A7 AirTap install (ASHP hot water heater) - Page 23

Xringer · 02-07-13, 08:30 AM

During the last few months, I've been using a timer to keep the A7 off during sleeping hours.

07:30 ON
22:00 OFF

It's worked pretty well. And on many mornings when I'm up early, I can hear the A7 start up at 7:30 AM.
(I don't like the idea of midnight water heating, since I may not be awake again until 8 or 9 hours later).

Now I'm using a PV Boost on the heater. But, the sun doesn't really hit the panels very hard, until 9 or 10AM..

In order to take advantage of solar hours, I changed the timer program last night.

07:30 ON
08:00 OFF

12:00 ON
22:00 OFF

The 30 minute run at 7:30 will give the tank a shot of heat,
and should be enough to handle morning HW needs. (Remains To Be Seen)

The OFF time between 8AM and noon should give the sun enough time to kick up the water temperature. (RTBS)

If the solar boost works, and not much HW was used in the AM, the A7 will remain off, for the rest of the day.?. Maybe..

Interestingly, the A7 didn't run this morning at 7:30AM.. Maybe the solar boost from yesterday's partly cloudy wasn't that bad..?.

It's 9:15AM and the sun is fully on the 800w array, but it's at too great an angle, to harvest much power. It's less than 30w..

