Daniel,
That sounds like an intriguing technology, much
along the lines of an air to air heat exchanger.
Thanks for the recommendation. These systems
could keep a lot of CO2 out of the atmosphere if widely used.
Drake
At 10:09 AM 3/19/2018, you wrote:
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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:
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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.
 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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