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#368555 - 31/03/2017 19:17 Calculating energy costs
Dignan
carpal tunnel

Registered: 08/03/2000
Posts: 11866
Loc: Sterling, VA
How do I calculate the cost of electricity and gas that's devoted to the heating and cooling of my house during the year? We have a gas furnace, but we use the same gas in our stoves and hot water heater. And I don't know how to calculate the electricity used specifically for the fan in our forced-air system and the compressor during the summer.

I'm curious about these numbers because I'd like to compare them to the cost of replacing components and/or making the house/HVAC system more efficient.

What advice do you folks have?
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Matt

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#368556 - 31/03/2017 20:26 Re: Calculating energy costs [Re: Dignan]
K447
addict

Registered: 29/05/2002
Posts: 584
Loc: Toronto, Ontario, Canada
No easy answers.

But you can start by comparing natural gas consumption during winter periods compared to summer periods. Presuming the hot water and cooking gas usage is similar year round, the delta will mostly be the furnace consumption.

Further math can normalize the furnace usage against 'heating degree days' during each heating season (or billing period). A colder winter will require more fuel, sometimes knowing how they correlate for your particular house can be useful, or not.

Furnace fan I don't worry about so much. In winter the electricity used to run the circulation fan effectively becomes heat into the house interior, so a bit of electric heat instead of a matching bit of natural gas heat. Any savings would be mostly the delta between gas and electric for the marginal cost of that energy,

Air Conditioning electricity cost, similar rough calculation comparing spring/fall and peak summer electricity consumption. Exclude the dark winter months when more indoor lighting is used. Again the 'cooling degree days' math can be applied.

Spring and fall moderate temperature periods would be your baseline approximation for electricity and natural gas consumption. Little need for AC or heating during those times.

Tip: Do not just look at the dollar costs per time period. Work from the actual fuel/electricity usage as the pricing of these can vary from year to year and season to season.

if your utility has significant delivery and customer charges/fees those can be a significant portion of the bill total, and may not change in direct proportion to reduced consumption.


Edited by K447 (31/03/2017 20:32)

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#368557 - 31/03/2017 21:14 Re: Calculating energy costs [Re: Dignan]
tanstaafl.
carpal tunnel

Registered: 08/07/1999
Posts: 5284
Loc: Ajijic, Mexico
[quote=]I'd like to compare them to the cost of replacing components and/or making the house/HVAC system more efficient.

What advice do you folks have?[/quote]

One of these. It cut my gas usage from about 12,000 pesos per year down to about 3,000 pesos per year, or a savings of about $450 USD per year. Cost of product and installation amortized in less than two years. You will not see a similar percentage reduction in your bill because in my case the hot water heater was my biggest gas expense; in your case it is more likely the furnace. But you should see a similar dollar savings. Or maybe not. You don't have as much solar input as I do high in the mountains of central Mexico.

tanstaafl.


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#368558 - 31/03/2017 21:51 Re: Calculating energy costs [Re: Dignan]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30578
Loc: Seattle, WA
Originally Posted By: Dignan
How do I calculate the cost of electricity and gas that's devoted to the heating and cooling of my house during the year?


I'd guess the easiest way would be seasonally. Since there are some months when you're only heating, and some months when you're only cooling, and perhaps some months at the cusps where you're doing neither. And your other nonheating and noncooling electric and gas usage is probably really similar across the board, so that's your noise floor on the cusp months.

My local utilities put nice little seasonal usage charts on my gas and electric bills. I think they do that to help people in your position, since their computers already have all that data and so it's easy to do the calculations automatically. Though I think they do it poorly: Their charts seem to like comparing things that are useless to me, such as my usage in March this year compared to March last year, or comparing my usage to my neighborhood average.

Still, the data is there in your montly bills and I'll bet you could suss out your winter above-baseline gas heating rate, and your summer above-baseline electric cooling rate, just by doing a little data mining.
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Tony Fabris

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#368559 - 31/03/2017 23:48 Re: Calculating energy costs [Re: Dignan]
Shonky
pooh-bah

Registered: 12/01/2002
Posts: 1914
Loc: Brisbane, Australia
Fit a gas meter on the line to the furnace? Would need a plumber of course.

For the electricity, a clip on CT (along with voltage) should be able to do what you need as long as the CT is placed after everything else but before your consuming devices. Needs to go only on one leg. I presume it's big enough that it's not a standard outlet.

I have this running on a Raspberry Pi (with a 14 channels of CT). I only have 7 CTs all running the main load at the moment and it's well within the rated accuracy of the utility supplied meter (i.e. <1% error). Can log pretty much anything it can measure at any frequency and has fully customisable dashboards. See https://openenergymonitor.org/ . It can be done fairly safely too with low voltage isolated measurement of the voltage and only a clip on CT.

There are other devices that try to "guess" based on the main load only. i.e. it knows the fan is a 1000W fairly resistive load so if it sees a jump in the main consumption of about that amount, it attributes it to the fan. A lot of assumptions and two loads nearly the same could not be differentiated. e.g. http://www.smappee.com/be_en/energy-monitor-home

If it runs on a separate circuit in you switchboard, you may be able to fit a DIN rail meter and just take manual readings too.
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Christian
#40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)

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#368575 - 06/04/2017 03:57 Re: Calculating energy costs [Re: Dignan]
Dignan
carpal tunnel

Registered: 08/03/2000
Posts: 11866
Loc: Sterling, VA
Thanks, folks. I'll look at our bills and see if I can make any conclusions from them. The annoying part is that I believe we are billed quarterly for our gas, and I'm not sure how detailed the bills are. Thanks again, and hopefully I can improve on our HVAC costs...
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Matt

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