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How do commercial heat pumps work?

Rinnai’s Pete Seddon details the workings of a commercial heat pump

The evaporator is the component that starts the process all over again and is another form of heat exchanger. By using a fan, it draws air across the Evaporator which allows the refrigerant to change state back into a low-pressure gas ready to go back into the compressor. This then goes back to the compressor to continue to the cycle.

Heat pumps have a leading position in the pecking order of appliances that can work on commercial sites and property and drive towards NetZero and decarbonisation. The ever-growing interest in heat pump technology means an equal amount of curiosity is devoted to how a heat pump works.

What are the main internal mechanisms that enable a smooth operational product life cycle of a heat pump? And what are the inner mechanisms that provide product functionality?

Rinnai have launched a range of blogs and Vlogs entitled Rinnai Pathways which seek answering questions such as this one visit for the latest content.

commercial heat pump operates and uses similar technology in a similar way to an everyday consumer product, a common refrigerator. A “fridge” operates by extracting heat from within the fridge cabinet and exhausts this heat into the room. A heat pump follows a similar process however it is installed outside and extracts heat from the outside air and then transfers the heat generated into a body of water.

A heat pump has four main components within the closed circuit which is also known as the refrigerant circuit.

These components are:

  1. The Compressor.

A compressor is used to move gaseous refrigerant through the refrigeration circuit, and a heat exchanger, which extracts heat from the source. The heat is then passed on to a heat sink through another heat exchanger.

  1. The Condenser.

The condenser is a form of heat exchanger and is used to transfer the heat from the hot compressed gas into the water without coming directly in to contact with each other. As a lot of the heat is removed from the gas it will now change state from a gas to a liquid but will still be high pressure.

  1. The Expansion Device

The expansion device allows the pressure of the refrigerant to be lowered which in turn will allow its state to be changed at lower temperatures which is crucial for the whole process.

  1. The Evaporator.

The evaporator is the component that starts the process all over again and is another form of heat exchanger. By using a fan, it draws air across the Evaporator which allows the refrigerant to change state back into a low-pressure gas ready to go back into the compressor. This then goes back to the compressor to continue to the cycle.

There are of course a lot more components within the heat pump that are integral to its operation and the overall heat pump efficiency such as thermistors to monitor the temperature of the refrigerant and the Control Board to ensure the desired output is achieved.

Commercial heat pumps can transfer heat even in minus temperatures, air source and ground source heat pumps could generate heat as low as -20°C ambient temperature. Conversely, they also create heat at extremely high temperatures. This is achieved because of the low boiling point of the refrigerant gases.

Commercial heat pumps generally use less energy to operate than they output in heat energy, making them extremely efficient – however when the temperature lift for commercial water heating or space heating is substantial (Temperature lift = outdoor air temperature and the temperature heat is delivered at within the building).

The heat pump efficiency i.e., COP or SCOP will reduce, therefore many heat pumps work at their optimum with low temperature heat distribution systems (such as underfloor heating) and why performance reduces dramatically when a heat pump is required to supply heat at high temperature for conventional domestic hot water.

Rinnai’s H3 range of products include domestic and commercial heat pumps that offer immediate property decarbonisation. Rinnai is determined to provide UK customers with cost effective low carbon solutions towards domestic and commercial hot water and building heating provision.


Rinnai’s H3 range of decarbonising products include hydrogen / BioLPG ready technology, hybrid systems, and a wide range of LOW GWP heat pumps and solar thermal. Also, within Rinnai’s H3 range is Infinity hydrogen blend ready and BioLPG ready continuous flow water heaters which are stacked with a multitude of features that ensure long life, robust & durable use, customer satisfaction and product efficiency.

Rinnai’s range of decarbonising products – H1/H2/H3 – consists of heat pump, solar, hydrogen in any configuration, hybrid formats for either residential or commercial applications. Rinnai’s H3 range of products offer contractors, consultants and end users a range of efficient, robust and affordable decarbonising appliances which create practical, economic and technically feasible solutions. The range covers all forms of fuels and appliances currently available – electric, gas, hydrogen, BioLPG, DME solar thermal, low GWP heat pumps and electric water heaters.

Rinnai H1 continuous water heaters and boilers?offer practical and economic decarbonization delivered through technological innovation in hydrogen and renewable liquid gas ready technology.

Rinnai’s H1 option is centred on hydrogen, as it is anticipated that clean hydrogen fuels will become internationally energy market-relevant in the future; Rinnai water heaters are hydrogen 20% blends ready and include the world’s first 100% hydrogen-ready hot water heating technology.

Rinnai H2 – Decarbonization simplified with renewable gas-ready units, Solar Thermal and Heat Pump HybridsRinnai H2 is designed to introduce a practical and low-cost option which may suit specific sites and enable multiple decarbonisation pathways with the addition of high performance.

Rinnai H3 – Low-GWP heat pump technology made easy – Rinnai heat pumps are available for domestic and commercial usage with an extensive range of 4 – 115kW appliances.

Rinnai’s H3 heat pumps utilise R32 refrigerant and have favourable COP and SCOP.

Rinnai is a world leading manufacturer of hot water heaters and produces over two million units a year, operating on each of the five continents. The brand has gained an established reputation for producing products that offer high performance, cost efficiency and extended working lives.

Rinnai’s commercial and domestic continuous flow water heaters offer a limitless supply of instantaneous temperature controlled hot water and all units are designed to align with present and future energy sources. Rinnai condensing water heaters accept either existing fuel or hydrogen gas blends. Rinnai units are also suited for off-grid customers who require LPG and BioLPG or DME.

Rinnai products are UKCA certified, A-rated water efficiency, accessed through multiple fuel options and are available for purchase 24/7, 365 days a year. Any unit can be delivered to any UK site within 24 hours. Rinnai offer carbon and cost comparison services that will calculate financial and carbon savings made when investing in a Rinnai system. Rinnai also provide a system design service that will suggest an appropriate system for the property in question. Rinnai offer comprehensive training courses and technical support in all aspects of the water heating industry including detailed CPD’s. More information can be found on Rinnai’s website and its “Help Me Choose” webpage.


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26 October 2023


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