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I am interested in purchasing a Primus washing machine but I get confused about the power rating that is recorded in the data sheet (link below). On page 2 of the data sheet, the manufacturer states that the machine consumes 27 kW. Is this not too high for a washing machine? I searched on the internet for what the average power consumed by a dishwasher would be and its typically around 700 W so I got confused when I saw that this one consumes 27 kW. Please advice.

http://www.primuslaundry.com/_media/primus-2a2f5bfe85cfb8271fb3eb5bac192566/techspecs_rx350_520_eng.pdf

Mujtaba
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  • Seems strange. Although this machine is professional (1.5m height! and 35 kg laundry!) it seems to me that it should not use more than 2-3kW of power. Better contact the manufacturer or their representative and ask them. – Todor Simeonov Oct 04 '17 at 08:07
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    That isn't a dishwasher. – HandyHowie Oct 04 '17 at 08:08
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    A while ago I was involved in the purchase of a 180 liter volume commercial clothes dryer with ~8kW of heating power, roughly doubling that for the same volume as the sample you showed, that would be 16kW, not nearly as much, but also not an order of magnitude off. It sounds reasonable, as it is doing washing too. – PlasmaHH Oct 04 '17 at 08:12
  • That 27kW is for heating the wash water. That takes power, especially for large amounts of water that you want heated fast. Since this is a commercial unit that could be used in a laundromat, you will want to heat the wash water fast - so, high power heating elements. – JRE Oct 04 '17 at 10:54
  • It also lists "Steam" and "hot water" heating, so presumably there are options for connecting to steam plant and saving 27kw. –  Oct 04 '17 at 12:14

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The drum has a volume of 332L. To fill it entirely with water for a boil wash from 10°C to 90°C would be 80K×332kg×4.2kJ/kg/K = 112MJ. Assuming it wants to be about a quarter full, 27kW would take about 1000 seconds to heat it up, which if anything seems a bit slow - alternatively, in five minutes of filling with heated water using 27KW to heat it, then it would have 24L of water in the drum. (I don't honestly know the volume of water it would use, but somewhere between 1/4 and 1/20 of the drum volume seems reasonable).

But certainly something of that order of magnitude is reasonable for a machine of that size. 600W would heat half a litre of water in five minutes, which is not enough to boil wash 37kg of clothes.

Pete Kirkham
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$$ t = \frac {m \times \Delta T \times SHC}{P} $$

where \$ t \$ is time in seconds, \$ m \$ is mass in kg, \$ \Delta T \$ is the change in temperature in K (°C), \$ SHC \$ is the specific heat capacity of water = 4.2 kJ/kg/K and \$ P \$ is power in kW.

Quick check for boiling your 1 L, 2.1 kW kettle from room temperature:

$$ t = \frac {1 \times 80 \times 4.2}{2.1} = 160 \ \mathrm {s} $$

which is about right.

For 25 L of water from 20° to 80° with 27 kW we get

$$ t = \frac {25 \times 60 \times 4.2}{27} = 2333\ \mathrm {s} = 38.9 \ \mathrm {minutes}$$

Transistor
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