New Tankless water heater

[ponyboy]

It uses microwaves to heat up the water. :shock:

http://www.theglobeandmail.com/servlet/story/RTGAM.20051122.gthotwater1122/BNStory/Technology

[eesnard]

I wonder how many watts it going to use.

[ponyboy]

I didn't see any kind of spec's on the power usage. :(

[thepizzaguy]

I've seen "point of use", water heaters that mount in the cabinet below the faucet. They range in price from 50 bucks and up. The use ceramic coils to heat water at the sink. The box/heater is only about the size of a 4x6 inches card. A switch inside the heater is triggered by water flow creating instant hot water.

The savings come in when you are no longer spending money to heat 50 gallons of water that sits in a tank. Just another gadget I liked.

[StressMan79]

I wonder how many watts it going to use.

probably about the same as a regular resistor-element unit... energy is energy after all... I would bet that this type of "technology" would use slightly more, say 10% than the more traditional, as some of the microwaves are lost; some heat is not transferred to H2O, but escapes as well.

I would think that this type of unit could be made cheaper, with the commodoties prices what they are. You don't need a big heat exchanger... only a microwave generator.

...for what it's worth.

[rreidnauer]

Yea, figuring it out should be possible, since it takes 1 BTU to raise 1 gallon of water 1 degree. They claim a 95 degree rise, but I'm sure that's at minimum flow. So let's say a 70 degree rise at 2.5 gallons per minute. (typ. shower head) So, knowing 3412 BTUs equals 1 kWh, I should be able to do the math.

1 BTU * 70 degrees * 2.5 gpm = 175 BTU per minute * 60 minutes = 10,500 BTU per hour / 3412 BTUs = 3 kWh, or 12.5 amps at 240 volts. (not counting losses)

I think I did that right. :? 3000 watts sounds kind of hungry, but it would only be on when hot water is flowing.

[jeffro]

It's lower than the heating element in a tanked water heater at least :?

I think you did that right too, but I am too lazy to pull out a thermo book and check the units.

Jeff

[StressMan79]

it takes 1 BTU to raise 1 gallon of water 1 degree.

Not quite. one BTU raises one POUND of water by one degree F. there are eight lb of water per gallon, so multiply your number by 8.

http://bbq.about.com/od/gasgrills/g/gbtu.htm

also, your units weren't quite right, 3412 btu = 1 kW-Hr, so dividing the BTU/hr, you get kW. W = V * A, so your number (aside from the factor of 8 ) is right, just a step along the way...

this begs the question: what gauge of wire do you need for 100 Amp line? :!: Is it impossible to get 2.5 gal/min through one of these units? am I full of it? We are assuming zero losses and requiring 24kW!

Rod, thanks for your continued input. Don't take this as a slam by any means!

[StressMan79]

Please note that the Stiebel Eltron Tempra 36 Whole House Tankless Water Heater requires 3 x 60 AMP breakers on 240 Volts.

http://globaltowne.com/product_info.php/cPath/33_40/products_id/126

I guess I'm not so full of it....

[rreidnauer]

Rod, thanks for your continued input. Don't take this as a slam by any means!

Wholly cow!!! Not at all, that was a stupid mistake I made.

Water = 8.333 lbs/gallon

So reconfirming, 8.333 * 2.5 gpm = 20.83 lbs/min * 60 minutes = 1250 lbs/hr * 70 degrees = 87,500 lb/degrees (or BTUs) over an hour / 3412 BTUs per Kwh = 25.6 kWh

Yikes! :shock: And I thought 3 kW sounded bad. :lol:

My solar hot water collectors and wastewater heat reclaimer intentions are sounding better and better by the minute. :lol: