Re: GBlist: hybrid systems: passive solar + everything??

[Chinery.Glenn@epamail.epa.gov]

Well said, Bion!



|--------+----------------------->
|        |          rnn@rnn.com  |
|        |                       |
|        |          01/27/2000   |
|        |          11:27 AM     |
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  |                                                        |
  |       To:     bdhoward@ix.netcom.com                   |
  |       cc:     rmd@rnn.com, greenbuilding@crest.org     |
  |       Subject:     Re: GBlist: hybrid systems: passive |
  |       solar + everything??                             |
  >--------------------------------------------------------|






Dear Bion,

I'm glad somebody, as well informed as you, has all the time in the world
to read and respond to list messages on these many issues.

It is possible to make a passive/hybrid system like this one work.  (And
pigs can fly, if you toss them from a plane at 10,000 feet.)  I hesitate
to critique designs in the abstract, but the logic of your observations is
very accurate according to my reading and actual experience.

If one wants to distribute thermal energy, you need temperature.  To get
temperature from the sun, one needs a flat plate collector component that
is designed to perform that task primarily, as opposed to a window
aperature that is doing other things as well, such as, providing a view
for occupants in a comfortable room temeperature space.

As for slabs, we often had to explain the failure of well planned passive
storage systems to work, on "user variables."  The engineering was
perfectly reasonable, but the rugs, the furniture, the toys and other
stuff all over the floor tended to throw all the calculated expectations
off.

And, as you say, heating a slab with auxiliary heat reduces the
effectiveness of the solar performance, generally speaking.
Designers and builders would know all this if the solar transition had
been allowed to continue, with proper developmental support, public and
professional education, and so on.

In these regards, I'd quibble with your characterization of past U.S.
Federal solar energy demonstration programs, in that, the purpose was to
discover what worked and where the problems were.  The natural and
necessary market shake-out was cut short, in the U.S., by President
Reagan, in a particularly gratuitous and vicious manner.  We need to be
careful, in that, if we want no more government solar programs, all we
have to do is keep saying that the past programs accomplished nothing of
any value.

...but, I hear you.

Yours truly,
Ross

encl:

On Thu, 27 Jan 2000, Bion D. Howard wrote:

