Theory T.1.

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August 2012

KE2 EvaporatorEfficiency
thermsolutions Theory of Operation

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KE2 EvaporatorEfficiency

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KE2 Therm Solutions,

Advanced Energy Saving Technology
for Commercial Refrigeration and AC Systems
Theory T.1.1 August 2012
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KE2 EvaporatorEfficiency
thermsolutions Theory of Operation

The KE2 Evaporator Efficiency (KE2 Evap) controller reduces

the energy used by the evaporator coil in refrigeration systems
through precise control of superheat, fan management, and de-
Table of Contents mand defrosts. The KE2 Evap was designed to be used in single
and multiple evaporator installations, with a payback period of
two years*, and a life expectancy that matches that of the sys-
Basic Refrigeration System tem. Once the controller pays for itself, it continues to pay divi-
dends for the life of the system.
Evaporator
Refrigeration System
Types of Defrost Before discussing the controller and its functions, it is necessary
Traditional (Mechanical Time Clock) to briefly introduce the refrigeration system. A refrigeration
Off -time system is defined as a group of devices serving the purpose of
transferring heat from an enclosed space to an external location.
Electric Heaters
As shown in Figure 1, it is comprised of 4 main components: the
Hot Gas Defrost evaporator, condenser, compressor, and expansion device.
Smart Defrost
The system’s cycle begins at the compressor A . A compres-
How KE2 Defrost Works sor is a motor driven device that converts low pressure vapor
to high pressure vapor. This is accomplished when the vapor
Valve Control enters the suction valve, is mechanically reduced in volume, in-
creases in pressure, and exits through the discharge valve. The
Communication heat created as a result of the increase in vapor pressure must be
removed to change the state of the vapor.
The condenser B removes the heat generated by compression
by transferring it to another media, typically air or water. As heat
is removed from the vapor, it begins to change from a gas to a
liquid. At the exit of the condenser, the refrigerant is in a 100%
liquid state. As the liquid exits the condenser, it travels through
the piping to the expansion device.
Figure 1 - Basic Refrigeration System

D
Evaporator

Restrictor,
TEV or EEV
C

B
Condenser

A
Compressor

* based on utility rate of $.09/kwh.

© Copyright 2012 KE2 Therm Solutions, Inc. . Washington, Missouri 63090
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The expansion device C is the divider between the high and the layer closest to the surface of the evaporator will tend to be
low sides of the system, and controls the amount of refrigerant hard, with a consistency similar to ice cubes. Depending on hu-
being supplied to the evaporator coil. As the refrigerant passes midity, evaporator temperature and air flow, subsequent layers
through the expansion device it enters the low pressure side of of frost may be more crystalline or snow-like. This is referred to
the system. At the new lower pressure, the refrigerant begins to as radiant frost or hoar frost.
boil and is transformed to a two phase liquid. The liquid contin-
ues boiling as it transfers heat from the air. Although building frost on evaporator coils ultimately causes
the evaporator to lose efficiency, initially it increases the capac-
The refrigerant in the evaporator D , absorbs heat while con- ity of the evaporator. Figure 2 shows typical evaporator perfor-
tinuing through the piping to toward the compressor. The mance as the coil builds frost. It is somewhat counter intuitive
evaporator’s function is to efficiently transfer heat to the refrig- for something that causes inefficiencies to improve a systems
erant. The evaporator transfers heat from the desired media: air, performance. However, the efficiency is boosted due to the
water, glycol, etc. While the evaporator transfers heat to the sur- increased surface area of the coil. Figure 2 illustrates how the
roundings, the expansion device controls the refrigerant flow, performance is enhanced initially, but declines over time. As the
ensuring all the liquid has fully vaporized prior to exiting the hoar frost continues to build, more and more air is trapped be-
evaporator. tween the ambient air and the coil, creating an insulating effect.
One result of this insulating effect is the temperature of the coil
Upon exiting the evaporator, the vapor continues to the com- must be reduced to maintain the desired space temperature.
pressor where the cycle begins again. When the temperature difference TD increases, it causes the
evaporator coil to accelerate the formation of frost.
Evaporator
As a major component of the system, an efficient evaporator The KE2 Evap controller is designed to harvest the energy stored
plays a key role in saving energy. An evaporator consists of the in the coil, which is not recognized by traditional control. Using
coil, fans, expansion device, defrost heaters, and can include the advanced algorithms to control the fans based on the systems
liquid line solenoid valve. By carefully managing each compo- coil and air temperature. KE2 Evap uses this information to cre-
nent, the KE2 Evap is able to provide the maximum output, with ate a coil profile for each system’s evaporator. Once the con-
the minimum amount of energy input. troller has learned the most efficient method of controlling the
evaporator, it uses advanced fan control to extract the energy
Although frost is unavoidable, it is also the most common cause from the coil. Maintaining a lower TD throughout the evapora-
of inefficiency in evaporator coils. When the evaporator tem- tor’s run time forms frost at a slower rate, extending the time
perature drops below the dew point, moisture begins collect- between defrosts.
ing on the cool surfaces. If the temperature continues to drop
below freezing, the moisture will begin to solidify, forming a thin To explain how the KE2 Evap reduces the temperature dif-
layer of ice. As moisture builds on the ice, frost begins to form; ference, it is important to understand how the evaporator

