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Through proper system design, steps can be taken to reduce the amount of power used while still maintaining high-quality ice.
The following are a list of some steps that can be taken to reduce the energy consumption in your facility.
Ammonia vs. CFCs/HCFCs/HFCsAmmonia is the most energy-efficient refrigerant and is manufactured using natural elements, namely nitrogen and hydrogen (NH3) It has been used successfully and safely for well over 100 years and will not be phased out like R-22.
However its toxic nature and pungent odor require that more stringent code regulations be adopted in the design of the plant room. When using ammonia, some jurisdictions require that a professional operator be on staff, which can increase the total facility operating cost.
For larger, multisheet facilities, you should strongly consider ammonia for its increased energy efficiency advantage.
R-22 and -507 are more expensive and less efficient than ammonia. However, HCFC and HFC plant room and operator requirements are not as rigid as ammonia.
R-507 is also totally ozone friendly and probably will not be phased out, like R-22 will be.
R-507 operates at much lower compressor discharge temperatures than either ammonia or R-22. This can extend the life of the compressors. R-507 and R-22 compressors require less maintenance than ammonia compressors.
High-efficiency motors, soft-start controllersIt is always important to use motors with a high-efficiency rating. To increase the total system efficiency, soft-start controllers can be installed on the compressor motors. A soft-start controller greatly reduces inrush current and the consequential peak demand loads. The soft start also reduces the strain on the compressor during the high torque generated at start up.
Any reduction in your power bills as a result of using a soft-start controller will depend on the method used to calculate the demand load. Check with your utility company.
Power factor correctionPower factor is the relationship (phase) of current and voltage in ac electrical distribution systems. Under ideal conditions current and voltage are “in phase” and the power factor is 100%.
If inductive loads (e.g., motors) are present, power factors of less than 100%, typically 80% to 90%, can occur.
Low power factor, electrically speaking, causes heavier current to flow in power distribution lines in order to deliver a given number of kilowatts to an electrical load. Because the utility company must invest in oversized equipment to serve low-power-factor loads, a charge is commonly assessed on a facility’s electric bill to recover the equipment costs and lost energy caused by low power factor.
Electric motors used to drive the refrigeration equipment commonly cause the voltage and current to get out of alignment. Power factor correction capacitors “re-align” the voltage and current with each other.
This is true with both fixed capacitors and automatic capacitor banks. These capacitors should be installed on all motors 25 hp and larger.
Computer controlThe computer system applies a technique known as floating suction. It monitors the rate that the ice temperature is changing and selects just enough compressor capacity to accomplish the required cooling task while maintaining consistent ice temperature.
For every degree the suction pressure can be raised, the power can be reduced by approximately 1% to 1.5%. The computer can respond to any type of sensor, including slab sensors, brine sensors, in-ice sensors, and infrared sensors.
The computer can be programmed to provide night setback to minimize running during unoccupied times; or, in areas with off-peak loads, the ice can be run down colder during periods with lower utility rates.
It is very cost effective to float the head pressure down during periods of colder ambient temperatures. Complicated formulas can be programmed into the computer to minimize the ratio of condenser fan to compressor horsepower. For every degree, the discharge temperature can be reduced by approximately 0.75%.
Dual-drive brine pumpsDual-drive brine pumps allow a 60% reduction in pump horsepower by stopping the large main brine pump and starting a lower-horsepower pony pump.
The reduced-horsepower pony pump still provides 60% to 75% of the pumping capacity of the main pump. Calculations must be run to determine the reduced flow capacity of the chiller and the level of staging offered by the compressors.
In most cases, a very favorable hp/ton improvement can be obtained. In addition to the energy savings, you and the rink owners will have the added security of a backup brine pump in the event of a failure.
Oversized evap condenserEvaporative condensers are the most efficient method of condensing. Consideration should be taken for local water conservation regulations, health regulations, and the mineral content of the water to ensure that it is appropriate for your area.
It is always wise to select a condenser for the lowest condensing temperature that can be practically achieved. It is good design practice to size a condenser for a maximum of 90Â°F condensing at full-load conditions. For every degree you reduce the discharge temperature, the efficiency will increase by approximately 0.75%.
A dual-drive fan system will reduce the fan horsepower by 60% to 80% during reduced-load conditions and during colder weather. This format will also provide a backup in the event of a fan motor failure.
A variable-frequency drive (vfd) fan control can also provide excellent condenser efficiency. For optimum efficiency, a computer should control the drive. The programming will factor in the condenser load profile, a refrigerant table, and relative humidity.
Oversized flooded chillerA properly engineered, oversized chiller will provide several benefits to the system:
- Suction pressures can be operated at a higher level, increasing refrigeration system efficiencies by 1% for every degree the suction temperature is increased.
- Pressure drops will be substantially reduced on the brine side, minimizing pump horsepower and destructive velocities.
- The additional size will minimize the negative effects of scaling, further increasing the life of the chiller.
- And the added surface area will facilitate rapid temperature pulldowns when required.
Titanium plate chillerTitanium plate chillers offer five major advantages:
l. Optimum corrosion resistance;
2. Herringbone counterflow pattern that enables excellent heat transfer at greatly reduced flow rates, thus minimizing the required brine pump horsepower;
3. Reduced floor space requirements;
4. An exceptionally reduced refrigerant charge of 35 lb vs. 1,200 lb for a conventional flooded chiller of the same capacity; and
5. Ease of field service.
An oversized plate chiller can reduce energy requirements as well as facilitate rapid temperature pulldown when required.
Subcooling/snow melt pitThe entire electrical load in a refrigeration system is used to make ice; then, up to 20 times a day, the ice is scraped off and allowed to melt. Many facilities even use more power by melting the snow with hot water.
Traditionally, snowmelt pits obtained their heat from high-temperature discharge gas. On a CFC/ HCFC/HFC system, a subcooling system will preserve the high-temperature discharge gas for heating water, where it is more valuable.
The liquid subcooling method melts the snow and recovers the cooling value of it which, in turn, is directed right back into the refrigeration system for a capacity boost of up to 30%.
With a snow-melt pit, snow can be eliminated without opening the outside doors and letting heat in.
Hot water heat reclaim, desiccant dehumidifierIt is very economical to reclaim waste heat from the refrigeration plant for heating hot water.
Hot water in arenas is typically used for the showers or for filling the ice resurfacer. This does not eliminate the need for a supplemental boiler, but does drastically reduce the cost of operating it.
One of the largest contributing factors of having a great ice surface is proper humidity control in the building envelope. Excess humidity also increases the refrigeration load on the ice plant.
The most reliable and economical way of dealing with the humidity is through the use of a desiccant dehumidifier. This provides an excellent ice surface during all weather conditions, at a fraction of the operating cost of the old-style mechanical dehumidifiers.
Diesel or gas compressorsIn some locations, due to the availability or cost of electrical power, it may be favorable to operate one or all of the compressors with internal combustion engines.
In areas with time-of-day billing, it can be advantageous to operate the engine during peak electrical demand periods.
Additional heat reclaim is also available from the engine cooling system. Some gas companies offer significant grants for the conversion to gas. In deciding if this is a good option, you must calculate the additional cost of maintenance the engines will require.