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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.

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International Institute of Ammonia Refrigeration. They are not official positions of the

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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

International Technical Paper #3 © IIAR 2015 3

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

4 © IIAR 2015 International Technical Paper #3

2015 IIAR Industrial Refrigeration Conference & Exhibition, San Diego, CA

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.



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



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



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.



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



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



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



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



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



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



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.



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



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



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



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:



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



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



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.



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.



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.



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



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.



References

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Chapter 2

2) Chen Hua, Zou Tonghua. Design and Energy Conservation of Indoor Ski Dome

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3) Clulow, Malcolm G. Indoor Snowmaking [J]. ASHRAE Journal. Vol. 48 (7),

2006: 18-23

4) Hua Jun, Chen Yiren, Liu Jianhua, Jia Zhaokai. Design of air conditioning

systems for Qiaobo Ice and Snow World [J]. Journal of HV&AC. Vol.36 (3),

2006: 66-71

5) Katunori Shibata, Special Edition: Sport & Leisure-related Freezing Facilities and

Equipment [J], CAR Magazine, 2004

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slopes, [M] (CTC Eco-Snow technologies manual)

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2004:72-72

8) Victor Raguso. Guidebook for coaches and officials-Chapter 11 Ice, Snow, and

Snow Morphology [M].New York State Ski Racing Association. 2000:1-20

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