Author: Mycond Technical Department
Ice arenas face a critical engineering challenge: moisture condensation on the cold ice surface at -3°C to -7°C when it comes into contact with warmer arena air (+10...+15°C). This physical process leads to serious consequences: fog formation over the ice, reduced visibility for athletes and spectators, increased load on the refrigeration system, corrosion of metal structures, and deterioration of ice quality.
The problem is often exacerbated by design errors, where engineers calculate only the ventilation system, ignoring the fact that with high outdoor humidity, increasing ventilation supply only makes things worse. An effective solution requires a comprehensive approach that accounts for the physics of condensation and integrates dehumidification, ventilation, and heating systems.
The physics of condensation in ice arenas: psychrometric conditions
Moisture mass transfer to the cold ice surface occurs via diffusion and convection. When warm, moist air contacts the cold ice surface, the boundary layer of air cools. When the temperature of this layer drops below the dew point, condensation occurs.
Consider a psychrometric analysis: if the arena air temperature is +12°C with 60% relative humidity, the dew point is about +4°C. Since this is much higher than the ice temperature (-5°C), condensation on the ice surface is inevitable.
The condensation mechanism has two stages. First, water vapor condenses on the ice surface, releasing the latent heat of condensation (about 2500 kJ/kg). Then the condensate freezes, releasing the heat of fusion (about 335 kJ/kg). The total heat (approximately 2835 kJ/kg of moisture) adds extra load to the refrigeration system, which is already working to maintain the low ice temperature.
A visible consequence is fog formation over the ice. When the air immediately above the surface cools below the dew point, moisture condenses as fine droplets that remain suspended. The higher the relative humidity of the air, the denser the fog becomes.
Quantifying condensation intensity: with arena air moisture content of 6 g/kg at +12°C, the dew point is about +4°C. The difference from the ice temperature (-5°C) is 9°C, causing intensive condensation. With a moisture content of 4 g/kg, the dew point drops to -2°C, the difference is only 3°C, and condensation will be minimal.
Apart from fog, condensation causes corrosion of the arena’s metal structures and degrades ice quality due to unevenness from frozen condensate, negatively affecting sporting events.
Sources of moisture ingress into the ice arena: quantitative analysis
To control humidity effectively, all sources of moisture entering the arena must be considered. Here are the main ones.
Moisture released by spectators: An adult spectator at rest emits about 50 g/h of moisture through breathing and skin. For an arena with 1000 spectators, this amounts to roughly 50 kg/h. For event durations of 2–3 hours, total moisture ingress can reach 100–150 kg. These values are indicative and used for engineering calculations.
Moisture release from the ice resurfacing machine: The resurfacer uses hot water (about +60°C) to flood and shave the ice surface. When hot water is poured onto a cold surface, part of it evaporates rapidly. With 300 liters of water, 5–10% may evaporate, i.e., 15–30 kg per operation. Since the machine typically runs 2–3 times a day, this adds 30–90 kg of moisture daily.
Infiltration of outdoor air: Doors for the resurfacer and athlete exits open periodically. Opening doors with an area of 12 m² for 2–3 minutes in winter (outdoor air -5°C, 80% RH, moisture content about 2 g/kg) brings in cold air with low absolute moisture content. In summer the situation changes dramatically: outdoor air (+25°C, 70% RH, moisture content about 14 g/kg) brings in 30–50 m³ of humid air with each opening, equivalent to 0,4–0,7 kg of moisture per opening.
Moisture from auxiliary rooms: Locker rooms with showers are intense moisture sources. One shower can release up to 200 g/min of moisture. If ventilation in these rooms is insufficient, moisture spills into the arena. With 20 players showering for 15 minutes, up to 60 kg of moisture can be released.
Method for calculating total moisture gains: For engineering analysis, total moisture gains are calculated as the sum from all sources. For a typical arena with 1000 spectators at full capacity during a hockey game, a rough estimate is: 50 kg/h (spectators) + 10 kg/h (resurfacer, averaged) + 5 kg/h (infiltration) + 15 kg/h (showers, averaged) = 80 kg/h. This is indicative and should be refined for each specific project.
Psychrometric balance: defining the target moisture content
The target air moisture content in an ice arena is set so that the air dew point is at least 2–3°C below the ice surface temperature to reliably prevent condensation.
