Big Grower November 2021 - 8

TECHNOLOGY
Modeling
GREENHOUSE
Energy Use
Looking to make your greenhouse more energy efficient? Curious about the potential energy savings by
updating or retrofitting an existing greenhouse? Interested in comparing different growing conditions for
a crop and assessing the net impact on crop timing and overall energy use? This is all possible with the
help of Virtual Grower, a software tool designed by scientists at the USDA's Agricultural Research Service.
BY JENNIFER BOLDT, KALE HARBICK AND YAHIA HEGAZY
o longer the " new kid on the block, " Virtual Grower continues to
provide growers the ability to model greenhouse energy use. In this
free decision-support software program, first released in 2005, users
build a virtual greenhouse - such as an existing structure, a planned
retrofit or a new dream facility.
Based on location, heating and lighting systems selected, and desired
greenhouse conditions, Virtual Grower will estimate energy usage (and
costs). It includes crop models for 40 ornamentals, allowing users to
identify target plant or finish dates based on selected light and temperature
setpoints. Running simulations in the program allows you to experiment
with a variety of " what-if " scenarios before making a final decision. Note:
while it does not supplant an actual energy audit, it will estimate energy
use and cost savings that may be attained by making small or large changes
to your greenhouse.
Some scenarios and simulations possible with Virtual Grower include:
* compare energy costs for different greenhouse designs and
materials;
* compare energy costs across multiple geographic locations;
* compare energy costs for different fuels based on current and
predicted pricing;
* estimate cost savings achievable by retrofitting an existing
structure with energy-efficient components;
* see the impact to crop timing and overall energy use of adding
supplemental lighting;
* assist in crop scheduling by calculating a start date for a crop based
on a target finish date (or vice versa), based on temperature and
lighting setpoints; and
* assess carbon footprint for greenhouse energy consumption based
on local electricity resource mix.
Currently, Virtual Grower is a Java-based program, compatible with Mac
and PC computers, and available in three languages (English, Spanish and
French). Version 3.1 is available for download at www.virtualgrower.net.
CURRENT TEAM
Our small team has grown in the past 18 months and currently consists
of three individuals. Kale Harbick joined in early 2020, and his expertise
in agricultural engineering and energy modeling complements Jennifer's
expertise in crop production and modeling plant responses to light and
8 NOVEMBER 2021
N
temperature. Together, they co-lead the development of Virtual Grower.
Yahia Hegazy joined ARS in summer 2020 and is the software programmer
for Virtual Grower.
WHAT'S NEW
In its 15-year history, Virtual Grower has undergone many iterations and
advancements. What's in store with the next version?
* New interface: We are developing a web-based version that users
can run on any browser without having to install any software
locally. This will allow growers to seamlessly run the latest version
with a simple refresh, and to store models in the cloud if desired.
* Engineering/modeling updates: This will standardize energy
modeling calculations according to the American Society for
Heating, Refrigerating and Air-Conditioning Engineers heat
balance method and improve simulation accuracy.
* Expanded lighting section: First, LEDs will be included as a
lighting option. Second, additional lighting programs, such as
target daily light integral (DLI), will be available. This will allow
you to compare lighting costs for different lighting strategies.
For example, if you are lighting for supplemental and not
photoperiodic purposes, you could compare no lighting versus
having supplemental lights on for a set duration daily versus
running lights during the day (if cloudy) and into the evening only
as long as needed to attain a target DLI.
* Cooling/ventilation section: A new tab will include energy use
and cost estimates for fans, evaporative cooling, and ventilation.
This can be considerable, especially in hotter months and
locations. This will also enable estimation of sensible cooling from
evapotranspiration.
* Cost calculator to estimate payback periods: A new tab will
enable users to input capital costs and energy prices, then calculate
the cost of installing an energy-efficient upgrade (e.g., energy
curtain), potential energy savings, and an estimated payback
window.
* Built-in language option: English, Spanish and French will be
available in the same download and selectable, like units. This will
let users instantaneously switch between languages, as needed, to
share simulations with colleagues or a supervisor.

http://www.virtualgrower.net

Big Grower November 2021

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