[RE-wrenches] On Demand Heaters for SDHW

Fri Sep 17 07:01:30 PDT 2010

It all depends on whether you are talking financial payback or wise energy
use.  The people who use the least amount of hot water are the people who
will experience the greatest energy use savings.  They are a great option
for weekend cabins since you don't have to remember to turn off the water
heater when you leave and you don't have to wait for the tank to heat up
when you return.

Kris

Legacy Solar
864 Clam Falls Trail
Frederic, WI 54837
715-653-4295
solman at legacysolar.com
www.legacysolar.com
-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Todd Cory
Sent: Thursday, September 16, 2010 1:55 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] On Demand Heaters for SDHW

The payback on a demand heater in energy savings is like 50+ years. A
traditional tank heater, super insulated has very little loss.

Todd

Peter Parrish wrote:
You’re right, Todd, there is often a space limitation. But overall, the
tankless approach is more economical, eliminating the need to keep 80 odd
gallons of water perpetually up to temperature. Remember the solar heated
water is "make up water" and can contribute to the temperature of the
traditional water heater only while hot water is being used. So, my guess is
that 1/2 of the day in a residence the traditional tank is keeping water up
to temperature for no apparent use.

- Peter

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

________________________________________
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Todd Cory
Sent: Thursday, September 16, 2010 8:17 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] On Demand Heaters for SDHW

I know this was not the question, but this whole thread is predicated on the
use of a demand hot water heater. Unless there is a space limitation, why
would this be done over a traditional tank unit?

Todd

Bill Loesch wrote:

Kris,

Boiler manufacturers today get starry-eyed when their machines are able to
provide a 10:1 turndown ratio. Even the venerable natural draft Bosch 125BS
* provided a better than 4:1 turndown ratio and all the condensing powervent
units compared below regularly offer 10:1 and some better than 20:1. With
each benefit comes a disadvantage, like with current production cars,
serious repair/maintenance takes place primarily at the dealer since they
are usually the only ones to pony up for the multitude of specialized test
equipment. I find it a bit of backward progress to have to tell someone that
the reason they don't have reliable hot water is because they don't have the
current software update (due in no small part to the marketing gurus who
have no qualms about using the customer as the proving grounds for their
product). Many plumbers have no clue to the workings of a combustion
analyzer, a necessary tool for  negative pressure gas valve tuning and
replacement (and a multitude
 of other tasks where the blue flame is no longer sufficient to be able to
deliver optimum performance).

Your Takagi needs AC power to (in order of decreasing current requirements
for a generic power vented tankless)
   power the freeze protection heating elements
   run the primary combustion fan
   run the secondary combustion fan
   provide control to
       gas valve
       water valve
       control board (oftentimes with digital display) which provides the
logic and timing circuits for the multitude of sensors and limit switches
and remote controls and wireless remote controls etc., etc.

Long live the thermocouple.

My compliments on your simplistic approach to coordinate the solar storage
tank and tankless. Simplicity is the ultimate sophistication.

Bill Loesch
Solar 1 - Saint Louis Solar

PS I reiterate, despite other RE-Wrenches list comments to the contrary
about
"modulate to
zero", NONE of ANY of the Big Five tankless manufacturers that market to
North America have a low fire rate which modulates to zero or anything near
it for the very same reason that you will never get a trickle of hot water
out of any tankless water heater. (~0.5 gpm minimum activation flow
requirement)

Comparing condensing heaters with ~200,000 max BTU/h input
Bosch GWH C 800 ES     19,900 BTU/h
Noritz NRC 111               11,000
Paloma   no condensing heaters
Rinnai RC98HPe                 9,500
Takagi T-H2                     13,000

Thanks for your patience, I hope it was not too technical.

----- Original Message ----- From: "Peter Parrish"
<peter.parrish at calsolareng.com>
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Sent: Tuesday, September 14, 2010 10:37 AM
Subject: [RE-wrenches] On Demand Heaters for SDHW

We have a SDHW client that wants to replace his old water heater with
a new tankless water heater. We do a SDHW system about once a year,
and only for clients that are getting a PV system from us to begin
with. So this is not a
big business line for us and we are behind the curve in terms of
understanding the latest technologies.

As I remember from an excellent workshop that I took about four years
ago: when used in conjunction with a SDWH system, the tankless heater
should

(1) Modulate heat input based on INPUT water temperature
(2) Be able to modulate down to ZERO BTU/hr

The only unit I knew of back then was the Bosch 125BS (I believe).
Today I can't find any bigger units that fit the above requirements.

Short of using two Bosch 125BS units in parallel, does anyone have a
solution?

- Peter

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26 peter.parrish at calsolareng.com
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

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--

Todd Cory
KE6SXS
toddcory at finestplanet.com
Mt. Shasta Energy Services
License C-10  #811428
P.O. Box 689
Mt. Shasta, CA. 96067
(530) 926-1079
 
“I'd put my money on solar energy...I hope we don't have to wait till oil
and coal run out before we tackle that."
∞ Thomas Edison, in conversation with Henry Ford and Harvey Firestone,
March 1931