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Calculating AC PK Capacity for Offices and Commercial Buildings

Solusi Karya Nusantara Technical Team · 2026-09-28 · 4 min read

One of the most common mistakes when planning a building's cooling system is sizing the AC based on floor area alone, without accounting for other factors. The result is either an undersized unit that never quite cools the room, or an oversized one that wastes electricity and wears out faster from frequent short cycling. For building owners, facility managers, and contractors, understanding how to correctly calculate AC PK capacity is the first step toward long-term comfort and cost-efficient operation.

Why AC Sizing Can't Be a Guess

PK (paardenkracht, a Dutch unit of power) is a common market term for AC cooling capacity, even though the official units are BTU/h (British Thermal Unit per hour) or Watts. The capacity a room actually needs depends on many variables: floor area and ceiling height, the number of people inside, the number and power draw of electronic equipment, direct sunlight exposure, and the room's function. An office packed with computers and a small server, for example, needs more capacity than a meeting room of the same size that is rarely used.

Base Formula for BTU Requirements

A practical formula commonly used for an initial estimate is:

BTU/h requirement = Room area (m²) x 500

The multiplier of 500 assumes a room with a standard ceiling height (around 2.5–3 meters) and no excessive heat load. For commercial spaces, this base result should be adjusted with the correction factors below for a more accurate figure.

Correction Factors You Should Account For

  1. Number of people in the room. Every adult occupant generates body heat. Add roughly 600 BTU/h for each person above the base assumption (typically two people per room).
  2. Electronic equipment. Computers, printers, small servers, and photocopiers add extra heat. Add roughly 300–600 BTU/h per unit, depending on its power draw.
  3. Sun exposure. Rooms with large west-facing windows or without curtains/window film receive a higher heat load. Add 10–20% to the base calculation for rooms exposed to direct sunlight throughout the day.
  4. Ceiling height above standard. Rooms with high ceilings (such as lobbies or open areas) have a larger air volume, so capacity needs also rise, typically by 10–15%.
  5. Building insulation. Buildings with thick concrete walls and double-glazed windows need less capacity than buildings with thin walls or air leaks.

Converting BTU/h to PK

Once the total BTU/h is calculated, convert it to PK using this common reference:

| PK | Capacity (BTU/h) | |----|--------------------| | 0.5 PK | ± 5,000 | | 0.75 PK | ± 7,000 | | 1 PK | ± 9,000 | | 1.5 PK | ± 12,000 | | 2 PK | ± 18,000 | | 2.5 PK | ± 24,000 |

For large commercial capacity needs, the more appropriate system is often no longer a per-room split AC, but a VRF/VRV system or chiller designed through a full cooling load calculation.

Worked Example: A 24 m² Office Room

As an illustration, here is the calculation for a 4 x 6 meter (24 m²) office room occupied by 6 staff, 6 computers, one printer, and an east-facing window with curtains:

  1. Base requirement: 24 m² x 500 = 12,000 BTU/h
  2. Occupancy correction: 6 people, 4 above the base assumption x 600 BTU/h = 2,400 BTU/h
  3. Equipment correction: 6 computers x 400 BTU/h + 1 printer x 400 BTU/h = 2,800 BTU/h
  4. Sun exposure correction (curtains installed, mild impact): 5% x 12,000 = 600 BTU/h
  5. Total requirement: 12,000 + 2,400 + 2,800 + 600 = 17,800 BTU/h

Based on this result, the room needs about 2 PK of capacity, or it can be split into two 1 PK split AC units for more even cooling across the room.

Why Manual Calculations Aren't Enough for Large Buildings

The formula above is reliable enough for a single office room, but multi-story commercial buildings, server rooms, production areas, or spaces with complex heat loads require a more detailed cooling load calculation that accounts for ducting distribution, per-floor zoning, and long-term energy efficiency. Mistakes made at this planning stage are difficult and costly to fix once installation is complete.

When to Contact an HVAC Consultant

Contact an experienced HVAC consultant or contractor when:

  • The building has more than one floor or multiple zones with different room functions.
  • There are server rooms, production areas, or spaces with high-power equipment.
  • You need shop drawings for ducting installation and refrigerant piping.
  • You want to compare the efficiency of several separate split AC units against a centralized VRF/VRV system.

Solusi Karya Nusantara helps building owners and contractors across Medan and North Sumatra calculate cooling requirements accurately, from site survey and cooling load calculation to 3D design and HVAC shop drawings, with Daikin-certified technicians for office, commercial, and industrial building installations.