Vergara - 1976 - Physiological and morphological adaptability of ri

I44
CLINIATE am Rica
we assume that outside air temperatures can be on average 5°C above mean
room temperatures, and give an additional heat load of 400 BTU ~ m4 - he‘ of
operating surface. lf that is translated as a combined heat load into refrigeration
requirement it becomes 0.269 tons (t) of refrigeration capacity per square meter
of room space. At a cost of $N7.900/ton of refrigeration capacity’, and a power
requirement of l kW/t of refrigeration delivered. plant costs for this heat removal
become $NZ242 per square meter/kilowatt and per square meter/kilowatt of
installed electric power.
Artificially lit rooms
For rooms lit ivith an average illuminance of U0 Wm-t PAR and a total shortyvavc
irradianec of 255 Wm = with reasonable wall insulation and temperature
control of the glass surface, heat loads for removal become 870 BTU - m4 -h-1
for short-wave radiation and 45 BTU - m-= -h-1 for ambient heat input. This
equates to a total refrigeration load of 0.076 t/m= at a cost of $NZ69/m= and a
power requirement of 0.076 kW.
Where there is no natural lighting. the COSI of the lamps must be added. Lighting
based on high-pressure vapor-discharge lamps and tungsten iodide lamps to
give an irradiance of I70 Wm~= requires I kWlm= of lamping poiver. The cost
is approximately‘ $NZltltlfkW for lamping and an additional cost of $30lml
for a water screen to remove excess infrared radiation. Thus, the lamping adds
a total of $l30/m1.
Total costs for refrigeration and lighting then become $242fm= for the
naturally‘ lit space and $l99fml for the artificially’ lit space (Appendix l).
Other aneilliaiy costs to be considered are: costs for iviring the lamps", costs of
piping connections between the rooms and the base refrigeration machinery
space; costs of the building structure in each case; and additional heating costs
required for the naturally lit space to compensate for its greater heat leakage
under cool-season conditions. When these are equated the basic conclusion
stands: the capital costs of providing controlled naturally lit space and controlled
artificially’ lit space on an equivalent scale are essentially equal.
Data for the SEPEL phytotrons in U.S.A. (Downs et al.. 1972) indicate that
the assessments of refrigeration requirements for naturally lit space are probably}
conservative. Their naturally lit rooms have installed refrigeration capacities of
().7—l.2 t/ml. That is twofold to threefold greater than the amount calculated
for the cost comparison above. The New Zealand Climate Laboratory with
artificially‘ lit rooms operates with an installed refrigeretion capacity of 0.30-
035 t/m=. much ofit used for ancilliary purposes such as humidity control.
It can be noted also that for operational costs in terms of electric poiver
consumption. or plant maintenance. the artificially lit space using modern
large wattage and long-life lamps can be equivalent to, or better than. the naturally
lit space‘