Refrigeration-based dehumidification: energy performance and cropping effect on commercial nurseries. 2nd year trials


Project summary:

Energy costs and associated CO2 emissions continue to be important to growers of high temperature protected crops. Refrigerant-based dehumidifiers have the potential to both reduce energy costs/emissions and improve crop performance. Results from the first year of trials show heat savings of 24% between January and May. Putting this into perspective, this is similar to the saving delivered by thermal screens.

However, a reduction in yield  (5.5% over the same period) was also recorded. Opposite to what was expected, the crop with dehumidifiers tended to be more vegetative early in the year and this is believed to be the primary cause of the yield reduction. The timely application of the normal 'basket' of generative actions in expected to reverse this effect but it remains to be proven. Without it, uptake of this technique and the potentially significant energy savings that it offers ti the edible crop sector will be minimal. The main driver for this project extension is to demonstrate that the yield reduction can be avoided whilst at least maintaining (if not increasing) the energy savings achieved in Year 1.

Note: the energy savings for ornamental crops is being determined by calculation, not commercial trials. The result is expected to be positive. The potential impact, if any, on crop development and the need for commericla trials or not is being discussed at the BPOA meeting on 22/10/13. If commercial trials are deemed necessary they will be the subject of a seperate funding proposal.

Benefits to industry:

For growers of protected edible crops in particular, energy costs represent 30-40% of the variable cost of production. There is an estimated 350 hectares (Ha) of high temperature edible crops in the UK, with an average energy cost of £100,000/Ha per annum (p.a.). The Year 1 project proposal identified potential savings of £25,000/Ha; we expect to beat this by as much as £5,000/Ha. If no reduction in yield is proven, a simple return on investment within 4-5 years is possible.

Although not monitored in detail, less botrytis was also present in the dehumidifer crop.

Once installed and an 'in practice' understanding of their impact on crop development is gained, a dehumidifier requires minimal management input and if disease benefits are proven they will, if anything, reduce labour requirements. There are no regulatory hurdles e.g. Specific Of-Label Approval (SOLA) applications to overcome. The need for further research and development is dependent on the results. A second year of lower yield could lead to the project ending. Alternatively, one year of negative results combined with one year of positive results may not be accepted as sufficient proof of concept.

If proven, the main limitation of uptake by the industry is likely to be the availability of capital. However, an uptake of only 2% of the edible crop growing area per annum would deliver compound savings of £2.6 million over five years and £9.6 million over 10 years. A significant benefit of the specific equipment under trial is that it can be retrofitted relatively easily and does not require hanging gutters.

As ever, communication of the results of the project is critical to ensuring maximum value is delivered to growers. Previous projects of this type have benefitted from a suite of knowledge transfer (KT) activites. We envisage:

  • New project article in HDC News;
  • Updates via
  • Attendance at tomato study group visits to the nursery;
  • Presentation of the results at an industry event;
  • Final results article in HDC News.
Project code:
PE 013a
01 January 2014 - 31 March 2015
AHDB Horticulture
AHDB sector cost:
Project leader:


PE 013a_GS_Final 2015 PE 013a_Report_Final_2015

About this project

Aims and objectives:

The overall aims of the project are to:

  • Reduce energy use and cost in heated glasshouses;
  • Reduce carbon dioxide (CO2) emissions associated with glasshouse production;
  • Improve yield quality;
  • Reduce disease incidence and therefore the use of crop protection chemicals.

The specific objectives are to:

  • Demonstrate that comparable yields can be grown with refrigerant based dehumidifiers;
  • Determine the impact, if any, on crop development and any measures required to correct it;
  • Optimise the energy saving delivered by a refrigeration-based dehumidification system in a commercial greenhouse;
  • Effectively communicate the results to HDC members.