Joined on May 3, 2011
Last Post on April 30, 2012
@ May 6, 2011 10:56 PM in Heat Loss CalculationNot at all, sir. Your pronouncements on things thermal are always welcome to this neophyte!
@ May 6, 2011 10:54 PM in Heat Loss CalculationSo, thermal master, these are my ciphers....
month T ave Therm-corrected HDD delta T BTUH
April '11 47 156.5 572 20 26308
March 44 177.3 592 23 33117
Feb 40 199.8 680 27 38140
Jan 42 187.9 685 25 32969
Dec 2010 44 193 647 23 32985
Nov 47 151.3 601 20 24206
Oct 55 86.6 351 12 14234
Sept 62 45.5 162 5 6751
Aug 67 4.3 130 1 159
July 65 8.9 145 2 590
June 59 44.9 247 8 6991
May 54 99.7 382 13 16312
April 51 127.6 456 16 21525
What this is telling me, I think, is that the 20'F design day BTUH of 51825 is probably pretty close to the mark (calculated on the builditsolar.com website)
Also, that my inclination to use a TriangleTube Solo 110 or a Viessmann 200W-26 would likely be appropriately sized.
@ May 6, 2011 9:04 PM in Heat Loss CalculationI was making a little joke about 'Huh, solar?' as I live in Seattle, where we have no sunshine, direct or otherwise.
@ May 6, 2011 4:52 PM in Heat Loss CalculationTook a bit - I guess the neurons are stiffening - ugh!
So, for Feb of this year
Ave T is 40, Ave low T is 33.5
I calculated BTUH for dT of 25, 30 and 35, and furnace efficiencies of .75 and .7
dT Cd=.6 Cd=.7
25 44041 37750
30 52849 45298
35 61657 52771
dT Cd=.6 Cd=.7
25 41105 35232
30 49325 42278
35 57547 49325
So, the data I derived from the builditsolar.com site, using data I entered for all the house wall/roof areas, window area, respective R values and insulation, and basement slab dimensions, at design T of 20 degrees and 4700 HDD per year, gives 51825 BTU/H. This seems pretty correct - yes?
@ May 6, 2011 1:52 PM in Heat Loss CalculationTo clarify, because I'm getting some screwy numbers.
The HDD is dependent on a temp chosen as a baseline, right? So if I pick 68', I'll get values based on that, and the 68' reflects the interior temp that were burning BTUs to achieve.
Also, the delta T is based on this interior temp, right? A question, the delta is between interior temp and average exterior temp?
So I totaled my therm use for the past year from the gas company. I averaged the 12 monthly average temps over that year, also provided by gas company, subtracted this from 68 to get dT. Or have I made a big mistake?
I'm using 1715 therms for the past 12 months (from my bill).
HDD from degreedays.net at 68' of 6294 for the past 12 months.
Average daily temp of 52.17 (from gas bill), therefore dT=68-52.17=15.83
Efficiency of 0.70 and Cd of 0.70.
From these I get BTUH of 8806, which seems 'off' by a factor of about 5-6, which seems bigger than subtle tweaks to efficiency or Cd would correct - seems like something fundamental is off in my numbers.
@ May 6, 2011 11:30 AM in Heat Loss CalculationI'm nearest this one:
KWASEATT116: Queen Anne - Southern Exposure, Seattle, WA, US (1mi/2km)
The other Queen Anne site is closer, but apparently very new and has little data associated with it.
I looked at several other sites in the vicinity and they all seem pretty close. What's interesting is that the HDD data from the gas company is much more variable - I suppose they're averaging over a larger area - because their data seems close to my station's at 62-65' as the baseline, but their highs are higher and lows lower.
Anyway, how do I translate the HDD from my local station into a heat loss estimate?
I was also thinking that if my present furnace is very inefficient (about 20 years old and not well serviced - my bad, I've learned!), then the gas use data is going to overestimate what I would need with a more efficient system - right?