The algorithm for determining the target moisture content includes:
- Determine the ice surface temperature (typically -3°C to -7°C depending on the sport: hockey about -5°C, speed skating down to -7°C, figure skating about -4°C).
- Set a safety margin: the dew point must be 2–3°C below the ice temperature. For example, if the ice is -5°C, the target dew point should be -7°C to -8°C.
- From the psychrometric chart for the arena air temperature (e.g., +12°C) and a dew point of -8°C, determine the target moisture content (about 3.5 g/kg).
- Compare to current moisture content. If the current is 6 g/kg, remove 2.5 g of moisture from each kilogram of arena air.
The arena moisture balance is given by: moisture ingress (total gains) = moisture removal (dehumidifier capacity + exhaust ventilation removal). Balance condition: removal must be greater than or equal to ingress.
The role of ventilation in maintaining humidity depends on the season. If the outdoor moisture content is lower than indoors, supply ventilation helps remove moisture. For example, in winter: outdoor air -10°C, 80% RH, moisture content about 1.5 g/kg; indoor air +12°C, moisture content 6 g/kg. Each m³/h of supply removes (6 - 1.5) × 1.2 / 1000 = 0.0054 kg/h of moisture.
In summer, it changes dramatically: outdoor air +25°C, 70% RH, moisture content 14 g/kg, which is far higher than indoors. In this case, increasing supply makes things worse by adding moisture. Air must then be recirculated through a dehumidifier.
Method for calculating required dehumidifier capacity
Step 1: Determine the moisture removal deficit. If total moisture gains are 80 kg/h and ventilation removes 20 kg/h (under winter conditions with low outdoor moisture content), the deficit is 60 kg/h. The dehumidifier must cover this deficit.
Step 2: Account for operating schedule. If the dehumidifier runs 24/7, the required capacity equals the deficit. If it runs only during events (e.g., 8 h/day) and moisture gains are concentrated in that period, the required capacity equals the deficit over those hours. If moisture accumulates throughout the day (resurfacer, infiltration) while the dehumidifier runs limited hours, capacity or runtime must be increased. For example, if daily moisture ingress is 500 kg/day and the dehumidifier runs 16 hours, the minimum required capacity is 500 ÷ 16 = 31 kg/h.
Step 3: Capacity margin. The dehumidifier should not run at its limits. A typical margin is 20–30% above the calculated capacity to cover unforeseen loads (larger audiences, humid summer days with high infiltration). If the calculated capacity is 60 kg/h, the recommended installed capacity is 60 × 1.25 = 75 kg/h.
Step 4: Capacity distribution. For large arenas, it is advisable to use several dehumidifiers instead of one large unit. This improves airflow uniformity, provides redundancy in case of a unit failure, and allows stepwise modulation based on arena load.
Detailed numerical example: The arena has 2000 m² of ice, a hall volume of 15000 m³, and seating for 1000 spectators. Total moisture gains during the event are 80 kg/h. Winter ventilation removes 20 kg/h, deficit is 60 kg/h. The event lasts 3 hours, the dehumidifier runs 12 hours per day (before, during, and after the event). Daily moisture ingress: 80 × 3 (during event) + 15 × 21 (resurfacer and infiltration at other times) = 555 kg/day. Required capacity: 555 ÷ 12 = 46 kg/h. With a 25% margin: 46 × 1.25 = 58 kg/h. Recommendation: two dehumidifiers at 30 kg/h each or three at 20 kg/h for flexible control and redundancy.
Interaction of ventilation, heating, and dehumidification systems
Ventilation and dehumidification are not alternatives but complementary systems. Ventilation provides code-required fresh air for spectators (about 20–30 m³/h per person), while dehumidification controls humidity.
Coordination algorithm for ventilation and dehumidification:
- If outdoor moisture content is lower than the target indoor moisture content, increasing supply helps remove moisture. Supply can be maximized up to code requirements or slightly above.
- If outdoor moisture content is close to or higher than indoor, supply is limited to the minimum required by codes, and the dehumidifier in recirculation handles the primary moisture removal.
- If outdoor moisture content is very high (humid summer days), reduce supply to the code minimum and increase dehumidifier capacity or runtime.
Air recirculation through the dehumidifier is organized so the unit draws air from the upper zone of the hall, where it is warmer and more humid due to heat from spectators and evaporation from the ice. After drying, the unit warms the air due to moisture condensation (heat is released) and returns it to the hall. A typical recirculation rate through the dehumidifier is 1–2 hall volumes per hour for effective mixing and drying.
