Gas meter clocking for btu loss. Trying to calculate.


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Old 01-03-13, 07:57 AM
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Gas meter clocking for btu loss. Trying to calculate.

I clocked my meter last night. It was 20f. Just trying ti figure this out, and since I am not the best mathologist I need help.

I found this.

For heating purposes, add up all the BTUs of the fuel you used and multiply by the AFUE rating of your heating appliance. A gallon of oil has 139,000 BTUs/gallon, a therm of natural gas has 100,000 BTUs/therm, and gallon of propane contains 91,000BTUs/gallon. Some gas utilities measure their consumption in ccf, which is 100 cubic feet, which is 102,000 BTUs of energy (these caloric gas value are averages at sea level, call your utility/gas provider if you live at higher elevations).

Next, divide the total number of BTUs by the number of HDD. The result is a measure of how many BTUs your home lost per Heating-Degree-Day. Now divide that result by 24 to obtain the number of BTUs your home loses per heating-degree-hour. Lastly, multiply the result by the difference between 65F and the coldest day of the year. For example, if the coldest day you expect to experience is -10F, then the difference you multiply your heating-degree-hours by is 75F.

Voil, you now have a reference point regarding your maximum heat loss. Ideally, spot check it by observing your heating appliance on a cold day and extrapolating the results. For the northern US, the heat loss per square foot of habitable space typically ranges from 15-35 BTUs per degree day. Depending on construction and location details, the number may be higher or lower, however.




Here is what I got.

5pm - 8 am used 14ccf
14ccf x btu content @ 1.069 = 15.26 therms
15.26 therms x 100,000 = 1,526,000 btu used
HDD = 36 --- 1,526,000/36 = 42,388 btu per day.
42,388 btu day /24 hours = 1,766.20 btu hr.

OK the last part i am not sure.

Diif from 65f - 10 f = 55f ?
55f x 1766.20 = 97,141 ???


What is this telling me? Its was 20 F or so here last night. 10f off my design temp.

My heatloss calc through slant fin calculates to be 24,041 btu...

This is 1050 sq ft shed.... Uh I mean home......LOL


Probably dont matter but I am running low boiler temps this year. 150f aquastst setting.
Boiler 85k
20f diff.
10f delta more or less once the slugs settle.
Hottest return temp 137f.
Takes 5 min to go from 130f - 150f.
Have not timed circ run time after boiler kicks off.
87 ft bb in home.


Any input will help......
 
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Old 01-03-13, 08:52 AM
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5 PM in the evening to 8 AM the next day?

Where/how did you get the 36 degree days from? Don't you need a full 24 hours to develop a degree day?

I don't understand that description either... I need to think about it some more.

I would clock several days from midnight to midnight and compare to DD data at Heating & Cooling Degree Days - Free Worldwide Data Calculation
 
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Old 01-03-13, 08:58 AM
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Where/how did you get the 36 degree days from?





Wunderground almanac.


History | Weather Underground
 
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Old 01-03-13, 09:11 AM
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Mike, something is wrong...

You could not possibly have burned 14 CCF in 15 hours.

Four maybe... but fourTEEN ?

Sure you read that meter right? Remeber that some dials are bass ackwards.
 
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Old 01-03-13, 09:14 AM
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0255 - 0269.... If I read it wrong the best it would be is 0259?
 
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Old 01-03-13, 09:15 AM
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I think that 36 DD is for the full day, not only for the 15 hr period you clocked.

Are you using KBLM as the source?

Try clocking from midnight to midnight and see what ya get... if that's too late for you to be up at night, clock before bed and go for a number of days to get somewhat of an 'average'.

I'm not clear on the reason for that last step either... doesn't make any sense to me.
 
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Old 01-03-13, 09:18 AM
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But doesnt this seem right on my original calc? 42,388 btu per day.

Its just that its 20k or so off my heat loss... Thats why Im asking....
 
