Why the North West afternoon sun changes the load
When people ask for the right size air-conditioner, the first answer should never be the room size alone. In Rustenburg, Potchefstroom and Klerksdorp, two rooms with the same square metres can behave very differently once the sun starts hitting the walls and windows after lunch. A west facing room with large glass areas may carry far more heat than a shaded room at the back of the same building.
The problem is not only the temperature outside. It is also how long the building stores heat through the day. Brick walls, concrete slabs and uninsulated roof space all hold warmth, then release it late in the afternoon when people want the room cool. That is why a unit that copes in the morning can seem underpowered by 3pm. You need to look at the sun path, not just the size of the room.
In the North West, load-shedding adds another layer. When a room warms up during an outage and the unit starts again later, it has to remove all that built-up heat. That extra strain is often what customers mistake for a faulty machine, when the real issue is the heat load was never allowed for properly.
Building orientation matters more than many owners expect
Orientation tells you where the building faces and which side gets the hard sun. A west facing office, clinic or shopfront can take a beating in the afternoon. East facing spaces usually get milder morning sun, while north facing areas in our region can get long hours of direct light depending on the roof overhang and glazing.
For commercial sites, this matters most in rooms with fixed occupancy and equipment. A manager’s office, surgery waiting room, boardroom or retail till area often has people, electronics and lighting adding to the heat load. If the room faces the sun and the roof is thin, the cooling demand can jump quickly even if the area is not large.
We normally check the following before recommending a size:
- Which direction the main windows and walls face
- How much glass is in the room and whether it is tinted or shaded
- What sits above the ceiling, including roof type and insulation
- Whether the room gets afternoon sun or only morning light
- How many people, machines or fridges add heat during the day
That kind of assessment often changes the final choice by one size up, sometimes more. It is a small adjustment on paper, but it can make the difference between a unit that cycles properly and one that runs flat out all day.
A Potchefstroom example: same floor area, very different cooling needs
A useful example comes from a small business in Potchefstroom with two similar rooms on opposite sides of the building. Both were about the same size and both needed cooling for staff and clients. The front room faced west with a wide shop window. The back room had a smaller opening and sat under deeper roof shade. On a mild day they felt close enough. On a hot afternoon the front room became much hotter by half past two.
The owner first wanted the same unit in both spaces. After a site assessment, the front room needed a higher cooling capacity, better shading and careful placement of the indoor unit so the air could move across the occupied area. The back room needed less cooling, but better air distribution. That saved the client from overbuying in one room and underbuying in the other.
That is why we always say a proper assessment is cheaper than guesswork. If you buy on floor area alone, you can end up with extra power draw, more wear on the compressor and poor comfort when the sun is strongest. In practical terms, the room may still cool, but not in time for the people using it.
What to check before choosing the unit size
If you are pricing an installation in Rustenburg, Klerksdorp or Potchefstroom, start with a simple checklist. It helps to tell the installer what the room is used for, when the worst heat hits and whether the building gets full sun after lunch. That gives a far better picture than saying, 'it is about 25 square metres'.
- Room size in metres, plus ceiling height if it is higher than normal
- West or north facing walls and large glass areas
- Roof type, ceiling insulation and whether heat builds up in the roof space
- Number of people in the room during the day
- Any heat from printers, servers, kitchen gear or retail lighting
- Whether the unit will run through load-shedding recovery periods
If the space is in a dusty area or near an industrial yard, filters also need regular attention. A blocked filter can make a correctly sized unit feel too small. The same applies in a room with doors opening often. The cold air leaks out faster than many owners expect, and then the unit seems to be battling for no reason.
Why afternoon heat can force a larger unit, but not always
It is tempting to think bigger is always better, but that is not how air-conditioning works. A unit that is too large can cool the air too quickly without removing enough moisture, which leaves the room cold but uncomfortable. It may also short-cycle, switching on and off too often, which wastes energy and wears parts out quicker.
That said, North West afternoon heat sometimes does justify a bigger capacity than the room size alone suggests. The trick is to balance heat gain against usage. A west facing restaurant dining area with glass frontage and full seating at lunch will need a different setup from a shaded storeroom or a small back office. One size does not suit every site, and that is often where customers get caught out.
We also look at the practical side of running costs. If a unit is undersized, it works harder for longer. If it is correctly matched to the room and sun exposure, it reaches temperature faster and settles into a steadier cycle. Over time that makes a real difference to comfort, noise and electricity use.
The right installation keeps the rating honest
Even a well chosen unit can underperform if the installation is not done properly. Indoor and outdoor placement, pipe length, drainage and airflow all affect how well the system handles heat. In the North West, where storms, dust and long hot afternoons are part of the picture, installation detail matters a lot.
Good practice includes:
- Putting the indoor unit where it can throw air across the room, not straight into a wall
- Mounting the outdoor unit where it gets clear airflow and less direct heat build-up
- Allowing correct drainage so condensate does not back up
- Checking electrical supply and isolators before commissioning
- Testing the system under load, not just at switch on
We also recommend scheduled servicing, especially for offices, shops and units that run most days. Clean filters, proper gas levels and clear drains help the system cope when the weather turns hot. It is a simple truth, but a neglected unit will always feel smaller than it really is.
