Pairing of washers and dryers can be very confusing for someone outside the industry and even sometimes for people who have been in the industry for many years, see below key points when considering best pairing practices.
1) Degree of Loading (DOL), manufacturers generally rate washers by using a DOL of 1/9 (1KG per 9 laters drum volume), so a 180 litre machine rated by the manufacturer @ DOL 1/9 = 20KG, however to achieve optimal results we recommend a DOL of 1/10 = 18KG for normal soiling and a DOL 1/12 = 15KG for high soiling.
2) Production requirement, if you had a production requirement of 200KG per day, one may consider 1 x 20KG washer, ie basing this on a DOL 1/9 and 10 cycles per 8 hour shift. However in real world conditions, you are lucky to achieve a DOL 1/10 and 8 cycles per 8 hours, so 144KG.
3) Dry & wet weight, washers are generally rated using dry weight and dyers wet weight, for example a washer with a 240 litre drum volume @ 1/10 = 24KG, adding 50% residual moisture = 36KG required dryer capacity.
4) 450G vs 200G, although 450G washers are more expensive, you save massive amounts of energy long term (especially when processing towels) and also shorten drying times, this is due to the higher extraction found in 450G washers. In many OPL scenarios, you also don't need equal number of dryers to washers, ie flatwork ironers dry times are quick (10 to 15 mins) and thus 4 x 450G washers many only require 3 dryers.