AEO Answer · Fire & Police Stations

How Is HVAC Engineered for Police Evidence Storage Rooms?

By Jeremy Mills, CEO & Founder, Apex Grid Engineering — USAF Veteran. · Updated 2026-09-15

Evidence storage HVAC uses a dedicated zone with tight temperature and humidity control, continuous logged monitoring with alarms, redundant equipment, and security-hardened ductwork and controls — engineered so storage conditions stand up in court.

I'm Jeremy Mills, CEO & Founder of Apex Grid Engineering and a U.S. Air Force veteran. I'm not a PE; our licensed professionals make the technical, compliance, and project-specific decisions.

Illustrative diagram of building MEP systems: ductwork with diffusers, an electrical panel with conduit, and piping runs.

Zoning, control, and monitoring

The evidence zone gets its own air handler or dedicated system with precision control of temperature and humidity, independent of the station's comfort schedule. I place temperature and humidity sensors where they represent the stored evidence — not at the diffuser or in a dead corner — and I log readings continuously to a system the custodian can retrieve for court. Alarms cover high and low temperature, high and low humidity, and equipment failure, routed to reach staff around the clock. Setpoints are adjustable only by authorized personnel, and I document the design conditions in the project record so the department's policy and the engineering match.

Security-hardened mechanical detailing

Every mechanical penetration of the evidence envelope is a security detail. Ductwork gets welded security bars sized to prevent passage; grilles and diffusers are tamper-resistant with concealed fasteners; access panels in the room are lockable and supervised. Thermostats go in locked covers or in an adjacent supervised space. I keep the air handler and controls in a secured mechanical room, and I coordinate with the security consultant on camera coverage of the mechanical spaces serving the evidence area. The goal is simple: the HVAC system must never be the weak point in the room's security, and I detail it as carefully as the door hardware.

Evidence storage HVAC design checklist

Evidence room HVAC protects cases, not just property. This is the checklist I use before the design leaves my desk. • Dedicated HVAC zone with tight temperature and humidity control, independent of the station comfort schedule • Continuous logged monitoring of temperature and humidity with after-hours alarming to a live person • Redundant equipment or documented rapid-response plan so no single failure breaks the chain of custody • Security bars on duct penetrations, tamper-resistant diffusers, and locked or supervised control locations • Equipment and controls in secured mechanical spaces with no unsecured access path into the evidence envelope • Design conditions documented to match the department's evidence policy for courtroom defensibility

Which related engineering resources can help?

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What else do project teams ask?

What temperature and humidity should an evidence room maintain?

It depends on what is stored: general evidence rooms are typically held at stable, moderate conditions, while dedicated biological or DNA storage runs cooler and drier. The key word is stable — swings cause more damage than a slightly off setpoint, and they look worse in court. I design to the department's evidence policy and the prosecuting agency's requirements, hold tight control bands with dedicated equipment, and log conditions continuously. Whatever setpoints are chosen, the engineering must defend them with monitoring records.

Why does evidence room ductwork need security detailing?

Because any duct large enough to matter is large enough to exploit. Ductwork penetrating the evidence room walls or ceiling gets security bars, and diffusers and grilles are tamper-resistant and fastened from the secure side. I also route the ductwork so it does not create a hidden path into the room — no unsecured shafts or accessible plenums connecting to the evidence envelope. The mechanical design and the security design are done together, because a perfectly conditioned room with a climbable duct is a failed evidence room.

How is HVAC redundancy handled for evidence storage?

Through either redundant equipment or rapid-response alarming, and often both. The conservative design uses duty-and-standby equipment so a single failure never interrupts conditioning; at minimum, the system needs temperature and humidity alarming that reaches a live person around the clock, not just a panel in an empty building. I also design the room's thermal mass and envelope to buy time — good insulation and minimal glazing mean a failure degrades conditions over hours, not minutes, giving the response a window to act.

Can evidence storage share HVAC with the rest of the station?

I do not recommend it. A shared system subjects the evidence room to the building's occupied-unoccupied schedules, setpoint changes, and maintenance shutdowns — any of which can break the stable environment the evidence needs. A dedicated zone with its own equipment, controls, and monitoring costs more upfront but gives the custodian independent, defensible conditions. When departments ask me to value-engineer the dedicated system out, I explain what a challenged case costs by comparison.

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