Refrigeration process is used in chilled water, brine for processes, ice plants, air conditioning, humidification – moisture removal etc. A generalised method of refrigeration can be explained in block diagram 1.
Refrigeration systems energy balance follows the following method as shown in diagram 2.
Energy efficient chiller has the requirement of Centrifugal Chiller 300 TR and above and 0.6 ~ 0.65 KW/TR.
Screw chiller has 50-200 TR and 0.7 ~ 1.0 KW/TR.
Reciprocating chiller has 10-50 and TR 1.0~1.2 KW/TR
VAR has 50 TR and above and 2000 ~ 2575 Kcal/HR.
Energy Conservation Opportunities in Refrigeration Systems
Use water-cooled condensers rather than air-cooled condensers.
Challenge the need for refrigeration, particularly, for old batch rocesses.
Avoid oversizing – match the connected load.
Consider gas-powered refrigeration equipment to minimize electrical demand charges.
Use free cooling to allow chiller shutdown in cold weather.
Use refrigerated water loads in series if possible. Convert firewater or other tanks to thermal storage.
Don’t assume that the old way is still the best – particularly, for energyintensive low temperature systems.
Correct inappropriate brine or glycol concentration that adversely affects heat transfer and/or pumping energy. If it sweats, insulate it, but if it is corroding, replace it first.
Make adjustments to minimize hot gas bypass operation.
Inspect moisture/liquid indicators.
Consider change of refrigerant type if it will improve efficiency.
Check for correct refrigerant charge level.
Inspect the purge for air and water leaks.
Establish a refrigeration efficiencymaintenance program. Start with an energy audit and follow-up, then make a refrigeration efficiency-maintenance program a part of your continuous energy management program.
Case Study: Replacement of Existing VAR Type Chiller with Centrifugal Chiller
Energy Efficient Capacity Selection of Refrigeration and chiller systems may be done by proper selection of load (1200 TR or 300 TR) or by RH (10 HR or 14 HR). Optimum set point temperature (Evaporator) is also important. Having optimum or minimum driving force (temperature difference between set temperature of motive fluid (water and refrigerant temperature) help to achieve highest possible suction pressure at compressor which leads to less energy requirements. Other ENCON opportunities in refrigeration systems are such as
1. Optimise process heat exchange
2. Maintain heat exchanger surfaces
3. Multi-staging systems
4. Matching capacity to system load
5. Capacity control of compressors
6. Multi-level refrigeration for plant needs
7. Chilled water storage
8. System design features
Energy Conservation opportunities in Chillers
Increase the chilled water temperature set point if possible. Use the lowest temperature condenser water available that the chiller can handle. (Reducing condensing temperature by 5.5 0C, results in a 20 – 25 per cent decrease in compressor power consumption)
Increase the evaporator temperature (5.50C increase in evaporator temperature reduces compressor power consumption by 20 – 25 per cent)
Clean heat exchangers when fouled. (1 mm scale build-up on condenser tubes can increase energy consumption by 40 per cent)
Optimise condenser water flow rate and refrigerated water flow rate.
Replace old chillers or compressors with new higher-efficiency models.
Use water-cooled rather than aircooled chiller condensers.
Use energy-efficient motors for continuous or near-continuous operation.
Specify appropriate fouling factors for condensers.
Do not overcharge oil.
Install a control system to coordinate multiple chillers.
Study part-load characteristics and cycling costs to determine the mostefficient mode for operating multiple chillers.
Run the chillers with the lowest energy consumption. It saves energy cost, fuels a base load.
Avoid oversizing – match the connected load.
Isolate off-line chillers and cooling towers.
Establish a chiller efficiencymaintenance program. Start with an energy audit and follow-up, then make a chiller efficiency-maintenance program a part of your continuous energy management program.
Diagram 2: Refrigeration systems energy balance
HVAC Systems
HVAC System consists of a chain of components designed to cool or heat, ventilate a specific area while maintaining a defined environmental cleanliness level. Purpose of HVAC system is to To Control/ Maintain Temperature – Heating,
To Purify the Air – Ventilation and
To Control/Maintain Humidity – Air Conditioning.
Energy Conservation Opportunities in HVAC Systems
Optimum Design (Heat Load and Air Flow Requirements)
Monitoring & Control
Automation
Effective Preventive Maintenance
Minimisation of Heat Energy Losses
Minimisation of Leakage Losses
Energy Efficient HVAC Components
Waste Heat Recovery
Tune up the HVAC control system.
Consider installing a building automation system (BAS) or energy management system (EMS) or restoring an out-of-service one.
Balance the system to minimise flows and reduce blower or fan or pump power requirements.
Eliminate or reduce reheat whenever possible.Use appropriate HVAC thermostat setback. Use morning pre-cooling in summer and pre-heating in winter (i.e. – before electrical peak hours).
Use building thermal lag to minimise HVAC equipment operating time.
In winter during unoccupied periods, allow temperatures to fall as low as possible without freezing water lines or damaging stored materials.
In summer during unoccupied periods, allow temperatures to rise as high as possible without damaging stored materials.
Improve control and utilisation of outside air.
Use air-to-air heat exchangers to reduce energy requirements for heating and cooling of outside air.
Reduce HVAC system operating hours (e.g. – night, weekend).
Optimize ventilation.
Ventilate only when necessary. To allow some areas to be shut down when unoccupied, install dedicated HVAC systems on continuous loads (e.g. – computer rooms).
