Hybrid Car – More Fun with Less Gas

Re: Attic to heat the house????

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Posted by nicksanspam on September 24, 2004, 2:09 pm
 


I woulda used R1...


And 0.9x250 in the numerator, which makes efic = (225-60)/250 = 0.66.


Another way to do this:

         ---      
     |--|-->|-----X-www--- 90
         ---    |   0.65
         214    |          breaking the circuit at X and replacing
          0.83  |          the part to the left with an equivalent,
    30 ---www---           Tt = 30+214x0.83 = 207.6. Rt = 0.83.

                   Q -->
      --www-------X-www--- 90
     |  0.83        0.65
     |  
    --- 207.6      Q = (207.6-90)/(0.83+0.65) = 79.45 Btu/h-ft^2.
     -
     |
     -


I woulda said U = 2+V/2 = 5.75, so Rout = 0.174.


                   Q -->
      --www-------X-www--- 90
     |  0.25        0.65
     |  
    --- 89.5       Q = (89.5-90)/(0.25+0.65) = -0.6 Btu/h-ft^2.
     -
     |
     -


You might hang a layer of dark shadecloth inside. Then again, daylight is
nice, from skylights in the attic floor. People often mistake my polycarb
roof for a metal roof.


A fan or blower, as in Soldier's Grove. A 600 ft^2 attic collecting
99K Btu/h (29 kW) with a 10K cfm fan might have 80 F air entering
the attic and 80+99K/10K = 89.9 F air leaving. Grainger's $20 86 W
4C853 48" ceiling fan might move 21K cfm up a stairwell into an attic
and push warm attic air down from the peak to the basement heat store
via a LARGE duct, eg 2 rooms with 4'x4' ceiling and floor grates. The
fan might have a 4'x4' motorized cover that opens when it is running.
The duct near the attic peak might have a one-way plastic film damper
or another motorized foamboard cover.


Warm air rises...


Mine did, under the BOCA code. It's held up well for the last 7 years,
altho it may eventually leak a bit, since the 4'x12' panels are attached
to the purlins with lots of hex head screws with neoprene washers.

A 1' slice of polycarb roof with a 20' slant height under a 5 Btu/h-F foot
of 90 F fin tube might look like this:

         ---      
     |--|-->|-----X-www--- 90
         ---    |   0.2
        20x225  |    
                |
         R1/20  |    
    30 ---www---           Tt = 30+20x225/20 = 255. Rt = 0.05.

                   Q -->
      --www-------X-www--- 90
     |  0.05        0.2
     |  
    --- 255        Q = (255-90)/(0.05+0.2) = 660 Btu/h-ft,
     -
     |                 with a 90+0.2x660 = 222 F attic air temp???
     -

efic = 660/(20x250) = 0.132, or 0.22 with two fin tubes. Not very efficient,
but cheap and easy. Less labor, no sheathing, no tarpaper, no shingles.

With a fan and a $00 800 Btu/h-F 2'x2' all-copper SHW 2347 Magicaire
air-water heat exchanger under a 32' ridge, we have

                    Q -->
      --www-------X-www--- 90
     |  0.05        0.04
     |  
    --- 255         Q = (255-90)/(0.05+0.04) = 1833 Btu/h-ft,
     -
     |                 with 90+0.04x1833 = 163 F attic air?
     -

A $28 32' 160 Btu/h-F attic ridge fin-tube or an 800 Btu/h-F fan-coil unit
might collect 21K or 58.7K Btu/h in full sun in December, enough to make
hot water for showers, with a foamboard hat and a PV/DC circulation pump
with battery backup to avoid freezing.

Nick


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