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Old 01-03-13, 09:18 AM
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0255 - 0269.... If I read it wrong the best it would be is 0259?
Yeah, four is reasonable I suppose... that seems about 25-25K BTUH ... but fourteen, no way... even before doing all the numbers, would you burners even be able to burn that much? It would have to be burning pretty much continuous to even get close to that usage!
 
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Old 01-03-13, 09:22 AM
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Are you using KBLM as the source?
Yes


I think that 36 DD is for the full day, not only for the 15 hr period you clocked.


I am sure there is a way to turn my 15 hr test into the proper math formula. Like I said I am not a matholigist.

I wanted last nights 15 hour time because its a true calc of the coldest temps. It was pretty cold last night, 20f, and this morning similar. Its only about 10 f off design.


If I clocked during the day when its 32 f that aint telling me S%$T...right?

 
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Old 01-03-13, 09:27 AM
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Yeah, four is reasonable I suppose... that seems about 25-25K BTUH ..
No I calculate 11,877 btu. That cant be right..... I think it is 14 ccf. Ugggggggggg...!!!!!!

Ok let me go look at the meter...it cant be too far off from this morning.


 
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Old 01-03-13, 09:55 AM
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It is 0259...... Geez possible I read the 0255 at the start wrong...

That stupid rule if a dial is on a # and the dial to the right is not on 0 or past, record the preceeding #.... Duh...
 
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Old 01-03-13, 10:45 AM
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OK, so if it is 4 CCF then for 15 hours,

that's 102,000 X 4 = 408,000 BTU / 15 = 27200 BTUH

but NOT accounting for AFUE...

So the ACTUAL heat loss is somewhat lower that this 15 hour AVERAGE.
 
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Old 01-03-13, 10:59 AM
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What the heck do you use the degree days for....???

Account for AFUE?

It says this but I dont get it.

For heating purposes, add up all the BTUs of the fuel you used and multiply by the AFUE rating of your heating appliance.

 
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Old 01-03-13, 11:40 AM
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What the heck do you use the degree days for....???
DDs would allow you to compare the fuel useage to the 'average' OD temperature.

A degree day is defined as:

'base temp' - '(high + low) / 2)

base temp is usually defined as 65 but due to increased 'better' building practices, a number of agencies are promoting lowering this to 60.

The base temp is essentially the temp that below which you will need to add heat to the building.

So, you take the HIGH for the day, the LOW for the day, average it (divide by two) and subtract it from 65.

High of 50 plus low of 30 = 80 divided by 2 = 40 subtracted from 65 = 25 degree days.

So, if you clocked your meter one day when it was less degree days, you would get less BTUH, next day was colder... you would get more BTU...

By 'referencing' this to degree days you end up with a number that reflects BTU / Degree Day.

You end up with somewhat of a 'constant' that you can reference to.

Here's an example (from my home):

Old boiler... tracked Degree Days per gallon (called K factor) for several years. Started out around a K factor of 7-ish... pretty poor... insulated here and there, sealed up some air leaks, etc... and got that K factor up to around 8.5 or so... better...

Installed new boiler this year... K factor is now approaching 10...

So it gives you a way of taking the outdoor temp out of the equation, giving you a number that you can use to determine effectiveness of improvements to the building in saving fuel.

For straight HEAT LOSS though, you don't really need to use the DDs ...

AFUE is different... it's "Annual Fuel Utilization Efficiency" and is a measure of how SEASONALLY efficient your heating system is.

So, if your AFUE is say 85% you want to take the 15% of fuel that is 'wasted' and not being used to heat the home out of the equation. Doing this would give you close to the true heat loss of the home, rather than the heat loss plus the 'up the chimney' losses.
 
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Old 01-03-13, 12:32 PM
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So, if your AFUE is say 85% you want to take the 15% of fuel that is 'wasted' and not being used to heat the home out of the equation

So for accuracy is this correct?
5pm - 8 am used 4ccf
4ccf x btu content NJNG @ 1.069 = 4.276 therms
4.276 therms x 100,000 = 427,600 btu used

427,600 - 20% ( if 80% AFUE ) = 342,080 btu / 15 = 22,805 btu/Hr

Now what do I do with the original calc with DD to compare that other formula? The #'s dont make sense there.


