[BLDG-SIM] hornets nest?

[Daniel H. Nall]

This has been the most stimulating discussion so far in this group.  I
think it is long overdue, because the impasse over DOE 2.2 and Energyplus
threatens to keep improved simulation tools out of the hands of users for
some time to come.  This is particularly frustrating because of the promise
of Doe2.2, which still could benefit from numerous additional HVAC
alternatives.  The circulation loop method of building systems is very
attractive and offers flexibility not available on any other program.  I
submit that the addition of packaged water-cooled VAV/PIU systems, a
revised and expanded scheme for waterside economizer, the addition of
cooling coil run-around heat recovery, the addition of photovoltaic
systems, and other components would be of much greater immediate benefit
than the revamping of the loads calculation procedure promised for Energyplus.

I must admit that I am mystified by the appeal of the energy balance
approach to loads-calculation for annual energy analysis.  In order
accurately to calculate the differential radiation balance among interior
surfaces, one must input those surfaces explicitly.  This would include
breaking down larger surfaces into a number of smaller surfaces in order to
accommodate surface temperature variations across the surface or within the
adjacent air mass.  This would be particularly important for any insolated
surface, and it would become necessary to calculate exactly the surface
components in direct sunlight.  In order to accommodate any air temperature
stratification that might occur, it would be necessary to input several air
temperature nodes and specify the coupling between them and different
surfaces.   The more complex becomes the load calculation, the more
difficult simultaneous solution of systems and zone air temperature
becomes. Ultimately, the loads program becomes a computational fluid
dynamics simulation with conjugate heat transfer. One has to question
whether this degree of complexity is appropriate for an annual energy
analysis, especially for a 40 story high-rise office building, or a medical
research laboratory.  It seems more appropriate to a short time period
investigation of temperature distributions within a single space or group
of spaces, a very legitimate investigation that is currently handled very
well by programs such as ESP-R, but one which perhaps should not be the
primary focus for federal funding in this area.

      Daniel H. Nall, AIA, PE
           Principal
Flack + Kurtz Consulting Engineers
        475 Fifth Avenue
       New York, NY 10017
Tel:  212 951-2691 Fax:  212 689-7489
     e-mail nall at ny.fk.com



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