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"
<[email protected]>
To: "'RE-wrenches'" <[email protected]>
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 [email protected]
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
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--
Todd Cory
KE6SXS
[email protected]
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
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