BULLETINS
& ARTICLES
HIGHER VOLUME
GREENHOUSES
PRESS RELEASE
A 4.5 metre (14’9”) stud/crop wire height greenhouse
is now available to larger commercial growers from Redpath.
The company says that the higher stud structures
are required by an increasing number of clients that are seeking to further
improve crop productivity and labour cost effectiveness per square metre/yard.
By using the Redpath Pandect automated track mounted picking trolleys the
management of a taller crops is a far simpler proposition.
Whilst the Redpath 3.5 metre (11’6”) stud structure
with its 9.2 metre (30’3”) span had offered an equivalent crop wire height
and internal volume to a ‘high stud Ven-lo type’ truss design, however,
it appears that with the latest long-cropping plant varieties and growing
techniques, growers now require a structure with greater internal air volume,
and post height, in some instances.
“We looked at increasing the volume by simply making
the structure a wider span which would also reduce the cost per square
metre, however this option could potentially promote a reduction in the
roof cladding pitch (especially on twinskin options). This could potentially
stall the run-off of any internal condensation before it reaches the gutter
edge. It would also lower the percentage roof ventilation, leading to poorer
environmental control in extreme conditions.”
The
4.5 metre (14’9”) post height structure is therefore based on Redpath's
proven 9.2 metre (30’3”) span Super-Twin and Super Light ‘A’ frame cosecant
designs. These have been re-engineered for the higher crop and wind loads
as required. The re-design includes sourcing a new steel post material
plus developing new fully bolted connection brackets and redesigning the
foundation system. With this done, the crop support/snow load capability
is above 50 kilos per square metre (112 lbs sq/yard) with a wind/load capability
of up to 50 metres (164ft) per second. This matches the specifications
for Redpath's lower stud structures, which they report have performed very
well, even in extreme conditions.
There are two main benefits to the grower using
the new taller post-height model. The ability to train/manage the
plant for a longer period vertically and thus reduce handling, plus the
greater volume of air within the structure. This gives a far larger ‘buffer
zone’ for the various environmental control devices used by today's grower,
and, minimises sudden environmental changes. A more ‘natural’ climate is
gained for the crop.
Greater internal air volume also reduces the external
environments ability to quickly the greenhouse conditions. The ventilation
system is then allowed a wider operational range to more closely maintain
the setting programmed by the grower for the crop. Humidity control
is also enhanced with the larger volume tending to reach saturation points
at a slower rate whilst the higher internal gutters allow improved airflow
throughout the structure and around the crop.
Energy efficiency is minimally affected, as the
roof area remains the same, however ventilation performance is improved
due to the taller apex height that the higher sidewall building has.
The large ridge mounted ventilators utilise the higher outside air speed,
available at this height. This can be quite an advantage on calm
warm days when natural air movement is slower near to the ground.
The drawing below of the new 4.5 metre (14'10")
stud structure end view outline overlaid on a Ven-lo style 4 metre truss
house shows the gain in volume is as much as 25%, whilst attainable crop
wire height is as much as 800mm (32") higher yet still keeping the head
of the crop a comfortable distance from gutter lines and roof cladding.
Construction costs for the new building are not
much greater, whilst the continued development of the Redpath cosecant
curved rafter technology allows for either an efficient twinskin cladding
or extra-high light singleskin roof panels using newly developed long-life
“Duratough” greenhouse film polymer technology.
The structure is supplied with Redpath's now standard
2-year structural warranty, with extended factory warranties on the EVA
greenhouse film cladding that is used.
For a free catalogue or free sample please click
on the appropriate links.
August 2000
