**Trading for energy
savings**

Recently, I heard from one chief
engineer, that energy savings in industrial refrigeration is not rocket science.
I do not completely agree with this statement. Energy savings in our industry is
not rocket science, but it is pretty complicated.

We can compare processes of electrical
energy savings in different areas of electrical energy
consumption.

If we can shut off the light or
electrical heater for a certain period of time, our energy savings can be
calculated as multiplication of light (heater) power by the shut off time. This
is straightforward.

If we can shut off the light in
refrigerated space and save 10 KWh of energy, our additional energy savings for
refrigeration plant would be around 5 KWh and total savings will be 15 KWh. This
is not rocket science.

Three parts of refrigeration plant
consume the electrical energy:

- A
condensers
- B
compressors
- C
evaporator fans

We can get majority of energy savings by
trading the energy between these 3 parts.

For example, we spend additional 5 KW of
**A** (**condenser**) power and condensing
pressure have decreased. This step has saved 10 KW of **B** (**compressor**) power. It is a good
trading. Our net power savings are

**( 10 â€“ 5 ) =
+ 5 KW. **

At other conditions, if we increase
condenser (**A**) power by **20 KW**, but our compressor (**B**) savings will be **15 KW**, our total power savings would be
negative or **(- 5) KW**. It means that
we are going to the wrong direction.

**A** and **B** are opposite functions. If **A** (**condenser power**) is going up, **B** (**compressor power**) is going down and
vice versa. Our goal is to get the point (setting), where sum **A+B** is **minimum**.

There is a similar relationship
between **B** and **C**. If we increase suction pressure,
efficiency of **compressor** (**B**) is going up (less power per unit of
refrigeration), but efficiency of evaporator fans is going down (more fan power
per unit of

refrigeration).

Finally, we have found the minimum
total power for the sum **A + B +
C**. This is the optimum for
certain refrigeration load and ambient conditions. If refrigeration load or/and
ambient conditions have changed, we need new optimum set points.

Therefore, our goal is a moving
target.

Optimization of refrigeration plant
operation is not an easy task because of many variables. Only the knowledge of
energy trading laws will give us an opportunity to run refrigeration plant at
optimum set points all year around.