MEASUREMENT AND MODELLING OF ICE RINK HEAT LOADS
Mazyar Karampour
Master of Science Thesis KTH School of Industrial Engineering and Management Energy Technology Department EGI-2011-094MSC Division of Applied Thermodynamics and Refrigeration SE-100 44 STOCKHOLM
Measurement and Modelling of Ice Rinks Heat Loads
Master of Science Thesis EGI 2011/ETT:094MSC
Measurement and modelling of ice rink heat loads
Mazyar Karampour
Approved Examiner Supervisor Date Björn Palm Joachim Claesson Commissioner Contact person
Master student: Mazyar Karampour Forskarbacken 19/1508 11415 Stockholm Registration Number: 801012-6558 Department Energy Technology Degree program Sustainable Energy Engineering Examiner at EGI: Prof. Dr. Björn Palm Supervisor at EGI: Dr. Joachim Claesson Supervisor at Industry: Eng. Lic. Jörgen Rogstam
2
Measurement and Modelling of Ice Rinks Heat Loads
ABSTRACT Ice rinks are among the most energy intensive public buildings in developed and developing countries. According to a research on Swedish ice rinks; a typical ice rink consumes approximately 1185 MWh/year which leads to more than 300 GWh/year for the 342 Swedish indoor ice rinks. The refrigeration system is usually the largest consumer by 43% average share of the total energy consumption. To decrease the refrigeration system energy demand, there are a variety of energy efficiency techniques known and available but the key to select the best ones is finding the major heat loads on the ice sheet and refrigeration system, which is unique for each ice rink. To fulfil this objective and in addition to review literature, this study has two main approaches. The first approach is to measure and evaluate the performance of the refrigeration system in two ice rinks, called Norrtälje and Älta. The estimated cooling capacity is approximately equal to the total heat load on the ice plus the heat gains in the distribution system. This goal has been accomplished by using a performance analyser called “ClimaCheck” which is based on an “internal method” because it uses the compressor as an internal mass flow meter and consequently, there is no need for an external one. The refrigerant mass flow rate is calculated by an energy balance over the compressor. By knowing the mass flow, enthalpy of the refrigerant, etc. the cooling capacity and COP of the system can be calculated. While the total heat load is known by the first approach, the second approach tries to discover different heat loads shares by analytical modelling. The measured physical and thermodynamical parameters plus the ice rink geometrical characteristics are input to the heat transfer correlations to estimate the heat load magnitude. The results of the measurements show that the total energy consumption in Norrtälje is about two third of Älta. The main reasons for this less energy consumption are smarter control systems for compressors and pumps, better ventilation distribution design and 1°C-2°C higher ice temperature. Analytical modelling for a sample day has estimated that about 84% of the total heat loads is originated from the heat loads on ice sheet while the distribution system causes the remaining 16%. Moreover, calculations show that convection plus small portion of condensation (altogether 36%), radiation (23%), ice resurfacing (14%) and lighting (7%) are the largest heat loads in winter while in summer condensation is another significant heat load (10%). Comparing two six-hour periods, one without ice resurfacing and four resurfacings in the second one, 30% more cooling demand has been calculated for the second period. Furthermore, it has been shown that the evaporator to brine is the contributor for 66% of the heat transfer resistances from ice to evaporator while brine to bottom ice and bottom to top ice accounts for 27% and 7% respectively. To conclude, a parallel “performance analysis of the refrigeration system” and “heat loads estimation” proves to be a useful tool for adopting proper design and control for energy efficient operation.
Key words: Ice Rink, Refrigeration, Heat Load, Power Consumption, Energy Efficiency, Modelling, Measurement
3
Measurement and Modelling of Ice Rinks Heat Loads
ACKNOWLEDGMENT
I like to express my deep appreciation and respect to Jörgen Rogstam, for his kind support, valuable lessons and never getting tired of my endless questions. Special thanks to my supervisor at KTH, Dr. Joachim Claesson and Kenneth Weber at ETM Kylteknik AB for their helpful comments and discussions. Kenneth was really a generous person in sharing the valuable experiences with me. Thanks to Swedish Energy Agency for financing this research as part of the Stoppsladd project. I am grateful to Jakob Månberg (ClimaCheck), Ari Penttilä (Prorink), Antoni Gosalvez (Mayekawa- MYCOM), John Ekwall (Swedish Meteorological and Hydrological Institute), Torbjörn Thoresson (REFCALC) and Pavel Makhnatch for their help to provide me some required data. I should thank Matthias Dahlberg for making the company Energi & Kylanalys a pleasant and friendly atmosphere to work.
The last thanks to my family, for their lifelong support.
4
Measurement and Modelling of Ice Rinks Heat Loads
CONTENTS 1. Introduction ...... 9 1.1 Objectives ...... 10 1.2 Methodology ...... 10 1.3 Scope and limitations ...... 11 2. Ice rinks ...... 12 2.1 Ice rink energy systems ...... 12 2.2 Ice rink energy systems shares ...... 18 2.3 Ice rink refrigeration system ...... 19 2.3.1 Ice pad structure and piping arrangement ...... 21 2.4 Heat loads in ice rinks ...... 23 2.4.1 Convection-Condensation ...... 23 2.4.2 Radiation ...... 23 2.4.3 Conduction ...... 23 2.5 Energy efficiency in ice rinks ...... 25 2.5.1 Heat loads decrease ...... 25 2.5.2 Refrigeration and distribution system performance improvement ...... 26 2.5.3 Ice/concrete slab quality enhancement ...... 27 3. Experimental measurements ...... 28 3.1 Ice rinks ...... 28 3.1.1 Norrtälje ice rink...... 28 3.1.2 Älta ice rink ...... 30 3.2 Performance analyser - ClimaCheck ...... 31 3.2.1 Energy balance method ...... 32 3.2.2 ClimaCheck method modification ...... 34 3.3 Measurement results ...... 36 3.3.1 “Cooling chain” temperatures ...... 36 3.3.2 Evaporation/Condensation temperatures ...... 37 3.3.3 Brine and coolant temperatures ...... 38 3.3.4 Air temperature and relative humidity over ice, indoor and outdoor ...... 39 3.3.5 Electric power input and cooling capacity ...... 39
5
Measurement and Modelling of Ice Rinks Heat Loads
3.3.6 Total energy consumption ...... 40 4. Analytical modelling ...... 42 4.1 Heat loads...... 42 4.1.1 Radiation ...... 43 4.1.2 Convection ...... 44 4.1.3 Condensation ...... 45 4.1.4 Lighting ...... 47 4.1.5 Ground Conduction ...... 48 4.1.6 Brine headers ...... 48 4.1.7 Ice resurfacing ...... 49 4.1.8 Pump work ...... 50 4.1.9 Skaters ...... 50 4.1.10 Results for heat loads shares ...... 51 4.2 Heat flux method ...... 53 4.2.1 Results ...... 54 4.3 Temperature resistances-differences ...... 55 5. conclusion ...... 56 6. Future work / suggestions ...... 57 6.1 Future work ...... 57 6.2 Suggestions ...... 57 7. Bibliograpgy ...... 58 8. appendix ...... 60 8.1 Compressor heat rejection sample calculations ...... 60 8.2 Cooling capacity sample calculations ...... 63 8.3 Norrtälje and Älta ice rinks photo gallery ...... 64
