Calculating heating costs/math problem

Steve Ebels_3

How do I translate degree day data into an estimated annual cost for a given fuel and a given structural heat loss.



For example:

 I have a building in an area that has 6,500 degree days, a heat loss of 100,000btu at design and a fuel cost of $21.00 / million btu and I need to find an estimated annual cost of operation.

Alan (California Radiant) Forbes

Math

Math............Ugh.



I have no idea.  So I looked around.  From this website: http://www.energytechpro.com/Demo-EM/Audits/Degree_Days.htm, I found a vague answer:



Graphing fuel usage and Degree Days on a spreadsheet will likely produce

similarly shaped curves. Calculating BTU use per Degree Day will produce

valuable data that can be used to estimate heating costs based on Degree

Days. For many facilities there is not an exact linear relationship between

BTU usage and Degree Days.



From this website: http://www.answers.com/topic/degree-day, I got:



A frequent use of degree-days for a specific building is to determine

before fuel storage tanks run dry when fuel oil deliveries should be

made. Number of Btu which the heating plant must furnish to a building in a given period of time is

where “Btu required” is the heat supplied by the heating system to

maintain the desired inside temperature. “Heat rate of building” is the

hourly building heat loss divided by the difference between inside and

outside design temperatures.



And this is a worksheet to determine the total supplemental heat required for a building in terms of BTU/hr. and BTU/degree day: https://engineering.purdue.edu/.../lab%20Heat%20Loss%20F07%20a.doc



When you get the answer, please show us how you got it.  : )

Brad White

Here is how I do it

Alan got you off to a good start. I could not dig into that Purdue link (it was the main page), but let me show you how I go about it, FWIW.



The numerator is as Alan said:



Heat Loss in BTUH x 24 Hours x Heating Degree Days



The denominator (D for denominator, D for Down, it is at the bottom is how I remember that from grade school):



Design Delta-T* x Efficiency x BTU per Fuel Unit. (This could be therms of gas, gallons of oil or propane, cords of wood, tons of coal, bushels of Lingonberries, whatever you burn, but expressed in the units you buy).



(The "Design Delta-T" is the indoor-outdoor temperature difference you used to derive the heat loss in the first place. If you change your heat loss basis, change this number, but make them consistent. Whatever you use to calculate your heat loss, use this number.)



Plug these in and you will get a "Raw" or "Gross Usage" number of fuel units.



This is then multiplied by what is called the "Cd" factor. (No, not "CD factor", which is the number of Lady Gaga discs you have divided by your Dwight Yoakam collection.)



The Cd factor is an empirical number which includes solar gains, internal gains, set-backs, basically credits for free heating which offset what you otherwise would spend on fuel. A good range for the Cd factor is 0.60 to 0.65 as a place to start. I can get into more of that later. Basically a tight house facing south will be lower (even down to 0.45!) and a looser, older house facing north will be higher, up to 0.90 or net.)



So, for your example, Steve, I will assume you are using Natural Gas at $2.10 per therm (100,000 BTU per),  and actual seasonal efficiency at 90 percent, (expressed as 0.90), aggressive low temperature.  Your design indoor temperature I will assume at 70 degrees to get your 100 MBH heat loss, and an outdoor temperature of -20F, just a guess, to arrive at a 90 degree indoor/outdoor difference. Sound OK? Oh, I will also use a 0.65 Cd factor.



Here we go:



(100,000 x 24 x 6500) / (90F x 0.9 x 100,000) = 1,926 therms



Then:



1,926 therms x 0.65 Cd factor = 1,252 net therms.



At $2.10 per net therm your annual cost would be about $2,629.



Mind you, Heating Degree Days are a 30 year average and can vary 20% year to year. Lots of variables and the user habits are the largest. If this is a tight house with radiant heat on a sunny spot (and good control, natch), the usage could be 75% of this number. But it gets you into a baseline range.



Work it out a couple of ways, a few times to get familiar with it. Nothing to be afraid of.



Hope this helps!



Brad

Mark Eatherton

That's a print....

Thanks Brad! I've seen that formula before, but couldn't find it when I needed it.



