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Author Topic: TED 5000 data logging and analysis with GNU/Linux
iteration69
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« on: July 27, 2011, 03:19:03 AM »

Hi,

I put together a cron job and shell script to log the ted 5000 data. The log is in archival format where i can go back to a given year, month, day, and then pick from hourly,min, second data. I focus on second data and log it every hour. I also sort and cut the data to make it easy to work with using common tools.

I commented on my personal blog (which is a blog for personal reference, not intended for net-wide eyes). If commenting gets crazy, or someone starts griping I'll pull it just as easily as shared it.

Otherwise, I hope it helps someone.
http://2s2t2e.dyndns-blog.com/?viewDetailed=00006

Be patient, this is on DSL and uplink is only a few hundred k.
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marcomwest
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« Reply #1 on: August 03, 2011, 09:21:30 AM »

hi.

this is great. i posted on the ted5000 support forum about using rrdtool to do this sort of thing. it was probably the wrong place, i realize now, but it may be good to leave it and get more eyeballs to see it.

anyway, i think that you have the "guts" of an rrdtool-based solution more or less done.

rrdtool will take care of graphing all of this information in a way that can be useful long term.

someone already has a solution working:



"RRDtool is the OpenSource industry standard, high performance data logging and graphing system for time series data. RRDtool can be easily integrated in shell scripts, perl, python, ruby, lua or tcl applications."

http://www.mrtg.org/rrdtool/

Here is an example with more graphed data:

http://energy.shadypixel.com/

In my case, I don't really care about actual numbers, just a graphical view of my usage over time.

what is your take on this? thanks.






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iteration69
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« Reply #2 on: August 04, 2011, 01:51:06 PM »

A friend had suggested rrdtool a few months ago, i checked it out and it was not for me. I need to perform somewhat complicated analysis on the data and gnuplot / gnumeric are the best tools that i've found so far.

Here is something i just pushed out to compare hot water heating energy use.



This is by no means the extent of which i need to work, but it will give a small indication of the difference between data graphing and  data analysis.

As i noted on my blog, i tend to graph 90,000+ points. I also perform various curve fitting algorithms on the plots so that i can forecast energy use, cite & remove outliers, and calculate confidence of a model.
 
As far as simply graphing, I agree, rrdtool is a pretty good solution.
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iteration69
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« Reply #3 on: August 11, 2011, 02:47:14 PM »

Early may, 2011 i determined that my hot water heater was using an excessive amount of power. At that point in time I only had a single MTU which was on the mains so It's difficult to cite and exact number but I figured that it was costing me about $80 / month. I was also very much so interested in heat pump hot water heater technology. I wanted to buy a heat pump hot water heater to replace my old resistive heat model but I was not sure which model to buy. To buy some time to make an informed decision I simply bought a cheap hot water heater from lowes on May, 11, 2011 and installed it.  It was the cheapest thing i could find, costing something like $200. I also installed another MTU directly to the hot water heater circuit that same day. The purpos of the addition MTU was so that I could profile a brand new hot water in order to do an apples to apples comparison. This owing to the fact that I had plans of installing a heat pump hot water heater and was very curious about the claims of a 2/3 energy reduction.

After looking at quite a few heat pump hot water heater models I settled on a hybrid model from ao smith, The voltex. The deal maker for me was their tech support / engeering team. I called ao smith and fired al kinds of questions at them in regards to warrenty, who can perform the repair, what is covered, what cop outs there are. etc. I was very,very pleased and got a quote from a local hvac house for $2,000 and was told there would be a 2-3 week lead time. So i waited a month then stopped back in to place the order. I was told that my quote was no longer valid (thinking oh great, now it's going to be $2,400. But I was prepared to buy regardless) But to my surprise the price dropped down to $1400!

So I had the heat pump hot water heater delivered late June, 2011. After a few weeks of sitting in my home (taking up space) I decided that I had collected enough data on the conventional hot water heater. I shut off the hot water heater July, 29, 2011. On the 30'th I installed the heat pump hot water heater. It was turned on around 7:30pm that night. After filling it with water and making sure all the air had been bleed out, I turn the breaker on.

