Seattle - Gas, Electric and Water Usage
While this section is about measurable performance, there is also an analysis of what worked and what didn't in the epliog.
Energy
Our gas bills are started out lower than expected, then went up to higher than expected and stayed there, the major factor apparently being flaws in the projection.
In July 2005 we added a 3KW PV system (the PV compatible meter came in l Aug). We subsequently continued to do minor improvement in efficiency. Starting in Jan 2005, we began contributing $6 per bill to the green power program (the costs listed included that $6). Here is our gas/electric usage thru March 2010:
| Month | gas (btus) | cost | elec (kwh) | cost |
|---|---|---|---|---|
| Apr 2004 | 1,050,000 | $14.88 | ||
| May 2004 | 940,000 | $13.96 | ||
| June 2004 | 830,000 | $12.95 | 699 | $39.15 |
| July 2004 | 620,000 | $11.14 | ||
| Aug 2004 | 720,000 | $12.02 | 790 | $47.25 |
| Sept 2004 | 620,000 | $11.46 | ||
| Oct 2004 | 2,870,000 | $35.07 | 1022 | $61.51 |
| Nov 2004 | 4,500,000 | $51.70 | ||
| Dec 2004 | 5,190,000 | $58.71 | 1109 | $67.57 |
| Year Total | 17,340000 | $221.89 | 3620 | $205.58 |
| Jan 2005 | 4,400,000 | $50.72 | ||
| Feb 2005 | 2,470,000 | $31.32 | 1318 | $80.32 |
| Mar 2005 | 1,700,000 | $24.49 | ||
| Apr 2005 | 1,790,000 | $25.39 | 912 | $53.09 |
| May 2005 | 1,040,000 | $17.60 | ||
| June 2005 | 1,040,000 | $17.53 | 977 | $68.37 |
| July 2005 | 720,000 | $14.20 | ||
| Aug 2005 | 820,000 | $15.29 | 672 | $43.18 |
| Sept 2005 | 830,000 | $15.70 | ||
| Oct 2005 | 1,260,000 | $21.83 | 293 | $24.25 |
| Nov 2005 | 4,640,000 | $62.36 | ||
| Dec 2005 | 4,980,000 | $66.38 | 388 | $48.42 |
| Year Total | 25,690,000 | $362.81 | 4560 | $317.63 |
| Jan 2006 | 5,050,000 | $67.24 | ||
| Feb 2006 | 3,240,000 | $45.58 | 752 | $42.46 |
| Mar 2006 | 1,920,000 | $29.77 | ||
| Apr 2006 | 1,900,000 | $29.49 | 390 | $23.42 |
| May 2006 | 1,150,000 | $20.42 | ||
| June 2006 | 720,000 | $15.32 | 213 | $20.20 |
| July 2006 | 410,000 | $11.61 | ||
| Aug 2006 | 930,000 | $17.79 | -59 | $9.44 |
| Sept 2006 | 730,000 | $15.69 | ||
| Oct 2006 | 2,540,000 | $40.04 | 341 | $25.87 |
| Nov 2006 | 4,530,000 | $66.26 | ||
| Dec 2006 | 4,870,000 | $70.65 | 764 | $43.15 |
| Year Total | 27,990,000 | $429.86 | 2401 | $164.54 |
| Jan 2007 | 6,541,000 | $95.26 | ||
| Feb 2007 | 4,082,000 | $63.01 | 614 | $35.39 |
| Mar 2007 | 3,827,000 | $59.65 | ||
| Apr 2007 | 2,438,000 | $41.24 | 367 | $25.64 |
| May 2007 | 1,055,000 | $22.82 | ||
| June 2007 | 1,044,000 | $22.67 | 76 | $14.51 |
| July 2007 | 1,028,000 | $22.48 | ||
| Aug 2007 | 931,000 | $21.17 | 36 | $13.48 |
| Sept 2007 | 1,992,000 | $34.40 | ||
| Oct 2007 | 2,978,000 | $43.18 | 315 | $23.58 |
| Nov 2007 | 5,509,000 | $72.44 | ||
| Dec 2007 | 8,248,000 | $104.34 | 749 | $40.19 |
| Year Total | 39,673,000 | $498.32 | 2157 | $152.79 |
| Jan 2008 | 6,972,000 | $89.56 | ||
| Feb 2008 | 5,057,000 | $67.37 | 716 | $29.34 |
| Mar 2008 | 5,925,000 | $77.45 | ||
| Apr 2008 | 3,736,000 | $52.12 | 366 | $25.50 |
| May 2008 | 2,305,000 | $35.52 | ||
| June 2008 | 2,394,000 | $36.56 | 133 | $16.55 |
| July 2008 | 1,554,000 | $26.81 | ||
| Aug 2008 | 1,241,000 | $23.18 | 10 | $12.41 |
