Results 1 to 12 of 12
  1. #1
    Dislocated Member
    Neo's Avatar
    Join Date
    May 2011
    Last Online
    31-10-2021 @ 03:34 AM
    Location
    Nebuchadnezzar
    Posts
    10,609

    Roof vent airflow calculation?

    Is there a calculation used for the input/output airflow volume to create effective airflow.. ie input volume 90% of output volume.

    Does the size of the roof space also have to be factored in to the size of the vents.. ie cm2 vent area per m3 of roof space?

    Cheers
    Life should not be a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside in a cloud of smoke, thoroughly used up, totally worn out, and loudly proclaiming "Wow! What a Ride!"

  2. #2
    last farang standing
    Hugh Cow's Avatar
    Join Date
    May 2015
    Last Online
    15-03-2024 @ 01:44 PM
    Location
    Qld/Bangkok
    Posts
    4,110

  3. #3
    Dislocated Member
    Neo's Avatar
    Join Date
    May 2011
    Last Online
    31-10-2021 @ 03:34 AM
    Location
    Nebuchadnezzar
    Posts
    10,609
    Cheers Hugh.. says there the ratio should be 2:1 to reduce heat loss.. but getting rid of heat is exactly what I'm looking for. I'm sure I'd read on a thread here that the intake should be less that the output to create a fast airflow in hot conditions.

  4. #4
    last farang standing
    Hugh Cow's Avatar
    Join Date
    May 2015
    Last Online
    15-03-2024 @ 01:44 PM
    Location
    Qld/Bangkok
    Posts
    4,110
    Roof vent airflow calculation?-cda-2018-attic-ventilation-amount-1346s

    See if this helps
    Attached Thumbnails Attached Thumbnails Roof vent airflow calculation?-cda-2018-attic-ventilation-amount-1346s  

  5. #5
    last farang standing
    Hugh Cow's Avatar
    Join Date
    May 2015
    Last Online
    15-03-2024 @ 01:44 PM
    Location
    Qld/Bangkok
    Posts
    4,110
    Roof vent airflow calculation?-df-cda-roof-venting-1346s-1-a


    You will see that the soffit inlet needs to be bigger than the outlet otherwise you will decrease airflow.
    Any more and I'll start the meter running.
    Attached Thumbnails Attached Thumbnails Roof vent airflow calculation?-df-cda-roof-venting-1346s-1-a  

  6. #6
    Thailand Expat OhOh's Avatar
    Join Date
    Jul 2010
    Last Online
    26-03-2024 @ 08:49 PM
    Location
    Where troubles melt like lemon drops
    Posts
    25,222
    ^Excellent and clear info.

  7. #7
    Dislocated Member
    Neo's Avatar
    Join Date
    May 2011
    Last Online
    31-10-2021 @ 03:34 AM
    Location
    Nebuchadnezzar
    Posts
    10,609
    Yes thanks Hugh. Same topic, different question so I hope you're not going to charge for this one.

    If the underside of the roof and the gable end walls are lined with radiant barrier foil, should I install fibre insulation, radiant barrier or nothing at all on top of the ceiling panels?

    I'm inclined to not put anything on top of the ceiling panels to allow heat dissipation from the room into the roof space, assuming the roof space is cooled sufficiently through venting.

  8. #8
    last farang standing
    Hugh Cow's Avatar
    Join Date
    May 2015
    Last Online
    15-03-2024 @ 01:44 PM
    Location
    Qld/Bangkok
    Posts
    4,110
    Installing fibreglass batts on the ceiling panels will cut heat transmission through the ceiling.
    The ceiling space temperature will decrease with ventilation but heat transmission through the ceiling panels will increase due to greater airflow across the ceiling which decreases the static air film insulating effect. Having both will greatly increase efficiency. Some batts discourage rodents etc as well and have fire retardent properties. If you have airconditioning batts should save you about 10% in energy costs or conversely you could install a 10% smaller system. Hope that makes sense.

  9. #9
    Dislocated Member
    Neo's Avatar
    Join Date
    May 2011
    Last Online
    31-10-2021 @ 03:34 AM
    Location
    Nebuchadnezzar
    Posts
    10,609
    Well the aim is to transfer heat upward, but I guess it's dependent on air changes per hour if that heat transfer is upward or downward. Kind of a suck it and see situation I feel not knowing exactly how efficient the venting will be until it's fixed and the hot season kicks in.

    Knowing that the radiant barrier under the roof and venting should reduce the heat I'm inclined to leave off the layer on the ceiling panels and fit retroactively if required.

    One issue is the main room absorbs a lot of heat from the long outside wall in direct sun most of the day.. my concern is that a insulation layer on top of the ceiling panels will trap that heat inside the room.

  10. #10
    last farang standing
    Hugh Cow's Avatar
    Join Date
    May 2015
    Last Online
    15-03-2024 @ 01:44 PM
    Location
    Qld/Bangkok
    Posts
    4,110
    The best remedy for walls is to extend a verandah to keep the western wall in shade. or plant trees that will keep the wall in shade. You could also consider a retractable awning which can be pulled out to shade the wall and especially any windows during the afternoon and retract it under the eaves at night.Maybe wooden lovers over the windows.
    Aircond tip: Dont wait untill the house gets too hot before turning on the A/C It can be false economy as the load from the hot walls will need to be absorbed by the A/C unit increasing the load and power usage.
    Alternative:
    If you have access to cheaper off peak power you can install a mini chilled water system by making an off peak ice bank. This way you use cheaper off peak power and store an ice bank overnight and use the cooling energy stored during the day time. I will give more detail if anyone is interested.
    If you are a handyman much of it can be DIY.

  11. #11
    I am in Jail
    stroller's Avatar
    Join Date
    Mar 2006
    Last Online
    12-03-2019 @ 09:53 AM
    Location
    out of range
    Posts
    23,025
    Quote Originally Posted by Hugh Cow View Post
    mini chilled water system by making an off peak ice bank
    Tried that years ago with bought in blocks of ice (can't have moving air from a ventilator or aircon for my work), didn't do much but caused a lot of condensation along the tubes. Gave up on it - I am not an engineer.

  12. #12
    last farang standing
    Hugh Cow's Avatar
    Join Date
    May 2015
    Last Online
    15-03-2024 @ 01:44 PM
    Location
    Qld/Bangkok
    Posts
    4,110
    Unfortunately you do need moving air to prevent stratification. In commercial applications sometimes it is better to use a false floor for supply air and return the air through the ceiling. This tends to mimick a more natural air draft by allowing cooler air to warm and naturally rise to the return air plenum.
    If you submit a plan of your system I maybe able to show you how to improve it. My system uses a refrigeration system in an insulated drum to form the ice and water is chilled by pump recirculation to and from the drum to a fan forced chilled water coil. Running expenses in the day are only from the fan and water circulation pump. Even that can be negated with solar panels.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •