[Greenbuilding] Night Time Insulation+Spreadsheet Model

[Eli Talking]

I was glad to see this list returning to my Greenbuilding folder.

I had begun a discussion prior to list maintenance break about the energy 
savings of night time insulation.  To better understand this issue, I 
developed a spreadsheet using separate lines for each of 24 hours and 
entered the predicted hourly temperature from the weather channel web site 
for my town.  This is a prediction and not a record.  However, I think it is 
in the ballpark.  I also enetered the sunrise and sunset so I can separate 
night from day.  From this information I can determine how may degree hours 
are it the daylight and in the darkness.  Therefore, I was able to assess 
heat load for a given area with a given R value.  Using the nightime degree 
hours I could see what the savings in energy was in btu's for covering 
windows at night.  What I discovered was the night time heat loads generally 
was between 61%-65% of the degree hours in the day.  This was the range on 
both  colder and warmer 24 hour calander days.  However, on one day, which 
was an exception, I got 55%.  Now, I have some bases for a rule of thumb 
being that 62%+- of degree day is for heating the night.  However, this 
likely will change as the days get longer.  So, I am going to continue this 
excersize.

I found a source of regional data from a regional airport that has hourly 
temperture as well as other weather data such as relative humidity that 
dates back to 1965.  From this I could determine an average hourly 
temperature for each hour of the year.  However, I could also get barried in 
numbers. To do this I need to learn more about importing data to 
spreadsheets.  I may also need to upgrade to Excel over the MS Works program 
I now use.  I am undecided about going that far.  However, I believe this 
has been a good excersize to get a better feel for temperature profile over 
the 24 hour period.

By the way, the savings was not that great.  However, I am pasting in the 
results from yesterday that was quite cold for 50sf of R6 night time window 
insulation over R2 window with current energy prices for propane and fuel 
oil.

Eli Fishpaw
Architect in Lexington, VA

Avg24 25
DD24 40
DH24 960
0
Day Hours 10
Night Hours 14
DH day 377
DH night 583
Night part of total 0.61
Area 120 sf
Window R 2 hr sf F/btu
Night 34,974 btu/night
 91,600 btu/gal propane
 0.3818 gal propane

Night 34,974 btu/night
 140,000 btu/gal #2 fuel oil
 0.250 gal #2 fuel oil

Cover R 6
Total R 8
 8,743 btu/night
 91,600 btu/gal propane
 0.0955 Gallons Propane Saved by Solar
nightly savings w/cover 0.286355076 gallons Propane
Propane Price $2.55 /gal
Savings/night $0.73

 34,974 btu/night
 140,000 btu/gal fuel oil
nightly savings w/cover 0.2498 gallons Propane
Propane Price $3.15 /gal
Savings/night $0.79