Pre-Cooling of HVAC &refrigeration Units Through Evaporative Fogging

Pre-Cooling of HVAC &Refrigeration
Units Through Evaporative Fogging
A Non-invasive Method of Reducing Refrigeration Related Energy

and Maintenance Costs While Increasing Peak Cooling Capacity
When applied to air-cooled systems, the application will reduce energy use
(kWh) and demand (kW) while increasing peak cooling capacity.
Why is a Pre-Cooling System an especially important technology?
• Refrigeration and air conditioning account for up to 70% of the typical commercial
building's energy usage. Groceries and restaurants can have an even higher
percentage.
• Cooling systems not only run longer under high ambient conditions, they also draw
more power when they run. Therefore both kWh and kW increase greatly.
• It is difficult to further reduce HVAC system energy use beyond typical practices, such
as night setback modes and warmer thermostat settings. Therefore, the only way to
reduce energy usage is to make the systems run more efficiently with a Pre-Cooling
System.
How does it work?
A custom evaporative fogging system is fitted to each Roof Top Unit, which
lowers the temperature of the air entering the condenser. This allows the
condensers to reject more heat which lowers head pressures and
compression ratios, thereby causing the compressors to draw less power.
Their cooling capacity increases, they run less, consume less energy, require
less maintenance, and last longer.
The application performs best at the exact time when commercial
buildings require increased refrigeration system performance: during peak
ambient periods. In fact, the higher the ambient temperature, the greater the
savings potential.
Substantial Benefits
A Pre-Cooling System provides a number of benefits:
1. Reduced Energy Costs

The reduced demand and energy usage leads to reduced demand and
usage charges and substantially lower energy costs.
2. Reduced Maintenance Costs

By lowering head pressures and extending compressor life,
maintenance costs can be greatly lowered. High head pressures can
greatly reduce compressor life. Conversely, by lowering peak head
pressures through evaporative fogging, compressor life can be greatly
extended.
3. Increased Peak Cooling Capacity

By reducing the saturated liquid temperature, the system will increase
peak cooling capacity by upwards of 20%.
4. Reduced Energy (kWh) Usage

The system will reduce kWh over the entire ambient temperature range
from 75 F and higher. Depending on the actual ambient conditions,
kWh savings of 11% to 20% can be expected.
5. Reduced Peak Demand (kW)

The system will reduce kW over the entire ambient temperature range
from 75 F and higher. Again, depending on actual ambient conditions,
peak kW savings of up to 30% can be expected.
FAQ's
Is it a good investment?
Yes. A Pre-Cooling system will usually pay for itself within two years and
continue to reduce energy and maintenance costs for years to come.
What is evaporative fogging?
Utilizing "thermal dynamics", water is passed through a pump, raising

its pressure to 1,000psi, and then sent through high-pressure piping
and fogging nozzles to atomize the water droplets to 10 microns or
less. When the water mist is injected into an air stream moving across
an air-cooled condenser (condenser air), it is “flash-evaporated" and
the temperature of the condenser air is lowered.
Is evaporative fogging a new practice?
No. Evaporative fogging started more than 25 years ago for outdoor
cooling in such applications as patios and outdoor restaurants. Today,
Coldmist supplies evaporative fogging systems for industrial cooling, wine
barrel storage, dust suppression, odour control, greenhouse climate
control, power turbine inlet fogging, cold storage facilities, wet rooms,
special effects, poultry, cattle and horse cooling, fire suppression, and
air-cooled refrigeration, air conditioning condensers, and more.
What are the differences between evaporative condensers, water towers, and
the fogging system?
All three systems dissipate heat through evaporation. The manner in

which they go about doing this, however, is decidedly different:
• With evaporative cooling of condensers, water is sprayed across condenser tubes. As air
passes over the tubes, the water evaporates, cooling the tubes and their contents.
• With cooling towers, water is passed through a heat exchanger in which it absorbs
heat. The heat is dissipated in the cooling tower as air is blown across the water.
• With the fogging system, a water mist is injected into the condenser air stream. As
the mist evaporates, the temperature of the condenser air is lowered. As the now cool
condenser air is blown across the condenser coil, the coil rejects more heat and the
performance of the air-cooled system is improved.
What evidence exists that fogging condenser air will improve the performance
of air-cooled condensers?
Studies show substantial savings. In addition, an independent study

