Setback for hot water tank?

We've had some long power outages here. You can still take a hot shower 24 hours after the power has gone out. Just not a really long one.
 
I recently investigated an electric tankless water heater for my house. Unfortunately it would require a major rewire to my water heater. The cost of rewiring and tearing up the walls makes this option somewhat unattractive. I would rather put that money into a geothermal heating system.

Steve Q
 
Tankless water heaters have their advantages, however they do not handle water pressure fluctuations well. If you have variable water pressure from your company or use thermostatic valves (like we do), the tankless heater is not going to be a good option.
 
I ran across this article earlier this week and think it applies to the expanded discussion of different water heater types. This article discusses two downsides of tankless water heaters and solutions to mitigate those issues.

http://www.finehomebuilding.com/how-to/articles/add-a-tank-and-pump-to-a-tankless-water-heater-to-save-energy.aspx?&lookup=auto&V27=&V28=&V29=&V30=&V31=&V32=&V33=&V34=&V35=&V55=&V56=&Taun_Per_Flag=True&utm_source=email&utm_medium=eletter&utm_content=20130401-labor-shortage&utm_campaign=fine-homebuilding-eletter

Picta, it does cover a solution to the issue you describe.
 
I'm not saying that tankless are perfect but having had homes with tanked (electric and gas), geo-thermal, and tankless (gas) water heaters, I like tankless the best and put it in my last two homes without regrets. I like being able to get up at any hour of the day (or night) and having all the hot water I want.
 
If I save money that's great but I did it for the endless hot water.
 
The issues that you read about all have solutions IF they occur but that varies house to house.
 
One issue mentioned in the article was the 5 GPM rating. That is not an issue for us as we installed dual 9 GPM units. Many brands have models that allow for hooking up multiple units with a controller that, in essence, gives you one big unit. We allowed for a total of four units but two worked fine.
 
As always YMMV.
 
How about this.
 
http://www.ebay.com/itm/DWYER-INSTRUMENTS-DBTA3601-Bimetal-Thermometer-Digital-Stem-6-/221192985448?_trksid=p3284.m263&_trkparms=algo%3DSIC%26its%3DI%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D21%26pmod%3D321078043107%26ps%3D54
 
Put a "T" fitting on your hot water tank outlet.  Thread the T fitting in with the long axis up and down so you have a straight shot into the tank from the top.  Use the side port for your water to the house.  Use the top port to thread that thermometer.
 
The thread of my original posts from 2009 are still on the board:
 
http://cocoontech.com/forums/topic/14720-shut-off-water-heater-during-peak-power-times/?p=124717
 
I am still using this exact same approach. It has worked flawlessly.
 
Here is a summary of how I monitor and control my hot water heater:
 
Monitor:
  1. A CR3110a current sensor is attached to one leg of the power feed to the water heater
  2. The CR3110a is connected to a small circuit which I designed to trigger an X10 DS10a wireless door/window sensor
  3. The DS10 sends a signal to the W800/ACRF2 receiver connected to HomeSeer when the water heater turns ON or OFF
  4. When Homeseer sees the DS10 state change it runs a script that saves each ON/OFF signal to a file on the Homeseer Computer
  5. At the end of each day, Homeseer runs a batch file that runs an Excel spreadsheet that totals the On time and creates a pivot table showing run time for each hour of the day and KWhrs used for each hour.
  6. The water heater data is combined with the data from the rest of my major appliances on a spreadsheet that shows total KWHrs for each appliance and the total for the house. 
Control:
  1. The water heater is turned ON and OFF by a "Relay In a Box" at the nain breaker panel.
  2. The Relay In A Box is triggered via a HobbyBoards 4 channel xAP relay board
  3. The xAP signal is sent via CAT5 cable to the xAP relay board from my Homeseer xAP network
  4. Homeseer has events to trigger On at 7 AM and 9 PM and Off at 11 PM and 5 PM
Lots a things are involved and it took many months back in 2009 to get this working.  But I am very satisfied with the results.
 
Here is a partial summary of my data from March 2013:
 
 
                                         Total KW Avg KW/day Total $ % of Total
Air Conditioner            -                                                 $        -   0%
Upstairs Air Conditioner            -                                    $        -   0%
Water Heater                   349.69           11.28       $   43.18           25%
Refridgerator                  35.47             1.14          $    4.38            2%
Freezer                           21.53             0.69          $    2.66             2%
Well Pump                       25.77             0.83           $    3.18          2%
Washer                          5.11             0.16            $    0.63                0%  
Dryer                            51.08             1.65             $    6.31              4%
Irrigation Pump            -                                                    $        -   0%
 
 
For the month of March my measurements (all appliances) totaled 1422 compared to my power company total of 1446 KWhrs.
 
Steve Q
 
Just curious, I see no listing for electric heat/heat pump, which I assume means you have NG.  Which, if indeed is the case, why don't you use the NG to heat your water?
 