Need some MPPT right now!!

~~~
Anyways Friday's blizzard is going to be a problem. It's going to conflict with my solar scheduling timer.

So, maybe it's time to set up the CAI controller to earn it's keep.
If I used a temperature sensor and a current sensor (on the PV line),
the CAI could look at those two variables and decide if the A7 needs power.
I could use a TTL output to an SSR, but the X10 appliance module would be a lot easier.

If it's starting to get nice and sunny, and water temp is climbing.?.
Then withhold AC grid power from the A7..

Xringer · 02-08-13, 11:35 AM

In this experiment, I connected 800w of PV (DC) directly to the 230VAC input of the GE hotwater heater.

It worked great! But, when the upper water got hot, and the upper T-stat
switched PV power to the lower heating element, there was contact arcing.

When the lower section of the tank got hot, the lower T-stat opened and arced.

After a few hours of switching back and forth, both T-stats malfunctioned.
This caused both heating elements to run simultaneously.
In parallel, their resistive load was cut in half, causing less heating to the tank.

Had I done a google check, I would have learned about this and saved the T-stats..
Just in case I ever wanted to use this heater on the grid..

I disconnected the upper element to get back to full power from the PV array.
When the sun was good yesterday, around noontime 70 to 80% power was logged.

For those who want to use PV on this type of water heater,
disconnect the AC wiring on the lower T-stat and element.
Then, use a Relay to control the PV power coming into the lower element.
Use the T-stat to apply low voltage to the Relay.

AC_Hacker · 02-08-13, 12:29 PM

Quote:

Originally Posted by Xringer

...there was contact arcing...

Ouch!

-AC

Xringer · 02-08-13, 12:55 PM

Quote:

Originally Posted by AC_Hacker

Ouch!

-AC

I figured that a device that could handle 240Vac at 20 amps
would be able to easily handle 122 Vdc at 8 amps.. Wrong!!

If I don't use the CAI to control the hotwater heater, I'll likely repair or replace
the lower thermostat, and use it to control a relay(or FET) to switch the PV on & off..

Shop Whirlpool Electric Water Heater Replacement Lower Thermostat at Lowes.com

Mikesolar · 02-08-13, 06:56 PM

Quote:

Originally Posted by Xringer

I figured that a device that could handle 240Vac at 20 amps
would be able to easily handle 122 Vdc at 8 amps.. Wrong!!

If I don't use the CAI to control the hotwater heater, I'll likely repair or replace
the lower thermostat, and use it to control a relay(or FET) to switch the PV on & off..

Shop Whirlpool Electric Water Heater Replacement Lower Thermostat at Lowes.com

Too bad it is such a cheap component. I have a whole box fill of them. Not worth the postage to send it.

Xringer · 02-19-13, 12:49 PM

My messy log book shows that our weekend of snow had some effect on A7 power use.

It kinda looks like we used about 3.77 kWh during the last few days.
And about 2.95 of that was burned during the weekend (of snow).

Of course, there were three loads of laundry done on the weekend!!

Maybe there will be some meaningful data after I log about 6 more months.
(need to computerize this logging job).

Anyways, today is a very poor solar day. It's now completely overcast!
http://maps.wunderground.com/data/64...ne_vi_anim.gif

But, the A7 isn't running very much, since a small amount of PV is keeping the temp stable..
I'm very pleased to see about 1 kWh per day, (from the grid) being used for hotwater.

I started logging on 2-4-2013 (just after midnight) and it's been about 15.5 days and 15.69 kWh..
I think that's going to drop when we start getting more sunny days per week..

warmwxrules · 02-20-13, 05:47 PM

I'd be interested in knowing where the heat is being pulled from? The basement walls, the house?

I put in a power vent nat gas 40 gallon a few weeks ago. Seems to be working great. I'll have to see how the power bill looks next month...no more 50 gallon electric beast.

Mikesolar · 02-20-13, 08:45 PM

But at a 50-55% efficiency!! What is your gas cost? Also, now you are venting building air that you paid to heat.

warmwxrules · 02-20-13, 09:03 PM

Mike-

I wasn't dissing the AirTap...I'd love to have one... but I probably wouldn't get it to work here in southwest WI in winter without dropping my basement to freezing (its 50F right now and that is with the furnace running often)... I'd love one for May/June/July/Aug/Sept/Oct to cool/dry my basement, but can't justify the cost...yet (plus...do they even sell them anymore?)

Natural gas charges on my last bill (xcel energy):
$.75/therm for supply/distribution (i combined them)... So I have no idea how that breaks down for what it will cost to run an AO Smith power vent 40 gallon tank? Family of 5 here...

Xringer · 02-20-13, 10:18 PM

Quote:

Originally Posted by warmwxrules

I'd be interested in knowing where the heat is being pulled from? The basement walls, the house?

I put in a power vent nat gas 40 gallon a few weeks ago. Seems to be working great. I'll have to see how the power bill looks next month...no more 50 gallon electric beast.

I think a lot of it comes down from above. The area where the A7 is, has
no overhead insulation, so conduction leakage from the heated house above
is being conducted down into the basement.
The floor slab is slightly warmer than items in the basement (drill press etc).
The ground a couple of feet under the floor slab is even warmer.
Which seems to indicate the floor is a heat source.
The walls are very cold, especially higher up..
The outside temperature greatly effects the concrete walls.

02-07-13, 08:30 AM	#221
