Geofence the wife?

[NeverDie]

There's another possible tweak here, which is: are you sure she really wants 120F?  Maybe she does, but for most people that's pretty hot.  If 105F is what she really wants, then you can recirc at a slower speed to achieve that, and your standby losses are considerably less.  In my case, the thermo-siphoning pretty much does that. i.e. there's no point delivering 120F if it's going to be mixed with cold water at the tap to deliver 105F.  Instead, simply recirc 105F to the sink and use just the hot water tap (assuming your particular installation provides adequate flow from just the hot water line.  If it doesn't, then you may be stuck delivering the higher temp water, which is perhaps your situation). 
 
It's actually difficult to get 120F all the time from tank heaters without setting them a lot higher and using a thermal mixing valve.  There can be a 20F degree difference between the cut-out and the kick-on temperatures, so if you set your tank for 120F, you might be getting only 100F if the tank has cooled but hasn't actually kicked on yet.  In practical terms, that can be the difference between a hot bath and a bath that's doesn't feel hot enough, all from the same tank, but on different occasions.
 
Regardless, I really like BSR's solution.  It's a platform you can do a lot more with than just trigger a recirc pump.  For example, you could use the same thing to turn on the HVAC or the exterior lights if it's dark out but your wife is coming home to an empty house...  

 

[JimS]

There's another possible tweak here, which is: are you sure she really wants 120F?  Maybe she does, but for most people that's pretty hot.  If 105F is what she really wants, then you can recirc at a slower speed to achieve that, and your standby losses are considerably less.

 
The losses will be less but still substantial.
 
The losses are proportional to the temperature difference between the water and the room temperature.  If the room temp is 75F then:
 
105F water is 30 degrees hotter
120F water is 45 degrees hotter
 
so by going to 105F water the losses are 2/3 of what they are at 120F. 
 
That's still about 10 kWh per day. 
 
This whole discussion makes me feel much better about my wife...  

 

[ano]

If the distance is 200 feet like the OP says, 3/4" copper pipe, that means this pipe holds 5.35 gallons of water.  In other words, just the water to run around the loop is 5.35 gallons. That doesn't include the extra water it takes to heat the pipes since the initial heated water is cooled when it makes it halfway around.  Now that is just water to heat the pipe, lets talk about heat dissipation from the pipe, especially if its cold out.  
 
Now you believe 2.5 gallon water heater located near the sink is less efficient?  The water stays in one small insulated area and those water heaters are very efficient. They won't work for taking a shower, obviously, but for hand washing, they are great. In addition, you can set the temp of the water lower because it does need to be hot, saving more. 
 
We have a hot water recirc. pump, but it is just too costly to run unless we know we are definitely going to need hot water.

 

[BraveSirRobbin]

I can see you point, but I guess I would really like to see just how often that point of service gizmo is drawing over 12 amps during the day.
 
I also wonder just how cold the water gets as it does indeed recirculate (i.e. you are not re-heating that water from a cold state).
 
It would be nice if someone had one of these and put a current donut on it and logged the on-off times for a few days.

 

[NeverDie]

It would be nice if someone had one of these and put a current donut on it and logged the on-off times for a few days.

That's one way to do it.  Most likely the spec sheet will tell you the standby loss rate, so you could calculate it from that also.  However, I would  concede his  point that most likely the standby losses would be less with a single POU tank, because the pipe would have much more surface area even if the volume were the same.  Moreover, you can get tankless POU which instantly heats up hot water for you on demand, and it's far more compact, but it requires higher amperage wiring.  In that case, the standby losses would be negligible.  If I had it to do over, I would probably do that rather than go through the extra effort to recirc just to accommodate a pedestal sink.  However, would I retrofit to that after-the-fact?  No way.  I can't speak for the OP, but I think most people are happy to have their remodel finished, and for it to stay that way, for all the reasons and hassles on display in Holmes on Homes.
 
Anyhow, a POU under the sink isn't going to shorten your wait time at a shower, or save your washing machine or dishwasher from having to heat up water like a recirc line will.    Sometimes it helps to see the bigger picture.  If you were to put POU's everywhere there's a benefit for rapid access to hot water, you'd need a lot of POU's.  A single POU might solve the one issue the OP delineated, but not address other issues in the background.  For instance, I am glad I'm able to use NG rather than electricity to heat the water, as I'm under  the impression NG is a lot more cost effective for heating water than electricity, not to mention you can still make hot water during a lengthy  power outage.  All of which is just to say, you're making trade-offs no matter what you pick.  This is probably one of those areas where there just isn't a single best answer.

 

[tmbrown97]

I installed a unit just like that under-counter one for my mother some time ago; but she's not in that house anymore so I can't test it.  I was pretty young and did the install myself in about 30 minutes.
 
As for the 10kWh/day - in my area that means the recirc pump would be costing $120/month - my wife is cheap so that'd just never happen.
 
Now proceeding on with the solution - BSR's approach sounds pretty handy and given the distance away from which the OP wants this to work, it may be about the best way; but if this were me, I'd probably solve the instant-availability issue if possible by putting the on-demand heater in the mud room or wherever she enters - if that's consistent, then I'd use another method - probably just a static assigned IP to her phone so that as soon as it hits wifi, it gets detected and kicks things on - just to avoid running the dedicated software on her phone.  I've never used Tasker - but how does it behave if you're on a call or using the phone at the time it needs to perform an action?
 
