Gustav Lorentzen – Key CO₂ Presentations

Over the last three days, more than 350 participants from 32 countries discussed state-of-the art research on CO₂ systems and real-life applications of natural refrigerants as an alternative to fluorinated gases. With more than half of all presented papers speaking about the natural refrigerant CO₂ (R744), attendees had to decide between presentations held at the same time.
A brief selection of presentations may serve as a first overview of major topics discussed in categories, such as “CO₂ practical”, “CO₂ scientific”, “heat pumps”, or “secondary fluids”:

CO₂ Cooling & Heating in American Office Buildings (KAV Consulting)

Using USA government data for energy consumption in US office buildings, it is shown that CO₂ cooling can reduce primary energy use, energy cost, water consumption, and greenhouse gas emissions by 55%, 57%, 75% and 53% respectively in existing buildings. In new buildings, the reductions would be even higher. These estimations apply to climates like in Sydney, Australia. In addition, the CO₂ compressor discharge is usually able to heat enough water for heating, reheating and hot water purposes, making fossil-fueled boilers unnecessary. The paper concludes: “There is no other refrigerant, natural or chemical, which can deliver such superior and sustainable results in the cooling and heating of buildings of any type.”

Multi-Chamber Blast Freezer (Star Refrigeration)

An R22 refrigeration system was replaced by a central plant using R744 as the low temperature refrigerant, cascaded with ammonia for the high temperature stage. The plant was installed in a cold storage complex with several rooms held at -25°C and six freezer chambers used for meat products. In total, the cold storage volume covered 21,400 m3. Since November 2007, the CO₂-NH3 plant has indicated excellent performance, with the freezers able to handle more than the nominal 20 tonnes of boxed frozen food per chamber, and the core temperatures of -18°C are being achieved within a 16 hour freeze cycle. Reduced freezing times and higher efficiency have led to exceeded expectations by the CO₂ system.

CO₂ Transcritical Chiller (Padova University, SCM frigo)

A CO₂ transcritical chiller for refrigerating propylene glycol down to -8°C supply temperature was developed and tested. Main targets were to optimize energy efficiency, reliability and simple management of the unit. The chiller was tested at external temperatures of 16 to 35°C. The chiller was designed to serve systems operating with secondary fluids for retail refrigeration above 0°C. In long endurance tests of up to 15 days of continuous running, the chiller proved high reliability without any serious drawbacks or instability problems. On the contrary, it provided the expected refrigeration capacity while being energy-efficient, supplying also additional thermal power for low-temperature heating applications. Using only components available on the market, it is ready to be supplied to refrigeration plants in large numbers.

Supercritical Ejector Cycle (Ecole des mines de Paris)

An ejector expansion transcritical CO₂ refrigeration cycle was investigated to improve the performance of the basic transcritical R744 cycle by reducing expansion process losses. More than 18 ejectors were tested regarding their performance in a sub-cooled/supercritical refrigeration cycle. The effect of the evaporating and gas cooler outlet temperature, as well as the ejector geometry were analysed. Results showed that the COP of the ejector expansion transcritical CO₂ cycle can be improved by more than 12% compared to the conventional transcritical cycle for air conditioning operating conditions.

CO₂ in North American Supermarkets (Hill Phoenix)

The use of R744 in US and Canadian supermarkets is still in its infancy as commercial refrigeration has not been subject to HFC bans or high taxation as in other parts of the world. Since 2006, several systems using R744 as a low-temperature two-phase secondary coolant have been installed, mainly driven by energy consumption and system costs. As of early 2008, at least nine CO₂ systems were operational in North America, ranging from small markets, to large supercenters and warehouses. Now, CO₂ secondary systems will go into full commercialization. An extension to medium-temperature applications is recommended. The first low-temperature R744 cascade systems installed in the U.S. will serve as a pilot project to plan further ahead. So far, both CO₂ secondary and direct expansion system have shown lower energy use than HFC DX systems.

Integrated R744 HP for Low-Heating-Energy Buildings (Graz University)

In low-heating-energy buildings heat pumps have become an attractive heating system due to a notable reduction of the space heating requirements, and the introduction of low temperature heating systems. The TU Graz has tested different concepts for integrated heat pumps (reversible air-air, brine/water, reversible brine/water HP) using R134a, R290 and R744. It decided to further investigate only a non-reversible brine/water with R744 due to safety and efficiency reasons, as well as its suitability for a wide range of low energy buildings. The prototype is currently constructed at the TU Graz.

Coming Next

Over the coming weeks, R744.com will publish more detailed articles about key presentation of its partners. First to come is the paper “Air Reversing R744 Air Conditioning System”, jointly authored by SINTEF, Modine, and the U.S. Army.

Purchase Papers

Please note: R744.com is no longer in the position to publish any paper from this International Institute of Refrigeration (IIR) conference. Proceedings can be purchased by contacting the IIR or by visiting the IIR’s Web site.