Cheap way to reduce hot water heater draw.

[Hedges]

Forgive me but I still don’t get it.. if the water is 150f and it only needs to be 120f then the cold water cools that 150f water to 120f so how isn’t the 30f wasted? The user isn’t delivered 150f that they heated it up to. They are still only getting 120f

The excess energy isn't dumped to ambient by letting it cool. Cold water is blended in, averaging out the two.

Cooled 30f by transferring 30f x volume worth of energy to the cold water blended with it. Which rises say from 60f to 120F, so that would be 60f x volume/2 that gets heated. You end up with 1.5 x volume at 120f.

Electric water heater, 100% of energy (that is dissipated in heating element) goes to the water whether 120f or 150f. The I^2R losses in wiring are same regardless.
Heat pump water heater, less efficient the greater the temperature differential, so if 200% efficient at 120f, something less than 200% but still well above 100% at 150f.

if that’s how the mixing valve works I still see no point.. however if the valve someone lowers the amount of hot water going thru the pipe and replaces that with cold it would all make sens, but I’m thinking the valve operates like I opened the valves..

What you do is open cold as well, fill sink in less time, then shut off both valves.

Mixing valve supports say 10 gpm. Your faucet adjusts from zero to 2 gpm. Total flow of hot + cold is set by faucet. Temperature balancing valve has thermal stack fighting spring, moving a shuttle back/forth to adjust ratio of hot cold.

My shower has that, and if someone flushes toilet, that reduces pressure in cold line to shower (more than it reduces pressure in cold line feeding water heater, due to pipe arrangement.) The temperature balancing valve adjusts to maintain steady output temperature. That one has a knob adjusting target pressure during use. One mounted on water heater would be set once.


All this is very different from maintaining excess pressure in an air tank, and dropping it with a regulator. Done properly, we get all finishing nails set to same depth. I've observed the difference with different compressors and different brad nailers. To achieve efficiency with air compressors, what we would want is to not bleed off excess pressure (generating heat), rather use that pressure to operate a variable displacement pump, so the excess energy is used to produce additional volume. In practice, burn off the energy and get job done. For blending hot water, no such inefficiency to consider recovering.

 

[timselectric]

If I open the left valve and it’s to hot and then I turn on the right valve to add cold to the existing amount of hot water flow, then it’s the same amount of hot water being used so there was no point to have it hotter. The added cold is wasting the extra heat.. if that’s how the mixing valve works I still see no point.. however if the valve someone lowers the amount of hot water going thru the pipe and replaces that with cold it would all make sens, but I’m thinking the valve operates like I opened the valves.. yes on a sink I could manually turn down the amount of hotwater flow and add cold to lower the temp, but if I didn’t turn down the hot flow and just added old it would be wastingbthe over heated waters extra heat.
as @sunshine_eggo explained, the cold water added to the extra heated tank will not lower the tanks temperature as much because the water is hotter. But why even have the water hotter to begin with if your still using the same amount of 150f water to get 120f, like I explained in the first paragraph..

You are going to use the total amount of water, whatever the dispensed temperature is. But you will always take less hot water to do so.
I'm not sure how you take a shower, but I run full blast and adjust the hot for temperature.

 

[wattmatters]

The lower tank section is pre hated with almost no heat loss if less than 80F.

And risks allowing legionella bacteria to grow in the tank. It's a deadly infection and to be avoided at all costs.

If you only need a small hot water storage tank, then get a small tank and heat all of it up correctly. But not regularly heating a larger tank of water to a high enough temperature to kill legionella presents a serious health risk. I don't know about where you are but here in Australia it is against the law for a water heater to operate in the manner you describe.

That smaller volume of cold water lowers the tank temperature less and requires less input energy to raise its temperature because it is simply less water to heat.

That's not correct. It's a lower volume of cold water entering the tank but that cold water needs to be raised to a higher temperature. That ends up using the same amount of energy.

if that’s how the mixing valve works

It's not.

 

[Cheap 4-life]

theres also sink faucets/mixing valves with only one handle. As the temp is changed with that handle the flow does not change like it would with two handles. I suppose with one handle the amount of hot is being reduced when cold is added to lower the temperature. The mixing valve used would have to function like the single handle faucet (reducing volume of hot water when cold is added) to have the benefit of the overheated water in the tank.

