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:
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This is what I came up with:
The calculation is Q = mcp delta T
Water Temp out =Â 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 =Â 167lbs/day/person
cp =Â 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)Â =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>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. 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.
Â
Mike Kocsmiersky
Principal
Spirit Solar Inc.
(413) 734-1456
Â
Â
Â
From: Barton Churchill
[<mailto:bar...@solarips.com>mailto:bar...@solarips.com]
Sent: Wednesday, March 14, 2018 7:31 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Electric Water kWh/ person
Â
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
On Wednesday, March 14, 2018,
<<mailto:drake.chamber...@redwoodalliance.org>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
--
--Â
Barton Churchill
406.587.5295 Â
2430 North 7th Bozeman, MT 59715
<http://www.solarips.com/>www.solarips.com
Image removed by sender.
Â
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