[RE-wrenches] On Demand Heaters for SDHW
Bill Loesch
solar1online at charter.net
Thu Sep 16 04:21:16 PDT 2010
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
*
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/125BSTechSupport/Specifications/tabid/536/Default.aspx
----- Original Message -----
From: "Kristopher Schmid" <solman at legacysolar.com>
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Sent: Wednesday, September 15, 2010 2:02 PM
Subject: Re: [RE-wrenches] On Demand Heaters for SDHW
> Bill and Peter,
>
> I stand corrected. Tankless units do not modulate to zero. What a shame.
>
> My Takagi needs AC power to the exhaust fan in order to operate. I will
> be
> installing an aquastat relay on my solar storage tank that removes power
> to
> the Takagi when the solar tank is at or above 110 degrees.
>
> 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 Bill
> Loesch
> Sent: Tuesday, September 14, 2010 7:29 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] On Demand Heaters for SDHW
>
>
>
> Peter,
>
> With all due respect, if you are only doing one SDHW system a year you
> might
> want to consider hiring (subcontracting) someone who does keep up with at
> least current technology and preferably state of the art.
>
> As you are hopefully aware there are a number of ways to construct a SDHW
> system. I personally prefer the single (larger than conventional) tank
> with
> integrated HX for simplicity and efficiency. That is the system type which
> will be addressed here. Since the tank in all but the latest (uninformed)
> solar johnny come lately scenarios, use an electric tank, the _need_ for
> gas
> fired backup is an expensive backup solution.
>
> Provided that the application does call for gas backup then the _ideal_
> machine would in fact be as you described. Such a machine has not existed
> and does not exist today. All tankless, including solar compatible
> (heaters
> which modulate fire rate based on _inlet temperature_) have a minimum fire
> rate which is well above zero. The current iteration (Bosch 1600PS) of
> the
> Bosch 117,000 BTU/h natural draft tankless water heater you cited uses
> 23,400 BTU/h as its minimum fire rate. Power vented tankless water heaters
> from Bosch that provide up to 225,000 BTU/h have min fire rates of ~
> 25,000
> BTU/h. You need to be exceptionally clear which flavor of heater you are
> working with as a natural draft heater has totally different installation
> and vent materials requirements compared to a power vented model. The vent
> materials differ within the power vented category depending upon
> condensing
> or non-condensing..
>
> While you can electrically gang/cascade/group multiple power vented
> heaters
> to provide increased flow (and you should be plumbing them in a reverse
> return configuration). The natural draft heater you previously mentioned
> has
> no inherent capability to provide such multiple unit compatibility (even
> with
> proper reverse return plumbing configuration).
>
> The biggest issue with the separate gas fired solar compatible tankless
> backup SDHW system is the incremental heating of the almost warm enough
> solar heated hot water.
>
> The biggest issue with any tankless water heater is the potential for
> scale
> and the resultant efficiency and functionality loss and descaling
> requirement.
>
> Best wishes to you and your solar hot water enthusiast client,
>
> Bill Loesch
> Solar 1 - Saint Louis Solar
> 314 631 1094
>
> FYI - The Bosch 125BS has had essentially only a name change to Bosch
> 1600PS.
>
> 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
>>
>>
>>
>> _______________________________________________
>> List sponsored by Home Power magazine
>>
>> List Address: RE-wrenches at lists.re-wrenches.org
>>
>> Options & settings:
>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>
>> List-Archive:
>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>
>> List rules & etiquette:
>> www.re-wrenches.org/etiquette.htm
>>
>> Check out participant bios:
>> www.members.re-wrenches.org
>>
>>
>
> _______________________________________________
> List sponsored by Home Power magazine
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive:
> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out participant bios:
> www.members.re-wrenches.org
>
> _______________________________________________
> List sponsored by Home Power magazine
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive:
> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out participant bios:
> www.members.re-wrenches.org
>
More information about the RE-wrenches
mailing list