Take The Chill Off Hothouse Plants

Keeping plants from freezing during the winter was an ever-increasing challenge and expense for Molenaar Greenhouses, a problem that was solved by installing Modine Effinity natural-gas condensing unit heaters in all 23 greenhouses. Keeping plants from freezing during the winter was an ever-increasing challenge and expense for Molenaar Greenhouses, a problem that was solved by installing Modine Effinity natural-gas condensing unit heaters in all 23 greenhouses.

The Molenaar Greenhouse operation, Ivyland, PA, includes 23 greenhouses, more than 100,000 sq. ft. under plastic, located on a 13-acres of land that comprises fields, historical barns, and outbuildings.

Keeping the plants from freezing during the winter was an ever-increasing challenge and expense. The greenhouses originally were equipped with 250,000-BTU upright heaters running at operational efficiencies between 50% and 60%. The two largest greenhouses had units that ran on natural gas, but the remaining units burned propane because that fuel was much cheaper when they were installed.

As propane rose in price, that fuel became less attractive. “Our monthly heating bill was $8,000 or more during the winter,” said Mario Murillo, owner Gerardus (Jerry) Molenaar’s son-in-law and a member of the team that operates the greenhouses. “That many heaters at 250,000 BTUs each, running constantly in the winter, was ridiculously expensive. We went through 1,000 to 2,000 gal. of propane per week. We were in constant fear that there would be a propane shortage and we wouldn’t get our weekly delivery, which could be devastating.”

To make matters worse, even when the heaters were firing at full capacity during the winter months, the greenhouses barely rose above 55 F. Also, there were troublesome cold pockets immediately behind the heaters. The physical mass of the heaters prevented those spaces from receiving warmth that circulated in convection cycles within the greenhouses.

“We tried to change the air circulation in the greenhouses, but it just wouldn’t work. The plants were suffering, and it was having a negative impact on our operations,” Murillo said.

The likelihood of propane rationing and the falling efficiency of the old space heaters were a call to action. Clearly, the greenhouses needed heating systems that could meet the growing challenge of keeping them operational through the winter months.

Murillo spent weeks researching options. Ultimately, he chose to install Modine Effinity (Racine, WI) natural-gas condensing heaters. Operating at 97% energy efficiency, the stainless-steel heaters can also withstand the high humidity that comes with the greenhouse environment.

Damian Luna (left), maintenance superintendent, and Mario Murillo, physical plant manager, lift a Modine Effinity 93 to its position in a greenhouse. Damian Luna (left), maintenance superintendent, and Mario Murillo, physical plant manager, lift a Modine Effinity 93 to its position in a greenhouse.

“We knew we had to make the move from LP to natural gas. Twenty years ago when the old heaters were installed, natural gas was much more expensive than propane, which is why only two of the greenhouses were natural gas,” explained Murillo. “But this was our opportunity to save on fuel, to invest in new heating systems, and to greatly improve our ability to sufficiently heat the greenhouses. There were no down sides to the decision.”

In addition, the Modine Effinity has a blower option, which the Molenaar Greenhouses use all summer to circulate air and keep humidity in check when there’s no need for heat. Air circulation is essential because too much moisture can cause fungus to grow, which can be devastating to plants.

As condensing units in the heating mode, the systems extract precious BTUs from the exhaust gases within the stainless-steel heat exchangers, leaving slightly acidic condensate behind. The condensate is simply channeled away and disposed of either through floor drains or outside the greenhouses. Built to tolerate temperature and humidity swings, the unit heaters are an ideal fit for greenhouse applications.

Because the investment of new unit heaters would reach $60,000, Molenaar chose to split the order in two. He placed the first order for 19 of the new unit heaters and installed the Effinitys in the largest greenhouses, which are always in use.

In December 2014, the second batch of unit heaters arrived, and by February of 2015, the remaining 18 systems had been installed. At last, Molenaar’s 23 greenhouses were being heated evenly and much more cost-effectively. Plus, there were no more nuisance cold pockets.

“We solved both issues the day we fired up the new heaters. Now, during the winter months, the greenhouses are spread with an even, consistent temperature of 70 F, while maintaining the proper humidity,” Murillo said.

“These new heaters will save us thousands of dollars a month because they’re so efficient,” he continued. “Having all units running on natural gas straight from the grid is much more affordable, especially since this year’s propane prices have skyrocketed to $5 per gal. It’s scary to think we could have been paying that much money.”

“The new heaters can keep up with the greenhouse demands, no matter how low or high the temperatures are outside,” said Molenaar, “and the plants are flourishing like they never have before.”

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