Combined Heat and Power units, condensing boilers and heat pumps all operate more efficiently at lower return water temperatures. Designing for lower water temperatures is therefore an effective way to improve plant energy efficiency and reduce carbon emissions.



The most efficient way to achieve low return temperatures is to reduce flow rates through the heat emitters, thereby allowing more time for the heat to be transferred through the heat exchanger.

This can be enhanced by incorporating weather compensation in the system, resulting in lower flow temperatures for much of the year and thereby aiding an improvement in plant energy efficiency.

Plant pumping efficiency

Reduced flow rates also result in increased efficiencies in other areas:

  • Reduced pipe sizes
  • Reduced pump sizes
  • Reduced pump energy

Weather compensation

As the weather constantly changes, there are corresponding changes to the heating requirements of a building. Adjusting heat supply so as to compensate for variations in the weather is a rational and sound way to achieve energy savings.

Weather compensation is therefore an essential control parameter within an efficient central plant DH system.

An electronic controller for weather compensationcan automatically adjust the , temperature of the primary flow circuit water.

By sensing a rise in external temperature, for example, flow temperature is automatically reduced, thus enabling savings in energy consumption of up to 40%.

Weather compensation systems can be further enhanced with override controls to limit return temperatures.

SAV have put together a CIBSE-accredited CPD Seminar, which explores the main issues arising from a 70/40 approach to designing for plant energy efficiency. The agenda for this is given under the CPD Seminars tab further along this website. The 70/40 method can be expected to have far-reaching implications, and discussions which are a normal part of each Seminar will sharpen your insight into developments in this field.

If you would like to explore the potential offered by the 70/40 method to improve plant energy efficiency in any building services project, please feel free to provide some information via the Contact Us page, or by phone / e-mail. We would then assess how best to develop the ideas further, either by CPD Seminar, round table discussion, site visit or other communication.

We look forward to hearing from you.

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