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Is cooling adequate via natural ventilation?

Matt_Salkeld_PEng | Posted in General Questions on

There was a lot of interest in natural ventilation I saw a while ago. Some people think this can also cool a house. Was this always a confusion of two separate goals and physics? What is the thinking today?

I am in a hot humid summer / cold winter climate.

The premise in summer is to seal the house to keep out heat in the day and open all the windows at night when the air temperature drops.  Problems with this idea:

1.  Would like house to be 75 F with 50% R.H. but the air temperature at night is also warm, 65 to 75 F and the R.H. is 65 to 80%. This drives very little to no air movement via stack effect.  Stack effect in winter when the outside is at -10 to +30 F is a lot greater.

So there may be enough air flow for ventilation but not for significant or any cooling.

2. Outdoor humidity is high, and R.H. is even higher at night if the air has cooled from 90 to 70 in a few hours.  You are bringing humidity into the house and reducing comfort. Even cooler air at 80% R.H. isn’t going to make you feel any cooler.

I can see natural cooling working okay in shoulder months when nights are cooler but not when it is needed the most.

PS I think climate change is partially responsible.  Old notions / rules of thumb die hard.

Any experiences?

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Matthew,

    The efficacy of natural ventilation is both climate and site specific. Here on Vancouver Island, sites close to the ocean usually see both quickly dropping temperatures and wind off the ocean most summer afternoons. Heat that has built up is quickly expelled and replaced by cool, dry air once windows are opened.

    But it's not something that can be relied on without consideration as to whether the factors that make it work are present on any specific lot.

  2. Expert Member
    BILL WICHERS | | #2

    I’d use a whole house fan when conditions are favorable (reasonable humidity and temperature outside). Humid summers rule out evaporative (swamp) coolers since their performance drops off rapidly in high humidity levels.

    What you’ll probably want to do is use a whole house fan whenever you can, and keep an air conditioner in reserve to deal with the humidity when you can’t use the whole house fan to keep things comfortable.

    Bill

  3. this_page_left_blank | | #3

    With the nighttime temperatures and humidity you list, you have zero chance of appreciably cooling your house by ventilation, natural or otherwise.

  4. Expert Member
    NICK KEENAN | | #4

    In climates where natural ventilation cooling is adequate, natural ventilation cooling is adequate.

  5. Expert Member
    Peter Engle | | #5

    The humidity load you describe is important, not only because of the comfort issues you mention, but also because of the heat load carried by that humidity. If you ventilate a house during warm/humid conditions, whether by natural or forced ventilation, the humidity is adsorbed by the materials in the building's interior. The next day, when the air conditioner is running, it has to deal with the latent load of that moisture as well as the sensible load of the heat in the building. This significantly increases the A/C loads.

    Night-time ventilation/cooling only works in climates with cool and dry evenings. Seaside and island locations, as Malcolm mentions above. Desert climates can also work if the average temperature is within a comfortable range. Shoulder seasons for the rest of us.

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