Absorption chilling in horticulture - Part 1
In this first of two articles Dr Andrew Marchant reviews a technology
that can cut the cost of operating cold stores, but is little known within
the industry. The second article next month will look at some specific
sites which are operating absorption chillers. Andrew is Director of
the horticultural engineering consultancy Hennock Industries Ltd.
Most refrigeration systems rely on a motor driving a piston up and down compress-
ing a gas (known as the vapour compression cycle) - absorption chillers put in heat
to achieve cooling! The technical aspects are complicated and beyond the scope
of an article like this, but it’s a system that's been around in the commercial world
for many years, and popular for certain applications because of the reasons de-
tailed below. It may seem strange to be using heat when we want to achieve cool-
ing, but as with all forms of refrigeration, it is a question of using one source of en-
ergy to move a second source, that is removing heat from the cold room to the out-
side. In fact there are several other methods of refrigeration, including one using
sound developed by NASA for use in outer space! Several refrigeration companies
manufacture absorption chillers in the range often used in horticulture, and they are
likely to become more common.
Why aren’t there many in horticulture?
In the past absorption chillers were limited in their application due to an inability to
achieve low temperatures (below around 5oC) on smaller units. New develop-
ments have changed this, and systems are now being installed (see photo) capa-
ble of reaching -10oC. There are already a few on horticultural sites, and some de-
tails of these will follow in next month’s issue.
A second reason is that refrigeration companies are not as used to this system as
conventional compressors, and it is not likely to be suggested unless asked for. A l-
though there can be a problem finding local service agents there