[TowerTalk] where the condensation comes from

[Roger (K8RI) on TT]

I was thinking of in the winter the wind across the conduit would suck 
relatively warm air out of the basement.
As for the tower end, I originally had a single  open stub to bring the 
coax out of the NEMA box.  Snow would drift through the tower and under 
the stub, pushing cold air into the conduit.  That would not have caused 
condensation as the underground conduit was warmer than the air going 
in, but it would make the basement a bit chilly.

Depending on the house construction a wind could create a low pressure 
in the house drawing the humid air in. A peaked roof, like an airplane 
wing will create a low pressure under it.  OTOH a large, flat wall with 
windows on the windward side could create pressure.  Houses should be 
checked for leaks.  Too many and they are inefficient to heat and cool.  
Fire places are one of the greatest heat losses in a home.  We have 2. 
One in the living room and one in the family room. As we discovered I am 
allergic to wood smoke, we capped off the chimneys to both. There was a 
substantial reduction in heating costs. It's warm in front of one, but a 
lot of heat from the rest of the house goes up that chimney.  Also, the 
fire needs air and that has to come in from the outside.  OTOH you can 
make a house too tight. They and you need some fresh air ingress for health.

73

Roger  (K8RI)

On 1/31/2016 Sunday 8:43 AM, StellarCAT wrote:
> Thanks Jim, But I’m not sure many would use 2” pipe... 3” minimum – and I’m thinking of 4” so the cross sectional area would reduce the flow/area correct? Also if at the ends where it is open that opening is pointing down and the open face is horizontal to the ground. Any air across it as far as pressure is concerned will be greatly reduced – if anything it would be a venturi effect sucking instead of blowing I’d think.  Gary    I did a bit of calculating about what might push damp air into a conduit.
>
> I assumed that I had 30 meters (100ft) of a 2" diameter tube where there was a pressure difference corresponding to a 10 mi/hr wind (it's about 1/4 lb/sq ft)
> You'd get a flow of about 2 liters/second (which is surprisingly high)
>
> In an hour, then you'd have 7200 liters. If you had 100% humidity air at 68F (20C) going in, and the soil was at 50F (10C), you'd be condensing out about 50 grams/hour.
> In reality, you probably don't have 100% humidity at 68F. But you might have 50% humidity at 85F, and that's about the same amount of water.
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73

Roger (K8RI)


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