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Night ventilation for cooling

Discussion in 'Home Power and Microgeneration' started by [email protected], Feb 22, 2005.

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  1. Guest

    Phila has an average daily min and max of 67.2 and 86.1 F in July. Two A ft^2
    vents with one-way plastic film dampers and a 16 ft height difference and a
    DT (F) temp diff would allow 16.6Asqrt(16DT) cfm to flow at night, cooling
    a house by cfmDT Btu/h. What would the average July temp be in a house with
    10K Btu/F of thermal capacitance and 200 Btu/h-F of conductance and no internal
    heat gain and 2 4'x4' vents with a 16' height difference, and no fan?

    10 PI=4*ATN(1)
    20 TH=76'initial house temp (F)
    30 FOR D=1 TO 100'simulate 100 average July days
    40 FOR H=0 TO 23 STEP .1
    50 TA=(86.1+67.2)/2+(86.1-67.2)/2*SIN(2*PI*H/24)'outdoor temp (F)
    60 IC=(TH-TA)*200'conductive loss (+) or gain (-)
    70 IF TH>TA THEN IV=16.6*16*SQR(16)*(TH-TA)^1.5 ELSE IV=0'vent cooling (Btu)
    80 TH=TH-(IC+IV)/10000*.1'new house temp (F)
    90 NEXT H
    100 NEXT D
    110 PRINT TH

    75.96505 (close to the average daily temp) with no vent

    69.50536 (2.3 F above the min) with 2 4'x4' vents

    With a higher house conductance, the vents make less difference, eg 73.3
    vs 69.5 F at 1000 Btu/h-F. The vents above would move a 24-hour average
    16.6x16sqrt(16(76.7-69.5)) = 2851 cfm, comparable to a whole-house fan.
    With humidity sensing and motorized dampers, they could help heat a house.

    Nick
     
  2. Dr. Hardcrab

    Dr. Hardcrab Guest

    They said there wasn't gonna be any math on this test..........


    ;-]
     
  3. I don't dispute any of the calculations. I have, however, lived in Philly
    in the summer. While the average max may be 86.1 degrees, that is the
    temperature taken at the weather station. In the city, it can easily be 90+
    for days on end and lows in the high 80's as the heat sink of a brick row
    house and concrete sidewalks holds the energy.

    Northing beat an air conditioner for comfort.
     
  4. I, too, have lived in Philly. Come July you won't feel like doing those
    calculations :)

    In the days of the British Empire, Philly was considered a "hardship post",
    due to the extreme summer heat. I have had friends from New Dehli, one of
    the hottest places on the planet, say that West Philly, where they resided,
    was just as bad.
     
  5. Bughunter

    Bughunter Guest

    I don't live in Philadelphia. What should I do?
     
  6. Steve Spence

    Steve Spence Guest


  7. Paul ( pjm @ pobox . com ) - remove spaces to email me
    'Some days, it's just not worth chewing through the restraints.'

    HVAC/R program for Palm PDA's
    Free demo now available online http://pmilligan.net/palm/
    Free Temperature / Pressure charts for 38 Ref's http://pmilligan.net/pmtherm/
     
  8. Who do they ship with, Airborne ?




    Paul ( pjm @ pobox . com ) - remove spaces to email me
    'Some days, it's just not worth chewing through the restraints.'

    HVAC/R program for Palm PDA's
    Free demo now available online http://pmilligan.net/palm/
    Free Temperature / Pressure charts for 38 Ref's http://pmilligan.net/pmtherm/
     
  9. Oscar_Lives

    Oscar_Lives Guest

    Don't use a humidifier. Those things are too expensive to run.
     
  10. snip calcs

    The solution for the Philadelphia climate is big-ass Trane or Carrier.
     
  11. Guest

    I think we can ignore humidity if ventilation is only used for cooling,
    vs heating in shoulder seasons. Can the outdoor dewpoint Tod be greater
    than the indoor wall temp Tw, if the outdoor dry bulb temp To is less than
    the indoor dry bulb Ti and Ti is close to Tw? Tdo = To/(1-TolnRo/9621),
    using a Clausius-Clapeyron approximation, with Tdo, To, and Ti in Rankine
    degrees and the outdoor RH Ro expressed as a fraction.

    To/(1-TolnRo/9621) > Ti makes

    To > Ti - TiTolnRo/9621, or equivalently,

    9621(To-Ti) > - TiTolnRo.

    This can't happen, since the left side is negative, since To < Ti,
    and the right side is positive, since 0 < Ro < 1.

    QED.

    Nick
     
  12. Guest

    Chinese peeled garlic costs $2 per pound.
    And igloos would melt.

    Nick
     
  13. ~^Johnny^~

    ~^Johnny^~ Guest

    -----BEGIN PGP SIGNED MESSAGE-----
    Hash: SHA1

    Very good! But it's in the molding, you know.


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    Version: PGP 7.1

    iQA/AwUBQhzO0AIk7T39FC4ZEQLSPgCeO73I8m6nZaNyB2y86dGum7DDGusAoOms
    iQB1DAGOEGJUlF8sVM1+lC1d
    =ZKTO
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