[RE-wrenches] Electric Water kWh/ person

[Mike Kocsmiersky]

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.

 

Mike Kocsmiersky

Principal

Spirit Solar Inc.

(413) 734-1456

 

 

 

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

 

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. 

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





-- 

-- 

Barton Churchill
406.587.5295  
2430 North 7th Bozeman, MT 59715
 <http://www.solarips.com/> www.solarips.com

Image removed by sender.

 

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