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View Subscription Details: Letter ( 07/21/2009 ) - HTML Format

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I have heard from several companies that they are involved in energy efficiency projects. Certainly, this is a good step to improve efficiency of the refrigeration plants. However, a much better opportunity exists. This opportunity is optimization of a refrigeration plant operation.

A typical energy savings project requires significant capital investment. Payback of these projects is 2-3 years. Very often this payback can be achieved with generous incentives from the governments and/or from the utilities. Optimization of the refrigeration plant operation can give you 1-2 months payback without any incentives. Sometimes the initial steps of this optimization can be free. How can you do that?

The first steps of the optimization can be done by operating engineers. In order to get a successful start to an energy efficient refrigeration plant, your operating engineers should be focused on energy savings. After initial tuning up, many companies believe that only significant capital investments can help them improve efficiency of their plants. Do they have a better way to save energy?

I think that an experienced consultant will be able to continue the optimization. Sometimes people claims that they had a consultant and he said that plant is fine. Optimization of the refrigeration plants operation is a new direction in industrial refrigeration. Unfortunately, as far as I know, just a few consultants have knowledge and experience to optimize operation of the refrigeration plants. Look for second, third opinions about the operation of your refrigeration plant.

Example.

Major energy savings in industrial refrigeration can be achieved through lowering the condensing pressure during periods of cool weather.

 A refrigeration plant has minimum allowable condensing pressure of 110 psig, because at lower condensing pressure liquid ammonia can not be delivered to the chiller at the far end of the plant. Suction pressure of this chiller is 30 psig.

The pressure difference to supply liquid ammonia to the mentioned chiller is 110 - 30 = 80 psig. Is 80 psig not enough to supply the liquid ammonia to the far end of the plant? Typical liquid ammonia pumps have 30 - 40 psig head pressure and they supply liquid to every corner of the plant. What is the reason for this phenomenon?  A liquid ammonia pump supplies subcooled liquid, meaning that ammonia is delivered to the chiller (evaporator) in a liquid state. When ammonia is delivered from a high pressure receiver (110 psig) to the chiller (30 psig) part of the liquid will evaporate because ammonia in a high pressure receiver is saturated but it is not subcooled. A mixture of ammonia vapor and ammonia liquid will be delivered to the chiller metering device and vapor will choke this device. The mentioned chiller will be undersupplied with liquid ammonia. To solve this issue we have 2 choices:

1.     Subcool liquid ammonia.

2.     Increase size of metering device.

 

Experienced consultant will help you to choose the right solution for your refrigeration plant.

During winter operation, condensing pressure will be lowered below 100 psig and a lot of energy will be saved.

 

 

 

 

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