What effect does refrigerant based dehumidification have on tomato crops?

On Monday 7th July a group of tomato growers went to an open day at Red Roofs Nursery Ltd. The focus of this event was the results of HDC project PE/PO 013 - Refrigeration-based dehumidification: energy performance and cropping effect on commercial nurseries. The project is currently in its second year of trials after delivering heat savings of 24% in 2013. However, offset against this saving is the electricity used and a reduction in yield. So, the main focus of the 2014 trials has been to overcome the yield reduction seen last year.

The open day was organised by HDC to report whether or not the yield had improved this year. Tim Pratt, Technical Director at Farm Energy Centre, shared what the aims of the project were and how it was carried out. Two greenhouses were used, both growing the same type of tomatoes. One had 4 DryGair dehumidifiers in and one was used as a control to compare energy use and yields.

For the 2nd year in a row the dehumidifiers reduced energy use significantly but the yield from the greenhouse with the dehumidifiers was smaller, the yield was actually 1 kilo behind the control greenhouse. Also, the quality of fruit set close to each machine was poor.

The group were asked for their ideas on what could be causing this reduced yield and poor fruit set, and how it could be corrected. The main suggestion was that the warm, dry air from the dehumidifier was being released in the wrong place; at the top of the plant. The group thought that it would be better to have the air released underneath and moved around the greenhouse by fans.

There was a real feel that this project was not complete. The energy savings were too good to ignore but the question over yield remained unanswered. The project runs through to November 2014 so we await the final results.

Ornamental growers should note that the yield effect seen on tomatoes is not expected to affect their crops.

Here are the presentation slides from the event. (PDF)

Source: www.growsave.co.uK