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.
