Wildly popular in Japan, CO2 heat pumps, known generically as EcoCute, are offered by all the top ac manufacturers. Sanyo is the first to bring the technology to the UK and product manager Graham Wright explains the concept.
AIR to water heat pumps are making inroads into the previous domination of domestic boilers, however at an annual sales level of around 10,000 compared to 1.6m boilers they still have a long way to go. Driven by the need to reduce carbon emissions as part of Government legislation, the technology is here to stay but existing HFC heat pumps do have some limitation at lower temperatures.

With the climate change argument and the inevitable pressure on the use of renewable technologies, market data suggests that demand for traditional heating products will slow down. This trend is leading to product diversification and innovation in the heating sector.

To answer environmental concerns the hvac industry has been working hard to improve the efficiency of traditional heating technology, however, conventional heating products, such as condensing gas boilers, have now reached the pinnacle of their efficiency.

In addition, reserves of fossil fuels, such as gas, are finite and produce carbon dioxide when they are burnt thus adding to the effects of climate change. This has led to alternative low carbon solutions such as heat pump systems which can significantly reduce Europe’s carbon dioxide emissions.

Eco-friendly CO2

Current models tend to utilise existing heap pump technology and therefore work with existing refrigerants; in fact there are some models out there that still use R22. This year CO2 refrigerant systems have been introduced into mainstream Europe (available in Scandinavia since 2004 and in Japan since 2001).

This technology leap has allowed higher water temperatures to be offered and much improved performance at lower outdoor ambient. The Japanese market even has a generic name for them – ‘EcoCute’. Cute they are not, but eco-friendly they certainly are.

In simple terms air to water heat pumps can either be in the form of a ‘split’ type or a monobloc – depending upon whether the heat exchanger is built into the outdoor unit or not. This can also effect whether the unit needs to be installed by a qualified refrigeration engineer or a ‘plumber’.

Sanyo CO2 units use inverter technology but do not suffer with any of the disadvantages of having to use specialist installers as all the refrigerant is kept within the outdoor unit and are connected to their thermal store by hot water piping. Moreover CO2 is a non-toxic natural refrigerant which is less harmful to the environment than other refrigerants.

CO2 refrigerant also allows a higher working temperature when compared to HFC heat pumps. CO2 heat pumps can achieve temperatures of 65°C, compared to 40-50°C with standard HFC units.

This means that there is no need for electric heaters to boost the water temperature to remove the risk of legionella. Higher temperatures also mean higher storage capacity and more flexibility for different heating applications. The thermodynamic properties also allow CO2 to operate down to -25ºC without any loss of capacity, whilst HFC units are often limed to -10ºC with a significant drop off in capacity below 7ºC.

The question of defrost has also to be taken into consideration. The Sanyo CO2 system uses hot gas defrost, ie it directly injects discharge refrigerant into the outdoor coil to remove accumulated ice during long periods of continued running. This guarantees both capacity and performance at low outdoor temperatures, in the case of HFC versions they tend to need to use either electric heaters (which reduces COP) or some of the heat stored in their associated water tank or heat exchanger, by reversing the cycle and in effectively a cooling mode.

At the heart of the CO2 ECO heating system is Sanyo's innovative rotary two-stage compressor system, a world first in compressor design. The compressor is resistant to high working pressure differentials and low vibration.

In terms of energy performance CO2 system can compete with HFC systems at lower water temperatures of 35ºC to 45ºC and where higher water temperatures are required when HFC units struggle to meet the demand by using free outside energy CO2 systems still meet the energy saving requirements of most system designs. In fact the harder the system has to work the better as CO2 systems work most efficiently when producing a high ?T, therefore 65ºC flow with 35ºC return is no problem for this system.

Sanyo's CO2 ECO is also incredibly light, with its compressor weighing in at 19kg for the 9.0kW capacity unit, while the compact body of the heat pump unit (outdoor unit) is just 609mm high x 840mm wide x 290mm deep.

Sanyo Air Conditioners Europe + 44 (0)845 6126364