Wednesday, April 12, 2023

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?

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 

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.

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