>
> The type of system you describe harkens back to the days (daze?) of the
> National Solar Demonstration Program where otherwise pretty good engineers
> and designers used a HEAP of Federal money to try a bunch of stuff that
> largely failed to follow the well known KISS principle.
>
> Unfortunately the main thing that these systems demonstrated is that solar
> was "too new", "too expensive" and "too unreliable" -- which then set back
> the solar industry about 30 years -- depending on who you talk to.  Gee,
> see the oil and nuclear folks told you so, right?   Anyway....
>
> Low temperature "solar" systems - particularly active charge / passive
> discharge, or systems where dual flows of energy from solar and from
> auxiliary non-renewable sources can occur into the same heat sink -- have
> often been shown to consume more electric operating power that they will
> provide in solar heating benefits.  This is a big problem that blows away
> many solar heating concepts that otherwise look good on paper -- mostly
> those involving "moving heat around."
>
> Please do (or have an energy engineer) have  a careful analysis of the
> energy flows in this system, and the power taken to operate same, and
> likely it will likely appear to be a big net looser.  With hybrid /
> "passive" systems like this there is no free lunch.
>
> The first best investment in any "solar" energy system on buildings is --
> you guessed it -- the building efficiency and whole-systems integration in
> the first place.  (Refer to previous messages about EEBA and Building
> Science manuals on topic, or join EEBA's energy efficient building list.
> There is a lot of traffic on the Greenbuilding list that is energy related
> for better or worse.)
>
> You really are better off collecting the solar heat passively and
> distributing it via conduction and radiation.  This is true passive design;
> harder and more elegant to achieve but really cool when it works.
>
> The passive solar heat (already suffering significant losses just making
> through the windows) striking the floor slab mass will be insufficient to
> consistently raise the slab temperatures to levels where expending the
> electric power to circulate heat transfer fluid to "move the heat to other
> areas" would be efficient.
>
> You are really describing an "absorber plate" of essentially "infinite"
> mass as far as the collector glazing is concerned.  And, what is the back
> insulation to the "absorber plate" concrete slab?   Will there be huge
> losses to the soil (@ ~ 55 deg. F)  Add the fact there is a conditioned
> space between the collector glazing and the "absorber plate," with its own
> losses due to UA and Infiltration, and you have the recipe for an expensive
> bunch of stuff that just sits there using electric power to operate the
> pump, or maybe never even comes on?
>
> The only "active" solar that might make sense for your hydronic slab would
> be to construct a proper solar hot water system sized for the floor heat
> load (load of space above it, perimeter loss, and deep-earth loss).  You
> could let it also pre-heat your domestic hot water so it would not sit
> there in summer stagnating the panels.
>
> In winter you would use all solar heat (design with small back-up boiler or
> tankless HW unit) and then in summer (less heat load on slab)  the solar
> system might produce most if not all your daily hot water needs (you could
> "dump" the rest to a swimming pool if you have one...).  Careful design is
> needed since in most North American climates there is a constant heat load
> derived from deep foundations, whereas slabs can have both a heating and
> cooling load (usually small) depending on if and how they are insulated.
>
> A second best approach is to use a small blower and destratify direct gain
> spaces (hybrid) into a system like the Air-Core ("block bed,"
> Katachadorian, whatever...) by using concrete block laid on their sides
> (cores line up to form ducts...)  under the floor slab.  Then your enjoy
> the once-passive collected heat, re-radiating via the underfloor mass back
> to conditioned spaces, warming the place naturally.
>
> Save the hydronic radiant flooring concept for delivering auxiliary heating
> when needed to rooms with little solar gain.  Any excess energy could be
> circulated in the conditioned spaces, then 'destratified' into the AirCore
> floor -- but this is as close as you should really get to deliberately
> mixing solar and aux. heat intentionally in a solar storage mass.  Field
> results have proven again and again that doing so wastes more operating
> energy that one imagines.
>
>     <<<<   Bion Howard
>
> PS - check local codes for permits of thinner slab without an engineering
> requirement...
>
> ====
> >Date: Wed, 26 Jan 2000 10:17:38 EST
> >From: BGuyton@aol.com
> >Subject: Re: GBlist: hybrid systems: passive solar + everything??
> >
> >  We are integrating a passive solar design with radiant foor heat. We are
> >putting a thin(21/2 inches)  slab on a framed floor over an inlulated
> >underground "basement" . The whole top floor will be one zone. When the slab
> >is overheated by the sun there will be a sensor to circulate the water
> >without adding heat from the boiler. this will distribute the heat to the
> >area unaffected by solar gain. this should increase the mass used by passive
> >solar as well as more evenly heat the floor (about 1100 sq ft.).  this
> allows
> >for smaller framing requirements than would be necessary for a thicker slab
> >and still provide significant mass. Sorta like a solar water heater
> collector
> >using the slab as both collector area and storage unit. We'll see how it
> >does.
> >boone
>     ||       Contact:  Bion D. Howard, President
> =(O) =     Building Environmental Science & Technology
>     ||      P.O. Box 1107   Edgewater, MD 21037  USA
>          Phone:  410.867.8000   Telefax: 301-889-0889
> <mailto:bdhoward@ix.netcom.com>  <http://www.energybuilder.com>
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______________________________________________________________________
This greenbuilding dialogue is sponsored by CREST <www.crest.org>
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For  instructions send  e-mail to  greenbuilding-request@crest.org.
______________________________________________________________________




______________________________________________________________________
This greenbuilding dialogue is sponsored by CREST <www.crest.org>
Environmental Building News <www.ebuild.com> and Oikos <www.oikos.com>
For  instructions send  e-mail to  greenbuilding-request@crest.org.
______________________________________________________________________