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Technical Papers37th Annual Meeting
International Institute of Ammonia Refrigeration
March 22–25, 2015
2015 Industrial Refrigeration Conference & ExhibitionSan Diego, California
ACKNOWLEDGEMENT
The success of the 37th Annual Meeting of the International Institute of Ammonia
Refrigeration is due to the quality of the technical papers in this volume and the labor of its
authors. IIAR expresses its deep appreciation to the authors, reviewers and editors for their
contributions to the ammonia refrigeration industry.
ABOUT THIS VOLUME
IIAR Technical Papers are subjected to rigorous technical peer review.
The views expressed in the papers in this volume are those of the authors, not the
International Institute of Ammonia Refrigeration. They are not official positions of the
Institute and are not officially endorsed.
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2015 Industrial Refrigeration Conference & Exhibition
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© IIAR 2015 1
Abstract
With reference to the design and operation of an indoor snow dome, many factors should be considered including the requirement of human body comfort, the quality of snow, energy saving operation and so on. As we know, the refrigeration system consumes most of the energy in an indoor snow dome and ammonia-based refrigeration systems are widely used in indoor snow domes. Therefore, the objective of this paper is to discuss the energy consumption and energy efficiency improvement strategies for ammonia-based refrigeration systems used in snow domes. First, it introduces four kinds of snowmaking methods and the principles of ammonia-based refrigeration systems used in the indoor snow domes. Second, it provides the refrigeration load and energy consumption of each system in a specified situation, followed by a discussion of different energy efficiency technologies: heat recovery technology and its application and thermal storage in snow base. Finally, a practical engineering example is given to show how to apply these energy efficiency strategies comprehensively to such aspects as energy efficiency, operation possibility, safety and economic viability.
Keywords: indoor snow dome, ammonia-based refrigeration system, energy efficiency
International Technical Paper #3
Energy efficiency improvement strategies of ammonia-based refrigeration system
used in indoor snow dome
Dr. Yiqiang Jiang Ian Zhao
CTC Group Ltd.Beijing, China
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Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
Introduction
As the interest in winter sports, especially skiing/snow playground has been
increasing, there is a general desire to remove geography and climate as factors
limiting the availability of skiing/snow playground. Thus an increasing number
of indoor snow domes have been or are being built. It is common knowledge that
indoor snow domes require a very substantial ground area and buildings with
impressive structures. Generally, ski slopes range from 300 to 600 meters long by
30 to 40 meters wide. An indoor snow dome is actually a large volume cold storage
that inevitably takes in heat gains from outdoors such as solar radiation heat and
infiltration heat. This means that it consumes enormous energy in terms of indoor
temperature, humidity and ventilation in order to provide suitable conditions for
indoor skiing/snow playground (Guy Evon Cloutier (1)). For instance, an indoor
snow dome in Dubai with a 400-meter-long 70-meter-wide snow slope and covered
with at least 0.9m of snow needs a refrigeration load of 5230kW with 1585kW
compressor motor input which shares more than 50% of the energy input of the
indoor snow dome (Katunori Shibata, 2004 (2)).
Figure 0. Field pictures of indoor snow dome
Therefore, it is obvious that most of the energy is consumed by the refrigeration
system. Usually, the refrigeration load ranges from 150W/m2 to 300W/m2 depending
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on the methods of snowmaking used. With regard to the refrigeration system in
indoor snow domes, ammonia-based refrigeration systems are widely used. As a
natural refrigerant, ammonia (R717) is so attractive due to its extremely high latent
heat, second only to water among commonly recognized fluids. And ammonia
refrigeration systems often have design conditions that span a wide range of
evaporating and condensing temperatures (ASHARE Handbook-Refrigeration, 2010).
As an example, an indoor snow dome “Qiaobo ice and snow world” in Beijing,
with a total refrigeration load of 1500kW, uses two ammonia refrigeration screw
compression system units (Hua Jun, 2006 (3)). However, the energy efficiency of the
refrigeration system is often ignored when an indoor snow dome is being designed
and operated. Therefore, it is important to study the energy efficiency improvement
strategies for ammonia-based refrigeration systems used in indoor snow domes.
