HLA Technology and Equipment

General Information

Example of data that can be provided to researchers


Our 24-zone, 31,400 ft2 greenhouse range was designed for a balance of durability, flexible-use and high technology. It is flexible because technology that is expensive and hard to repair/replace, such as in-floor heating or retractable roofs, was not utilized. It has no permanent benches, blackcloth or grow lights installed. Rather, each 1200 ft2 (108 m2) greenhouse zone can be modified quickly according to need with that equipment. It is an easy facility to retrofit with new technology, and the design includes abundant water, electric and data utilities to support upgrades.

The greenhouses are Nexus-built, ridge and furrow design with 32-inch wide tempered glass glazing. The superstructure is anodized aluminum with a 30-inch curtain wall. Floors are cement with trench drains, making for easier clean up and fewer pests. The greenhouses are heated with radiant hot water pipes and cooled using exhaust fans and evaporative pads. No vents are present in the ridge or sidewalls (other than fan shutters), allowing for reduced maintenance, reduced insect pressure and a better seal from the weather. The air brought in for ventilation comes from an open-topped plenum (a little hallway between the greenhouse and corridor) so greenhouses do not share or compete for air. Insects have to be 15 feet above ground and over the greenhouse to get into the intake air stream.

Each greenhouse bay is independently controlled and monitored. All that equipment in each bay makes for an expensive range, but allows us to achieve 24 different environments--at any one time we are producing crops of over 50 species, not including the dozens of specimen plants in the collection greenhouse!

Growth Rooms

The growth rooms are used for research requiring a greater level of environmental precision than a greenhouse, or for providing uniform lighting so that seasonal light level doesn't effect a long-term experiment. The two, 900 ft2 growth rooms have features similar to the greenhouses including compressed air, tap water, purified water, fertilizer solution and environmental monitoring. Twenty-eight 1000 watt high intensity lamp fixtures (a mix of metal halide and high pressure sodium) up to 250 µmol/m2/sec of light at bench top level.

Chilled water exchangers are used to cool the room and for dehumidification. Fifteen-percent of the air volume is continuously exchanged with fresh air. Temperature capability range is 16 - 38° C independent of outdoor ambient temperature. Typical temperature setpoints are 22° C during light period (16 hours) and 18° C during the dark period. Temperature error is less than 1° C. Humidity is purged through fresh air exchange. Since air is particulate-filtered and positive pressure maintained, insect pressure is greatly reduced--they have to be carried in on plants or people.

Limitations are high demand. Multiple users mean the rooms are not used to full capability because a "compromise" environment is necessary to maintain success of all projects. The rooms are controlled by Purdue Environmental Control Systems personnel, which means somewhat less responsiveness than if greenhouse personnel were controlling them, particularly during after-hours. High heat load of lights makes necessity for limit switches to cut off power to lights if cooling fails. Temperature climbs to 130° F in thirty minutes otherwise.


Within our 4,500 sq. ft. headhouse are greenhouse team offices, lockers, team break area, potting room, fertilizer injector cage, soils handling room, storage rooms, shower facility for our pesticide applicators, and pesticide storage room. The overhead rolling door for receiving is equipped with a blower that creates a curtain of warm air when loading/unloading perishables.


The polyhouse was built with the idea of creating an environment closer to the industry standard, but with durability to match the rest of the facility. Our Jaderloon polyhouse is 3,400m-sq. ft., with polycarbonate sidewalls and double-layer polyethylene film over the arched frame. Posts, joists, and framing are galvanized structural steel. The film is 6 mil thick with UV inhibition. The environment is controlled by a Wadsworth Envirostep Controller, and monitored with a redundant Priva sensor for data tracking and alarming similar to our glass houses. It has fan and evaporative pad cooling and radiant hot water heating. Sidewalls are 14 feet high, with concrete foundation walls and gravel floors. Fertilizer and domestic cold water are plumbed independently.


Each compartment of 90 ft2 is controlled independently and alarmed. One is outfitted with fluorescent lamp fixtures and shelves as a cold stress and vernalization environment, and another as a seed stratification chamber. The other three are utilized for general storage, cold storage of flowers, dormant woody branches, tubers and bulbs, and for teaching projects.

Growth Chambers

Thirty three chambers were purchased and installed in three areas of the Agriculture campus as part of a decentralized multi-user facility obtained through a $450 K National Science Foundation MRI grant plus equivalent matching funds from Purdue University.