6
Measurement and Modelling of Ice Rinks Heat Loads
FIGURES
Figure 1: Refrigeration system energy vs. total purchased energy for ice rinks (Rogstam (c), 2011) .... 9 Figure 2: Energy systems in ice rink (Retscreen, 2005) ...... 12 Figure 3: Configurations of heat rejection and heat recovery from a refrigeration system (Sawalha, 2010) ...... 13 Figure 4: A ventilation duct over the stands in an ice rink ...... 14 Figure 5: Dehumidification by water vapour condensation (IIHF, 2010) ...... 15 Figure 6: Dehumidification by Desiccant wheel (IIHF, 2010) ...... 16 Figure 7: An integrated ventilation and desiccant dehumidification system (Munters, 2011) ...... 16 Figure 8: Energy systems consumption shares (Rogstam (a), 2010) ...... 18 Figure 9: Refrigeration plant with recovery (IIHF, 2010) ...... 19 Figure 10: Refrigeration components electricity consumption shares (Rogstam (b), 2010) ...... 20 Figure 11: Ice pad structure (How ice rink works?, 2011) ...... 21 Figure 12: Typical piping arrangement in a distribution network (Ingvar, 2007) ...... 22 Figure 13: Daily indoor ice rink heat loads (ASHRAE, 2010) ...... 24 Figure 14: Norrtälje Sportcentrum, a) Ice hockey hall, b) Bandy, c) Artificial soccer field, d) Indoor sport hall, e) Track and field pitch, f) Pool (to be constructed) ...... 28 Figure 15: “Green soccer field” in “white winter” thanks to condenser waste heat ...... 29 Figure 16: Norrtälje ice rink spectators stand (top-left), machinery room inside (top-right), compressors (bottom-left), and machinery room outside (bottom-right) ...... 30 Figure 17: Älta ice rink hall and spectator stand (top-left), machinery room (top-right), flooded evaporator (bottom-left), and one of the two compressors (bottom-right) ...... 31 Figure 18: ClimaCheck basic instrumentation configuration ...... 32 Figure 19: Energy balance over compressor ...... 33 Figure 20: ClimaCheck flowchart for Norrtälje and Älta ice rinks ...... 34
Figure 21: Relative heat rejection versus RPM and tcond (teva=-10°C, superheat =7K, subcool = 5K)35
Figure 22: Average relative heat rejection versus tcond (teva=-10°C, superheat =7K, subcool = 5K) ... 36 Figure 23: Ice, brine and evaporating refrigerant temperature fluctuations, 15 March 2011, Norrtälje ...... 37 Figure 24: Evaporation and condensation temperatures, 15 March 2011 ...... 38 Figure 25: Brine and coolant temperatures, 15 March 2011 ...... 38 Figure 26: Air temperatures and relative humidity, 15 March 2011 ...... 39 Figure 27: Electric power and cooling capacity, 15 March 2011 ...... 40 Figure 28: Total refrigeration system energy usage and outdoor temperatures in March 2011 ...... 41 Figure 29: Heat loads in ice rinks and their impact points ...... 42 Figure 30: Angle factor between two aligned parallel faces (Çengel, 2007) ...... 44 Figure 31: Cooling capacity versus heat loads at midnight, 15 March 2011 ...... 46 Figure 32: Air and ice temperatures and air relative humidity, 12 July 2010, Norrtälje...... 46 Figure 33: Condensation heat transfer coefficient, 12 July 2010, Norrtälje ...... 47 Figure 34: Lighting fixtures in Norrtälje ...... 48 Figure 35: Hourly average ice temperature, 15 March 2011, Norrtälje ...... 50
7
Measurement and Modelling of Ice Rinks Heat Loads
Figure 36: Heat loads shares in the total heat load ...... 52 Figure 37: Top and bottom temperature sensors embedded in the ice ...... 53 Figure 38: Top and bottom heat transfer rate on days 14, 15 and 16 April 2011 ...... 54 Figure 39: Ice average temperature fluctuations on 14, 15 and 16 April 2011 ...... 54 Figure 40: Heat flow from ice to refrigeration plant ...... 55 Figure 41: MYCOM software interface ...... 60 Figure 42: Cooling capacity calculation sample for 23:00-23:59 on March 15, 2011 ...... 63 Figure 43: Flooded evaporator (right) and brine pumps (left) - Älta ...... 64 Figure 44: Coolant pumps and condenser (left corner) - Älta ...... 64 Figure 45: DX evaporator (right), desuperheater (top-left) and condenser (bottom-left) - Norrtälje 64 Figure 46: refrigeration system for outdoor bandy field - Norrtälje ...... 64 Figure 47: heat recovery pump for ventilation - Älta ...... 64 Figure 48: District heating system - Norrtälje ...... 64 Figure 49: desiccant wheel dehumidification and ventilation heat recovery unit - Älta ...... 65 Figure 50: dehumidification piping (right) and heating/cooling coils (left) in ventilation ducts - Norrtälje ...... 65 Figure 51: ClimaCheck central control unit - Älta ...... 65 Figure 52: Instruments for over ice temperature and humidity measurements- Älta ...... 65 Figure 53: ventilation ducts and lighting - Älta ...... 65 Figure 54: ice resurfacing machine - Älta ...... 65
TABLES Table 1: Available lamps for ice rinks (IIHF, 2010) ...... 17 Table 2: Ice pad and piping dimensions (ASHRAE, 2010)(IIHF, 2010) ...... 22 Table 3: Sample temperature control (Everything Ice, 2000) ...... 27 Table 4: Reasons for higher energy consumption in Älta ...... 41 Table 5: Physical properties for brine headers for heat load calculation ...... 49 Table 6: Heat loads summary ...... 51 Table 7: Daily heat load calculations, 15 March 2011 ...... 52 Table 8: Heat transfer resistances and temperature differences ...... 55 Table 9: Heat rejection calculation results by MYCOM software ...... 61
8
Measurement and Modelling of Ice Rinks Heat Loads
1. INTRODUCTION Imagination of a prosperous sustainable society without smart energy strategies seems impossible. While the amount of world energy consumption increases nonstop, there are only two solutions to avoid the fatal consequences: producing energy more sustainably and using the produced energy more efficiently. While there are big efforts to use renewable energies, it seems that still there is a long way to go and the dominating resources are still non-renewable energies. Keeping this in mind, using this energy more efficiently is the best answer to problems following by enormous energy consumption. Ice rinks are among the most energy consuming public areas which roots in simultaneous cooling, heating, ventilation and lighting demand. In small municipalities, ice rinks are the biggest energy consumers. Average annual energy consumed in a Swedish ice rink is 1185 MWh/year which this amount is supplied 82% by electricity and 18% by heat and the total energy consumption for Sweden ice rinks exceeds 300 GWh/year. The refrigeration system has the biggest share with 43%. (Rogstam (a), 2010) The relation between the refrigeration system energy usage versus the total purchased energy (including electricity and heat) is shown in Figure 1 for a number of ice rinks. It is expected that refrigeration energy consumption should increase with the total consumption increase but a considerable spread is seen. Very different operation and activities patterns and not considering the heat recovery potential in some ice rinks would be justifications for this spread. (Rogstam (c), 2011)
