HVAC Absorption Chillers vs Electric Chillers
In any system of ventilation and conditioning,selection of chillers involve many factors that must be considered judiciously.These factors simultaneously present many advantages and disadvantages for end users.To select water chillers,HVAC engineers take into account all these factors, taking into account all of the resources they have on their site.
Comparison of Absorption Chillers and Compression (Electric) Chillers
The following is a comparison of the absorption and electric chiller is presented below with aim to help You to decide the type of chillers for ventilation and air-conditioning.
- Absorption chillers have COP (coefficient of performance )of only 0.54–1.1 and it competes poorly with electric pumps (rotary compressor chillers). Electric chillers on the other hand, the COP from 1.0 ~ 8.0.
- Absorption HVAC chillers occupy approximately 50% more floor space than the equivalent electric chillers (vapor compression chillers).
- Additionally, due to height of absorption chillers, mechanical equipment rooms must be 6-10 ft taller than rooms housing electric chillers. Finally, since the liquid solution is contained in long, shallow trays in an absorption chiller, the floor must be as close as possible to the maximum level.
- In ventilation and air conditioning systems,an Absorption chiller will weigh at least twice the equivalent electric chiller (vapor compression refrigerating machine).
- Because of the greater size, absorption chillers are sometimes shipped in several sections, requiring field welding for final Assembly.This is not the case with a colleague chillers electric chillers or compression.
- Most electric water chillers are shipped from the factory with their refrigerant installed.While the Refrigerant and absorbent (including additives) must be field installed in absorption HVAC chillers.
- When we talk about noise and vibration, absorption chillers (unless direct-fired) are quiet and essentially vibration-free in comparison with compression chillers (electric chillers). Noise and vibrations in HVAC systems, more annoying than anything else .
- Due to the potential for crystallization of the lithium bromide in the chiller if it becomes too cool, the condenser water temperature must be above 75–808F.No problem of crystallization in electric chillers (vapor compression chillers). Forget about crystallization and stay cool, if you set the compression chillers .
- Water absorption chillers sometimes require emergency power in cases of prolonged power outages often expected. Without electricity and heat supply, the chiller begins to cool and the lithium bromide solution may crystallize. However, as absorption chillers consume very little power, so a small separate backup generator can serve this purpose well.
- Ventilation and air conditioning systems also gives the value of quantity of heat is rejected in condenser by cooling water or air-cooling media.The rate of heat removal from the condenser of lithium bromide chiller is 20-50% greater than for the equivalent electric chiller, requiring higher prices on condenser water Flow and large cooling towers and condenser water pumps.
- Finally, indirect fired absorption water chillers will be at least 50% more expensive to purchase than the equivalent electric-drive chiller. Direct-fired absorption chillers will cost almost twice more expensive than electric, machine, and additional costs associated with the provision of air for combustion and ventilation (stack).
- Water chiller or lithium bromide chiller uses natural refrigerants such water and eliminate the need for the use of CFC or HCFC refrigerants that possess high global warming potential.
- If you have a large amount of waste heat or direct fire available and want to reduce electrical load ,probably absorption chillers are the best solution.But, obviously, all the above factors should be considered for the selection of the climatic water chillers.
Air Cooled vs. Water Cooled Chillers Operating Costs
Traditional thinking has been that water cooled chillers are more efficient than air-cooled chiller. If we look at the cost of the compressor, it may be true. However, using state-of-the-art technology with centrifugal compressors and variable speed, air-cooled chillers are often the better choice. Taking a deeper look at air cooled chillers vs water cooled chillers, it is recommended to consider the operating costs associated with each chiller system.
It is important to look at total operating costs associated with the chillers, not only the cost of the compressor. As the graphic indicates, cooling operating costs tower should be added to the current expenses of the water cooled chiller. System, cooling tower includes tower fan, water and sewage, costs of chemicals and pumping equipment. In the process of application, tower plants typically have process pumps and recirculation pumps, which can add significant value. The figure below shows a comparison of the cost of operating air-cooled variable speed centrifugal chiller or water cooled chiller screw. This comparison is based on 140 tons of cargo and information about Chicago weather, $.07/energy costs, kWh, 5.00 $/1000 gallon water and sewer costs and 6,000 hrs/year operation.
Because the air cooled chiller uses floating head pressure control energy consumption of the compressor is actually less than with water cooling is the compressor cooler $4,757 difference ($20,585-$15,585). Add in the cost of operating the system tower from $17,429 results in 22,186 $/year operating costs. More efficient variable speed water cooled centrifugal chiller reduces the difference in cost to $16,725-still a significant annual cost penalty.
The heat exchangers
An end view shows five modular chillers and heat exchangers at the bottom of the units with two compressors on the top. This project was modular chiller is the only option for the basement of the existing building due to limited space. The next Category of chillers is defined very based on the Type of heat exchanger used in the chiller. The choice of heat exchanger can be either air or water cooling and will have a big impact on the efficiency and cost of the chiller. The air-cooled chiller are limited in size to 500 thousand tons of capacity, while water-cooled chillers of a series of nearly 9000 tons.
The air-cooled chiller work on the concept of using air to reject the building's heat demand, which approaches the external environment temperature on the dry thermometer. Hence, air-cooled chillers must raise the refrigerant temperature and pressure at a higher level and require more energy to do the same amount of cooling compared to water-cooled chiller. Despite this, the air-cooled coolers allow a packaged system from a single source of responsibility. Design and installation time are reduced due to less equipment of participation: no requirements for cooling towers and associated problems with freezing, the flow rate of feed water and chemical treatment, or the condenser water pumps. The air-cooled chiller use scroll compressors up to 200 tons and use screw compressors above 200 tons capacity.