Figure 2 - Typical Evaporator Performance as Coil Builds Frost

1 Evaporator
Capacity Evaporator with
Evaporator with Evaporator with
no frost buildup - HIGH TD LOW TD
capacity 100% 2
100% 1
10 %
Capacity
Loss
90% 3 3
2 Defrost
Evaporator with Required
slight frost -
capacity over 100% Inefficient
Optimal Optimal Operating
Defrost Start Defrost Start Range
capacity lost
3 due to excessive
frost
Evaporator with 0%
significant frost -
capacity below 90% Time

© Copyright 2012 KE2 Therm Solutions, Inc. . Washington, Missouri 63090

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temperature changes during the cycle. During normal opera- Types of Defrosts
tion, the refrigeration cycle pulls the coil down to temperature It is inevitable that all systems operating near the freezing point
and continues running until the space temperature is satisfied. of water will eventually need to defrost the coil. This is done to
When the space temperature is achieved, the controller closes prevent frost from disturbing the space temperature. Systems
the liquid line solenoid valve and turns off the fans. The system clear the coil using a variety of methods to raise the coil tem-
continues to run until any liquid refrigerant is fully vaporized. As perature above the freezing point, until the frost has melted.
the refrigerant is pumped out of the coil, Figure 3 shows how
the temperature of the coil continues to drop from the refriger- To effectively address frost we first need to understand what
ating effect of the refrigerant remaining in the coil. This residual causes it. There are several factors that influence frost building
refrigeration acts as a flywheel, dropping the coil temperature on an evaporator:
further below the space temperature. Normally this excess en- The thermal conductivity (K value) of the coil
ergy is wasted, sitting in the coil until the system starts the next Atmospheric Conditions
cycle. Figure 3 shows how the KE2 Evap is able to capture this Product Humidity
wasted energy, pumping it back into the system. Coil Location
Plant Design
Using the fans in place of the compressor reduces the amount of
energy used to maintain the space temperature. The energy of Some of the most common defrost methods are: off time,
the coil is depleted until the compressor must be started again electric heaters, and hot gas.
to maintain the space temperature.
Off-time defrost is the least complicated system. Off-time de-
In the process of returning additional cooling, frost is reduced frost requires stopping refrigerant flow for a period of time suf-
naturally through the process of sublimation. Sublimation oc- ficient to eliminate frost on the coil. For this type of defrost to
curs when frost is transformed directly into vapor, skipping the work, the space temperature must be above freezing. Defrost-
liquid phase. By cycling the fans, the controller extends the time ing with off-time, forces the fans to run at all times. Continuous-
between compressor runtimes. In addition to adding time be- ly running the fans will impact the energy usage of the system.
tween compressor cycles to save energy, the transition of the
frost from solid to vapor returns valuable moisture to the space. Electric heaters are the most common type of defrost on low
Maintaining higher humidity levels reduces product shrinkage. temperature applications. The evaporators must be designed
Even the most advanced defrost controllers currently on the and built for this type of defrost, and incorporate passages ei-
market melt the frost, running the water and energy down the ther on the face of the coil, or through the evaporator fins, par-
drain. allel to the refrigeration tubing. Electric resistance heaters are
placed into the provided passages and are energized to raise
the temperature of the evaporator surface above freezing.
Figure 3- Latent Energy Recovery

Cooling Demand
Compressor CUT-IN Temp
Actual Room Temp Fan ON Temp
Coil Surface Temp Optimum Temp
Fan OFF Temp
Compressor CUT-OUT Temp