1200
1000
800
600 (MWh/yr) 400
200 Refrigeration system energy usage 0 05001 000 1 500 2 000 Total purchased energy ( MWh/yr) Figure 1: Refrigeration system energy vs. total purchased energy for ice rinks (Rogstam (c), 2011)
9
Measurement and Modelling of Ice Rinks Heat Loads
As a comparison, Québec ice rinks average energy consumption is around 1 500 MWh/year, while the most efficient ones consumes 800 MWh/year and the least efficient ones 2 400 MWh/year (Nicolas, 2009). For the whole Canadian ice rinks the total electricity consumption is approximately 3 500 GWh/year. (Bellache, 2007) In Sweden there are about 341 indoor and 140 outdoor ice rinks, sized about 1800 m2 (60 m×30 m). Furthermore, 60 outdoor bandy rinks, around 8000 m2 each, exist in Sweden. Nine indoor bandy arenas are built during the recent years. The operating months for indoor ice rinks is 6-10 months, with an average of 8 months. For outdoor ice rinks, the winter period which lasts 3-5 months is the operating time. (Rogstam (a), 2010) While the total energy consumption by indoor ice rinks is more than 300 GWh/year, the ice rink numbers and the working periods is increasing continuously and it seems that Swedish people need more and more ice rinks, all year round. It means that the energy consumption will increase steadily if there are no policies adopted for better energy efficiency techniques. To find the best energy efficiency solutions, the first step is to know various heat loads and their shares on the load to the refrigeration system which is the largest energy consumer.
1.1 Objectives The objective of this study is to evaluate the heat loads in ice rinks. To obtain the best results the following steps are intended: a) Study literature on measurements and models on heat loads in ice rinks or similar applications. b) Evaluation of two ice rinks with ClimaCheck instrumentation enabling monitoring the cooling capacity/ice rink heat load. c) Build a simulation model with an appropriate tool for simulating the ice rink heat load in order to find the heat transfer mechanisms shares in the total heat load.
1.2 Methodology To fulfil the objectives of the research, three main steps are decided. The first step is to review the ice rink energy systems, the technology and different users of the input energy to the ice rinks, heat loads in the ice rinks and furthermore, to introduce the most promising energy efficient methods used to decrease the energy consumption in ice rinks. The second step is the experimental part; two ice rinks will be introduced. Moreover, a measurement system installed in these two ice rinks will be described. Finally, the results of the measurements will be presented. The most important output of theses measurement is to find the cooling capacity and, indirectly, total heat load which refrigeration system should compensate.
10
Measurement and Modelling of Ice Rinks Heat Loads
Trying to break the total heat load into various components will be discussed in the third step, analytical modelling. A correlation or estimate to calculate each of the major heat loads in the ice rinks will be presented and then the total heat loads will be compared with the provided cooling capacity.
1.3 Scope and limitations While the refrigeration system and heat loads of the indoor and outdoor ice rinks are to some extent similar, this research concentrates mainly on indoor ice rinks and in particular two indoor ice rinks in the Stockholm region. This makes the results and conclusions applicable the best for similar climate and built environment conditions, for example Scandinavian or North American locations above 50°-55° latitude. The interactions between the heat loads, as the driving forces, the ice, as the object of cooling, and the refrigeration system, as the responding/cooling system, is of main interest in this research. That is why other energy systems in ice rinks including the heating and ventilation systems are not discussed and analysed in any extend. The limitations of the research are few unknown parameters in the measurement and modelling process. Whenever such a parameter is encountered, it has been mentioned and the best possible logical assumption is made.
11
Measurement and Modelling of Ice Rinks Heat Loads
2. ICE RINKS
2.1 Ice rink energy systems Ice rink energy system is comprised of several energy systems, indicated in Figure 2, because there are various demands in the ice rinks. What makes the ice rinks unique in comparison with other public buildings is the wide range of demands. For example, there is a permanent need for cooling and heating to provide temperatures ranging from -4°C (ice) to around +60°C (Domestic Hot Water) in the ice rinks, simultaneously and in a stable condition. There is a second difficulty as well; there are very few internal partitions to separate these energy systems targets. The energy systems that every ice rink should have are: refrigeration, heating, ventilation, dehumidification and lighting. The first three ones require distribution systems as well which are powered by pumps and fans for mass and energy transfer.
Figure 2: Energy systems in ice rink (Retscreen, 2005)
Refrigeration system is the most important energy system as it makes the ice and keeps it from melting. Considering the huge ice mass, for a typical ice rink the cooling capacity should be around 300-350 kW (IIHF, 2010). The most conventional refrigeration system used is electricity powered vapour compression indirect system. This system is explained more in section 2.3.
12
Measurement and Modelling of Ice Rinks Heat Loads
Heating system provides the required heat for space heating, ventilation, domestic hot water (DMW), ice resurfacing water, floor heating, snow melting, and subsoil heating. The heating system can be fed by fossil fuels, electricity or district heating but the most energy efficient, cost effective and environmentally friendly method is to use the heat rejected by the refrigeration system through the condenser and desuperheater (if available). The amount of heat pumped by the refrigeration system can cover a great share of the heating demand, sometimes even 100% of the need (ASHRAE, 2010). Using this integrated method is smart as the refrigeration system is used both in the evaporator side and the condenser side; hence it is not only a refrigeration system but also a heat pump. There are various ways available to exploit this waste heat. Some examples have been shown in Figure 3.
