Drake,
Have you or the client looked into the drainwater heat recovery units? They make both a vertical and horizontal mounted version. They just help recover the waste heat from shower water going down the drain. My understanding is that economically they are barely past the breakeven point when considering offsetting grid power. If using PV costs as the benchmark, the economics would be better. If somehow this is off grid, then Id say its a home run. (Hopefully though this is not an all-electric off-grid building.) The main benefit, as far as I understand it, is that you can get by with a smaller unit, with a smaller heating element to perform the same task, OR you can get much longer showers from the same sized unit. Depending on the clients goals, this might be a useful tool to bring into the situation. Here are two brand names that I know of. Vertical mount: renewability Horizontal mount: ecodrain I have not used these products, so I cannot endorse any of them, just though it may be worth consideration. With Regards, Daniel Young, NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90 From: RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org> On Behalf Of Drake Sent: Thursday, March 15, 2018 1:00 PM To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Subject: Re: [RE-wrenches] Electric Water kWh/ person 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 <https://www.google.com/search?safe=active&source=hp&ei=Z3KqWvXiNsGb5wKJ2Kf4 DA&q=electric+water+heater+use+annual+consumption&oq=electric+water+heater+u se+annually&gs_l=psy-ab.1.2.33i22i29i30k1l3.279.9222.0.12475.35.19.0.7.7.0.4 51.2360.0j6j4j0j1.11.0....0...1c.1.64.psy-ab..18.16.1952.0..0j0i67k1j0i131k1 j0i22i30k1.0.CiU8wYZigpI> &source=hp&ei=Z3KqWvXiNsGb5wKJ2Kf4DA&q=electric+water+heater+use+annual+cons umption&oq=electric+water+heater+use+annually&gs_l=psy-ab.1.2.33i22i29i30k1l 3.279.9222.0.12475.35.19.0.7.7.0.451.2360.0j6j4j0j1.11.0....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] 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 <mailto: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  2430 North 7th Bozeman, MT 59715 www.solarips.com <http://www.solarips.com/>  _______________________________________________ List sponsored by Redwood Alliance List Address: <mailto:RE-wrenches@lists.re-wrenches.org> RE-wrenches@lists.re-wrenches.org <mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> 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 > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: <http://www.re-wrenches.org/etiquette.htm> www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: <http://www.members.re-wrenches.org> www.members.re-wrenches.org <http://www.members.re-wrenches.org> --         Christopher Warfel, PE       ENTECH Engineering, Inc. 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