A condensing dehumidifier releases the latent heat of condensation (about 2500 kJ/kg of removed moisture) plus compressor heat. If the dehumidifier removes 60 kg/h of moisture, the thermal output is 60 × 2500 ÷ 3600 ≈ 42 kW. This heat enters the hall and can raise the air temperature. If the hall temperature must not exceed +15°C, dehumidifier operation must be coordinated with the heating or cooling system: reduce heating or increase cooling to offset the dehumidifier’s heat.
To determine the optimal balance between ventilation and dehumidification, it is recommended to calculate the average outdoor moisture content for each month using regional climate data. In winter months, the ratio of moisture removal by ventilation to total removal can be 30–50% (ventilation contributes significantly), while in summer it may be 0–10% (ventilation contributes almost nothing).
Energy efficiency of preventing condensation: saving refrigeration capacity
When moisture condenses on the ice surface, it releases the latent heat of condensation (2500 kJ/kg), and then the condensate freezes, releasing the heat of fusion (335 kJ/kg). The total heat (2835 kJ/kg of moisture) loads the refrigeration system and must be removed to maintain ice temperature.
Quantifying the additional load: if 80 kg/h of moisture enters the arena and all of it condenses on the ice, the additional thermal load is 80 × 2835 ÷ 3600 = 63 kW. For a refrigeration system with a coefficient of performance (COP) of about 2.7 (typical for ice arenas), this means additional power consumption of 63 ÷ 2.7 ≈ 23 kW. Over 10 hours per day, that’s 230 kWh daily, or about 7000 kWh per month.
If a dehumidifier is installed that removes 60 kg/h of moisture before it reaches the ice, only 20 kg/h remains to condense. The added refrigeration load drops to 20 × 2835 ÷ 3600 = 16 kW, with power consumption of 6 kW. The savings are 23 - 6 = 17 kW or 170 kWh per day.
A condensing dehumidifier consumes electricity to run the compressor. The specific energy consumption of a typical condensing dehumidifier is about 0.6–0.8 kW per 1 kg/h of capacity. For a 60 kg/h dehumidifier, consumption is about 40 kW, while refrigeration savings are 17 kW. At first glance, the energy balance seems negative; however, the heat from the dehumidifier (about 42 kW for 60 kg/h) partially offsets the hall’s heating demand.
Total savings consist of three components:
- Reduced electricity consumption of the refrigeration system
- Reduced hall heating demand (heat from the dehumidifier)
- Reduced envelope heat losses due to lower relative humidity
A detailed energy balance should account for all three components and be performed for the specific project. Indicatively, total savings can be 20–40% of the dehumidifier’s consumption depending on climate and operating mode.
Additional benefits of preventing condensation include longer service life of metal structures (reduced corrosion), improved ice quality (no unevenness from freezing condensate), and better visibility for athletes and spectators (no fog).
Common design mistakes in humidity control systems
Mistake 1: Underestimating moisture emissions from spectators during mass events. Designers often calculate moisture gains based on average occupancy (50–60%), not accounting for peak loads at full capacity during finals or major events. Consequence: the dehumidifier cannot handle peak loads, fog forms, and visibility deteriorates.
Mistake 2: Ignoring infiltration through doors in summer. Designers calculate the moisture balance for winter conditions when outdoor air is dry and fail to check summer conditions with high outdoor moisture content. Consequence: in summer, door openings bring in large amounts of humid air, and the dehumidifier cannot keep up.
Mistake 3: Lack of coordination between ventilation and dehumidification. Systems are designed by different contractors or at different times without integration. Ventilation operates at maximum supply year-round, bringing in humid outdoor air in summer, which increases the dehumidifier load or makes humidity control impossible. Consequence: inefficient operation of both systems, high energy consumption, inadequate dehumidification.
Mistake 4: No automatic humidity control and system integration. The dehumidifier and ventilation are controlled manually or by separate timers without humidity sensor feedback. Consequence: suboptimal operation, energy waste, or insufficient drying when conditions change.
Mistake 5: Insufficient capacity margin for the dehumidifier. The dehumidifier is sized exactly to the calculated load with no reserve. When arena occupancy increases or weather is unfavorable, the unit operates at its limits and cannot cope. Consequence: periodic fog and condensation.