Figure 3: Configurations of heat rejection and heat recovery from a refrigeration system (Sawalha, 2010)
The middle layout is a refrigeration system without heat recovery and the refrigerant heat is rejected to atmosphere. It is called floating condensing as the condensation pressure follows the ambient temperature. In this case, all of the heating demands should be covered by a separate heating system including district heating, heat pump, etc. Top-left layout is a heat recovery system by a desuperheater. This system is suitable when the discharge temperature is relatively high. Refrigeration systems that use NH3 or CO2 can use this desuperheater heat recovery. The regulating valve after the condenser/gas cooler can adjust the discharge pressure and, consequently, the desuperheater heating capacity. Top-right and bottom-left figures are two heat pump cascade solutions. In the bottom-left layout heat is recovered from the condenser and delivered to a heat pump as the low grade heat. Then the heat pump upgrades it to higher temperatures for HVAC demands. This allows the refrigeration system to have lower discharge pressures. This system is called heat pump cascade. Top-right
13
Measurement and Modelling of Ice Rinks Heat Loads
solution (heat pump cascade for subcooling) is similar to the heat pump cascade but the heat is recovered in a subcooler after the condenser. This increases the efficiency of the refrigeration system. The bottom-right system is a fixed-head pressure heat recovery system. In this solution the discharge pressure is adjusted according to the HVAC system demand. There is a coolant which transfers the heat from the condenser to the HVAC system. (Sawalha, 2010)
Ventilation system delivers the fresh air to the inhabitants and provides the standard air change rate to avoid pollutant, smell, fog and biological disease sources concentration. During the design of the ventilation system, it can be divided into two zones; the ice rink and public areas. In the ice rink, spectators’ stand and emissions from ice resurfacing machine (if it is not an electric one) are to be considered. Moreover, direct air blown to the ice surface should be avoided. For public areas, air change required in the closed spaces including restaurant, offices, locker rooms for players, coaches, referees and linesmen, drying rooms, medical rooms and toilets/showers should be considered (IIHF, 2010).
Figure 4: A ventilation duct over the stands in an ice rink
14
Measurement and Modelling of Ice Rinks Heat Loads
Dehumidification system keeps the relative humidity of the indoor air up to a standard level. Too humid indoor air causes the corrosion of the metal and rotting of the wooden structures. Moreover, fungi and mould growth is more probable in a humid atmosphere. Another problem with too much water vapour content in the air is the fog created over the ice that makes it hard to play or control the movements. The last problem is the heat load on the ice due to condensation. To dehumidify the air, two primary solutions are available. The first one is to cool the humid air below its dew point. This leads to condensation of part of the air water content. For cooling the air, part of the cold brine can be used. Figure 5 illustrates this dehumidification process. Dehumidification by condensation can be integrated with ventilation or refrigeration system.
Figure 5: Dehumidification by water vapour condensation (IIHF, 2010)
The second method is to use water absorbing materials like silica gel. The most well-known equipment which uses this technique is called “desiccant wheel”. Desiccant wheel is the major component in a desiccant humidification system. It is a slow rotating wheel containing some absorbent chemicals (normally silica gel). When moist air passes one portion of the wheel, the moisture is absorbed. While it is rotating, in other portion of the wheel a drying air is blown to the wet absorbent to dry and “regenerate” it. In this system, the desiccant wheel plays a role of a “moisture transporter”; takes the moisture away from the supply air to the ice rink and transports it to the exhaust air. A simple desiccant dehumidification is shown in Figure 6.
15
Measurement and Modelling of Ice Rinks Heat Loads
Figure 6: Dehumidification by Desiccant wheel (IIHF, 2010)
Desiccant dehumidification system can be integrated with an air handling unit of ventilation system. Figure 7 indicates an example of such a system. The return air from the ice rink (pink stream) is divided into two streams: one to be exhausted to the atmosphere and a portion is mixed with the fresh make-up air. The heat from the return exhaust air is recovered in an energy recovery wheel to preheat the make-up air. Then, a mixture of return and make-up air passes the desiccant wheel in the middle of the unit. The desiccant wheel removes some portions of moisture from this air. The desiccant wheel is reactivated (regenerated) by a hot air stream in the upper part of the wheel to be used as a moisture absorbent again in the lower part. The supply air after the desiccant wheel can be heated or cooled by heating/cooling coils. However, in ice rinks cooling coils are not used most of the year. The air enters the ice rink as the “supply air” from left side of the unit.
Figure 7: An integrated ventilation and desiccant dehumidification system (Munters, 2011)
16
Measurement and Modelling of Ice Rinks Heat Loads
Lighting is an energy system that provides a clear and pleasant indoor environment for the skaters and spectators as well. Different activities in an ice rink require different light intensities. Lighting intensity is normally measured in units of lumen (lux) or foot candle (FC). Each foot candle is equal to 10.76 lux. In general, figure or recreational skating requires10-15 foot-candles and curling 10-50 FC while ice hockey needs 80-150 foot candles. As a consequence, a method to decrease the energy consumption by the lighting system is to control the lighting intensity. (DOE, 1980)(Everything Ice, 2000) Another method to have an efficient and smart lighting system is to select energy-efficient lamps and lighting fixtures. Lamps can be categorized to incandescent and burst illuminates according to their operational principle. Generally, incandescent lamps are only suitable for general lighting, except for halogen lamps. Incandescent lamps consume relatively high electricity compared to the produced visible light. They have short life time but good controllability. Burst lamps, in contrast, have high efficiencies and long lifetime but poor controllability. Generally, Burst lights are more suitable for rink lighting (IIHF, 2010). Table 1 shows some of the more well-known lamps available for ice rinks. Luminous-efficacy of a lighting source is defined as the ratio of emitted visible light, in lux, to the total consumed electricity, in W. This parameter shows how much energy efficient the lighting device is. The luminous-efficacy for some incandescent lamps are 15-20% while some burst lamps including metal halide and florescent lamps can have 80-90% efficacy (Luminous, 2011). This means that, for example a 13 W compact florescent lamp can provides the same lighting of 800 lumens as a 60 W incandescent lamp (Everything Ice, 2000). Table 1: Available lamps for ice rinks (IIHF, 2010)
Type Applicability Power range Life Note
Compact Good energy General lighting 5-55 W 8 000-12 000 h fluorescent lamps efficiency
Standard General lighting Good energy 30-80 W 20 000 h fluorescent lamps Rink lighting efficiency
Good for rink Metal halide lamps Rink lighting 35-2000 W 6 000 - 20 000 h lighting
High pressure Poor colour Rink lighting 50-400 W 14 000 – 24 000 h sodium lamps rendering
Long life, expensive Induction lamps Rink lighting 55-165 W 60 000 h (so far)
Excellent colour Halogen lamps Special lighting 20-2000 W 2 000 – 4 000 h rendering, good dimming capabilities
17
Measurement and Modelling of Ice Rinks Heat Loads
2.2 Ice rink energy systems shares Through a statistical study of more than one hundred ice rinks in Sweden it is revealed that the refrigeration system has the largest share in total energy consumption, 43% (in average) as indicated in Figure 8. (Rogstam (a), 2010) Heating with 26% share is the second biggest energy consumer. In Sweden the main sources of heating are district heating and/or electricity plus the heat recovered from the refrigeration system’s high pressure side and the heat recovered from exhaust air in ventilation system. Lighting, ventilation system fans and dehumidification system are the next largest energy consumers.
