The units, being trialled at East Yorkshire tomato grower Red Roofs Nursery, take in and refrigerate warm, wet air, taking the energy out of the water vapour, which is recycled to reheat the now cooler air, which is passed into the glasshouse.
A single dehumidifier typically removes 45 litres of water per hour and consumes 10kW of electricity. Four are being used in Red Roofs' 6,000sq m of glass. Pratt put the capital cost of the system at an "optimistic" £100,000 per hectare.
"It would be tempting but for the yield hit, which is around seven per cent and which we were at a loss to explain," he admitted.
Tomato Growers Association technical chairman Philip Pearson added: "The numbers are significant and could benefit the industry."
Giving an overview of the energy market, Pratt's colleague Chris Plackett said: "This year gas has been plain sailing. Supply has outstripped demand, with only blips from Russia. Though there has been an up-tick in prices since July, the sentiment is that we are in for a period of low prices."
But he warned that larger companies now have to undertake energy audits under the Government's recent Energy Savings Opportunity Scheme.
"You have to register for it if required to do so by the end of December and submit a compliance report by the end of 2015. There's a £45,000 fine if you get caught."