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Trane R1234ze heat pumps in pioneering wastewater scheme

UK: Trane has provided two heat pump chillers using Honeywell’s low GWP HFO refrigerant R1234ze in a groundbreaking district heating network in Scotland.

The district heating network will supply local public buildings and businesses in Stirling, using a variety of renewable energy sources including wastewater from the Stirling Waste Water Treatment Works.

The £6m project, developed in partnership with Scottish Water Horizons and Stirling Council, with support from the Scottish Government’s Low Carbon Infrastructure Transition Programme (LCITP), has the potential to save up to 381 tonnes of carbon per year.

The technology is the first of its kind in the UK to use sewage and wastewater heat recovery technology alongside a CHP engine to generate heat and electricity in a single, highly efficient process. 

The two CITY RTSF units, with a total capacity of 800kW, will extract heat from sewage and wastewater. They are based on inverter-driven screw compressor technology and use stainless steel brazed plate heat exchangers as both the condenser and evaporator. This helps to prevent corrosion at higher heating temperatures and with water that could have different ph levels. 

The operating map of the RTSF is very wide and can produce hot heating water at a temperature of 80ºC and yet still be used in cooling systems to produce water at more conventional temperatures of 6ºC, or even low temperature applications of -12ºC.

“Innovations like our advanced heat pumps used in the Stirling project aim at bending the curve on global warming by replacing fossil fuel-based heating,” commented José La Loggia, president of the Trane commercial HVAC business in the Europe, Middle East and Africa region.

The district heating network, owned and operated by Stirling Council, includes a number of key public buildings in Stirling, including the leisure centre, stadium and nearby high school. The scope of the project allows the network to expand across the city and provide energy cost savings to households and local businesses.

“The Stirling Project is a key example of how we’re supporting the Scottish Government and Scottish Water in their ambitious Net Zero Emissions targets,” said Donald MacBrayne, business development manager for Scottish Water Horizons. “Over half of the energy consumed in Scotland comes from heat, and we are dedicated to continuously utilising Scottish Water assets to generate low carbon energy, contributing to a greener Scotland. The energy centre, has been designed to allow for future development, supporting further, subsequent expansion of the low carbon network.”

The CITY RTSF is a one compressor technology chiller or heat pump, which has also been designed to fit within existing buildings and fits easily in to a standard lift/elevator. It can be used as modular heating system, allowing amongst many pipework configurations, serial counterflow installation to further enhance system efficiency both for heating and for cooling.

R1234ze, with its GWP of less than 1 under AR5, is designed for medium-pressure chillers to cool large buildings, infrastructure projects, process chillers in refrigeration applications, district cooling and heating, organic Rankine cycle, high-temperature heat pumps, and medium-temperature self-contained refrigeration cabinets.

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