[RE-wrenches] On Demand Heaters for SDHW

Peter Parrish peter.parrish at calsolareng.com
Thu Sep 16 08:28:44 PDT 2010


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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