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How To Use CO2 Heat Pumps

For Heating & Hot Water


The optimal design point for a CO2 heat pump is 65-70/30°C this is where the most incredible efficiency can be achieved.
The design return temperature shall be 30°C

Clade heat pumps will accept a higher return temperature, after starting, up to 37°C, for short periods, for example as transitory rises due low demand. This is more flexible than other manufacturers, making them suitable for a wider range of applications.

Clade advanced control CO2 heat pumps (available at 700KW+) can accept a permanent 40 °C return temperature.

COPH as a function of return temp. at 4 °C ambient and 65 °C supply temp.

Our Tips For An Efficient System

Designing a heating system for wide DT with low return temp is simple and follows set variable flow principles.

  1. Heat emitters: Size them for correct mean water temperature, available for wide DTs. Change existing emitters as needed.
  2. Control valves: a. TRV: Use pressure independent TRVs on large systems to achieve the correct DT. b. Circuit: Implement PICV valves for smaller systems; settings determined by the designer. Install another PICV on the main return line for backup temperature protection and lower pump flow rate when the return temperature is high.
  3. Main pumps work on pressure control to maintain a minimum service level during low demand. Use a differential pressure relief control valve for re-circulation without increasing return temperature.
  4. Buffer control:
    • Minimise flow in/out to preserve stratification using external headers.
    • Buffers should have baffle plates to protect the lower portion of cool water.
    • The heat pump control strategy follows Clade DESOPs.
  5. Domestic hot water:
    • Use plate heat exchangers to generate DHW as shown on the standard schematic.
    • Maintain water temperature above 55°C within the distribution pipework using a variable flow pump and temperature sensor TH.
Contact Us

No buffer domestic hot water heat pump

We’re thrilled to announce that our heat pumps can be used to generate domestic hot water without a buffer. This innovation makes installation easier, reduces costs, system size, and simplifies controls. Moreover, this method boosts the system’s efficiency.

To guarantee a successful project, here are some suggestions:

  • Make sure you choose a larger cylinder for more fluid operations and efficient defrosting.
  • If you opt to use Acers, bear in mind you’ll need two of them.
  • The low-temperature hot water (LTHW) should be kept within a range of 70-30°C.

Secondary return domestic hot water (DHW) should be reheated with direct electricity, to avoid cyclical temperature control issues.

  • The DHW should be produced at temperatures varying from 10-65°C. Note that pasteurisation at this temperature range will take around 6 minutes.
  • To ensure proper communication with the Air Source Heat Pumps (ASHPs), the cylinders should be fitted with temperature sensors that can transmit a 10V, 5V, or 0V signal.
  • The Plate Heat Exchangers (PHX) and pumps should be sized according to the ASHPs’ summer condition output.

Download a brochure by clicking here


Of course, every building is different and so our team are always happy to talk through a project and share insights that will help.

The end-user benefits of spending a bit more on design, installation and commissioning are very high, especially as utility costs are rising. Our estimates show at least a 30% improvement in the total cost of ownership when using CO2 over other refrigerants.

Northumbria Uni PSDS Lift 3 April 2022


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