CALLING ELECTRICIANS...........ADVICE PLEASE

[pedrob]

Hello all....

I am in need of a little electrical expertise......i have a large bakery oven and am wondering if one can actually work out what kind of power (rands) its using per month. The label on it says it has a power rating of 60kw. Lets say for example it works 8 hours a day, what does that cost me??

Just in case anyone is wondering, i have a smallish supermarket and my electricity bill is on average 30k a month, i been told my rather old oven may be pulling too much for what its worth.




Thanks in advance

[AndyD]

It's impossible to work out the running cost because when the oven is switched on it's not always drawing power because it has a thermostat control intermittantly switching the elements on and off.

You'd need to install a temporary power monitor of meter to assess the power consumption. It might be worth investigating one of these. They do a 3-phase model as well as a single phase one but check it can monitor a 3-phase 60kW load before you buy.

[Justloadit]

Lets take a worse case scenario that the oven is always on for 8 hours.
Electricity Kw cost can vary based on the area you are in and what tariff you are paying. So lets say you are paying R1.27 per Kwatt
60Kw * 1.27 = R76.20 an hour
8 hours * R76.20 = R609.20 per day
30 Days * R609.60 = R 18,288.00 a month.

There could be other expenses that you may not consider, which is part of the basic requirements of your supermarket, such as fridges and freezers, they are connected 24 hours a day.

[pedrob]

Lets take a worse case scenario that the oven is always on for 8 hours.
Electricity Kw cost can vary based on the area you are in and what tariff you are paying. So lets say you are paying R1.27 per Kwatt
60Kw * 1.27 = R76.20 an hour
8 hours * R76.20 = R609.20 per day
30 Days * R609.60 = R 18,288.00 a month.

There could be other expenses that you may not consider, which is part of the basic requirements of your supermarket, such as fridges and freezers, they are connected 24 hours a day.

Thanks for that, i know i have a few freezers and fridges but remeber im working departments, so what im saying is if that oven uses so much power, im losing money according to sales in that department.

Another thing, the name plate on the oven says it was manufactured in 1989, so im assuming it cant be very economical as that time it was much much cheaper to run.......
Secondly, im interested in buying a new one, according to specs its power rating is 12.5kw, so am i right in saying that it will be much cheaper to run?

[AndyD]

Thanks for that, i know i have a few freezers and fridges but remeber im working departments, so what im saying is if that oven uses so much power, im losing money according to sales in that department.

That figure of R18,288.00 a month is the worst case scaeario, it might only be costing half or a quarter or a fifth of that, you won't know unless you record some actual figures.

Another thing, the name plate on the oven says it was manufactured in 1989, so im assuming it cant be very economical as that time it was much much cheaper to run.......

Doesn't necessarily follow that old is less efficient, they had a habit of over engineering things in the 80's which is rarely the case nowadays. If the old oven has thicker insulation then it might be cheaper to run.

Secondly, im interested in buying a new one, according to specs its power rating is 12.5kw, so am i right in saying that it will be much cheaper to run?

With an oven it's all down to how good the insulation is. If you have two identically built ovens and one of them has 20kW of elements the other has 40kW of elements it could actually cheaper to run the latter one.

Here's why;
To produce a given amount of heat you will use exactly the same electrical energy regardless of how powerful the elements are. It just means the 20kW elements will be running for twice as long as the 40kW elements would be.
Both ovens have the same amount of heat loss per hour because they're identically insulated.
The smaller kilowatt oven will take longer to heat up to cooking temperature and longer to recover to its set temperature once you open the door and put the cold food in to start baking.
Because it's running for longer to do the same work the smaller kilowatt oven has heat loss happening for a longer time each day. Losses for longer periods equals less efficient equals higher cost to do the same job.

[pedrob]

Thank you for the reply.......i have bought a monitor, 3 phase which shoulb be delivered in the new week, ill get it monitored and take it from there. Should give me some answers before i make a costly mistake and fork out on a new oven!

[AndyD]

Your welcome and I think you've made the right decision to collect evidence before making such a large purchase based on guesswork.

I'd be interested to know the actual performance figures for the oven if you can find time to post them up next week.

[ians]

This is where my customers benefit, having all the right tools to do the job in my toolbox, A thermal imager to take pics of any heat loss on furnaces, ovens etc and 3 phase power quality analysing equipment, which can measure and verify consumption.