Electric water heater with timer and thermostatic mixing valve

magic8192

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Would this honeywell mixing valve and this mechanical timer work?
I have a 50 gallon commercial water with dual 180F 2500Watt thermostats.
It is the #1 power user in my home.

Rewire the dual thermostats individually and connect the mechanical timer to 1 element.
Set the thermostat for the water heater element on the timer to 180F
Set the thermostat for the water heater element not on the timer to 120F
Set the timer to allow the 180F element to come on at 10:00 a.m. and turn off at 3:00 p.m.
- Heat water during max PV
Set the mixing valve at 120F
 

snoobler

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The only thing that gives me pause is the 180°F. That just seems too dang high.

IMHO, usability will be impacted. If it's just you, you can probably manage it, but I wouldn't want the uncertainty of getting 120 vs. 180°F water out of my hot faucet for anyone else in the home.

EDIT: DERP... missed the mixing valve.

Have you considered using the timer to allow normal operation only during solar PV hours and upping the temperature to something like 140° on both thermostats?
 
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Hedges

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Yes, but a couple issues.

The timer is 120V (edit, it is 240V). You'll have to determine if it can run on 120V but have its switch complete a 240V circuit (yes I think it can).
(or else run heating element on 120V, which will be 1/4 the wattage.)

Is the timer to use off-peak time utility rates?
If you ever have a power failure it might shift to using peak rates instead.

I use that timer for my espresso machine because the lightweight ones failed. Sometimes it has ended up starting later in the morning than intended (maybe that won't happen now that it is fed by my battery backup system.)

You could have it start at Midnight or whenever off-peak starts. Unless you're trying to consume PV generated power to avoid export.

I used this timer and 120V hookup (for both water heater elements) to avoid peak rate hours. The 1/4 wattage is within its power handling:

 
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magic8192

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The only thing that gives me pause is the 180°F. That just seems too dang high.

IMHO, usability will be impacted. If it's just you, you can probably manage it, but I wouldn't want the uncertainty of getting 120 vs. 180°F water out of my hot faucet for anyone else in the home.

Have you considered using the timer to allow normal operation only during solar PV hours and upping the temperature to something like 140° on both thermostats?

The mixing valve should maintain a constant 120F to the house. Only the tank gets to 180F and it is a commercial tank that should handle it.
 
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magic8192

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Yes, but a couple issues.

The timer is 120V. You'll have to determine if it can run on 120V but have its switch complete a 240V circuit (yes I think it can).
(or else run heating element on 120V, which will be 1/4 the wattage.)

Is the timer to use off-peak time utility rates?
If you ever have a power failure it might shift to using peak rates instead.

I use that timer for my espresso machine because the lightweight ones failed. Sometimes it has ended up starting later in the morning than intended (maybe that won't happen now that it is fed by my battery backup system.)

You could have it start at Midnight or whenever off-peak starts. Unless you're trying to consume PV generated power to avoid export.

I used this timer and 120V hookup (for both water heater elements) to avoid peak rate hours. The 1/4 wattage is within its power handling:

As noted, I am using the 240VAC one
The timer is to use the hot water heater during max PV. I have lots of PV.

The theory being that I heat the water only during the middle of the day when I have extra free power. Then I hope the hot water stays above 120F before the next day. If it goes below 120F then the water is heated from the grid.
 

Hedges

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In theory the mixing valve maintains a constant 120F to the house.

I have one in my shower valve.
Worked well for years, but eventually got sticky.

I knew sediment would come through. I found a high temperature rated strainer for potable water at Grainger (but not that high).
So my problem wasn't chunks, rather deposits.
Be sure to put a strainer before the mixing valve.
 
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Hedges

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As noted, I am using the 240VAC one
The timer is to use the hot water heater during max PV. I have lots of PV.

The theory being that I heat the water only during the middle of the day when I have extra free power. Then I hope the hot water stays above 120F before the next day. If it goes below 120F then the water is heated from the grid.

Yes, and with a big tank it should. I did that without the always enabled thermostat.