342080/36 DD = 9,502 Whats that?

9,502 / 24 hours = 395.9 Whats that?



Calculating your Home's Heat Gain and Loss








 
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Old 01-03-13, 01:00 PM
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So for accuracy is this correct?
5pm - 8 am used 4ccf
4ccf x btu content NJNG @ 1.069 = 4.276 therms
4.276 therms x 100,000 = 427,600 btu used

427,600 - 20% ( if 80% AFUE ) = 342,080 btu / 15 = 22,805 btu/Hr
Yes, that looks right... and remember, it is the 15 hour AVERAGE of heat loss in that time period.

342080/36 DD = 9,502 Whats that?
That would be your BTU per DD 'reference' number, but it is not valid because you're comparing 15 hours of BTUs to 24 hours of DD.

IF you knew what the HIGH and LOW temps were for the period from 5 PM to 8 AM you could cipher a number called "Degree 15 hours" and the result would be sorta valid.

9,502 / 24 hours = 395.9 Whats that?
This would be BTU per DEGREE HOUR and this is where VonWentzel is losing me... but I can't read that article here at the day job... blocked... I'll look at it later.

I can't understand yet what reason he is breaking down to Degree HOUR...

But still, you aren't comparing apples to apples because you are using two different time periods.

You have 15 hours of clocked gas usage, and a Degree DAY (24 hours) worth of temperature data.

If you have a thermometer that will record HIGH / LOW, when you read the gas meter in the evening, RESET the high / low on the thermometer. When you read the meter in the AM, record the high and low temps.

Average the high/low and subtract from 65 to get your "Degree Xtimeperiod" number and use that in the calcs... this way the usage data will match the time period of the temp data.
 
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Old 01-03-13, 01:15 PM
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342080/36 DD = 9,502 Whats that?
BTU per DEGREE DAY

You can use this number to 'extrapolate' heat loss to different temperatures. (I'm going to use this number for the following examples even though it is NOT an accurate number, just for discussion only)

EXAMPLE:

You've determined that your home will require 9500 BTUH per ONE DD.

So, on a day with an average temperature of 64 your heat loss would be 9500 BTUH.

Let's say that we have a day when it's ZERO out, all day long, for 24 hours...

65 base - ((HIGH + LOW) / 2 )

65 - (0 + 0 / 2) = 65 Degree days

In this example, one could expect that the heat loss at 0 would be:

65 DD X 9500 = 617500 BTU / 24 hrs = 25,730 BTUH @ 0F OD temp
 
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Old 01-03-13, 01:55 PM
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IF you knew what the HIGH and LOW temps were for the period from 5 PM to 8 AM you could cipher a number called "Degree 15 hours" and the result would be sorta valid.


It was a hi/31-lo/21

31+21=52/2=26-65=39

39x9502=370578/24=15440 btu hr @ 26f OD temp?

I hates marithmatic!!!!
 
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Old 01-03-13, 02:27 PM
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And lets use my design temp of 10f in a 24 hour period.

65-10=55x9502=522610/24 21,775

My heat loss calc is 24,041 I am 2266 off.......


Here is a twister.. Since I had the t stat only on 68 last night I figure this...

150f boiler water with 60 ft bb downstairs = 375 btu ft x 60 ft = 22,500 hence why I am using cooler boiler water. although the boiler water is not a constant 150f.

Although do I take my total BB ft? Up stairs rarly kicks on.

87ft x 375 f = 32,625 btu

Whats the correlation? I dont know... Just doing math and felt the need.

http://comfort-calc.net/pictures/Old...ard_BTU_Ft.JPG
 
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Old 01-03-13, 02:47 PM
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Well, no....