College of Agriculture Plant Growth Center

Tissue Culture Lab

The tissue culture lab consists of four rooms, totaling 1,809-ft2 (167 m2). A preparation room has counters, equipment cabinets, dishwasher, sinks, refrigerators, freezer, and two Getinge Castle Model 122 gravity steam sterilizers. The transfer room has six laminar flow hoods and is operated under positive pressure. Two culture rooms are also under positive pressure for sanitary environment. One contains 540-ft2 (50 m2) of shelf space lit with fluorescent lamps for petri-dish culture, and the other contains shaker tables for liquid culture and an additional 540-ft2 (50 m2) of lighted shelf space.

Lab / Classroom Facility

In January 1999, renovation was completed on our old headhouse building. Former offices and work areas were converted into an extra laboratory classroom, along with asbestos removal and upgrade of utilities. The classroom is 800-ft2 (74 m2), with an adjacent 170-ft2 (15.8 m2) preparation room complete with cooler, sink, cabinets, and counter space.

Environmental Control Systems

Each of the greenhouse zones is controlled using Priva Computers sensors, microprocessors, weather station and software. Weather station data of light, temperature, humidity, rain, wind speed and wind direction allows the microprocessors to anticipate heating and cooling requirements. This ability to anticipate need for heating and cooling gives accurate temperature control while minimizing equipment cycling. The computer calculates a heating requirement or a cooling requirement to decide which, if any, equipment to activate. To make this calculation, it determines

  1. how far the measured temperature is from the setpoint
  2. how long the temperature has been away from the setpoint
  3. how fast it is changing
  4. outdoor conditions

Different equipment may be on at one moment when the zone is 79-degrees F than another moment when it is 79F, because the proportional control calculation is anticipating based on the outside conditions and rate of change.

The bottom line of all this sophisticated equipment is maintaining the tight environmental control necessary for plant science research and teaching. During winter and on cloudy, cool days in summer, we can maintain temperatures within two degrees. On hot, humid days the evaporative cooling can't keep up with cooling demand, and the best we can achieve is nine degrees below outdoor temperature. The greenhouses had no trouble handling the continuous sub-zero temperatures and record-setting snowfall of January 1999. Venting with fans purges high humidity in the greenhouse.

Sensors in the greenhouses measure temperature and humidity continuously and record data points every 10 minutes to a host computer in the manager's office. We can print out graphs and reports of environments for scientific publication. We can also see graphs and reports of how many minutes each piece of equipment was on. This has helped us learn how to use the heating/cooling wisely, and can detect faulty equipment.

The computers also set off environmental alarms we’ve programmed. If the alarms aren't acknowledged in the greenhouse or on the main computer, the computer calls the manager. The main computer can be accessed with a laptop computer plugged into a phone jack, or an iPhone, so the manager can answer alarms remotely and fix most problems. Undoubtedly, the alarming feature has saved experiments from being ruined on several occasions. If the experiment involves uniquely bred plants, those plants may be irreplaceable. If we lose a crop for HORT 101, we've lost a teaching opportunity for those students forever.

Other Features

Clear water and fertilizer solutions are independently plumbed into each greenhouse, and reverse-osmosis purified water plumbed into nearly half of the greenhouses. Compressed air for oxygenating hydroponics culture is in every greenhouse. Computer ports for portable computers are also available in each greenhouse, allowing investigators to enter data or make computations in the greenhouse. Web-cams can also be used in these ports.

Fertilizer solution is injected into the hose stream using an Anderson injector with J-Plus controller located in the headhouse. Two brass fertilizer pumps (one as a spare) inject the fertilizer concentrate, a 3:1 mix of Scotts Excel 15-5-15 CalMag and Scotts 21-5-20, into the water stream at a final solution rate of 200-PPM nitrogen. An acid pump injects 96% sulfuric acid to neutralize alkalinity and achieve a final solution pH of 6.0-6.2.

HLA Greenhouses: FAQs

How do we control temperature, humidity, light, irrigation?


Heating in the greenhouses is done by several pieces of equipment that can come on independently or simultaneously; likewise with cooling. Programming this progression is called "staging": a little cooling or heating when only a little is necessary, full cooling or heating when reaching limits of what the greenhouse can achieve. Without staging, large swings in temperature occur.

Heating stages are, in order of when they come on, 1) perimeter heat, 2) unit heater 1, and 3) unit heater 2. We use steam from the university power plant to boil water in a boiler in our mechanical room. Large pumps carry the hot water in a loop around the greenhouse facility, in large overhead pipes in the corridors. Computerized valves allow hot water into greenhouse pipes as needed. 

