Refrigeracion Co2

A Natural Refrigeration System for Supermarkets using CO2 as a Refrigerant.
CIBSE National Conference 21-22 March 2006,
Campbell, A.1,2, Maidment, G.G.2and Missenden, J.F. 2
1

Space Cooling Systems, Causeway Central, Pioneer Park, Bristol, BS4 3QB
2
London South Bank University, 103 Borough Road, London, SE1 OAA,
02078157626, maidmegg@lsbu.ac.uk

Abstract
The average globaltemperature is predicted to rise by between 1.5 and 4.5K in the
next 100 years. The principal cause of global warming is the emission of
greenhouse gases into the Earth’s atmosphere. Supermarkets contribute both
directly and indirectly to global warming. Directly, greenhouse gas emissions occur
through the leakage of HFC refrigerants used in refrigeration systems for display
and storage of food. Theserefrigerants have very high global warming potential.
However, supermarkets are also indirectly responsible for producing CO2 as they
are large consumers of electricity, consuming as much as 15 000 GWh (54 000 TJ)
per annum and approximately 50% of this is consumed by refrigeration equipment.
This paper describes a natural system that has been developed to reduce
significantly both direct andindirect greenhouse gas emissions. The system uses
both R-404a and CO2 (R-744) as refrigerants. The CO2 has very low global
warming potentials compared with conventional HFC systems which reduces
significantly direct emissions. Indirect emissions are also much reduced as the
system efficiency is much greater than achieved using conventional HFC
refrigeration.
The paper firstly describes anexperimental system that has been used to
demonstrate the new technology. It then compares the relative efficiency, operating
cost and CO2 emissions from the new system with that from a conventional system.
It can be seen that greenhouse gas emissions are approximately 66% of those from
a conventional installation.
Introduction
The effects of refrigerants on the environment are welldocumented. Supermarkets
contribute both directly and indirectly to global warming. Directly, greenhouse gas
emissions occur through the leakage of HFC refrigerants used in the refrigeration
systems for refrigeration of food. These refrigerants have very high global warming
potential with GWP’s in excess of 1000. However, supermarkets are also indirectly
responsible for producing CO2 as they arelarge consumers of electricity,
consuming as much as 15 000 GWh (54 000TJ) per annum and approximately 50%
of this is consumed by refrigeration equipment.
Over the last 20 years, legislation has prohibited the use of ozone-depleting CFC
refrigerants however; the use of the HFCs is still legal and commonplace. In recent
years natural refrigerants have been proposed as an environmentally friendlysolution for the refrigeration industry, these refrigerants which include ammonia,
hydrocarbons and carbon dioxide, do not contribute to ozone depletion and have
low global warming potentials.

Carbon dioxide offers a long-term solution suitable for many applications in
refrigeration and heating, from domestic applications utilizing heat pumps to provide
hot water and heating to commercialapplications for supermarket refrigeration. The
technology is future proof requiring no further retro-fitting to the next refrigerant
“solution” promoted commercially.
To investigate the performance of R-744 refrigeration, a prototype system was
constructed and tested to demonstrate proof of principle. This paper reports on a
practical investigation of a R-744 system in a commercialapplication and describes
an investigation of its design, commissioning and energy performance. Also
discussed are the practical experiences gained from building a R-744 system and
the benefits of using such a natural refrigerant.
R-744 (CO2) as a Refrigerant
R-744 has been used in refrigeration for many years. Figure 1 shows a timeline
detailing its proposal and discovery, decline in the 1930s, to...