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-   -   Looking for water heater timer (https://ecorenovator.org/forum/showthread.php?t=3038)

Pirate 06-09-13 09:54 AM

Looking for water heater timer
 
Does anyone know of a elec. water heater timer, that can be programmed to turn on for periods less than 30 minutes? Like 15 or 20 minutes.
My current one has a min of 1 hour.

NiHaoMike 06-09-13 10:01 AM

Harbor Freight sells a digital timer that is programmable down to 1 minute resolution. It can switch a 120V unit (up to 15A) directly or use a contactor for 240V.

Pirate 06-09-13 02:44 PM

Thanks, I didn't think of using a contactor, which I guess is a relay. Can you recommend a particular contactor and source?
I have a digital timer I use on my lanai metal roof wattering/cooling system that would work. It goes down to 10 sec. on or off.
Thanks again

herlichka 06-10-13 06:49 PM

I installed an Intermatic EH40 electronic timer several years ago on a hot water tank at my Parish hall. The timer wires inline to the heater, can be set for up to 7 starts/stops per day, has a manual "on" button, and a battery backup. The time can be set for as little as one minute. It has been in service for several years now, and has worked flawlessly. At the time it cost me about $135.00Cdn, and I'm sure you can find the same product in the U.S.

If you do a search on this site with the key word "hot water timer" you will find the thread. Never mind, found it:

http://ecorenovator.org/forum/conser...ank-timer.html

Ryland 06-10-13 08:22 PM

You can build a timer using a solid state relay like one of these:
Dayton 5Z972 Solid State Relay 5Z972 40 Amp | eBay

Some solid state relays need to have a DC trigger while others work off AC, they are NOT interchangeable.
Then get a cheap digital timer that has 1min resolution.

NiHaoMike 06-10-13 09:45 PM

Beware that a SSR will need a heatsink if used anywhere near its ratings. (A PC CPU heatsink will work nicely.) A contactor will not and will be more efficient for this application. On the other hand, a SSR (or SCR/triac) can be used to throttle back the power with the proper control logic.

Ryland 06-10-13 10:39 PM

Small computer fans draw very little power, I have some on my desk that draw less then 2 watts and if you combine them with a heat sink everything should stay cool and happy, you can also get solid state relays that can switch 100 amps, so switching 30 amps is not an issue, but I agree that a heat sink is a good idea.

WyrTwister 07-15-13 11:19 AM

electric water heater timer - Google

God bless
Wyr

ham789 07-16-13 08:23 PM

What are the advantages of a water heater timer?

What's the thermal time constant of a water heater?

How does shorter time help?

where2 07-16-13 10:58 PM

Quote:

Originally Posted by ham789 (Post 30703)
What are the advantages of a water heater timer?

What's the thermal time constant of a water heater?

How does shorter time help?

For me, my WH is located inside my air conditioned space. Lost heat from my WH, means additional cooling $$$ and additional WH heating $$$. So, I have mine timed to run 30 minutes before dawn. I put a hi/low recording digital thermometer with remote sensor probe against the wall of my WH to track the temperatures, and adjusted the timing of the run cycles to fit accordingly. Mind you, my water comes out of the tap at 76F from the cold faucet, not that ice water you folks up north have to heat up and shower with. :thumbup:

WyrTwister 07-17-13 05:55 AM

Quote:

Originally Posted by ham789 (Post 30703)
What are the advantages of a water heater timer?

What's the thermal time constant of a water heater?

How does shorter time help?

Any water heater looses some heat . The idea is to shut it off at times whan tou are very unlikely to need / use HW .

For instance , turn it off at nite , after your regular bed time . Turn it off early enough , before you regularly get up , to allow it to bring the water up to temp , so you can have HW for your shower .

The schedule can be made more complicated than that .

God bless
Wyr

ham789 07-17-13 08:12 PM

OK, but with most things in life, the devil is in the details.
What's the temperature of the water when you turn off
the heater?
What's the temperature of the water just before you turn
it back on.
What's the capacity of the heater.
From those three numbers, you know how many BTU's
it's gonna take to get the water hot again. Time is not a
factor, it's all about the BTU's.

