How to have a good laugh in the morning...

Dirk Wright

Actually, it's a great idea because it will sterilize the water at the same time it heats it. At least, I'm pretty sure zapping bugs with microwave energy will end their lives...It will be a little noisy from the cooling fan though.

Ah yes, the vacuum tube is with us still...

Constantin

So I read the morning news and...

... this, allegedly NEW, technology is being touted... an tankless water heater using microwaves! More efficient? I am so underwhelmed, but it sure made me laugh.

Time for some letters to the editor.

Al Corelli

"Powered by electricity and unaffected by the volatile gas markets"

Um, don't they make electricity with natural gas? My energy supplier say so.

thp_8

Don't laugh too hard,

Because we will turn-around and buy a foreign high tech boiler and controls that when you crunch the numbers and apply the laws of science is no more efficient than one made here at home.

jerry scharf_3

underwhelming web site

So I went to the web site, which is only one page saying under contruction. Perhaps they put the press release out too soon.

They say it's capable of doing multiple things at once. If they hit the small takagi size, they only need about 20KW power. If they are doing multiple units, it may be 40KW+. That's no toy! Better make darn sure it doesn't leak microwaves, EVER. Any unit I've seen that has a 25KW microwave output is certainly bigger than what they describe.

On the good side, they get cold water to cool the electronics. Also, there should be no flow problems through the radiation cavity.

we'll have to visit once the web site is up.

jerry

Dirk Wright

Ah, no fan

ah, so there's no fan! that'll make it quiet, except for the hum of the tube I guess.

I can see a potential problem with keeping the high voltage separate from the water. What if there's a leak? That could a spark flying mess!

Given that an ordinary kitchen microwave oven still draws almost 15 amps, I'd be surprised if this thing can really heat water very fast. We'll have to wait and see what they put up there though.

Constantin

The thing is..

... one of my colleagues once had to develop a high-powered microwave/convection oven. RF leakage is a serious issue under the circumstances. Magnetrons in that power class are not cheap either and require active water cooling.

Plus, the Physics don't change, i.e. 1 BTU is still needed to heat one lb of water 1°F. Relatively simple and well-proven resistance-based instantaneous water heaters will achieve the same effciency as this unit, the heat pump water heaters will surpass it, even if you account for the standby losses.

The only marginal benefit is the potential for sterilizing that water, something that I can achieve with a resistance heater, buffer tank, and mixing valve just as well, and at a much lower cost. I say KISS...

jerry scharf_3

no tubes

Dirk,

Since they don't care about how quiet or precise the output power spectrum is, they use the cheapest solid state magnatron they can find. This avoids the high voltage exciters and the hum.

As for the current, folks like stiebel-eltron make whole house instantaneous electric water heters. They go up the 36KW for a nice 150A max draw at 240V.

jerry

jerry scharf_3

yes, yes and yes

Constantin,

I too appreciated the humor of it. Like I said, the cooling water is free.

Maybe it's just a regular resistance coil heater with a small RF stage in line... There might be some theory that that microwaves are better against legionella compared to UV (penetrating cysts,) but it's still a whole bunch of effort to go to.

jerry

S Ebels

So

A KW is a KW is a KW. I'm failing to see how any major breakthrough in efficiency is achieved compared to an instant on resistance element type. An immursed resistance element is 100% efficient and I have to think that anytime a transformer/magnetron is involved in a system, such as with said microwave unit, there will be losses involved with it.

Constantin

Come on, Steve

Don't put that thinking cap on, you might prevent some stray criticial thoughts from escaping! :-P

So far, I call snake-oil. Barnum would have been proud!

Brian (Tankless)

Turbulence water-heating.

There was a thread here a couple of years ago about water heating using some kind of pump/cavitation principle.

I'm a "Foggy Notion" type, but don't have the foggiest notion on how to find a way back to Google it.

Any ideas ?

My mind's cavitating right now and "Bud Select" isn't helping any :O)

BTW, Wheez, do you put beer in the fridge to PREVENT it from freezing?

Brian, in 66* 99% RH Muggyland.

ttekushan

vacuum tube is

with us still because sometimes they're just more appropriate for the particular task at hand. Magnificent ancient devices, they.
-terry

ttekushan

Shock-wave steam generators?

If you're referring to the controvertial shock wave boiler here it is:

http://www.hydrodynamics.com/industries/petroleum/marathon98.htm

jerry scharf_3

efficiency

as a waterheater would not appear to be it's strong point.

Dirk Wright

juice!

That's a whole lotta juice just to heat water! Good grief! 150 amps!!

Dirk Wright

I agree

I agree, this is more complicated than it needs to be. I looked into the heat pump water heaters, but they work better in warm climates. I hear they are popular in Hawaii. They keep them outdoors. If they are indoors, you have to pay for the heat they take out of the room, so that seems like a waste.