[Greenbuilding] distribution of radiant heat

Sat Jan 8 18:34:50 CST 2011

I'm a little confused. I had no problem with the term fireplace as here they
are typically sealed units and the term is used to differentiate from
freestanding wood 'stoves'. I have not seen an 'open fireplace' built (that
is the term that used to be used here) for over 20 years (and it was a
rumford).

What I am confused about are what the calculations are in reference to? (I
don't really understand them) and what the point is of making a comparison
to propane? I get the point about embodied energy and financial cost but the
question here is about distributing heat from a central source.

I think using a fan or some design to distribute heat from a stratified
ceiling area is not unreasonable as a long term provision. The comment that
heat will migrate eventually in a well insulated building is not really
reasonable based on the comments we have had here and most experience. 

The stratified air in a cathedral ceiling can easily be 10deg higher
(especially over the heat source). All it is doing is warming the ceiling
mass and migrating out regardless of how well insulated so it is not
unreasonable to look at ways of improving air flow and distributing that
heat a little more effectively warming a few more surfaces.

The fantech 125(cfm) inline is rated at 18watts (.18 max amp) - 125 cfm will
throw a lot of warmed air into a small bathroom space quite quickly. It
takes .018btu to warm 1 cu.ft. of air 1degF. So if the stratified air temp
is 78deg (which is think is more realistic over a fireplace) then 1 cuft. of
air is holding about 1.4btu. the fan moving 120cfm can theoretically move
about 10000btu/h with an energy consumption of roughly 60btu/h. The room
probably only needs about 1500btu so an actual fan requirement can be worked
out from that.

Not unreasonable to throw that wattage or solar draw into a design. Venting
that ceiling area is also not a bad idea for its own sake.

JOHN SALMEN ENVIRONMENTAL DESIGN
4465 UPHILL RD,. DUNCAN, B.C.  CANADA, V9L 6M7
PH 250 748 7672 FAX 250 748 7612 CELL 250 246 8541
terrain at shaw.ca

-----Original Message-----
From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Corwyn
Sent: January 8, 2011 12:44 PM
To: Environmentally-preferable design, construction, building elements
Subject: Re: [Greenbuilding] distribution of radiant heat

On 1/8/2011 12:03 PM, Chris Koehn wrote:
> Hey Corwyn, If you'd like more info before jumping to conclusions just
ask:

I worked with what you provided.

> The "open fireplace" is not open: it's an enclosed, sealed combustion
> unit with outside combustion air and heat circulation. Not my
> preference, but again, I'm not the architect.

'fireplace' around here means open fireplace.  Sorry that that caused 
confusion.

> The clients have in place a 12 KW propane generator. We won't be
> powering the home exclusively with solar; solar will be used to top up
> the batteries when the genset isn't running.

Barged over propane for a 12kW generator doesn't make me feel _less_ 
anxious about the idea of this contrivance.

> I am building a case to revamp the design to abandon the fireplace (on a
> gable wall- largely aesthetic) in favour of a centrally located masonry
> heater.
> Propane has to be barged over, so it's usual cost and efficiencies are
> not applicable here.

Sort of.  You will need to barge over the fan and ducting as well. 
Unless you can convince me that those materials are going to be less 
weight or volume than a corresponding amount of propane, I stand by my 
assessment.

> There is currently no heat source called out for the bathroom, so your
> assumption that we're starting with 65 degree air is invalid.

Which only makes it worse.  The air is bringing over 145 BTUs / °F.  The 
thermal mass of the bathroom is at least 600 BTUs / °F.

If the bathroom is 57°, you get 73-57 * 145 = 2320 BTUs out of the air. 
  Which raises the temperature of the bathroom 3.8°, to 60.8°.

> We are working with 4500 HDD but heating typically starts in late
> September and ends in early June. It's oceanfront, so there's a really
> big 45 degree mass out there.
> It may prove to be more efficient and practical to provide a separate
> propane heat source for the bathroom area but the clients have asked me
> to look for alternatives and so I am.

Try increasing the insulation in the house, and see how much heat that 
saves.  If the heat isn't leaving in a hurry, it will have time to 
migrate to all areas of the house.

Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.greenfret.com/
topher at greenfret.com
(207) 882-7652

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