ON
Compressor
OFF
ON
Fans
OFF

Time

© Copyright 2012 KE2 Therm Solutions, Inc. . Washington, Missouri 63090

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Although simple to install and control, electric defrost can be Unlike off-time defrost, during the electric heater and hot gas
expensive. The heaters are energized at the beginning of the cycles, the fans should not only be off during the defrost cycle,
cycle and remain on for the entire duration of the defrost cycle. but must be held off for some time after the defrost is termi-
On average they use 1 kW per foot of evaporator length. nated. During defrost, water is formed on the evaporator as the
ice melts. Once the defrost terminates, water must be allowed
Since standard timed defrosts are usually set for 3 or more per to drain from the coil. This ‘drain time’ prevents moisture from
day and may last 45 to 60 minutes, the power consumption being blown off the coil to refreeze on the cold product or other
will affect the energy efficiency. When energized, the heaters’ surfaces in the room. Some evaporators are equipped with a
surface temperature can exceed 300˚F. When the melting frost thermostat to delay starting the fans until the coil has dried or
comes into contact with the element, it can flash into steam, cre- gotten cold enough to re-freeze the remaining moisture.
ating a fogging effect. The fog will re-condense on cold surfaces
in the refrigerated room, often creating unwanted ice. It is not Within the different types of defrosts methods, there are also
uncommon to see ice on the ceiling of a room with this problem. different types of control.

This new ice formation will not be removed during a routine de- Time-initiated, time-terminated defrosts are most effective
frost, so occasionally an electric defrost will be extended to try when conditions are consistent. Consistent conditions allow the
to remove this buildup. Running the heaters beyond the time minimum amount of defrosts per day with minimum amount of
needed for defrosting the evaporator creates excessive heat. By time. Unfortunately, refrigerated spaces rarely have consistent
trying to fix the symptom and not the cause, damage may occur conditions due to space access, product loading, seasonality,
to the surroundings. Figure 4 shows a walk-in before and after etc. Due to the inconsistent conditions, the defrost schedule
the KE2 Evap was installed. Despite the system going through must be setup to handle the worst case scenario. This is inef-
over four defrosts per day for months, without the KE2 Evap the ficient most of the time.
before picture still shows ice remaining in the walk-in. Electric
defrost, though simple and common, is not always controlled as Time-initiated, temperature-terminated defrosts are more
effectively and efficiently as possible. advanced than the time-time method. Time-temperature
Figure 4 - Before and After KE2 Evap Installed defrost controllers can be mechanically or electronically con-
(results from actual field installation) trolled. They are more advanced than the time-time controllers.
By terminating defrost on temperature, the defrost heaters re-
duce the addition of excess heat being transferred to the con-
trolled space. This is better than a strictly time based system.
However, this type of defrost control still requires additional,
unnecessary, defrost cycles to be performed on the system in
anticipation of the worst case scenario. Some, more advanced
time-temperature models, measure the amount of compressor
runtime to estimate the proper time to defrost the system.

Advanced time defrosts have used a variety of techniques re-

lated to measuring run time of the system, but have only had
limited effectiveness when applied in the field. This type of con-
trol still relies on time. Most of these algorithms estimate the
reaction of the system to a series of events. By using estima-
tions, the system will need to plan around worst case scenarios,
causing the system to be less efficient. They are also susceptible
to being reset by power outages.
Before After
Hot gas defrost is the third type of common defrost method. The KE2 Defrost approaches defrost in a revolutionary way. The
It is the most complex, and requires the most upfront capital KE2 Defrost uses an advanced defrost control algorithm, elimi-
to install. The quality and effectiveness of this defrost method nating the dependency on time. Instead, KE2 Defrost monitors
is more efficient than the other styles. In hot gas defrost, the the systems efficiency. By monitoring the coil efficiency, the KE2
liquid refrigerant flowing through the evaporator is interrupted Defrost determines the optimum time for the system to run a
and replaced by gas directly from the discharge of the compres- defrost cycle.
sor. This “gas” is really a superheated compressed refrigerant
vapor and can easily exceed 200˚F. Since the heat source is be- How the KE2 Defrost Works
ing supplied from inside the tubes of the evaporator, it applies The KE2 Defrost is a proprietary algorithm used by the KE2 Evap
heat to the frost where it forms on the tube. The hot gas travels controller to maximize energy efficiency, while minimizing the
throughout the entire tubing circuit and will therefore defrost effects of defrosts on the space temperature.
areas of the evaporator that are not reached as effectively by
electric resistance heaters.

