Optimal IP

[Superfridge]

Probably, you provide required cooling. However, a lot of energy is wasted.
I looked at current weather in Welligton(I don't know where is your plant located). Temp. 6 degC, humidity 81%. I assume that your plant has evaporative condensers. Current optimum(the best) condensing pressure is in the range of 600 kpa. This is huge energy savings by changing condensing pressure from 1000 kpa to 600 kpa.

Thats an interesting point, every industrial plant I have ever worked on has had a fixed condensing pressure in the range of 1000kpa and yes it wastes energy.

It is best practice in this neck of the woods to keep condensing pressure up when ambient is down.

Would the hand expansion valves from HP to IP need to be opened if the condensing pressure was lowered from 1000kpa to 600kpa to compensate the lower deltaP and lower liquid flow? As the IP pressure is fixed, the liquid flow rate to LP would stay the same.

[Segei]

Thats an interesting point, every industrial plant I have ever worked on has had a fixed condensing pressure in the range of 1000kpa and yes it wastes energy.

It is best practice in this neck of the woods to keep condensing pressure up when ambient is down.

Would the hand expansion valves from HP to IP need to be opened if the condensing pressure was lowered from 1000kpa to 600kpa to compensate the lower deltaP and lower liquid flow? As the IP pressure is fixed, the liquid flow rate to LP would stay the same.

Condensing pressure should "float" based on wet bulb temperature. Hand expansion valve setting is one of many issues that should be solved. Recently, I've posted several newsletters related to floating condensing pressure and energy savings. You can read them.

[Superfridge]

Superfridge ,
what type of oil cooling do you have thermosyphon , water cooled ?
Do you have VSD fan on condenser or on/off ?

Thermosyphon and VSD, why do you ask?

Condensing pressure should "float" based on wet bulb temperature. Hand expansion valve setting is one of many issues that should be solved. Recently, I've posted several newsletters related to floating condensing pressure and energy savings. You can read them.

Many of the compressor skids I work on do not have an oil pump and require pressure differential for lubrication. If the system ran at 500kpa differential (100kpa LP & 600kpa HP) that would be very close to minimum lube requirements. Have you experienced issues with this situation?

[Segei]

For Frick compressors minimum pressure differential should be 55 psig(370 kpa). You don't need to go below 470 kpa. Compressors with high suction pressure should have full lube oil pump. This pump will run at low condensing pressure and it will be off at high condensing pressure. Typically, hot gas defrost and liquid injection oil cooling are first barriers to low condensing pressure.

[Segei]

Superfridge.

Unfortunately, many people believe that energy in industrial refrigeration should be saved by VFDs(VSDs). This is significant misconception. I found that VFDs can save 20-30% of total energy savings and they have several years payback. Optimization of refrigeration plant operation can save 70-80% and payback a few months. Look at your plant. Compressors have VSDs. They are very expensive. Reduction of condensing pressure from 1000kpa to 800kpa doesn't require capital investment and it will save more energy then VFDs. I saw several plants where people installed VFDs for compressors, condenser fans and evaporator fans, but they were operated at 150 psig of condensing pressure all year around. This is clear example that these people have little information about energy savings in industrial refrigeration.

[Superfridge]

With low condensing, do you tend to have the associated low condensing issues? Like liquid hang-up in the condensers? Some plant I deal with suffer from this when at low load. I know it comes down to poor design and poor plant management and these are generally out of the average fridgie's control.

Is it a bit of "trial and error" when undertaking the optimization process? as some plant fall over when outside of design conditions or unforseen issues arrise.

How do you get over the lack of heat available for hot gas defrost?

[Segei]

With low condensing, do you tend to have the associated low condensing issues? Like liquid hang-up in the condensers? Some plant I deal with suffer from this when at low load. I know it comes down to poor design and poor plant management and these are generally out of the average fridgie's control.

Is it a bit of "trial and error" when undertaking the optimization process? as some plant fall over when outside of design conditions or unforseen issues arrise.

How do you get over the lack of heat available for hot gas defrost?

If you have enough liquid, liquid hang-up won't affect operation. Sometimes during cold weather plant will have very low condensing pressure. This happen when cold wind blow through the condensers. In this case I suggest to install shields to prevent direct wind.
Unfortunately, we have many misconception in industrial refrigeration. One misconception is that pressure drop in hot gas line is major reason of poor hot gas defrosting at low head pressure. This is wrong. I think that misbalancing of hot gas supply, ammonia condensation and ammonia condensate draining is major reason of poor hot gas defrosting. Read couple newsletters about defrosting.

[Segei]

With low condensing, do you tend to have the associated low condensing issues? Like liquid hang-up in the condensers? Some plant I deal with suffer from this when at low load. I know it comes down to poor design and poor plant management and these are generally out of the average fridgie's control.

Is it a bit of "trial and error" when undertaking the optimization process? as some plant fall over when outside of design conditions or unforseen issues arrise.

How do you get over the lack of heat available for hot gas defrost?

Typically, to optimize operation of the refrigeration plant 3 steps should be done. Assume that every step will save $50,000 in energy costs.
1. Initial optimization. Usually, done by the operators. Cost of implementation is from $ 0 to $10,000. This is the step of "trial and error".
2. Final optimization. Usually done by consultant. Cost of implementation is $10,000-20,000.
3. Investment in energy saving equipment(VSDs, PLCs...). Cost of implementation is $100,000 - 200,000.
Probably, your company doesn't have information about optimization and they invested in step 3. This is the most expensive investment.
In North America, many companies are focused on steps 1 and 3, but they miss step 2. Final optimization doesn't require significant investment, but it can save additional 30-40% of total energy savings.