The Voltex, being hybrid, has a touch panel interface with icons to select the operating mode. There are four modes. Vacation, Electric only, Hybrid, and Efficiency. I set it efficiency mode and adjusted the temperature to 125 (very close to what my previous hot water was set to). The computer had a message indicating that it was detecting dry fire.  This message was displayed for about 15 mins when I began to think that I may have faulty control. So I i began to read the manual again with no relief. No sooner than I decided to turn off the system and call tech support-- it turned on. Be warned that the Voltex may take a little time checking for dry fire. When the Voltex finally starts the fan will run for about 20 seconds then the compressor turns on. Also it is a little noisier than I had expected, imagine running a large window ac inside your home; that is the entire unit inside your home. Though it's a little noisy, it's not terrible, especially for someone who's main goals are to reduce their energy consumption. Finally, I could get some figures.

I opened up Footprints Web interface and was very pleased to see the current consumption was 750watts. Remember this is the first time the system has been run so it had to heat cold water, in heat pump terms this was the best conditions I'd ever see. As the heat pump continued to run and heat the water i noticed an ever so slight slop in the power consumption. After two hours it had reached holding temperature and shut off. The ending power consumption was a few watts over 1kw. The total energy used to heat the water was 2.5kw/hr. Looking back at the traditional hot water heater it used a little over 6kw/hr for the initial heat up.

So far the heat pump is doing well. I'm not convinced that it will live up to the 2/3 energy reduction but I am fairly certain that the reduction is at least 1/2.

Here is a graph I made a few days ago.



Even though this graph only contains a few points in regard to the Voltex heat pump hot water heater energy consumption, it is quite obvious of the energy savings. Take note of the far right side of the graph.

To be complete, my family contains three members. Myself, my Wife, and my daughter. We have not made any other changes that would effect our hot water usage.

In case someone is interested in heat pump hot water heater energy use, I'll continue to periodically add up to date graphs indicating the heat pump hot water heater energy consumption.
« Last Edit: August 11, 2011, 03:12:45 PM by iteration69 » Logged
rotus8
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« Reply #4 on: August 11, 2011, 07:42:40 PM »

This is quite interesting to me as I have been considering installing one of these water heaters. Can you tell me what your installation does with the cold side of the compressor? Does it make cold air? Where does the cold go, does it vent to the outdoors? Can it be used for air conditioning if you want? Thanks for the data!
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iteration69
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« Reply #5 on: August 11, 2011, 10:11:27 PM »

For brevity I'll refer to the heat pump hot water heater simply as "Voltex" from here on.

The Voltex evaporator (cold side) discharges inside the home. The manufacturer recommends installing this unit in the basement where it can provide supplemental dehumidification / air conditioning. Initially I had a different idea. I wanted to install the Voltex in the bath room on the second floor.

The reasoning behind installing such a system in the bathroom is three fold.
  • Extract the latent heat of the byproduct steam vapor from taking a shower, effectively defogging the room and mirror
  • Decrease the time taken for hot water to arrive at the shower
  • Install a waste water heat recovery system to extract energy from the shower drain and preheat the cold water supply to the Voltex

The realities are:
  • The Voltex is rather large and requires a great deal of working room should it need serviced (too big for most bath rooms)
  • The Voltex does not always run while taking a shower, making it very difficult to utilize the latent heat of waste steam vapor
  • When the Voltex does operate it tends to run between one and two hours and would very likely chill the bath room beyond comfort.
  • The Voltex is quite bulky and may be difficult moving to a second floor

I could have installed the Voltex in my bath room, though it would have been tight. Due to lack of space for servicing / repair I ultimately decided to install the Voltex on the first floor in the laundry room. At first I was a little upset that I could not do things the way I had planned. In hind site I'm glad that I did not install the Voltex in the bath room because it would not have been able to extract heat from the steam vapor as I had hoped(due to the long idle periods). One option would be to modify the controls and force the Voltex compressor to operate while, but one would have to have a great deal of data to back up this up in terms of energy savings. I still plan to install a waster water heat recovery system on the shower drain. I'll have to plumb a little more tubing in than i initially suspected but it should still work.

Recall that the manufactured recommends installing the Voltex in the basement for "supplemental" dehumidification / ac purposes. It's difficult to be exact this early on, but the Voltex seems to have a 10-12 hour idle period between operation. When it does run, it operates between one and two hours. Using 1kw as a base input figure, and assuming a COP of 3.0 (which is probably wishfully thinking with condensing temperature above 125f).  

1 kw = 3412 btu. Most window units are 5,000 btu.  Comparing these two figures we see that the Voltex will provide about 68% the cooling capacity of a typical window ac unit for a period of two hours.