1%
5% 6% Refrigeration 9% Heating 43% Lighting Ventilation Fans 10% Dehumidification Miscellaneous Misc. Pumps
26%
Figure 8: Energy systems consumption shares (Rogstam (a), 2010)
There are several other researches confirmed that refrigeration system is the biggest energy consumer in majority of world ice rinks. In a research by CANMET, the research organization of Natural Resources Canada, refrigeration consumption is estimated to be 50% of the total energy consumption, by electricity or heat (AAQ, 2003). In a research by International Ice Hockey federation, refrigeration plant consumes 57% of the electricity input to a prototype ice rink in Munich, Germany (IIHF, 2010). A research published in ASHRAE journal estimates that while in an inefficient arena (1950 MWh/year consumption) refrigeration share is only 23%, in an efficient arena with heat recovery systems (840 MWh/year) refrigeration consumes about 42% of the total. (Nicholas, 2009)
18
Measurement and Modelling of Ice Rinks Heat Loads
2.3 Ice rink refrigeration system The refrigeration system is known as the heart of the ice rink because it is the guard to keep the ice in its most desired form. A refrigeration system for the ice rink is direct, indirect, or a combination of them called partly indirect. In the direct system the refrigerant is pumped below the ice pad and the whole refrigerant distribution pipes serves as a large evaporator. This method is less used as there is a need for huge amount of refrigerant charge. R-22 and ammonia are the most used refrigerants for the direct systems but R-22 is banned now in many countries due to its global warming potential and ammonia has a charge limit according to its hazards and cannot be used in large systems including ice rink direct systems. Indirect system is the most conventional layout for ice rink refrigeration system. In this system a primary refrigerant cools a secondary refrigerant, known as “brine”, and then the distribution system circulates this secondary refrigerant below the ice pad and returns it back to evaporator. In Sweden, more than 97% of the ice rinks are indirect or partly indirect. (Makhnatch, 2010) Partly indirect are systems that either evaporator or condenser is connected to the source or sink by a secondary fluid for heat exchange. In partly indirect systems some portion of the cooling is provided by a direct system as well. (Melinder, 2009) A drawing of a typical ice rink with indirect system is demonstrated in Figure 9. As mentioned, refrigeration unit cools the brine in evaporator and the brine is sent to the embedded cooling pipes below the ice pad. The refrigeration system typically consists of a vapour compression cycle driven by electricity as the primary cycle. About 85% of the Sweden ice rinks use Ammonia as the refrigerant while the remaining use R404A, R134a or other HFC refrigerants. (Makhnatch, 2010)
Figure 9: Refrigeration plant with recovery (IIHF, 2010)
19
Measurement and Modelling of Ice Rinks Heat Loads
In the secondary loop there are one or more pumps that circulate the brine. Calcium Chloride
(CaCl2) and Frezium are the most conventional brines in Sweden. In some ice rinks a small portion of the brine flow can be used in dehumidification units, as indicated in Figure 9. Compressors for ice rinks are traditionally reciprocating compressors while screw compressors are the other choices. Generally, more than one compressor is used for ice rinks and among the several compressors one of them can be selected to be ample capacity to adjust “cooling production” in harmony with fluctuating heat loads. In the ice making period or heavy activities on ice during high activity hours, the second compressor will be engaged to assist the first one. The rejected heat from condenser can be recovered to supply a number of heat demands in an ice rink including ventilation unit, floor heating, hot water storage (which is used for domestic hot water and/or ice resurfacing water) and ground frost protection. There are some other heat demands which are not shown in the sketch; for example, part of the heat can be used to melt the snow, produced during ice resurfacing, or a portion can be used for a nearby swimming pool. 75% to 100% of the space and water heating requirements can be supplied by smart heat recovery (ASHRAE, 2010). The excess unexploited heat is removed in outdoor cooling coils which are installed on ice rink roof, generally. The most conventional cooling units are dry air coolers and the most used coolants in Sweden are Glycol, Ethylene Glycol and Propylene Glycol (Makhnatch, 2010). Looking at the power consumption in refrigeration system as shown in Figure 10, it has been revealed that compressors account for 80% of the total electricity consumption while brine pumps, coolant pumps and dry cooler fans consume 10%, 5% and 5% respectively. (Rogstam (b), 2010)
5% 5%
10% Compressors Brine Pumps Coolant Pumps Dry Cooler Fans
80%
Figure 10: Refrigeration components electricity consumption shares (Rogstam (b), 2010)
20
Measurement and Modelling of Ice Rinks Heat Loads
2.3.1 Ice pad structure and piping arrangement Ice pad structure consists of a number of layers and each layer is designed in response to a requirement. As indicated in Figure 11, the topmost layer is ice. The most conventional structure for the second layer is concrete while in some ice rinks sand or asphalt is used as well. The distribution system of brine pipes is embedded in this “chilled concrete slab”. The level of concrete and pipes should be completely flat to have a well-distributed cooling and uniform ice thickness.