Remember that 9502 is not an accurate number, that is based on the wrong number! you gotta back up some more.

But if those are truly the high and low from the period in question, then 39 is a good number, so we'll use that.

342080 BTU/39 (D 15 hours) = 8771 BTU per (D 15 hours)

Then, you would convert this to DEGREE HOURS by dividing

8771 / 15 = 585 BTU per DEGREE HOUR

So, at ZERO degrees (which is 65 DD) your heat loss would (might) be

65 X 585 = 38025 BTU

I looked at the guys webpage and THINK this is what he is driving at, but confess that I'm not 100% certain.

So let's do 10 HIGH / LOW which is 55 DD

55 X 585 = 32175

My heatloss calc through slant fin calculates to be 24,041 btu.
What DESIGN TEMP did you use? [edit: never mind, I see you used 10]

If this 585 number is correct, that works out to be a design temp of 24 which I don't think you would have done that?
 

Last edited by NJT; 01-03-13 at 03:21 PM.
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Old 01-03-13, 03:17 PM
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One other thing to mention...

Even a HALF CCF error in the calcs makes a pretty big diff...

Let's say your usage was actually 3.5 CCF in that time period.


At 0 this gives 33258 BTUH

At 10 this gives 28105 BTUH


so read meter as closely as possible, and record temperatures locally and run the numbers again.
 
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Old 01-03-13, 03:29 PM
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This is 1050 sq ft shed.
Is that both floors?

28105 / 1050 = 27 BTU / SQ FT

Which is more or less right in line...

Last night was also pretty calm, wasn't it? Wind needs to be accounted for...
 
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Old 01-03-13, 04:13 PM
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If this 585 number is correct, that works out to be a design temp of 24 which I don't think you would have done that?


Right... The temps are right on the calculator. 10f out 70 f indoor.

so read meter as closely as possible, and record temperatures locally and run the numbers again.


So it does not matter if I do this on a colder or coldest day ? I will do again from 12am to 12 am record the meter and record the temps. 24 hour clocking is best I would assume?

This is 1050 sq ft shed.
Is that both floors?


You try'in to be funny?????


I am just being anal and dont want to put too small a boiler in. Thats why I want to fine tune this and determine actuals.

The two boilers in question are a DOE 29k 84% afue or a DOE 31k 82.3% afue

I brought this up on another post about the boilers but the consensus was to clock the meter to be sure.

Is it wise to state that I can lower my fuel bill by replacing old betsy at 85k input, with a 34 k input boiler?




 
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Old 01-03-13, 05:50 PM
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So it does not matter if I do this on a colder or coldest day ? I will do again from 12am to 12 am record the meter and record the temps. 24 hour clocking is best I would assume?
In theory, heat loss is mostly linear... not perfectly linear but close enuf for gummint work.

So the answer is that it doesn't really matter at what temp you do the test.

Since the DD data on WU appears to be based on midnight to midnight, it would be best if you can clock the meter during that same time period. Of course during the day other gas usage is going to skew the results.

I would be more comfortable with a multiple day approach myself. That way any small errors in readings will sort of average out. You can start with one day, run the numbers, add the second day, run the numbers, etc... until you are satisfied that you 'filtered out the data noise'.

You try'in to be funny?
Actually, this time, no... so your home is about 24 x 24, two floors? A square cape? are you counting the area under the knee walls upstairs as heated space?

(my place ain't that much bigger! ... well, unless you factor in the 60 year old chicken coop converted to a big azz garage, which has more sq footage than the house!)

I am just being anal...
I understand that, and you KNOW I do! This from a guy who has an elapsed time meter on his oil valve and a sub-meter on the well pump electric and a water meter on the supply! (my water costs 0.0007 cents per gallon!)

Is it wise to state that I can lower my fuel bill by replacing old betsy at 85k input, with a 34 k input boiler?
I think so... but I wouldn't expect an earth-shattering difference. Preliminary data going from a 30 year old 140K boiler to the MPO 84K is showing perhaps an optimistic 15% so far this winter. I was wishing for 20% but I don't think that's gonna happen. Waiting to see what how it goes when it gets good and cold out.
 
