Q-ton CO₂ heat pumps support low-carbon hot water strategy
UK – The Q-ton CO₂ heat pump from Mitsubishi Heavy Industries (MHI) is providing the domestic hot water solution for a new-build hotel development at Adagio Hotel, Fieldgate Street, London.
The project needed a system capable of supporting hotel demand while responding to the London Plan, BREEAM1 requirements and wider carbon reduction targets. With the need to avoid local NOx emissions, and gas availability noted as a consideration, the project team needed an alternative to traditional gas-fired hot water generation.
Q-ton uses CO₂ refrigerant (R744) to provide high-temperature sanitary hot water for commercial applications. As a natural refrigerant CO₂ has a global warming potential (GWP) of 1 and zero ozone depletion potential (ODP) so provides a future-proof solution for heat pump systems. R744 operates at a higher pressure than refrigerants used in other heat pump systems, and as such has the ability to reliably generate high temperature water, making it suitable for this application as well as space heating.
Because the GWP is less than 1, it can support the project’s BREEAM assessment under the impact of refrigerants criteria, helping the design team demonstrate reduced environmental impact compared with systems using higher-GWP refrigerants.
The installed system comprises three MHI Q-ton ESA30EH-25 units, configured as one master and two slave units, providing a total system capacity of 90kW. The system serves five 1,000-litre storage tanks with hot water recirculation and has been designed to produce hot water at 75°C.
Supplied by wholesaler Beijer Ref UK, the system is also designed as a direct domestic hot water solution. The water passing through Q-ton is the same water delivered to the taps, rather than being separated through an intermediate heat exchanger. This helps avoid the efficiency losses that can occur when heat is transferred through secondary heat exchange stages, while also reducing the capital expenditure associated with additional heat exchanger equipment.
Q-ton is designed to produce hot water from 60°C to 90°C and can operate when outside temperatures fall as low as -25°C. According to MHI, the system maintains 100% heating capacity down to -7°C ambient, further supporting the project’s need for dependable hot water production throughout the year.
Because the air-to-water heat pump approach also produces no local NOx emissions at the point of use, it supports the project’s response to the London Plan and helps reduce reliance on gas-fired hot water generation.
Mick Matthews, M&E Consultant at DMS, who delivered the project alongside contractor Direct Cooling Services, said: “The Q-ton was chosen as it was the ideal solution to allow us to meet the ‘no local NOx emissions’ requirement of the London Plan and also significantly helps towards meeting our carbon reduction requirements for BREEAM and the London Plan requirements.”
The system has been designed for integration with the building management system through Modbus, allowing the hot water plant to be monitored and controlled as part of the wider building services strategy.
1BREEAM, the Building Research Establishment Environmental Assessment Method, is a sustainability assessment framework used to measure the environmental performance of buildings. It considers areas such as energy use, carbon impact, materials, water, waste, health and wellbeing, and pollution. For building services specifications, the choice of refrigerant can contribute to the overall assessment where systems use refrigerants with a very low GWP.