Wow, i really botched that one up. It should be:
1 kw/hr = 3412 btu. Assuming as COP of 3.0 that works out to 3412 x 3 = 10,236 BTU. Since the Voltex seems to run for about two hours we end up with 10,236 x 2hr = 20,272 btu/hr. Most window units are about 5,000 btu/hr.  Comparing these two figures we see that the Voltex will provide about 20,272 btu-hr / 5,000 btu-hr = 4.05, That is the same cooling capacity a typical window ac unit will provide over a period of 4.05 hours.
 
But remember that the Voltex has an off period of 10-12 hours. Getting these events to line up in a contributing manor may be very difficult. It is very likely that the Voltex will operate during non peak cooling time.

My preliminary thoughts of the Voltex as supplemental dehumidification / ac are mixed. It's obvious that it will help reduce dehumidification and cooling costs to some extent but it certainly will NOT replace either. It will be very difficult to predict these figures using models. Empirical methods are probably the most reliable way to cite meaning contributions in terms of reduced dehumidification and cooling costs.

More analysis, graphs, and ideas to come.



« Last Edit: August 12, 2011, 11:24:06 PM by iteration69 » Logged
rotus8
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« Reply #6 on: August 11, 2011, 11:34:14 PM »

It seems to me that in the winter, if it is installed in a heated space, while the dehumidification might be nice, you will lose a significant portion of the efficiency gain (maybe even more than all of it) if you have to run the furnace to re-heat the air the Voltex cools off. In my case it would have to be installed in a heated space, meaning I would also have to add ducting to vent the cooled air to the outside.

Thanks for the detailed explanation.
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iteration69
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« Reply #7 on: August 12, 2011, 01:21:14 AM »

This will be a lengthy post, as this is a subject that I've invested a fair amount of consideration. Hopefully, I can shed insight on to a subject rarely covered.

Winter certainly posses a problem for the Voltex, especially in areas where there are drastic temperature changes.  I for example live in south western Pennsylvania and we have moderate winters where a heating costs generally out number cooling costs. The fact that I have to pay to heat my home, and then the heat pump will extract that heat to in turn heat domestic hot water, posses both a challenge in operation and analysis. This is something I'm going to learn hands on. This in part what lead me to choose the hybrid model which allows a mix of heat pump mode and electric heating elements. Worst case I can revert to electric mode and since the Voltex is insulated much better than the previous water heater I'm still slightly ahead.

Another feature of the Voltex is that the heating elements are sized differently. There are two different sizes of heating elements so that hybrid mode does not consume nearly as much energy when using resistive heat as compared to electric mode alone. The manual is not very specific, but my understanding is that when operating in hybrid mode there is a timer function in combination with the heat pump event. After the timer expires the less of the two heating elements is then turned on in addition to the heat pump in order to help maintain tank temperature in a timely manor. I suppose this is for scenarios in which a large amount of water is used in a short period of time.

The information gray area seems to be worse for electric mode. Considering that the Voltex has two difference sizes of heating elements, I would be logical to operate one element for a given duty, then operate another for a given duty, and then operate both elements in tandem. The bases of this logic is water stratification. Considering the data I've analyzed, I'm suspect the Voltex computer employs a basic stratification control algorithm.

Your end goals will dictate the equipment utilized as well as any architectural modifications. My end goal is to reduce my electric use as much as possible, if not eliminate a meter all together. The motives are not so much "green" or "tree hugger" as much as I simply do not want to end up stuck with ridiculous utility bills. But to be fair there the green notion and tree hugger are also part of the drive, they are simply not the contributing force.

For me payback is the first portion of the analysis, but long before payback may be calculated some details need to be understood.

Equipment cost is comprised of, but not limited to:

  • Purchase cost
  • Operating cost
  • Maintence cost

The sum of the above should provide a fair indication of equipment cost. This is something that should be considered long before a choice is made.

First consider the inexpensive hot water heater I bought from lowes. My intentions were two fold.
  • Replace the costly old water heater with an inexpensive new water heater
  • Extract as much data as possible from the new water before before purchasing and installing a heat pump water heater

I paid around $200 for the conventional hot water heater. I was able to determine the monthly operating cost to be $23. The water heater uses a corrosion inhibitor known as an anode. This is a chemically active device that naturally depletes in order to prevent the tank and heating elements from corroding. It's not outlandish to expect to replace an anode every two years. And it seems that going prices on anode rods are about $20.

