Comparing HDDs to Coal Used

[Lightning]

HDD = Pounds / [ 65 - ( OAT, high + OAT, low / 2) ]

Converting to a formula from Lightning's post .. folks can check and confirm

Yeah, that looks good for calculating a daily pounds per HDD. What I do is add up the coal used for 9-10 days and divide by the total HDDs for that same time period.

[davidmcbeth3]

Substitute for ( OAT, high + OAT, low / 2)

Σ (OAT, high + OAT, low)*
_______________________
days * 2

* sum of OAT differences for each day over which is being tested


And Pounds being substituted with

Pounds / days

days= time of examination

For HDDavg calc. over time period > 1 day

[davidmcbeth3]

So basically, what you do is take an average (mean) temperature for the day and subtract that number from 65 (which is the base temperature).. For example, if the low is 10 and the high is 30, then the mean temp for that day is 20 degrees. Then you subtract the mean from 65 degrees. 65-20 would be 45.. so 45 of those degrees are "heating degrees". Suppose you burn 68 pounds for that day. You then divide 45 heated degrees into the 68 pounds you used. In this example you used about 1.5 pounds of coal for each heated degree. Which is stated as 1.5 pounds per HDD.

Picking your brain here, Lightning.,,,

Is the 68 (clearly a reference to 68F) meant to mean to effect a constant 68F inside air temp. (IAT)?

So that there could be other HDDs based on target such as HDD68, HDD70, HDD72, etc ?

And would one expect the HDD68 calculated value to be pretty much a constant regardless of OATs and poundage of coal consumed for temp/coal use that is normally experienced ? For a specific system (ie stove, stove efficiencies, coal source, and location specific).

I would be surprised to see the various HDDs, like HDD68 and HDD72, to be equal (assuming the specific HDDx values are basically constant). Possibly be relatable to a natural log curve instead. So one could calculate from any HDD value how much coal would be used more or less when adjusting to a new AIT.

It maybe worthy of a study to conduct next season. Equipment needs would include a couple of temperature measurement recorders (one for OAT , one for AIT) and a good quality scale (perhaps one that can shoot the weight data right into a computer would be optimal). Then change the AIT target every 10 days and plug and chug the numbers. A computer dedicated to the study would be nice too.

[Retro_Origin]

Substitute for ( OAT, high + OAT, low / 2)

Σ (OAT, high + OAT, low)*
_______________________
days * 2

* sum of OAT differences for each day over which is being tested


And Pounds being substituted with

Pounds / days

days= time of examination

For HDDavg calc. over time period > 1 day

yikes, once I see the omega symbol I know we're not doing kindergarten math anymore! This has just increased to high tech! All for coal burning, an alleged dirty and ancient practice of uneducated bumpkins! Obviously not so!

[Lightning]

Is the 68 (clearly a reference to 68F) meant to mean to effect a constant 68F inside air temp. (IAT)?

The number 68 in the example I used was in reference to the coal used.. What I think you are referring to is the 65. 65F is the normal base number for calculating HDDs. 65F is used for the base temperature because its thought that a home doesn't require any heating until it gets below 65 degrees outside. This allows accountability for anything in the house that creates heat other than the heating system. Examples of these other things would be TVs, lights, computers, people, cook stove, the list goes on. In other words, your house would always be 7-8 degrees warmer than it is outside without the heating system. Counting those degrees (by using a base higher than 65F) would skew your fuel used vs HDDs.

would be surprised to see the various HDDs, like HDD68 and HDD72, to be equal

They would not be equal since HDD72 would be counting 4 more degrees as being heated.

And would one expect the HDD68 calculated value to be pretty much a constant regardless of OATs and poundage of coal consumed for temp/coal use that is normally experienced ? For a specific system (ie stove, stove efficiencies, coal source, and location specific).

That is correct, the coal used per HDD does stay pretty consistent as temperature and the amount of coal used, change. Like Rob mentioned, you can gauge the efficiency of changes made to the home or heating system by comparing coal used per HDD to before and after those changes.

Overall, I do see fluctuations in my coal used per HDD. Solar heating and wind can make big differences. It also seems that once the average outdoor air temp is below 25 degrees I see a lower consumption of coal per HDD. I chalk it up as my Axeman being more efficient when it has more work to do as compared to less work.

[davidmcbeth3]

The number 68 in the example I used was in reference to the coal used.. What I think you are referring to is the 65. 65F is the normal base number for calculating HDDs. 65F is used for the base temperature because its thought that a home doesn't require any heating until it gets below 65 degrees outside. This allows accountability for anything in the house that creates heat other than the heating system. Examples of these other things would be TVs, lights, computers, people, cook stove, the list goes on. In other words, your house would always be 7-8 degrees warmer than it is outside without the heating system. Counting those degrees (by using a base higher than 65F) would skew your fuel used vs HDDs.


They would not be equal since HDD72 would be counting 4 more degrees as being heated.


That is correct, the coal used per HDD does stay pretty consistent as temperature and the amount of coal used, change. Like Rob mentioned, you can gauge the efficiency of changes made to the home or heating system by comparing coal used per HDD to before and after those changes.

Overall, I do see fluctuations in my coal used per HDD. Solar heating and wind can make big differences. It also seems that once the average outdoor air temp is below 25 degrees I see a lower consumption of coal per HDD. I chalk it up as my Axeman being more efficient when it has more work to do as compared to less work.

Yes, I mistyped a "68" value for the correct "65". Hmmm..I must do more research ... think think think I will. Think if the 65F was just an arbitrary picked number, or has some more significance.

65F is an OAT value ? That IAT > OAT by several degrees...perhaps that is all that it means..

That 65F is OAT so inside it is 72F IAT.

Hmm examination of the "zeros" can be useful. I shall do that ... results likely in a couple of days to report if anything interesting shows up.

[Hoytman]

All for coal burning, an alleged dirty and ancient practice of uneducated bumpkins! Obviously not so!

Ha! I much prefer simple bumpkins. Far less jargon to cypher through as their language is simple and by the “letter”. They just open up their mouth and “letter” fly.

[davidmcbeth3]

Ha! I much prefer simple bumpkins. Far less jargon to cypher through as their language is simple and by the “letter”. They just open up their mouth and “letter” fly.

It used to be that way..now its recommended you get a PhD in math, engineering, and have a MD.

Times change.

I failed my MD test when I said that boys have testicles and girls have ovaries.

[Hoytman]

It used to be that way..now its recommended you get a PhD in math, engineering, and have a MD.

Times change.

I failed my MD test when I said that boys have testicles and girls have ovaries.

[waytomany?s]

It used to be that way..now its recommended you get a PhD in math, engineering, and have a MD.

Times change.

I failed my MD test when I said that boys have testicles and girls have ovaries.

So did that kid in kindergarten cop get cancelled as well?

[BigBarney]

That website has a lot of information that allows you to customize

for more exact location and adjust the temperature for the basis of

the degree days,I use 70* degrees.

https://www.degreedays.net/

BigBarney

[davidmcbeth3]

That website has a lot of information that allows you to customize

for more exact location and adjust the temperature for the basis of

the degree days,I use 70* degrees.

https://www.degreedays.net/

BigBarney

Ahhh you use that site ?

[BigBarney]

yes very good data.

Checking my electric efficiency per KWHr.

BigBarney