It is said that HVAC systems typically consume around 70% of a building’s energy usage, with 25-35% of energy consumed by chillers producing chilled water for air-conditioning.
Therefore, the efficiency of chillers and the optimization of their performance within the HVAC systems they operate are important in achieving high performance.
When it comes to energy-efficient HVAC system, several questions come to mind:
What are the green technologies behind them?
A: The chiller system is still the best choice for the large scale buildings, for a single chiller cooling capacity can be up to 4,000 Tons or above, which can reduce the numbers of equipment and reduce the installation space.
The most dramatic improvement in operating efficiency can be achieved by replacing an older chiller with a new, high-efficiency chiller. Centrifugal chillers that are 15-20 years old had a peak efficiency of 0.75-0.85 kw/ton when new, while those that are 10-15 years old had a peak efficiency of 0.60-0.70 kw/ton but even with a comprehensive chemical water-treatment program and regular tube cleaning, those efficiencies have declined, resulting in peak efficiencies of 0.80-1 kw/ton or lower.
New-generation centrifugal chillers offer peak efficiencies of 0.50 kw/ton or higher. When coupled with variable-frequency drive, they can deliver higher efficiency over a range of cooling loads. High-efficiency chillers can reduce annual cooling energy requirements by 30%-50% in most applications compared with the existing old chillers.
Such as the Midea’s high efficiency DC inverter falling film centrifugal chiller adopts core technologies such as aerospace aerodynamics, a high-speed inverter electric motor, two-stage complete enthalpy, and falling film evaporation. The chiller has overcome the energy efficiency bottleneck for small cooling tonnage, enhancing the IPLV to 10.69W/W (0.33kW/Ton), lowering noise to 75 dB(A). Highly efficient and stable operation is achieved under multiple working conditions. Due to the use of full falling-film evaporation technology, the refrigerant charge can be reduced by 40% compared with flooded type.
In the HVAC industry, Energy conservation and restriction of the use of hydrofluorocarbons (HFCs) with high global warming potentials (GWPs) are the current major issues for HVAC equipment. To improve the overall energy efficiency in chiller systems, technical development is now focusing on larger oil-free centrifugal compressors with permanent magnet (PM) motors, growing use of variable speed control by Variable Frequency Drives (VFDs) and two-stage compression systems maintaining high efficiency with wide operating ranges.
But now, the VRF (Variable Refrigerant Flow) HVAC systems, have been the HVAC system of choice in Europe, Japan, China and other parts of the world for quite some time. Over the past 10 to 20 years, VRF HVAC technology has become increasingly popular in Europe and Asia market and now to Middle East, the extraordinary Al Ain 5000 Villas project sets a very good example of VRF installation.
This sophisticated new VRF HVAC technology is capable of providing not only cooling, but also heat, and even both simultaneously to different areas within the space. What’s more, these VRF HVAC systems are very quiet and energy-efficient because the variable-speed compressor runs only at the capacity needed for the current conditions by varying the flow of refrigerant to the indoor units based on the exact demands of the individual areas.
Full DC Inverter V6 series VRF system
Recently Midea launched its new generation Full DC Inverter V6 series VRF system in Dubai, featuring the world’s largest capacity single module outdoor unit at 38HP and combination capacity at 128HP, as well enjoys a 40% reduction in footprint compared with conventional design. The VRF is significantly penetrating not only the residential but also the commercial HVAC market which chiller has a strong position.
How open is the market when it comes to natural refrigerants?
A: So-called natural refrigerants for chillers, ammonia (R717) and pro-pane (R290) are used mainly in Europe, and have advantages such as low GWP, an ODP of zero, superior performance, and low cost. However, toxicity and flammability remain high barriers to use in HVAC systems installed in commercial buildings.
R717 refrigerant has traditionally been used in industrial refrigeration, but it is also used in HVAC chillers, mainly in the European market.
R290 well known as propane, several manufacturers in Europe have released air- and water-cooled chillers with R290 refrigerant as standard.
