Reversible DC motor for attic fan ?

[Externet]

Hi. Winter approaching, am thinking if there is in the market any attic fan, reversible, temperature controlled.

But not the typical attic venting fan. One that flows air between the attic and the house interior. One that when the attic is warmer than the house, limited to 20C, will transfer warm attic air inside the house trough ceiling. If house interior is over 20C, reverse the flow.
Is there such animal before reinventing the wheel with thermistors and comparators and H bridge ?

Even on winter days, at a certain times and sun exposure, attic air can be useable for warming. Just as a solar heat collector over the roof. Well, almost.

Gable vents would need solenoid actuating blocking louvers, I think.
Automotive and RV fans are applicable, Klixon switches, hacking thermostats...
Suggestions ?

 

[MaxHeadRoom78]

What diameter are you anticipating? You would need to select a room or area that would be the recipient of the fan.
Regardless you would not succeed in blocking the attic completely as you would develop negative pressure.
So it could not conceivably be that high a volume.
A small bathroom fan may do it with the motor replaced with a DC version if bi directional is needed.
No H bridge needed if simple relay reversal is done.
Max.

 

[Externet]

Thanks. Not a huge volume; somewhere around 15 cm/6". Attic would not be fully blocked; gable louvers are leaky.

 

[ChrisP58]

Just make sure you don't expect to reverse the airflow by running a squirrel cage fan backwards

 

[alec_t]

If your attic is anything like mine, include an air filter to prevent dust being blown into the room .

 

[cowboybob]

Given that you want to capture the heat generated in the attic, and not suck in cooler air into the attic (thereby diluting the captured heat), a Passive Heat Exchanger arrangement might be a workable concept.

Some information to consider: https://www.heatpipe.com/HomePage2/HPTEngineerManual/Tab 5 - HRM-V/HRM-V Engineering Manual 2014.pdf

 

[alec_t]

I haven't done the maths, but if you extract heat from the attic then the attic will cool. That will increase the temperature differential between attic and room, and hence increase the rate of heat loss from the room .

 

[Externet]

I will start the project only non-reversible for heating evaluation.
Thanks, alec_t.
Still prefer to increase the loss by differential than not-using the heat that can be obtained from attic at certain times/season/conditions.

Thanks, cowboybob.
Such linked complexity interchanger and suspected way-too-high cost for the application can be instead, just a duct along the highest point of an attic ending and starting in house rooms, with an in-line duct fan.

 

[MaxHeadRoom78]

If wanting to reverse a normally uni-directional fan ensure it has flat style blades, the uni-direction type often have curved blades.
Max.