Electric instantaneous Water Heater

Wayco Wayne

A neighbor called me to check out his electric instantaneous water heater. Turns out it gets a 50 degree rise at a flow rate of 3 gallons per minute. Of course the incoming water has gotten colder in the winter and his temps have fallen accordingly (I found out) The incoming water temp today was 50 so his output emp was only 100. I throtlled the flow using the incoming gate valve down so he has 107 availible but was thinking on the way home if there was a flow valve that would regulate the flow according to output temperature. Also what would be some ways to pre-warm the incoming water so he could keep his flow higher and still have hot water. For instance I have heard of recovering heat from the shower water drain water. How do you do that??? Thanks for any input.

<A HREF="http://www.heatinghelp.com/getListed.cfm?id=255&Step=30">To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"</A>

Brian (Tankless) Wood

Mornin' Wayne

The HX you're looking for, is the GFX. You should find the right model at www.endlessshower.com

I've used these, it'll do exactly what you're asking. There are different models for various efficiency/recovery rates.

Good luck, and please post back with pics.

I'l try posting a pic, but no guarantees, I'm having tons of problems with my machine.

Brian in freezing swampland.

Sorry Wayne, I had to edit this. "My Doc's & Photoshop" are screwing up. Please get the info from the website I posted above. There are single HX's there, in different lengths for showers and many other applications.

hot_rod

Lets do some math, shall we...

3 GPM @ a 50 degree rise would be how many BTU's?

3 x 8.33 x 60 x 50 = 74,950 btuH

Whereas, 3 = GPM, 8.33 = pounds per gallon, 60 = minutes per hour, and 50 = degrees F rise.

There are 3413 btu's per KWH, hence, 74950 divided by 3413 = 21.9 KW.

Now the tough questions, what KW is this unit rated for?

As for an ambient preheater tank is concerned, I'd be careful. That tank would be subject to a lot of sweating and potential mold growth issues.

As for application of the waste heat recovery unit, absolutley, if you can make it fit. It's rather long and is supposed to be piped into the vertical portion of the stack serving the shower drain. Not that easy to do in most cases.

As for a variable flow restrictor based on temperature, nothing is impossible, but nothing that is off the shelf comes to mind. The best bet is to install ultra low flow shower heads and restrictive orifices at the points of use.

With a 1.5 GPM shower head, the following could be expected.

with a 140 degree supply temp availability, and a 110 degree F shower temperature (HOT), approximately 80% of the flow would be straight hot water (140 degree). hence, 1.5 x .8 = 1.2 GPM. therefore, 74,950 (original delivered btu's ased on known flow parameters) divided by 8.33 divided by 60 divided by 1.2 equals a 125 degree F rise in temperature at that flow rate (1.2 GPM).

It would appear to me that the heater is working exactly as specified. Looks like your friend needs to invest in a little simple water conservation. Now if he wants to use a 2.5 GPM head, he's going to still be in trouble. But you now know how to do the math...

Therein (gosh, I've used up almost every big word in my engineering vocabulary)lies the problem with tankless instantaneous water heaters.

I hope you've learned something about water/energy conservation, mass, flow and time today...

G'Luck!

PS, How's the shoulder doing?

Warm Regards,

heatboy's best friend west of the Mississippi

ME

Associated "Expert in Silent Warmth" ™

Brian (Tankless) Wood

Thanks, Mark

That's what I was looking for.

The company makes shorter, double or parallel HX's.

You're dead right on the math too. This a 22kw heater. If it's a Seisco, and the wiring and service will handle it, the 7,000 watt elements can be fitted in place of the 5,500's, bigger breakers too.

I have an RA-22 in my house but the shower heads are 2.25gpm, no problems at all. And we have frigid water coming in at the moment.

If the neighbour wants comfortable hot showers, change the heads. If he wants to lower bills and more flow, get the GFX.

Endlessshower.com is not there, try www.gfxenergy.com I think.

Thanks for the math, Mark. And good luck, Wayne.

Brian.

Brian (Tankless) Wood

I meant www.gfxtechnology.com (NM)

Brian.

Jack_23

For Performance

You need to go to gas for instantaneous (actually I like to call it on-demand or continuous flow). 21kw looks like a pretty serious load. I'm not sure how they control them but your starting amp draw must be somethi8ng to behold. Look at the Rinnai Continuum. 15,000-180,000btu w/ flow rates from .5gpm-8.5gpm. Flow control so you get only the correct set temp. At a 50F temp rise you get about 6.3gpm. For tub temp (105) you get about 5.7gpm all day long if you like. EF of 82 on NG and 87 on LP. 45lbs, Direct vent. Dealer must have attended a training certification seminar. Rinnai wants to make sure its dealers get off on the right foot. Check it out!

ta finnegan

Tandem

Recently installed (4) SEISCO RA-28 in (2) tandem loops in an 18,000 square foot house! Five bathrooms!

Works great.



To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Wayco Wayne

Thanks for all the input guys

The heater was actually a 28 KW Seisco(?) I just marked a drywall bucket into one gallon increments with a magic marker and estimated the flows by timing for 30 seconds and doubling to get my aprox GPM. The problem was not his showers. They worked fine at 2 gPM. The bathtub was way cooler. It turns out the faucet was letting cold water beeld through with the hot and diluted the water temps for the bath. I went to check amps and output and flound everything working fine. I adjusted the water flow to 3gpm and then found the bathtub was putting out 4 GPM. Not possible with the water throtled to 3 gpm. Love the Math Mark. I was just going through the same stuff yesterday showing 2 of my helpers how to project how long it would take to heat up a 40 gal domestic tank using our 90,000 btu output boiler. (About 20 minutes from 50 degrees to 140) Shoulders doin great. The only time it's limiting is when I play with my 3 foot pipe wrench on some old gravity system pipe. That's when I am missing some of my influence. That's why I keep my helpers ( and a 3 foot cheater bar) in close proximity. These heat exchangers look cool. My wifes out for the day and I may just cut some drywall to see how much verticle I have in under my showers. (She WILL have a conniption if that happens)

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"