A7 AirTap install (ASHP hot water heater)

[AC_Hacker]

Originally Posted by Xringer

It's been cold down in the basement this winter, but the run-time of the A7 seems to be the same as before it got so cold...

Have you been down cellar reading scripture to your A7?

This is right up there with the miracle of the loaves & fishes!

-AC

[Xringer]

Remember, there's only two old people using the hot water here..
I double checked the Elapsed Time on the Kil-a-Watt. It says 1474 hours. (61 days).
So, I'm assuming it's working okay and hasn't been re-set or anything.

Right now, it's sunny and that 800w array is pumping about 700w into the tank.
That's about 2,388 BTUh, and it's been clear all day.
When we have sun like this, and don't use a lot of hot water, the A7 mostly stays off.
Today, it ran up 2 kWh, when we did three loads of laundry.

It's been warming up here lately. Average for the last 60 days was 34.4 °F.
For the last 30 days it's averaged 37.2 °F. The basement is now up to 50F.

When the basement gets up into my comfort range, I'll reset and start another log.
Of course with the solar PV assist, and taking more showers during hot weather,
the data is not going to be of much interest to most people.
Unless someone else besides me is running this kind of Hybrid water heater.?.

I think my wife has the most interest in these numbers. She watches the Nstar bill.
She liked it when I told her we've been using 1 KWh per day (16.66 cents)
for hot water, instead of burning 1/2 gallon of oil ($2) every morning.

[Drake]

After an informative conversation with a technical person at AirGenerate on the A7 manual saying not to reconnect standard heating elements after installing the A7 I was told of the possibility of shorting out the elements if in contact if both were wired hot at the same time. Wiring so that only one or the other is hot would be fine. No doubt the new hybrid one piece design addresses this possibility with internal safety controls.

[Xringer]

On the GE heater, the way the switching works to power to the lower element,
it's just about impossible for both to be powered up at the same time.
Plus, that kind of load would greatly exceed (2x) the breaker rating, and it would pop.

Note how the yellow and black wires connect the elements.


It 'looks' like it would be impossible to light off both elements..
But it can be done, if you first cook the switches with 100+ volts of DC..

[Drake]

I agree that it is a highly unlikely scenario, but enough to make their liability lawyers nervous about not disavowing it. As would , I think, contact between A7 HX tubing in tank and elements shorting. I plan to only use one standard element for off peak use where I will have several hours for tank to recover so cross element shorting would be impossible.

[Xringer]

Cross shorting inside the tank??? Not with normal heating elements.. The heating coil wire is insulated.

Protective Metal Sheath Electrically Isolated-^-

Hot Water Heater Elements | Wattco Offical Blog

You can't allow current to flow in the water!

I think those guys were feeling you a line..
They likely don't know why that restriction was included in the manual.
The guy that wrote that was fired 5 years ago..?.

Maybe they didn't want to take a chance on having you reconnect the 230ac
just in case you screwed up and got zapped.

I used to proof-read maintenance manuals, when I was an electronics instructor.
I even wrote a very nice user manual for a computer I/O board that I designed and
got into production (in under 90 days we were shipping product).

Anyways, here's the problem I have with this. When you put anything in a manual,
that is a little off-the-wall, or not-logical etc.. You ALWAYS explain it! You give clear reasons etc..
Most especially, if something bad can happen to the user or product..

Otherwise, the end-user/installer/tech will read that part and instantly think it's wrong.
Just another mistake in a manual, like millions of other mistakes in manuals..

The problem with 'manuals' is a lot of them are written by 'tech writers' and marketing people.
The guys who actually have a complete understanding of the product, inside and out.?.
They end up proof reading it.. And sometimes they have to rewrite the whole thing..

But, when the engineering dept is too busy to proof-read..
Those crappy manuals get shipped with the product.. To be revised later..

[Drake]

I agree with you Xringer. But not being an electrical engineer or anything I thought it due diligence to see what manufacturers reasoning may have been from. They confirmed that they see no problem if A7 and standard elements are both used and controlled to not be hot at the same time. As that is a recommendation that will work for me I'm good.

[Xringer]

Originally Posted by Xringer

Starting 2-4-2013
Ending 4-5-2013
KWH used 60

It's been 78 days total & 73.33 kWhs ($12.22) later on the KilaWatt meter..
Now using almost 1 kWh per day on average.

Still pretty cool in this area..

This is a plot of the last 28 days..

We are getting slightly better solar now, so I'm hoping for less power use, soon..

[Xringer]

I hooked the tracker array to the upper heating element..




At noontime, they were putting in 1063 watts (3627 BTUh).
So, since that's about 1/2 of the water heating provided by the 7000 BTUh A7,
that means 2 hours of good sun is the same as 1 hour of A7 use.

This configuration might make more hot water than we need.
So, I might have to add a relay to shut down 500w array.

The array is tracking again (after resting during the winter), so it's going
to put out watt-hours that might close to what the fixed array is supplying.

I've pulled out all the old AC power/temperature control hardware.
Also moved the temperature sensor into direct contact with the upper tank.

The 13 ohm load of the upper element seems to coexisting with the TS45
(TriStar controller) and the 48v battery bank is being maintained.

http://ecorenovator.org/forum/attach...1&d=1367429968

[Xringer]

Results so far (after adding tracker array)

I didn't check the tank temperature this morning, but it was pretty hot my guess is around 40C (104F).
That's about the peak temperature we've been seeing lately.
I took a shower (really hot), went out and came back at lunchtime.
The A7 is on a timer and only has grid power between 13:00 & 21:00.
So it never came on today.

Monitored temps starting at noon.
12:00 50.6C (123F)
13:00 54.8C
15:00 60.8C
16:00 63.9C (147F)
________________
Gain 13.3C (24F)
___________________
Per Hour 3.325C (6F)

~~~~
Edit 5/2/13
We used a good amount hot water in the sinks today. A bit more than normal.
Not in any large amount. Just hand-washing, some dish-washing by hand etc. We used it liberally, like it was free.
At the end of the day, the A7 had stayed off and the tank was at 64C.

It looks like some clouds coming in on the 8th..
Woburn May Weather 2013 - AccuWeather Forecast for MA 01801
So, I'm not going to just unplug the A7 after all..