Air conditioning controls for offices: how to stop wasted cooling
Updated 23 October 2026 · SEO Dons Editorial
Which controls cut the most wasted cooling?
The government-backed Energy Technology List (ETL) publishes criteria for HVAC building controls. Read as a checklist, they describe what a capable office controller does, and each feature maps to a common source of waste:
| Control | What the ETL criteria describe | Waste it removes |
|---|---|---|
| Weekly schedule with holiday dates | Occupation times set per zone in intervals of five minutes or less, with at least two periods a day, plus future dates such as holidays set to standby, economy or off | Plant running outside occupied hours |
| Optimum start | Calculates when heating or cooling must begin to reach the setpoint by the start of occupancy | Starting early as a precaution |
| Separate setpoints with a lockout | Separate heating and cooling setpoints in each zone, and a mechanism that prevents simultaneous heating and cooling and frequent cycling | Heating and cooling working against each other |
| Temporary, resetting overrides | User adjustments are temporary and reset after a set interval or at the next scheduled switching time | Overrides left on all week |
| Occupancy sensing | Presence or activity sensors move a zone to economy or standby, and ventilation is minimised in unoccupied zones | Cooling and ventilating empty rooms |
| Anti-tampering | Strategy and configuration cannot be changed or automatic control disabled except during commissioning, maintenance or testing | Settings that drift over time |
The ETL is a procurement tool, not a legal standard, and it states that there are no testing requirements for listing: manufacturers provide brochures as evidence. Use it as a specification checklist, and note that its criteria are written so that controllers can function in an EN ISO 52120-1:2022 class A system.
How do heating and cooling end up working against each other?
Through inappropriate control or settings, according to the government's air conditioning inspection guide, which says costs can be reduced where heating and cooling are in use at the same time unnecessarily. CIBSE Journal adds that in an integrated building the BMS needs to know what the air conditioning is doing to avoid simultaneous heating and cooling. HSE adds the occupant's view: unless air distribution is uniform, some workers feel cold while others feel hot.
A short check for each zone:
- List the heating and cooling setpoints. If the two are close, or the controller has no lockout, they can overlap.
- Compare start and stop times for heating, cooling and ventilation.
- Look at where the sensors sit. The inspection guide lists the appropriateness of control zones, control sensors and their locations among the elements an assessor reviews.
- Ask for the logs. Where a BMS runs the system, the inspection guide says the relevant information may need to be extracted before an inspection.
What do user overrides do to energy use?
Left unmanaged, they can raise it. CIBSE Journal notes that giving building users control can increase energy consumption as they wrestle with the controls, for example by setting cooling to 16°C on the misapprehension that this will cool the room more quickly. HSE, meanwhile, lists allowing workers to adjust thermostats among its comfort measures, and employers also have a duty to keep temperatures reasonable, as the workplace temperature law guide sets out. The workable middle is adjustment within a narrow band that resets automatically, which is what the ETL criteria describe.
What could a corrected schedule save? A worked example
This is a hypothetical illustration of the method, not a forecast. Every input is an assumption to replace with metered data.
| Step | Assumed value |
|---|---|
| Hours on per weekday, current schedule (06:00 to 20:00) | 14 |
| Hours on per weekday, corrected (07:30 to 17:30, including a one-hour start-up lead) | 10 |
| Hours saved per week (4 hours x 5 days) | 20 |
| Weeks of cooling per year | 20 |
| Hours saved per year | 400 |
| Average electrical draw in those hours | 6 kW |
| Electricity saved (400 x 6) | 2,400 kWh a year |
Multiply the result by the unit rate on your own bill. The running costs guide gives a published average price and further worked examples. If the saving looks large, check the draw assumption first, because a measured figure from a sub-meter or the BMS beats any assumption.
When is a central controller enough, and when does a BMS pay?