| Sept 2008 | 1,460,000 | $26.18 | ||
| Oct 2008 | 2,125,000 | $36.81 | 178 | $18.63 |
| Nov 2008 | 3,742,000 | $60.45 | ||
| Dec 2008 | 8,446,000 | $123.03 | 475 | $30.28 |
| Year Total | 44,907,000 | $657.64 | 1878 | $132.71 |
| Jan 2009 | 6,529,000 | $97.53 | ||
| Feb 2009 | 6,293,000 | $94.09 | 932 | $46.88 |
| Mar 2009 | 4,969,000 | $76.57 | ||
| Apr 2009 | 3,426,000 | $56.26 | 1043 | $61.42 |
| May 2009 | 1,989,000 | $37.00 | ||
| June 2009 | 1,557,000 | $30.99 | 27 | $13.05 |
| July 2009 | 1,236,000 | $26.80 | ||
| Aug 2009 | 1,663,000 | $32.37 | 27 | $12.96 |
| Sept 2009 | 1,677,000 | $31.48 | ||
| Oct 2009 | 3,089,000 | $43.77 | 289 | $22.71 |
| Nov 2009 | 5,505,000 | $69.68 | ||
| Dec 2009 | 6,780,000 | $83.35 | 660 | $37.61 |
| Year Total | 44,703,000 | $679.89 | 2978 | $194.63 |
| Jan 2010 | 4,204,000 | $55.78 | ||
| Feb 2010 | 3,240,000 | $45.43 | 459 | $32.76 |
| Mar 2010 | 3,771,000 | $51.21 |
Gas usage analysis:
Our predicted heat loss was 9854.7 BTU/deg/day, or about 44Mbtu for a 4500 degree day year, of which our guesstimate was that 7-9Mbtu of that would come from passive solar, so we'd need about 36Mbtu of supplemental heat. Note that internal gain isn't factored here because degree days already accounts for it, in fact the flaw in using degree days is that it assumes a standard amount of internal gain, and hence is adjusted down to 65F instead of the more normal interior temperature of 68F or 70F. So if our internal gain is low, we'd actually need more than 36Mbtu/yr. Our internal gain is ballpark 15Mbtu, which is maybe half of typical, so based on that the expected energy use would be about 52Mbtu/year.
During our 1st two and a half years of occupation, we used around 27MBTU a year, which is lower than our expected, hence was probably an anomaly. After that our use has been more like 45Mbtu/year--at least until we started leaving for much of the winter. Interestingly enough, 45Mbtu/year + 7Mbtu from passive solar is 52Mbtu/year. But since that doesn't account for hot water use, dryer and cooking use, some number is wrong by a bit. At least the predicted and actual sort of match, but there are so many guesses in the estimate, that's about all you can say: it looks good.
But then it still begs the question, why did our use go up? For one, the base use went up 500Kbtu/month (ie summer use), and some of this is probably due to leaving the tank set at 160F instead of 140F (ie tank A=40SF, U=.1, Delta-T=20, or about 57Kbtu/month), but the rest would have to be due to more usage of hot water, dryers & cooking. The rest could only be due to having the thermostat set higher or some system not working right. I suspect the thermostat was set higher, because from 2010-2014 we've been gone more, and usage has gone back down significantly to more like 30Mbtu/year.
Comparison to other houses:
Another way of looking at this is in energy used per square foot of heated space, or energy use per finished space. Our finished space is around 2500, and our heated space is about 2900SF. Our total energy consumption is ball park 52Mbtu/year (gas+electric), so for heated space that's about 17,900Btu/SF/yr, or for finished space its about 20800Btu/SF/yr.
