demand of point of use water heaters

[dbuckley]

All a bit sad really, as instant heat water heaters work really well in 240V-land, and especially are very widely used for showers. A shower with a 9KW instant heater is.... nice...

The actual total amount of electricity used when using instant heat is less than is used with conventional storage water heating, as there are no storage losses. However, for small amounts of time you need a lot of electricity. In 110V-land that can be hard, as noted above, as in many cases each dwelling has it's own transformer, and thus there is a need for per dwelling upsizing of transformers, whereas in 240V-land there are usually large communal transformers that feed many dwellings (often dozens or hundreds), so the diversity averaging make transformer upsizing unnecessary.

 

[petersonra]

All a bit sad really, as instant heat water heaters work really well in 240V-land, and especially are very widely used for showers. A shower with a 9KW instant heater is.... nice...

Even a miserable water saving shower will use about 2.4 gpm. A 9 kW heater will only raise the temperature of the water by about 25 deg F. If nothing else it would encourage a quick shower, thus saving both energy and water.

 

[dbuckley]

I think you have a math error, for 2.4gpm at 9KW, I get 57F.

Converting to real units, 9KWH = 32.4m joules, 2.4gpm = 540L/hr, to raise 1KG(=1L) of water by 1K(=1C) takes 4184J, so... 32.4m / 4184 = 7744, 7744 / 540 = 14.3K, which expressed as F is 57F.

A 9KW shower is more than I can stand on full Ah... those were the days, now I'm used to a gravity fed shower from stored hot water system, which can theoretically go as hot as hell itself (55C, 131F), but theres no pressure

 

[petersonra]

Hmmm

2.4 gpm = 2.4*8.331*60 = 1200 pounds of water/hour

9000 watts for one hour = 9kwh

1kwh = 3412 btu

9 kwh = 30708 btu

1 btu = 1 lb degf

30708 btu/ 1200pounds = 25.6 degf

14.3K, which expressed as F is 57F

14.3 kelvin = 25.74 deg F which is pretty close to what I came up with

 

[Bob NH]

I think you have a math error, for 2.4gpm at 9KW, I get 57F.

Converting to real units, 9KWH = 32.4m joules, 2.4gpm = 540L/hr, to raise 1KG(=1L) of water by 1K(=1C) takes 4184J, so... 32.4m / 4184 = 7744, 7744 / 540 = 14.3K, which expressed as F is 57F.

A 9KW shower is more than I can stand on full Ah... those were the days, now I'm used to a gravity fed shower from stored hot water system, which can theoretically go as hot as hell itself (55C, 131F), but theres no pressure

14.3 Celsius degrees x 1.8 Fahrenehit degrees per celsius degree = 25.74 F

In my part of the country where we use surface water (from a frozen lake) we need to raise the temperature of water from 35 F to 115 F for a half-decent shower. That would require 27 kW for a 2.4 GPM shower.

I have used these things in Europe where you get a spritz of 1 GPM or less and not very hot at that. They are terrible. And the power companies allow only one such heater per home.

If you don't have natural gas, you can usually get propane, which will provide enough energy for the instant heaters.

 

[dbuckley]

Maybe my maths is screwed, I dunno.

In my part of the country where we use surface water (from a frozen lake) we need to raise the temperature of water from 35 F to 115 F for a half-decent shower. That would require 27 kW for a 2.4 GPM shower.

Ouch! Yeah, perhaps an instant is "inappropriate" for that purpose

And yes, in Europe, some instant showers are terrible. Others are most definitely not.

And yep, gas instant heat is much better than electric. They are very popular here in New Zealand in new residential build. Only bits of NZ has piped gas, so they generally run off gas cylinders.

 

[boboelectric]

Some of the point of use heaters that we've installed were 120 volts.

I got one to hook up, 3000 watt @120 volt,25 amp.Fired wireboy roughed in 14 romex on 15 amp breaker.Finished basement,real challenge.

 

[LarryFine]

Fired wireboy roughed in 14 romex on 15 amp breaker.

At least he used the right breaker for the wire.

 

[stickboy1375]

What was he thinking? And where is the supervision?

 

[frenchelectrican]

well ,, i heard plenty story about instant water heater but IMO some are really crappy one to work on it and i have one installed on one house not too long ago and the poco was not too thrilled with this set up.

I did warn the HO about the large instat waterheater that ran on 24 KW load and end up getting 400 amp service and poco have to put in larger transformer to handle the " cycling " load when the instat waterheater kick in [ it ran in 2 or 3 stage depending on water flowage]

Majorty of instat water heater useally are single phase at 240 volt but the size will varies depending how they used it .

as for load caluation i treat them as contouns load so i can use slightly heveier service system .

Merci , Marc

 

[Dave_PE]

Check out this link, I would guess that other POCOs would have similar requirements.

http://www.progress-energy.com/custservice/flares/builders/tankless.asp

 

[Psychojohn]

If I paid to have a 200A service installed originaly, I dont understand how the POCO can charge me to upgrade their equipment because I use what I paid for?

 

[Psychojohn]

If I paid to have a 200A service installed originaly, I dont understand how the POCO can charge me to upgrade their equipment because I use what I paid for?