Quote Originally Posted by Tesla View Post
In many places the energy supplier charges the customer on the highest kWh during any 30 minute period of the month, so in this case you would be charged the same if you had the plant shut down for 27 days and only ran the plant for 30 minutes as you would if you ran the plant all month. There is usually peak (spike) in power consumption for say a commercial building when the AC starts in the morning and another in mid afternoon when the load is higher. These charges are to pay for the maximum size of power cable required to transmit the electricity from the power station to cover the I2R losses. Power factor increases the I2R losses for inductive loads so there is a penalty charge for that too. Some large power consumers use power factor correction (big capacitors) to minimise the penalties.
Quality VSD's like Danfoss correctly installed and commissioned have good protection from spikes and bearing damage.
Compressors are usually the largest power consumers and their efficiency is very important. I have seen chiller COP as high as 18 in Sydney using the Turbo Cor.
In Aus NABERs will become regulation in August forcing most buildings to list energy ratings. There are new products like Building IQ which can override control systems to ensure maximum efficiencies using live weather data for load matching and much much more. Energy efficiency is my favorite subject and career.
How does VSD at full load reduce stress on bearings? Screw comopressor VSD use 3-3.5% of additional energy. At 100% load compressor with VSD is less efficient than compressor without VSD.
Different energy suppliers charge for energy differently. When we shift the load for cold storage, we increase demand charges and refrigeration load will increase as well. However, we will save on cheap energy. As far as I remember, one research was done in Industrial Refrigeration Consortium. They determine that on peak energy should be at least 2.2 times more expensive to justify full load shifting.
COP 18 tell me nothing, because COP depends of the cycle. Can you get COP 18 for cold storage?
Compressor definitely the major energy consumer, but we pay for energy use of whole plant not only compressor. So condensing pressure, suction pressure, defrost should be optimized to minimize energy use of whole refrigeration plant.