diy solar

diy solar

Cheap way to reduce hot water heater draw.

efficientPV said:
I don't know what that means. Is that white wire a neutral or a ground or not part of the incoming feed?
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I also see two of what seem to be uninsulated wires. The cable may have had red/black/white/bare and previous owner used white for ground. Replacement wire can be done according to convention.

Ampster said:
Correct me if I am wrong but do you mean Watts or power? i thought wre size and current were irrespective of voltage?
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Yes, except with fixed resistance and two choices of voltage, 240V will push twice the current through same heating element as 120V would. I'm just suggesting sizing the wire for current it would have to carry in case of 240V. Probably 10 awg.

BentleyJ said:
Hedges was simply suggesting to size the wire for the full current draw at 240V so in the future its not necessary to pull a new cable. In the meantime 120V draw will be less so the wire is oversized during that time.
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Yes.
 
efficientPV said:
Is that white NEUTRAL connected to ground screw?
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Probably. That's allowed in some cases if taped as a green wire.
What's odd is he has red/black. "romex" here doesn't come in red/black/white (without a ground wire)
If this is the insulated feed wire, this whole thing is sketchy as heck:

1683234202646.png
 
Think About It said:
I've worked on a few 4500W dual element hot water heaters. They only draw 4500W because the lower element/thermostat goes on first and heats the lower part of the tank. When the upper thermostat kicks in the upper element it cuts the power from the lower element. It's called a flip/flop system.

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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
 
sunshine_eggo said:
What about a timer that shuts off the hot water heater after running during off peak times. Turn the temp up notably and add a mixing valve to blend cold water with the much hotter water to yield the typical 120-130°F. You might be able to build up enough reserve to take showers without actually needing to draw power. Timer enables water heater again when power is cheap.
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Never understood why so many recommend using a mixing valve to cool the hot water with cold water. Why over heat the water if your just going to waste that heat by cooling it with cold water
 
The heat isn't wasted, it is delivered to the user. Only waste would be faster loss through tank insulation due to greater temperature differential.
A tempering valve is nice, feeds continuous water at constant temperature even as cold water enters the tank. My shower and my espresso machine have them.

The mixing valve on tank is recommended so you can increase (energy) storage capacity of tank 20% to 50% by heating to a hazardous temperature, yet not scald anyone. You get that increase in (comfortably) hot water volume.
 
Hedges said:
The heat isn't wasted, it is delivered to the user. Only waste would be faster loss through tank insulation due to greater temperature differential.
A tempering valve is nice, feeds continuous water at constant temperature even as cold water enters the tank. My shower and my espresso machine have them.

The mixing valve on tank is recommended so you can increase (energy) storage capacity of tank 20% to 50% by heating to a hazardous temperature, yet not scald anyone. You get that increase in (comfortably) hot water volume.
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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
 
Nvm I think my slow brain understands.. there is less hot water volume needed (going thru the pipe) if the water is at 150f. Or is that what’s happening.. doesn’t the amount of water coming out of the pipe simply increase when cold water is added. Meaning there’s still the same amount of hot water regardless of its temp but there simply more water volume added via the cold water.. I’d assume there would just be more pressure. Maybe not
 
dcg9381 said:
Probably. That's allowed in some cases if taped as a green wire.
What's odd is he has red/black. "romex" here doesn't come in red/black/white (without a ground wire)
If this is the insulated feed wire, this whole thing is sketchy as heck:

View attachment 147821
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Yes, it is the feed cable which is a rubberized cloth covered cable with plastic covered conductors inside. I'm not sure exactly on vintage but house was built before 1950 and has the 60A fuse panel.
 
Cheap 4-life said:
Sorry sunshine I edited after u liked
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No worries. Still like.

Given that the hot water heater tank has some air in it by design, I would expect it to be at a slightly higher pressure due to the higher temperature.

From:

Water Heating Calculator for Time, Energy, and Power

The calculators on this page compute how long it takes to heat water, how much energy is consumed, and how much heating power is required.
bloglocation.com bloglocation.com

1683262069715.png

Heating to 150°F allows you to "bank" 3.67kWh of additional input energy.

This would be advantageous if you had supplemental heating from PV, or you want to only run the water heater when power is cheap yet retain decent hot water availability.

To restate your post with an example:

Consider two scenarios - tap is 50°F and the hot water is 120°F or 150°F.

To get 100°F water out at tank 120°F, you would need about 70% of the water to come from the hot water tank.
To get 100°F water out at tank 150°F, you would need about 50% of the water to come from the hot water tank.

With 150°F tank water you will use less and retain a higher temperature. The total energy extracted from the tank is the same in both cases, but there's more left over when it starts at 150°F.
 
