US: CO2 heat pump with variable compressor and expander in the works

By Alexandra Maratou, Sep 02, 2013, 13:25 3 minute reading

The US Department of Energy (DOE) has announced funding for several projects to develop innovative heating and cooling technologies, including a project to develop a CO2 heat pump for commercial building heating and cooling at the heart of which will be oil free, variable compressor and expander technology that allows maximum efficiency at all operating conditions.

A total of $400,000 (€300,600) of funding by DOE will be dedicated to this project that will develop and help commercialise an oil-free heat pump that does not use any high global warming potential refrigerants. Announced on 14 August 2013, the DOE funding is part of the Obama Administration's efforts to reduce energy bills and curb emissions of hydrofluorocarbons (HFCs).

Delivering a 20-ton cooling and 240,000 BTU/h heating capacity CO2 heat pump

As part of the project, leading project partner S-RAM Dynamics will deliver a 20-ton cooling and 240,000 BTU/h heating capacity heat pump targeted for commercial buildings and industrial applications. It is expected that the heat pump will be able to efficiently operate between -35°C and 85°C enabling excellent performance in both cold climates and in high temperature food service and industrial applications.
We are excited that the DOE recognises the potential impact of this technology”, Lee Jestings, President of S-RAM, told “Our first systems will be sized for commercial building heating and cooling and transportation refrigeration applications. We will manufacture these systems in the United States and in other countries where we see a major market potential."

The system is being developed in coordination with Purdue University and performance testing will be done at DOE’s Oak Ridge National Laboratory. Another project partner is ReGen Power Systems.

The technology will be demonstrated at three major US retail and commercial facilities in late 2014.

Variable compressor and expander technology to allow maximum efficiency at all operating conditions

The heat pump will use an oil free, variable compressor and expander technology that is currently being tested at the Herrick Laboratories at Purdue University on one of the largest CO2 test stands in the US.

By varying the hot side and the cold side temperature as desired by the use of a variable displacement compressor/expander, the pre-production heat pump unit is expected to demonstrate a significant efficiency improvement compared to current state of the art heat pump systems.

This will allow the unit to run at constant speed while still being able to control both variable temperatures and capacity. The variable technology allows the use of a constant speed motor eliminating the need for variable frequency drives. The unit will run at maximum efficiency at all operating conditions. The unit will also operate down to -35°C and can deliver hot side temperatures of 90°C. Both hot side and cold side temperatures will be accommodated along with intermittent hot water demand.

Reducing energy consumption for commercial and industrial users

The performance of the new heat pump will be driven by technological innovations built around the variable stroke compressor and the use of a mechanical expander that recovers a significant amount of energy.

As a result, the heat pump is expected to reduce energy consumption for commercial and industrial customers by up to an estimated 50% when compared to common refrigeration and heating systems.

This could be significant, considering that commercial and residential buildings use nearly 40% of the total energy consumed in the United States each year and produce more than 40% of the nation's carbon pollution. Moreover, emissions of HFCs in the United States are expected to nearly triple by 2030, and double from current levels of 1.5% of greenhouse gas emissions to 3% by 2020. 


By Alexandra Maratou

Sep 02, 2013, 13:25

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