 

[timselectric]

The mixing valve used would have to function like the single handle faucet (reducing volume of hot water when cold is added) to have the benefit of the overheated water in the tank.

That's exactly how it works.
It doesn't control how much water flows. That's done by the user, at the outlet. Only the percentage of hot versus cold. To achieve the desired temperature provided to the hot water piping.

 

[sunshine_eggo]

We're not talking about the mixing valves in faucets. We're taking about:

https://www.supplyhouse.com/Resideo-Braukmann-AMX300TLF-DirectConnect-Water-Heater-Kit-w-3-4-Mixing-Valve-8-SS-Corrugated-Hose-Connector-Lead-Free

This is AT the water heater, so the house is supplied with the 120-130°F out of a typical water heater. To the user, there is no perceptible difference.

 

[rhino]

We're not talking about the mixing valves in faucets. We're taking about:

https://www.supplyhouse.com/Resideo-Braukmann-AMX300TLF-DirectConnect-Water-Heater-Kit-w-3-4-Mixing-Valve-8-SS-Corrugated-Hose-Connector-Lead-Free

This is AT the water heater, so the house is supplied with the 120-130°F out of a typical water heater. To the user, there is no perceptible difference.

Oh that is cool. I didn't even know that existed. Any idea how reliable those are? I've heard stories about point of use mixing valves failing after only a few years.

 

[timselectric]

All of the ones that I have seen installed. Lasted for many many years. I don't think that I have ever seen one fail. But I'm sure that some probably have.

 

[rhino]

Maybe it might depend on water quality? I have hard well water and do have an iron filter but still have iron stains.

 

[Hedges]

Mine in the shower (your "point of use" example) did jam up after 10 or 15 years. And then I discovered that cutouts for the factory installed valves were too small to pull the core out. I need to set up a hole saw guided by outside not by a drill in the middle.

I had installed it with a filter on each supply. Hot water is the one that sometimes gets chunks of sediment, but cold water might too when utility works on pipes.

It was sure nice while working.

I think some sort of strainer on the inlets would be prudent, ideally one you can easily clean out.

 

[mountkay]

it does “flip flop” but the top element turns on first to keep up with demand. Once the top thermo turns off the bottom element heats up the bottom of the tank

pretty sure the bottom heating element usually turns on first, unless you are talking about a specific heater that works in a different manner.

Ill post a video below about how they work, but basically cold and hot water in a water heater stratify amazingly well. when cold water is pumped into the bottom of the tank, it barely mixes with the hot water at the top at all. You draw the hot water from the top, which is already sufficiently heated, so the top element does not need to come on, unless enough hot water has been used that cooler water is reaching the upper element/thermostat. then the top element turns on instead of the bottom, so it is heating a smaller volume of water, right near the outlet of the hot water.

as soon as you start drawing hot water, the bottom element will kick on and start heating. if you use enough hot water that the top element needs to kick on, it will be heating that smaller volume of water that has already been preheated by the bottom element.

water tanks often have a "1st hour rating" for example, my water heater is 27 gal, but has a 44 gal "1st hour rating", It is a 4500W single element. If it was a dual element the same 27 gal tank would have a greater "1st hour rating"

some pics from the video

 

[timselectric]

Actually the top element has priority.
But is rarely needed unless you used half of the tank.
The top element heats to desired temperature. Then allows the lower unit to run. As cold water is brought in to replace the hot water used. The bottom element will turn on (as long as the top thermostat is still satisfied). If enough hot water is used to lower the temperature at the top of the tank. The lower element is switched off. And the top element takes over. The top has priority because that's where the output is at.