In this paper, different energy efficiency strategies such as the application of heat
recovery technology and thermal storage in snow base are discussed and a practical
engineering example is given to show how to apply these energy efficiency strategies
comprehensively.
Snowmaking methods and refrigeration system in an Indoor Snow Dome, ski dome and snow playground
Although an indoor snow dome has the advantage of offering the facility of skiing/
snow playground 365 days per year and making the availability of skiing/snow
playground unrestricted by geography and climate, it also has the disadvantage of
large energy consumption. Since the first indoor snow dome was set up in Belgium,
reducing the energy consumption has been the paramount issue.
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Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
Snowmaking methods in an Indoor Snow dome
The requirements of any indoor snowmaking system is to produce a quality snow
at low operating costs without the use of chemicals and to maintain the quality
consistently 365 days a year at an acceptable capital and operating cost. Thus the
following problems will be considered:
• Conventional outdoor snowmakers are very large and are designed to cope with
sunlight, which is not suitable for an indoor snow dome.
• Atomizing liquid water droplets into a controlled atmosphere below the freezing
point of water is difficult because the air is close to saturation.
• An indoor snow dome is actually a large volume cold storage that inevitably takes
in heat gains from outdoors such as solar radiation heat and infiltration heat, so
maintaining a steady temperature is difficult.
• Snow undergoes a destructive metamorphism which causes snow crystals to
transform into spheres and diffract light in a different way, thus making the snow
less suitable for snow sports (Clulow, Malcolm G, 2006 (4)).
In order to solve these problems, different kinds of indoor snowmakers were
invented. The so-called “snowmakers” actually do not make snow. Instead they
produce atomized liquid water droplets or ice flakes to eventually form the indoor
snow. Four kinds of snowmaking methods commonly used indoors are introduced
below:
The first is a compressed air method which uses high-pressure cold water (just
above its freezing point) and compressed air to form tiny water droplets through the
nozzles of a “snowgun” (Steve Ritter, 2004 (5)). With the help of compressed air,
tiny water droplets are atomized and crystal nuclei are produced in the process of
droplets dispersing into the air. Before hitting the ground, crystal nuclei are combined
with larger droplets or environmental moisture to form snow. In the snowmaking
process, compressed air is used to accelerate the movement of water droplets into
the air, provide energy to atomize the droplets, and assist in the dispersal of the
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water stream to form snow. This method requires a strict and accurate control of
indoor air temperature, humidity and ventilation. Therefore, the colder the indoor air
temperature, the more efficiently snowmakers operate. Figure 1 shows the operation
process of this kind of snowmaking method.
Figure 1. Compressed air type Figure 2. Ice-breaking type
The second method is the ice-breaking type which produces snow from flake ice
and then spreads the ice onto the slope. This particular method can make snow
production possible whatever the ambient temperature and humidity may be. The
production principle consists of replacing the ambient cold, normally provided by
the refrigeration system, with a refrigeration unit to freeze the water. In this process,
three subsequent operations are essential: ice flake production, ice crushing and
pneumatic distribution of snow. For example, an indoor snow dome in Shanghai
(China) adopted this snowmaking method by installing six ice generators producing a
total of 400 m3 of snow per day. Figure 2 shows the operation process of this kind of
snowmaking method.
The third method is the Permasnow type which was invented in Australia by Alfaro
Bucceri in 1984; however, the first commercial center using this method did not open
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Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
until 1988 in Adelaide Australia. The snow is made by mixing water with a water
soluble polymer to approximately 50-70% of the maximum water retention capacity
of the polymer, aerating the mixture and freezing the mixture to produce snow
crystals which can be laid on a refrigerated floor to form a skiing slope. The concept
of a Permasnow center is based on the same as an ice rink with a cold surface
operating in a warm environment, however there is one basic difference in that an
ice rink is flat and the surrounding wall holds in a layer of cold air whereas a ski
slope is on a slope. Thus the cold air falls down the slope because it is heavier and is
replaced by warm air at the top, the warm air contains a high level of humidity and
this is drawn to the cold surface where it freezes. This causes a layer of mist on the
slope and the ice damages the existing snow layer. The other issue is the increased
operating costs.