Naturally :-)



How would your approach change if you had access to good reliable degree day bin data?



Does the Cd factor still apply?



Thanks for the education. Speaking of which, are you still teaching? I haven't had enough students for a quorum for going on 4 years. Haven't taught at RRCC for three.



Educational apathy ;-(



ME

Paul Rohrs_14

He's baaaaack....

Brad, you are hysterical.  Who told you about my Lady Gaga CD collection?

Sage advice as always.  Good to "see" you again.

How is the lovely Susan doing?  How about the Vito200?

Paul

Unknown

Calculating heating costs/math problem

OK boys, I have a stupid question...



Is there any way of determining the energy savings observed by either maintaining a lower system temperature or running the system near it's design temp diff instead of the small temp differential typically seen?



It's fairly simple to calculate the electrical savings with ECM pumps but I need a simple procedure to predict system energy savings (the system where the ECM pump is installed).

Brad White

Degree-Daze

OK, so no one glazed over! Coffee helps..



Mark, you asked, "How would your approach change if you had access to good reliable degree day bin data? "



Funny you should ask. I use a web site:  http://www.degreedays.net/

which gives me up to three years of data date-specific to a given site and in spreadsheet form no less. Easy.  As a typical application, say I have a new client and want to establish a heat loss for their building.  I do an ASHRAE heat loss calculation, sure.



But I also take their fuel use for heating (oil is easy usually, it is all heating, or subtract out summer months for a net non-heating gas load).  I then use the HDD formula we are discussing, for each year and "back-calculate" from knowing the answer (how much fuel they used) and how many HDD's have accumulated over the same time period. I know there are 24 hours in a day, but I also guess, reasonably, at the other variables, the Cd factor, the efficiency and the presumed indoor/outdoor temperature difference.  (I can at least ask them.) 



I use at least three years worth of fuel use and HDD data, to cancel out or level out unusual years. More is better but user habits change too. So three years is ideal for me.



From this I get a range, using different Cd factors, plant efficiencies and less so, temperature differences.  The heat loss becomes apparent (the new "x" I am solving for). 



As an added twist, I might use their radiation take-offs to get a third number. Sure, radiation is not heat loss (except on Long Island), but it is another benchmark for triangulation.



A typical job I did had roughly the following numbers:

Calculated Heat Loss: 79,500 BTUH

Fuel Use Heat Loss: 76,500, 79,900, 77,600

Radiation by EDR at 170F: 81,200.



So you can see the "grouping" and how close the numbers can be, often within a 10% spread.



The Cd factor ALWAYS applies. It just may be different. All that factor really is: The unexplained difference between what you DID spend and what your numbers say you SHOULD have spent. In engineering, we call that a Fudge Factor.  OK, we admit it!



Not teaching formally (as I used to at Boston Architectural Center (now College). I do teach an annual seminar called, "The Monster in the Basement" at my local Building Materials Co-Operative. But informally every day I teach my mentees in the office. (No, not manatees, dammit!). Best of all, I teach myself every day and learn from others. All good.



Sorry to hear about the apathy- it is not you I am sure!

Brad White

Paul!

We all KNOW about you and Lady Gaga. Never mind your CD rack.

Q: How do you annoy her?

A: "Poker Face"



OK, the 14 year old thought it was funny....

All are well, thanks! We sold the house for a song. If not for the Vitodens, it may not have sold it at all! Lucky contractor bought it, I hope he appreciates it. Stay tuned for my W-M pre-Gold make-over.

Brad White

That is an EXCELLENT question, Steve.

I do not know the answer.

(As my dad always said, "If you do not know something, say, "I do not know" -and you will be right!) My Dad Rocks.



I do have some thoughts though and this would make for a good "White Paper".



-ECM savings, as you said, fairly easy to quantify and as a cube-root function, a no-brainer in most applications. 



-Anything you can do to tailor heat input closely to heat loss is a good thing, any way you can do it.



-VS circulation is an ideal way if used as a blending/injection pump, BUT, if it is a matter of varying flow to meet demand, I think it is not a "big fish" approach. Because flow is so forgiving, (e.g. cut your flow in half and you still get 90% of distribution output in rough terms), it is not linear therefore not a good control variable. 