Sometimes when we play games with the controls something trips. I think I remember an over-temp cutout activating.
Maybe there is mineral buildup and running one heater at higher temperature pushes that over the edge?

Why do you care whether it is max PV, unless you're off grid?
Wouldn't lowest demand on utility grid be the best time? Maybe 10:00 AM to 3:00 PM is that now. Or maybe after Midnight, at least in summer.
 

Hedges

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Yeah. Reading fail. mixing valve didn't register.

It's what you do to make plucking birds easier.
I didn't think to do that with the first couple (pheasant, turkey) my dog presented us with.
 

Hedges

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In other news, the 40 gallon Kenmore gas water heater which came with this house I bought January 2000 is still working fine.
I replaced a couple mixed-metal plumbing connections, also the temperature/pressure relief valve which started leaking, but that's it.
 

magic8192

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Yes, and with a big tank it should. I did that without the always enabled thermostat.

Sometimes when we play games with the controls something trips. I think I remember an over-temp cutout activating.
Maybe there is mineral buildup and running one heater at higher temperature pushes that over the edge?

Why do you care whether it is max PV, unless you're off grid?
Wouldn't lowest demand on utility grid be the best time? Maybe 10:00 AM to 3:00 PM is that now. Or maybe after Midnight, at least in summer.
I am trying to use less grid power. I hate sending my extra power to the grid because they pay me wholesale for it.
 

Hedges

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OK, it's sell low buy high so you want to consume power rather than export where possible.
Timer is simple and can be a big help.
Will water heater heat all the water needed while just reducing production, not becoming a consumer? If so, that is good enough.


More optimum but more complex is varied consumption.
It isn't difficult to get a measure of current in main connection (current transformer) but a bit harder to determine which direction power is flowing.

Heater element can be run 100% at 240V or 25% at 120V
A triac based dimmer would be continuously variable. If you could get a good 240V one.
Not sure how accurately the smart meters measure power with that waveform.

I imagine an Arduino or similar programmed to adjust dimmer setting to keep net export at zero if possible.
 

magic8192

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OK, it's sell low buy high so you want to consume power rather than export where possible.
Timer is simple and can be a big help.
Will water heater heat all the water needed while just reducing production, not becoming a consumer? If so, that is good enough.


More optimum but more complex is varied consumption.
It isn't difficult to get a measure of current in main connection (current transformer) but a bit harder to determine which direction power is flowing.

Heater element can be run 100% at 240V or 25% at 120V
A triac based dimmer would be continuously variable. If you could get a good 240V one.
Not sure how accurately the smart meters measure power with that waveform.

I imagine an Arduino or similar programmed to adjust dimmer setting to keep net export at zero if possible.
It would be nice to only heat water with the 180F thermostat when there was PV available.

I could use a stepped curve for the 180F thermostat. maybe power the 180F element with 120VAC at 8:30 a.m. and then step up to 240VAC at 10:30 then step down to 120VAC at 3:00p.m. and power off the 180F element at 5:00 p.m.
 

Hedges

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Could, that draws 22% more power.
I think that would require a second timer "T106R - - 1NO/1NC* (can be wired SPDT)"
May not be worth the cost, especially if 4.5 hours at 240V provides all heating.

Are you on a smart meter with granularity of remote reading typically 15 minutes? Or does utility distinguish production/consumption some other way?
 

magic8192

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I have a sense and I can see when the HW heater is on. My meter just tells me how much I have used and how much I have sent to the grid.
 

Hedges

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Does your utility have a meter that records import and export separately, so buy/sell prices applied continuously?
Some people have dual meters, one dedicated to PV.

I have one bidirectional meter with one reading that the utility can access remotely. Seems to me that they can't simultaneously access everyone's meter at 3:00 PM when rates change, so maybe they tell it to store a reading at that time and access it later at their convenience.
 

magic8192

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I have one bidirectional meter. It seems very simple. I can look at it and it tells me the current KWh usage and after a few seconds, it tells me the total sent to the grid.
 

magic8192

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I have the parts for this. They arrived yesterday. Should be a fun little project this weekend.
 
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