I had thought of this a long time ago for an island project, but the
cost of plumbing cold inlet water past the heat exchanger was too high.
I think this can work at time of construction or easy renovation. We do
this for large thermal dump loads for fabric mills for example.
On 3/19/2018 10:09 AM, Daniel Young wrote:
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 I’d say it’s 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 Professional^TM : 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 =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
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]
*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 Â
2430 North 7th Bozeman, MT 59715
www.solarips.com <http://www.solarips.com/>
Image removed by sender.
Â
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