 

[Cheap 4-life]

My tank is always cold when an element starts heating. I warm it up everyday from cold when my battery reaches float/full. when fully warmed it’s enough for everyone in my house to have a hot shower. Then the water heater is off all evening due to battery no longer being floated during the evening. The top element of most water heaters takes priority over the bottom element. When my water heater begins to heat my top element always comes on first because the water temp in my tank is below both of the thermostats (bottom and top) set points. Under normal operation (for most people I guess) you are correct the bottom element comes on first. By normal I mean a water heater that’s left on all of the time.. for me that’s not normal because I heat my water for free when there’s excess solar and automatically shuts off the water heater any other time

 

[Jet]

While this would probably double the time for it to heat the water you could consider converting your water heater to a DC one. Especially if you have a 48 volt battery. You could use a 2000W 48 volt heating element like Connect the leads from the board that go to the heating element to a 5 or 12 volt DC power supply. Connect those wires to an DC-DC 60 amp relay. Lastly, connect the relay to your new DC water heater Element using high temperature wires and ring lugs. Now you have a DC powered water heater that runs directly off your battery. Use appropriate wire gauge for your run, length and fuses.

Low Voltage DC Submersible Double Water Heater Element

This unique double element DC Water Heating design allows you to determine the wattage by connecting either two or four posts. See the listing for more details!

windandsolar.com

[/URL]

https://www.amazon.com/LCLCTC-Power-Supply-1-25A-Volts_of_Direct_Current/dp/B0BY46H47M/ref=mp_s_a_1_4?keywords=LCLCTC&qid=1684925333&sr=8-4

Sensata - Crydom - D1D60 - Solid State Relay Surface Mount DC MOSFET 60 A 32 V, 1-DC Series - RS

D1D60 from Sensata - Crydom at RS

us.rs-online.com

Heatsink for relay:

https://www.newark.com/sensata-crydom/hs301dr/heatsink-din-mount-3deg-c-w/dp/52R3576?gclid=CjwKCAjw67ajBhAVEiwA2g_jEAEQi07ieiKI0MMLaQx-Ke54bON9qIUeQ1D3n_IE9_8WJJXC1aSHLxoCVQoQAvD_BwE&mckv=_dm|pcrid||plid||kword||match||slid||product|52R3576|pgrid||ptaid||&CMP=KNC-GUSA-GEN-PMAX-LOW-ROAS-Shopping-V1

 

[eXodus]

Since we’re going through every possible scenario how about this??
Problem with going from 240 volt to 120 volt is that you drop the wattage by three quarters.

Toggle water heater between 120V and 240V using 3-Way Switch​

To switch the circuit between 120V and 240V for water heater by using a 30 amperes 3-way switch, just connect a line (L1) from main distribution board via 30A circuit breaker to the water heater. Connect the second line (L2) from CB and neutral from DB to the upper terminal and lower terminal of three way switch respectively. The common terminal on left should be connected to the water heater. Don’t forget to connect the 3-way switch and water heater to the ground/earth wire.

Just change the lower element to a 240V 1500W - it's like $8-12
Leave the upper at 4500w or 3500w 240V

Most of the time the lower 1500W will do it's job and keep the tank nice and toasty. I got one in my 40 gallon Tank, On the occasional case that you need hot water fast - the upper one will give you a boost.

Keep it simple

Add a timer for the TOU if necessery.

 

[Bad Randy]

I replaced both 4500w. elements with 2000w.
a timer set 10AM-8PM, and 40 to 50 gallons.
Simple, reliable and cheap.
Over a year now with a family of four.

 

[sunshine_eggo]

I replaced both 4500w. elements with 2000w.
a timer set 10AM-8PM, and 40 to 50 gallons.
Simple, reliable and cheap.
Over a year now with a family of four.

You're in Phoenix though. Your cold water is hot.

 

[Bad Randy]

You're in Phoenix though. Your cold water is hot.

You are correct, I have used 1840 KW heating water this year.
And 2514 KW in 2022.
I love my Emporia monitor.

 

[oldbigfoot]

Yes, that sounds correct.
I would do the same whether feeding it 120V, or 240V (no neutral, so white is hot, use red tape to indicate.)
If you use sufficient gage it can carry the higher current at 240V or the lower current at 120V. For future options rewiring at the breaker panel.

 

[altenergy20]

I've taken about 20 "cold" showers so far. It's actually room temp water that goes through a disconnected water heater.
There's a temp. difference between cold water from the well and room temp water.
It takes about 4 rinses for the soap to no longer get slippery. Turn off the water between scrubbing.