It should be understood that hot water heaters do have maintenance, that is, if you intend to keep your hot water heater operating at peak efficiency and would like to avid wasting $60 / month. Anodes, which were previously mentioned are one aspect of this maintenance. Yet another is annual draining to remove sediments which can build up and impede the heat transfer of the heating medium and the water.

To get an idea of how long a conventional water heater may last I'll consider my previous energy guzzler which was 20 years old. I've lived in this house for 8 years and never once drained the water let alone replaced the anode. And thus my outrageous water heating costs.

As I stated, my previous water heater lasted 20 years. Assuming a steady state power use of $23 / month.

$23 /month * 12months = $276 / year (operating costs)
 $276 * 20 years = $5520 total operating cost

Expecting to replace an anode every two years, for a life of 20 years.
20 / 2 = 10 anodes.  Anode cost $20 * 10 = $200 maintenance cost.

Now I can find the real cost of this inexpensive water heater.
Purchase cost + operating cost + maintenance cost = Real cost

$200 + $5520 + $200 = $5920 real cost.

A properly maintained water heater should last much longer than this. But this is what I have to work with.

Now let's consider the Voltex. First, the Voltex has a one year parts + labor warranty. And a ten year parts warranty, which includes the tank. They can offer a ten year warranty on the tank because the Voltex uses a powered anode. Instead of depleting a material to balance the chemistry inside the water heater, it takes a few electrons from the power supply. The cost is minimal too, so far the Voltex computer + powered anode seem to cost about a penny a day.

Since I intend to perform any repair myself I'm basically looking at ten years no maintenance cost for the first ten years, and for the second I'll simply plug in a worst case figure, the price of the Voltex.

I paid $1400 for the Voltex
Using current figures, the monthly operating cost is $8
$8 month * 12 months = $96 / year
$96 /year * 20 years = $1920 operating cost
After ten years i intend to buy a new model so:
maintenance cost = $1400

Finding real cost for the voltex.
Purchase cost + operating cost + maintenance cost = real cost
$1400 + $1920 + $1400 = $4720


In review:
Voltex real cost = $4720
Inexpensive water heater real cost = $5920

This may not seem very substantial over 20 years but also consider that the Voltex maintenance figure essentially covers a new unit and is still in the positive.

All of this considered, I have other motives for moving to a heat pump hot water heater. I'd like to move to solar some day and expecting to operate a 4.5kw energy guzzler from PV cells is not the wisest choice.

Consider the graph below, which is a minute-data profile of the inexpensive hot water heater.


It's obvious that a conventional hot water heater, tends to cycle a fair amount. Also consider that each cycle consumes about 4.5kw/hr. It may be difficult to correlate this graph because we generally do not look at such things, which goes to say there is not much common sense in the area.

To provide a correlation, consider the graph below, of the Voltex heat pump.


From the begging I have invested considerable thought in to the analysis of the energy log. To the best of my current abilities, I have provided an apples to apples comparison between an inexpensive hot water heater and a heat pump hot water heater. Note that both graphs have the same scale on the y axis, that's  0 - 5 kw. The x axis does not include the same date because I'm obviously using the heat pump now in place of the hot water heater. But I did choose a representative sample from each device log period which had the highest confidence value. Statistically, these graphs represent what they claim to.


Some digression is required:
I'm not out to sell anything or BS anyone, I'm simply sharing what I have found so far. BS figures, graphs, and misrepresentation of data among the media and marketing are very common, which owes to the fact that no one believes a damn thing they read. On a side note I highly recommend reading "How to lie with statistics" By Darell Huff.  It's a common sense eye opener as to why we never trust what we read.
End of digression.

Take note of the well regulated consumption of power from the heat pump. This certainly moves hot water heating in to the PV solar class.

Digging deeper in to the analysis and profiling of devices, I consider the last graph of the heat pump. This time i adjust the y axis range to be between .8kw and 1.1kw.  This exposes the slight slope that is common with all heat pumps.



Note the slop of these events. The device starts with the lowest power consumption and gradually works to a peak.
I'd also to note that devices operating in cooling mode (freezers, refrigerators, and air conditioners) have a slightly different characteristic. Instead of starting low and gradually consuming more energy, freezer, refrigerators, and air conditioners start with a peak and slowly fall off. -- This is something that I'd like to see replicated by others, as i believe it is a fair indication of a much more fundamental heat transfer function.

Though not quite the same style as my previous graphs, Here I use gnuplot to zoom in on the first event to show curve details. - Remember, I used minute data here, Had I used second data an entirely new data set would be realized.


This part of the analysis is particular useful for micro-trends and equipment "health" for lack of a better word.

More to come later.





« Last Edit: August 13, 2011, 01:53:37 AM by iteration69 » Logged
rotus8
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« Reply #8 on: August 12, 2011, 07:53:46 AM »

Very interesting, thanks again. You have really got me thinking...
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GAR
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« Reply #9 on: August 12, 2011, 03:05:07 PM »

110812-0653 EDT

iteration69:

What does your unit of measure kW/hr mean? Also kW do not equal BTU. You need a factor of time in that relationship.

kWh is a measure of energy, BTU is also a unit of energy.

From answer.com
 
1 BTU = 1.055 kilojoules. 1 joule per second = 1 watt, or 1 joule = 1 watt.sec.

1 kWh =1000 x 3600 watt.secs = 1000 x 3600 joules = 3600 kilojoules = 3600/1.055 BTU = 3412.3 BTU

.
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GAR
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« Reply #10 on: August 12, 2011, 04:53:14 PM »

110812-0813 EDT

iteration69:

Of all the plots here the one on 8/3/2011 by marcomwest is the only one that makes sense. The graph heading and the Y axis correlate in the type of units, and the shape of the curve is what is expected.

Most electric and gas water heaters on on-off (bang-bang) servo systems. Thus power consumption does not gradually increase and decrease. Rather it is on or off. If you do a running average of power then a rounded curve will develop. You have not indicated a running average.

In the 8/4/2011 plot the title is energy use and the Y axis is kW/hr. These do not correlate. If the plot was of energy, then it would be monotonic of 0 or + slope, and would not be labeled kW/hr. I suspect the curve is some form of a running average of power.

Now under a heat pump curve in the notes I see where you reference 0-5 kW, yet the graph is labeled kW/hr. So it appears that kW/hr is actually kW with maybe a running average period of 1 hour sometimes, and other times maybe a minute under the heat pump. If it was the average over discrete time periods. then it should have been a step curve in the 8/4/2011 plot.

Your time bases are another problem. Hard to make any comparison when oddball values are used and curves that should be compared with one another have different scale factors. For a 24 hr period why can't you use 0, 1, 2, .... 23, 0 as major tick points?

.



 

 
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iteration69
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« Reply #11 on: August 13, 2011, 01:19:33 AM »

GAR.
 Ah, I see. I forgot to add the "hr" to the kw unit in the BTU conversion. - Corrected.

Quote
Most electric and gas water heaters on on-off (bang-bang) servo systems. Thus power consumption does not gradually increase and decrease. Rather it is on or off. If you do a running average of power then a rounded curve will develop. You have not indicated a running average.

Agreed, power consumption does not tend to change with resistive heating. Perhaps I was not clear enough. The power consumption of vapor compression systems (heat pumps, refrigerators, freezers, air conditioners) does change and it is something worth noting because the trend provides a detailed characteristic regarding the operating conditions of the equipment.

A running average is not what I'm looking for in this analysis. And this is where you really need to be careful because when you say average you really should indicate what type of average it is. Is it mode, median, or mean? I need to determine the peak event so that I can design a PV solar system and an average will effectively filter out the specifics that I'm looking for.

Quote
n the 8/4/2011 plot the title is energy use and the Y axis is kW/hr. These do not correlate. If the plot was of energy, then it would be monotonic of 0 or + slope, and would not be labeled kW/hr. I suspect the curve is some form of a running average of power.

Good eyes! You caught a labeling goof up.  Y should be kw not kw/hr and the title should be Voltex event-trend, not energy.

Quote
Now under a heat pump curve in the notes I see where you reference 0-5 kW, yet the graph is labeled kW/hr. So it appears that kW/hr is actually kW with maybe a running average period of 1 hour sometimes, and other times maybe a minute under the heat pump. If it was the average over discrete time periods. then it should have been a step curve in the 8/4/2011 plot.

Ugh! y label on those graphs should be kw not kw/hr.   If i still have the script I'll regenerate them with proper labels, but I'm pretty sure they are gone now. (I'm tinkering with styles and these were test run plots for a new style)

Quote
Your time bases are another problem. Hard to make any comparison when oddball values are used and curves that should be compared with one another have different scale factors. For a 24 hr period why can't you use 0, 1, 2, .... 23, 0 as major tick points?

