Energy Cost Tracking Through Decades of Actual-Cost Data, Charted in Microsoft Excel, Two Example Homes

This post is a further challenge of home energy-efficiency rating as a home owner asset for real estate purposes.  Why shouldn't we just rely on actual operating costs as measure of home energy efficiency?  (Google that, and the question is not recognized. Far down the results, a UK EPC, Energy Performance Certificate  is discussed; and no, it is not on-topic.) 

For any home, there is no better measure of energy efficiency than actual utility-cost data. That data will have complexity. Whatever, it will be more real and inspiring than transitory numbers of some rating scorecard. Every improvement or degradation nullifies a score; cost data is perpetual.

Where cost-tracking is continuous, it becomes useful for verifying effects of a continuous process of home improvement and varied usage. Is a new appliance working correctly and as-claimed? What costs are seasonal, or dependent on the number of house occupants? A home energy score is if anything, a drag upon making changes.

Here is a display of monthly data of natural gas usage in my now-a-rental home, for the past eighteen years:

Annual totals for July through June heating seasons are more informative. 

See that through 2012 with the house unimproved and kept chilly in Winter, I tolerated annual cost of about $460. Improvements from 2012 to 2016 reduced the natural gas cost by half, still with Winter thermostat setting of 55°F. From 2019, the house has been a rental with an average of two occupants and comfortable thermostat setting, with return to annual cost of about $460. See that extreme economy is met with increased importance of base charges, and bills are reduced less than expected. Results with careful weatherization are unambiguous, when accomplished scattered over time. A very big further improvement is still needed: replacement of the like-new high-efficiency gas furnace with a heat pump unit. As with everything else I have done, this will happen with study, with work done and documented by-myself except the final commissioning. I hope to find a good  Heat Pump Coach , as advocated in today's email feed of Onward Oregon . I hope I will be favored with early access in this, for my role as a reporter. I aim to be a good reporter in the similar matter of Heat Pump Water Heater evolution, where I have coped with an early-technology failure. I learn by doing my own work, but must not fail to benefit from a depth of experience.

Now look at to-date electricity usage:

Large consequence of a  heat pump water heater failure is evident in  tracking of electricity consumption in my now-rental home. Large electricity savings with  a 40 gallon Rheem Professional Prestige ProTerra Hybrid Electric Water Heater PROPH65 T2 RH375-SO, were wonderful, for one year. I have detailed the factory-offered repair in replacement of the control board, which did no lasting good.   Electricity usage rose to a brief historic high at year-end 2022. At last the 40 gallon Rheem HPWH was scrapped.

Such an undignified end for my "exceptional" first-try HPWH. Nothing in the nearly-new unit was of interest for salvage. Rheem provided a replacement at no cost except that of increasing size from 40 gallons, to 50 gallons. Perhaps renters used exceptional amounts of hot water, that forced generation with resistance heaters. A bump-up in size might not help, but give it a try.

House in transition, it will take several months to know that weird electricity consumption is at an end, with this brand-new 50 gallon Rheem heat pump water heater.

PRO H50 T2 RH310UM

SN 0322208450

Wall Pads; that's what I'll call the four wood assemblies that, with ropes, secure the position of the tank in the event of an earthquake. The 40 gallon tank was 20.25" OD. This is 22.25" OD. To accommodate the change, I reshaped the painted-white 2x4s, and moved each pad assembly an inch away from the walls corner. I am serious in belittling the steel straps sold for this. What, really, do they anchor to? The 3/4" plywood at the wall is anchored to the wall studs by 3" deck screws. How could steel strap-ends conveniently align with wall studs? Earthquake loads are lateral, for sure splitting the  studs at bending lag screws. Here with diagonal 1x8 shiplap behind 5/8" drywall and very many pad screws, this tank is anchored.

Isn't this an exceptional installation?










At April 2024, note new professional acclaim of this Rheem model, by highly-followed YouTube creator Matt Ferrell: https://www.youtube.com/watch?v=abGiNL9IT54

Know that I maintained 1/4" per foot downward slope of drain lines all the way to this new high point.

See that with vent and drain plumbing behind the wall, in the now-conditioned crawl space, it was easy to create a new P-trapped drain for HVAC. The little Tygon tube for high-efficiency gas furnace condensate, no longer dangles across steps to a utility sink. The convenient dedicated drain will accommodate more drainage from heat pump HVAC.

