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
Total real energy savings will be
$5913 + $7140 = $13053
This saving is half of saving
presented by manufacturer sales representative. Real payback is around
4 years.
Minimum allowable condensing
pressure for this plant is 110 psig. Hot gas defrosting is the reason for this
minimum. I think that every evaporator coil can be defrosted at 100 psig of
condensing pressure or lower. Defrosting at low condensing pressure required
precise adjustment of this process. Lowering minimum condensing pressure to 100
psig will save more energy than condensing fan VFDs described above. You will be
able to save $52,000
of
capital investment.
I
know that estimation of real energy savings is not a simple task and sometimes
can be tricky. Therefore, this month I start free service of assisting in
estimation of potential energy savings.
How
does it work?
You
have got proposal from contractor (manufacturer) about investment in energy
saving equipment. Ask him about calculation of potential energy savings. I will
help you to check this calculation to make sure that this is a real potential
energy savings.
I would like to remind you, that I
continue another free service that I started last year. This service is an
initial tuning up of refrigeration plants. Potential energy savings is
$10,000 - $40,000. Your cost is $0.
If
you have any questions or concerns about free services, do not hesitate to
contact me.