Figure 11: Ice pad structure (How ice rink works?, 2011) Below the cold concrete layer there is an insulation pad to decrease the conduction heat gains from the ground. The next layer is “heated concrete”. It holds the weight of the top layers and it is heated to eliminate or minimize the hazards of ground heaving. Ground heaving which is contributed by soil freezing can lead to collapse of the whole ice pad structure. One of the most conventional methods to keep the concrete layer warm is to run warm water in a pipe system, similar to the brine pipes. The condenser heat recovery system can be the water heating source. All the layers are laid on a layer of sand and gravel. A ground water drain collects any water to avoid the water to be absorbed by the top layers. For the concrete and insulation layers being as dry as possible is a requirement. Figure 12 shows a typical piping arrangement for an ice rink. There are two brine pipe headers which one of them is the brine supply header and the other one is return header or collector. As it is shown, the brine distribution pipes are branched from the headers and have a U shape. This simple U shape is called two-pass arrangement but a four-pass arrangement is applied in some ice rinks as well. Four-pass layout has a W shape. Four-pass systems are claimed to be more energy efficient and decrease the energy consumption. (AAQ, 2003) As it can be seen in the figure, the brine header size is decreased gradually when the flow decreases as well. The reason is to have a uniform flow, and as a consequence, heat transfer distribution. Another method for uniform flow distribution is to use some small orifices in the inlet of the small brine distribution pipes. In this arrangement the brine header sizes remain constant.
21
Measurement and Modelling of Ice Rinks Heat Loads
Figure 12: Typical piping arrangement in a distribution network (Ingvar, 2007) Dimensions of the ice pad structure and header and distribution pipes are indicated in Table 2. It can be seen the concrete thickness is 150 mm and the brine distribution pipes are located such that pipes top point is 25- 50 mm lower than ice bottom surface. Smaller the distance, less heat transfer resistance occurs. Furthermore, less concrete thickness leads to less load on the refrigeration system and there are some tries to decrease the 150 mm thickness to 125 mm. Header pipes are 6-8 inches (150-200 mm) typically and made of steel or Polyvinyl Chloride (PVC). Small brine distribution pipes are 25-32 mm and can be steel or polyethylene plastic pipes. There are some new materials including copper tubes which demonstrate a good heat transfer and flexibility properties (Shahzad, 2006). The distribution pipes are fixed in 100 mm spacing with some supports or spacers. Table 2: Ice pad and piping dimensions (ASHRAE, 2010)(IIHF, 2010)
parameter size Ice thickness 25-30 mm Concrete thickness 150 mm Insulation thickness 100 mm Brine headers diameter 150-200 mm Brine distribution pipes diameter 25-32 mm Pipes spacing 75-125 mm (100 mm typically) Top pipe – bottom ice distance 25-50 mm
22
Measurement and Modelling of Ice Rinks Heat Loads
2.4 Heat loads in ice rinks Heat loads in ice rinks can be categorized into three dominating heat transfer mechanisms: Convection - Condensation Radiation Conduction
Brief explanations of these will be given here but the detailed mathematical correlations used for calculations are discussed in chapter four, analytical modelling.
2.4.1 Convection-Condensation In convection heat transfer of air to the ice, air temperature, ice surface temperature and air velocity are important parameters. Higher temperature gradient between air and ice surface and higher air velocity lead to higher convective heat transfer, hence lower air velocity over ice and closer air and ice temperature are factors to decrease this heat load. Furthermore, water vapour in the humid air rejects its heat to the ice and condenses on the surface. This phenomenon is more serious in the ice rinks which are in operation during a humid summer climate. Dehumidification of the supply ventilation air is necessary to avoid condensation and keep the relative humidity low. Condensation could be a source of bad ice surface quality which brings the ice resurfacing requirement, hence has an indirect negative impact as well.
2.4.2 Radiation Two major sources of radiation are ceiling radiation and lighting. In several ice arenas radiation is reported having the largest share in heat loads on the ice (ASHRAE, 2010). The radiation from ceiling to ice could be estimated by the Boltzmann correlation which will be used later. One of the most important factors in ceiling radiation is emissivity index which is normally 0.85-0.95 for conventional materials used for roof ceiling construction. It is possible to do some coverings as aluminium foils or aluminium based clothes and paints which can reduce the ceiling radiation considerably, sometimes to 10%. Lighting is the second source of radiation to the ice as up to 60% of the light can be converted to heat and absorbed by ice (ASHRAE, 2010). A smart way to reduce this heat load is to control the light intensity according to the demand. In other words, it is not necessary to have lighting with full intensity all the working hours of the ice rink. When only few children play on the ice the lighting should be less intense in comparison with a professional match with hundreds of spectators.
2.4.3 Conduction Main contributors to conduction are ice resurfacing, brine pump work, brine headers, ground conduction and skaters. Ice resurfacing is a requirement to maintain the ice surface in a good condition. To fulfil this, ice resurfacing machine shaves the ice surface and then pours down a layer of hot water on the ice. The
23
Measurement and Modelling of Ice Rinks Heat Loads
normal volume of water is 400-700 litres and the resurfacing water temperature is 30-80. The lower the water temperature, less heat load on the ice sheet would be dropped. (ASHRAE, 2010) Pump work causes an increase in the enthalpy of the secondary refrigerant passing the pump. Typical power consumption for these pumps is 15 kW. This 15 kW can be considered as a 15 kW heater in the brine circuit and that is why it should be tried to use variable speed pump to decrease this power consumption during unnecessary occasions including night shut down period. Headers are located along the length or the width of the ice rink. As they are colder than their environment, they should be insulated or covered with ice to decrease the heat gains (cooling losses) as much as possible. Ground conduction is a source of constant heat load on the system. The ground is separated by about 10cm insulation from the cold concrete but still there is some heat flux as the ground is heated to avoid the soil freezing. Skaters’ activities on the ice transfers heat through the ice surface but this is the only heat load that ice rink owners like to be as high as possible.
To exemplify the heat loads shares, in Figure 13 there is a comparison of the shares of heat loads for two ice rinks in Canada and US, during three seasons. It can be seen that radiation, convection, pump work and ice resurfacing are the largest heat loads. Condensation has a significant effect during summer (humid season) but it is not considerable during winter (dry season).
100,00% 90,00% skaters 80,00% headers
(%) 70,00% pump work 60,00%
shares ground conduction 50,00% ice resurfacing load 40,00%
30,00% condensation Heat 20,00% lighting 10,00% radiation 0,00% convection Edmonton, Winter Pittsburgh, Summer Pittsburgh, Spring (95.4 W/m2) (135.5 W/m2) (114.3 W/m2)
Figure 13: Daily indoor ice rink heat loads (ASHRAE, 2010)
24
Measurement and Modelling of Ice Rinks Heat Loads
2.5 Energy efficiency in ice rinks There are several methods to use the input energy in ice rinks more efficiently but all of them can be categorized in one of the three classifications below: Heat loads decrease Refrigeration and distribution system performance improvement Ice/concrete slab quality enhancement
It should be noted that in energy efficiency applications instead of only focusing on the refrigeration system, it is better to study the whole building in an integrated approach. For example, maybe a method decreases the refrigeration system efficiency a little but in general, helps the waste heat recovery systems to supply the heat demands better.
