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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Heating and cooling: Moving hot air

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    • CommentAuthorrevor
    • CommentTimeNov 18th 2020
     
    Have built an Atrium on the gable end of the house. Whilst doing the build made a 100 mm hole to allow for ducting the hot air that collect in the top into the house. I installed the duct during the build to take the air to the bottom of the staircase so it can be distributed via the MVHR to the rest of the house. . Have no experience of moving air in this situation so am having difficulty specifying the fan size. I need to drive the air down against its natural inclination to rise It think it can reach up to 50 /60 deg C at the top and currently let the warm air in via a door into the bedroom but don't capture what is at the top, and if it get too hot ventilate via the Velux on the N side of the roof. Anyone any thoughts? Have tried appending photo to illustrate the structure which is approx. 6m wide 4.5m deep and 7 m high to the ridge but get error message "cant' find discussion".
    • CommentAuthortony
    • CommentTimeNov 18th 2020
     
    Feels hot yes but has very little heat in it, 100mm fan should do it, more expensive one, ducts should be smooth inside
    • CommentAuthorrevor
    • CommentTimeNov 18th 2020
     
    Ta duct is smooth 125 mm most of way then rectangular drop from loft to GF. There many fans available I guess a centrifugal in line type would be best I appreciate not much heat in a particular volume but there is a lot of it. Probably a multispeed fan would be good choice so can optimise. Just wondered if anyone done a similar job?
    • CommentAuthorGreenPaddy
    • CommentTimeNov 18th 2020
     
    I've used the monsoon UMD's a few times. 2 speed settings. With some duct back pressure, maybe looking at 125m3/h at low speed, and 175m3/h high speed for a 100mm unit. I suppose you won't want too many air changes per hour, to avoid drafts, or constant on/off.

    On one occassion I fitted a key fob wireless controller in line (a few pounds off ebay), so the client could on/off the fan as it suited, to move warm air along their bungalow corridor to the bedrooms at the far end. They reckoned it made a big difference. You may well go for a temp stat located at fan level, set at say 25oC to switch?
    • CommentAuthorLF
    • CommentTimeNov 18th 2020
     
    You will need a few Watts in for the fan to move it.
    It may be hot and wet - surely going into the extract would be better than distributing it ? Or am I reading incorrectly.
    You recover the heat with the fresh air coming in then?
    • CommentAuthortychwarel
    • CommentTimeNov 18th 2020
     
    I have a cathedral ceiling in my lounge, and the room has a wood burner so I also installed a duct from the highest point of that roof and as suggested above it feeds into the extract part of the MHVR. The heat is thereby recovered and any fumes from the stove are removed from the building. Tests have shown that the highest point of that ceiling can get to nearly 40C when the stove is running so capturing the heat is worthwhile.
    • CommentAuthorrevor
    • CommentTimeNov 22nd 2020
     
    Thank you some really good ideas there. The air is unlikely to be wet although may need to keep an eye on it when it cools down at its destination Green paddy given me an idea with the remote control as the intention was to have the stat next to the fan but how to control on off when needed?. Also could do with not having to get ladders out when needed to adjust the thermostat and then thought I could link it in to the heatmiser neo system I have for the UFH could then control it from the pc or phone and have the unit itself in the loft with a remote sensor like I have in the bathroom. The house is sealed so the air will be replaced with what is in the house providing door between the kitchen and the atrium is open. The outlet air will hopefully circulate into the MVHR I have an extract vent close by. Not heard of monsoon fans will take a look was thinking of xpelair or ventaxia found them in the past to be very reliable.

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