UPS continuity for climate computers and critical processes

A backup generator (§551) solves a mains failure, but not instantly: the generator has to start and come up to speed, which results in an interruption of several seconds. For a climate computer controlling ventilation, screens, and heating of a greenhouse complex, even that brief interruption can already cause serious crop damage. That is the domain of a UPS (Uninterruptible Power Supply) — standardized in the NEN-EN-IEC 62040 series.

Why a UPS solves something different than a generator

A UPS sits permanently between the mains and the load, with a battery and inverter as a buffer. It is meant to cover the short bridging time until a generator has started up and switched over — not to bridge a prolonged power outage on its own. In practice, a UPS and a generator therefore often work together: the UPS covers the first seconds, the generator takes over the load as soon as it is running.

Classification per IEC 62040-3: VFD, VI, VFI

IEC 62040-3 classifies UPS systems by their performance against mains disturbances:

For a critical, continuous process such as a climate computer, generally only a VFI/online double-conversion design is suitable: the inverter delivers uninterrupted power at all times, even with a normally functioning mains supply, so that there is no switchover moment at all during a mains failure.

Autonomy time and N+1 redundancy

• Autonomy time is the time the UPS can carry the load on its own battery — meant to bridge the generator's start-up/switchover time plus margin, not to bridge a fault lasting hours on its own.
• N+1 redundancy: alongside the minimally required UPS capacity, one extra module is included, so that the failure of one module does not interrupt the supply of the critical process. For a climate computer controlling an entire greenhouse complex, this quickly outweighs the consequential risk of a fault.

Common mistakes

1. Sizing the UPS only for the power of the climate computer itself, without accounting for the inrush current of connected actuators (screen motors, valves) that can temporarily demand a multiple of their rated power.
2. Regarding a UPS as a replacement for a generator during a prolonged outage — the battery autonomy time is meant as a short bridge, not as a standalone emergency power supply for hours.
3. Not applying N+1 redundancy for a process whose failure (even for just a few minutes) can cause major consequential damage.

Related

• Backup generators & low-voltage generation — §551
• Energy storage/home battery