The best baseline comparison is from the dept of energy website http://buildingsdatabook.eren.doe.gov/TableView.aspx?table=2.1.12 , which lists newer single family residential houses as using about 44,700 BTU/SF/year, and 58,700Btu/SF/yr for all houses. I also found alternative values for new houses down near 30,000BTU/SF/Year, which is probably a more valid comparison. Just based on straight utility averages for comparable homes, Seattle city light says that the average usage is 9200Kwh a year, and Puget Sound Energy says the average is 700 Therms(70MBtu), although I have no idea what the average house size those numbers represent. In my view these comparisons aren't really apples-apples because electric use is reasonably dependent on the number of occupants, plus our house includes a rental unit. Ignoring these issues, we use at most only half the energy of the average house, and possibly as little as 1/3.
Yet another measure I found is from www.2010imperative.org, a site dedicated to reducing energy use in buildings. They use essentially the same baseline usage (44,700BTU/SF/year), and say we need to cut that number in half immediately, and by 90% by 2025. In 2006, at 14KBTU/SF/year I'm already about 70% lower, but further lowering will not be easy (click here to read about the difficulty of building zero energy/zero carbon homes). Subsequently, my value of 20KBTU/SF/year is just over 50% better.
2010 update: we had a leak in the heating system in feb-mar, which when it was found was spraying water at the rate of a few gallons an hour. (We didn't measure the rate, its just a visual guess). The leak probably started slowly, but may have been spraying for a few weeks. No one noticed until there was mold. How much this affected gas use is unclear, but the resulting usage of fans sure drove up electric use. Our February use is also high, but there is no obvious reason.
Electric usage analysis:
Our electric usage is mostly for the 2 refrigerators, lights, computers and other electronics and the various equipment motors. I use a kill-a-watt meter to measure most of the plug loads, and hence target which phantom loads to remove. I also installed a meter on the ADU in May 2007 to measure their consumption, which for the first year came to 2100kwh (out of about 4500 total for both units, including HVAC and other equipment). This isn't completely out of range, since they have virtually all the same load requirement, plus an electric stove, a less efficient dish washer, and a refrigerator that uses nearly twice as much electric. Upgrading their fridge would lower their use by about 300kwh/year. Now slightly more than seven years later, the meter reads 22,600kwh, which comes out to more like 3000kwh/yr.
For electric comparison, I ran the city's resource calculator: http://www.seattle.gov/conserve/homeprofile. That showed by data for Jun 21, 2004 thru Jun 21,2005 (pre PV install), so its a good comparison of our actual use. In that period, we used 17Kwh/day and the average comparable house used 25Kwh (single family with no electric Heat or H/W). Since we have an ADU, our comparable usage is pretty good, although a more fair comparison would probably be based on number of occupants. During the last year, we converted a significant portion of our lighting to CFLs, and upgraded one computer. Unfortunately the hibernate feature on the new computer works only when it feels like it, and the hibernate feature on the computer in the ADU doesn't work at all. In addition the refrigerator in the ADU uses 2.2Kwh/day, which could be reduced to 1.1Kwh/day by buying a new one. See PV section for info on the PV aspect.
Our PV generation started at about 2500kwh/year and and is now just under 2200khw/year.
Update: Jan 2014: I've stopped entering data because the only difference is due to occupant behavior. We've worked to get our electric usage down by putting as many things on plug strips as we can, but in the meantime usage has gone up in the ADU. Alas, the output of our PV system keeps shrinking: age would account for some of it, but the two trees that partially shade it have both gotten bigger, so that is more likely the bigger factor. Unfortunately the fix in both cases would be to top them, which is not good for the tree so this probably won't happen.
On a more subjective basis, we find this is the most comfortable house we've ever lived in: there are no perceptible drafts, and when the thermometer says 70, it feels relatively warm even when its fairly cold out. The one exception is in sitting by windows, which alas still have relatively cold surface temperature. One other thing, is that the upper floors are no warmer than the lower floors. On cool sunny days, the main floor gets a bit warmer than any other floors because it has more window area per square foot of floor. In early 2005, we had unusually long sunny spell, and as a result we were often able to go days with little or no supplemental heat.
One positive surprise is how well the house performs on hot days. Even when the temperature was in the 90s out, the house never got warmer than 76, provided we kept the windows open all night and closed them by 10am or so.