With the new 50 gallon HPWH, in time, I expect to see lasting return to annual electricity cost of about $500 per year. Judging that electricity consumption is not seasonal, prefer annual totals for calendar years. 

Conclude that with two-person occupancy as a rental, my well-documented energy-efficient home has annual natural gas cost of about $470 per year. The total electricity cost is also  about $470 per year. Elimination of natural gas service would reduce natural gas cost by about $200 per year, and increase electricity cost by about $100 per year. The home draws about 4000 KWH per year, ahead of a conversion to heat pump HVAC.

Can I know how my house measures up to standards? A resource of interest to me in learning tried better methods of house construction - - is Portland, Oregon 501 (c)(3), Earth Advantage . I look to them now.

Compare energy efficiency of my well-improved 1000 sf house, to that of a 832 sf super-well-built single-story ADU built in Portland in 2020. Consult this training video , at time 9:31:

$45 per month energy cost, per-year, scaled to 1000 sf: $649 per year. Presume that the EPS-label energy cost is the sum of electricity and natural gas costs.  For my house that sum is a bit less than $1000.

I hope that Earth Advantage collects and studies actual-cost data, now two years of it here. A score that has physical meaning, is interesting.

My house has room for doable improvement, probably by less than $200 per year. Compared to neighboring homes, mine surely is very efficient.

Actual Decades-Long Cost Data for Another Home, Where I Improved the Attics

A two-story Ranch home in Sandy, Oregon:
Now begin charting for another home with extensive energy usage data, that of my older sister, whose house has also been improved by my weatherization.  I look for proof that my work produced savings, and seek to learn more about what constitutes good record-keeping, and charting in MIcrosoft Excel.

This is a two-story home well-built in 1973, 2052 sf conditioned space. Heating is also natural gas, with no air conditioning. Expect natural gas cost to be more than double that of my 1000 sf single-story home, with nearly-same electricity cost.

This home and its natural gas usage history were described in a previous post, October 23, 2012, Making Sense of Gas Usage History . There see detail of very-substantial attic floor sealing and added insulation.

An additional decade of data is interesting. Was the Winter of 2020 exceptionally cold; or staying warmer and healthy in the epidemic? This home used more than twice as much natural gas than mine, from the same supplier, Northwest Natural, and at reduced dollars per therm. There were years before the weatherization where fewer therms were used. Were they exceptionally mild? What happened in 1997? Whatever the complexities, I think the charting is a rewarding exercise. We're doing good things. What will we see if now there is conversion to heat pump HVAC? History matters.

See annual natural gas usage of about 1200 therms, $1000, as expected.

See electricity usage well-tamed by LED lighting and technology improvement in appliances and connectedness to information, costs steadily declining, while approaching a doubling of electricity rates.

The annual electricity cost is nearly double that of my 1000 sf single-story home. That's a bit surprising.

See consistent Excel charting with some different trial of logic for colors.

The Odd Insulation Math of US Department of Energy, Home Energy Scores

The following is public sharing of one persons' trial of US Department of Energy's Home Energy Scores Tool. The tool is a product of SRA International, Inc., in public ownership through US Government contract.


In a first post, I address access to the HES tool, and then finding of odd math of USDOE in dealing with a divide-by-zero problem in conversion of R-value to U-value, done stupidly as simply a number inversion of the insulation-only R-value. Energy is transmitted through resistances in addition to those of conduction through insulation and framing. The additional "surface" resistances are substantial and well known, though variable in every path. Where the savings achievable in any bid of weatherization must not be over-estimated, a highest value of surface resistance generally applicable, is wanted. In a derivation of Insulation Math , I offer that the wanted round number as a resistance value in USA units, is 3. 

Google search "u-value of an empty wood-frame wall "  finds this number affirmed by Colorado Energy and by Build It Solar .

USDOE sets a wildly low surface resistances number, 0.4 without explanation. Perhaps such is possible for a shed with very-perforated walls. This might be in an odd very mild climate, else not habitable. 

As insulation varies in effectiveness from full to worthless, energy waste changes in linear fashion in proportion to a Transmission Coefficient, U. A realistic particular situation must be considered to understand consequences of the USDOE error. Let that situation be a 2x4 @16 framed wall with at best R15 full filling of insulation .

