[Strawbale] [SB-r-us] Radiant energy and Law of Inverse Squares (was Re: Forced air)

[Mark BP / Low Energy Design Ltd]

Robert Tom wrote:

>On Tue, 08 Jan 2008 16:48:36 -0500, Lance Collins  
><collinsl at bigpond.net.au> wrote:
>
>Stronzo di Nord writ:
>
>  
>
>>>The thing about radiant heating energy is that it obeys the law of  
>>>inverse squares --
>>>      
>>>
>>You might want to check this out.   I have an idea that the inverse  
>>square law applies to a point source and not to a plane source such as a  
>>wall.
>>    
>>
>[snip]
>  
>
>>At the moment I'm more focused on cooling with many days over 40 degrees  
>>and several nights with the minimums above 25.  I need a ground source  
>>cool pump.
>>
>>Cheers
>>
>>Lance
>>Melbourne
>>Australia
>>    
>>
>
>Geeze, how do I get sucked into these things ?
>(Rhetorical question to which the answer is: "By opening your %^@*@% yap,  
>stoopit".
>
>Lance;
>
>I thought my days of having to do school homework assignments ended along  
>with my days of pimples, fast cars and even faster women. (ie. I'm not  
>looking it up. You look it up.)
>Okay, okay. I still get a pimple now and then, but I'm still not looking  
>it up.
>  
>
I take it the fast women drove off in the fast cars...


> From distant memory of long-ago studies for an undergrad degree in a  
>discipline (physics) that I never actually practised professionally in the  
>Real World ...  radiant energy consists of a discreet spectrum of  
>wavelengths (infrared and near-infrared ?) and that energy obeys the Law  
>of Inverse Squares as it relates to IIRC, the Second Law of  
>Thermodynamics. ( And IIRC, the law of inverse squares applies to other  
>phenomena as well ... sound and optics perhaps ? And maybe Alan's liquids  
>too ?) I'm sure that any practising physicists on these Lists will make  
>the necessary corrections to the blatherings of my foggy memory.
>
>  
>
The inverse square law applies to a point source.  A wall is a 
2-dimensional array of point sources: add them all together (i.e. 
integrate with respect to both x and z), and you lose the dependence on 
distance from the wall.  (At least you would for an infinite wall.  Real 
walls are more complicated.)



>But I don't see why it would matter whether that radiant energy emanates  
> from a point source or any other-shaped source. ie  The type of energy is  
>the same. The means of measurment of  distance does not change. What else  
>is there to consider ?
>
>And about cooling and that ground-sourced heat pump ... maybe it'd be  
>simpler and more reliable to just dig a deep hole in the ground, put a  
>thick, well-insulated lid on it, hop in and call it "home" ?
>  
>
I can't help thinking that certain Australian termite species have 
sussed this one out... but I don't know enough to make intelligent 
comment on the subject.


>(Most of the ground-sourced heat pumps that I've encountered in my  
>neighbourhood (or more correctly, the owners of those GSHP systems)  
>reported failures of the heat exchangers, usually within 3 years, at $2000  
>- $10,000 a pop to replace the HX, leading one of the afore-mentioned  
>owners to rip out the GSHP in disgust after the 3rd failure, offering it  
>for free to anyone who wanted it.)
>
>  
>