[RE-wrenches] Electric Water kWh/ person
cwarfel
cwarfel at entech-engineering.com
Mon Mar 19 14:23:57 EDT 2018
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-bounces at lists.re-wrenches.org> *On
> Behalf Of *Drake
> *Sent:* Thursday, March 15, 2018 1:00 PM
> *To:* RE-wrenches <re-wrenches at 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;
> Â 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:barton at 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.chamberlin at redwoodalliance.org
> <mailto:drake.chamberlin at 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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> --
>
>         Christopher Warfel, PE
>       ENTECH Engineering, Inc.
> PO Box 871, Block Island, RI 02807
>               (401)466-8978
> Â
> EEI logo <http://entech-engineering.com>
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--
        Christopher Warfel, PE
      ENTECH Engineering, Inc.
PO Box 871, Block Island, RI 02807
              (401)466-8978
EEI logo <http://entech-engineering.com>
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