Alternative to water-cooled chillers. They work by using water to reject the building's heat, which approaches the outside ambient air temperature wet—bulb which, as a rule, lower than the temperature of the dry thermometer. Thus, water-cooled chillers are more energy efficient, since the condensation temperature is lower and they require less work of the compressor to increase the temperature of the refrigerant and pressure. Although the chiller energy may be less than that of a comparable air-cooled chiller, one must still assess all costs of the system, the chiller, including cooling tower and condenser water pumps. The smallest water-cooled chillers (200 ton) to start with multiple scroll compressors, those With 200 to 500 tons use screw compressors, and above 500 tons mainly use centrifugal compressors. Water-cooled chillers are usually much longer than the air-cooled chiller due to the location of the cooler inside the building and reduction of operational loads using water as sealing liquid.
It shows two 400-ton air-cooled screw chillers in parallel for industrial building. Courtesy: ring & DuChateauAnother item to be aware is the method of cooling compressor and motor, which can be an open drive or hermetic design. Open cooler storage, heat is rejected directly to the premises and needs to be cooled or ventilated with ambient air, possibly requiring large volumes of air to cool the room. In addition, contaminants can potentially get into the engine and coolant seals can leak if the seals are not maintained properly. Hermetic or semi-hermetic chillers are refrigerant cooled, and the heat is rejected to the refrigerant, reducing the load of heat removal in the mechanical room. These machines do not require seals, as the engine is completely contained within the app, so there is the potential for refrigerant leakage from the system.
The modular chillers
Modular chillers are the newest option on the market of refrigeration equipment, and are very popular. They are like building blocks that you can add modules of varying capacities to achieve the desired power. Typical modules are available in sizes 30, 50, 70, and 85 tons consisting of scroll or screw compressors. The chillers are designed specifically to fit through doorways in new or modified installation, and extremely compact. Chiller modules up to 85 tons will require only 10 to 12 sq. m building area without large clearances required for evaporator or condenser to pull the pipe. Then these modules can be combined nearly 1,000 tons with a total capacity of refrigeration unit. When you build increasing the load or the built-in add-on, the add-on module required capacity can be installed, provided that the distribution system set up for the additional load. Similarly, instead of purchasing a completely unnecessary chiller for N+1 capacity, an additional module can be added, providing redundancy for one module at a fraction of the cost of acquisition excess of the whole packaged chiller.
Despite the advantages of modular chillers, one major drawback is its high initial cost. Most modular chillers about 150% to 200% of the cost of similar tonnage chiller with water cooling. Secondly, the modular efficiency of the cooler, as a rule, are not as attractive as standard water-cooled chiller efficiency through compressor used in refrigeration. Thirdly, water treatment is extremely important because modular chillers plate and frame heat exchangers instead of shell and tube heat exchanger which should be cleaned to prevent contamination and clogging of heat exchangers. Duplex, external filters must always be used to ensure the maintenance of one strainer while maintaining operation through the other filter. Similarly, the heat exchangers must be fully serviceable with individual shut-off valves to isolate the heat exchanger without shutting down the chiller. Figure 3 shows an example of a modular chiller with heat exchanger in operating position.
Water-cooled and air-cooled chiller options based on power are shown for major manufacturers, based on unit tonnage.
Categories cooler, as a rule, have much in common, and variants within each category the power range described above. In figures 5 and 6 provide a simplified method to observe the ranges and types of compressors, air-cooled and water-cooled chillers with major manufacturers chiller.
The initial investment
Initial costs are always a critical discussion of any project. In some projects, the initial costs can outweigh the life cycle and operating costs. Since the cooler costs vary so much, it is difficult to provide an overall initial cost of the cooler based on its size, as many factors associated with each cooler Size depending on the manufacturer.
In General, a scroll chillers are the most expensive of the three types of considered chillers. Centrifugal chillers are the most cost effective option, but not all of the tonnage. When screw and centrifugal compressors are available, depending on capacity, screw compressors generally 10-15% more expensive. Similarly, the air-cooled chiller is generally more expensive initial investment than the same size of water-cooled chiller when comparing strictly the initial cost of air-cooled chiller water-cooled chiller.
However, when evaluating the total installed cost air-cooled or water-cooled systems, including all the necessary components for the system to operate at full capacity, investing in the necessary components in the system with water cooling is always more expensive. The reason: the air-cooled system requires only coolers and cooling water pumps, while in the system of water-cooled chillers require a chilled water pumps, water pumps condenser and cooling towers to full operation of the system and reap the rewards of energy efficiency.
In figures 5 and 6: water-cooled and air-cooled chiller options based on power are shown for major manufacturers, based on unit tonnage.
The example project is also presented to illustrate the differences in initial costs of the chiller. This project involves the replacement of two 180-ton centrifugal water-cooled chillers since 1980.To determine the best cooler for the project was the Specification of the procurement, indicating the capacity of the chiller, the maximum evaporator and condenser pressure drops, performance criteria, maximum sound level, and maximum size restrictions. Then it was recommended to producers in trading any type of chiller that meet the requirements of the technical specifications. These results included a mixture of performance levels, scroll chillers, screw chillers and modular chillers. This tonnage is 44% of the variation in costs.