When used in injection pumping, that goes to changing the temperature of the distribution loop and it is temperature difference that makes the output rise and fall more closely to linear than anything.



Not to open the Delta-T vs. Delta-P control strategy discussion, I find Delta-T control can drop your pump rpm significantly over Delta-P control. When in Delta-P mode, your variable ultimately is flow (see above, not a tight control variable). In this mode, your "20 degree Delta-T" may often be half to a quarter of that, five to ten degrees. This means that you are moving two to four times as much water as you need to. Cut the flow in half, cut the Watts drawn to 1/8th and all that.



Delta-P has it's place with highly dynamic systems using modulating control valves with high authority, high DP emitters and systems where the emitters are selected for various Delta-T's on the same system. (Some of my systems use 20F for fin tube, 40 to 60F for reheat coils and 30F for unit heaters, averaging 30-35F across the system, for example. No true Delta-T target there.)



But for simple systems, say a house with converted gravity HW, low differential pressure anyway, Delta-T will ramp down an ECM circulator to minimum most of the time.



As an aside, my current house renewal will use two Wilo Stratos Eco in essentially constant volume mode, one for the boiler circuit, one for the old CI/Gravity circuit.  Very low heads and not responding to a variable to speak of. A waste? I do not think so. The Watts drawn are less than the smallest PSC circulator I can find. I will keep you posted.



Brad

NRT_Rob

watch out!

cd factors are intended to back out degree days during summer months as well.



if you are manually doing that (as I am too, degreedays.net is a great site) then your cd factor should be adjusted as well.



I haven't used a cd factor when I back out manually, though a good step would probably be to take a stab at typical electrical draw and occupancy gains and at least back that out.



If you want to account for building mass, solar gain, etc... well, you need techniques I sure haven't mastered.

Brad White

Amen, Brother Rob!

True and good point on backing out summer HDD's. There are a few especially June and late August, when there is enough stored structure heat and insolation (solar gains) to offset them. You are correct, the HDDs accumulate and no one does anything with them!



In practice, the Cd factor is so widely variable, even amongst identical houses with identical orientation, the differences fall outside the margin of error.



When doing "investment grade audits", with appliance aggregation, you can see the contributions. (Actual vs. Theoretical differences are wide just the same.) But when using the more accurate check meters, a typical 2,000 SF home has a constant background draw of 300 Watts baseline with the lights off and appliances not running. All of those "MELs" (Miscellaneous Electrical Loads), cell phone chargers, cordless phones, doorbell transformers, etc. add up.  Throw in computers on standby and you have 500 Watts, roughly 1700 BTUs per Hour if all heat, purring away. In a tight house, that heats some rooms.

CMadatMe

Barba's Blog

Here's a nice little blog that put's it in a nutshell.



 http://jbblog.flopro.taco-hvac.com/?p=898

Steve Ebels_3

I'm Cd'ed?

So here's the actual scenario. And I'll say at the outset that my Cd's are a bit jumbled and in need of sorting out...........



Working on a plan for a brand new church building, approx 8,500 sq ft. with the 3,600 sq ft sanctuary part in the center having 24 foot ceiling height.



Two gc's have two very different building types proposed to this congregation and I have a heat loss calc generated for each.  GC #1 has proposed a steel frame building such as one would see used for a warehouse only dressed up accordingly. It uses the typical vinyl wrapped fiberglass insulation which is supposed to avg R-19 for walls and ceilings. Heat loss for that one is about 230Kbtu at -6* design temp. I used winter infiltration factor of .7ach for it and 400cfm ventilation air through an ERV. (this will run only when the building is occupied by a large group)



GC #2 has proposed an entirely different design using ICF's (ASTM rating of R-28) for the side walls and a ventilated attic with blown cellulose worth R-44. Air change per hour on this one was punched in at .5  with the same 400 cfm ERV. Heating load at design for this building is substantially less coming in at 164,000 btu.



