Power-and-Heat, the amount of power required to heat the water to the correct temperature, and the amount of power that is left for the pumps and other uses within the machine is so crucial to your choice of machine.

Power-and-Heat the page for insider information on what heating water requires.

Power-and-Heat. The amount of power required to raise the temperature of an amount of water from one temperature T1 to a higher temperature T2, is a matter of physics, so there are NO SHORTCUTS, which is why the right choice of machine will need to be studied in detail.

If you can imagine the power supply to your machine as a piece of cake or a pie chart, it will have to be portioned out to the tasks required within the dishwasher or washing machine.

If we take a dishwasher, there will be a circulation pump minimum 700watts, for a basic machine, a wash tank heater 3/6/9Kwatts or higher depending on type of machine.

There may be a separate rinse tank boiler heater of 3/6/9Kwatts or more, which would be the major slice of the pie chart.

Then the drain pump if supplied about 250watts approx, the smallest portion if you don't count the contro circuitry which is normally mW these days with micro-processors.

If there is low pressure hot water supply (less than 1 bar or in some machines 2bar) then a boost pump will be required another 700watts.

So you can see if you have a 13amp 240V single phase supply with a large quantity of dishes to be washed with only a cold water supply you have a BIG Problem. A major challenge as they say today.

Below I have included a couple of charts which shows you how to work out the amount of power consumed to heat the measured water.

This is normally between 3.5 and 5 litres in a rinse tank boiler within the front loading "Tank Dishwasher" or the "Pass Through Dishwasher".

The wash tank boiler itself is normally between 25 and 50 litres so by using the formulae you can quickly ascertain the amount of time required to pre-heat the dishwasher in the morning before work.

Calculation of the Amount of Power to heat Water.

Power-and-Heat a major consideration for choosing the right machine first time.

This may be gas or electrical power but normally electrically heated elements emersed within the the wash tank or boiler.

Using The Formula Q=MC(t2-t1) in KW

Amount of water in Litres = 3.5 in Litres

Final Temperature (t1) Required °C = 85.00°C ( this is the normal rinse tank boiler final temperature)

Ambient Temperature (t2) water °C = 45.00°C (This is the incoming water temperature)

Q (KW) = 5.49KW (The figure for the total amount of KW consumed in this example)

M=Kg per Second Mass = Litres/(60 x The Time allowed)

t2-t1=Temperature Increase °C = 40.00°C 40

C= Specific Heat of Water (a constant)(4.18) =4.18

The Number of minutes allowed to reach the temp. 2.00 Calculation of the Amount of Power to heat Water.

Using The Formula Q=MC(t2-t1) in KW

Amount of water in Litres = 3.50 in Litres Final (t1)Temperature Required °C = 85.00°C

Ambient (t2) Temperature water °C = 20.00°C

Q (KW) = KW. 7.92KW

M=Kg per Second Mass =Litre/60 0.03

t2-t1=Temperature Increase °C = 65.00°C

C= Specific Heat of Water (A Constant)(4.18) = 4.18

Number of minutes allowed to reach the temp. 2.00min Power-and-Heat all the insider knowledge on laundry and dishwashing.

It looks a lot easier to read when it is in a spreadsheet which I can send you if you like.

If you would like me to send you a spreadsheet in excel I keep them on Google docs where I can give you access if you wish to apply.

So it can be seen from the above calculation that it would require 7.9KW of heating power to raise the temperature from 20 °C to 85°C in the rinse tank boiler, (a difference of 60 °C) in two minutes, which is the common time that people think is needed to wash a load of dishes. "I want a two-minute dishwasher" is what we in the trade are always requested to supply. When the customer really needs their dishes moved from being dirty to clean in the shortest and most efficient amount of time. No-one wants a dishwasher, what they really need is clean dishes. How that happens is normally within the walls of a dishwasher with many compromises to accomodate price, power, space, water supply, ease of use, yes and even fashion, not so much in commercial situations.

Power-and-Heat, If we make some adjustments to the formulae to try to reduce the amount of power required you will see it is quite significant to the time element, or you must supply the machine with very hot water from your own supply. This causes problems with the wash quality as too hot water at the start of a cycle will fix soiling as opposed to removing it.

Number of minutes allowed to reach the temp. 3.50

Power-and-Heat calculations.

By increasing the temp of the incoming water to 40°C and allowing 3.5 minutes as you can see the power comes down to about 3Kw for the task to be completed in the time.

40°C is not too hot for soiling problems, but you may find the occasional bit of egg stuck to a plate but this should not be a major problem.

The main point of this page is to show you that by allowing just a little extra time and by pre-heating the incoming water to a dishwasher the amount of power required is reduced dramatically. It is the main restraint on any dishwasher installation and should be studied carefully where your salary depends on the outcome. Remember no-one wants a dishwasher they want clean dishes, so if you buy the wrong machine and end up with a tailback of dirty dishes your job may be ob the line.

Below is a quick calculation of the time to heat 25 litres in your wash tank from 40°C to 60°C an increase of 20°C in 12 minutes will require a power rated element of 2.9KW

Calculation of the Amount of Power to heat Water in main wash tank at start of the day. Using The Formula Q=MC(t2-t1) in KW. Amount of water in Litres = 25.00 Litres

Final Temperature Required °C = 60 °C

Ambient Temperature water °C = 40 °C

Q (KW) = KW. 2.90 KW

M=Kg per Second Mass =Litre/60 0.03

t2-t1=Temperature Increase°C = C 20.00 °C

C= Specific Heat of Water a constant (4.18) = 4.18

Number of minutes allowed to reach the temp. 12.00

Power-and-Heat all the best in insider knowledge.

So as you can see from my Power-and-Heat calculations to arrive at a useable machine for normal supplies you will need hot water and plenty of time of at least 3.5.to 4 minutes.

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