Facility Infrastructure Calculators: Lighting, Ventilation, HVAC, Power and Electrical Distribution

Facility infrastructure calculators are the tools a plant or engineering team uses to size the building systems that light, ventilate, cool, and power a site. They answer the practical questions behind a facility: how many light fixtures a floor needs to reach a target lux, how much airflow a room needs for its air changes per hour, how large an HVAC cooling load a space carries, what size standby generator backs up an outage, what kVA a distribution transformer must supply, and what conductor size safely carries a load. Each one runs in your browser and shows the working behind the answer.

The lumen method sets the number of luminaires from luminaires = E x A / (lumens x UF x MF), where E is the target lux, A is the floor area in square meters, lumens is the light output per luminaire, UF is the utilization factor, and MF is the maintenance factor. The utilization factor captures how much light reaches the working plane after the room shape and surface reflectances take their share, and the maintenance factor allows for dirt and lamp aging. You pick the target lux from the task, look up the two factors, and round the result up to a whole number of fixtures that lays out in a sensible grid.

Air changes per hour is how many times the full volume of air in a room is replaced in one hour. The required airflow follows directly: airflow = room volume x ACH, which you can report in cubic meters per hour or convert to CFM. The right ACH depends on the space, roughly 4 to 8 for general workshops, 6 to 12 for warehouses with light process, and much higher for kitchens, welding areas, or rooms with fumes and heat. Codes and industrial hygiene guides set minimums by occupancy and hazard, so you size the fan to the larger of comfort, contaminant removal, and heat removal.

A cooling load is the total heat a space must reject to hold its temperature, added up from every source. The main gains are the people in the space, the lighting, the equipment and process heat, and the envelope gains through walls, roof, and glazing, plus the load from the fresh air the ventilation brings in. You sum the sensible and latent parts, apply the local design temperatures, and report the total in tons or kW, where one ton equals about 3.52 kW. A quick area estimate gives a first number, but a load built from the actual gains is what sizes the equipment without leaving it oversized and short-cycling.

Sizing a standby generator starts with the running load, the steady kW and kVA the plant draws once everything is on. To that you add the starting surge of the largest motor, since a motor pulls several times its running current for a moment as it spins up, and that inrush sets the momentary kVA the generator must supply without the voltage collapsing. A safety margin on top, often 20 to 25 percent, covers future load and keeps the engine off its limit. The generator is then chosen to satisfy both the running kW and the starting kVA, whichever demands more, so a motor start never stalls the bus.

A distribution transformer is sized in kVA from the load it must serve. You start with the connected load, apply a demand factor because not everything runs at once, and divide by the power factor to convert working kW into the apparent power kVA the transformer actually carries: kVA = connected load x demand factor / power factor. A growth allowance on top reserves capacity for load added later, so the transformer is not replaced in a year. The result is rounded up to a standard rating. Sizing this way avoids both an overloaded unit that runs hot and an oversized one that wastes money and runs at poor efficiency.

A cable is chosen against two limits, and the larger conductor wins. First check ampacity: the conductor must carry the load current without exceeding its insulation temperature rating, using the NEC or IEC tables with corrections for ambient temperature and for grouping several cables together. Then check voltage drop: over the run length the drop must stay within an allowed percentage, commonly about 3 percent to a panel and 5 percent to the load, so equipment still receives usable voltage. On short runs ampacity usually governs; on long runs voltage drop often forces a bigger size. Pick the conductor that satisfies both checks at once.

Yes, every tool is free with no sign-up, and all calculation happens in your browser. The numbers you enter are never sent to a server, stored, or shared. Each tool also exports a clean PDF or CSV. These calculators are for education and planning; confirm any figure that informs a capital, electrical, or safety decision with a qualified engineer and the governing code for your site.