Energy efficiency measures- Institutional - Arena - hockey & skating - Heat recovery - Refrigeration system / Canada
Introduction
A municipal skating and hockey arena in the Gaspésie region (QC) has been experiencing rising energy costs and operating the rink is becoming expensive. Furthermore, at times the refrigeration system has insufficient capacity to maintain the ice sheet at the desired temperature. A suite of upgrades to the arena facility has been proposed to improve the quality of the ice and to achieve significant annual energy savings, while reducing the carbon footprint of the building. The RETScreen Software Energy Efficient Arena & Supermarket Project Model (Version 3.1) has been used to verify that these measures make sense, before proceeding with a feasibility study.
Site information
Description of the facility
The arena has two ice rinks. One rink is 60 m by 26 m, housed in a 2,936 m² space; the second rink, in an addition of 1,680 m², is slightly smaller, at 53 m by 23 m. The original rink has bleachers that can seat 1,900, while the smaller rink can seat 350. The average number of spectators is around 10% of the total seating capacity. The ceiling is 9 m above the ice surface. The rest of the arena area can be broken down as follows:
Introduction
A municipal skating and hockey arena in the Gaspésie region (QC) has been experiencing rising energy costs and operating the rink is becoming expensive. Furthermore, at times the refrigeration system has insufficient capacity to maintain the ice sheet at the desired temperature. A suite of upgrades to the arena facility has been proposed to improve the quality of the ice and to achieve significant annual energy savings, while reducing the carbon footprint of the building. The RETScreen Software Energy Efficient Arena & Supermarket Project Model (Version 3.1) has been used to verify that these measures make sense, before proceeding with a feasibility study.
Site information
Description of the facility
The arena has two ice rinks. One rink is 60 m by 26 m, housed in a 2,936 m² space; the second rink, in an addition of 1,680 m², is slightly smaller, at 53 m by 23 m. The original rink has bleachers that can seat 1,900, while the smaller rink can seat 350. The average number of spectators is around 10% of the total seating capacity. The ceiling is 9 m above the ice surface. The rest of the arena area can be broken down as follows:
The building is over 50 years old, but underwent major renovations around 30 years ago, when the second rink was added. At that time, insulation was also installed, to the R-12 level in the walls and the R-20 level in the ceiling. The arena is open 16 hours a day from August 20th to March 20th.
The ice thickness is kept at 75 mm. A propane ice resurfacer is used 55 times per week on the larger rink and 48 times per week on the smaller rink. On average, resurfacing one rink requires around 370 L of hot water.
It is estimated that the hockey players take an average of 800 showers per week, and that around 200 L/d of hot water is consumed at the arena for domestic usages.
Description of the mechanical system
The refrigeration system employs six industrial, open-type reciprocating compressors, driven by low-efficiency 25 HP motors. Together they provide 110 tonnes of cooling capacity at a refrigerant evaporating temperature of -15ºC (5ºF) and a condensing temperature of 35ºC (95ºF). The leaving secondary fluid temperature at evaporator is -9.5ºC (15ºF). Their design coefficient of performance (COP) is 2.9. Freon (R-22) is used as refrigerant. It is estimated that the refrigeration system looses around 15% of its charge each year, which is equivalent to 23 kg of Freon that need to be replaced annually in the system.
The ice surface is cooled by a calcium chloride brine solution. Heat is transferred from the brine to the primary refrigerant in a direct expansion tube-in-shell evaporator. The secondary fluid circuit utilizes a four-pass configuration, installed during a recent renovation.
All heat from the refrigeration system is currently rejected to the exterior via three air-cooled condensers. The condensing temperature is fixed.
Description of the space and water heating system
The bleachers are kept at 13ºC (55.5ºF) by air handling units with design fresh airflow rates of 5,700 L/s for the larger rink, and 2,400 L/s, for the smaller rink. The operating ventilation airflow rate is manually adjusted based on the activities in the rink and the occupancy. On average, it appears that the system operates at roughly 25% of the design fresh airflow rate. The temperature of the rest of the building, including the dressing rooms, is maintained using similar systems. The relative humidity in the arena is around 55% on average.
A 300 kW diesel oil boiler provides heating to a hydronic loop that transfers its heat via heat exchangers to the air handling units and to the resurfacing and domestic water storage tanks, which are maintained at 82ºC and 60ºC respectively. The boiler's efficiency was recently evaluated at 75%.
Description of the lighting system
Forty-seven 400 W metal halide lamps illuminate the larger rink; 43 of these lamps provide light to the smaller rink. A further six 250 W metal halide lamps illuminate the bleachers. In addition, 30.4 kW of lighting is used in the other areas of the building. Lighting is turned off when the building is unoccupied.