With best insulation and correct usage of value 3 surface resistance, computed U-values are reasonably close, 0.063 my number vs. 0.087 by USDOE.  With worst insulation, none, 
my U-value is 0.316, just a bit less than if a wispy wall had no framing thickness, U=1/3. At this condition the USDOE U-value is 2.28, over-estimating energy transmission and heating cost by a multiple of 7.2, roughly 3/0.4 = 7.5. Aside from other allowance by a Insulation Derate Tool, the wrong USDOE math will lead to excessive shaming of found conditions and to large over-estimate of weatherization benefits.  The whole USDOE process will fail to discover and report that perfect, fullest placement of insulation is absolutely required in weatherization. Perfect full-filling coverage is far more important than insulation depth or available thickness. The USDOE hire-an-interest-conflicted-auditor process will often lead to hiring of the auditor to pile more crummy insulation on top of a bad situation not repaired, doing more harm than good.



Content at this post will grow as I critically examine and try tools and the scoring process. Large errors found, will justify this examination.

Content for Home Energy Assessor Candidates is at beta.homeenergyscore3dtraining.com.
As I work in this online as a candidate, I am forced to employ a laptop computer with 64-bit OS and with unbearable difficulty of scrolling on the small screen. Offline I transfer lessons learned to my capable desktop computer running 32-bit but with large screen and other needed advantages. I must choose a 32-bit OS and hence 32-bit browsers with the desktop setup. I employ 32-bit to not give up important old software. HES training resources behave better on this full size desktop computer, employing the links that follow.

Primary Resources:

Introduction Video

https://www.youtube.com/watch?v=2_XXBonQubk

Sim User's Manual

https://docs.google.com/presentation/d/1v7HozriVAk3aiE_NfSkxGF3DwmOP-q1htcZ5LKiWWzU/edit#slide=id.p4

Here be sure to find critical information at Slide 6, not mentioned anywhere else:

"Driving" through a simulated house is not intuitive, and will be happily forgotten, irrelevant to life.

Step-By-Step Guide to Training House #1

https://docs.google.com/presentation/d/1g6xNpYC934hHx1Ieqc20YcaMQC9g5bs5b-mZkQbgPVc/edit#slide=id.p4

Step-By-Step Guide to Training House #2

https://docs.google.com/presentation/d/1Gv3Yo4wOnZnffy_QLzd_FxrmJcHCDVmkWWf_KZnVBoE/edit#slide=id.g1a6247c8e3_1_0

Home Energy Score Overview (Part II Study Guide)

https://docs.google.com/presentation/d/1q8Tkfcx8YvHpKMWogKDcIZ_dFe8707OMslVoncp-p8Y/edit#slide=id.p4

Beware: This slide show contains the information needed to pass the final step in the assessor training, a twenty-question quiz. Read at Slide 2:

You will need to study this presentation to pass the Assessor written exam.
Print its 26 pages, and consult them as you sift through the multiple choices for each question. It isn't a "Part II Study Guide". It is the Multiple Choice Test answer key that you would surely have in hand if you have paid for assessor training.

Assessor Calculator

A URL for the calculator download is not offered. The online download is an Excel 2010 file usable only with Microsoft Office 2007 and newer. Such commercial offering is inconsistent with US Government policy. Here then is a free version of the calculator:

https://docs.google.com/spreadsheets/d/1xfPr0NgL53ZyMq5yVzXrarN12onuHQbsKDyXNYryRlM/edit?usp=sharing 

Secondary Resources:

Part 1: About This Home

https://docs.google.com/presentation/d/1ISUgyl4ORwd2N01e9JeCzRq8WboXL3iBO0BZ5fXdsuM/edit#slide=id.g106ee94aeb_9_22

Part 2: Roof, Attic & Foundation

https://docs.google.com/presentation/d/1mmM8znmYz9ZD5ZxmdsB7bOAuL-9t-TSZC-mvQpd6Rsw/edit#slide=id.g106f121b6e_4_22

Part 3: Walls

https://docs.google.com/presentation/d/1ZZr6vtyjNPVp7myqb91_VUA3dbFcyDiFXPTF_yBEH40/edit#slide=id.g106f03cc8a_2_22

Part 4: Windows & Skylights

https://docs.google.com/presentation/d/1XUq4oACRw9BIz5i3o01UtHtvRLxhZcB3HOmMt-pSI1U/edit#slide=id.g106f22e042_2_22

Part 5: HVAC & DHW Systems

https://docs.google.com/presentation/d/1MuJ3FFXUocEK6U2WKiMTYcVBB58blUuRTqeT6AprkU0/edit#slide=id.g106ef0ca3f_2_22

Extra Resources:

Building Science

https://docs.google.com/presentation/d/1xChpAXRMkjhSUNRFBLLLvHNKXQvUw5u597vMwaGcwZ8/edit#slide=id.g348f11ae0_2_170

Remaining content is accessible only to those admitted to the beta web site.

