Across The WALL a Universal Efficiency Measure - BTU/DD/SF

Uni R_3

Most of us would agree that DDs are a pretty good "rough" measure of how the temperatures affect fuel consumption. Likewise every fuel has a very specific gross number of BTUs per unit and a measure of fuel that can be multiplied to get the gross BTUs (net out the non-heating uses such as indirect DHW, gas range, dryer, bbq, water heater, etc and multiply consumption by the BTU factor of the fuel). Then divide it by the number of days used for the measured consumption. Get an average of DDs over the consumption period (it could be daily for gas if you're that bent (or even using electric), and then between fill-ups when calculating the period for oil. Then divide it by the square feet to get an equivalent measure between different methods of construction and house sizes.

This gives the house an overall efficiency score. The lower the score, the fewer the heating BTUs each square feet of living area used by averaging over the total of the DDs.

It will be single digit score for better homes, and 5 will probably be an average efficiency for older construction methods. I'm not sure where newer houses should all be.

I'd like to know this number for some European homes for comparison. Constantin? Would you, could you get some numbers from a few people in Europe with different efficiency potentials?

I'm not sure what the "ultra" efficiency target will be. Can anyone guess? And oh yeah... what's your BTU/DD/SF at your place?

Mine? 4.5 -- It's easy to work out.

Second Example -- An office.

For example:

Since commission on the ides of December, I've consumed 244 cubic meters in natural gas solely for heating, and on a daily basis added up a total of 795 Degree Days. I have 2400 square feet area of normal code height living space that I keep within my envelope. Each cubic meter equates to 35,300 BTUs (139,000 btus per U.S. gallon of #2, 3,413 per KWH if electric, 96,000 per gallon for LPG, and 100,000 per therm for all the U.S. natural gas consumers). It sure makes the math easier for this group.

My example is what would the same number in gallons (244) equate to using an 18,000 square foot office building also kept at 68-70. Through summer usage they estimate the indirect DHW burns 44 gallons. 244-44=200 gallons used for heat.

244 m3 x 35300 BTU/m3 = 8613200 BTUs

200 gallons x 139,000 BTU/gallon = 27800000 BTUs


Then divide by the total of the daily degree days to match the period of consumption. I measure daily, but I could just do periods and the look up the DDs in between. For oil, it's simple - it is the number of degree days since your last fill. This is like a K factor but enables you to compare between gas, oil, electric, big house and small.

8613200 / 795 = 10834.21 BTU/DD (like a K factor for oil people)

27800000 / 795DD = 34968.55 BTU/DD

Divide again by the full area of heated full height space within the envelope (A-frames could measure area at a 4' wall height if they wanted to be accurate).

10834.21 / 2400sf = 4.5

34968.55 / 18000sf = 1.9

I'm not sure if mine is good or bad, but that commercial space would be pretty good. Mine is for a 1975 brick backsplit, tight construction but below average wall insulation, a very large insulated crawlspace area not counted as space, and it is using a gas modcon. I'm thinking that 1.9 on the commercial space would be very tough to beat.

Let's hear the good, the bad, the ugly and the average?

Maine Doug_52

I hear

someone making a nice spreadsheet to enable one to plug in the fuel type etc. and voila, a number.

Brad White

I will have to dig out mine and post it...

I like the idea- the "SF" part is of course arbitrary by itself (heat loss per SF can vary enourmously) but as a constant, it does give a more accurate number when in the company of the other variables.

Let me dig up my DD formula spreadsheet and add in a SF factor... Opportunity to clean it up at least.

Steamhead (in transit)

I see

someone taking that idea further and writing an easy-to-use stand-alone program that will run on the sometimes-ancient hardware we heating guys have. Slant/Fin did this with their Heat Loss Explorer.....

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Uni R_3

Here Doug...

Fill in the yellow boxes. Fuel type, whether or not you're reading a continuous meter or using discrete billing quantities and the square footage of heated space.

Then add dates, DDs and fuel quantities. If the fuel bill isn't purely for heating then estimate that portion (example 1.2 gallons per day for domestic water).

Maine Doug_52

Thanks

I will send a note to my oil supplier to get the numbers for last year. Has anyone tried cubic feet instead of square feet to allow for high ceilings?

ttekushan_3

How ancient do you mean,

Something like this:

http://www.fourmilab.ch/babbage/

Its not your imagination. They said "brass, steam powered" computer. The Babbage Difference Engine and Analytic Engine were precursers to everything digital in the present age. He had it all figured out. He wanted them to be steam powered.

Here's one that was completed in 1991 based on his drawings. It works perfectly:

Doug_7

Universal Efficiency Measure - BTU/HDD/SF

See attached article from Home Energy on Benchmarking Energy Use.

This works well and provides a good way to compare energy efficiency.

Doug

Constantin

Hello...

... I'll see if I can dig up any info "over there", but it'll be a bit of a challenge. For one, storage facilities for oil are usually measured in seasons (big tanks), which is what most of my friends use. Then there is the question of finding degree-day data to hang a hat on.

I am in the process of collecting data to see what the heat loss of the house is vs. the water heater consumption. I have some pretty good external temp vs. burner run time data, but I still have to ferret out the contribution of the solar.

Uni R_2

Big Tanks

I can totally empathize - I think the last time my twin tanks were actually topped up was Jan '03. I had been working them down since then (either for replacement to appease my insurance company or for removal for NG) and as such I have to go back to then to do any efficiency comparisons. The only other big structural change to occur in there was windows. They weren't that much better I found out later, although they do look a lot better - next time I want to take Geoff McDonell "window shopping" with me.