demand water heater

[jcassity]

Good points. I still think there may be some benefit of increasing incoming temperature in places where incoming water is otherwise pretty cold. but maybe the preheating should only be to 75 or 80 degrees at the most. Maybe just an unheated storage tank would gain enough heat on its own in many applications resulting in room temp being the max input to the instantaneous water heater.

this is the code i have been trying to crack in my home, something that works well and get to those temps you say.
still trying to find that one solution that works in both summer and winter.

 

[kwired]

this is the code i have been trying to crack in my home, something that works well and get to those temps you say.
still trying to find that one solution that works in both summer and winter.

I have a geothermal heat pump with a domestic hot water loop. You essentially get free hot water when running in cooling season. The heat pump is going to move the heat out of your home anyway, why not put some of it into your water heater? A small circulation pump is all the extra energy necessary to get it there. If you use hot water at too fast of a rate then the water heater elements will kick in though, but you need to have a large tank to help keep this from happening. Some setups do use a preheat tank heated by the heat pump, and a secondary tank that is just an ordinary water heater supplied by this preheated water, the elements do kick on as needed for output maintenance, but the input temp is high enough that it still saves considerable amount of energy cost over just pumping cold water into a regular water heater.

 

[greenspark1]

well you said commercial and odds in the same sentence ,

exhibit A ~ Hampton Inn

Good point. But how long will they run for, a max 10 minute shower? I don't think you'd cook the insulation of a wire by slightly overheating it for that long. But a hotel is definitely a good example. I was thinking more of a school or office building, let alone a house. I understand NEC uses worst case, but seems like there is some gray area.

 

[GoldDigger]

Good point. But how long will they run for, a max 10 minute shower? I don't think you'd cook the insulation of a wire by slightly overheating it for that long. But a hotel is definitely a good example. I was thinking more of a school or office building, let alone a house. I understand NEC uses worst case, but seems like there is some gray area.

I would venture a guess that it would take industrial (process water) use to get into a really long use cycle.
But a five member family each taking a ten minute shower, along with washing machine before and dishwasher after could break an hour.

When you have an on-demand heater you get very good at serializing your hot water use, regardless of the number of bathrooms you have.

 

[kwired]

I would venture a guess that it would take industrial (process water) use to get into a really long use cycle.
But a five member family each taking a ten minute shower, along with washing machine before and dishwasher after could break an hour.

When you have an on-demand heater you get very good at serializing your hot water use, regardless of the number of bathrooms you have.

The shower is still the big consumer. If someone wants to lay down the up front cost of an on demand water heater they are looking at efficiency and probably also have low consumption washer and dishwasher. They will not be drawing hot water through their entire run time just a gallon or two for the dishwasher and maybe up to 10 gallons max for the higher efficiency clothes washers.

 

[mivey]

When you have an on-demand heater you get very good at serializing your hot water use, regardless of the number of bathrooms you have.

But then everybody suffers and you can't play the "Hah! You should have gotten up earlier losers!" game.

 

[dwjhatton]

100%

100%

I believe NEC requires instantaneous hot water heaters at 100% nameplate for feeder/service calcs. It is a major pain if you are designing a commercial building using solely instantaneous. Maybe your local AHJ allows some diversity. Seems like there should be some allowed, odds of say 10 water heaters firing at the same time for an extended period is quite low.

What code paragraph are you thinking requires 100% demand for feeder/service calc? Under engineering supervision tends to fit these items. Witht he large electrical load for most IWH I'm questioning the appropriate code reference. One can look at the intended use and most applications will not be continuous use in restrooms, kitchens, Eye Wash stations.

 

[Little Bill]

This is a 7 year old thread and should be closed but it slipped through when the software was changed.
Please post this as a new question in a new thread.