That would be a good analysis to share. I can see how it could be
possible with lower module costs, but I haven't seen any studies on this
comparison. Chris
On 3/15/2018 1:17 PM, Darryl Thayer wrote:
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
<mailto: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 =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 <tel:%28413%29%20734-1456>
Â
Â
Â
*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
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,
<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
--
--Â
Barton Churchill
406.587.5295 <tel:%28406%29%20587-5295> Â
2430 North 7th Bozeman, MT 59715
www.solarips.com <http://www.solarips.com/>
Image removed by sender.
Â
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