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so how are we doing?

Last Post 03 Jan 2011 01:13 PM by alecponting. 9 Replies.

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jerkylips

Basic Member

Posts:359

30 Dec 2010 05:59 PM
Now that we're starting to get to the time of year where we have more meaningful numbers, I'm curious how my numbers are comparing. The house we built this year is a 1985 sq ft walkout ranch with an unfinished basement. Heating is a Luxaire 98% modulating gas furnace. We have 2x6 wall, 16"OC &did a flash & batt system for insulation (inch of spray foam then R19 batts) with an inch of XPS outside. Lots of high solar gain windows on the south side. Our latest utility bill showed - 11/3-12/3 Avg temp - 36 HDD - 859 Electric usage - 390 kwh total (avg 13/day) Gas usage - 92 therms (I know rates vary dramatically, but the total bill was $148) As far as the gas usage, we have a gas dryer, & my wife does what seems to be a lot of laundry. We have a direct vent gas fireplace, & she was using it quite a bit (I think because it's new & just starting to get colder). Our old house (emphasis on old) was 950 sq ft, 50 years old, & our winter utility bills were never under $250 - so I'm happy with these numbers right now, but I know that's comparing apples to oranges. So...anyone else with a similar size, similar climate, etc, care to share their numbers or give me a "grade"?

Lee Dodge

Advanced Member

Posts:714

30 Dec 2010 11:08 PM
jerkylips- A benchmark for comparing to existing homes based on a 1997 survey is given at: http://www.homeenergy.org/consumerinfo/benchmarking-energy-usage.php which basically gives: Range of Energy Use Relative Frequency Under 5.0 BTUs/HDD/Sq.Ft. 12.2 percent Between 5.0 and 10.0 BTUs/HDD/Sq.Ft. 39.4 percent Between 10.0 and 15.0 BTUs/HDD/Sq.Ft. 23.9 percent Between 15.0 and 25.0 BTUs/HDD/Sq.Ft. 14.7 percent Over 25.0 BTUs/HDD/Sq.Ft. 9.8 percent This reference may have come from GreenBuildingTalk, but I have forgotten who or where for sure. I have just put onto the web some results for my house which is a little smaller than yours at 1602 sq.ft., and has one occupant most of the time. Home page is at: http://www.residentialenergylaboratory.com/ Natural-gas usage is at: http://www.residentialenergylaboratory.com/rel_energy_use_natural_gas.html Electrical use is at: http://www.residentialenergylaboratory.com/rel_energy_use_pv.html Lee

Lee Dodge, <a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a> in a net-zero source energy modified production house

jerkylips

Basic Member

Posts:359

31 Dec 2010 10:11 AM
Thanks Lee! Based on my numbers, the btu/hdd/sq ft comes out right at 5 - but as I think about it further, a good chunk of that 90 therms was used on laundry, cooking (gas stove) and water heating. Is that btu/hdd/sq ft calculation intended to look at total usage or only heating? I'm still curious to see where others fall on this scale..

Lee Dodge

Advanced Member

Posts:714

31 Dec 2010 12:19 PM
jerkylips- That benchmark is in terms of energy used for space heating. Natural gas usage for cooking is usually down in the noise. Gas usage for heating domestic hot water is usually significant, and the dryer might also be. You need to plot up results over a year so that you can get summertime usage when you are still heating hot water, drying clothes, and cooking. Then you can subtract that out from winter rates to estimate the amount used for space heating. I would estimate about 25 therms for the other uses besides space heating if you have a conventional gas-fired hot water heater, but lower if you have a tankless water heater, maybe 18. Of course, I pulled these numbers out of the air; you need to plot results over a season. Using this same benchmark, and counting my total natural gas usage for space heating, tankless water heater (but downstream of solar preheater), and cooking, I get about 1.5 BTUs/HDD/SQ.FT for my house. However, it looks like I will be able to offset this use in terms of source energy by excess electricity sent to the grid by the solar photovoltaic system. Therefore, count me at zero net source BTUs/HDD/SQ.FT :-) Compared to the (oddball in my mind) passive house standard of <4.75 kBtu/sq.ft./yr, my 1.5 Btu/HDD/sq.ft. for 7355 HDD translates into 11 kBtu/sq.ft./yr, so more than twice the passive house standard. However, I should get close to zero kBtu/sq.ft./yr of primary source energy, and certainly less than the passive house standard of 38.1 kBtu/sq.ft./yr. People building energy efficient homes should probably all be in the "top" category of less than 5 BTUs/HDD/SQ.FT, although a sustainable home needs to be at zero. Lee

Lee Dodge, <a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a> in a net-zero source energy modified production house

Lee Dodge

Advanced Member

Posts:714

31 Dec 2010 12:33 PM
Looking again at that website (http://www.homeenergy.org/consumerinfo/benchmarking-energy-usage.php) with the benchmark data, they may have included total natural gas or propane usage. Not sure

