If you routinely use ‘minimum pipe’ as a method of humidity control, you could be wasting a significant amount of money. Delegates at the recent two-day GrowSave workshop on Humidity Control learned how other strategies can be much more effective, not to mention cheaper. We deliver the GrowSave project on behalf of AHDB Horticulture, the project aims to give growers access to the latest energy-saving information and demonstrate how energy saving techniques work in practice. 

Following the popularity and success of the first Humidity Control workshop in 2018, GrowSave decided to make the topic a key focus of the 2019 programme. Given the complexity of the subject matter, the workshop was split over two days. The first day focused on the basic principles and introduced delegates to some of the science and terminology, while also providing some practical tips on how to manage the greenhouse climate with regard to humidity. The day was well received and generally hit the mark in terms of conveying the fundamental messages.

The second day was targeted at those who already had some understanding of the subject, but wanted a firmer grasp of some of the ideas behind effective climate control. The morning session delved deeper into the science than the previous day, and introduced the Mollier diagram. The complex looking chart can be used to calculate the moisture carrying capacity of air based on known parameters such as temperature, Relative Humidity (RH) and Absolute Humidity (AH).

The importance of good humidity control was not lost on those in attendance, with many stating a desire to reduce disease risk as a primary reason for wanting to learn more. After practising a few calculations using the Mollier diagram, the group was able to determine Humidity Deficit (HD) and dew point based on some given conditions.

One of the main take-home messages from both days was that outside air is almost always drier than inside the glasshouse. This is especially true on a cold day, when the outside air cannot physically hold much water. Venting warm, moist air for colder, drier air, and then heating it (‘vent then heat’) is an advisable strategy for those trying to maintain a healthy growing environment. Furthermore, it is more cost-effective than the more traditional ‘heat then vent’ approach. A simple air movement setup can also go a long way to ensuring an even climate, making sure moisture is moved away from the crop and mixed with the drier surrounding air.

GrowSave is likely to re-run these sessions in the future, so keep an eye on the website to book your place.