Obviously these are two very different buildings with the factor affecting the Cd collection the most being the significant increase in building mass with the ICF construction.  I would assume that there will be very little internal heat gain due to the nature of use and neither is there going to be much solar gain due to layout and building orientation. Plus this is Michigan where it is cloudy due to lake effect probably 70% of the time during winter.



So that leaves the last major influence on the Cd rating which is the tremendous difference in building mass. One is sheet metal, fiberglass and interior wall. The other of course is 2' foam/6" concrete/2" foam in the walls and a minimum 14" of blown cellulose in a ventilated attic. 



So. How close am I, guessing  the Cd factor at the following...........Steel building at .85 and ICF building at .70.

Brad White

Cd ADHD, ASAP

Steve,

First off, I think your Cd factors are as good as anything anyone can come up with. Remember, you are chasing variables in a range and which cannot be defined until after the building is built. 



(Cd factors are/were generated this way after nailing down the other variables, not the least volatile of which is the efficiency. You know how that varies across a winter!)



If I want a good comparison, I dismiss the Cd factor and just compare raw numbers.



For the buildings though, I think both of us favor the ICF option. Nothing against "The General" or similar buildings, but the insulation in those, as good as they get, are pinched, sometimes torn and with gaps. Under infrared scrutiny, so far as I have seen (warehouses and "temporary" garage repair facilities), there are stripes. Every girt and purlin says "hello".   Also, the lower mass means faster temperature drop. For Sunday-only services, this may not be an issue and heating up will take less time. But there is something about banking thermal mass inside insulation that feels really good, especially with radiant heat.



I do have a code concern re: the 400 cfm ERV. That may be fine for a smaller building with a smaller population, but ASHRAE 62.1 (a reference standard sometimes incorporated into code) or similar standards in IBC, dictate higher airflow rates during occupancy.



I do not have my copy here, but I believe for large occupancy spaces the current standard is 5 cfm per person plus 0.06 cfm per SF.  That is the 2010 edition, I believe. (We just designed a Buddhist temple so my recollection is that current, but check your local codes.)



It used to be, "last code", 15 cfm per person with an allowed "3-hour rule", which presumed that the building would have been pre-flushed before and after, and only one assembly per day. Sounds like a church to me.



Anyway, if your sanctuary is 3600 SF, that requires 216 cfm just for the floor area. That leaves 184 cfm for population. At 5 cfm per, that is 36-37 people. All choir, no congregation.



I do not mean to rain on the jello mold salads, but I thought that I should mention this.

Steve Ebels_3

Glad to hear

Thanks for the affirmation on the Cd numbers. I'm thinking I should mention the difference in the building/fuel consumption to the committee. The numbers generated by the formula above plus those Cd factors show a serious difference.



As to the ventilation air issue you raised, that is absolutely correct. The AHJ and I have been working on some alternatives. We are both in agreement that sizing the ventilation system for max occupancy  when the building will have maybe 6-10 people in it for all but about 6 hours/week is ludicrous. We will come to some kind of a compromise between code and common sense that allows us to keep the place smelling fresh and healthy. Probably wind up using some type of fresh air through the A/C system. Which btw is also substantially reduced in size in the ICF building.



Thanks again for setting me on the straight and narrow path to hydronic accuracy.

Brad White

Some more thoughts, Steve-

Another factor the Cd factor might absorb in your case (and driving it higher as you already have suggested),  is the time the space will be in setback, the sanctuary specifically. For this reason, Cd factors aside, I would present the raw numbers (pre-Cd factor) as an apples and apples comparison. Any credit you get for various solar gains, mass (or Mass), will just be a bonus. I think the committee will understand that.



Regarding the ventilation, I am reflecting upon the Buddhist temple we are just finishing up in design.  Within that we have multi-purpose spaces, meditation space, the Temple itself and other spaces with highly variable populations. Empty for days, then full for several hours. There was no grace in the code so we used DOAS (dedicated outside air systems), indexed on just for these events. We kept the distribution simple but effective, using high supply and low returns. Your church might benefit from the opposite, "displacement ventilation", with low level and very low velocity supply and very high extraction.