2.5.1 Heat loads decrease 1. Low-e ceiling. Ceiling radiation is one of the largest heat loads in the ice rinks. The conventional materials for ceiling (wood, steel, etc.) have an emissivity index 0.85-0.95. The low-e ceiling concept referred to ceilings covered/painted with low-e aluminium based paints or suspended aluminium based clothes over the ceiling trusses. These low radiating ceilings have emissivity indexes in the ranges 0.05-0.2. By using low-e ceilings the radiation load can be decreased to 50% or less (Retscreen, 2003). It has an indirect impact as well which increases the light reflections and as a consequence less lighting is required in these arenas. The effect of less lighting is discussed in the lighting section. 2. Dehumidification. Humidity control is a way towards thermal comfort in all public areas but in ice rinks it has other significant effect as well. Water vapour in humid air over the ice rejects its heat to ice to condense on the surface. As a consequence, the humidity should be controlled and normally it is kept up to 50%-55%. Desiccant wheels are one of the most efficient dehumidification systems which fulfil the heat recovery from exhaust air and humidity regulation simultaneously. 3. Lighting. Less lighting has two impacts on the energy consumption, direct and indirect. The direct impact is less electricity consumption of the lamps. The indirect impact is according to the less heat transferred by radiation to the ice which decreases the refrigeration system electricity consumption. One way to decrease the lighting is to use more efficient lamps, for example using T5 or T8 fluorescent lamps instead of the metal halide lamps. Furthermore, the lighting intensity is not required to be max during the whole day and it can be adjusted according to the activity on the ice. 4. Resurfacing water. Ice resurfacing water quality, volume and temperature have significant effects on the heat loads. More purified/treated water makes a better ice with higher thermal conductivity. Moreover, less resurfacing water temperature and volume decreases the load. In Sweden 30°C-40°C is the normal temperature range (Makhnatch, 2010) while in North America 55°C-80°C is the case for many ice rinks. 5. Header pipes. Header pipes lying in the trenches should be insulated or frozen with an ice layer on them to reduce the cooling losses. Parts of the header pipes which are outside the trenches should as well be insulated. Other way to decrease the losses is to increase the brine temperature in pipes and
25
Measurement and Modelling of Ice Rinks Heat Loads
then there is less temperature gradient between brine pipe headers and surrounding air. (Refer to section 2.5.3 and Table 3) 6. Air convection and air tightness. Temperature and velocity of the air moving above the ice surface has a great influence on the convection heat transfer. To control these parameters, direct air flows from ventilation diffusers should be avoided. At night, the ventilation system can be turned off or reduced down or the temperature of the supplied air during the less-crowded hours can be lowered. Pollution controllers is another way to adjust the ventilation demand as the big space inside the ice rinks buildings has too many leaks that sometimes ventilation looks unnecessary. Air tightness is to stop the uncontrolled movement of air into and out of a building which is not for a specific and planned purpose. Air tightness is another important factor to keep the building interior atmosphere isolated from outdoor conditions as in warm and humid seasons it can increase the convection and condensation heat loads severely. 7. Stands heating. To select the heating method for the spectators, its side effects as a heat load on the ice should be considered. One of the best solutions is infrared heater over the stands as it provides spot heating. If it is not possible and the ventilation system is used simultaneously for heating, it should be considered that the air should not be blown to the ice directly.
2.5.2 Refrigeration and distribution system performance improvement 1. Waste heat recovery. The refrigerant after the compressor is cooled in desuperheater and condenser. This heat can be recovered for heating demands. In this point of view, refrigeration system can be considered as a heat pump which the heat loads on the ice plays the role of the low level heat sources and the heat pump (refrigeration system) upgrades the heat level to distribute it in the required location and applications. According to the temperature degradation from desuperheater inlet to condenser outlet, the heat can be used for various applications including DHW, floor heating water, resurfacing water, snow melting, swimming pool heating, subfloor (soil) heating water, ventilation and space heating. 2. Brine pump. A full speed brine pumps working 24 hours a day can account for 15% (Retscreen, 2003) of the total electricity consumption in the refrigeration systems. Furthermore, this consumed electricity by brine pumps is converted as heat to the brine and therefore, it has direct and indirect negative effects on energy consumption. To decrease the consumption, variable speed pumps are one of the best solutions. They can be controlled by brine temperatures. 3. Brine pipe passes. The brine pipes are generally two pass configuration (as shown in Figure 12) but four pass configurations have been installed in several ice rinks over the world and no problem has been reported. Four pass layouts require less pumping power. (AAQ, 2003) 4. Compressor demand control. Similar to brine pumps, constant-speed compressors are not enough energy efficient as the amount of cooling required should be controlled by ice or brine temperature. At night or low-activity day hours it is not wise to have all the compressors on with full speed. For controlling the provided cooling capacity, electric motors equipped with frequency converters are used. In addition, using more than one compressor is a way to adjust the refrigeration with cooling demand. During the rush hours, the auxiliary compressor(s) can run in parallel with the first compressor.
26
Measurement and Modelling of Ice Rinks Heat Loads
2.5.3 Ice/concrete slab quality enhancement 1. Ice temperature and thickness. Considering the huge mass of ice (more than 40 ton for a typical 1800 m2, 25 mm ice sheet) each degree colder ice requires a significant amount of cooling. Therefore, any effort to keep the ice thickness as thin as possible or the ice temperature as high as possible will help using energy more efficiently. The recommended ice thickness is 25 mm. Recommended ice temperature varies according to the sport/activity. For hockey -6.5°C to -5.5°C, figure skating -4°C to -3°C and recreational skating -3°C to -2°C is satisfactory (ASHRAE, 2010). Overcooling the ice compared to these recommended values means energy waste and the ice rink owner should pay for it unnecessarily. During the night, when there is less heat load, these temperatures can be raised. Table 3 is a sample for ice temperature control. During midnight or early in the morning the ice temperature can be kept 2-3°C higher than the high load periods. It should be mentioned that the ice temperature can be manipulated by brine temperature adjustments and setting the control system for a schedule similar to Table 3, as an example.
Table 3: Sample temperature control (Everything Ice, 2000)
Typical Daily Brine Cycle Period Brine Temperature Rink Function 0.00-6:00 -4⁰C Night setback 6:00-8:00 -4⁰C Ice maintenance 8:00-16:00 -6⁰C Low load 16:00-18:00 -7⁰C Figure skating 18:00-24:00 -8⁰C Hockey
2. Concrete thickness and thermal conductivity. While the main object of cooling is ice, the heat transfer medium from ice to brine is concrete and less heat transfer resistance through concrete will cause less required cooling capacity. Concrete thickness in Swedish ice rinks is, typically, 150 mm which 25-50 mm is the distance from brine pipes top to the concrete surface (ice bottom). In parallel to concrete thickness, concrete thermal conductivity is very important. Better concrete quality leads to better heat transfer and less resistances.
