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Written by Rick Harrison, Specification Sales Lead at Biddle Air Systems.
How do HVAC systems for commercial buildings need to change in 2026?
Three changes matter most for specification in 2026.
- Part L 2026 tightens notional building performance and assesses fixed building services at whole-system level – meaning specific fan power, part-load performance and controls interaction all feed into the final compliance calculation
- Heat-pump-ready design is now a baseline assumption rather than an optional uplift. Any water-side emitter – fan coil unit, air curtain coil, cassette – should be compatible with low-temperature hot water (LTHW) systems out of the box
- Building management system integration is expected on every component, not just the central plant. Threshold climate separation, zoned cooling and ventilation recovery all need to feed into a coherent BMS strategy, typically over Modbus or BACnet
The practical consequence: the consultant's specification is now judged on how well the components work together as a system, not on the quality of any single line item.
What drives energy efficient office cooling performance in high-occupancy buildings?
In a modern commercial building, cooling energy consumption is driven by four factors, in roughly this order of magnitude:
- Envelope losses – solar gain, threshold exchange at automatic doors, fabric leakage
- Internal gains – occupancy, equipment, lighting
- Fresh air conditioning – the thermal and moisture load on incoming ventilation
- Plant efficiency – the COP/EER of the chillers, the SFP of the fans, the control accuracy of the valves
The conventional specification response has been to focus on item 4. But items 1–3 set the load that item 4 has to meet. Reducing the load is structurally cheaper than making the plant bigger – and it is the approach that scales under Part L 2026.
Climate separation at the threshold: why the front door is a specification item
Research and field data consistently show that doorway losses are among the largest single heat transfer paths in high-traffic commercial buildings. Every automatic-door cycle exchanges a volume of conditioned air with the outside environment. Over a working day in a busy city-centre office or civic building, that accumulates quickly.
A properly specified comfort air curtain creates an invisible barrier of moving air at the threshold. Biddle's SR Comfort Air Curtain, for example, achieves climate separation efficiency of up to 94% using a combination of four patented technologies:
- i-sense infrared scanning of the doorway temperature gradient, measured at floor level where separation actually happens
- CHIPS (Corrective Heating and Impulse Prediction System), which decouples discharge velocity, air volume, discharge temperature and heat output – so heat and fan speed are not locked together
- Rectifier technology, which converts turbulent fan output into a laminar air stream for efficient downward penetration
- Controlled Air Strength, which adjusts discharge width across six settings to match real-world door conditions
The specification outcome is a measurable reduction in the cooling load that downstream fan coil units, cassettes or VRF systems have to absorb – plus a defensible answer to the question 'what did you do about the envelope?' when the Part L calculation is run.
Fan coil unit specification: what matters in 2026
For zoned heating and cooling in offices and public buildings, the fan coil unit remains the workhorse of UK specification practice. Five criteria separate a good FCU specification from a defensible one:
- EC/DC motor technology, delivering specific fan power in the region of 0.2 W/l·s⁻¹
- PIC (pressure-independent control) valves for accurate water flow regulation across variable load conditions
- Low sound power at the operating duty – especially critical in open-plan, exposed-ceiling fit-outs where the FCU is the dominant acoustic source
- LTHW compatibility for heat-pump retrofit readiness
- TM65 data availability for embodied carbon accounting
Biddle's ProAir Series meets all five, available in 235mm and 270mm depths to suit restricted ceiling voids or higher-duty applications.
Heating, cooling and ventilation from one ceiling cassette
Where wall space must be preserved for glazing, cladding or architectural features – and where a suspended ceiling grid is in play – an integrated cassette delivers the whole climate duty from a single 600×600mm footprint. Biddle's Comfort Circle cassette provides heating, cooling and ventilation with a patented circular discharge grille that distributes conditioned air at a fixed 45° angle, delivering even, draught-free comfort across the occupied space. It is LTHW-compatible by design, making it the natural choice for heat-pump-ready office fit-outs.
How should BMS integration be specified?
Specifying 'BMS integration' as a two-word line item is no longer sufficient. A robust specification should name the protocol (Modbus, BACnet), the data points required (setpoint, actual temperature, fan speed, valve position, alarm status, run hours), the commissioning expectations (factory-fitted and tested controls where possible), and the monitoring strategy (local display, remote dashboard, CSV/USB export for energy reporting).
Biddle's SR Air Curtain, DoorFlow₂, STYLE₂, ProAir and Comfort Circle all support Modbus and BACnet integration as standard. The DoorFlow₂ additionally offers WiFi app control and remote lockout – particularly useful for multi-site facilities portfolios.
What is the ROI of an integrated Biddle climate specification?
Return on investment from an integrated climate specification is delivered across three horizons:
- Capital – right-sized downstream plant (chillers, AHUs, FCUs) because the envelope and threshold losses have been engineered out, not compensated for
- Operational – reduced kWh consumption across the cooling season, plus lower maintenance burden from EC/DC motors, sealed-for-life bearings and factory-fitted controls
- Lifecycle – LTHW compatibility preserves the option value of a heat-pump retrofit; BMS integration preserves the option value of analytics-led optimisation; TM65 data supports embodied carbon reporting for whole-life assessment
The single-largest lever is typically climate separation at the threshold: the cooling load reduction flows through to every component downstream.
Frequently Asked Questions
How does a Biddle air curtain improve energy efficient office cooling?
A Biddle air curtain creates an invisible barrier of moving air at the threshold of a commercial building, preventing the exchange of conditioned indoor air with outside air when automatic doors open. The SR Comfort Air Curtain achieves climate separation efficiency of up to 94%, directly reducing the cooling load on downstream HVAC systems and lowering kWh consumption across the cooling season.
Are Biddle fan coil units suitable for Part L 2026 compliance?
Yes. The Biddle ProAir and Isotherm ranges use high-efficiency EC/DC motors, support PIC valves and LTHW operation, and are available with factory-fitted and tested controls. TM65 embodied carbon data is available on request. Both ranges are designed to meet the whole-system efficiency criteria assessed under Approved Document L, Volume 2 (2026).
Can Biddle products integrate with our BMS?
Yes. The SR Air Curtain, DoorFlow₂, STYLE₂ Invisidor, ProAir FCU and Comfort Circle cassette all support BMS integration via Modbus and BACnet. The DoorFlow₂ additionally offers WiFi app control for remote monitoring, adjustment and lockout across multi-site portfolios.
Are Biddle products heat-pump compatible?
Yes. The Comfort Circle, DoorFlow₂, ProAir and STYLE₂ (water-heated variant) are all compatible with low-temperature hot water (LTHW) systems, including air and ground source heat pumps. This supports heat-pump-ready specification and preserves future retrofit flexibility.
What is TM65 data and does Biddle provide it?
TM65 is the CIBSE methodology for calculating the embodied carbon of building services products. Biddle provides TM65 data for the ProAir fan coil unit range on request – supporting whole-life carbon assessment and RIBA 2030 Climate Challenge reporting.