That's also the number of BTU's of waste heat that your
air conditioner will have to get rid of.

If the water temp changes a LOT, you need more insulation
on the water heater.
If it's not a lot, you can make a linear estimate of the
heat lost at maximum temperature vs the heat lost
at lower temperatures as the water cools...that we already
calculated.

My guess is that, for a well insulated water heater,
the difference is in the noise level.

The bottom line in all this is that it takes about the same
amount of energy to reheat the water as you lost by turning
it off. All you're saving is the difference between the
total heat lost at max temp vs the total heat lost
at an average temperature about half way between
the two temps we measured above. That's the extra
heat your air conditioner has to take out.

And that having microsecond resolution in when you
turn it on or off is inconsequential.
Hence, the question about thermal time constant.
You may discover that turning it off at all is mostly
wishful thinking.

But, it's all about the exact details of your particular
situation.

WyrTwister 07-18-13 02:08 AM

Quote:

Originally Posted by ham789 (Post 30726)
OK, but with most things in life, the devil is in the details.
What's the temperature of the water when you turn off
the heater?
What's the temperature of the water just before you turn
it back on.
What's the capacity of the heater.
From those three numbers, you know how many BTU's
it's gonna take to get the water hot again. Time is not a
factor, it's all about the BTU's.

That's also the number of BTU's of waste heat that your
air conditioner will have to get rid of.

If the water temp changes a LOT, you need more insulation
on the water heater.
If it's not a lot, you can make a linear estimate of the
heat lost at maximum temperature vs the heat lost
at lower temperatures as the water cools...that we already
calculated.

My guess is that, for a well insulated water heater,
the difference is in the noise level.

The bottom line in all this is that it takes about the same
amount of energy to reheat the water as you lost by turning
it off. All you're saving is the difference between the
total heat lost at max temp vs the total heat lost
at an average temperature about half way between
the two temps we measured above. That's the extra
heat your air conditioner has to take out.

And that having microsecond resolution in when you
turn it on or off is inconsequential.
Hence, the question about thermal time constant.
You may discover that turning it off at all is mostly
wishful thinking.

But, it's all about the exact details of your particular
situation.

I am guessing a lot would depend on how well insulated the WH is , to begin with ? Wrap the WH in a bunch more insulation and it may not be saving a lot .

Something else , if the hubbie , wifey & crumb crunchers are away from the house in the day time , a second off cycle saves more , except on the weekend ( indicating a need for a somewhat / potentially more $$$ time clock that can be programed for a different schedule on the week ends ) .

A different thought , in an all electric house , especially with resistance heat , only , the lost heat in winter is not really wasted . It helps heat a small part of the house . ( If the WH is not out in the garage . )

God bless
Wyr

where2 07-18-13 07:44 PM

Quote:

Originally Posted by WyrTwister (Post 30729)
Something else , if the hubbie , wifey & crumb crunchers are away from the house in the day time , a second off cycle saves more , except on the weekend ( indicating a need for a somewhat / potentially more $$$ time clock that can be programed for a different schedule on the week ends ) .

Actually, building the 7 day programmable WH timer isn't all that expensive. Get a contactor with a 120V coil and 240V load side. Get a plastic project case to contain the contactor. Get the #95205 digital timer from harbor freight to operate the contactor. At this point, you might be in for $30, but you have an 8 On/Off digital timer.

I don't have crumb crunchers, but I am running an idea I found on waterheatertimer.org It uses an old Decora switch sized Intermatic 7 day programmable digital timer I bought from my local Habitat ReStore. I'm only using 3 of the 7 on/off cycles available. I still don't understand why most water heater timer manufacturers still use mechanical timing devices?

The HF digital timer I suggested above is actually more sophisticated than my Intermatic timer. The HF timer will do groups in addition to individual days, groups can be: MTWRFSS, MTWRF, MWF, TR, SS (M=Monday, T=Tuesday, etc). The Intermatic doesn't do groups of MWF, TR. I really need to get another one and gut the mechanical timer out of my sprinkler timer. I'm using that HF timer to cycle the dehumidifier in my garage.

Daox 08-19-13 02:18 PM

Has anyone made a 220V timer out of a 110V timer? That would be an awesome write up.


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