Air conditioning and ventilation in a commercial EPC upgrade

Heat recovery is the main event

Air leaving a building in winter is warm and has been paid for. A heat recovery unit transfers that warmth to the incoming air, so the building spends far less bringing fresh air up to temperature. In a building with mechanical ventilation and no recovery, this is frequently the largest single available saving after lighting.

It is also a plant decision rather than a quick fix, so it tends to arrive with a plant replacement or a refurbishment.

Demand control: the right amount of air, when it is needed

A ventilation system set for full design occupancy runs at full design occupancy all day, whether the building is full or has four people in it. Demand-controlled ventilation modulates against actual occupancy, usually sensed by carbon dioxide level.

That is a controls retrofit rather than a plant replacement, and in a building with variable occupancy, meeting rooms, or hybrid working patterns, it is one of the better value measures available.

• Carbon dioxide sensing in meeting rooms and open plan, which are the spaces with the most variable load.
• Time scheduling matched to real occupancy rather than lease hours.
• Making sure the system is actually off when the building is empty, which is an embarrassingly common finding.

Cooling, lighting and the hidden second saving

Every watt of lighting in an air-conditioned space is a watt the cooling system has to remove in summer. Reducing lighting load therefore reduces cooling load, which is a real saving that almost never appears in a lighting quote and is worth asking about.

The same is true of IT and equipment load. In a cooled building, anything that reduces internal heat gain pays twice.

Refrigerant is a separate question

Older cooling plant may use refrigerants being phased down, which affects the cost and availability of servicing rather than the energy performance directly. It is worth knowing the position for the plant in your building before committing to repair rather than replace, because it can change which is the economic choice.

This is a question for a qualified refrigeration engineer, not something to resolve from a web page.