Cohousing-L Mailing List: Re: Re: Energy/heating/design issues

[Roger Diggle (diggle]

 Ray Gasser wrote:
 > Architect is leaning toward
 > having one boiler for each unit (though all located in the energy center),
 > primarily because he feels banks may not like having a lien on 1/8 of a 
 > common boiler if one household defaults on a mortgage. Most residents want
 > to stress the "Eco", and get fewer/larger/more efficient units, possibly
 > 2 or 3 for each cluster with a primary/secondary/tertiary load and
possibly
 > dynamic switching between the three to even out the usage/lifespans. 

Just a couple of ideas, in case nobody has thought about them:
I heard no mention of using solar in your discussion...  it is expensive to
set up and my guess would be that there is little help from the banks.  IMHO,
a reasonable approach to initial installations might be to build "solar
ready."  that is, try to think ahead about what might be needed in a
different energy future and provide things that will make later installations
easier, like extra electrical raceways for solar voltaics, pipe chases and
mounting supports for wet solar collectors, or whatever.

In this regard, high on my list for hot water heating system preparation
would be provision for adequate (large) indoor heat exchange design.  The
ability to use "active" solar collectors as part of a heating scheme will
depend on getting adequate heat into the house at low (less than 140f) water
temperatures.  140f is the typical design temperature of a "modern" hot water
heat system, though in typical homes it is not unusual to see 180f required
on a "design day" (the coldest day that the system is designed to maintain,
say, 65f indoors running full tilt, full time).  The larger the indoor heat
exchanger (fin-tubes, under-floor tubing, what have you) the lower the water
temperature can go before you are forced to supplement the heat with the
boilers.  This could mean many more available hours of solar-only operation,
and more hours of solar assisted operation if the system is capable of doing
that.

The second idea has to do with the possible necessity of using 8 boilers (one
per unit) rather a single or a few larger boilers.  Depending on the piping
and control systems, there are some advantages in using a flock of small
boilers.  Best boiler efficiency in a hot water system is achieved when the
boiler runs continuously, producing the lowest water temperature that will
heat the building.  This requires fairly careful matching of the size of the
boiler burner to the size of the heat load.  One of the easy ways to control
the burner/load match is to use several small boilers and, as you mention,
increase the number of boilers that are firing as the load increases.  And
some of the most efficient boilers available these days are small ones.

You get the added comfort of knowing that, if a boiler needs repair, there
will be several others ready to heat the system, giving increased
reliability.  Single boilers that can provide equivalent burner control are
usually much larger than the total load you present.  First cost for a system
using 8 boilers as opposed to three is obviously higher, but if the bank
pushes you to it, the efficiency can be somewhat better.  And in this scheme,
if the bank ever felt the need to usurp one of the boilers and assign it to a
housing unit, it could be done with simple piping changes (heaven forbid).

The other possibility, depending on local codes, depends on the source of
domestic hot water you will use.  It is possible, in many locales, to use
domestic hot water directly for heating if the piping, the heat exchanger and
pump all use materials acceptable in domestic hot water piping.  Here in
Wisconsin, where plumbing codes and enforcement are fairly strict, apartments
are sometimes heated by circulating water from the standard domestic hot
water heater through baseboard fin tubes.  The floor slab could be used as
easily if the piping materials were appropriate.

Roger Diggle    Porchlight CoHousing Group    Madison, WI

- via BulkRate 2.0

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