Warehouse HVAC Design Guide | Commercial Heat Gain, Ventilation, Ductwork, Plant Rooms
September 3, 2025
Commercial Air Conditioning: Replacement and Retrofit
September 8, 2025
A well-designed air handling unit (AHU) keeps air clean, stable and predictable. It moves the right air volume, filters what matters, and does it at the lowest sensible energy cost.
That outcome depends on three things working together. Sound installation, targeted upgrades and disciplined maintenance. Below, we break down how Inergy Group approaches each stage to reduce risk, protect compliance and lower lifetime cost.
Table of Contents
What an Air Handling Unit (AHU) Does
An air handling unit conditions and distributes air through a building or process space. Typical sections include intake, filter banks, heating and cooling coils, supply and extract fans, heat recovery, dampers and controls. Filtration is selected using ISO 16890 classes, which rate filters by particulate matter efficiency such as ePM1, ePM2.5 and ePM10. For example, an ePM1 85 percent filter removes a high proportion of fine particles when correctly sized against airflow and pressure drop.
For context on duct layouts and connected systems, see our guide to industrial and commercial ventilation systems.
AHU Installation: Getting the Fundamentals Right
Installation quality sets the ceiling for future performance. At Inergy Group, our process includes:
- Survey and sizing: Air volume, external static pressure and noise criteria are established with realistic allowances for filters, coils, silencers and fittings.
- Access and hygiene: Clear access to coils, fans and filter banks is planned for safe maintenance. Drain pans, slopes and traps are specified to prevent standing water.
- Controls and BMS integration: We define points lists, sensor locations, variable speed control for fans, supply air strategies and demand-based ventilation logic.
- Commissioning, validation and documentation: Airflow, specific fan power, temperature and pressure profiles are measured and recorded. Handover packs include O&M manuals, commissioning sheets and trend log templates.
Upgrade Strategies that Cut Energy and Risk
When an existing air handling unit has sound structure, upgrades often beat full replacement.
EC Fan and Variable Speed Retrofits
Replacing belt-driven fans with EC plug fans or adding variable speed drives to existing motors can deliver strong savings in variable-load applications. A modest speed reduction often yields a large energy reduction for fan systems.
Heat Recovery additions or Replacements
Where a unit is extract-only or uses a low-efficiency exchanger, adding a high-performance plate or rotary device can reduce heating and cooling demand. Selection and control should address leakage, frosting and pressure drop to keep efficiency high without compromising air quality.
Filtration and Hygiene Improvements
Upgrading to ISO 16890 ePM1 filters improves fine particle capture in offices and clean manufacturing zones. We model pressure drop and fan capacity to avoid raising specific fan power beyond design targets.
Controls Refresh
Modern sensors, better zoning, free cooling strategies and fault detection reduce wasted run-hours and expose drift. We integrate with site controls to give clear alarms and trends for airflow, filter pressure, specific fan power and coil performance.
Maintenance as Part of a Full Package
Inergy Group provides maintenance as part of design, installation and upgrade programmes. This keeps accountability clear and performance measurable. Typical tasks include:
- Filter changes at agreed pressure drop thresholds
- Fan and bearing inspections or EC fan diagnostics
- Coil and drain hygiene with documented cleaning regime
- Sensor calibration and strategy verification
- Trend log reviews to keep specific fan power and temperatures within design bands
Where local exhaust ventilation connects to process lines, a thorough examination and test is required at least every 14 months. We schedule this within planned works and retain records for audit.
Read more about scope and response in our service and maintenance overview.
Compliance and Standards
Whether you’re installing a new air handling unit or upgrading an existing AHU system, remaining compliant is key. Some of the key standards you need to be aware of are:
- BS EN 16798-3, which sets the framework for ventilation performance and the determination of specific fan power. Designing to target SFP limits reduces energy and supports compliance.
- Approved Document L influences fan efficiency targets and heat recovery choices through energy performance requirements.
- ISO 16890 defines ePM filter classes used for general ventilation. Selecting the right class balances indoor air quality and energy.
- SFG20 provides the UK maintenance reference used to structure planned tasks and evidence compliance.
- F-Gas company certification is required where refrigerant equipment is present. We maintain certification and records as part of our delivery.
Heat Recovery and Lifecycle Cost
Plate exchangers are simple and avoid cross-contamination. Rotary wheels offer high compact efficiencies and can recover latent heat with the right matrix. The right choice depends on indoor contaminants, allowable leakage, frost risk, cleaning regime and space. Good selections deliver strong savings, but total pressure drop and fan sizing must still meet energy expectations under Approved Document L.
Integration with Ducted Systems and Cooling
Air handling units interface with ducted cooling, evaporative systems and direct expansion coils. The duct network design, diffuser selection and balancing determine comfort and noise as much as the unit itself.
If you are exploring ducted options, our explainer on ducted air conditioning in the UK outlines layouts and integration notes.
Sector Snapshots
Food Production
Hygiene risk and audit evidence are paramount. We combine ePM1 filtration, hygienic drain designs and cleanable sections. Where process extraction is present, LEV testing follows the 14-month rule with documented corrective actions.
See our article on food factory ventilation for typical drivers.
Plastics Processing
Heat loads, fumes and particulates vary by process. We pair air handling units with well-designed capture hoods and make-up air to maintain pressure balance and product quality.
A recent local extraction and ventilation case study shows a typical delivery approach.
Pharmaceuticals
Pressure regimes, staged filtration and validation are critical. We specify tight control bands with clear alarm rationalisation.
Our manufacturing services page outlines how we handle regulated environments and documentation.
FAQs
When should an AHU be replaced rather than refurbished?
Consider replacement where casework is corroded or leaking, where geometry restricts access and hygiene, or when meeting energy targets requires a full redesign. Otherwise, EC fan and heat recovery upgrades can extend life with a strong payback.
What filter grade suits offices versus production areas?
Offices typically use ePM1 classes between 50 and 70 percent depending on outdoor air quality and recirculation. Production spaces with fine particulates or sensitive processes may require higher ePM1 classes with staged prefilters. Final selection depends on load, risk assessment and fan capacity.
How often should coils and drain pans be sanitised?
Set intervals using recognised maintenance schedules, manufacturer guidance and measured biofouling risk. Evidence with photos and pressure trends to prove effectiveness.
What data should be trended to prove performance?
At minimum: supply and extract airflow, specific fan power, filter differential pressure, supply and return temperatures, heat recovery efficiency, and key valve and damper positions.
How do heat recovery upgrades interact with existing plant?
They reduce heating and cooling demand. Control sequencing must avoid simultaneous heating and cooling, and frost protection should be tuned to climate and occupancy.
Why Choose Inergy Group?
At Inergy Group, we design, install and upgrade air handling units with a clear line of sight to performance and compliance. Our projects include structured maintenance as part of a full package, not as a stand-alone contract. That keeps accountability simple and results measurable.
Ready for a technical review of your site? Request a free site survey today.
