Sam
I'd love to be down to 15 KWh /day. I'm glad my 25 kWh/Day heating is along the same lines as yours. I'm trying to think what all the phantom loads might be...
2 alarm clocks
2 microwaves
the fridge (I got a Kill-A-Watt) draws only 160 watts when running approx 30% of the time...not too bad, I think.
Wii
TV on standby
DVD on standby
Blu-ray on standby
2 laptops - I guess even in sleep the brick draws a little power
Wii remote charger
clock on stove
AirTap DHW heater
Plug-in clock
Cordless phone
Laser printer
Print server router
Fios router
Phone DSL box

Guess they all add up.

That's about it, I think.

DISCLAIMER - Hope I'm doing my sums right!  Data can be abused, but here goes.  I've had the geo system (you can read the previous posts on this thread) for about a year now.  I computed my base electrical usage at about $85-$90 per month (computers, lights, washer, etc.) and feel fairly confident after checking and double-checking with Google PowerMeter, Current Cost Envi, and Kill-A-Watt, that my numbers are pretty accurate.  I realize that some people prefer to count kilowatts, but for me, it's all about the cost.  Right now, electricity is about 15 cents a kilowatt, which includes all generation, taxes, transmission, etc.  There is no off-peak available, but I do have "residential heating rate" which discounts above a certain # of kilowatts used.  For the sake of these numbers, though, I've averaged the monthly bills with the monthly usage to determine the 15 cents/kw rate.

Below is a graph showing heating degree days (red), cooling degree days (blue), and cost (green) above and beyond the $90/mo for base electrical usage.  So if it says $4, that means my electric bill was $94 and I'm assuming that the geo used the extra $4.


Please note that Dec 09, Jan 10, Feb 10, I was having duct issues, blower speed issues, incorrect thermostat wiring issues, etc.
House kept at 69 F in winter when we're awake/at home, 65 at night and during day when we're out.
House kept at 79 F in summer when we're awake/at home, 83 when we're out.

I like the graph. :-) What program did you use?
I imagine that kWh usage would follow a similar trend to CDD & HDD everything else being equal.

It's just Excel. All the actual numbers are in a spreadsheet, because I'm also trying to determine what my house *would* cost if I kept oil/baseboard. So far, I think I've saved about $2,500 over what oil heat would have cost if I kept it. With the geo ultimately costing 15k, my payback looks to be about 6-7 years.

Here's my numbers since I installed the system.

Month	Bill	Meter Reading before	Meter Reading After	Power used	Average Temp This month	Average Temp Last Year	KWH Daily Averages This Month	KWH Daily Averages Last Year	Date of last Meter Reading
Nov-08	$222.37	6287	7824	1537	51	47	38.3	54.9	Nov. 14
Dec-08	$340.61	7824	10189	2365	41	42	73.9	60	Dec. 16
Jan-09	$403.78	10189	12999	2810	37	40	90.6	85	Jan. 16
Feb-09	$362.06	12999	15512	2513	33	36	78.5	88.7	Feb. 17
Mar-09	$360.27	15512	18016	2504	39	40	86.3	75	Mar. 18
Apr-09	$244.69	18016	19704	1688	47	48	56.3	61.2	Apr. 17
May-09	$138.23	19704	20640	936	61	58	30.2	43.7	May. 18
Jun-09	$124.80	20640	21365	725	66	68	24.2	45.3	Jun. 17
Jul-09	$173.57	21365	22272	907	72	76	30.2	65.7	17-Jul
Aug-09	$214.55	22272	23385	1113	76	78	35.9	5.5	Aug. 17
Sep-09	$206.61	23385	24457	1072	73	73	35.7	29.3	16-Sep
Oct-09	$133.02	24457	25224	767	63	61	23.8	25.6	Oct. 16
Nov-09	$192.30	25244	26452	1228	53	51	39.6	54.9	Nov. 16
Dec-09	$274.74	26452	28223	1771	46	41	59	73.9	16-Dec
Jan-10	$464.56	28223	31236	3013	32	37	91.3	90.6	18-Jan
Feb-10	$473.49	31236	34311	3075	32	33	106	78.5	16-Feb
Mar-10	$355.22	34311	36610	2299	41	39	79.3	86.3
Apr-10	$203.70	36610	37913	1303	54	47	43.4	56.3	17-Apr
May-10	$165.81	37913	38966	1053	60	61	34	30.2	17-May
Jun-10	$169.48	38966	39905	939	70	66	31.3	24.2	16-Jun
Jul-10	$278.58	39905	41277	1372	79	72	45.7	30.2	16-Jul
Aug-10	$315.17	41277	42825	1548	80	76	49.9	35.9	16-Aug
Sep-10	$226.83	42825	43942	1117	73	73	36	35.7
Oct-10	$143.00	43942	44734	792	65	61	24.8	25.6	18-Oct
Nov-10	$230.49	44734	46170	1436	52	53	51.3	39.6	15-Nov

I have no way to compare what the saving are, if any, since the house has always been Geothermal. I track the meter reading because at some point the meter was replaced by the power company, It was a digital meter then one day it was an analog meter, not sure why it was switched. I'm a little disappointed with my Nov. bill, my wife and I were suffering by not turning on the heat upstairs for weeks thinking we were saving energy, it was as low as 61 degree many mornings.  One day when I went to check on my dehumidifier in the basement, I noticed a red light on the geothermal system, the water wasn't flowing. Turned out to be a bad pump, I was probably running off of emergency heat for a week or two. I wish there was some thing more than a flashing light when a fault occurs, a distinctive loud beep that repeats every few minutes until cleared would be more ideal. If you don't check the system on occasion to make sure its working, I would imagine you get an $800 electric bill one month when its running on emergency heat. .
 
