Re: [GBlist] question about turning heat down

["Dr. C.F. Vasile" <gfx-ch@msn.com>]

Corwyn: Regarding your comments: "Teaching a teacher; what fun!" ... "Simple
version: A house loses a certain amount of heat every hour.  A furnace can
replace that as it is lost, or the next morning.  Fuel use is the same.
Thus, turning down the heat can never use more energy."

Fuel use would be the same, as you claim, if 100% of the furnace's input
energy entered the living space. This is not so in millions of homes if a
large fraction of their furnace's input energy goes elsewhere. So large
setbacks can lead to needless waste by increasing cycling-, stack-, and
standby-loss.

A Practical Example:
One of the worst systems to use large setbacks with are overpowered,
tankless-coil, oil-fired systems that provide heat and hot water in millions
of homes throughout New York and New England. Their thermostats control
circulators and their aquastats control the oil burner, so setback
thermostats will not reduce standby loss because they don't set back the
aquastat. (Our old system had a "sticker" standby loss of about 14.3 million
Btu/yr)

To eliminate complaints of cold showers cause by limed-coils, oil servicemen
routinely install oversize oil nozzles. In our case, the rated 1.0 GPH
nozzle was replaced with 1.5 GPH model. This not only reduced the conversion
efficiency, it caused the oil burner to cycle many time per hour because a
210,000 Btu/hr input was too much with a maximum space-heat-loss around
45,000 Btu/hr on the coldest of days, with a wind-chill of minus 45-deg. F.

But, a 1.5 GPH firing-rate still couldn't sustain a low-flow shower.

Large setbacks only increased cycling/stack/standby-loss because of heat
lost at the end of each cycle up an overheated stack and out the utility
room's vents.

AN UNEXPECTED SOLUTION:
In 1993 I began testing the first pre-production prototype of our DHR system
and noticed the oil-burner began to cycle on & off with the shower running.
This never happened before, so I replaced the 1.5 GPH nozzle with one rated
@ 0.75 GPH and lowetred the aquastat setting from the 160 to 180F range to
the 140-160F range. We still had plenty of hot shower water and the on/off
ratio of the oil burner increased. Cycling/stack/standby-loss all dropped.

So, in 1995 we decided to get rid of the oil burner and replace it with a
"combi" like that shown @ www.oikos.com/gfx/combi.html. Ours is a tankless
electric version of the one described in the following testimonial from a
customer living in Vermont: "My testimonial would be that my GFX allows me
to increase the capacity of my 40 gal. LP-fired water heater which is being
used to provide heat in a 2000 sq. ft. home and domestic hot water for a
family of 4. Cool, huh? -Matt." (Quote from
www.oikos.com/gfx/testimonials.html)

Matt's and our systems work well with programmable thermostats because they
are not over-powered, hence do not suffer huge cycling losses common to
over-powered systems controlled by programmable thermostats having large
and/or frequent setbacks.

Numerical Example
Since switching away from oil in 1995, annual energy savings have ranged
between 50 & 60 million Btu/yr compared to our baseline-year, 5/94 to 5/95,
when our house, which has central AC, consumed:

    700 gallons of oil +
    3,658 kWh from 5/6/94 to 11/5/94 +
    4,874 kWh from 11/5/94 to 5/8/95 for a grand total of
    37,232 kWh = 127 Million Btu

Energy Tip Discovered For Homes With Central AC:
    Install a programmable thermostat in the coolest part of the house to
control the central AC system.
    Install another programmable thermostat in the kitchen to control space
heating.  (This works especially well if the lady of the house is
experiencing hot flashes and is prone to open kitchen windows & doors
whenever they arrive.)

*******************
----- Original Message -----
From: "Corwyn" <corwyn@midcoast.com>
To: "Anja Kollmuss" <anja.kollmuss@tufts.edu>
Cc: "Greenbuilding List" <greenbuilding@crest.org>
Sent: Monday, January 28, 2002 12:03 PM
Subject: Re: [GBlist] question about turning heat down


>
> On Monday, January 28, 2002, at 10:51 AM, Anja Kollmuss wrote:
>
> > I teach environmental classes and I run into this question again and
> > again:
> >
> > How much should one turn down the heat at night: It it true that it is
> > better not to lower the heat by more than 10 degrees (eg. to 58 from
> > 68), because it would take more energy to heat the rooms back up (say
> > fom 50 to 68)?
> >
> > Can someone explain this to me?
> > Thanks so much!
>
> Teaching a teacher; what fun!
>
> Simple version: A house loses a certain amount of heat every hour.  A
> furnace can replace that as it is lost, or the next morning.  Fuel use
> is the same.  Thus, turning down the heat can never use more energy.
>
> Slightly more complicated, more realistic version:  The amount of heat a
> house loses is related to the difference in temperature between it and
> the outside.  Thus as the house gets colder it loses less energy.  The
> furnace only needs to recover what was lost.  Fuel savings ensue.
>
> Extreme case:  You leave the house off for a year. come back in July,
> No heat is required to bring it up to temperature, you saved an entire
> years supply of fuel.
>
> Realistic extreme case: You leave the house for a year, and use the fuel
> savings to fix plumbing, roof, and social problems associated with
> having an empty house.
>
> Hope This Helps.
>
> Corwyn
>
> --
> Corwyn
> Kermit didn't know the half of it...
> corwyn@midcoast.com









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