Cooling stages vary according to season. In summer they are: 1) evaporative pad shutter open and fan 1 low speed, 2) fan 2 low, 3) pad pump ON to wet pad, and 4) fans 1 & 2 high speed. In winter, the first stage is gable shutter (in the roof peak) with fan 1 low. This is so outside air can be heated up and mixed before reaching plants. Other cooling stages are the same except that the pad shutter and pump are 'locked out' by the computer if the outside temperature is below 44F. Of course, in coldest days of winter the first stage of cooling is sufficient. As higher stages of cooling come on, lower stages also stay on.

The most difficult time to control temperature uniformly during spring and fall, when outdoor sunlight levels are high but air temps are cold. Heat load builds in the greenhouse, but temperature inside quickly drops when outside air is drawn in by cooling fans.

Temperature control range of our greenhouses can be described as:
  • Summer: Lower range is 5-9°F below ambient outdoor temp if above 85°F and RH above 50%, much cooler if temp and humidity are low—as much as 20°F below ambient. Upper range is 25°F above ambient in summer.
  • Winter: Lower range is as cold as you want to work in and not freeze the pipes. Upper range is 85°F day/75°F night under worst cold/windy conditions.


Our humidity control is not sophisticated in that (in all but two zones) we have no “addification” such as fog nozzles or atomizing fans. We count on humidity being increased by plants transpiring, irrigation water evaporating, evaporative pad usage and, of course, outdoor air being drawn in by ventilation. We dehumidify using venting of indoor air in exchange for (hopefully) less humid outdoor air—called “purging.” Computer performs purges when humidity rises above setpoint. One fan comes on low speed and the gable shutter opens for 10 minutes, then waits 40 minutes before it is allowed to purge again, if necessary. Unit heaters can be activated to heat incoming air to lower its relative humidity. RH setpoints are usually 50-70%, depending on season, and—in the absence of a researcher’s requested setpoint—our simplistic goal is to keep condensation from forming on glass, which could signal that the environment is suitable for disease.


We add light using metal halide or sodium vapor fixtures provided by researchers, and reduce light by using shade curtains. Photoperiod is lengthened using incandescent bulbs or, alternatively, closing blackout curtains to shorten days. Light is measured from the weather station, not inside each zone. Daytime outdoor light intensity varies from less than 100 µmol/m2/s on cloudy January days to 2000 umol/m2/s in summer. Glass only blocks a small percentage of this but superstructure casts shadows so indoor levels of light are significantly lower, perhaps 40%.

Intensity of most HID lamps at a level of 2 meters above a greenhouse bench is 150 µmol/m2/sec, so it does not reproduce summer levels. HID supplementation can be very significant winter months, especially when activated for 16 or more hours.

We have learned to provide a prescribed amount of accumulated light (called Daily Light Integral) by programming lighting and shade curtains to activate throughout the day. This has lead to very important discoveries about the best propagation methods of floriculture crops like geranium and New Guinea impatiens.

Interior shade curtains are controlled by computer and can be activated to cover the greenhouse at a specific time, by temperature, by sunlight level, or a combination of these. We use them primarily in high-light season (April-October), having them cover when light exceeds 1000 µmol/m2/s, for example. They provide 50% shading. Curtains are primarily for reducing solar heat load and secondly, reducing water loss—only Arabidopsis and a few other crops would be damaged by high light itself. A solar filter program acts as a “delay” to keep the curtain from opening and closing excessively on days of broken clouds.


Irrigation can be provided by watering with a hose or with automated drip systems, capillary mats, or overhead sprinklers. Researchers can choose between tap water, reverse-osmosis purified water, or fertilizer solution. Fertilizer solution is provided by a water-pressure-driven pump called an injector because it injects a measured amount of concentrated fertilizer into the tap water stream. The injector has another pump head that delivers concentrated sulfuric acid to neutralize alkalinity of our tap water supply and reduce pH to 6.0-6.2. For more specialized fertilization, we use portable injectors.

For automating irrigation, electronic solenoid valves are placed in the line after a faucet that is pressurized (on), so that when the solenoid gets the signal, it opens and water flows to the delivery system. We use solenoids on timer outlets and have many wired to outputs of the computer-control panels. The computer can activate the irrigation system            by timeclock, moisture sensor, or accumulated sunlight level.

What environmental interactions have we noticed when trying to control temperature, humidity, light, and irrigation?

High light affects temperature. Big time! We'd be toast without shading in summer - at or above ambient outdoor all day long. In spring/fall, it's tricky to control temp when solar radiation heats up a zone, because the ventilation air is still freezing cold.

High light affects irrigation. Much more watering in summer. Watering time doubles by late March from late January; as soon as we activate shade curtains, irrigation frequency drops. High temperature  doesn't noticeably affect irrigation - a warm house in winter doesn't require a great deal more irrigation than a cool one until the sun comes out.