No arguments here.  Ive been wrestling with myself over the labeling of the x ticks for quite some time.  I still can't quite decide which way I'd prefer to see it. Most of the times I want to see dates so that I can correlate events and for me the easiest way is to think about a given date and remember what was going on.  Other times I need to abstract and consider actual sample number, and yet others I'd like to see sec,min, hr, or day tick marks.

I do appreciate the heads up on the typos and label errors. I'm still in the phases of getting all the styles and feeds so I may not be able to regenerate exact graphs with corrections (different image typos, styles, formats, etc) but I'm getting there!

Knowing those graphs have incorrect y labels is eating at me.  I'll correct the graphs and comments relating to them as soon as I get some pressing matters taken care of.
Thanks again
« Last Edit: August 13, 2011, 01:55:50 AM by iteration69 » Logged
GAR
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« Reply #12 on: August 14, 2011, 05:47:05 AM »

110813-1718 EDT

iteration69:

Consider your plot in post #2. Now I understand that the Y axis is power (kW). By average I am referring to arithmetic mean.

This plot does not make sense to me in terms of what I might expect. I would not expect a rounded curve as shown. The original data appears to be going thru a rather long time constant low pass filter to get this rounded curve. I would expect a reasonably consistent pattern from one day to the next with possibly a change on weekends. I see some periodicity of minimums on about a 8 to 10 day period. I would expect a more consistent pattern week to week.

If you want peak power information, then you need to look at raw 1 second data, no filtering (i.e., no averaging outside of what generates the 1 second data). TED provides nothing finer than 1 second results.

To get peak power does not take any very long time analysis.

Is your PV system going to have to power the heater off grid?

On the old resistive heater you could probably just use the nameplate data to determine peak power. On your heat pump system you do need to study its characteristics as you are doing.

Later you have two plots of what appears to be the same time base, and data, but a different Y axis. But these don't scale to one another. What is the difference between the plots? You should be using 1 second data instead of 1 minute. The cycle period is about 12 to 13.5 minutes and an on time of maybe 1.5 minutes and less.

The curve with the shaded blue lasts 1.5 minutes, and cannot originate from 1 minute data. If it is really 1 second data, then it should show steps, or points, or a drop line form (a comb of 90 points) to indicate the quantizing level.

.
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GAR
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« Reply #13 on: August 15, 2011, 04:10:16 AM »

110814-1930 EDT

iteration69:

Your plots stimulated me to look at average data from my home for 6-28-2011 thru 8-14-2011.

I used the TED one hour average data for both power and voltage plotted relative to time from 0 to 2300 and overlaid all these days. The power is plotted as points, and the voltage as connected points to distinguish the two data groups. This form of plot provides an interesting view.

There is a noticeable difference between daytime and nighttime.

For voltage from 0000 to 0700 the range of averages falls between 123 and 125 volts. Into the time frame of 1600 it broadens to 120.5 thru 126 volts. By 2000 it falls in the 123 to 125 range. There was one day when the voltage was clearly outside this range with a peak 1 hour average at 1300 of 127.5 V.

For power the nighttime 1 hour averages ranged from 0.8 to 1.9 KWH. After about 0700 this moved up to a visual average of about 2 KWH, and the lowest to highest range was 1 to 4 KWH.

The basic conclusion is a fair consistency at night with a more varied range during the day. But definitely a correlation with time of day. From this data and visually looking at it without analysis I might ballpark daily average consumption at about 1.2 * 7 + 2.0 * 17 = 42.4 KWH. This is somewhat above my typical bill. My actual bills for this period were:
36.4 KWH 6-10-2011 to 7-11-2011
49.4 KWH 7-11-2011 to 8-11-2011 more fan or blower use.

.
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GAR
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« Reply #14 on: August 15, 2011, 06:41:24 AM »

110814-2224 EDT

iteration69:

Another item to consider if you expect to operate off grid. My measurements on motor type loads using the TED 1000 series usually show a peak power in excess of 3 times the steady state power. This is looking at 1 second data. The actual amount of the peak is probably greater. TED 1000 is doing about a 1 second average on the power, the 5000 might be in the range of 2 to 3 seconds.

Motor inrush current and related power to a motor might be 6 to 8 times rated steady-state full load current. Some of this is inertia load, and a more variable part is magnetizing current. The TED system probably shows more variability from about 0 to above said 3 times in this inrush because of motor timing relative TED sampling time.

This kind of short time peak power must be handled by adequate capacitors in the PV inverter. It certainly does not need to be supplied by the array. But also the inverter must be able to handle this peak load. It might do it by current limiting, and this may be OK.

.
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