<div dir="ltr">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. </div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Mar 15, 2018 at 12:00 PM, Drake <span dir="ltr"><<a href="mailto:drake.chamberlin@redwoodalliance.org" target="_blank">drake.chamberlin@redwoodalliance.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
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.<br><br>
Thank you all!<br><br>
Drake <br><br>
<br><br>
At 09:21 AM 3/15/2018, you wrote:<br>
<blockquote type="cite" class="m_-2933207039044196130cite">Content-Type:
multipart/alternative;<br>
boundary="------------<wbr>EE4E9806B711DEF636076840"<br>
Content-Language: en-US<span class=""><br><br>
<font face="Verdana">This is what I came up with:<br>
</font><br>
<font face="Verdana">The calculation is Q = mcp delta T<br>
</font><br>
</span><font face="Verdana">Water Temp out =Â 120<br>
</font><span class=""><br>
<font face="Verdana">Water Temp in = ground source Temperature @
50F?<br>
</font><br>
<font face="Verdana">delta T = 70F<br>
</font><br>
</span><font face="Verdana">m = mass flow rate. ASHRAE is the
source for this. 20gals per person per day = 20 gallons x 8.34 lbs/gallon
=Â 167lbs/day/person<br>
</font><br>
<font face="Verdana">cp =Â 1 BTU/lb-degree F<br>
</font><span class=""><br>
<font face="Verdana">Q = 167 x 1 x 70 = 11,676 BTU/day/person<br>
</font><br>
</span><font face="Verdana">Divide this by the efficiency of the water heating
system (I'll assume = .86)Â =11,676/.86 = 13, 577
BTU/person/day<br>
</font><span class=""><br>
<font face="Verdana">convert to kWh if necessarym 13,577/3412 = ~4
kWh/person/day, 120 kWh/month<br>
</font><br>
<font face="Verdana">I checked this against one month and it seems
reasonable. <br>
</font><br>
<font face="Verdana">Website assuming ~3.5 family size comes up with @
400kWh per month. They approached it another way with assuming run
times.<br>
</font><br>
<font face="Verdana">
<a href="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" target="_blank">
https://www.google.com/search?<wbr>safe=active&source=hp&ei=<wbr>Z3KqWvXiNsGb5wKJ2Kf4DA&q=<wbr>electric+water+heater+use+<wbr>annual+consumption&oq=<wbr>electric+water+heater+use+<wbr>annually&gs_l=psy-ab.1.2.<wbr>33i22i29i30k1l3.279.9222.0.<wbr>12475.35.19.0.7.7.0.451.2360.<wbr>0j6j4j0j1.11.0....0...1c.1.64.<wbr>psy-ab..18.16.1952.0..<wbr>0j0i67k1j0i131k1j0i22i30k1.0.<wbr>CiU8wYZigpI</a>
<br>
</font><br>
<font face="Verdana"><br>
Chris<br>
</font><br>
<font face="Verdana"><br>
</font><br><br>
On 3/15/2018 8:09 AM, Mike Kocsmiersky wrote:<br>
</span><blockquote type="cite" class="m_-2933207039044196130cite">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. Â 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.<br>
 <br><span class="">
Mike Kocsmiersky<br>
Principal<br>
Spirit Solar Inc.<br>
<a href="tel:(413)%20734-1456" value="+14137341456" target="_blank">(413) 734-1456</a><br></span>
 <br>
 <br>
 <br><span class="">
<b>From:</b> Barton Churchill
[<a href="mailto:barton@solarips.com" target="_blank">mailto:barton@solarips.com</a>]
<br>
<b>Sent:</b> Wednesday, March 14, 2018 7:31 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] Electric Water kWh/ person<br></span>
 <br>
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.Â
<br><span class=""><br>
On Wednesday, March 14, 2018,
<<a href="mailto:drake.chamberlin@redwoodalliance.org" target="_blank">
drake.chamberlin@<wbr>redwoodalliance.org</a>> wrote:<br>
Hello Wrenches,<br><br>
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. <br><br>
Does that seem high? There will be a maximum of 2 people per unit.
<br><br>
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. <br><br>
How can we get a good estimate for a per person energy usage for electric
hot water? Any other suggestions are welcome.<br><br>
Thank you,<br><br>
Drake<br><br>
<br><br>
-- <br></span>
--Â <br>
Barton Churchill<br>
<a href="tel:(406)%20587-5295" value="+14065875295" target="_blank">406.587.5295</a> Â <br><span class="">
2430 North 7th Bozeman, MT 59715<br>
<a href="http://www.solarips.com/" target="_blank">www.solarips.com</a><br>
<img width="100" height="100" alt="Image removed by sender.">
<br></span>
 <br><span class=""><br>
<br><br>
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