Vergara - 1976 - Physiological and morphological adaptability of ri

142 (rut-tars mo arcs
closely related to our own experience and which we believe merit attention in
future design and operation of controlled-environment facilities.
For a number of reasons we have chosen the latter course. These include the
belief that research results available in this field need further development before
they are ready for coordination to bring out major principles. With the
approach adopted we can provide information which may be new and of i1n1nediate
assistance in the development and use of phytotrtin facilities.
We shall consider first certain aspects of the basic physics in the strategy of
design, and thcn some aspects of the interaction of controlled-environment
conditions with the plants themselves.
In the various types of phytotrons which have been constructed to date there
has been a wide diversity of design solutions. Table l, which is taken predominantly
from data assembled by" de Bilderling (pers. comm), illustrates this. It
presents representative data for major installations in various parts of the world
and is not intended to cover all facilities of this nature.
lt is apparent from Table l that a major design difference is whether an i11-
stallation has a large proportion of its controlled space naturally lit, or whether
it is completely artificially lit. This is a fundamental distinction for most environments.
First. it has a major effect on heat exchange physics and their costs.
Second, it generally has a major effect on the amount of environmental ‘variability
that both the plants and the control machinery have to cope with. Third, it
may substantially influence uncertainties as to how far conditions in a phytotron
are duplicating or controlling the important factors of the natural environment,
i.e. will plants grow and respond as they would in a supposedly similar
natural environment‘? Accordingly. each of these three aspects Will be considered.
HEAT EXCHANGE PHYSICS
In phyitotrtiits. removal of excess heat from the plant-growing area is the dominant
load both in quantity and in costs. The naturally lit space design must allow
for the maximum heat load coming from the external environment while the
artificially lit space design can be for the mean heat load.
Naturally lit rooms
Machinery for a naturally lit space must handle the maximum summer solarheat
load. This will vary somewhat with location. but for a representative figure
we have taken the design level quoted for the SEPEL Phytotrons. i.e. those at
Duke and North Carolina State Universities. USA. (DOWIIS et al.._ 1972). This
was for 283 BTU - ftr? -hr' per sq ft per hour for incoming radiation onto a horizontal
surface which equates to approximately 2.830 BTU - rnr? - hrl. Additionally.
allowance in cooling capacity has to be made for inward heat transfer through
the glass surfaces when outside temperature conditions are substantially above
those of the rooms. This will ‘vary with the conditions in the various rooms. but