Cheap 4-life said:
Never understood why so many recommend using a mixing valve to cool the hot water with cold water. Why over heat the water if your just going to waste that heat by cooling it with cold water
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The water in the tank must be hot enough to kill legionella bacteria. That means a minimum heat temperature of 59-60°C is required to be reached on a regular basis (at least every few days but generally once a day is more typical). Allowing water to stand for long periods between 30-50°C can result in legionella bacteria taking hold and it is a deadly infection.

Water delivered to the user needs to be safe, so heating it to 60°C avoid bacterial growth but can cause severe scalding and burns. Young children, the elderly and frail are at great risk so as to avoid scalding, hot water output temperature is usually restricted to no more than 50°C (and 45°C in some health/aged/child care facilities).

Hence thermostatic valves are often fitted to the outlets of water heaters, or sometimes to areas they are required such as bathrooms.

Hot water storage is a form of energy storage. The higher the water temperature set point in the tank, the more energy is stored and the more hot water (at the desired outlet temperature) the tank can supply. Adding 5°C to the water temperature adds a bit over 10% of effective hot water output capacity.
 
The higher the temperature, the more heat is lost. For solar applications I believe in using tank stratification. It takes 1.5KWH just to maintain tank temperature each day. Many don't have large water use and heating the top 15 gallons is enough. The lower tank section is pre hated with almost no heat loss if less than 80F. With PV heat only from the bottom you are forced to heat the entire tank.
 
sunshine_eggo said:
To get 100°F water out at tank 120°F, you would need about 70% of the water to come from the hot water tank.
To get 100°F water out at tank 150°F, you would need about 50% of the water to come from the hot water tank.
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is that roughly the percentages of hot water that actually come out of the tank? Or does the same (or very close amount of hotwater come out regardless of its temp and extra cold is added if the temp needs to be lowered. is there’s just more water flow from the extra cold added if cold is needed.
yes it’s more energy stored in the hotter water from excess pv for example, but let’s say excess pv is used to heat the house but then cold air is introduced from unnecessarily opening a door similiar to adding cold water. Then the extra heat (power stored) is simply wasted
 
richwolf said:
Don’t need a timer.
My battery will cover it. I just need to reduce the amp draw.
I want the water heater to turn run during and between showers.
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This is all fine and good. If the reduced heating capability is sufficient to keep you in hot water.
Otherwise, someone will have to take a cold shower.
I'm trying to understand why you asked a question. And then reject every reply that doesn't align with your pre chosen solution.
Hopefully it works out for you.


Edit: didn't notice it was an old post.
(It was new to me. lol)
 
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Cheap 4-life said:
is that roughly the percentages of hot water that actually come out of the tank? Or does the same (or very close amount of hotwater come out regardless of its temp and extra cold is added if the temp needs to be lowered. is there’s just more water flow from the extra cold added if cold is needed.
yes it’s more energy stored in the hotter water from excess pv for example, but let’s say excess pv is used to heat the house but then cold air is introduced from unnecessarily opening a door similiar to adding cold water. Then the extra heat (power stored) is simply wasted
Click to expand...
Think of it like your sink. When you wash your hands, you adjust the hot and cold to get the temperature you want. Warm water doesn't use as much hot water from your water heater. If you raise the temperature of the hot water. It will take less hot water to get warm water. Therefore raising the capacity of stored heating capacity in the tank.
 
Cheap 4-life said:
is that roughly the percentages of hot water that actually come out of the tank?
Click to expand...

Yes.

Cheap 4-life said:
Or does the same (or very close amount of hotwater come out regardless of its temp and extra cold is added if the temp needs to be lowered. is there’s just more water flow from the extra cold added if cold is needed.
Click to expand...

The mixer draws cold water at the tank exit. The water drawn from the tank is also replaced with fresh cold, which lowers the temperature less than it would if the tank was at a lower temperature.

Cheap 4-life said:
yes it’s more energy stored in the hotter water from excess pv for example, but let’s say excess pv is used to heat the house but then cold air is introduced from unnecessarily opening a door similiar to adding cold water. Then the extra heat (power stored) is simply wasted
Click to expand...

For a required output, a hotter tank releases less water and takes on less cold water as replacement for a given water demand. 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.

Lower tank temp = more cold water to replace = tank temperature lowered more.

Is there a net energy reduction required for a given demand of hot water? No. It's simply a means of storing additional PV energy OR for energy banking during rate arbitrage.
 
timselectric said:
Warm water doesn't use as much hot water from your water heater.
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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 volume/flow of hot water. 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 lowers the amount of hot water going thru the pipe and replaces that with cold it would all make sense, 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 cold it would be wasting the 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..
 
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Cheap 4-life said:
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
Click to expand...
In that case, at your sink, you are increasing the flow by the amount of cold water added. In the case of a mixing valve the flow is determined by the hot water source you turn on and the mixing valve adds the proportions of hot and cold to achieve the desire temperature and the total flow does not change. Therefor only enough hot water is added to the cold water to raise its temperature to the desired setting. Alternately you could also say cold water is added to the hot water to lower its temperature to the seting. The result is the same.
 
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