Proposed improvements
In order to improve ice quality and energy efficiency, the following improvements were proposed:
1. Replace the existing R-22 refrigeration system: The proposed refrigeration system will have a refrigeration capacity of 120 tons (10 tons more compared to the existing system) and will use 225 kg of ammonia as the refrigerant (R-717). The refrigerant losses are lowered to 2%. The ammonia system with a COP of 3.5 is more efficient and has a lesser carbon footprint than the Freon system. It will employ new industrial, open-type reciprocating compressors. A flooded evaporator will take the place of the existing direct expansion evaporator; by enhancing heat transfer between the refrigerant and the brine, this new evaporator will allow a refrigerant evaporating temperature of -13ºC (8ºF), somewhat higher than in the existing system. It has been further recommended that the evaporator be fabricated from titanium, such that the existing type of brine, which is highly corrosive, can continue to be used. An advanced control system will adjust the condenser temperature based on outdoor temperatures and the operational requirements of the arena; such "floating" head pressure operation will improve efficiency. The minimum operating condensing temperature is set to be 20ºC (68ºF).
2. Install a low emissivity ceiling: The low-e ceiling will enable to reduce the load on the refrigeration system due to heat radiating from the ceiling to the ice surface.
3. Allow the temperature of the ice to rise during night-time: The target temperature is -1ºC (30ºF) during the unoccupied night-time periods. This measure will enable to reduce the electricity required by the refrigeration system.
4. Implement heat recovery strategies: It is proposed to recover the heat currently being rejected by the refrigeration system to the outside air at two temperature levels:
- Refrigerant superheat energy (sensible heat) for domestic and resurfacing water heating. This will be achieved through the use of a desuperheater at the output of the compressors. An advantage of ammonia over other refrigerants is the high temperature of the compressor discharge gases-well in excess of even the 82ºC (180ºF) required for resurfacing. To maximize the use of the recovered superheat, the existing hot water storage capacity will need to be increased. The existing preheated water distribution network can also be used for the proposed installation. The existing diesel boiler will satisfy hot water requirements beyond what can be provided by the desuperheater.
- Refrigerant condensing heat to be transferred, by the means of a heat recovery condenser, to a secondary fluid loop containing warm water or a glycol mixture. This secondary loop will provide heat to the air handling systems. When the recovered heat is insufficient, it will be supplemented by heat from the existing boiler. When the condensing heat exceeds the total heating load, the excess will be rejected to the exterior via a new evaporative cooling tower. This measure will involve the purchase of new heat recovery coils.
Financial information
Initial investment for the existing system
Much of the equipment in the existing system is at or near the end of its useful life. If the arena is to operate with the existing system, within a year around $65,000 will have to be invested in replacement evaporators, condensers, and other equipment.
Initial investment related to the proposed improvements
Normally a detailed estimate of costs for the proposed efficiency measures is not available at the prefeasibility stage of project assessment. Rather, the analyst must draw upon his or her prior experience to estimate costs. For this case study, the following cost estimates were given by the equipment and service suppliers:
Project life and equipment residual value
For the purpose of the financial analysis, the project life is set to 20 years. Even with these repairs that need to be performed on the existing refrigeration system, the value of the equipment at the end of the arena's 20 year planning horizon will be only $50,000. The lifetime of the proposed equipment is 30 to 40 years; therefore, the value of the equipment after 20 years can be estimated to $350,000.
Utilities and various levels of government have incentive programs to encourage energy efficiency in ice arenas. It is believed that the proposed system would qualify for a total of $130,000 in grants.
The funds for these proposed improvements would come out of a municipal capital projects budget. The municipality uses a discount rate of 5% to determine the financial attractiveness of proposed investments.
Operating costs
Both systems will incur costs for operation and regular maintenance. The existing system will cost around $23,000 per year for operation and maintenance (excluding electricity purchase), while the proposed system would cost only $10,500 per year. However, regulations arising due to ammonia's toxicity and flammability necessitate certain measures including daily inspections by a specially trained mechanic. This results in an additional $5,000 per year to be allocated to the operation of the proposed system.
R-22 refrigerant is very damaging to the ozone layer and is being phased out under the Montréal Protocol. By 2020 it will no longer be produced. Presently it costs around $8 per kg, but driven by demand from existing R-22 systems, its price is expected to rise by around 10% a year as production tails off. The cost for ammonia is around $4 per kg.
The arena pays $0.065 per kWh of electrical energy used, a price that is not expected to rise more than 2% a year. Diesel fuel costs around $0.55 per L, and is expected to rise at around 3% per year.
Periodic costs
Major repairs on the existing system of approximately $65,000 would be required in five and ten years. The proposed system will require periodic maintenance, costing around $10,000 each time, after 7, 14, and 19 years of operation.
