Winter Weather and the benefits of integrated controls

If the temperature in a greenhouse drops below the heating set point while the energy curtain is opening, the integrated control pauses the curtain preventing a large temperature drop around the crop.
Photo by Randy Van DamIntegrated controls can save growers time and money, and they can protect crops and greenhouses against harsh and unpredictable winter weather. Integrated controls can sustain an array of support systems including energy curtains, ventilation and heating systems, exhaust fans, weather stations and alarm systems.

Unlike staged controls, integrated controls operate on a series of “if…then” statements. Integrated controls respond to information gathered from sensors inside and outside the greenhouse. These sensors can include humidity, temperature, light accumulation and intensity, precipitation and wind speed and direction. This information allows integrated controls to maintain an optimal growing environment even during dark, snowy winter months.

Accounting for multiple factors
The information gathered by sensors allows integrated controls to make decisions based on multiple factors. The controls integrate time, indoor and outdoor temperatures, precipitation and light levels to decide when to close energy curtains.

One vent might be responding to a signal from wind speed and greenhouse orientation, another from temperature and precipitation readings. This behavior is based on parameters to which the controls respond.

Integrated controls offer many choices in programming. On a cold winter morning, many growers set their controls to uncover energy curtains after accumulating some solar gain, rather than opening them at sunrise. This allows the air space above the curtain to warm while slowly opening the curtain. If the temperature in the greenhouse drops below the heating set point while the curtain is opening, the integrated control pauses the curtain, resulting in the slow mixing of warm and cool air, preventing a large temperature drop around the crop.

“We don’t open the curtain until 9-9:30 a.m. That lets the sun warm the air above the curtain,” said John Goode of Goode’s Garden Center in Des Moines, Iowa. “Based on the temperature, the control pauses the curtain opening so it doesn’t dump the cold air above the curtain into the greenhouse. A cold air dump can stunt poinsettia growth.”
The integrated control allows Goode to determine the rate of speed at which the curtain opens and the amount it opens.

The information gathered by sensors allows integrated controls to make decisions based on multiple factors.Know your structure
Russ Elkins, facilities manager at Pleasant View Gardens in Loudon, N.H., and Ron Peterson, head grower at Milaeger’s in Racine, Wis., both leave their energy curtains closed if the predicted snow amount is minimal. However, every decision is based on the actual greenhouse structure and its contents.

“I’m more concerned about greenhouses without crops, weighing the cost of heat versus the cost of damage,” said Peterson. “You really need to know your house, and how much (snow) load it can bear.”

John Ray, research associate at Colorado State University in Fort Collins, has a similar situation.

“I have greenhouses with a heating set point of 45ºF, and those are the structures I worry about,” Ray said. “The snow doesn’t melt because it’s just too cool inside.”

Growers accommodate each unique situation by taking into consideration the type of structure and the set points. An integrated control can respond to both precipitation and temperature, but ignore low temperatures when the weather is dry.

Some growers check conditions during the night and use a remote access computer program to adjust settings based on snow accumulation. Tim Pollak, outdoor floriculturist at the Chicago Botanic Garden and a grower at Clesen Wholesale in Evanston, Ill., said he only wants to respond if there is a significant amount of snow. The response varies depending on the greenhouse. On glass houses, he leaves the curtain closed but raises the heating set point to 66°F. He does this remotely using STEPsaver software that connects him to his greenhouse controls. Pollak said he doesn’t want to heat up the houses for five to eight hours if it isn’t snowing. If it is snowing he can remotely raise the heating set point so the snow melts as it lands on the houses.

Gutterline heat
Gutterline heating is another important system during snowy winter weather. Hot-water or steam-filled piping runs along the greenhouse gutterline to keep snow from accumulating.

Like the energy curtain program, gutterline heat has time- and temperature-based settings. The snow setting tells the control when to turn the gutterline heat on and off. It can also be programmed to supplement the main heating source.

At Clesen Wholesale, the gutterline is the third stage of heating, which is rarely necessary. Pollak said the gutterline heat always turns on if there’s snow. Integrated controls can be set to turn the equipment on based on temperature and precipitation as dual parameters.

Prepared for changing weather
While many manufacturers offer stand-alone control systems with their boilers, integrated controls can handle this task as well and also offer an override safety system to independently run boilers. The program requires a weather station to identify a drop in outdoor temperature and light levels. These readings anticipate incoming fronts and critical changes in the weather. Both light and temperature parameters must be met to fire the boiler. In the morning, the boiler shuts off if either the outdoor light or temperature reading is above the set point.

“I like the program because it’s energy efficient,” Pollak said. “I keep it on standby because during the winter it’s good to have hot/warm water already in the pipes.”

Integrated controls offer other options including an override system that works from indoor temperature readings. The controls accommodate low volume boilers by cycling the boiler on and off as needed to maintain the water temperature returning from the greenhouses within set parameters.

Anticipating winter weather
Adding a weather station to integrated control gives growers the ability to anticipate winter weather and respond quickly. If snow is blowing in from the north and the temperature is dropping rapidly, a weather station provides the control the information it needs to close the greenhouse vents and to crank up the heating system. With the addition of software that allows remote access to greenhouses, growers can respond and modify their automated program any time day or night.

Wet, heavy snow can down power lines and can cause growers to switch to a standby generator. Integrated controls allow growers to use load shedding, which designates the greenhouse equipment that will function while on standby power, alleviating concern for stressing a backup generator.

Unpredictable storms can happen at any time. An alarm managing system can contact a programmed list of emergency responders sending an alert and description of the problem, whether it’s a drop in temperature or a power outage.

Energy-saving mixing valves
Whether a boiler is run independently or as part of the integrated control’s duties, programming the mixing valve can save energy costs. Like the hot and cold water mixed to create an optimum temperature in a household shower, mixing valves dictate the ratio of hot to cold water within the heating system. These modulated valves add Btu to the environment at the same rate they are being lost, while the valve is virtually still.
 

Patricia Dean is vice president, Wadsworth Control Systems Inc., (800) 821-5829; www.wadsworthcontrols.com.