Big Grower November 2021 - 9

TECHNOLOGY
Angelonia 'Angelface Blue'
(9 weeks after
transplant from
84-cell liner)
Days per week
in cool/low light
Days to flower
Flower number
Plant dry weight (g)
Energy savings (%)*
47
72
13.4
-
1
53
57
11.5
4%
2
54
43
9.6
12%
4
63
9
5.3
27%
7
-
0.9
**
* Based on the reduction in energy costs relative to growing plants continuously in normal greenhouse conditions.
** Estimated energy savings were not calculated since plants did not flower by the end of the study.
Dianthus 'Telstar Pink'
(6 weeks after
transplant from
288-cell liner)
IMPROVING PRODUCTIVITY AND
PROFITABILITY
Let's run through two case studies.
Case study #1: Growing plants at lower
temperature/irradiance to save energy costs: A few
years ago, we looked at the potential of growing
annuals at lower than optimal temperatures
and DLIs for one or multiple days per week as a
potential strategy to reduce greenhouse energy
costs. The working hypothesis was it should
be feasible, but it would likely delay flowering.
Would a longer production window increase
or decrease total energy costs? The " normal "
greenhouse was 72/65° F day/night, with a DLI
~15 mol·m-2
·d-1
cool/low DLI greenhouse was 55/50° F day/
night, but with a DLI ~6 mol·m-2
and 14 hour photoperiod. The
·d-1
achieved
by closing the energy curtain during the day for
heat retention.
In general, " cold-sensitive " or " warm-season "
crops (e.g., angelonia, lantana) experienced
a delay in flowering with only one day per
week in cool/low light and the other six days
per week in " normal " conditions. However,
" cold-insensitive " or " cool-season " crops (e.g.,
dianthus, pansy and petunia) could be grown
two days per week in cool/low light conditions
without impacting crop timing or plant quality
(Figure 1).
Furthermore, they could be grown for four
or even seven days per week at cool/low
light if longer production times and fewer
crop turns per season were not critical. For
this study, we turned to Virtual Grower to
calculate the projected energy savings. At our
location in Toledo, Ohio, total energy savings
across all crops were estimated to be roughly
10% and 25% when plants were grown two
or four days per week, respectively, at cool/
low light conditions. (More details of the
study are available at www.doi.org/10.21273/
HORTSCI10289-17)
Case study #2: estimating cost savings by
implementing energy-efficient design elements:
Consider a new or existing " bare bones''
greenhouse installation with six spans (25 x
100 feet each; 15,000 square feet total). It has
a glass roof and bi-layer polycarbonate siding.
Including a foam-insulated knee wall would
reduce heating costs by roughly 25%. Addition
of an energy curtain would further reduce
energy costs by roughly 40% (depending on
geographic location). Of course, the potential
reduction in heating costs would need to be
weighed against the cost of installation for any
retrofit or upgrade, but the payoff time could
range from less than a year to a couple of years
(or even quicker if fuel costs increase). With
Virtual Grower as your " crystal ball, " you can
virtually create as many scenarios as you would
like, compare them, and run cost calculations
before deciding.
LOOKING FOR FEEDBACK
We would like Virtual Grower to be as
useful and user-friendly as possible. Many
improvements in earlier versions came from
user feedback. Let us know what you like, what
could be improved, or features you would like to
see added. Also, please reach out if you would
like to test the next version when we get closer
to release.
Jennifer Boldt is a research horticulturist, Kale
Harbick is a research agricultural engineer, and
Yahia Hegazy is an IT specialist with the USDAARS
Greenhouse Production Research Group in
Toledo, Ohio. They can be reached at jennifer.
boldt@usda.gov, kale.harbick@usda.gov or
VirtualGrower@usda.gov.
NOVEMBER 2021 9
Days per week
in cool/low light
Days to flower
Flower number
Plant dry weight (g)
Energy savings (%)*
·d-1
35
39
14.3
-
1
35
29
13.4
8%
2
37
28
11.6
13%
4
42
10
8.3
27%
Figure 1. Plants were grown in " normal " greenhouse conditions (72/65° F day/night,
DLI ~15 mol·m-2
DLI ~6 mol·m-2
·d-1
, 14 hour photoperiod) or a cool/low DLI greenhouse (55/50° F day/night,
, 14 hour photoperiod) for 0, 1, 2, 4 or 7 days per week.
7
56
1
5.8
51%

http://www.doi.org/10.21273/

Big Grower November 2021

Table of Contents for the Digital Edition of Big Grower November 2021