Guidance
CHPQA guidance note 28: The determination of Z ratio
Guidance on determining the trade-off between heat to site and power for CHP schemes - the Z ratio.
Documents
Details
For CHP Schemes which include fully or partially condensing (pass-out) steam turbines, Power Efficiency will decline as steam extraction increases for a given fuel consumption, so there is a balance between increasing heat recovery and reducing power output.
The trade-off between heat to site and power for these CHP Schemes is known as the Z ratio.
Updates to this page
Published 1 September 2021
Last updated 26 March 2026
+ show all updates
-
Updated 2026 to align with the CHPQA Portal now hosted on GOV.UK.
-
First published.