Water Usage
In spite of not being able to use rainwater for toilets in the summer, our water use, remains very low. Here is a chart of our water usage:
| Usage Date | Usage (gallons/day) | Cost | Sewer+Water |
|---|---|---|---|
| Apr-Jun 2004 | 84.5 | $32.24 | $56.11 |
| Jun-Aug 2004 | 105 | $40.64 | $58.34 |
| Aug-Oct 2004 | 112 | $37.98 | $55.68 |
| Oct-Dec 2004 | 114 | $36.34 | $81.70 |
| 2004 Avg | 103.9 | $36.79 | $62.95 |
| Dec-Feb 2005 | 103 | $33.58 | $84.82 |
| Feb-Apr 2005 | 84 | $31.97 | $78.03 |
| Apr-Jun 2005 | 81 | $33.73 | $79.79 |
| Jun-Aug 2005 | 81 | $33.96 | $80.02 |
| Aug-Oct 2005 | 96 | $35.81 | $88.45 |
| Oct-Dec 2005 | 62 | $26.45 | $59.35 |
| 2005 Avg | 84.5 | $32.58 | $78.41 |
| Dec-Feb 2006 | 98 | $34.27 | $88.02 |
| Feb-Apr 2006 | 26 | $18.40 | $31.92 |
| Apr-Jun 2006 | 98 | $35.97 | $75.06 |
| Jun-Aug 2006 | 72 | $32.68 | $66.48 |
| Aug-Oct 2006 | 123 | $42.17 | $75.97 |
| Oct-Dec 2006 | 47 | $25.76 | $52.80 |
| 2006 Avg | 77.3 | $31.54 | $65.04 |
| Dec-Feb 2007 | 78.7 | $30.21 | $73.97 |
| Feb-Apr 2007 | 84.5 | $34.35 | $86.50 |
| Apr-Jun 2007 | 98.1 | $38.08 | $92.71 |
| Jun-Aug 2007 | 156.8 | $55.33 | $107.48 |
| Aug-Oct 2007 | 124.7 | $43.09 | $95.26 |
| Oct-Dec 2007 | 108.6 | $39.41 | $103.26 |
| 2007 Avg | 108.6 | $40.07 | $92.20 |
| Dec-Feb 2008 | 99.7 | $38.96 | $100.40 |
| Feb-Apr 2008 | 122.6 | $45.31 | $122.81 |
| Apr-Jun 2008 | 110.4 | $43.92 | $113.67 |
| Jun-Aug 2008 | 142.5 | $55.01 | $124.76 |
| Aug-Oct 2008 | 88.7 | $37.70 | $91.95 |
| Oct-Dec 2008 | 73.6 | $34.83 | $81.33 |
| 2008 Avg | 106 | $42.62 | $105.82 |
| Dec-Feb 2009 | 139.45 | $51.78 | $146.38 |
| Feb-Apr 2009 | 124.66 | $52.00 | $140.90 |
| Apr-Jun 2009 | 120.64 | $58.29 | $147.19 |
| Jun-Aug 2009 | 172.61 | $81.47 | $179.26 |
| Aug-Oct 2009 | 156.63 | $68.94 | $166.73 |
| Oct-Dec 2009 | 93.5 | $44.55 | $106.78 |
| 2009 Avg | 134.6 | $59.50 | $147.87 |
| Dec-Feb 2010 | 71.23 | $46.53 | $100.27 |
Our usage is nominally for four people, but we've been traveling about two months a year. Countering this is the fact that we work at home, so we're home more than most people. I'm guessing that the drop in usage for the Mar 2005 billing was due to the rainwater tank working, and the rise in Sept 2005 was due to the pump breaking. The low number for Nov 2005 is probably due to all of us being away a lot in Sept & Oct.
The low number in Feb-mar 2006, is again due to travel, and the higher number in Aug-Oct is because we ran out of water in the rainwater tank and had to hand water plants for a three weeks or so.
Update Jan 2009: Our water usage has crept up, possibly because we're home more, possibly just because we use more water. Still, with four occupants, our usage per person remains remarkably low. The higher water use may indicate more hot water use, which may be part of the reason for higher gas usage.
Update Apr 2010: our water usage has crept up again, with the dec-feb 2009 usage being inexplicably high. The Feb-Apr usage includes somewhere between 20 and 50 gals/day due to the leak, but then weren't home then, so the Apr-Jun period is similar. The summer was the hottest & driest I could remember, and as a result I was hand watering my not exactly drought tolerant landscaping.
Update May 2014: our water usage has now stayed stable. The rainwater tank now works reliably, but we still run out of water in later summer and have to water some plants by hand. We use 25-30 gal/day/person, and an extra 30gal/day or so when we have to water the yard.