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Old 01-03-13, 06:19 PM
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so your home is about 24 x 24, two floors? A square cape? are you counting the area under the knee walls upstairs as heated space?

Yes, but a small addition 156 sq ft plus 576 sq ft + 732 sq ft

Yes square... But its a 4 bedroom dang it !!!!

And,

How do you mean heated space? I am not counting those walls as cold partitions if thats what you mean. Same as ceiling factor for 1st floor.

2 rooms 11x13 and a 6x7 bath 328 sq ft


I would be more comfortable with a multiple day approach myself. That way any small errors in readings will sort of average out. You can start with one day, run the numbers, add the second day, run the numbers, etc... until you are satisfied that you 'filtered out the data noise'.
You mean a couple 24 hour tests over several days?


I think so... but I wouldn't expect an earth-shattering difference.


I only compared last months gas bill, and I know there are a lot of factors, but I used more gas then last year this time. I almost think because I lowered the boiler temp. But the following month was identical.

Usually it spikes Jan, Feb but I wonder if it will stay level like the last two months......








 
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Old 01-03-13, 07:42 PM
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I used more gas then last year this time. I almost think because I lowered the boiler temp.
Nope... last winter was very much warmer than any in the past decade or so. This is the EXACT reason why comparisons of the bills are worthless and exactly why one needs to use DDs in order to make any comparisons that mean anything at all.

Go here:

Weather Data Depot - Your source for free heating degree day and cooling degree day reports and charts!

enter your zip, 65 base temp, and click on the "Heating Degree Days" tab and look how much lower the 2012 curve is than the rest. Click the SEASONAL tab for just the winter months.

[table="width: 680, class: grid, align: center"]

[tr]

[td]Year[/td]

[td]Jul[/td]
[td]Aug[/td]
[td]Sep[/td]
[td]Oct[/td]
[td]Nov[/td]
[td]Dec[/td]
[td]Jan[/td]
[td]Feb[/td]
[td]Mar[/td]
[td]Apr[/td]
[td]May[/td]
[td]Jun[/td]