Mistake 6: Incorrect placement of dehumidifier air intake and discharge. Intake is located in the lower zone near the ice, where air is colder with lower moisture content, with discharge in the same zone. Consequence: short-circuiting circulation; the dehumidifier processes cold, already dry boundary-layer air and does not affect the warm, moist air in the upper zone.
Mistake 7: Ignoring moisture from the ice resurfacer. Designers overlook the intense evaporation of hot water during ice flooding, considering it minor or occasional. Consequence: after resurfacing, humidity spikes and fog forms, persisting for 30–60 minutes until it gradually dries.
Limits of standard approaches: when to adjust the methodology
Very low ice temperatures (speed skating): For speed skating, ice temperature can drop to -10°C or lower to ensure maximum hardness. At such temperatures, the difference between ice temperature and dew point increases, intensifying condensation. Standard sizing may underestimate required dehumidifier capacity. Adjustment: increase calculated capacity by 30–50% or reduce the target moisture content to 2.5–3 g/kg instead of the typical 3.5–4 g/kg.
Arenas with exposed roof structures or large glazing areas: Older or atypical buildings may have large cold surface areas besides the ice where moisture also condenses (uninsulated roof, large windows in cold periods). The standard method considers only condensation on the ice. Adjustment: calculate additional condensation on other cold surfaces using a similar method and add it to the overall moisture balance.
Multifunctional halls with transformation: If the hall is used as both an ice arena and a concert or sports hall (ice covered by flooring), the humidity regime changes drastically. Without ice, there is no cold surface, and the need for dehumidification decreases or disappears. A constant-capacity dehumidifier is inefficient. Adjustment: provide stepwise or modulating capacity control and the ability to switch the dehumidifier off entirely in non-ice mode.
Older buildings with high air leakage: Older facilities may have high infiltration through envelope leaks, old windows, and doors. Calculated moisture ingress via infiltration may be significantly underestimated. Adjustment: conduct an airtightness assessment, correct the infiltration estimate, and consider improving building airtightness before selecting the dehumidifier.
Regions with extremely humid climates: In tropical or subtropical regions, outdoor moisture content in summer can be 18–22 g/kg. Even small infiltration or supply introduces large amounts of moisture; ventilation does not help at all, and full recirculation through a dehumidifier is required. Standard methods may underestimate the problem’s scale. Adjustment: minimize outdoor air to the absolute code minimum, provide additional dehumidifier capacity, and consider adsorption dehumidifiers (more effective at high outdoor temperatures).
Regulatory limits on air humidity: Some regions or standards may set a minimum relative humidity for spectator comfort (e.g., not below 30–35%). At +12°C hall air and 30% RH, the moisture content is about 2.5 g/kg, and the dew point is about -10°C. If the ice is -5°C, a 5°C margin is sufficient. But if the standard requires 40% RH, the moisture content rises to 3.5 g/kg, dew point is -4°C, margin is only 1°C, and condensation is possible. Adjustment: agree with regulators on lower relative humidity for ice arenas or raise the hall temperature to increase the margin.
Frequently asked questions (FAQ)
Can increased ventilation replace a dehumidifier?
It depends on outdoor moisture content. If outdoor moisture content is lower than the target indoor value (typically in winter, outdoor 1–2 g/kg, target indoor 3.5–4 g/kg), increasing supply helps remove moisture. However, the required airflow can be very large.
Numerical example: 60 kg/h of moisture must be removed. If outdoor moisture content is 1.5 g/kg and indoor is 6 g/kg, the difference is 4.5 g/kg. To remove 60 kg/h, supply needed is 60 ÷ 4.5 ÷ 1000 ÷ 1.2 = 11111 m³/h. For a hall volume of 15000 m³, this is an air-change rate of 11111 ÷ 15000 = 0.74 per hour — quite high. Heating such a large supply flow from -10°C to +12°C requires about 82 kW of thermal power.
In summer, when outdoor moisture content exceeds indoor, increasing supply makes the situation worse. Therefore, a dehumidifier is essential.
What is the optimal relative humidity in an ice arena?
The question is incorrect. The optimal parameter is not relative humidity but moisture content. Relative humidity depends on air temperature and does not uniquely define condensation. Dew point is the criterion for preventing condensation.
Algorithm for determining optimal moisture content: ice temperature (e.g., -5°C); dew point must be at least 2–3°C lower (from -7°C to -8°C); hall air temperature (e.g., +12°C). From the psychrometric chart for +12°C and a dew point of -8°C, the moisture content is about 3.5 g/kg. The corresponding relative humidity is about 33%.