The last method is a chemical type using liquid nitrogen which provides a
temperature of minus 176°C to form the snow. The snow is produced by a normal
snowgun and liquid nitrogen is discharged into the plume to provide the cooling to
freeze the water into snow. This process is ideal for special events as the snow can
be produced anywhere but it is expensive to produce as it takes one ton of liquid
nitrogen to produce one ton of snow. It is also dangerous to use indoors, as the
expanding nitrogen gas displaces the oxygen from the surrounding air, so anyone
entering this area will be suffocated.
Improvements in snowmaking methods have resulted in more efficient snowmaking
operations. Furthermore, the better the snowmaking system, the “drier” snow
that is being made. The most important issue for us is to select the most suitable
snowmaking method while considering air-conditioning load, equipment power,
snow quality and the cost.
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Ammonia-based Refrigeration System Principles in Indoor Snow Dome
Because of the scheduled phase-out and increasing costs of CFC and HCFC
refrigerants, there is renewed interest in using ammonia for HVAC systems. Besides
that, as a natural refrigerant, ammonia has a high latent heat, second only to water in
commonly recognized fluids. Therefore, it could provide better refrigerating effect per
unit of mass flow than any other refrigerant used in traditional vapor compression
systems.
In this section, a commonly used ammonia-based refrigeration system is introduced.
The refrigeration system in the indoor snow dome operates in two different modes
(operation mode which means the indoor snow dome is open to the public and
non-operation mode which means the indoor snow dome is in snowmaking period)
and the corresponding flow charts are shown in Figures 3 and 4 respectively (the
snowmaking method used here is the ice-breaking type).:
Figure 3. Operation mode Figure 4. Non-operation mode
As shown in Figures 3 and 4, the refrigeration system is a screw compression
ammonia system with an economizer. Economizers are often used in ammonia-
based refrigeration systems due to their many advantages. First, with the help of the
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economizer, liquid refrigerant is subcooled before it flows into the evaporator, thus
resulting in reduced enthalpy and a higher net refrigerating effect. Second, vapor
generated during subcooling is injected into the compressor through its compression
cycle and compressed from the economizer outlet pressure (which is higher than
suction pressure) to the discharge pressure, which produces additional refrigerating
capacity with less increase in unit energy input. Last but not least, compared with a
common single stage compression system, its COP can be increased by 10% to 20%.
Therefore, economizing is a good energy efficiency strategy for an ammonia-based
refrigeration system in an indoor snow dome. The operating principle is as follows:
In the operation mode (solid line), the high-pressure gaseous ammonia from the two
refrigeration units flows into an evaporative condenser and releases the condensation
heat, then flows into a high pressure storage tank. After that, a part of the high-
pressure liquid ammonia is throttled to flow into the shell side of the economizer
to evaporate and absorb heat, and its pressure decreases. Meanwhile, the other part
flows into the tube side of the economizer to be subcooled, and is throttled before
it flows into the evaporator to participate in the heat exchange with the secondary
refrigerant for the cooling requirement. Then liquid ammonia turns into gaseous
ammonia and is finally inhaled into the compressor to start the next refrigeration
cycle. In addition, flash steam from the economizer is inhaled into the medium
pressure filling port of the compressor. The two refrigeration units in Figure 3 are
both running under the same conditions.
In the non-operation mode (solid line), two refrigeration units are running under
different conditions. A portion of the liquid ammonia from the economizer flows into
the snowmaking system after throttling to produce the cold source for snowmaking,
and then the gaseous ammonia is inhaled into refrigeration unit #2. Whereas the
other portion of liquid ammonia from the economizer flows into the evaporator to
participate in the heat exchange with the secondary refrigerant; after this process,
the gaseous ammonia is finally inhaled into refrigeration unit #1. With the solenoid
valves’ opening controlled, the flow rate is controlled. In addition, the high pressure
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gaseous ammonia from the compressor splits in two paths: a part of it flows into the
evaporative condenser, the other part flows into the condenser to participate in the
heat exchange with the secondary refrigerant for the heating requirement (melting
snow).
Energy Consumption of the Commonly Used Ammonia-based Refrigeration System in an Indoor Snow Dome
The design of an indoor snow dome has a lot in common with that of cold storage
facilities; however, it also has its own characteristics as follows:
• Usually copes with great indoor and outdoor temperature differences, resulting in
high-demands on the refrigeration system.
• Substantial ground area and buildings with impressive structures which make
the energy consumption of the air-conditioning system much larger than the
conventional system of an air conditioned building.
• Requires artificial snowmaking methods to provide good skiing / snow
playground conditions.
• Requires a certain amount of fresh air supply.
• Requires a good lighting design as it is a sealed area.
From the above analysis, the energy consumption shares in an indoor snow dome are
introduced in this section.
Refrigeration system
Typically, an indoor snow dome is open 16 hours to the public with an air
temperature of -1.5°C ± 0.5°C. When it is closed, 4 hours of snow grooming is
done using a conventional snow grooming machine with air temperature falling
from the normal -1.5°C to -6.0°C. Also, 4 hours of snowmaking occur when the
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Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
air temperature is maintained at -6.0°C. This means the overall refrigeration load
consists of two types of loads: the refrigeration load and the snowmaking load which
results in different evaporative temperatures in the refrigeration system. As is seen
in Figures 3 and 4, a part of the high-pressure liquid ammonia is throttled to be
low-pressure ammonia liquid, then heat exchange between the liquid ammonia and
the secondary refrigerant (usually 40% ethylene glycol in mass) occurs in the plate
heat exchanger. After that, the gaseous ammonia is inhaled into the compressor.
This process is mainly to undertake the load of the air cooler, dehumidifier and the
secondary refrigerant flowing in the pipe under the ski slope if it is set. In addition,
it can provide cold water just above the freezing point for producing snow if the
snowmaking method is the compressed air type. The other part of the high pressure
liquid ammonia is throttled to be lower temperature liquid ammonia. This process is
usually carried out to produce snow if the snowmaking method is the ice-breaking
type.
Table 1 shows the refrigeration load of each system in a general indoor snow dome in
the specified situation in which the cooling specification of the dome, the outdoor air
temperature and humidity to be supplied are assumed and calculated uniformly.
Equipment system
Compressed
air type
Ice-breaking
type
Chemical
type
Indoor air temperature -5°C~-10°C -5°C -5°C
Floor area 24,000m2
The amount of fresh air taken in 2000m3/h
Air-conditioning load 4460kW 1670kW 1670kW
Fresh air load 740kW 740kW 740kW
Water supply cooling load or
snowmaking load 980kW 280kW 1280kW
Total load 6180kW 2690kW 3690kW
Table 1. Refrigeration load
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Then the corresponding rated electric energy capacity shown in Table 2 is calculated
for each equipment system based on the refrigeration load in Table 1.
Equipment system
Compressed air
type
Ice-breaking
type
Chemical
type
Air conditioning of dome 1260kW 450kW 450kW
Fresh air cooling 395kW 225kW 280kW
Floor cooling 510kW 450kW 510kW
Water supply 450kW 0kW 0kW
Snowmaking machine 300kW 260kW 0kW
Total load 2915kW 1385kW 1420kW
Table 2. Rated electric energy capacity
Snowmaking system
Energy consumption by the snowmaking system depends on the time spent on
snowmaking, snow quality, meteorological conditions and especially the snowmaking
method which differ a lot in energy consumption. As the snowmaking system is
interrelated to the refrigeration system, the snowmaking methods not only affect the
energy consumption of the snowmaking system, but also the refrigeration system.
As is seen in Table 2, the compressed air type requires a large rated electric energy
capacity; this is followed by the ice-breaking type and then the chemical type. As
for the refrigeration load, the compressed air type also ranks first, followed by the
chemical type and then the ice-breaking type. The ratios of refrigeration load and
rated electric energy capacity of the three snowmaking methods are 2.1, 1.9, and 2.6,
respectively. Although the chemical type is considered to be the most efficient, it is
rarely used in indoor snow domes. Little difference is seen between the compressed
air type and the ice-breaking type, so the selection of the snowmaking methods
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Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
should be based on other considerations, such as the initial cost, running costs and
snow quality.
Discussion of energy consumption in indoor snow dome
Based on the rated electric energy capacity in Table 2, someone might think that the
total energy consumption of an indoor snow dome is relatively large, a cause for
concern for the snow dome owners. However, the design values of the refrigeration
load and the corresponding rated electric energy capacity are under the worst case
scenario, which usually assumes the highest outdoor dry-bulb temperature. In fact,
the real operating conditions of the refrigeration system will be adjusted according
to the outdoor meteorological parameters. Thus, the actual total energy consumption
will be much lower.
For example, at the Shanghai Snow Dome (Shanghai Dashun Beihaidao) located at
121° eastern longitude and 31° northern latitude, the maximum daytime temperature
during the summer reaches over 38°C. The refrigeration system is ammonia-based
and the snowmaking method is the ice-breaking type. The design value of the
refrigeration load and the corresponding rated electric energy capacity are 2680kW
and 1155kW. If the system operates at full load conditions all the time, the annual
energy consumption is 1.01×107kW∙h, which is really large. In fact, the actual total
energy consumption will be reduced if the operating conditions of the refrigeration
system are regulated according to outdoor meteorological parameter changes
(regulating the condensing temperature or pressure of the refrigeration system is a
good way). Figure 5 shows the annual dry-bulb temperature frequency at all grades
in Shanghai. It seems that the hours of the dry-bulb temperature in each temperature
interval is 0h, 137h, 885h, 1430h, 1237h, 1373h, 1857h, 1538h, 290h, 13h. We can
say that the worst operating condition is when the dry-bulb temperature is higher
than 30°C, which only accounts for 3.5% of the whole year. Usually, for every
1°C reduction in the condensing temperature the power consumption mainly will
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decrease by about 3%. So it can be concluded that the total energy consumption will
decrease notably if some control strategies are implemented.
Figure 5. Annual dry-bulb temperature frequency at all grades in Shanghai
Different Energy Efficiency Improvement Strategies for Indoor Snow Domes
Heat Recovery Technology and Application
As indoor snow domes are great energy users, the potential for increased energy
efficiency is enormous. One option is to utilize heat recovery (or heat reclaim) from
condensers to heat the premises, such as restrooms, restaurant, equipment room and
so on. As is seen in Figure 4, the condensation heat also consists of two parts: most
of the condensation heat is released by the evaporative condenser and a part of it is
used as the heat source to conduct heat exchange with a secondary refrigerant for
heating requirements. For instance, in the defrosting process, after absorbing the heat
from the condenser, the hot secondary coolant flows in the cooling pipe to melt the
frost adhered to the cooling coils. This system is adopted because the operation is
stabilized and the energy consumed by heating is reduced.
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Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
Thermal storage technology in snow base
The fact that short term heat gains such as envelope gains and infiltration gains result
in a large cooling demand during snowmaking makes thermal storage an attractive
choice. Thermal storage is a major tool to reduce the cooling plant size and allow
a cooling effect to be produced during peak electricity periods. What is more, the
inertia mass slows down any tendency to rapid temperature fluctuations. However,
when the prospect of thermal storage was first considered, the requirement of long
charge (20 hours), short discharge (4 hours) and the high heat flux requirements
during snowmaking precluded the use of all available thermal storage systems, such
as low-temperature phase-change and sensible heat stores. Hence, a new medium
is required that provides slow charge with rapid depletion heat flux capacity. What
was needed was either some form of metal wool or a porous material with high
conductivity that is mixed with the ice, can lie on the floor pipes and allow rapid heat
flow into the concrete/ice mass. The medium chosen was activated alumina, which
is a relatively cheap, chemically inert medium readily available as an aggregate that
could be mixed into concrete and spread over floor-cooling pipes to provide thermal
inertia. Ice was also considered, but it had a low thermal conductivity which could
not contribute to rapid heat flow in the inertia mass. Figure 6 is the cutaway view of
snow base showing alumina and cooling pipes.
Figure 6. Cutaway view of snow base showing alumina and cooling pipes
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Various grades of alumina have been tested and a mix of high conductivity/low
porosity and high conductivity/high porosity was found to produce the best results
(see Table 3). The alumina, mixed with sand and cement, provides a high mass of
inertia. In a 10,000m2 snow center, the mass of concrete/alumina is shown in Table 3.
Mass Specific heat(kJ/kg∙K)
Cement 61 500kg 0.67
Sand 153 750kg 0.80
Ice in Concrete 61 500kg 2.07
Alumina 67 650kg 0.40
Ice in Alumina 30 420kg 2.70
Table 3. Comparing media
All in all, thermal storage reduces the amount of capital expenditure necessary to
meet the cooling requirement by a large percentage, thus making indoor snow a
commercial possibility. An ongoing benefit is being able to meet a majority of the
cooling requirement by running the chillers at 100% load during off-peak periods
and switching them off during peak periods (deriving the cooling fully from the
thermal store). Thermal storage provides flexibility by boosting the cooling effect for
special events and functions as a reliable standby during a major cooling breakdown.
Although the peak sizing of the cooling system is matched to the maximum ambient
conditions, the skiing/snow playground is actually more popular in the winter.
Therefore, real peak use is likely only in low ambient conditions, especially in low
winter temperature regions. This allows more use of the thermal storage than other
commercial buildings.
Ski Slope Structure Optimization Technology
As the snow on the bottom of the ski slope continues melting, water drainage should
be equipped in the ski slope structure, and a permeable chemical fiber board should
also be set between the bottom of the snow and the drainage, which can absorb the
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Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
water and lead it to the drainage. Furthermore, the entire bottom must be equipped
with waterproofing, which can protect the bottom from erosion caused by water.
Besides the ski slope, a double-deck external envelope is used with an exterior layer
of sun block which can minimize the heat produced by solar radiation. The material
of the interior envelope is polyurethane foam plastic board, and there is a layer that
consists of air in the middle which can form natural convection and further reduces
the heat load by solar radiation.
Recovery of melted snow technology
Since the whole system is designed for the purpose of energy-saving and good ski
slope conditions, new snow is always filled up, leaving snow always melting. As
a result, it is necessary to adopt an efficient recovery structure to drain the melted
snow. The concept is that a large deep layer of fresh snow is produced at night; this
then melts during the day as the room temperature is maintained above freezing.
As the snow melts, the water is collected in drain channels which are connected to
a main storage tank. The water is then filtered to remove the impurities of dirt, skin
and fabric fibers before being recycled to the ice makers. This ensures that the skiers
have fresh clean snow each day. The drain should be covered with a special mat and
snowfall is carried out on it (Chen Hua, 2001 (6)). Otherwise, as is seen in Figure 7,
melted snow flows from the surface into the snow pack (Victor Raguso, 2000 (7)). As
the temperature of the base is lower than the surface, the water finally freezes and
releases condensation heat which is entrained onto the recirculation of air coolers.
Thus, melted snow should be drained and reused in the cycle of snowmaking.
Figure 7. The structure of snow pack layer
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A Case Study of a Practical Engineering Application
Brief Introduction to an indoor snow dome in China
An indoor snow dome in Changsha in the south of China is introduced here to
present the practical issues.
The indoor snow dome in Changsha with a total investment of 8 billion yuan was
under construction from 2013 and will be completed in 2016. Figures 8 and 9 are the
internal and external design drawings.
Figure 8. Internal design drawing Figure 9. External design drawings
This indoor snow dome is not only intended to be the largest indoor snow dome in
the world, but it also has an indoor water world for entertainment, a group of high-
end hotels, and a business and shopping district. Therefore, it will be regarded as a
so-called comprehensive amusement and commercial world. The design conditions
are shown in Table 4:
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Item Value
Internal conditions
Temperature and relative humidity
during public occupancy -1.5°C ± 1°C℃
70%∼85%
Temperature and relative humidity
during snowmaking period-6°C ± 1°C℃
95%∼98%
External conditions
Average ambient dry point temperature in summer 35.8°C
Average ambient dry point temperature in winter -3°C
Table 4. Design parameters and set points
Featured Energy Efficiency Improvement Strategies in the Project
This indoor snow dome is constructed with the most advanced equipment and many
advanced technological innovations are devised. Some technical innovation measures
are introduced as follows.
• Insulated floor
The floor of the snow dome is made up of several elements:
• Hot glycol under floor heater mat where necessary.
• A suitable vapor seal, the floor construction shall be sealed against vapor
penetration and the type of barrier to be used shall be determined by a full
consideration of the existing conditions.
• 150mm extruded polystyrene insulation laid in two layers with staggered
joints to increase the temperature gradient through the cross section of the
floor construction, in order to achieve the operating temperature at the surface
specified by the engineer.
• The floor insulation will be finished with a 35mm profile heavy duty
galvanized sheeting to accommodate the floor glycol piping network
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with concrete mix with Thermogenesis (TGM), a thermal heat transfer
enhancement material added to the concrete mix.
• Air cooler
The design of the cooler is one of the most important as it affects not only
the temperature but also the humidity within the ski / snow playground
area. In this snow dome, a special coil will be used to provide the required
humidity without the use of reheat or dehumidifiers and it will not be blocked
by the free floating snow that is sucked back into the cooler return. By using
a mixture of coil spacing, the bypass factor provides the humidity levels
required for the freezing of the water in the outlet plume of the snowgun.
Efficient defrosting is also an issue not only to reduce operating costs but also
for health and safety requirements; the coil fin design is also important in this
matter given that if the coil is not defrosted properly, ice will build up on the
rear face which could then fall down onto the skiers below .
The design of the fans is critical, as small particles of snow will pass through
the cooler and adhere to the low pressure part of the fan blades; this is
increased rapidly if the coil becomes blocked and the fan goes into a stall
condition as it will draw snow in through the fan outlet. The correct type of
aerofoil blade and operating speed ensures the fan performance is not affected
throughout the snowmaking period.
• Under snow cooling
Producing good quality snow is important. Once snow is produced, it changes
its crystalline structure almost immediately. So, to provide an insistent surface
that is hard wearing and economical to maintain, the design of the under
snow cooling matrix is as important as the snow production equipment. By
providing a temperature gradient through the snow, the snow crystals are
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regenerated; and although the density changes, the quality of the under snow
is improved to provide a solid base. The matrix comprises cooling tubes
through which the cold glycol passes and these are surrounded by a mixture
of activated alumina and concrete which are located in a profile sheet over the
floor insulation. This provides a firm base for the snow layer to stop the snow
slipping down the slope and forming an avalanche.
• Ventilation
As the indoor snow dome is basically a large cold store, fresh air is required
for the occupants; this is expensive as the air has to be cooled down to the
same temperature and humidity as the space, otherwise misting will occur
and the snow layer will be damaged. The ventilation system is based on
using a variable air volume to meet the occupancy levels, this is achieved by
monitoring the CO2 levels within the extract air and controlling the supply air
volume with variable speed fans. The energy is recovered from the extract air
by means of a thermal wheel and this precools and dehumidifies the ambient
air. A set of two coils cool the air down to the room condition and, because
frost forms on these coils, they are operated and defrosted in sequence to
provide a constant supply of air.
22 © IIAR 2015 International Technical Paper #3
2015 IIAR Industrial Refrigeration Conference & Exhibition, San Diego, CA
Prediction of energy consumption
Figure 10 shows the annual dry-bulb temperature frequency at all grades in
Changsha. It can be seen that the hours of dry-bulb temperature between -5°C and
30°C accounts for more than 95%. As is mentioned above, this will bring remarkable
energy saving potential and the prediction of energy consumption is listed below.
Figure 10. Annual dry-bulb temperature frequency at all grades in Changsha
Based on the meteorological parameters, the refrigeration loads for different system
equipment in this indoor snow dome using different snowmaking methods are
predicted in detail respectively for a single day in July which can be called the worst
case scenario. The results are shown in Figures 11 and 12.
