Heating and cooling design

Heating and cooling design determines how a building is warmed and cooled: the system type, the plant, the distribution, and the control strategy that makes them work together. It is the H and the AC of HVAC — the V is covered separately under ventilation design, and on most projects the two are designed as one system.

The system selection is the consequential decision. It sets plant space, riser sizes, incoming supply capacity, maintenance burden and a large share of the building's operational carbon for the next twenty years. SDE appraises options against the brief at concept stage, when changing the answer is still cheap.

On any new build, extension, refurbishment or change of use where the existing systems cannot serve the proposed occupancy — and on any project where a Part L or Section 6 compliance route depends on plant efficiency.

Also where an existing building overheats, has poor air quality, or has plant that is failing and needs replacing with something that will still be compliant in ten years' time.

Loads first, then system selection, then plant, then controls — in that order. Selecting plant before the load is calculated is how buildings end up with oversized boilers running at poor part-load efficiency for their entire life.

Where the brief allows it, two or three system options are modelled and compared on capital cost, running cost, carbon and space requirement, and the comparison is issued rather than summarised.