A central controller handles schedules and setpoints for a group of indoor units, and for a single-tenant floor with one system it may be all that is needed. The ETL separates control units that cannot communicate with third-party devices from those that can, which matters if the controller must later join a wider system. Carbon Trust notes that typical timeclock and temperature controls lack the sophistication multi-occupancy, multi-function buildings need, which often leaves out-of-hours heating and cooling running, and that a building management system automates control to stipulated occupation and temperature requirements. The building management systems guide covers the architecture, parts and upkeep.
Do the Building Regulations and inspections cover controls?
Yes, in two ways. Under the Building Regulations 2010, "fixed building services" includes any controls associated with fixed systems for air conditioning, and providing a controlled service is building work. The reworded Part L requirement, which comes into force in England on 24 March 2027, states that fixed building services must have effective controls, as the Part L explainer sets out.
For existing systems above 12 kW, an energy assessor must inspect at intervals of no more than five years, and the report must cover the adequacy of installed controls and control settings. Since 28 December 2020 it must also consider the system's capability to optimise its performance under typical operating conditions. There is no legal requirement to act on the recommendations, but they are a ready-made list of control fixes. The SEER guide covers seasonal efficiency ratings.
What should you ask a contractor about controls?
- Can heating and cooling run in the same zone at once, and where is the lockout?
- What range can users adjust, and how long before an override resets?
- Does the controller use occupancy, and can window contacts be added?
- Who holds the passwords? Carbon Trust advises that password protection sits with the system operators and not maintenance providers, with access matched to role.
- Is seasonal commissioning in the maintenance agreement?
Zoning by the building's aspect, which gives controls something sensible to act on, is covered on the office air conditioning page. Readers who want a system reviewed can send an enquiry through the site's form.
Sources
- HVAC building controls (Energy Technology List criteria), Department for Energy Security and Net Zero (Energy Technology List), checked 22 October 2026
- Energy Technology List (ETL), DESNZ (GOV.UK), last updated 10 July 2024, checked 22 October 2026
- A guide to air conditioning inspections in buildings, MHCLG (GOV.UK), checked 22 October 2026
- Energy Performance of Buildings (England and Wales) (Amendment) Regulations 2020, legislation.gov.uk, checked 22 October 2026
- Workplace (Health, Safety and Welfare) Regulations 1992, regulation 7, legislation.gov.uk, checked 22 October 2026
- Building Regulations 2010, regulation 2, legislation.gov.uk, checked 22 October 2026
- Building Regulations 2010, regulation 3, legislation.gov.uk, checked 22 October 2026
- The Building Regulations etc. (Amendment) (England) Regulations 2026, legislation.gov.uk, checked 22 October 2026
- On a mission, CIBSE Journal, checked 22 October 2026
- Smarten up or risk dumbing down your BMS, CIBSE Journal, checked 22 October 2026
- Digital technologies for energy management: building the business case, Carbon Trust, checked 22 October 2026
- Digital technologies for energy management: user guide, Carbon Trust, checked 22 October 2026
- Thermal comfort, Health and Safety Executive, checked 22 October 2026
Common questions
Can I stop staff setting the cooling too low?
Yes. The ETL criteria describe controllers that let the building manager define setpoints for each mode, treat user adjustments as temporary and reset them automatically. Pair that with a clear comfort policy, because employers must still keep temperatures reasonable.
Is a time switch enough for an office?
For one tenant with one system it can be a start, and the government's inspection guide says improvement can be as simple as adjusting time switches or thermostats. Carbon Trust warns that timeclock and temperature controls lack the sophistication multi-occupancy buildings need. A weekly schedule with holiday dates and optimum start goes further.
Does the equipment have to be on the Energy Technology List?
No. The ETL is described as a procurement tool for purchasers, and the Enhanced Capital Allowance it once supported ended in April 2020. Use its criteria as a specification checklist, remembering that listing involves no testing requirement.
Will an energy assessor change my settings?
No. The inspection guide says the assessor would not reset time switches or thermostats but will report to the building owner or manager. The report covers the adequacy of installed controls and control settings, with suggestions for improvement.
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