commissioned by Southern California Edison recently validated the
savings to be achieved from evaporative fogging. In addition,
manufacturers’ data sheets suggest that air cooled systems perform
better under cooler ambient conditions.
Why does cooling system energy usage increase as the ambient temperature
rises?
There are three primary reasons:
• As the ambient temperature rises, the condenser cannot reject as

much heat, therefore the head pressure also rises. This increases
the compression ratio (head pressure/suction pressure) so the
compressors draw more power when they run.
• As the head pressure increases, the saturated liquid (refrigerant)

temperature rises and system cooling capacity falls. Therefore, the
system must run longer to satisfy the load so it uses more energy.
• In applications where higher ambient temperatures increase the

load in the space to be cooled, the cooling system must run longer
so energy use increases.
Can it be retrofitted without major modifications?
Evaporative condensers and cooling towers are typically installed

pre-construction; The system is most often retrofitted to existing
systems. While evaporative condensers and cooling towers could
also be retrofitted to existing systems, the process is much more
difficult, invasive, and costly. By comparison, our system does not
require that the condenser be shut down or modified. It is simply
installed in a suitable location, water piping is run to the
condensers, and the system turned on.
What benefits are derived when condenser air is cooled through evaporative
fogging?
• As the temperature of the condenser air falls, the condenser is able
to reject more heat, so the head pressure is reduced. This lowers
the compression ratio so the compressors draw less power when
in operation.
• As the head pressure falls, the saturated liquid temperature also

falls and cooling capacity increases. Therefore, the system does not
have to run as long to satisfy the load and energy use is reduced.
• Reduced head pressures lengthen compressor life, increase cooling
reliability, and lower maintenance costs.
Will fogging condenser air reduce peak demand (kW), energy usage (kWh), or
both?
Both. Since the compressors will draw less power when they run
because of lower head pressures, demand will be reduced. Since the
cooling capacity of the system will be increased, the compressors will
run less, so energy usage will be reduced.
Will the energy savings be relatively constant over the entire range of ambient
conditions?
No. The greatest temperature reductions will occur under the hottest
and driest ambient conditions. During those periods, the percentage of
energy savings will be greatest. However, in the course of a year there
are many more hours when the conditions are far more moderate, so
the greatest kWh savings will be accumulated during those periods.
Can it cause coil corrosion?
The high pressure micro-orifice nozzle and installation design is done

in a manner that helps ensure flash-evaporation, thereby reducing
moisture contact.
Int. +61 2 4369-5711

Australia 1-800 773 778
www.coldmistcooling.com.au

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Pre-Cooling of HVAC &Refrigeration

Units Through Evaporative Fogging

A Non-invasive Method of Reducing Refrigeration Related Energy

Why is a Pre-Cooling System an especially important technology?

How does it work?

1. Reduced Energy Costs

2. Reduced Maintenance Costs

3. Increased Peak Cooling Capacity

4. Reduced Energy (kWh) Usage

5. Reduced Peak Demand (kW)

What is evaporative fogging?

Utilizing "thermal dynamics", water is passed through a pump, raising

Is evaporative fogging a new practice?

All three systems dissipate heat through evaporation. The manner in

Studies show substantial savings. In addition, an independent study

There are three primary reasons:

• As the ambient temperature rises, the condenser cannot reject as

• As the head pressure increases, the saturated liquid (refrigerant)

• In applications where higher ambient temperatures increase the

Can it be retrofitted without major modifications?

Evaporative condensers and cooling towers are typically installed

• As the head pressure falls, the saturated liquid temperature also

Can it cause coil corrosion?

The high pressure micro-orifice nozzle and installation design is done

Int. +61 2 4369-5711

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