[/tr]
[tr]
[td]2003 - 2004[/td]" "[td]0[/td]" "[td]0[/td]" "[td]24[/td]" [td]370[/td]" "[td]846[/td]" "[td]1717[/td]" "[td]2966[/td]" [td]3860[/td]" "[td]4555[/td]" "[td]4946[/td]" "[td]5043[/td]" [td]5074[/td]"
[/tr]
[tr]
"[td]2004 - 2005[/td]" "[td]0[/td]" "[td]4[/td]" "[td]25[/td]" "[td]357[/td]" "[td]900[/td]" "[td]1772[/td]" "[td]2830[/td]" "[td]3693[/td]" "[td]4551[/td]" "[td]4963[/td]" "[td]5236[/td]" "[td]5265[/td]"
[/tr]
[tr]
"[td]2005 - 2006[/td]" "[td]0[/td]" "[td]0[/td]" "[td]22[/td]" "[td]289[/td]" "[td]766[/td]" "[td]1724[/td]" "[td]2509[/td]" "[td]3355[/td]" "[td]4068[/td]" "[td]4410[/td]" "[td]4567[/td]" "[td]4583[/td]"
[/tr]
[tr]
"[td]2006 - 2007[/td]" "[td]0[/td]" "[td]0[/td]" "[td]67[/td]" "[td]388[/td]" "[td]818[/td]" "[td]1520[/td]" "[td]2377[/td]" "[td]3421[/td]" "[td]4145[/td]" "[td]4644[/td]" "[td]4797[/td]" "[td]4810[/td]"
[/tr]
[tr]
"[td]2007 - 2008[/td]" "[td]2[/td]" "[td]14[/td]" "[td]61[/td]" "[td]209[/td]" "[td]829[/td]" "[td]1696[/td]" "[td]2616[/td]" "[td]3436[/td]" "[td]4133[/td]" "[td]4520[/td]" "[td]4755[/td]" "[td]4755[/td]"
[/tr]
[tr]
"[td]2008 - 2009[/td]" "[td]0[/td]" "[td]1[/td]" "[td]35[/td]" "[td]380[/td]" "[td]988[/td]" "[td]1802[/td]" "[td]2940[/td]" "[td]3748[/td]" "[td]4513[/td]" "[td]4921[/td]" "[td]5075[/td]" "[td]5128[/td]"
[/tr]
[tr]
"[td]2009 - 2010[/td]" "[td]2[/td]" "[td]2[/td]" "[td]57[/td]" "[td]377[/td]" "[td]813[/td]" "[td]1714[/td]" "[td]2738[/td]" "[td]3681[/td]" "[td]4259[/td]" "[td]4576[/td]" "[td]4692[/td]" "[td]4699[/td]"
[/tr]
[tr]
"[td]2010 - 2011[/td]" "[td]0[/td]" "[td]0[/td]" "[td]16[/td]" "[td]276[/td]" "[td]853[/td]" "[td]1913[/td]" "[td]3071[/td]" "[td]3899[/td]" "[td]4621[/td]" "[td]4967[/td]" "[td]5088[/td]" "[td]5095[/td]"
[/tr]
[tr]
"[td]2011 - 2012[/td]" "[td]0[/td]" "[td]0[/td]" "[td]25[/td]" "[td]271[/td]" "[td]683[/td]" "[td]1361[/td]" "[td]2200[/td]" "[td]2904[/td]" "[td]3363[/td]" "[td]3688[/td]" "[td]3760[/td]" "[td]3772[/td]"
[/tr]
[tr]
"[td]2012 - 2013[/td]" "[td]0[/td]" "[td]0[/td]" "[td]42[/td]" "[td]277[/td]" "[td]947[/td]" "[td]1650[/td]"
[/tr]
[/table]
 
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Old 01-03-13, 07:49 PM
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I am not counting those walls as cold partitions
But what about the floor space between those walls and the roof? that triangular cubby closet area? I wouldn't quite be sure how to treat that myself, I guess it's heated though, at least to some degree?

You mean a couple 24 hour tests over several days?
Yes. Take data each midnight for as many days as you feel up to it. Gets tedious after a while though!

BTW, on that weather data website, go all the way back to 2002-2003 and notice how much COLDER that year was! There is a FLAW in the data though and it affects the chart... notice that there is no value for JUL 2002. That skews the graph some... the graph for 02-03 needs to be moved over to the right one month. It was still colder as shown by the cumulative degree days in the last column of the data, but not as much as the graph makes it appear.
 
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Old 01-04-13, 03:31 PM
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But what about the floor space between those walls and the roof? that triangular cubby closet area? I wouldn't quite be sure how to treat that myself, I guess it's heated though, at least to some degree?



Yeah that where the flaw is in the calculation. If I add the 200 sq ft in the calc then its not really a full space because the roof slopes.

Additionally when asked about the first floor ceiling and if the up stairs is heated you can technically say half the ceiling is heated and half is not heated and call it attic....

I even put in the calc that I only have 2" insulation in the walls. It does have asbestos siding over the original clap board. The insulation in the roof is there and possibly 3". One side was sheet rocked right on the rafters, and the other side had those wires holding it in.

My mistake when I renovated is not to put insulation in the knee walls when I replaced the sheet rock on those walls. I guess I can cut a hole one day and crawl in there on each side and do that.

I will revisit this post when I run a few meter clocks.
 
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Old 01-04-13, 03:40 PM
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I guess I can cut a hole one day and crawl in there
You didn't put small doors in there so you could use the storage space? When I was a kid I had me a fort in one of them... hid my girlie magazines under the floor boards. I might even have one today if I still lived there!

