Economics of Active Solar Space Heating

Janette Dudley
1 Posts
Oct 27, 2005 10:02 am
Economics of Active Solar Space Heating

Most of the solar air heating companies claim paybacks of 3-6 years and reduction in heating bills of $300 - $700 per year, but so far I haven't seen the calculations that prove this.  I've seen a map of typical energy savings for transpired solar collectors which shows that in my area the typical savings would be 120 -180 kBtu/m2/yr.  I can't reconcile this with the promised savings of $300/year at current delivered gas prices of $1.63/ therm.  Can anyone help verify that these claims are true?
 
 
Ken Hall
351 Posts
Oct 29, 2005 02:19 am
calculations

Can anyone verify that these claims are true ?

No, but we might determine if they are reasonable.  All we can do is a reverse calculation.

At your rate of $1.63/therm, a $300/yr savings would be 184.0491 therms/yr

The statement is �Typical savings 120-180kBtu/m2/yr�
The traditional BTU is 1 times 10 to the �5 therms. So we can translate the statement to 1.2 -1.8 therms/m2/yr.

The 184.0491 therms per year divided by the 1.2 therms/m2/yr is 153.3742 m2.
The 184.0491 therms per year divided by the 1.8 therms/m2/yr is 102.2495 m2.

153.3742 m2 times 10.7639  (conv. Rate m2 to ft2) is 1650.905 ft2.
102.2495 m2 times 10.7639 is 1100.603 ft2.

So at the 1.2 therms savings rate, your heated space would have to be at least 1650 square feet to save $300 per yr.
At the greater savings rate of 1.8 therms , your heated space would have be 1100 square ft or larger to save the $300.

So, based on the numbers you provided, the $300 end seems reasonable.  


 
 

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