  

It would be interesting to know what is causing the lack of a 1:1 ratio between the change in HDD and power usage.

Tech- rThat elec included non-heating/cooling, right (tvs, dishwasher.etc.)?  I remember your house is about 3000 sq ft w/ open loop 4 ton.  I don't think I"m doing too badly in comparison.

Jonr - I wonder if the lack of a proper 1:1 might be the rate change kicking in about 6 kw or whatever it is (Excelon/PECO)...I tried to average it out for my math, but perhaps it's a significant factor?

Posted By stuart.wyss on 03 Dec 2010 10:21 PM
Tech- rThat elec included non-heating/cooling, right (tvs, dishwasher.etc.)?  I remember your house is about 3000 sq ft w/ open loop 4 ton.  I don't think I"m doing too badly in comparison.

Yea,

October would be a good month to figure out what portion is non-heat/cooling of the bill, since the systems are off that month. Actaully the house is 3,300 sq ft., but it is a 4 ton open loop.

Actually, it looks pretty 1:1 except for cooling in July/August...but that's because my wife or I are at home all summer, rather than letting the setbacks go into effect during the day.

I see costs varying from 2.6 cents/HDD (or heating degree month) to 10.8. So something is quite non-linear. You would need more data regarding balance point and electric usage to get closer to constant.

The baseline average looks like it's about 700-800kwh/month, which would be close to the "typical" US background load of about 1kw for a single-family dwelling. (720 to 744 hours/ month x 1kw= 720 to 744kwh)

Subtract 24kwh from the average daily use, see how well that correlates with HDD. If your house is very well insulated, use base 60F rather that 65F for heating degree day calc.

Of course, the COP of the geo will drift over the season as the groundwater/subsoil cools/heats with use, which will be one source of non-linearity.

Solar gain will be another large variable in very well-insulated homes with significant exposures of south facing glass.

Here's another chart...not just any random chart.  It's a graph of average daily temperature in Willow Grove, PA (about 10 miles south of me, according to weatherunderground.com) and my daily KWHs use according to Google Powermeter.  Left side of chart is temperature (F).  Right side axis is total KWH.  October 25th to Dec 16th/2010.

It's interesting to note the almost perfect relationship between temperature and KWHs.  The giant red spike on Dec 9th was when the unit went into lockout and the aux heat came on.  After the 9th, I lessened the setbacks to only a few degrees, rather than about 5 degrees.

Interesting chart,  thanks for sharing.

Cool!

Stuart, can you add kwh to your Dec 3rd graph?

Thanks!

Yeah, all the same disclaimers that Stuart made... but I think my data is good.  I only have 2 months worth so far.
(Oil cost is base off my oil usage from last year using HDD and this year's oil prices.)

House: 1200sq.ft. Cape with 400 sq.ft. addition.
Zone 1-1200sq.ft. house, heated with oil fired steam heat.
Zone 2- 400sq.ft. addition heated with oil fired hot water baseboard.
DHW 40gal. Oil fired Mega-Stor Indirect Water Heater.
Location: Wethersfield CT.
30 Year Average Heating Degree Days = 6100 approx.
30 Year Average Cooling Degree Days = 600 approx.
Thermostat: 68* House
62* Addition
Fuel Use: 630gals. for heat/yr. @$3.00 $1890.00/yr $.31/Degree Day
70gals. for DHW/yr. @$3.00 $210.00yr.

Changes: 3000 watt PV Grid Tie Solar Array Approx. 3900kw/yr.
50 Gal. Electric Water Heater
Use the Mega-Stor Indirect Water Heater for PreHeat Tank
CM Ultra Classic VT 3 12 ton 2 stage w/hot water generator
8-105' vertical wells 3/4" U Tubes connected in 4 pairs to 1 1/4" manifolds

The Geo is only used to replace the steam portion of the house at the moment.
The system has been online since Dec 1, 2010.
Water Heater and Geo have their own KWH Meters
Usage: Dec. 1066 HDD 892kwh @ $.17/kw = $151.64
Jan. 1254 HDD 957kwh @ $.17/kw = $162.69
Average cost is $.135/HDD
I'm going to try stat setback, I think I can do better.
Considering this is a 17 year old heat pump I think this is pretty good.
Oil usage by tank gage 40gal. for past 45 days won't know actual til next Dec. fillup.
Electric Water Heater used an average of 2000kw/yr 2 yr average.
Need some time to calculate anual savings for DHW.