Lee Dodge, <a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a> in a net-zero source energy modified production house

jerkylips

Basic Member

Posts:359

31 Dec 2010 12:40 PM
my 'out of the air" numbers were about what you said - I was thinking roughly 2/3 for heating, 1/3 for everything else. Looking at the summer numbers is a good idea. We moved in July 1, so I should be able to pull some of those for comparison. I found a link to the Wisconsin Focus on Energy site that had some Energy Star guidelines and btu/hdd/sq ft calculations. The one thing I found interesting is that they include basement square footage in the calculations, even if the basement isn't heated. My original number of 5 btu/hdd/sq ft was factoring in only the first floor. if I look at the basement as well, it drops to just over 2.5 btu/hdd/sq ft. I realize that the usage is the same, but in terms of comparing to other standards, it makes me wonder if your ranges in your first reply factor that in or not..

Lee Dodge

Advanced Member

Posts:714

31 Dec 2010 12:46 PM
To quote from the website, "Next you need to calculate the square feet of heated space that is in your home." Therefore, it is only heated space. It does not make sense to me to include unheated space. I provided the link to the website, so you can look yourself and see what you think.

Lee Dodge, <a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a> in a net-zero source energy modified production house

Brock

Advanced Member

Posts:599

03 Jan 2011 11:40 AM
Ours from 11-15 to 12-15 (1128 HHD) was a bit higher, across town from you but we are in a larger house with the indoor pool. Last month our WPS will was $191 using 7 KWH on peak ($.22) and 2032 KWH off peak ($.07) with 53.3 therms. The solar array generated 94.5 kwh during the same period, mostly offsetting our on peak usage. Including our pool room we have about 3600 sq ft of heated or conditioned space. Typically kept about 72F Comparatively last month was high for us, I think mostly because the kids (8,7,5 and 4) are starting to take longer more frequent showers, we used more than what I thought we would be anyway. I would say yours nice and low, I compared ours to both my sisters in laws, they had almost identical WPS bills both very close to $240 last month, one house is a 1700 sq ft ranch with 3 teenage kids and the other is a 2400 sq ft 1 1/2 story with one teenager, both are less that 10 years old. Our neighbor right next door was $220, he supplement heats with wood and the house is 70 years old and maybe 1000 sq ft. He thinks my bills are low because of our solar... Hey did you sign up for the google power meter thing with WPS? I did, pretty neat, but it is a bit delayed, yesterdays results show up at 2:30 the following day.

Green Bay, WI. - 4 ton horizontal goethermal, 16k gallon indoor pool, 3kw solar PV setup, 2 ton air to air HP, 3400 sq ft

Dana1

Senior Member

Posts:6991

03 Jan 2011 12:06 PM
Posted By jerkylips on 31 Dec 2010 12:40 PM my 'out of the air" numbers were about what you said - I was thinking roughly 2/3 for heating, 1/3 for everything else. Looking at the summer numbers is a good idea. We moved in July 1, so I should be able to pull some of those for comparison. I found a link to the Wisconsin Focus on Energy site that had some Energy Star guidelines and btu/hdd/sq ft calculations. The one thing I found interesting is that they include basement square footage in the calculations, even if the basement isn't heated. My original number of 5 btu/hdd/sq ft was factoring in only the first floor. if I look at the basement as well, it drops to just over 2.5 btu/hdd/sq ft. I realize that the usage is the same, but in terms of comparing to other standards, it makes me wonder if your ranges in your first reply factor that in or not.. Summer numbers are misleading for a couple of reasons- the incoming water temps to the HW heater are higher, and for most peops the total HW usage is lower in summer as well. I suspect your 2/3 - 1/3 estimated split between space heating/everything-else is still a bit too weighted toward the "everything-else" side. The vast majority of the everything-else side is hot water heating. Most families of 4 would only use 20-40 therms per YEAR in a gas dryer, but HW heating will be 6-8x that. Assuming you're a 250 therms/year hot-water user, dividing that evenly by 12 months would mean only 21 therms of that 92 was for hot water. Even rounding up to 25-28 therms for allow for the "everything-else" factors including colder incoming water, which would be at most 30% for that billing period. A 25/75 split would be more likely, and as you move deeper into winter it'll be an even wider split as heat loads rise. For a combined use of ~0.11 therms/HDD you're still WAY ahead of my 1920s antique of comparable square footage, which tends to run 0.180-0.185 therms/HDD, combined-use. If your basement stays 65F or above you can count it as conditioned space on those BTU/ft² calculations IMHO, but not so much if it drops to 60F or below. (Prior to insulating my foundation walls I had considered controlling the basement as a separate zone, but it's temp stays within a fairly narrow cool but comfortable mid-60s range due to the heat leakage from the heating system plumbing/ducts, and from the fully conditioned spaces above. As I continue to tighten and insulate elsewhere the basement temps now bump up & down a bit, but not by much.)