[RE-wrenches] Electric Water kWh/ person
cwarfel
cwarfel at entech-engineering.com
Tue Mar 20 13:48:10 EDT 2018
What are the issues with tankless water heaters? I have heard them
described as having "issues", but I haven't read anything that describes
what they are. They are very popular where I live. Any info? Thanks, Chris
On 3/20/2018 1:07 PM, Dave Angelini Offgrid Solar wrote:
> And a big maybe for Offgrid where we like multiple ways to
> charge/heat/cool and make hot water. The default method is almost always
> the most reliable. For a typical home a 50 gallon propane tank water
> heater with a zinc change every 7 years is the norm.
>
> An air to water heat pump, an open loop solar water panel or closed loop
> if conditions warrant it are great secondary methods. To me heating water
> with electricity does not work because of winter and is a last thing to
> add.A tankless and their issues are near the end of the list. Ground
> source heat pumps are even lower to me with very nice prices on extremely
> efficient mini split air source pumps.
>
> I always try and minimize generators but if you need them then it allows
> one to have more options.
>
> Dave Angelini Offgrid Solar
> "we go where powerlines don't"
> http://members.sti.net/offgridsolar/
> e-mail offgridsolar at sti.net
> text 209 813 0060
>
>> Maybe. I designed my own house to incorporate this. The most efficient are
>> the vertical type, and at 6' the company advertised 20% recovery for about
>> $1,300 if I remember correctly. This I'm sure is for a new copper pipe,
>> and
>> anyone who's ever taken apart a sewer pipe after a few years will know all
>> pipes get a bacterial mat of a couple mm thick. I suspect this might be a
>> pretty good insulator. At any rate there is a whole lot of copper involved
>> and associated inherent environmental challenges. I can't help but think
>> for the house design challenge to accommodate such a long perfectly
>> vertical pipe and expense another kW or more of solar would offset more
>> energy.
>>
>> On Tue, Mar 20, 2018 at 9:50 AM, Drake
>> <drake.chamberlin at redwoodalliance.org
>>> wrote:
>>> 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:
>>>
>>> Content-Type: multipart/alternative;
>>> boundary="----=_NextPart_000_0077_01D3BF6A.5EF88420"
>>> Content-Language: en-us
>>>
>>>
>>> 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 ProfessionalTM: 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;
>>> 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
>>> <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>
>>> 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 <(406)%20587-5295> Â
>>> 2430 North 7th Bozeman, MT 59715
>>> www.solarips.com
>>> [image: Image removed by sender.]
>>> Â
>>>
>>>
>>>
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>>> --
>>>
>>> Â Â Â Â Â Â Â Â Christopher Warfel, PE
>>> Â Â Â Â Â Â ENTECH Engineering, Inc.
>>> PO Box 871, Block Island, RI 02807
>>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â (401)466-8978
>>> <(401)%20466-8978>
>>> Â
>>> [image: EEI logo] <http://entech-engineering.com>
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>>
>> --
>> --
>> Barton Churchill
>> 406.587.5295
>> 2430 North 7th Bozeman, MT 59715
>> www.solarips.com
>> _______________________________________________
>> List sponsored by Redwood Alliance
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>> List Address: RE-wrenches at lists.re-wrenches.org
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>
> Dave Angelini Offgrid Solar
> "we go where powerlines don't"
> http://members.sti.net/offgridsolar/
> e-mail offgridsolar at sti.net
> text 209 813 0060
>
> _______________________________________________
> List sponsored by Redwood Alliance
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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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