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Solar assist for the A7 During the last few months, I've been using a timer to keep the A7 off during sleeping hours. 07:30 ON 22:00 OFF It's worked pretty well. And on many mornings when I'm up early, I can hear the A7 start up at 7:30 AM. (I don't like the idea of midnight water heating, since I may not be awake again until 8 or 9 hours later). Now I'm using a PV Boost on the heater. But, the sun doesn't really hit the panels very hard, until 9 or 10AM.. In order to take advantage of solar hours, I changed the timer program last night. 07:30 ON 08:00 OFF 12:00 ON 22:00 OFF The 30 minute run at 7:30 will give the tank a shot of heat, and should be enough to handle morning HW needs. (Remains To Be Seen) The OFF time between 8AM and noon should give the sun enough time to kick up the water temperature. (RTBS) If the solar boost works, and not much HW was used in the AM, the A7 will remain off, for the rest of the day.?. Maybe.. Interestingly, the A7 didn't run this morning at 7:30AM.. Maybe the solar boost from yesterday's partly cloudy wasn't that bad..?. It's 9:15AM and the sun is fully on the 800w array, but it's at too great an angle, to harvest much power. It's less than 30w.. Need some MPPT right now!! ~~~ Anyways Friday's blizzard is going to be a problem. It's going to conflict with my solar scheduling timer. So, maybe it's time to set up the CAI controller to earn it's keep. If I used a temperature sensor and a current sensor (on the PV line), the CAI could look at those two variables and decide if the A7 needs power. I could use a TTL output to an SSR, but the X10 appliance module would be a lot easier. If it's starting to get nice and sunny, and water temp is climbing.?. Then withhold AC grid power from the A7.. __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less..

02-08-13, 11:35 AM	#222
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	High voltage from PV can cook AC water heater controls In this experiment, I connected 800w of PV (DC) directly to the 230VAC input of the GE hotwater heater. It worked great! But, when the upper water got hot, and the upper T-stat switched PV power to the lower heating element, there was contact arcing. When the lower section of the tank got hot, the lower T-stat opened and arced. After a few hours of switching back and forth, both T-stats malfunctioned. This caused both heating elements to run simultaneously. In parallel, their resistive load was cut in half, causing less heating to the tank. Had I done a google check, I would have learned about this and saved the T-stats.. Just in case I ever wanted to use this heater on the grid.. I disconnected the upper element to get back to full power from the PV array. When the sun was good yesterday, around noontime 70 to 80% power was logged. For those who want to use PV on this type of water heater, disconnect the AC wiring on the lower T-stat and element. Then, use a Relay to control the PV power coming into the lower element. Use the T-stat to apply low voltage to the Relay. Attached Thumbnails __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less.. Last edited by Xringer; 02-08-13 at 12:09 PM..

02-19-13, 12:49 PM	#226
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	A log page.. My messy log book shows that our weekend of snow had some effect on A7 power use. It kinda looks like we used about 3.77 kWh during the last few days. And about 2.95 of that was burned during the weekend (of snow). Of course, there were three loads of laundry done on the weekend!! Maybe there will be some meaningful data after I log about 6 more months. (need to computerize this logging job). Anyways, today is a very poor solar day. It's now completely overcast! http://maps.wunderground.com/data/64...ne_vi_anim.gif But, the A7 isn't running very much, since a small amount of PV is keeping the temp stable.. I'm very pleased to see about 1 kWh per day, (from the grid) being used for hotwater. I started logging on 2-4-2013 (just after midnight) and it's been about 15.5 days and 15.69 kWh.. I think that's going to drop when we start getting more sunny days per week.. Attached Thumbnails __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less.. Last edited by Xringer; 02-19-13 at 12:58 PM..

02-20-13, 05:47 PM	#227
warmwxrules Helper EcoRenovator Join Date: Nov 2011 Location: La Crosse, WI Posts: 78 Thanks: 0 Thanked 3 Times in 3 Posts	I'd be interested in knowing where the heat is being pulled from? The basement walls, the house? I put in a power vent nat gas 40 gallon a few weeks ago. Seems to be working great. I'll have to see how the power bill looks next month...no more 50 gallon electric beast.

02-20-13, 08:45 PM	#228
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	But at a 50-55% efficiency!! What is your gas cost? Also, now you are venting building air that you paid to heat.

02-20-13, 09:03 PM	#229
warmwxrules Helper EcoRenovator Join Date: Nov 2011 Location: La Crosse, WI Posts: 78 Thanks: 0 Thanked 3 Times in 3 Posts	Mike- I wasn't dissing the AirTap...I'd love to have one... but I probably wouldn't get it to work here in southwest WI in winter without dropping my basement to freezing (its 50F right now and that is with the furnace running often)... I'd love one for May/June/July/Aug/Sept/Oct to cool/dry my basement, but can't justify the cost...yet (plus...do they even sell them anymore?) Natural gas charges on my last bill (xcel energy): $.75/therm for supply/distribution (i combined them)... So I have no idea how that breaks down for what it will cost to run an AO Smith power vent 40 gallon tank? Family of 5 here...