Being 100 percent outside air and over 5,000 cfm, our energy code required us to use energy recovery. Even if not required, we could justify it. Not by hours of use, but by the fact that it took about 35 percent of the cooling load tonnage off the grid.  So even if it is used 10 hours a week and is off the rest of the time, it is there at the ready.



If you are not needing cooling (or even if you are), an on-grade outdoor package unit might make sense for "the big show". Just a thought.



Best,

Brad

Steve Ebels_3

Details

Thanks for your ongoing interest Brad.



What I have on the drawing board for this building is a combo/2 stage system. I'm going to propose that we do the entire building with radiant floor in 3 zones. We will run this at a "baseline" output, maintaining the building at 60-62*, or whatever they want)  on programmable stats, which because of the mass, will seem like they are running at the wrong times.......but sometimes it makes sense to be backwards......

The auxiliary heat for boosting temp from baseline to occupied levels will come from a Lifebreath Clean Air Furnace, which is an air handler designed to run on low water temps + an additional 140CFM of ventilation constantly. At water temps below condensing in the Vitodens (of course) it will provide about 70-80k btu of pick up and 3.5T of A/C capacity if they do desire to add that. It can run in fan/ERV mode only during the summer months.

How that AHU actually gets zoned will be determined by the final building layout but it will primarily serve the office/entry area (occupied every day) and the sanctuary/multipurpose room.  The third zone is kitchen, storage, mechanical so there's little need for a quicker picker upper there..............grandkids are makin a ruckus, better go check that out.

 

Brad White

You are welcome, Steve

Happy to lend another set of eyes. Keep me posted. I love this stuff.



Zoning is oh, so critical to a church, with the very small but daily office and rectory loads and then the sanctuary side.



One of my areas of design specialty is in performing arts centers, so very similar profiles with a front office and large population halls which are vacant many hours. Another form of church I suppose!



Hope the grands did not get into too much trouble! I just read that you have #13 on the way, a Baker's Dozen. Must be a great feeling and I am glad they have you to both spoil them and give them sage advice which is more easily absorbed than from their parental units.



My paternal grandfather, Ernest D. White (1888-1978), could impart such deep thinking in so few words and sometimes, a glance.

He must have known heating and air conditioning too. When asked, "how hot is it?", he did not give a temperature. Rather, if it were a scorcher, it was, "Hot as a June bride in a feather bed."   I miss him.

Steve Ebels_3

Grand people of all ages.............

The 1 year old we were supposedly keeping track of was taking great delight in unloading the book case in a very egregious and purposeful manner. This was shortly after ripping about 8 keys off the computer in the office........ He's a mover to say the least. And grand fathers......what can you say about an old man who has learned much about the attributes of human nature and has lost many inhibitions regarding their description.

Grandpa Ebels was known throughout the area as someone with a quick and somewhat acerbic wit, He was standing at his customary spot at the foot of the stairs in the hardware department (where he could give everyone the "eye" as they left) when a rather dour looking and absolutely filthy young man descended the stairs  toward him. The guy had clothes on that appeared to have been slept in for a week, after he had used them to wipe the fluid out of the rear differential on his pickup. Still distinctly visible though was the slogan on the front of his tee shirt which obviously summed up his worldview and in simple print spelled out the immortal words "S**T Happens".

Grandpa regarded the young man with the same gaze one would reserve for a dinner plate full of maggots and casually but very audibly to all said, "To some people more than others" as the young guy made his way past. I will never, ever forget the look on the guys face. For just a second or two I thought the line had been crossed and we would have a fight on our hands but after a glare that would defrost a freezer from Gramps the young guy just shuffled off. I just about died and so did everyone else who witnessed the interaction. Hilarious! He always called 'em like he saw 'em and 99% of the time he was correct.



 

Steve Ebels_3

Hey Brad

As a point of general discussion, how far would you go with this assumption/statement.



In comparison to building with a low mass, a high mass building will have the effect of knocking the highs and lows off the outdoor temperature.

Brad White

I would invert that a bit

Steve, I would probably phrase that this way:



"In comparison to a building with low mass, a high mass building will

have the effect of knocking the highs and lows off the indoor

temperature, or rather, lengthening the time it takes for those extreme temperatures to be reached from a given starting temperature."



I would further qualify this, stating that the compared buildings have equal (and preferably external and continuous) insulation and air-tightness and are under equal conditions.



How does that sound?



Basically you are using presumed higher specific heats and more pounds of material to level out the indoor temperature. I call that the Thermal Piggy Bank.



I would LOVE to have a bunch of high mass buildings change the outdoor temperature though.

Steve Ebels_3

OK, I think I follow you,,,,,,

I was looking at in this way.......



Given that heat goes to cold, or in other words the building is what is actually transferring the heat........ wouldn't a higher mass structure be able to use its "flywheel" to coast through an overnight dip in temperatures more easily than a low mass building? The rationale being that the high mass structure has more btu's available to give up than an equivalent low mass building.

In a low mass building the heat storing ability of 6" of fiberglass is next to nothing

compared with 4-6" of concrete.



I don't know what the correct engineering terminology is for this but I assume it exists. (Cd factor perhaps).... And I also don't know how one would quantify it but I have seen this phenomena take place in structures where the mass is on the heated side of the wall. Example being tightly sealed, large diameter log homes and ICF buildings.

Jean-David Beyer

High Mass building...

I am associated with what may be a high mass building. It is almost 200 years old.

It is two tall stories high. It is framed with big beam-like wood (bigger than 4x6s); they seem to be hand cut and fastened together with pegs.. Outside is ceder shake shingles. Inside is sort-of plaster. All the empty space is filled with bricks. The building was not designed to be heated, though for a long time it was heated with three pot-bellied stoves that may have burned coal. They are gone now, and the building is now heated by two Rheem 125,000 BTU/hr furnaces. We tend not to heat the building except the days it is used. On a cold day, if we start heating about midnight, it is often not up to 65 degrees by 9AM. On a really cold day, we cannot get it up to 65 at all. We certainly do not have enough mass to coast over a week.



Right now the building is pretty leaky, and we are working on that, but since it is historical, there are a lot of things we cannot do, such as putting in thermopane type windows (even if we could afford them). We are trying to seal the leaks, put storm windows on some of the windows (will take a few more years to come up with the money for that). There is some fiberglass insulation above the ceiling, but we are putting in more. We had to have the roof redone first, including some structural work.



Once we get the rest of the windows rebuilt and storm windows put on, and some more insulation in the ceiling, we can investigate how a high mass building actually works. Right now, it is probably too leaky to make much sense from what we have.

Brad White

I think you nailed that one, Steve

The flywheel effect works and would enable the building temperature to coast with little effort, especially if the insulation is on the outside.  We are thinking the same thing, but I was just expressing it differently.  And yes, having fun with you, hope you do not mind.



A neighbor had an old 1920's concrete garage, walls, roof, all that. We insulated it externally with rigid board, good windows and an exterior roof with rain screen. Makes a nice shop/retreat and heats with a small electric space heater, at least until we run a gas line out there. Point being, VERY stable indoor temperatures and practically air-tight.



Same for this discussion, if relatively tight from infiltration and high mass, that thermal piggy bank will take a jagged mountain scape of a temperature graph and make it into gently rolling hills or swells. I think everyone likes that.

Steve Ebels_3

I always look at it this way.......

A person has to consider three primary things when developing a :theory" on how much heat is necessary to maintain a given building. 

R-value



Air infiltration



Building mass



I assign more bias to the air infiltration than the R-value. A person can have great insulation in the walls and fight to heat a building with drafts around every window and door. I would also rather see a "dense" type of construction rather than nothing but siding, 2x4's, fiberglass and drywall.

Give me a choice between a tight building with R-5 insulation on the outside of a block wall and a drafty one with R-19 wood construction and I'll live happily ever after in the cement house.  

Steve Ebels_3

FYI Brad

I ran the numbers for the two building types and they are eye opening to say the least. Using the numbers I described above there's about 40% difference in heating costs alone.  

Brad White

I would be careful of overstating

the differences without refining what is in your Cd factor. It may narrow a bit and it is better to under-promise/over-deliver. Basically, yes, there should be a difference but in practice, and with equal heat losses, that spread seems kind of wide, absent any number crunching.



So, you have a direction! Now comes costing it out.



If you can get me the delta construction cost between the two, I can run an ROI string for you, see what the life cycle cost might be in a simple form.



Brad

Steve Ebels_3

Difference

That would be sweet. The cost difference between the two buildings is near $110,000. Not all of which is simply attributable to the ICF part of the building.

The main source of the difference in the heat loss is the air infiltration factor between the two and then the R-value of the walls and ceiling.

The ICF proposal has a higher value in the walls of course and the ceiling will be under a ventilated attic at R-44 rather than R-19.

Heat loss came to 233K for the steel and 162K for the ICF construction.

Fuel source will be propane.

Brad White

Let me work on that

between tasks, today maybe.



The variables seem binary- regardless of cause/construction, the heat losses and construction costs follow each other, so that makes it simpler.



The R value as we know means much less than the infiltration rate, but I will take it regardless. I may write to you off-line with more questions, Steve.



Brad

Steve Ebels_3

Many thinks my good man

I don't want to spout knowledge I know nothing about.......know what I mean?



I'll be out and about  but we'll see if the Blackberry works in the basement of the day.

Brad White

Steve

What is your local cost of propane? (You had mentioned $21.00 per MMBTU which works out to $1.92 per gallon, does that sound correct?)



You also said 6500 HDD's. Is there a specific location/town? I may be able to narrow that down a bit, but will use 6,500 absent that.



For a Cd factor in each case, I will use 0.70, which is the ASHRAE median for a 6,500 HDD area. (Range is 0.40 to 0.85, but at least they will be comparable and less likely to overstate one over the other.)



Let me know and I can get on this soon.



Brad

Steve Ebels_3

numbers numbers numbers

Local cost of propane is running about $1.70/gl on a prebuy program. Our heating degree days are listed as 7800. I used a Cd factor of .85 for the steel building and .70 for the ICF.



Does your program factor in annual increases in fuel costs? 10 years ago propane was selling for $.59 here.

Brad White

P.S.

I am also going to assume that your heat loss was based on a 68F indoor temperature and an outside temperature of -20, just a guess. But do get back to me with real numbers if you can.



The actual efficiency, even if 90-95% combustion efficiency, I will use 85% for each. I think that is more realistic given ramp-up hours for the sanctuary.  But let me know your thoughts on that too.



You can call me at (617) 997-5560 until 9:30 EST today. Operators are standing by.



Brad

Steve Ebels_3

Here ya go............

Design delta T is 76* for our area. Those are the numbers from HVAC-CALC.

  I used an efficiency of 95% for the Vitodens that will be running the system. I'm curious as to what factors would reduce that? My experience with those boilers applied to a low temp system shows that if parasitic losses are minimized it will easily hit that.

Of course dear sir, I will yield to your expertise in this area. I'm just a humble pipe fitter.........:)  

Brad White

All good

I will use $1.70 per gallon and your given HDDs and sure, 95% efficiency, maybe 90% but I will declare what I use, the basis. What diminishes the number is in the warmer weather when you cycle more, but if you have tight control on your water temperatures, I can go with a higher (95%) number. But that is a laboratory number so I want to be cautious extrapolating that into a full real-life year.



As for escalation, I will take a 5% discount (interest) rate on financing the $110K difference. (Even if it is cash-in-hand and you do not need to borrow it, there is that "lost opportunity" cost to be considered.)



I would also take a 5% escalation in fuel prices, per year. There will be spikes, but I use a 20 year useful life assumption over which all of this is averaged. No fancy program, just a spreadsheet I developed from my CEM (certified energy manager) work.



I have to run for my meeting but will do this when I get back this afternoon.



Have a great day!



Brad

Brad White

Well, Here You Go...

