Energy Efficiency and Payback - Concrete Example

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Old 10-25-08, 06:39 AM
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Energy Efficiency and Payback - Concrete Example

I have two buildings that I believe have over sized and/or inefficient boilers.

House 1:

3000 sq. ft. - calculated heat loss 135k
This building has large old style rads. (many of them)
The current boiler is 250k btus from 1983 and 83% efficient. Has not been maintained well. Basic controls. Current heating gas bill $5000/year.

Proposed boiler (prestige?)
Mod Con.
90+% efficient
all the modern controls
sized properly.

House 2:
2700sq ft. calculated heat loss 115-120k
Large old style rads. (many of them)
Current boiler is 270k btus from 1997 80% efficient. Maintained. Basic Controls.
Heat bills are $4700/year.

Proposed boiler (prestige?)
Mod Con.
90+% efficient
all the modern controls
sized properly.

What do you calculate my savings in gas consumption are, all else being equal with these two boilers?
 
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Old 10-25-08, 09:59 AM
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First, you cannot calculate fuel cost because the cost per BTU is not a constant. As I'm sure you are aware the cost of crude oil has dropped significantly with the recent fall of the economy in general. This might sound like good news but OPEC is now considering curtailing oil production which would have the effect of rising oil prices. Other fuels will also have this rise-fall-rise pattern.

It is also impossible to predict the temperature extremes and length of any significant deviation from past heating seasons with high accuracy. If last winter was unusually warm and this winter is more normal, or even colder, then your fuel consumption WILL increase, regardless of what equipment you have. Even with a lower price per BTU of fuel you could have a higher total cost simply from burning more fuel.

Second, the "efficiency ratings" of the new boilers you are comparing are NOT system efficiencies but are Annualized Fuel Utilization Efficiency (AFUE) numbers of the boiler only AND since they are calculated from laboratory testing they are rarely achievable in real-world applications. Differences of only a few percentage points are usually meaningless in the real world. The "efficiencies" of the existing boilers is a combustion efficiency test and while important for adjusting the burner it is not comparable to the AFUE rating nor does it take into consideration the rest of the heating system.


All that stated, it appears that your current boilers are at least 100% oversized. Installing properly sized boilers along with other energy saving improvements WILL save you on fuel consumed, maybe a very significant saving.
 
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Old 10-25-08, 04:26 PM
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Furd I appreciate the response.

I am looking for a general guess.

With incentives and government grants and so on I am thinking of replaceing a boiler that is working fine and does not need to be changed.

I would like to know what is the approximate savings - all else being equal if I were to change the boilers. If I am saving 1500+ a year then something begines to look attractive. Do you think that is possible/likely in this situation?
 
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Old 10-25-08, 04:36 PM
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While I am quite sure that some saving is likely I can't state any dollar figure. It would take a fair amount of number crunching with far more data than you have supplied to even come close to making any kind of educated guess.

When I still worked for a living the company position was that an equipment upgrade that was done solely to save operational expenses had to recover the capital costs in 12 to 18 months. Many times this was impossible and then it became necessary to include the avoided costs associated with equipment breakdown and other such things. To my mind this was an extremely short-sighted view and often I had to justify the saving of expense money in addition to capital in order to get new equipment that I knew would continue to save money for decades. Sometimes the numbers are just not available and you have to go with your gut feeling.
 
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Old 10-25-08, 08:17 PM
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Originally Posted by blurr View Post
...
I would like to know what is the approximate savings - all else being equal if I were to change the boilers. If I am saving 1500+ a year then ...
The problem is that no one can predict the future. Which of course is the price of fuel. Many people this past spring made a decision based on the cost of fuel at that time. However, based on todays fuel prices, the payback will never occur.

Then again, if the fuel prices double in the near future they may break even. Or if they triple, the payback may be within 5 to 7 years.

Al.
 
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Old 10-26-08, 03:18 PM
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I have found through the last 30 years that a boiler replaced with a heat loss calculation was 25-40%. We found out by sizing off the old boiler saved about 10 - 20%. When we started doing heat losses we saw the larger savings. Than add OD reset and maybe another 10-15%.
With that said what else can affect the fuel savings?
Flow, near boiler piping and control strategies.
The greatest savings in order of importance is boiler sizing, piping & flow, condensing(if required), control stategy, eficiency and modulation.
 
 

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