3D Practical Training

House #1

House #2

House #3

3D Practical Test

Multiple Choice Test

User Review

(Submit feedback to SRA.)

Assessing The Assessor Calculator Tool:

The goal for existing home energy efficiency ratings shall be that anyone can find a score by himself if such has value, and with that believingly see how home improvements can move the score. Improvement is the need, not assignment of nonsense scores that do not motivate home improvements. There must not just be instead, an enrichment of cooperating organizations and auditors, in an absurd system. A home owner must find only self interest in the engagement with home-quality scoring mandates. We must not tolerate any involvement of persons not thinking first of the home owner interest.

Please see calculation as I perform it, superimposed on the insulation averaging portion of the HES calculator: 

https://docs.google.com/spreadsheets/d/1VjFHWQPSRtP56HNuzTgrB5CfVgG_m7XaRTjZ_DQB9jc/edit?usp=sharing

Applied math is evident in spreadsheet cell definitions:

For each of several parallel paths:

A pathway contribution of U-Value where all pathways add to 100% of path areas: This is simply (Fraction of Total) * (Path U-value). I can readily define as many parallel paths as are needed, typically four or more.

The HES Averaging Calculator imagines at most three parallel paths and poses for each a computed value UA, for example at Cell B30:

UA =B29/IF(B28=0,0.4,B28)

where B29 is a path's percentage of the total of all path areas, and B28 is the R-value of that path and has value not less than 0.4.

For this path in the first column at the Google Sheets link, HES computes 1.250 for a tiny piece of uninsulated drywall, an evil access hatch, and I correctly compute Ui = 0.005*0.333 = 0.00167, and 100*Ui = 0.167.

Average U-value, called "Cavity U-Factor," is simply the sum of values of (Fraction of Total) * (Path U-value). Instead, the tool poses a calculation such as:

B38 =(IF(B30=0,0,B30)+IF(B33=0,0,B33)+IF(B36=0,0,B36))/(IF(B30=0,0,B29)+IF(B33=0,0,B32)+IF(B36=0,0,B35))

computed by HES calculator for this path as U = 0.074, then inverted as R = 13.52. 

For this attic floor with well-placed R19 batts, joist thermal shorts and, a little uninsulated hatch, I correctly compute U = 0.0519, then resolved as inverse minus 3, value R = 16.28.  At the next column, see that if the hatch is fully insulated R19, floor values change very little: U = 0.0504, R = 16.83.

CONTENDING WITH HYPE 

We must counter false statements such as this of 1999, Don’t leave a hole in the ceiling ,  passed along by Habitat for Humanity, as written by southface.org:. It is way past time that the offending web page should be deleted or disconnected. Attic access is necessary, not evil. USDOE and Lawrence Berkeley Lab have not gotten the message. In wanting to demonstrate evil of a hatch if without an absurd stapled batt-on-top, the training considers a hatch 5% of floor area, perhaps of dimension 2 ft by 25 ft with a 1000 sf floor!

I wonder about behavior of complex if-statement HES calculator cell definitions that avoid a divide-by-zero problem. Examine this with study of a 2x4 wall that is well insulated with R16 batts, then with increasing decrepitude of the insulation batts as missing or not in contact with bypass:

https://docs.google.com/spreadsheets/d/1nixHgs42iPZKq3UvB0Au3gl7_dr7mNhstf4_dM-wBqw/edit#gid=1218195801

Observe linear drop-off of value with decrepitude. Present again the tables at the top of this post:

There is not a razor's edge transition with "no insulation," but there are odd results if input no-insulation R-values in the HES calculator are less than 0.4. There is only an up to times seven error in U-value and energy cost with decrepit insulation (see discussion at top of post).

Now examine a crude provision for decrepit insulation in HES Calculator.

Here is a screen capture of the Excel form of the calculator, with function selectors in four tabs at bottom.

Where the Insulation De-rate Calculator is dysfunctional in the free version of the calculator, look instead for taught methods of USDOE perhaps mandated in Home Energy Scores, at an Insul-calcs tab now visible. 

Here, defy an unfounded and outmoded bias for blown cellulose and against all batt insulation. Want well-placed insulation of highest quality as in filling a 2x4 wall to R15, regardless of insulation form . Completely filling the wall is what matters, then stilling bypass in convective loops.A rater may not be commanded to believe the HES calculator.