27
Measurement and Modelling of Ice Rinks Heat Loads
3. EXPERIMENTAL MEASUREMENTS As the second step of this research, the performance of two refrigeration plants in two ice rinks is to be evaluated. To fulfil this objective, first, the ice rinks and their refrigeration systems are described in brief. Then, ClimaCheck, as a tool and method to analyse the performance of the refrigeration system is discussed and some modifications for more accurate calculations are suggested and applied. Finally, the results of the measurements (including power consumption and important temperatures) and estimated cooling capacity for some sample time periods are shown and discussed.
3.1 Ice rinks Two ice rinks which are studied in this research are situated in Norrtälje and Älta. Ice rink in Norrtälje belongs to the “Norrtälje Sportcentrum” which is located about one hour north-east of Stockholm. Älta ice rink is located in the Nacka district, Stockholm.
3.1.1 Norrtälje ice rink Norrtälje sport Centrum is comprised of two ice rinks, one indoor for hockey and figure skating and another one outdoor for bandy. Through this report only the indoor ice rink is considered and studied and for the outdoor rink another research project is in process. Moreover, there are an artificial soccer field, an indoor sport hall, a track and field pitch and a pool –to be constructed - in the sport facility. (Figure 14)
Figure 14: Norrtälje Sportcentrum, a) Ice hockey hall, b) Bandy, c) Artificial soccer field, d) Indoor sport hall, e) Track and field pitch, f) Pool (to be constructed)
28
Measurement and Modelling of Ice Rinks Heat Loads
Among the neighbour sport fields, the artificial grass field is of particular interest as it uses part of the waste heat from the refrigeration system condenser to prevent freezing, even during the harsh winter climate (Figure 15). The heating piping system is similar to an ice rink but here the pitch is heated by the underground pipes containing ammonia 15% - water which is heated by condenser. In other words, the refrigeration system acts as a “heat pump” to keep the soccer field from freezing.
Figure 15: “Green soccer field” in “white winter” thanks to condenser waste heat
Norrtälje ice rink is about 1800 m2 (60 m×30 m) and its spectator capacity is 700-800 people, as shown in Figure 16 top-left. It is open all year round except for mid-April to mid-June. The refrigeration system is indirect with ammonia as refrigerant, calcium chloride 21% - water as secondary refrigerant and the coolant is ethylene glycol 35% - water. The refrigeration system is bought and shipped prefabricated from Finland. It is located outside the ice rink building as the inside old machinery room became useless after a price increase in district cooling water (Figure 16 bottom-right). Two MYCOM reciprocating compressors with nominal total cooling capacity of 300 kW and nominal 55 kW motor capacity are the driving forces of the refrigeration system. The evaporator is direct expansion and VAHTERUS shell and plate heat exchanger. The condenser and desuperheater are from the same manufacturer. There are two 15 kW brine pumps but only one is in operation during the measurements period of this research project. All the involved electrical motors mentioned are equipped with frequency converters. The humidity of the ice rink is controlled by a dehumidification system using a part of the cold brine to decrease the humidity ratio of the incoming air, mainly in the humid months. The heat rejected from the desuperheater is used to supply part of the heat required for space heating, ventilation, hot water and ice resurfacing water.
29
Measurement and Modelling of Ice Rinks Heat Loads
Figure 16: Norrtälje ice rink spectators stand (top-left), machinery room inside (top-right), compressors (bottom-left), and machinery room outside (bottom-right) .
3.1.2 Älta ice rink The Älta ice rink is similar to Norrtälje ice rink comparing the size, spectator capacity and length of the season. The refrigeration system is indirect with ammonia as refrigerant, calcium chloride 24% - water as secondary refrigerant and the coolant is propylene glycol 40% - water. Two GRAM reciprocating compressors with total nominal cooling capacity of 400 kW and 90 kW nominal motor capacity are the driving forces of the refrigeration plant in Älta ice rink, which are shown in Figure 17. These compressors were built in 1976 and brought from another ice rink, after being used a couple of years. It seems that they are over-sized for the required cooling capacity that might be a source of inefficiency. The evaporator is a flooded type plate heat exchanger (Figure 17 bottom-left). The condenser is an ALFA LAVAL plate heat exchanger and the desuperheater is a shell and tube heat exchanger. In Älta two nominal 15 kW brine pumps and two 11 kW coolant pumps run and none of the machineries are controlled by frequency converters. To control the humidity in Älta one desiccant wheel is installed in the hall.
30
Measurement and Modelling of Ice Rinks Heat Loads
Figure 17: Älta ice rink hall and spectator stand (top-left), machinery room (top-right), flooded evaporator (bottom-left), and one of the two compressors (bottom-right)
3.2 Performance analyser - ClimaCheck ClimaCheck is a tool to analyse the performance of refrigeration, air conditioning or heat pump systems. The motivation to use this tool is that from January 2009, an EU regulation requires that all air conditioning systems above 12 kW are to be “performance inspected”. The basic flowchart of ClimaCheck can be seen in Figure 18. For a simple basic refrigeration cycle, seven temperature sensors, two pressure sensors and one electrical power meter are used to determine the performance of the system from a thermodynamic point of view. The data which are measured are refrigerant temperatures and pressures before and after the compressor(s), air/water temperatures in and out from evaporator/condenser and refrigerant temperature before the expansion valve. Furthermore, compressor electrical voltage and amperage are measured to know the electrical power input to the refrigeration system.
31
Measurement and Modelling of Ice Rinks Heat Loads
Figure 18: ClimaCheck basic instrumentation configuration
The ClimaCheck instrument can be a portable field kit or permanent fixed installation. Both of them can be connected to the internet to be monitored anywhere and the logged data can be processed through the ClimaCheck software to obtain the required calculated results.
3.2.1 Energy balance method To analyse the performance of the ice rinks refrigeration system an “internal method” is used. This method is referred to as the “ClimaCheck method”. In the internal method the compressor is used as a mass flow meter and therefore there is no need installing an external mass flow meter. The refrigerant mass flow rate is calculated by an energy balance over the compressor (Berglöf, 2010). By measuring the pressure and temperature before and after the compressor and the electricity input to the compressor it is possible to calculate the mass flow rate according to Figure 19: