[RE-wrenches] On Demand Heaters for SDHW
Bill Loesch
solar1online at charter.net
Fri Sep 17 03:29:14 PDT 2010
Todd & Peter,
The _benefits_ of tankless water heating include:
endless hot water
no standby loss
smaller unit, wall hung (no floorspace requirement)
repairable unit - you don't have to trash it every seven years (reported
national average)
The _disadvantages_ of tankless water heating include:
flow limited heater (proper sizing is critical if hot water needs are to be
met during wintertime (high delta T) conditions)
reduced hot water pressure (resulting from the additional piping of the heat
exchanger)
"cold water sandwich" on units missing a pilot light
no trickle of hot water
routine maintenance in hard water quality areas (no different than a tank
except you don't have to replace, you can maintain)
IMHO there needs to be a very, very good reason to keep the existing tank
when adding a larger than conventional solar tank. You are definitely not
saving space or minimizing standby losses with dual tanks.
If you are asking why use the tankless _instead of_ the solar tank, you may
want to refer to Tom Lane's ever expanding "Solar Hot Water
Systems..."Lessons Learned ..." (now available with an Instructor edition
and in color)
for a further discussion of system configurations.
Bill Loesch
Solar 1 - Saint Louis Solar
----- Original Message -----
From: "Peter Parrish" <peter.parrish at calsolareng.com>
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Sent: Thursday, September 16, 2010 10:28 AM
Subject: Re: [RE-wrenches] On Demand Heaters for SDHW
> 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
>
>
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