OT: Separate hot and cold valves on kitchen taps save energy.

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That's all the cold we get and its been a warm, but wet, Winter so far (el Nino, and all). I don't think we've had a day where the high was below freezing and it's already been in the 50s and 60s every day for a couple of weeks (and into the foreseeable future). We weren't sad to leave the North East!
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They may be "designed" for a 40F rise but they will raise the temperature to whatever they're "designed" for. They are thermostatically controlled.

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snip

whatever degree rise then that is all that they can do.
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Thermostats don't measure temperature rise.
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They sure don't, but a 40 deg rise with a colder HW supply than called for ensures that the water temperature will be too low and the thermostat will always be calling for full heat. It could never achieve full temperature while operating. 120 deg supply, add 40 degrees output on a booster heater will only give you a maximum of 160 deg. If the thermostat was set for 180 it would never be achieved.
Plus, the 40 deg rise could be rated if the supply HW as a minimum of 140 and that as the Supply HW decreased so would the minimum temperature rise across the booster heater.
I guess I should say that a booster heater has its designed limitations, and should be purchased sized according to the needs of the facility.
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Sure it will, or the machine will sit there forever. They will operate on cold water.

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Then I don't think you understand what a booster heater is, or its purpose.
Here is a video on the subject by a manufacturer whose products I was well familiar with over the years.
And a link to their website if you are interested. While it is not for residential usage the principle is the same.

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I understand what a dishwasher is and what it's for.

Where?

I think we're talking past each other. I'm talking about the heater in the DW itself. Every DW I've had will suspend the cycle until the water is at the optimum temperature.

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Odd, I know the links were there before posting then, yet they disappeared. ??

I was speaking of both maybe I should have just stuck to the one, like the domestic version. One poster here said that his Kitchen Aide published the degree rise of their internal heating coil, I had one years ago that also did but I don't remember reading anything about them in the later models.
I don't think the plastic used in these new dishwashers would withstand 180 degree's without aging very fast.

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says...

If you were talking about a continous flow system you might have a point, but that's not how dishwashers work, they fill and then they run. You could put ice water in one and if it ran long enough it would get that ice water to whatever temperature it was designed to achieve.
The limit is not the incoming water temperature, it is the heat loss through the top, bottom, and sides of the machine.

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On 2/6/2016 6:14 AM, J. Clarke wrote:

For a DW to give 40 degree rise it would have to know the temperature of the incoming water so it knows to turn off the heater at incoming +40. I imagine that is simple enough with all the electronics used today.
There are design limitations though. The heating element is restricted in size to what the machine will draw to run the pump motor plus the heating element that won't blow a 15A breaker. Some machines may have a time limit for the heater to be on before stepping to the next portion of the cycle. If not. it could go for a very long time hooked to a cold water tap.
Seems contradictory, but new machines run longer to use less energy. Our machine has an optional 1 hour cycles that uses more energy than the regular 4 hour cycle. The long cycle has some built in pauses to let the detergent soak off the crud.
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Why?

The pump and heater don't have to run simultaneously. I don't think they do (and I know they run independently).

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On 2/6/2016 10:22 AM, krw wrote:

It needs some way to set the differential. To give a 40 degree rise (with an upper limit) it has to have a way of sensing the point to start so it knows the stopping point. A simple bi-metal can tell if it is below say, 180 and have a shutoff at 180 but if the incoming is more that 40 degrees from the upper limit it has to be on a sliding scale.
A more sensible method is to simply have a maximum temperature and let it rise to it with no restrictions. I image most are probably like that in reality, not a set 40 degrees.

Could be. Not life changing for me either way. The dishes come out clean so my reasons for using the machine are satisfied.
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In looking at today's residential DW the temp rise factor is determined differently, in a commercial application what I said still stands. For the home they only require 155 degf as a minimum for rinse sterilization as opposed to the 180 degf for commercial applications.
DW have changed a lot over the years, I never worked on any, residential ones, I only knew some of the specs for those years ago as I compared them to the commercial products of that day.
Along with HVAC we also did restaurant equipment back in the 70's and 80's. Motto was wall to wall ceiling to floor. Equipment wise.
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Sorry, I meant "why would you even want to do a 40F rise?", rather than a constant temperature.

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I just selected Whirlpool for a domestic DW regarding sanitation it is an option. It will raise the final rinse to approx 155 def F according to NSF/ANSI standard 184 for residential use.
It also says that the option adds heat and time to the cycle.
I can only guess at this point, but I'd bet there is a time limit for it as the cost to heat up 32 deg F water would be prohibitive for energy standards.
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Why do you say that? Does it matter if you heat the water in a water heater or the DW? Most water heaters are electric, so it seems it would be a wash. ;-)
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Most water heaters in Calif are gas. Electric water heater coils in the bottom of a residential DW. It was those I was speaking about having a probable time limit to operate in one DW cycle. Purpose, to keep operating costs reasonable.
Gas heating costs here are far more reasonable than electric.
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But if the water isn't up to temperature, a DW will suspend the cycle until it is (obviously lengthening the cycle). ...at least if it's on any of the "sanitization" or heavy duty cycles.

Natural gas, anyway, isn't available in much of the country. Even where it is, electric water heaters are popular because they're cheaper and simpler. Of course, we don't pay the outrageous electric rates that you do in Kalifornistan.
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Yes, that is what the whirlpool sight said. But it also said it may never get to 155. So there must be a time/temp termination involved.
On the heavy duty cycles while it was variable due to the amount of dirt, it was also time limited. IOW, there was a max time that it was to complete inside of it.

That may be true. Might be why solar is finally taking off. But there are still too many snake oil salesmen in that area.
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