© Copyright 2012 KE2 Therm Solutions, Inc. . Washington, Missouri 63090

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The KE2 Defrost uses a two-tier approach to extend the time be- Figure 6 illustrates how the algorithm determines when the
tween defrosts. First, it reduces the amount of frost built on the evaporator is losing efficiency. The sensors function together
coil. This is accomplished when the controller controls the fans to maintain a constant measurement of the coil temperature vs.
as discussed in the Evaporator section. Although it is intuitive air temperature, shown as (TD1), providing a reference point for
that reducing frost buildup on the coil will allow the system to the controller. The sensors provide the input to the algorithm
go longer between defrosts, the system must be able to deter- to determine when the coil temperature is falling more rapidly
mine the amount of frost on the coil. Instead of using a time than expected. This indicates the coil is becoming less efficient
based formula, the controller monitors the coil performance transferring heat. If the coil begins to lose efficiency, shown as
to extend the time between defrosts from hours to days, yet (TD2), the controller knows to initialize defrost.
is smart enough to reduce the time back to hours, to adjust to
changing system conditions. The second tier monitors the coil’s Once the controller initializes defrost, it shows a distinct differ-
efficiency and only calls for defrost when necessary, rather than ence in the defrost cycle control. A traditional defrost controller
based on the time since the last defrost. will power the heaters and keep them on until it receives a sig-
nal to terminate based on time or a temperature cut out. Figure
The KE2 Evap creates the evaporator profile from a series of 7 illustrates how a traditional defrost cycle operates the heaters.
measurements the controller makes and records when power- This type of control will remove the frost from the coil; however,
ing the controller initially. The controller completes a sequence it has the potential to create other issues.
of operational tests of the system, identifying a temperature re-
lationship between the coil temperature and the space temper- One of the issues is a fogging effect. This is caused when the
ature. (The air sensor is located in the return air of the coil, while resistance heaters’ surfaces become hot, heaters can reach 300°
the coil sensor is located in the coldest point in the coil fins. See F. When the water dripping from the coil touches these hot sur-
Figure 5 for an example of sensor location.) It initially brings the faces, it vaporizes, creating a fog in the room. As the fog exits
space down to temperature, and then defrosts the coil. This is the coil, it will move to the coldest point in the room. This may
repeated as necessary, to ensure the coil profile is accurate. be another evaporator coil, the product, the ceiling, etc. When
the vapor refreezes it can create a buildup of frost and ice in an
Figure 5 - Coil and Air Sensor Locations area of the space without defrost heaters, making it difficult to
remove. The KE2 Evap controls the defrost cycle differently.
Air Sensor
Figure 8 illustrates how KE2 Evap’s defrost cycle saves energy.
Instead of applying power to the heaters for the duration of the
cycle, the KE2 Defrost carefully monitors the coil temperature
throughout the cycle. As the temperature of the coil increases
to a predetermined point, the controller turns off the heaters,
allowing the heat in the elements to be transferred to the coil.
Locate sensor in return air When the heat has dissipated, the heaters are powered again to
approx. 6” from coil continue defrosting the coil.

Coil Sensor The KE2 Defrost manages the frost level of the coil to maintain a
concise defrost cycle, returning the system to cooling the space
in a time comparable to a traditional defrost cycle, while using
40% less energy than traditional control. In addition to creating
a fogging effect, traditional defrost methods, using resistance
heaters, waste approximately 80% heat due to high heater tem-
peratures. The KE2 Defrost’s heat recovery control reduces the
heat loss to just 20%. This is a savings of 60%.

Locate sensor approx. Valve Control

1-1/2” from end, in the As a key component of refrigeration systems, expansion devices
bottom third of coil have been a focused area for improvement. The KE2 Evap offers
the latest in electronic expansion valve control technology to
maximize the evaporator surface area, by maintaining precise
When the system is in normal operation, the controller monitors superheat control.
the efficiency of the coil, comparing the temperature of the coil
to the space temperature. The incoming data is compared to The addition of KE2 Therm’s Hybrid Stepper Valve (HSV) pro-
the evaporator profile data stored in the controller’s memory. vides the opportunity for additional savings to the end user.
Once the efficiency is determined to be outside of the accept- However, Thermal Expansion Valves (TEVs) are installed on many
able limit, 90% efficiency, the KE2 Defrost signals the controller existing units. TEVs provide consistent control on most systems
to initialize the defrost cycle. and are not required to be replaced. TEVs are widely used due to