Water (R718) as a refrigerant has been used for thermal-driven absorption chillers. Meanwhile, research and development conducted with a view to using water for vapor compression chillers/heat pumps, as an ideal refrigerant free from GWP and toxicity/flammability issues, has been carried out for a long time in Europe, the United States, and Japan. As a result, large centrifugal chillers with water refrigerant have been installed in large ice-making and air conditioning systems, mainly in Europe.
As a refrigerant, water is fundamentally different from conventional HFC refrigerants. That is, the required suction gas volume of water is about 150 times bigger than that required by R134a, and water has a compression ratio 3.4 times higher than that of R134a. Therefore, centrifugal compressors using water need to be much bigger.
There’s still a long journey to find better Alternative Refrigerants, it will be even more difficult to find a Better Natural Alternative Refrigerant which should have lower cost but better performance in efficiency and capacity for the chillers, especially the large capacity centrifugal chiller.
In conclusion, it’s hard to predict how open can the market be when a perfect natural refrigerant comes. If it really comes, it will bring a revolution in the industry, it may change the games of chiller industry even the whole HVAC industry.
And most importantly, what are the tips for designing such a system?
- Understand the variety of chiller options based on load requirements.
- Learn to calculate a simplified cost/ton estimate for estimating chiller initial investment costs.
- Know the appropriate calculations for determining chiller plant operational costs.
Chilled water systems are cooling systems that circulate chilled water throughout a building for cooling and dehumidifying a building’s air. They come in all shapes, sizes, and configurations. Chilled water systems are closed-loop systems, meaning that the system water is continually recirculated and not exposed to atmospheric pressure, similar to domestic water systems.
The first step in chiller selection is understanding the options available. A building’s block load will determine the overall capacity, whereas part load will determine the number and quantity of chillers required, with multiple chillers providing the ability to stage chillers in response to load. Such as the Midea Aqua Super II series DC Inverter scroll chiller with A++ rated energy efficiency under CE Erp regulation and the odular design enables up to 16 units combination.
Second is the type of chiller compressors. Most small chilled water plants—from 10 tons up to approximately 200 tons in capacity—use scroll compressors for production of chilled water. As the capacity increases, the chillers increase the quantity of scroll compressors, typically of equal sizes to provide the total chiller capacity required. The disadvantage is that chiller capacity control is provided as stepped control instead of modulating control. Although the multiple compressors may be a disadvantage for capacity control, generally they are piped with multiple refrigerant circuits which provide some system redundancy. Inverter driven scroll compressor have been widely used for the chiller which can improve the part load efficiency quite a lot.
Once the capacity exceeds the size of multiple scroll compressors, typically, chillers use screw compressors. Screw compressors are available in sizes from 50 up to about 500 tons. Screw compressors have the ability to vary the cooling output capacity from 100% to 20% via the use of a slide vane to limit refrigerant delivery to the compressor and provide a smooth, modulating transition between capacities. It is important to note that screw chillers have only one compressor, so a loss in the compressor would cause a complete loss in chiller capacity.
The third type of compressor is centrifugal compressor which starts at approximately 100 tons and go up to thousands of tons depending on the number of compressors. A variable frequency drive (VFD) also could be used for capacity control to vary the speed of the impeller rotation in conjunction with inlet vanes. Inlet vanes and VFDs accomplish different objectives: inlet vanes are used for buildings that may have a large load variation, while VFDs should be used for buildings that have large variations in lift, which equates to changes in condenser relief. VFDs are not always an appropriate option for chillers and their use greatly depends with their ability to vary temperatures. Centrifugal chillers operate at high speeds which are extremely reliable and robust devices. Centrifugal compressors have great efficiencies throughout their operating range and are relatively compact for the amount of tonnage that can be provided per sq.m of mechanical room space.
At last, control sequences for HVAC system are very important. Using a BMS/BEMS software can help to manage all the devices such as chiller, water pumps, air side terminals (AHU and FCU) In plants that use multiple chillers, the programs can identify chillers that can help meet the current load at the highest operating efficiency.
Taken together, the recent advance in chiller design means significant savings for institutional and commercial facilities. Designers that take advantage of new technologies and design features can expect these systems to use only 50%-60% of the energy required by systems installed as recently as 10-15 years ago.