Solution
Click here to download the worked-out solution (207 KB).
Analysis of RETScreen results
The project has a simple payback in excess of ten years, which would deter many municipalities. That is unfortunate, because the project has a return on investment (IRR) in excess of the discount rate of 5%, indicating that this is a profitable investment opportunity. With the proposed measures, the annual costs for fuel, operation and regular maintenance will fall by around $50,000. This demonstrates how focussing on the simple payback, which favours a quick return over a good return, can discourage investment in financially attractive projects.
Not only does this project offer a good return, but it is also a relatively safe investment. This is seen in the sensitivity and risk analysis. The sensitivity analysis shows that letting initial costs, operation and maintenance costs, base case fuel costs, and proposed case fuel costs move up or down by up to 25%, generally still permits profitable project outcomes, although the combination of higher than expected initial costs and lower than expected base case fuel (electricity and diesel fuel) costs makes the project look quite poor. Similarly, the risk analysis reveals that, letting these parameters all vary independently and randomly by up to ±25% (with a uniform distribution), only a small fraction of the resulting combinations will have a return on investment less than the 5% discount rate.
It is important to note that the financial analysis conducted with RETScreen software does not take into account, for the proposed improvements, benefits that can not be quantified such as the improvement of the ice quality.
The analysis excludes as well energy savings that will be achieved with the implementation of the proposed improvements that are hard to quantify such as: savings possible through managing building loads to reduce peak power requirements with the implementation of the centralized control system.
Although this does not currently translate into any financial benefit, the greenhouse gas emissions of the arena are greatly reduced by the proposed measures. The major part of this reduction results from the use of ammonia as a refrigerant, which eliminates the leakage of R-22 (which contributes 1,800 times more to the greenhouse effect than CO2), a potent greenhouse gas. The remainder of the reduction arises due to reduced consumption of diesel fuel.
Notes on parameter selection
- Rink area for a twin pad arena: The two rinks of different sizes can be accommodated within RETScreen by assuming two rinks of the same size that together have the same surface area as the real rinks.
- Building envelope insulation factor: The R-value for insulation can be converted to an RSI-value by multiplying by 0.176.
- Cost of initial refrigerant charge: To take into account that the analysis should not include the cost of the initial refrigerant charge in the base case the following was done: the incremental cost cell for "Refrigerant type" has been set equal to the initial cost of refrigerant in the base case. When the refrigerant initial cost credit calculated by RETScreen is subtracted from this, only the initial cost of the proposed case refrigerant remains.
- Brine pumps: the cost of the brine pumps are excluded from this analysis, because they will be replaced in the base case as well as the proposed case.
- Superheat recovery rate: the superheat recovery rate was set to 70% (and not 100%) for the proposed case to take into account the mismatch between the water heating load and the availability of the rejected heat that occur during some periods of the day and night, and the limiting storage capacity.
- Condensing heat recovery rate: the condensing heat recovery rate was set to 50% (and not 100%) for the proposed case to take into account the mismatch between the water heating load and the availability that occur during some periods of the day and night.
- Air-conditioning parameters: Since there is no air-conditioning installed, Free cooling has been selected as the Equipment type.
- Inflation rate of R-22: the price of R-22 refrigerant is expected to rise at 10%, well above the 2.5% rate of general inflation that is applied by RETScreen. To account for this in a most rudimentary fashion, the current price of refrigerant has been raised from $8 to $12.
- Periodic costs: To enter data for the periodic cost in the Cost Analysis sheet, the following was done:
- Base case periodic maintenance costing $65,000 has been set to recur every 5 years (i.e., years 5, 10, 15, and 20); the spurious base case periodic maintenance credit in year 15 has been eliminated with a $65,000 cost in that year; the spurious base case maintenance credit in year 20 has been eliminated by reducing the end-of-project life value of the proposed case by $65,000;
- For the proposed case periodic maintenance costs $10,000 has been set to recur every 7 years; the year 19 proposed case maintenance unaccounted for with a periodic maintenance interval of 7 years has been included in year 20 by further reducing the end-of-project life value by $10,000.
- Base case periodic maintenance costing $65,000 has been set to recur every 5 years (i.e., years 5, 10, 15, and 20); the spurious base case periodic maintenance credit in year 15 has been eliminated with a $65,000 cost in that year; the spurious base case maintenance credit in year 20 has been eliminated by reducing the end-of-project life value of the proposed case by $65,000;
References
All data describing the arena and the proposed improvements are coming from a feasibility study conducted by the engineering firm Thermeca for the municipality of Matane. In this study, Thermeca studied several scenarios that are not presented in this RETScreen case study.
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