A different Heat Loss calculator

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  #1  
Old 01-23-09, 06:15 PM
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A different Heat Loss calculator

I think I remember seeing a description of a different way to calculate a home's heat loss on this site. For the life of me, I can not find it again.

This method used the amount of oil used over a given period and the daily temperature over that period.

Can somebody point me in the right direction?

Thanks.
 
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Old 01-23-09, 08:42 PM
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Heat loss is calculated at DESIGN TEMP. For my area, it happens to be 10F.

IF you were able to CLOCK your fuel useage and accurately measure it, AND you were able to take this data at design temperature for a long enough period to get accurate data, you could theoretically measure the fuel useage, calculate the BTUs, factor that all together and come up with a number...

Problem is, the outdoor temp is not likely to cooperate and STAY at design for a long enough period to do so.

You would have to extrapolate and graph the results at many different temps...

As an example... One 24 hr period last week, with an overnight low of 9.1, I clocked 4-1/2 hr of oil valve open time. Firing rate 1.25 GPH. Let's call #2 at 140,000 BTU/GALL ...

Sooo, 4.5 hrs X 1.25 GPH = 5.625 GALLONS

X 140,000 BTU/GALL = 787500 BTU divided by 24 HRs

= appx 33,000 BTUH AVERAGE for that period.

Now, it wasn't 9.1 for that entire 24 hr period... I believe the high during that time was around 15 or so. So, the average was around 12 which yields about 52 DEGREE DAYS (65-12).

My home is a little under 2000 sq ft... and that works out to about 17 BTU/SQ FT at THAT temperature.

You can work up a 'constant' that is a little more useable...

BTU / SQ FT / DD

In that period, I burned 787500 BTU, let's say 2000 sq ft, and 52 degree days. Let's do the math:

787500 / 2000 / 52 = Appx 7.5 BTU per SQ FT per DD

Using that number, I should be able to predict how many BTU I would need for a full 24 hr period of design temps...

At my design temp of 10F, 24hrs would be 55 DD

So multiply 55 DD X 2000 SQ FT X 7.5 BSD = 825000
and divide that result by 24 to get BTUH = 35K BTUH (or MBH)

This is just a LITTLE MORE THAN HALF of what SlantFins program said... it told me I needed a 65 MBH boiler! Also keep in mind that the 35K number INCLUDES all losses... it's the ACTUAL BTUs BURNED... what went into the home, AND what went up the chimney, everything... that's the GROSS INPUT to the boiler system.

Is it a realistic number? I think so... is my math somehow flawed? maybe... would I size a boiler based on that? I don't think so... BECAUSE: if it went down to zero for a period of time, the house would cool ... what if we had a freak cold snap and it went down to -10 for a week straight... I'd be frozen after 2-3 days ... the response and recovery time would be awful... what if spousey was chilly and wanted to bump the indoor up a few degrees? It wouldn't happen ... and she'd be pissed... besides, you can't buy an oil boiler that small.

Just some info for you to ponder if yer inclined.
 
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Old 01-24-09, 07:18 AM
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Question Degree day charts?

Trooper,

Do you know of a source for 'degree day' data over the last few years (I could use avg monthly temps, but this doesnt account for fluctuations as you suggest)? I am thinking my oil company uses such data to predict usage, and am wondering if it is available from a public source. (say, by month or by day)

From this I could pull my historical oil usage to come up with an overall factor?

Am thinking I could compare A/B, before and after a major mod (equipment, insulation, etc) and see what impact on the 'Constant' or 'Factor'........ At the end of the day any economic payback is going to be determined by changing this overall factor.

This might also include impact of modifying 'setback', and/or avg house temp.

Maybe you have already done something like this?
 
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Old 01-24-09, 08:19 AM
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I use the Weather Underground site..search for your town, scroll down to History and Almanac, view the current day, and then you have access to all sorts of data, including HDD.

I would think its pretty hard to do some modification to a house and then spot check the hdd vs fuel use in a short term kind of way.. too many other factors like sun loading, wind effect, how many times the doors opened etc.
 
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Old 01-24-09, 08:23 AM
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I think there is another issue that may be overlooked: infiltration. Also, even if the house were 100% air tight, with zero infiltration, there is greater heat loss with higher wind speeds due to conductive loss. This wouldn't necessarily be reflected in heating-degree-day data.

The various heat-loss programs, including Slant/Fin's, have an allowance built in for infiltration (and maybe conductive losses). But what is it? Evidently it's the same approach for all locations, adjusted of course for windows, weather stripping, etc. - including my house on the prairie, immediately east of a 300-acre corn field? Believe me, with a strong west wind, my boiler goes into overdrive.

There is one saving grace: when temperatures here are bitterly cold, say -20 or lower, the wind is often calm. Probably, my worst combination for heat loss would be about +10 deg with a 30-40 mph west wind.
Doug
 
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Old 01-24-09, 08:42 AM
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Resettable hour meter

I installed an hour meter in the 110 volt burner disconnect circuit on my CT-3 boiler. The hours on the meter X the .75 gallon per hour flow rate of the burner tracks my oil usage.
 