Thermal expansion of a water heater tank IS a problem, especially if you decrease the water heater temp to save power. 
This explains it and doesn't even consider the added stress of powering and unpowering the water heater.
 
http://www.wvdhhr.org/phs/water/thermal_expansion2.pdf
 
As stated here, at best, the pressure relief valve opens and you loose hot water when the tank heats.  From experience I can tell you the seals when the pipes connect to the water heater are also stressed.  This can be really improved with an expansion tank which is what I added after my third water heater. 
 
From my experience, shutting off an electric water heater located in a 45 degree winter garage does not maintain its temp the next morning.  When I used to control my water heater, I would calculate the warmup time each day based on the outdoor temp, and it was usually 90 minutes to 2 hours at the coldest.  Still the measurements I did showed turning my electric water heater off at night (when my electric rates are lowest anyway) saved very little electricity. And if we ever had to get up earlier than planed, we faced a cold shower.  Instead I bought a water heater blanket and that DOES save some costs.  And thermal expansion was decreased if anything.
 
I don't think people were arguing that it isn't a problem, I think the argument is that the main driving force behind this problem is expansion that occurs after using hot water, not after letting the tank sit idle for a few hours.  The basic jist is that the temp swings from using the tank are far greater than the temp swings from letting it sit idle.  Also as it mentioned, the check valve situation makes a difference.  If your water can run backward to the city, then it won't ever pressurize.  
 
Perhaps your tank sitting in an ice cold garage is different.  I had never seen a tank in a garage until I moved to Texas.  Garages around here almost never see temps below 50 and even that is rare.  Of course in the summer the garage can be over 100 which pretty much means the tank would take forever to cool off, and even then it wouldn't get below 100.  In my old house, (NG in garage tank), my NG bill was like $5 for gas and then another $10 just for the privilege of being connected during the summer.
 
'Lou Apo' timestamp='1365169652' post='193783']Just curious, I see no listing for electric heat/heat pump, which I assume means you have NG. Which, if indeed is the case, why don't you use the NG to heat your water?


I did not include the whole table. There are 15 more lines which include electric baseboard heaters and the propane furnace. Gas water heaters in a garage area are not permitted by code in my area.

Steve Q
 
'Lou Apo' timestamp='1365125428' post='193756']How about this.

Put a "T" fitting on your hot water tank outlet. Thread the T fitting in with the long axis up and down so you have a straight shot into the tank from the top. Use the side port for your water to the house. Use the top port to thread that thermometer.



A solar powered manual gauge is not quite what I was looking for. I wanted something that I could connect to my home automation system. I can manually measure the water temperature by opening the sillcock about 3feet from the water heater and sticking a thermometer in the outflow. Installing a tee fitting on the top of my water heater is a major issue; a lot of soldering would be required. I don't really need to know the temperature, do I?

Steve Q
 
I don't have a thermal expansion issue because I have a well and a pressure tank. The large bladder pressure tank can handle the minimum expansion that occurs. I also have " anti hammering" air gaps on all my sinks. These also serve as expansion areas.

Steve Q
 
SteveQ said:
'Lou Apo' timestamp='1365125428' post='193756']How about this. Put a "T" fitting on your hot water tank outlet. Thread the T fitting in with the long axis up and down so you have a straight shot into the tank from the top. Use the side port for your water to the house. Use the top port to thread that thermometer. A solar powered manual gauge is not quite what I was looking for. I wanted something that I could connect to my home automation system. I can manually measure the water temperature by opening the sillcock about 3feet from the water heater and sticking a thermometer in the outflow. Installing a tee fitting on the top of my water heater is a major issue; a lot of soldering would be required. I don't really need to know the temperature, do I? Steve Q
Click to expand...
 
"I don't really need the temp, do I?"  I don't really know, I was just responding to an earlier post you made asking if there is a way to do it.  I did only a simple search to find that thermometer.  The point of my search was to find one with an NPT design so you could get it into the tank without risk of leak.  I am sure someone makes the same thing in digital.
 
I suppose you could use it along with your relays as the temp controller.  You would use the built-in thermostat on the tank only for protection against an overheat.  In other words, set it to like 150 and then use your HA stuff and the that type of thermometer to create algorithms for when to heat the tank and to what temp.
 
Lou Apo said:
Perhaps your tank sitting in an ice cold garage is different.  I had never seen a tank in a garage until I moved to Texas.  Garages around here almost never see temps below 50 and even that is rare.  Of course in the summer the garage can be over 100 which pretty much means the tank would take forever to cool off, and even then it wouldn't get below 100.  In my old house, (NG in garage tank), my NG bill was like $5 for gas and then another $10 just for the privilege of being connected during the summer.
Click to expand...
 
Yeah, In AZ, in the summer, my water heating bill is nothing. The water will easily stay over 100 degrees with no energy at all.  I guess in this case insulation is bad.  Also, another benefit of the garage is your car tends to give off lots of heat and it helps efficiency as well. 
 
In AZ with natural gas, my gas bill in the winter is $100 a month tops, and that includes gas heat for a 3000 sq ft. home, stove and the water heater.
 
You must log in or register to reply here.

Similar threads

Teken
Aquanta Hot Water Tank - Controller / Energy Management
Replies
1
Views
727
Sunnovations
S
Back
Top