When I did my study of solar water heating I found that PV water heating gave more hot water at a lower cost than solar thermal. the Heatpump water heater was the big winner.
On Thu, Mar 15, 2018 at 12:00 PM, Drake < drake.chamber...@redwoodalliance.org> wrote: > This discussion has been a great help. The house is built and the plumbing > is in, but could be modified. Wood stoves are not a likely solution. I > think we need a different water heating strategy. > > Thank you all! > > Drake > > > > At 09:21 AM 3/15/2018, you wrote: > > Content-Type: multipart/alternative; > boundary="------------EE4E9806B711DEF636076840" > Content-Language: en-US > > This is what I came up with: > > The calculation is Q = mcp delta T > > Water Temp out = 120 > > Water Temp in = ground source Temperature @ 50F? > > delta T = 70F > > m = mass flow rate. ASHRAE is the source for this. 20gals per person > per day = 20 gallons x 8.34 lbs/gallon = 167lbs/day/person > > cp = 1 BTU/lb-degree F > > Q = 167 x 1 x 70 = 11,676 BTU/day/person > > Divide this by the efficiency of the water heating system (I'll assume = > .86) =11,676/.86 = 13, 577 BTU/person/day > > convert to kWh if necessarym 13,577/3412 = ~4 kWh/person/day, 120 kWh/month > > I checked this against one month and it seems reasonable. > > Website assuming ~3.5 family size comes up with @ 400kWh per month. They > approached it another way with assuming run times. > > https://www.google.com/search?safe=active&source=hp&ei= > Z3KqWvXiNsGb5wKJ2Kf4DA&q=electric+water+heater+use+annual+consumption&oq= > electric+water+heater+use+annually&gs_l=psy-ab.1.2. > 33i22i29i30k1l3.279.9222.0.12475.35.19.0.7.7.0.451.2360. > 0j6j4j0j1.11.0....0...1c.1.64.psy-ab..18.16.1952.0.. > 0j0i67k1j0i131k1j0i22i30k1.0.CiU8wYZigpI > > > Chris > > > > > On 3/15/2018 8:09 AM, Mike Kocsmiersky wrote: > > Barton makes a good point with regards to the incoming ground water > temperature and the amount of heat required to bring it up to shower temp. >  My recollection is that ASHRAE states 20gal/person/day for the first 2 > people, then 15gpd or 12gpd thereafter. However those rates vary wildly > with consumers, from those that never bathe to the high schooler that needs > 3 showers a day. In the northeast water heating can be up to 19% of the > total household energy load for the year. Also, I would recommend the air > source heat pump water heaters if you have significant humidity or an on > demand unit. Water tanks are typically under insulated and can lose > 2kWh/day in standby losses. >  > Mike Kocsmiersky > Principal > Spirit Solar Inc. > (413) 734-1456 >  >  >  > *From:* Barton Churchill [mailto:bar...@solarips.com <bar...@solarips.com>] > > *Sent:* Wednesday, March 14, 2018 7:31 PM > *To:* RE-wrenches > *Subject:* Re: [RE-wrenches] Electric Water kWh/ person >  > You first need to know your ground temperature. Then figure a delta to 100 > or so degrees. Most but not all showerheads flow 2.5gpm and showers are > typically 10 minutes. You can then find a calculator online to calculate > how many Btus are required to raise water temp for your delta per gallon. > Convert to kWh, add some contingency and you should be good. > > On Wednesday, March 14, 2018, < drake.chamber...@redwoodalliance.org> > wrote: > Hello Wrenches, > > Is there a good way to estimate the power that will be consumed for > electric water per person per day? We are estimating the amount of power > that will be used by an all electric duplex, and the water heater amount > seems high. The current model we have claims 3493 kWh/ year per 26 gallon > tank will be consumed. With the two units, that would add up to 6986 kWh / > year for hot water, pushing the system size to humongous for a 1300 ft sq > building. > > Does that seem high? There will be a maximum of 2 people per unit. > > The owner is considering going to 115 V units with a 15 gallon tanks. I > think the smaller tank would help, but it would seem that the amount of hot > water consumed would be the main issue. > > How can we get a good estimate for a per person energy usage for electric > hot water? Any other suggestions are welcome. > > Thank you, > > Drake > > > > -- > -- > Barton Churchill > 406.587.5295 <(406)%20587-5295>  > 2430 North 7th Bozeman, MT 59715 > www.solarips.com > [image: Image removed by sender.] >  > > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: > RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > -- > >         Christopher Warfel, PE >       ENTECH Engineering, Inc. > PO Box 871, Block Island, RI 02807 >               (401)466-8978 <(401)%20466-8978> >  > [image: EEI logo] <http://entech-engineering.com> > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches. > org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches. > org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > >
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