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.

• From: Department for Energy Security and Net Zero
• Published: 1 September 2021
• Last updated: 26 March 2026 — See all updates

Documents

CHPQA guidance note 28: The determination of Z ratio

PDF, 143 KB, 3 pages

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.

Published 1 September 2021

Last updated 26 March 2026 + show all updates

1. 26 March 2026

   Updated 2026 to align with the CHPQA Portal now hosted on GOV.UK.

2. 1 September 2021

   First published.