Keep us posted, I'm interested to see how real world numbers relate to Slant-Fin!
 
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Old 01-07-13, 10:38 AM
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OK so I did a 24 hour test on the meter.

Lets see if I could figure this out. ( I did one day and no other gas appliances were used except two showers and normal HWH running to keep tank warm. 40K heater)


12am - 12 am used 4ccf on Jan 5
4ccf x btu content NJNG @ 1.069 = 4.276 therms
4.276 therms x 100,000 = 427,600 btu used

427,600 - 20% ( if 80% AFUE ) = 342,080 btu / 24 = 14,253 btu/Hr


29 dd per almanac. Hi 42 lo 30 mean 36 DD 29

342080/29 DD = 11,796

11795/ 24 hours = 491



So at design temp at 10f

55 x 491 = 27,032

If I use the official DD which is in Newark then the DD is 27 and I come out to 29,034.

But I think real temp is whats nearest myself. There are closer weather stations but I cant get an almanac reading from them The closes is the Belmar/farmingdale airport. Lakehurst is close too

Lakehurst is 32 DD which is 24,487


With that said I went through every line item in my calculator. I crossed my i's and dotted my t's.

Example : I had room height at 7 ft when indeed they are 7.6. So I changed that. Also my crawl is not insulated. But I do have 8 ft BB to keep it warm and dry down there. Instead of taking a 0 factor for heated space I took a middle of the road.

15 unheated or .09 heated with no insulation which I have. So I took a .04 which is heated with 3" insulation. ( Sound right?)

Also since it is colder upstairs then down I did treat the knee walls as a cold partitions as well as half the walls of the dormer that sides the dead space. I fear some insulation leaks severly in certain bays.

How do I know? I watch how the snow melts on my roof. Certain bays melt fast so you see these strips of no snow from gutter to peak. I have several of these. ( I should have insulated the knee walls when I renovated dang-it!!! Stupid me...)


With that said slant fin goes by IBR and suggests an s 60. I wrote in the s 34 specs.

I can tell you its pretty close but did I fudge my calc with the crawl to make it match or other areas?

My original was 24,041.

Oh I guess we need to deduct for my water heater that ran 2 showers in this 24 hour period? Nothing else ran.


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Old 01-07-13, 01:20 PM
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Mike, I think you can remove some variables by measuring gas usage overnight when nothing else is consuming gas. The temperature will also be more consistent over night.

You can get DD for KBLM at degreedays.net. You can also go to weatherunderground.com. I'm not sure if they post the DD there, but you can use the info provided to calculate it yourself.
 
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Old 01-07-13, 02:44 PM
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remove some variables by measuring gas usage overnight when nothing else is consuming gas.
Yes, true... we went over that actually.

The problem with that is that your usage data does not correspond in time with the degree day data.

Measuring at midnight each day aligns the two data sets.

Yes, there will be other usage, no way around that really except to estimate it out. It will be FAR less than the gas used to heat the home.
 
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Old 01-07-13, 03:14 PM
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Dang! that's REAL CLOSE to SF ain't it?
 
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Old 01-07-13, 03:43 PM
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Dang! that's REAL CLOSE to SF ain't it?
Yeah... 122 btu? What do you think? Safe with a S 34 slant fin or say a Burnham seies 2 - 202?


 
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Old 01-07-13, 05:11 PM
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I dunno man... I'm a 'nervous Nellie'...

(I sized mine for five below!)

What happens if you run the numbers at 0 or even -5

Yeah, I know that 10 is the 99% point, but what happens we get an extended cold snap? OK, put on a sweater or two... but are you REALLY going to take that much of a 'hit' if you go up one size?

How would these lower temps relate to the amount of installed radiation?

I know you are over-radiated, but by how much?
 
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Old 01-07-13, 06:08 PM
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What happens if you run the numbers at 0 or even -5
Your scaring me now. What about global warming.....