International Technical Paper #3 © IIAR 2015 23
Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
Figure 11. Prediction of refrigeration load for a single day in July (snowmaking method: compressed air type)
Figure 12. Prediction of refrigeration load for a single day in July (snowmaking method: ice-breaking type)
As is shown in Figures 11 and 12, it is noteworthy that the refrigeration load of the
compressed-air type snowmaking system is larger than that of the ice-breaking type.
This phenomenon coincides with the data in Table 2. Then the energy consumption
in each month is also obtained, as shown in Table 5.
24 © IIAR 2015 International Technical Paper #3
2015 IIAR Industrial Refrigeration Conference & Exhibition, San Diego, CA
Month Compressed-air type Ice-breaking type
Max.
Power(kVA)
Total.
Power(kW∙h)
Max
Power(kVA)
Total
Power(kW∙h)
January 1,779 963,531 2,011 1,009,334
February 2,054 945,279 2,292 989,258
March 2,157 1,098,013 2,399 1,145,486
April 2,214 1,126,125 2,460 1,169,916
May 2,354 1,210,480 2,603 1,241,951
June 2,393 1,181,829 2,642 1,226,981
July 2,409 1,274,498 2,658 1,304,444
August 2,325 1,269,282 2,575 1,298,500
September 2,302 1,183,783 2,551 1,230,414
October 2,198 1,165,602 2,445 1,213,160
November 2,064 1,040,889 2,305 1,086,386
December 1,883 1,007,404 2,117 1,048,619
Table 5. Energy consumption by month
From Table 5, it can be calculated that the energy consumption totals of the two types
of snowmaking systems for the whole year are 13,466,715 kW∙h and 13,964,448
kW∙h, respectively. These figures are close to each other, so there is a need to
compare other aspects of the two snowmaking methods. The main issue is comparing
on the same scale as most ice-breaking type systems produce very small quantities of
snow, so the dirt levels become high and the overall quality is low. In fact, the system
is always designed based on the cooling capacity for the normal operation so that
the chillers are selected for this duty and not for the snowmaking; so in theory the
capital and running costs for this period should be the same. Besides this, for the ice-
breaking type, if they make ice during the day and store it, then the operating costs
for this period as well as the overall capacity of the chillers will be higher.
In other words, in order to investigate the energy efficiency improvement strategies
mentioned above, it is important that the refrigeration load, rated electric energy
International Technical Paper #3 © IIAR 2015 25
Energy efficiency improvement strategies of ammonia-based refrigeration system used in indoor snow dome
capacity and the corresponding energy consumption are calculated in detail. In
operation mode, the refrigeration load consists of the air-conditioning load and the
secondary refrigerant cooling load. While in non-operation mode, the refrigeration
load consists of air-conditioning load, secondary refrigerant cooling load and water
supply cooling load or snowmaking machine load. Besides, the refrigeration load
should be no less than the total of the envelope load, fresh air load, facility load,
lighting load, dehumidification, human body load and snow grooming load. Then the
energy efficiency can be obtained by calculating the value of the total load divided by
the corresponding rated electric energy capacity. The detailed energy efficiency will
be explained in detail in the future.
Conclusions
In this paper, a general understanding of the various systems such as the refrigeration
system and the snowmaking system in an indoor snow dome can be acquired.
Furthermore, it is obvious that the energy consumption in an indoor snow dome
is tremendous, resulting in immense running costs (especially the electricity cost).
Using energy efficiency improvement strategies such as wide fin spacing, heat
recovery, thermal storage in the snow base, ski slope structure optimization and
recovery of melted snow for snowmaking, the annual energy consumption of
operating the indoor dome will undergo a sharp change. If the attention is paid
to load change, it can be said that the load changes from 100% to about 20%.
Therefore, with the increasingly high demand for indoor snow domes in urban areas
and areas without snowfall, the most important consideration is the application of
energy-saving strategies. It is indispensable to reexamine and attain further energy
efficiency improvement strategies from a different viewpoint for indoor snow domes.
26 © IIAR 2015 International Technical Paper #3
2015 IIAR Industrial Refrigeration Conference & Exhibition, San Diego, CA
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