Temperature affects relative humidity. Hence the term 'relative.' The same water vapor in the air at 75F has a much lower RH than at 55F. We’ve seen RHs soar in practically empty zones because of lowered temperature setpoint; then humidity purging frequency increases according to its programming.

Temperature affects insects. We can slow or hasten metamorphosis in insect populations by changing temperature (not always possible if research requires tight temperature control). This allows us to time our applications of pesticides better. For example, many of our products don't work on larval forms but do kill adults of the same insect species, so we hasten adulthood by adjusting temp, usually upward.

Some interactions affect disease. We see seasonal incidence of diseases that are predictable by the calendar, but not very predictable by the environmental graphs. A closer look may identify the right combination of light, humidity, photoperiod, temperature that leads to these, and then allow us to change the environment to reduce disease. Low light brings out diseases that may have been "masked," such as INSV in Arabidopsis.

High light affects surface radiation. Yes, the liquid thermometer in your zone says 90F but the computer using the aspirated sensor in a closed box says 75F. Measure the metal bench with an infra-red thermometer and it says 110F, but the air is 75F! By the way, use that IR thermometer on your plants' leaves and it says 72F. Why?

Irrigation affects temp, RH. We can see when our team has watered a zone by the humidity blip on the graph. Relative humidity may suddenly increase by 30% and last 2-5 hours. People swear the zone is too hot after irrigation, but it’s just the RH creating the "heat index" effect. Watering frequently means more purging occurs. Proper watering keeps leaf surface temps cool, but what happens to leaf surface temp if we miss watering that plant and it begins to wilt?

Irrigation affects nutrient uptake. Our clear water is not acidified, so crops irrigated frequently with clear water may develop high root zone pH, resulting in micronutrient deficiency. Water stress from several days ago may only be evident today by yellow leaves from lack of nutrients, whether using clear or fertilizer water.

What are the limitations of the greenhouses?

We struggle with this. It is our goal and firm belief that no faculty member will retire from our department thinking, "If only our facility could have allowed me to _____." Anyway, here is our priority ranked Top Sixteen List of Limitations:

  • Poor cooling in summer: high heat/humidity can lead to thermal stress
  • Low light in winter slows growth and increases disease
  • Seasonal variability in light level hampers long-term experiments
  • Non-uniformity of light in greenhouse because of structural shading
  • Polyhouse environmental control equipment is controlled by a step controller rather than computer control, meaning it can't use outdoor weather data to calculate heating and cooling requirement. This results in our having to adjust the programming as seasons change more than we do the computer-controlled greenhouses. With computer control, it could be our most controlled zone because of its large volume.
  • Non-durable shade curtain fabric
  • Shade curtains not easily accessible for repair
  • Lights in most zones not activated by computer
  • Temperature gradients around zone—not formally documented, but exist
  • Humidification passive in all but two zones with special humidifiers.
  • Light timers very difficult to program
  • No generators. I’m confident we’ll be all right, but would sleep better.

What are the capabilities/limitations of the Priva computer system?

We haven’t touched what the computer system can do. We are far more limited in time, know-how, patience and creativity than the system is limited in capability. Realize that optimizing environmental control often requires making a small change, waiting and observing, making another small change, waiting and observing, then doing it all over again in the next season because the programming will need to change according to time of year. I struggle to name any current limitations.

Capabilities include:
  • Anticipatory logic function for calculating what heating/cooling equipment needs to come on even before the temperature has moved beyond the setpoint.
  • Summary screens for easy monitoring of the whole facility.
  • Spare inputs so that sensors such as soil temperature probes or moisture probes can be installed and data recorded.
  • Spare outputs for irrigation solenoids or other equipment.
  • Equipment usage logging--we can track how many minutes each piece of equipment was activated each day.
  • Customized program features that allow any output (equipment) to be turned on by any input (sensor).
  • Override programming to manually override equipment ON or OFF.
  • Pesticide programming allows us to ventilate prior to anyone coming into the building, improving safety.
  • Four programmable periods of day rather than just day and night, with ramping of temperature for gradual change between periods. Allows us to use height-regulating environmental programming called DIF.
  • Snow melt programs to reduce load on roof and disease preventing environmental programs.
  • Graphing in color, down-loadable data, remote access to control computer for alarm response.
  • Technical service experts who can dial in to the computer from Priva’s Canada headquarters and diagnose problems.
  • Alarms that auto-call manager.
  • Water monitoring for pH, EC
  • Wireless access