Assessment must allow  there is never instruction to give allowance for joist thermal shorts or for any decrepitude, as one might then do, shown here. In fact a subsequent step of derating insulation forbids direct allowances.

 

Fair and Poor installations may in fact have large areas without insulation contact, hidden from view and having no value. Regardless, the visually-interpreted table penalties are too small.

Flawed Measurement Of R-Value With A Certainteed InsulSafe4 Gage

I want to at last dispose a gage saved from a job in which I concluded the following:
The Builders Statement of found insulation states that for intended R38, one bag covers 44 sq ft. 37 bags were applied, sufficient for 1628 sq ft. The installer was unaware of actual area  2315 sq ft, then with 30% under-fill,  R26 before discount for overwhelming consequences of missing insulation.

General fill of insulation was 10", not a goal of about 15".  A greater depth of insulation did not exist at time of construction, then lost by settling. A failure of inspection occurred, on top of a perhaps-conscious failure of math. Was compensation for the job not proportional to cost of materials?

Adjacent to the found access hole where inspection would be expected, the gage is revealed at 10" depth. By human nature, depth is less at a majority of area not accessible for inspection.

Here is a cropped photo of the gage, with marking of depths at values of common interest, a black line and arrow under-lining each named value.  For example, named value R60 is at depth 22.0".The gage corresponds to a table in PDF document InsulSafe® SP Installation Guide - CertainTeed .

Having insulation generally R26 where R38 was wanted, is mean. Call the weighted average of loose fill R24.  The overall effective R value of the attic floor is diminished by areas bare of insulation and by thermal equalization of interior walls through assorted floor openings often large. Bare areas are mainly at edges of the attic, and are typically 5% of floor area.

Do the Insulation Math , of found effective R-value:

Allow for thermal shorts of 2x8@24" framing.

1/(R_eff + 3) = f_joists/(R_joists +3) + f_{insulation in contact}/(R_insulation +3) + f_bare/3

For 2x8 framing, R_joists is  6.8.

1/(R_eff + 3) = 0.06/9.8 + .89/27 + .05/3

R_eff = 15

The work of sealing the attic floor is an insulation cost, and I think the expenditure should be encouraged by allowing its result is that of finding another 5% floor bare area:

1/(R_eff + 3) = f_joists/(R_joists +3) + f_{insulation in contact}/(R_insulation +3) + f_bare/3

1/(R_eff + 3) = 0.06/9.8 + .84/27 + .10/3

Found attic floor insulation:

R_eff = 11

The now-accessible attic has a large decked area 18.6" up from ceiling drywall, and much additional area accessible with movable flooring upon raised floor supports. HVAC ducts are more efficient and are buried under floor insulation where allowed. Conditioned space below the attic floor is 2315 sq ft.

A section of hallway ceiling ruined by step-though during electronics wiring is now occupied by a wonderful European attic ladder.

Ladder installation at a 45° diagonal across 2x8 floor joists is supported by 2x18 box beams, a first-ever feat of cleverness.

I imagine a 150 sq ft work room 8' tall from the new flooring level, at the attic space with greatest headroom. The space might be a wood shop or music room, conditioned or not. An attic has congenial temperature a portion of most days of the year.

With dispersed insulation,  f_bare is zero. One bag of R21 insulation, 89 sq ft, 89/2315 = 4% of the floor, is placed over the master bedroom loft ceiling. 5% of the floor at eaves is insulated to R30 with pushed loose fill. The remaining loose fill is 3" to 4" deep everywhere else, called R11.

1/(R_eff + 3) = 0.06/9.8 + .04/24 + .05/33 + 0.85/14

In the now-accessible attic:

R_eff = 11.

This is the same as-found, not diminished. Where this condition must exist for some time, my churn of insulation beyond just creating safe attic access, has not hurt my customer. This finding is very important to me. I hope you agree with my math. Distributing insulation to eliminate bare areas is smart, even where found unstable loose fill insulation is collapsed in the churning.

Find then:
Perfect, fullest placement of insulation is absolutely required in weatherization. Perfect full-filling coverage is far more important than insulation depth or available thickness. Where insulation has been placed carelessly, do not hesitate to trample insulation if necessary, to perfect the installation. Never delegate placement of insulation to be done without caring, in haste. The value of insulation placement is proportional to time spent.

Back to that now-disposed gage then. Don't believe it, even where it reads correctly in perhaps revealing fraud. Diligent work is harder to gage.