Or messing around with other options... depending on how many ways in/out of your area, could a Beacon be located to where she really couldn't avoid it from 5 minutes away?  Upon detection it could activate the tasker item. 
 
If you don't mind the cloud, then IFTTT also does location based events which could trigger a WeMo or SmartThings device or even trigger an email or something like that.  This works for iOS too for those who don't have Tasker available.

 

[wkearney99]

Let's not forget that spouses are not always entirely logical, let alone reasonable, when it comes to, well, anything. Sometimes the hoops jumped through and the "money wasted" are easy and cheap compared to other nonsense.

I'd aim for something in-between. Use set schedules for most of the time and then have a temporary override for circumstances where those schedules don't fit. Working from home, holidays, etc. Just be sure to layer the logic appropriately so things like vacation away modes take priority. As in, your cars might still be in the driveway, but you're off on vacation.

The simplest route is likely something that senses the presence of her car. Phones get carried, but they don't always stay charged.

One somewhat clever way to detect a car is to use a bluetooth OBD dongle. Plugs into the OnBoard Diagnostic port of the car. Tangentially you also get to run an app like Torque to see the vehicle's diagnostic state (among other things). But it'll only be detectable while the OBD has power, which might be a small window of time while the vehicle comes into range until the ignition is turned off.

I'm debating the use of an active RFID gizmo on the cars for this. But I've yet to begin experimenting with the various RFID gizmos. Passive ones require being close, active ones leech power or have self-contained batteries to maintain. TANSTAAFL.

 

[NeverDie]

So, just trying to understand: are your automotive RFID's serving the purpose of providing a very nearby geofence?  i.e. they vet whether or not a particular vehicle is in the garage?  Or, is that only part of what they are doing?

 

[pete_c]

are your automotive RFID's serving the purpose of providing a very nearby geofence?

Yes

hey vet whether or not a particular vehicle is in the garage?

Yes.
 
Removed post moving it to my DIY blogging stuff. 
 
http://cocoontech.com/forums/blog/29/entry-433-diy-rf-id/
 
Not worth burying the verbiage here in this thread. (an exercise in futility).
 
I only use it for the vehicles and its been working fine now for many years.

 

[dpilati]

Great stuff guys. Gives me lots to try.
 
Reply to a couple of points - total transperancy. There are actually 3 sinks that she could wash her hands in right away and she really does want 120. We agreed to that sometime ago as I was perfectly happy with 105. She would probably want 130 but we do have a 4yo so I was able to easily stop that. Honestly 120 hurts me. And really 120 only happens at the kitchen sink, not the powder room unless you let it run for awhile.
 
The element is set at 150 and we have a mixing valve (actually 2 - one on the solar tank before the traditional tank). 
 
When you have solar, a POU seems crazy but if it was only the powder room, I might do it. I've seen her go right to the kitchen sink mainly because it is hotter. People get in their minds that hot=clean. Not really true but I can't win that battle. Just to defend my wife a bit - she does drive a 2007 Accord when SUVs are certainly the norm in our neighborhood. That trumps everything when it comes to energy use and dollars. And honestly that 15 kwh a day costs us $200 a year if we didn't have solar (5c kwh) and with solar it probably comes to $50. This isn't a logical issue based on money. My goal is net zero electricity for the house and car. I'll have to live with the $100 in NG a year for heat (backup for the heat pumps). 

 

[jmed999]

You could use an ISY controller and install Mobilinc on her phone.  I have an Android and also installed Tasker.  You can set up Tasker with the Mobilinc plug-in to detect when she is within a certain radius of your house 200 ft, 100 ft, 3 miles, etc.  Once she is in that radius Tasker will tell Mobilinc which will tell an ISY controller to turn on the pump.  If you have an ISY it's kinda simple.

 

[BraveSirRobbin]

Yup, good idea.  I basically showed him how to do this in post #16 and #17 in this thread, though I trigger an HTTP 'GET' event in lieu of an ISY.

 

[batwater]

If your wife has an android phone you could couple AutoLocation and AutoRemote plugins for Tasker and have substantial automation flexibility. AutoLocation provides geofencing on steroids.
 
For more sophisticated 2 way communication between Tasker and HA Software you could use AutoRemote + EventGhost and an HA Software driver /  plugin. Personally I am using AutoRemote + EventGhost to interface Tasker and CQC HA Software via an EventGhost CQC Driver. End result, all of our android devices & CQC HA software can talk to each other. I imagine you could do the same thing with HomeSeer and the EventGhost plugin for it if that were your software platform of choice. 
 
-Ben

 

[JimS]

And honestly that 15 kwh a day costs us $200 a year if we didn't have solar (5c kwh) and with solar it probably comes to $50.

 
$200 per year is a little low by my calculation even at 5c/kwh.  And where do you get power for that?  Wish that was my rate.

 

[Automate]

5c/kwh.  And where do you get power for that?

 
Yea,  my power company advertises 5c/kwh but then they have all these other fees that are also proportional to your power usage so the effective rate comes to around 10c/kwh and this is without the fixed fees you pay regardless of how much power you use.