[RE-wrenches] On Demand Heaters for SDHW
Bill Loesch
solar1online at charter.net
Sat Sep 18 01:57:45 PDT 2010
MessageHi Kris,
Sorry that the terminology is decidedly a bit confusing to even my esteemed, clever, and resourceful fellow wrenches.
Most folks are familiar with a typical natural draft, gas fired, storage tank, water heater. It has a burner. A non-modulating burner. When the tank doesn't call for heat, the main burner can just sit there doing nothing. In a 40 gallon tank typically, 30,000 - 40,000 BTU/h, all 40,000 BTU/h on or nothing. The nothing is _not_ the minimum fire rate. The nothing is off.
Every gas fired tankless water heater I have seen in the US uses a modulating burner. When it is a _flow_ actuated machine a large flow will bring on the high fire rate, ~200,000 BTU/h in the previous thread example. A smaller flow will modulate that 200,000 BTU/h fire rate downwards. When the flow reduces further, but still something more than a trickle (technically the actuation flow) the machine will fire at the minimum fire rate which varies from heater to heater but to use the previously cited example ~10,000 to 20,000 BTU/h. Now, if you have a _temperature_ actuated machine and you are already at set point the heater just sits there, _not_ firing when set point water passes through the tankless. The perfect backup companion for SDHW, IMHO. Not firing (off) is not the same as a fire rate that modulates to zero.
As I said (or should have said) early on, the trick to use a gas fired tankless for SDHW backup is when the solar heated water needs just a tad more heat.
Class out. Enjoy the weekend.
Bill Loesch
Solar 1 - Saint Louis Solar
----- Original Message -----
From: Kristopher Schmid
To: 'RE-wrenches'
Sent: Friday, September 17, 2010 11:12 AM
Subject: Re: [RE-wrenches] On Demand Heaters for SDHW
Wayne,
Your statement that "The unit will turn off automatically once input water temp reaches its programed output temp." seems to contradict the statement from Bill saying "All tankless, including solar compatible (heaters which modulate fire rate based on _inlet temperature_) have a minimum fire rate which is well above zero."
Am i missing something?
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 Wayne Irwin
Sent: Friday, September 17, 2010 9:40 AM
To: Wrenches
Subject: Re: [RE-wrenches] On Demand Heaters for SDHW
In our off grid home I installed a Rinnai propane tank less to support
the double pump drain-back system and have had no problems.
The tips that I suggest are: that the tank less be flushed out regularly,
even when not being used in-order to reduce any sediment.
If the water is hard, add a softener or at least a micro filter.
Scale build up can also be a problem.
If this tank less unit is being used as a back up, turn it off unless needed.
The unit will turn off automatically once input water temp reaches its programed output temp.
However, the initial water flow is cold enough to trigger the unit to fire-up, wasting
100,000 btu's of fuel for a minute or so.
Wayne Irwin
Director of Engineering
Pure Energy Solar International Inc.
State Licensed Solar Contractor
License # CVC56695
Wayne at PureEnergySolar.com
http://pureenergysolar.com
352 377-6527 Office
352 336-3299 Fax
The content of this message is Pure Energy Solar Confidential. If you are not the intended recipient and have received this message in error, any use or distribution is prohibited. Please notify me immediately by reply e-mail and delete this message from your computer system. Thank you.
> From: solman at legacysolar.com
> To: re-wrenches at lists.re-wrenches.org
> Date: Fri, 17 Sep 2010 09:01:30 -0500
> Subject: Re: [RE-wrenches] On Demand Heaters for SDHW
>
> 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< br>> [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:
&g t;
> 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 w orkings 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 storag e
> 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 techn ical.
>
> ----- 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 modula te 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
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> March 1931
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