If the hall temperature is raised to +15°C at the same 3.5 g/kg moisture content, RH drops to about 28%, but the dew point remains -8°C, and the condensation prevention criterion holds. Therefore, the optimal parameter is 3–4 g/kg moisture content, not relative humidity.
How long does it take to dry the hall after a mass event?
It depends on the excess moisture accumulated, dehumidifier capacity, and hall volume.
Numerical example: Hall volume 15000 m³, air density 1.2 kg/m³, air mass 18000 kg. After the event, moisture content rose from the 3.5 g/kg target to 6 g/kg, an excess of 2.5 g/kg. Excess moisture mass in the hall air: 18000 × 2.5 ÷ 1000 = 45 kg.
If the dehumidifier is 60 kg/h and operates solely to reduce moisture (no new gains), drying time is 45 ÷ 60 = 0.75 hours or 45 minutes.
In reality, the dehumidifier does not process the entire hall in one pass; it operates on recirculation. Effectiveness depends on air mixing. If the recirculation rate through the dehumidifier is one hall volume per hour, effective mixing and drying may take 1.5–2 hours.
Does the type of ice (hockey, figure skating, curling) affect dehumidifier selection?
Yes, indirectly via ice temperature. Hockey requires hard ice at about -5°C, figure skating prefers softer ice at about -3...-4°C for better blade grip, and curling requires highly specific pebbled ice at about -5...-7°C.
Lower ice temperature increases the difference from the dew point, intensifying condensation and requiring a lower target moisture content. For curling at -6°C ice temperature, the target dew point should be about -9°C, which corresponds to about 3 g/kg at +12°C hall temperature. For figure skating at -3°C ice temperature, the target dew point is -6°C, about 4 g/kg.
Thus, curling requires higher dehumidifier capacity or lower moisture gains than figure skating under otherwise equal conditions.
How does opening arena doors affect the moisture balance, especially in summer?
The impact of door openings on the moisture balance depends critically on the season and can significantly change all calculations, especially in summer.
In winter, when outdoor air is cold (e.g., -5°C) with 80% RH, its moisture content is only about 2 g/kg. Opening doors with an area of 12 m² for 3 minutes can bring about 50 m³ of air with 2 g/kg moisture content. Total moisture: 50 × 1.2 × 2 ÷ 1000 = 0.12 kg per opening. This is even beneficial as it lowers the average arena moisture content.
In summer, when outdoor air is +25°C at 70% RH, moisture content reaches 14 g/kg. The same door opening brings in 50 × 1.2 × 14 ÷ 1000 = 0.84 kg of moisture. If doors open 10 times a day, the additional ingress is 8.4 kg.
For arenas actively used in summer, it is recommended to install air curtains on doors, create vestibules/airlocks, or provide additional dehumidifier capacity to account for this moisture source.
Conclusions
Humidity control in ice arenas is a critical engineering task that cannot be solved by ventilation alone due to seasonal changes in outdoor moisture content. The key parameter is not relative humidity but moisture content and dew point. The dew point must be at least 2–3°C below the ice temperature to reliably prevent condensation.
The dehumidifier selection method is based on the moisture balance: calculate all moisture sources (spectators, resurfacer, infiltration, showers), determine ventilation’s contribution to removal by season, and cover the deficit with a dehumidifier with a 20–30% capacity margin.
The dehumidifier and ventilation must operate in coordination, not as competing systems. In winter, ventilation helps remove moisture; in summer, the dehumidifier in recirculation carries the main load. Heat from the dehumidifier partly offsets hall heating demand, and preventing condensation reduces refrigeration load. A detailed energy balance may show total savings of 20–40% of the dehumidifier’s consumption.
Common design mistakes (underestimating peak gains, ignoring summer infiltration, lack of system coordination) lead to fog, structural corrosion, and increased energy consumption. Standard approaches require adjustments for extreme conditions (very low ice temperatures, older leaky buildings, humid climates).
Design engineers are advised to perform a detailed moisture balance for all seasons and operating modes, provide dehumidifier capacity margin, ensure automatic coordination of ventilation and dehumidification based on humidity sensor data, and consider energy efficiency holistically (cooling + heating + dehumidification).
All numerical values used in the article are engineering guidelines and depend on project-specific conditions.