© Copyright 2012 KE2 Therm Solutions, Inc. . Washington, Missouri 63090

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Figure 6 - Recognition of Necessity to Defrost

Temperature Cooling Demand

Compressor CUT-IN Temp
Actual Room Temp
Optimum Temp

Coil Surface Temp TD2 Compressor CUT-OUT Temp

TD1

Temperature
Difference Defrost
Between Needed
Actual Room TD1 TD2
& Coil Surface
ON
Cooling
OFF
ON
Defrost
OFF

Time
TD1 Difference between actual room temperature and coil surface temperature - Normal Operation
TD2 Difference between actual room temperature and coil surface temperature -Indicating Defrost

Figure 7 - Traditional Defrost Cycle

Set Defrost End Temperature

120°F Maximum Coil
Surface Temperature
Sensible

80% Heat Loss

Latent Defrost Heaters ON

32°F
Defrost Heaters OFF
Coil Surface Sensible
Temperature
Drain Time
Drain
Defrost Duration 100% Time
ON
Defrost
OFF

Defrost Heaters ON Time 100%

Time

© Copyright 2012 KE2 Therm Solutions, Inc. . Washington, Missouri 63090

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Figure 8 - KE2 Defrost Cycle Chart

Only
20% Heat Loss
50°F Maximum Coil
Max Surface Temperature
Sensible

Latent
32°F
Defrost Heaters ON
Sensible
Coil Surface Defrost Heaters OFF
Temperature
Drain Time
Defrost Duration 100% Drain
Time
ON
Defrost
OFF

Defrost Heaters ON Time 60%

Time

their inexpensive nature. The KE2 Evap can be used effectively the complexity, there are several options for wiring controllers
on these types of systems, especially when it is not feasible to in a refrigeration system. Serial bus is the topology used for
break into the system. most implementations. Although many are familiar with this
antiquated approach, it is not the best choice in terms of costs,
Installing an HSV does offer advantages. Since an HSV does not performance and availability. Ethernet is the standard of choice
require a pressure differential to operate, the HSV controls down for communications in most markets.
to a fraction of the total capacity of the valve. A traditional TEV
can only control down to 50% capacity, while an HSV can con- KE2 Therm approaches communications in a different way. In
trol down to 10%. This provides an opportunity for the system the KE2 Refrigeration Network, the controller provides the abil-
to operate at lower head pressures. ity to monitor and communicate. ALL KE2 Therm controllers are
Ethernet Network Devices, supporting industry standard proto-
Lowering head pressure is possible during times of lower ambi- cols (ie:TCP/IP), can easily be plugged into an existing network,
ent temperatures. Since condenser capacities are designed for natively support remote access and can be managed by a web
the hottest temperatures of the year, they are oversized during page.
cooler ambient temperatures. Mechanical valves require con-
trols to raise the head pressure to maintain the pressure drop The KE2 Evaporator Efficiency is the first product to perform true
required by the TEV. Being able to reduce the head pressure demand defrosts. The KE2 Evap uses real-time measurements of
increases the energy savings of the system. the system’s performance to determine when to initiate defrost.
Defrosting the system only when required reduces the number
Communication of defrosts by 84% compared to traditional control. Fewer de-
Ethernet communication continues to gain popularity in in- frost cycles also eliminates the associated temperature spikes;
dustrial and commercial refrigeration installations. One of the providing more uniform product temperature, helping reduce
many benefits is that it allows owners and contractors to re- product shrinkage. While it is advantageous to maintain con-
motely view refrigeration system’s performance. This informa- stant product temperature, the energy saved through the ad-
tion can be invaluable – potentially saving time and money in vanced control techniques provides further benefit by reducing
service calls. overall energy usage. The combined benefit of reduced prod-
uct shrinkage and reduced energy use effectively pays back the
Communication has been complicated in refrigeration by the owner over and over again.
many different protocols (languages) being used. Adding to

© Copyright 2012 KE2 Therm Solutions, Inc. . Washington, Missouri 63090 KE2 Therm Solutions
Theory T.1.1 August 2012 supersedes Theory T.1.1 June 2011 and all prior publications. 209 Lange Drive . Washington, MO 63090
1-888-337-3358 . www.ke2therm.com