So I'm currently investigating moving my electricity rate structure from my current (RE) which is pretty much set at $0.086/kWh (
http://www.duke-energy.com/pdfs/NCScheduleRE.pdf ) to a time of use rate structure (
http://www.duke-energy.com/pdfs/NCScheduleRT.pdf ). Yeah, there is a small tier when you use over 350 kWh where it goes down to 0.078 in the summer...but that isn't significant. Well, thanks to my TED 5000, I analyzed my historial data to see if it was worthwhile.
First the rates...the time of use rates (TOU) as shown below have a higher facility charge and lower overall rates. However, there's this "On-peak demand" charge. Well, that charge is defined as "
the maximum integrated thirty-minute demand measured for the On-Peak period during the month". So that means if I use 10 kW for 30 minutes in the Winter, then I'll get: 10 KW x $3.33 = $33.30 demand charge. Sounds expensive right? Well, let's see if it really works out...
Below is the my historical hourly energy usage from January 18, 2011 to April 18, 2011.
As you can see, in the winter I had some pretty high 1-hr usages (Note: I did 1 hr usage to get more historical data - 90 days - vs the minute data which would have only stretched 48 hrs).
But how does this fall during peak times? See the graph below which segregates out only the data during peak times:
Generally speaking, the vast majority of the elecrical usage is below 2 KW. But...there were some pretty noticable peaks. The extremely large peaks (8-16 KWH) were from that old crappy heat pump using the emergency heat (i.e. electric) because it couldn't keep up. Those in the 4-6 kWH range are most likely either the dryer or the hot water being generated. Those between 2-4 KWH could be a bunch of things...and most likely it was one heat pump on (~3.5 KW). Not to mention this is a 1-hr average.
So...if I take this hourly data and apply the on and off peak rates, then determine the max 1-hr power usage and apply the on-peak demand charge, what does that get me? See the table below:
| | | | | | | | |
| Ex Cost | Peak TOU | Off TOU | TOU Total | Fac Charge | Max 1 hr KWH | OnPeak Chrg | Total |
| Jan-11 | $153.36 | $12.75 | $67.23 | $79.98 | $13.88 | 15.49 | $51.59 | $145.45 |
| Feb-11 | $104.82 | $9.19 | $45.26 | $54.44 | $13.88 | 5.52 | $18.36 | $86.69 |
| Mar-11 | $99.41 | $9.15 | $42.04 | $51.19 | $13.88 | 6.55 | $21.82 | $86.89 |
| Apr-11 | $43.02 | $3.75 | $19.06 | $22.81 | $13.88 | 3.97 | $13.23 | $49.92 |
| Total | $400.61 | $34.83 | $173.58 | $208.42 | $55.52 | | | $368.95 |
| | | | | | savings | $31.66 | |
The "Ex Cost" column is the TED estimated cost for the month. Overall, it's pretty close. "Peak TOU" and "Off TOU" are the costs at the "on-peak" and "off-peak" rates. Then I add in the Facility charge (a constant montly value). Finally, I determine the Max 1-hr demand and multiply it by the winter charge ($3.33/KW). Note that April-11 is currently an anomaly because its less than 1/2 the month so the facility+on-demand charge make up 1/2 the cost.
Overall, it shows that I could have saves ~$32 over 4 months with the TOU rates. It doesn't seem like a lot right? Well, one thing to remember is that I wasn't even trying to curb my electricity usage. When I look back at the raw data...the vast majority of the peak usages occured between 7 - 8am (see below):
| Sum of Winter Peak Elec | | |
| hour | Total KWH | |
| 0.00 | 0.000 | |
| 1.00 | 0.000 | |
| 2.00 | 0.000 | |
| 3.00 | 0.000 | |
| 4.00 | 0.000 | |
| 5.00 | 0.000 | |
| 6.00 | 0.000 | |
| 7.00 | 238.660 | |
| 8.00 | 75.460 | |
| 9.00 | 61.612 | |
| 10.00 | 57.602 | |
| 11.00 | 62.269 | |
| 12.00 | 66.023 | |
| 13.00 | 0.000 | |
| 14.00 | 0.000 | |
| 15.00 | 0.000 | |
| 16.00 | 0.000 | |
| 17.00 | 0.000 | |
| 18.00 | 0.000 | |
| 19.00 | 0.000 | |
| 20.00 | 0.000 | |
| 21.00 | 0.000 | |
| 22.00 | 0.000 | |
| 23.00 | 0.000 | |
Well...that's due to how I have my programmable thermostate setup and when we take showers for work. If we get the house heated up 1 hrs earlier and we finish our showers 30 min earlier those peaks are off-demand. Now there still is some demand (see below), but its significantly less. Not to mention I now have a significantly higher efficiency HVAC system. So I would expect these peaks to be much lower. The worst load would be when the hot water heater runs (4.8 KWH) and that typically lasts only about 10-15 minutes.
| | |
| Max of Winter Peak Elec | | |
| hour | max 1-hr KWH | |
| 0.00 | 0.000 | |
| 1.00 | 0.000 | |
| 2.00 | 0.000 | |
| 3.00 | 0.000 | |
| 4.00 | 0.000 | |
| 5.00 | 0.000 | |
| 6.00 | 0.000 | |
| 7.00 | 15.492 | |
| 8.00 | 3.785 | |
| 9.00 | 6.554 | |
| 10.00 | 3.214 | |
| 11.00 | 3.977 | |
| 12.00 | 5.078 | |
| 13.00 | 0.000 | |
| 14.00 | 0.000 | |
| 15.00 | 0.000 | |
| 16.00 | 0.000 | |
| 17.00 | 0.000 | |
| 18.00 | 0.000 | |
| 19.00 | 0.000 | |
| 20.00 | 0.000 | |
| 21.00 | 0.000 | |
| 22.00 | 0.000 | |
| 23.00 | 0.000 | |
So overall...if we can keep our peak demand to below, say 4 KW, during those peak times (that would be both the upstairs and downstairs geothermal systems running for 30 minutes), then I could increase those historical savings from $32 to $107.
Moving forward...I think with all the energy effiicency stuff I've done (insulation, geothermal, etc), I think I can reap some great benefits. During the summer, the hot water running won't be an issue thanks to the desuperheater. It'll just be the A/C...which I can mitigate by setting the thermostat high during that short period of time. Plus, I'll probably only have the upstairs system run and will have the downstairs system essentially off.
It'll be interesting to try out...I'll try to post something up after this summer to show the results...
