucked up the chimney) when the fire is 
burning.

One despairs.

Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
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