Replies

1. 
   walta100 | Apr 22, 2021 05:31pm | #1

   It is a very simple question with a very complex answer.

   There are so many variable what does your electric cost, how do you predict it will increase in the next 20 years, what would the money earn if you did not spend it on the more expensive system, your local weather, the R value in your attic , the R value in your wall ,How many square feet of wall face each direction, how large are your windows what direction do they face, how large are your doors what direction do they face, how much air leaks into your house and dozen more.

   The only real answer to build a computer model of you home enter all the variable and crunch the numbers for both systems.

   I used a free computer program called BEopt. I am guessing 20 -40 hours to do the training and build your model. It will draw a graph and showing what system used least and most energy and the one that cost the least to own and operate for 20 years.

   Generally if you move every 4 or 5 years like a lot of people do buy the system with the lowest upfront cost.

   https://www.nrel.gov/buildings/beopt.html

   Training videos
   https://www.youtube.com/playlist?list=PLHC0xDtkdjgec8QhVt7exJY3tpSLEFk-d

   Walta

1. 
   beedigs | Apr 23, 2021 08:30am | #3

   i started playing around the beopt software this week while watching the tutorial but i must have done something wrong as i did not get any graphs to show when i “run” the numbers..thanks for ur feedback

2. 
   walta100 | Apr 22, 2021 05:38pm | #2

   Note any system that get the equipment and ducts out of the attic will cost 25% less to operate.

   Walta

3. 
   walta100 | Apr 23, 2021 03:09pm | #4

   Wild guess is you selected 3 or 4 types of windows or some other item and hit the run button.

   Now the program is busy running a model for each variable in 15 minute increments for 365 day using your weather data even the fastest computer will take hours to run several variables doing billions of calculation.

   You can change to once an hour it will run 4X faster but you lose some accuracy.

   I would hit run go to bed and look at the data in the morning. I would only a few variables at a time.

   Walta

1. 
   beedigs | Apr 23, 2021 07:24pm | #6

   thanks walta! great tips!

4. 
   creativedestruction | Apr 23, 2021 03:52pm | #5

   Here's the wildcard I love[loathe] to throw into ROI calcs: what is the probable rate of failure for each unit? What is the cost of replacement when either unit ultimately fails measured in dollars, stress & my time? Do the brands have good service and warranty reputation? These factors often matter orders of magnitude more than specs and simple payback. They almost can't be quantified.

   By all means do the ROI calc, but then do the 'gut check'.

1. 
   beedigs | Apr 23, 2021 07:25pm | #7

   thanks for the tips!