Provide dedicated outside air supply to kitchens, cleaning rooms, combustion equipment, etc to avoid excessive exhausting of conditioned air.
Use evaporative cooling in dry climates.
Reduce humidification or dehumidification during unoccupied periods.
Establish an HVAC efficiencymaintenance program. Start with an energy audit and follow-up, then make an HVAC efficiency-maintenance program a part of your continuous energy management program.
Use atomisation rather than steam for humidification where possible.
Clean HVAC unit coils periodically and comb mashed fins.
Upgrade filter banks to reduce pressure drop and thus lower fan power requirements.
Check HVAC filters on a schedule (at least monthly) and clean/change if appropriate.
Check pneumatic controls air compressors for proper operation, cycling, and maintenance.
Isolate air-conditioned loading dock areas and cool storage areas using high-speed doors or clear PVC strip curtains.
Install ceiling fans to minimise thermal stratification in high-bay areas.
Relocate air diffusers to optimum heights in areas with high ceilings.
Consider reducing ceiling heights.
Eliminate obstructions in front of radiators, baseboard heaters, etc.
Check reflectors on infrared heaters for cleanliness and proper beam direction.
Use professionally-designed industrial ventilation hoods for dust and vapor control.
Use local infrared heat for personnel rather than heating the entire area.
Use spot cooling and heating (e.g. — use ceiling fans for personnel rather than cooling the entire area).
Purchase only high-efficiency models for HVAC window units.
Put HVAC window units on timer control.
Don’t oversize cooling units. (Oversized units will short cycle which results in poor humidity control.)
Install multi-fueling capability and run with the cheapest fuel available at the time.
Consider dedicated make-up air for exhaust hoods. (Why exhaust the air conditioning or heat if you don’t need to?)
Minimise HVAC fan speeds.
Consider desiccant drying of outside air to reduce cooling requirements in humid climates.
Consider ground source heat pumps.
Seal leaky HVAC ductwork.
Seal all leaks around coils.
Repair loose or damaged flexible connections (including those under air handling units). Eliminate simultaneous heating and cooling during seasonal transition periods.
Zone HVAC air and water systems to minimize energy use.
Inspect, clean, lubricate, and adjust damper blades and linkages
Energy Efficient System Design & Selection
The greatest opportunities for energy efficiency exist at the design stage for HVAC system. HVAC Design should not be tailor made as its operating cost and performance in totally depended on local environmental condition, optimum capacity by considering season variation as well as energy efficiency is the most important part of any pharmaceutical HVAC systems.
Energy Monitoring & Control System
An energy monitoring and control system supports the operation of HVAC system by monitoring, controlling and tracking system energy consumption. Such system continuously manages and optimises HVAC System energy Figures of Waste heat recovery and saving energy consumption and indentifying potential technical problem in HVAC system.
Example: For monitoring and control of HVAC, BMS System should be preferred along with configuration of current or power measurement HVAC System also for maintaining room pressure motorised damper should be installed to maintain the required parameter with energy efficiency.
Figures of Waste heat recovery and saving energy.
Automation and Loss Miniminsation
Installation of VFDs for Air Blower Modulation accordingly air flow requirements will reduce energy consumption at part load operations.
Installation of 2-way or 3-way valves will modulate chilled water flow as per indoor environmental condition which reduce load on chiller.
Heat energy losses from leakages through door and windows lead to lowering energy efficiency in HVAC systems.
Example:
Door Size: 1800 x 1500 (Area = 2.7 sqm),
Air Velocity: 0.25 – 0.3 m/s, Air Losses = 715 CFM
If door remains open for 5 sec, Air losses = 60 CFM
Equivalent Power = 0.08 KWh, Door Open Frequency = 50 -70 Times / Shift
Equivalent Power = 4 KWh/Shift
Case Study: Waste Heat Recovery
Utilisation of heat energy available in exhaust air by reducing fresh air temperature through heat transfer between fresh air and exhaust air.
If existing return air is through common false celling area between AHU room and conditioned area, additional load (of above false celling area) approximately 15 to 18 per cent has been added in actual requirement of HVAC System.
Appropriate size of return air duct required which is to be connected with AHU inlet with provision of fresh air duct with damper on both return air as well as fresh air duct.
Fresh air damper and return air damper open or close position to be set accordingly temperature of return air temperature and fresh air temperature.
Lower temperature air intake rate to be increased by setting damper accordingly
Provision of return duct in place of return through false celling for recirculation Type HVAC System.
Case Study: Evaporative Cooling System
Objective
Utilisation of ETP/ STP treated water to maintain zero discharge condition and simultaneously utilisation of treated water for fresh air cooling media.
Principal of Operation
After being cooled by Cooling Tower Treated Water has been recirculated in fresh air cooling unit to reduce the Inlet Air Temperature (Ambient).
Air Cooled by Fresh Air Cooling System has been supplied to main HVAC Systems instead of taking fresh air directly at ambient temperature HVAC System have inlet air with reduced temperature than ambient air which in turns reduction of reduction of heat load on chilled water cooling coil, ultimately, saving in power consumption of chilling plant.
Conclusion
In this article, author has tried to explain the methods of energy conservation and saving energy and at this era, the labour cost, material cost and transportation cost is increasing much in India and worldwide. So, it is important that by doing proper energy conservation and audit, industry can enhance its profit margin. These case studies and simplified block diagram can be useful for understanding chiller, refrigeration and HVACR systems.