How would these lower temps relate to the amount of installed radiation?
What lower temps? Outside temps? Boiler temps?

I know you are over-radiated, but by how much?

Running the calc as it is at 0 F nets me 31,678

-5 nets me 33,941




I have 60 ft first and 23 second floor 45,650 btu @ 180f ( Older style BB 550 btu ft I would say )

Slant fin stuff is discontinued that is close to mine is fine/line 15 @ 580 btu ft

http://slantfin.com/images/stories/T...neline15_r.pdf

@10f slant fin suggests 50.5 ft of fine/line 15

@0 59 ft

@ -5 63 ft


So @ -5 I will need 155f water @ 83 ft x 410 btu per ft to generate 34,030 btu. Worst case senerio????

http://comfort-calc.net/pictures/Old...ard_BTU_Ft.JPG














 
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Old 01-09-13, 07:49 AM
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With all this I would have to say that the S34 is probably a safe choice. Ya think?

Looks like there is enough margin in all directions.
 
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Old 01-24-13, 09:38 PM
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Clocked the meter these past two days of the cold snap. Pretty much design temps. 9f or so at night.

Posting just for reference.


1/23/13

meter 331-337 6 ccf 12am - 12 am

6ccf x 1.069 btu content = 6.414 therms

6.414 therms x 100,000 = 641,400 btu

641,400 btu - 20% = 513,120 / 24 = 21,380 btu/hr

19f hi- 10f low- 14f mean..... DD 50

513,120/50 = 10,262.4 / 24 = 427.6 x 55 = 23,518 btu/hr



1/24/13


meter 337- 344 7 ccf 12am - 12 am

7ccf x 1.069 btu content = 7.483 therms

7.483 therms x 100,000 = 748,300 btu

748,300 btu - 20% = 598,640 / 24 = 24,943 btu/hr

24f hi- 8f low- 16f mean..... DD 49

598,640/49 = 11,197 / 24 = 467 x 55 = 25,659 btu/hr




Note: The second night I forgot to lower the t stat..... LOL it was at 71f all night.... I usually set it to 68f. Coild that of cost me the 2000 btu?


With that said I am satisfied that my heat loss from the calculator was pretty close. Origially it was a heat loss calc of 24,041. I then tweeked it to match better to my first meter clocking.


Also a note, the dryer was ran for one load on one day, and 3 showers a day plus one bath for the baby....


The burnham 202 is 31k btu ..its the smallest. The control is way different then the slant fin.... It seems like all it has is a thermal purge for the circ to run...

http://www.usboiler.net/products/boi...tDataSheet.pdf


The slant fin looks like it monitors the t stats. The s 34 is 29k btu.

http://slantfin.com/images/stories/P..._10.pdf%20.pdf

It has this HYDROLEVEL HYDROSTAT CONTROL.

http://www.hydrolevel.com/pages/pdf_...structions.pdf.
 

Last edited by lawrosa; 01-24-13 at 10:04 PM.
  #39  
Old 01-25-13, 04:19 AM
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Nice.

That is not much of a heat loss is it.
When you say the dryer, is that gas fired as well ?
And you DHW is gas I'll assume ?

This just goes to show that heat loss calcs always seem to have some "fat" in them.

I put a clock on my gas valve for a while, and clocked the meter once or twice during firing once or twice to confirm the firing rate. I could see how many hours and minutes each day it ran. Then could calculate usage and cost. Was pretty cool for a while
 
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Old 01-25-13, 05:35 AM
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We've found that the SlantFin program adds about 20-25% in general, and that even if one did a Manual J on paper, they would end up with roughly the same overage.

It was more or less concluded that this 'fat' is to account for absolute worst case conditions, like a 25 MPH wind blowing from all four directions at once!

Recovery comes into play also, let's say you've selected a boiler for the exact heat loss and on a design day you want to raise the home from 68 to 70 ... with no fat at all, you will never be able to do it. Ya need a little extra horsepower to pass that semi on the uphill on I64.
 
 

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