**Real
energy savings**

To
estimate return on your investment in energy saving equipment, potential energy
savings should be calculated.

Very often you can hear from sales
persons that their equipment will save **$50,000, $100,000**
and etc. Is it real
numbers?

To
verify the estimation of potential energy savings, two steps should be done.

Step 1. Ask
a sales person to provide the calculation of potential energy
savings.

Step 2. Verify all numbers used in this calculation.

__Example.
__A
refrigeration plant has compressor power of 2000 HP. Condenser power is 200 HP
(120 HP of condenser fans and 80 Hp of water pumps). Condenser fan VFDs can be
installed at costs of **$52,000**
. Energy cost is $0.1/KWh. Minimum allowable condensing pressure is 110
psig.

At 50% of VFD speed some energy can
be saved. This energy savings will be 60 HP (fan cycling) - 20 HP (fan VFDs) =
40 HP

Manufacturer sale representative estimated a potential
energy savings of condenser fan VFDs as follow:

40HP x 0.75KW/HP x $0.1/KWh
x 8760Hrs =
$26280

Payback is about **2
years.**

It
looks like a good investment. Closer look at real life operation of this
refrigeration plant will give us a different picture.

During periods of hot weather (2000Hrs) and high
refrigeration loads, condenser fans will operate at 100% speed. Condenser fan
VFDs will not save energy during summer operation.

During winter operation (50% of operating time or
4380Hrs), required refrigeration capacity will be significantly lower than 50%.
Average required condenser capacity will be 20%. Energy savings at this capacity
will be 18 HP. Total winter energy savings from condenser fan VFDs will
be

18HP x 0.75KW/HP x $0.1/KWh x
4380Hrs = $5913

Fall and spring total energy savings from condenser fan
VFDs will be:

40HP x 0.75KW/HP x $0.1/KWh x 2380Hrs = $7140