With the factors you gave me, Steve:



[7800 HDD, 233K and 162K heat losses, Cd factors of 0.70 applied to each, 76F design delta-T (indoor-outdoor), propane at $1.70 per gallon, 95% efficiency (atta-boy!) and a construction difference of $110,000] all with 5% borrowing/interest cost of capital and 5% annual escalation in fuel prices.  NO rebates or tax credits included. (Tax exempt church anyway, but whatever rebate you get applies to the system, not the building usually.) No service contract differences, same system.



This is what I get:



The 233K heat loss building would consume about 4622 gallons of propane and cost $7,857 per year.



The 162K heat loss building would consume about 3214 gallons of propane and cost  $5,463 per year.  Annual savings is about $2,394, call it $2,400 per year.



After 20 years of use and escalation, the higher heat loss building would have cost you $142,174 in net present dollars. This presumes the lower construction cost and not having to borrow the difference nor lose use of that capital. 



The tighter building with lower heat loss would have cost you $208,854, also in net present dollars. Now, the difference, ($66,680) includes the capital cost ($110K) over that period.



So on a strictly "dollars" value, the upgrade at those conditions would not pay for itself. However, if the higher value/lower heat loss building is desired for other reasons (greater comfort, maintenance advantages, aesthetics, etc.), you can make a case for it. I would hold out for the tighter building.



But those are the numbers I get.

Let me know your thoughts.



Brad

Steve Ebels_3

So......

You wouldn't assume any difference in Cd factor for the high mass/low mass buildings?

Brad White

Not for these

purposes, Steve.



The building mass might drop your Cd factor from our median 0.70 to, (I can only guess without an energy model and even then), 0.55 or 0.60.  I wanted to keep "apples to apples" to be conservative in my numbers, given the elasticity of Cd factors.



I mean, ICF mass is higher than a steel Butler Building, but ICF construction is not nearly the mass of a 14 inch cast in place structure with continuous insulation on the outside. I do not see the mass alone as the driver of the Cd factor.



 But overall and regardless,  I did not see the savings delta to justify the high mass based on energy performance alone.



I just ran it again with a Cd of 0.55 on the high mass option and the overall life-cycle cost delta dropped from $67K to $45K, but you are still in the red by that much, if you are relying totally on heating savings to pay back the investment.



Not that you asked, but your "break even point", would be to spend not more than $43,000 on the better construction, as an FYI. So the "intangible premium" in quality of the ICF construction would be +$67,000 to the budget.



EDIT: Another way to look at your break-even point is, "how low must my propane consumption be to get the numbers to work over a 20 year time?"



I figure to make that happen, your annual cost of propane in today's dollars would need to be no more than 1045 gallons or $1,778 per year, in order to pay back the $110K ICF construction premium. This is a significant expected drop from 3214 gallons in our best-case base scenario and quite a bit less than the 4622 gallons the low-mass building might consume.



Let me know your thoughts and how I can assist.



Brad

Steve Ebels_3

Many thanks Brad

I'm asking these questions mainly for my own information/education as I don't get a chance very often to really look hard at these ICF buildings. As is the case on this job, and most in the economic armpit of the USA, commonly called Michigan, the first cost is the only thing that is considered.



Cd factors that reduce heating equipment input will be scarce for this building because of its largely uninhabited nature, so the only tangible difference would be the building mass. Other than that, the difference in R-value and AC/H are the only things that would really influence the building performance. Correct?



I looked up some records of propane prices locally since 2000 and found that they have increased an average of a little over 7-1/2% per year. I don't know if that rate will continue or what difference it would make in your model but I think that it's safe to say no fuel costs are going to go down. I listened to a webinar featuring an oil industry CEO a couple weeks ago and his position was that it is very likely we will see prices back at 2007 levels by the end of next year. Scary thought.



Thanks again my good man.

Brad White

You are always welcome, Steve.

You asked, "Other than that (building mass), the difference in R-value and AC/H are the only things

that would really influence the building performance. Correct?"



Pretty much, all other things being equal, solar gains, etc.



It really is too bad because the tighter, denser and less leaky structure will have so much of a greater value when done. Remember the premium above break-even was only ("only? Did he say that?"), $67K.



But the numbers are the numbers and scale proportionately, pretty much. 



Keep me posted on this and if I may be of further assistance. Keeps me young, you know