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Old 01-24-09, 09:24 AM
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Yes, Weather Underground ... Welcome to Weather Underground : Weather Underground ... there is TONS of historical data available. If you have an airport (local or otherwise) near you, the data from those may be the most reliable, although my local airport always seems to be COLDER than my own personal weather data, and that of nearby PWS's (personal weather stations, also numerous on WU).

hint: click CUSTOM when in the history view to set a date range. You can get one year at a time, I usually spec FROM July 1 to June 30 as my range.

As Dave mentioned, you can definitely NOT do 'spot checks', you MUST average data over an appropriate time period.

SOME oil delivery companies use the "Johnson Degree Day Meter" which takes into account wind (infiltration), and solar gain (insOlation (NOTE: NOT a typo)) to produce WEIGHTED DEGREE DAY data. But they are expensive...

Delivery companies use what they call "K factor" ... NOT to be confused with the 'other' K factors (there are a few), ... which is a simpler constant... DD / GALL ... because they do not know how many SQ FT your home is.

If they use the SIMPLE DD data, without factoring wind and sun, you might discover why they sometimes let customers RUN OUT accidentally! They are a HUGE influence on performance...

I use an old 24 hour wall clock as my elapsed time meter on my OIL VALVE... whenever the valve is open and I'm burning oil, the clock runs... if you have a primary control that does NOT have any valve on, motor off delays (Honey 7184) aka pre-post purge, you can run your ET meter off the burner control directly.
 
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Old 01-24-09, 09:36 AM
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Originally Posted by CT3MAN View Post
I installed an hour meter in the 110 volt burner disconnect circuit on my CT-3 boiler. The hours on the meter X the .75 gallon per hour flow rate of the burner tracks my oil usage.
I like this idea! But to measure elapsed time that my burner is on will take a 24-V clock (natural gas valve voltage). A quick Google search didn't turn up any real good possibilities.

I suppose I could hookup a 24-V transformer, backwards, to give 120-V for a regular analog, electric clock - but that seems like a long way around the mulberry bush.
Doug
 
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Old 01-24-09, 09:41 AM
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Maybe you have already done something like this?
Yes... I have far too much time on my hands, or maybe I'm just far to 'cheap' or A.R. ... I dunno... but I have charts, graphs, 27 8x10 colored glossy photographs with circles and arrows on the front of each one and a paragraph on the back of each one explaining what each one was to be used as evidence... but Arlo digressed, and so do I.

Just to further the discussion of the effect that wind and sun has... much of my data is 'noisy'... there may be a huge upward or downward 'spike' on a day or 2, 3, period. I haven't gotten so sick as to factor in the wind and sun yet, and I'm SURE that these spikes are due to that effect. If I went in and looked at the wind data on wunderground, I bet I would find correlation of those spikes to wind... (solar data isn't available in a useable, downloadable form)...

If one were electronically and computer oriented, one could easily and inexpensively build a device that would track solar radiation and collect it ... Hobby Boards : Complete 1wire Solutions ...
 
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Old 01-24-09, 09:46 AM
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Doug, I'm certain that I've seen "Elapsed Time Meters" that run on 24VAC ... but a small control transformer in reverse would work too.. and probably cheaper than a dedicated ET meter...
 
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Old 01-24-09, 10:48 AM
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Originally Posted by gilmorrie View Post
I like this idea! But to measure elapsed time that my burner is on will take a 24-V clock (natural gas valve voltage). A quick Google search didn't turn up any real good possibilities.

I suppose I could hookup a 24-V transformer, backwards, to give 120-V for a regular analog, electric clock - but that seems like a long way around the mulberry bush.
Doug
Try Manhattan Supply Co., or McMaster Supply. Or try running a 24 volt relay to control a 110 volt timer.
 
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Old 01-24-09, 11:47 AM
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Originally Posted by CT3MAN View Post
Try Manhattan Supply Co., or McMaster Supply. Or try running a 24 volt relay to control a 110 volt timer.
Thanks. McMaster has what I need: 24-VAC elapsed time meter. But I'll try to run a price check, first.

I'm going to get two: one for burner hours and one for circulator hours. The burner hours will correspond to fuel usage.

The circulator hours will give me the total time calling for heat. Don't ask me what I intend to do with that data.
Doug
 
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Old 01-24-09, 12:01 PM
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That's the spirit Doug! Can't have too many measurement devices!

I'm not gonna ask what you intend to do with the data, but if you come up with any cool charts, or interesting info, I'd be happy if ya shared it! (I know you will...)
 
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Old 01-24-09, 12:18 PM
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thermostat log

My new thermostats (LUX 9000TS) have a feature that tracks 'ON' time. I believe this would be circulator on - basically zone run time. It captures total cumulative and 'daily' (dont know if this is 24hr elapsed or since midnight of that day).

And the Logamatic on the boiler has an hour meter (total run time). So I can keep this log (we could pontificate on the meaning of the difference between thermostat call time (all of them) and boiler run time..... I also have DHW priority which might confuse the issue).

I was thinking I would just wait a year or three and plot total oil used and see if there was an inflection point when the new system was installed..... but in the meantime I can speculate and guess from shorter duration 'data'.
 
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