@ May 5, 2011 11:48 PM in Heat Loss CalculationThat last paragraph should read...
Subtracting out about 30 therm/MONTH for a baseline...
and ratio of therm/month/HDD yields 0.264 for the heating season.
@ May 5, 2011 11:45 PM in Heat Loss CalculationI'll head right down to the 7-11. MegaMillions drawing is tomorrow, IIRC. ;)
@ May 5, 2011 11:44 PM in Heat Loss CalculationThanks for the vote of confidence, and the advice!
I'll be back with my thoughts on design soon - hope your confidence is rewarded!
@ May 5, 2011 11:42 PM in Heat Loss CalculationBrad - thanks so much!
The data I can get from my gas company only goes back two years. What I can get is total use, therms/day, ave temp and heating degree days. It is as follows (I hope this stays in register by just typing in):
Month therm/day Ave temp HDD
5/2009 2.97 54 303
6/2009 1.14 64 39
7/2009 1.13 68 21
8/2009 0.76 69 14
9/2009 2.36 65 40
10/2009 3.93 53 345
11/2009 4.85 48 486
12/2009 6.76 40 741
1/2010 4.69 46 626
2/2010 4.87 47 528
3/2010 4.69 49 462
4/2010 4.92 51 447
5/2010 4.47 54 294
6/2010 2.50 59 179
7/2010 1.21 65 59
8/2010 1.14 67 21
9/2010 2.36 62 83
10/2010 4.02 55 264
11/2010 6.25 47 514
12/2010 6.75 44 666
1/2011 7.26 42 669
2/2011 7.66 40 723
3/2011 6.69 44 637
4/2011 6.43 47 522
The baseline (ie summertime) use seems to have gone up some - which I attribute to my older child going from 13 to 14 and discovering hygiene! Gawd those sowers can be long!
Subtracting out about 30 therms/day for baseline (hot water and gas rangetop - alas the grill is propane, though in use all winter!), and then ratioing to HDD - one gets a pretty constant 0.264 therms/day/HDD, at least in winter - it's much more variable in summer, with less actual heating use.
@ May 5, 2011 9:39 AM in Heat Loss CalculationThat should be...700 sq ft on each the first and second floors, as well as the basement - for a total of 2100 sq ft.
@ May 5, 2011 9:20 AM in Heat Loss CalculationHello all - fantastic site you guys have here - immensely informative, nice community - a really great find. I'm a newbie to this, not a professional in the heating/comfort industry(a scientist/doctor type, actually), but I love learning and am pretty handy, and I'm trying my hand at designing a radiant hot water system for my house. I've got Siegenthaler's book (and have been doing the problems!), and I've been reading the Idronics semiannual publications, reading the installations manuals for Triangle Tube and Viessmann modcons, essentially reading reading reading all I can.
I'm starting out with a heat loss calculation, as advised. I'm wondering if any have come across this site:
It seems to actually calculate UxAxdT, and takes into account different building materials and windows and such, as well as air infiltration, and I'm getting numbers that seem to make sense.
I have a 105 year old frame house in Seattle, some insulation and window upgrades, but we still have some big singe-pane bay windows with that cool old wavy glass that I just don't have the heart to rip out - however they leak heat like a sieve.
(Presently we have gas forced air, the plant at the end of its life and needing replacing.) The house has about 700 sq-ft on the first and second floors, and the same size heated basement.
From the builditsolar.com site calculator, I'm getting a total heat loss of 46870 BTU/hr. When I look at my gas bill over the past year, the biggest monthly use was 7.5 therm/day this past February - or 31250 BTU/hr on average. I went back and looked at daily temps around here that month, and on only two days did we get down to the design temp of 20'F. On average we were 38.3'F for the lows - or about 18.3'F higher than design temp. I took the dT at design (68-20) and the dT that month (68-38.3) and ratio'd them and got 0.62. Dividing the ave BTU/H that month (31250) by this ratio (0.62) and I get 50400 - which agrees pretty closely with the prior calculation.
Am I on the right track?