[Greenbuilding] Opinions on electric tankless HW heaters?
Bob Waldrop
bwaldrop at cox.net
Fri Apr 22 12:11:04 CDT 2011
Probably we were using that much. At that time we our household had
increased temporarily by the addition of 2 teenagers, 2 adults, and 2
smaller kids, all of whom seemed to like long showers. IIRC, one of my
reasons for turning the heater on and leaving it on was to see what the bill
would be like for a more conventional household (the additional folks living
with us had not been habituated to our lower level of energy consumption).
So maybe its not completely apples to apples with our present lifestyle 5
instead of 8, with all 5 (one of whom is age 5 going on 15 today) having
become habituated over time to being frugal with energy.
We already have a blanket around the heater. I've never been able to test
how long it takes to cool to the ambient temperature by itself without
withdrawing hot water and adding cold water.
Bob Waldrop, Okie City
-----Original Message-----
From: Paul Eldridge
Sent: Friday, April 22, 2011 8:27 AM
To: greenbuilding at lists.bioenergylists.org
Subject: Re: [Greenbuilding] Opinions on electric tankless HW heaters?
Hi Bob,
You mentioned that your electricity consumption increased by more than a
thousand kWh per month when you operated your electric water heater
continuously, which suggests a hot water demand in excess of 33.0 kWh per
day. The Energy Factor rating for a newer, conventional model would be in
the range of 0.92 to 0.94, which means the standby losses are roughly equal
to that of a 40-watt light bulb, or less than 30.0 kWh/month. [Note that if
you were to add an insulating blanket, you could probably cut that by a
third or more, but first check with the manufacturer to ensure this won't
void your warranty.] After subtracting these standby losses, some 970+ kWh
would be attributable to water heating; assuming an inlet temperature of 10C
and a supply temperature of 50C, that's roughly 180 gallons or three and a
half tank's worth of hot water demand per day. Are you sure you were using
this amount of hot water?
+--------------------------------------------------------------------+
We use to heat our DHW with oil (there's no natural gas service in our area)
and have since switched to electric. We installed a small, 70-litre,
115-volt, 1.38 kW model that is plugged into a Kill-a-watt power monitor.
Our two person household averages a little less than 5.0 kWh per day,
including standby losses, and we both shower daily, wash clothes in hot
water and operate the dishwasher twice a week. We've made a concious
decision to wean ourselves off fossil fuels to the greatest extent possible,
and as part of this purchase 12,000 kWh/year of 100 per cent renewable
energy through Bullfrog Power. That $20.00 a month effectively offsets 115
per cent of our home's total energy needs, i.e., space heating (ductless
heat pumps), DHW, cooking (induction), lighting, appliances and plug loads.
>From our perspective, electricity is our best option.
Cheers,
Paul
----- Quote -----
We put in an off the shelf mid-price electric water heater, and added an
on off switch, so most of the time it is off and we turn it on maybe twice a
week. People periodically tell me that that doesn't save any energy, for
various reasons, and while it is true that I am not a scientist. . . as an
experiment we left it on 24/7 a couple of months in the fall when it wasn't
especially hot or cold and our bill went up over a hundred dollars each
month (more than a thousand kilowatt hours) so I would say that the simple
on off switch does in fact save energy. Not to mention giving my poor frugal
heart pains when I opened the bill. The plan when we get more money is to
add a solar water heater.
Bob Waldrop, Oklahoma City
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