[Greenbuilding] [BULK] Re: hot water versus forced air--and window AC versuscentral

Mon Oct 8 12:16:06 EDT 2007

OK, here is another angle:  

You could go with a very high efficiency furnace, and maybe beat the
efficiency of the radiators.  

Yes, a furnace uses more energy to move the air than a radiator uses to
pump hot water, however, all of that fan energy ends up as heat in your
house, so it helps you in the winter (and hurts you in the summer).  Fan
energy can be as much as 6% of the air conditioning load, not
insignifigant.  

A third option is a heat pump.  You are substituting electricity for
gas, so the utility rates in your area make the economics go or not.
You'll use about 1000 watts of electricity to make about 3000 watts of
heat, so the efficiency usually kills any competition with gas.  In my
area, electric rates are cheaper in the winter, and one utility gives
you a discount for having a heat pump, or a "dual fuel" setup that
switches to gas when the heat pump wimps out on too-cold winter air. I
did a simulation on a house recently where the gas bills would be $200 a
month but the heat pump bills would be $75 a month at the same
conditions.   

If you live in a climate with a lot of time above 30F (anywhere south of
St Louis or much of California) then a heat pump can work for you most
of the winter.  If it gets really cold where you are (much below 30F)
you need a backup source of heat, but the heat pump still saves a lot of
dough in shoulder months. 

Here is another plus on heat pumps:  Many utilities now let you buy
"green" power.  If you are using "Green" power through a heat pump to
heat your house, your carbon footprint is dramatically reduced versus
gas heat.  

Of course, the heat pump costs more to install and is more complex.  

Lawrence Lile, PE, LEED AP
Project Solutions Engineering

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of John
Straube
Sent: Thursday, October 04, 2007 4:23 PM
To: Carmine Vasile
Cc: GREENBUILDING at listserv.repp.org
Subject: [BULK] Re: [Greenbuilding] hot water versus forced air--and
window AC versuscentral
Importance: Low

Carmine is of course correct (provided a condensing boiler is used and
the return water temperature atctually goes through the boiler), but I
did not mention it since that once not one of the choices :(. My place
has radiant floors and I personally check frequently to make sure that
the condensate line is running and the exhaust gases are not too hot.

Carmine Vasile wrote:
>    You will never find an unbiased opinion. Hydronic radiant floor
heating is
>    the most efficient.
>        ______________________________________________________________
> 
>      From:  Ben Pratt <prattb at uwstout.edu>
>      To:  <GREENBUILDING at LISTSERV.REPP.ORG>
>      Subject:  [Greenbuilding] hot water versus forced air--and window
AC
>      versuscentral
>      Date:  Wed, 3 Oct 2007 16:43:30 -0500
>      >I would like to know which uses less energy to heat a home-all
else
>      >being equal: forced air or cast iron radiators.
>      >     I have radiators now, and like the even heat, but feel
wasteful in
>      >that It is usually impractical to turn down the heat at night or
when
>      >leaving the house for work.  I could get a deal on a forced air
>      >system (from a friend that pulled a newer one out of his house),
but
>      >do not have a clear understanding of whether my gas bill would
go up
>      >or down.
>      >     I was also wondering whether having window AC units, and
only
>      >using them in only certain parts of the house, makes sense
versus
>      >getting a central air system.
>      >      Certainly, the forced air and central AC is more
convenient, and
>      >takes up less space, but which is more efficient? In surfing the
web,
>      >it is hard to find a unbiased opinion.
>      >-Ben
>      >
>      >--
>      >B  e  n  j  a  m  i  n   P  r  a  t  t
>      >Professor
>      >Department of Art and Design
>      >University of Wisconsin-Stout
>      >Menomonie, WI 54751
>      >
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-- 
Dr John Straube, P.Eng.
Associate Professor
Dept of Civil Engineering & School of Architecture
University of Waterloo
Waterloo, ON Canada

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