Applications
- Large Tonnage Space Cooling
- Industrial Process Cooling
- Cogen Waste Heat utilization
- Waste-to-Energy utilization
Overview
With the exception of very high cost electric areas, absorption chillers cost more to operate than electric chillers. They also cost about twice as much to purchase. Therefore, a reason other than average electric cost is needed to justify a base-loaded absorption system, unless the chiller is powered by “waste heat”. In areas of very high cost on-peak electric power, hybrid systems combine absorption chillers for use during on-peak electric hours and electric chillers for base load operation.
Steam-fired absorption is a good application where there is a low cost of steam such as a cogen or waste energy plant. Direct-fired natural gas units are used in hybrid and high-cost electricity areas. Absorption chillers do NOT use a CFC or HCFC refrigerant; therefore, some users purchase absorption chillers for this environmental advantage. Larger tonnages (above 500 tons) have a more favorable first cost when compared to electric technologies. Therefore, larger tonnage units are more common for absorption applications. They may also be used in places like campuses with a central steam loop and not enough electrical power distribution to run decentralize electric chillers. This may be the case where buildings either did not have chillers or used older single-effect absorption units and have upgraded to double-effect or direct fired absorption technology.
Food processing facilities use absorption chillers for facility and process cooling, but absorption chillers cannot be used for freezer operations.
How it works
One of the oldest methods to mechanically cool a space is with absorption technology. It seems unreasonable to burn a flame to produce cooling, but that is what happens inside an absorption chiller.
The refrigerant used is actually water, as that is the working medium that experiences a phase change that causes the cooling affect. The second fluid that drives the process is a salt, generally lithium bromide. Heat is used to separate the two fluids; when they are brought back together in a near vacuum environment, the water experiences a phase change to remix with the salt at a very low temperature (at normal atmosphere pressure, water vaporizes at 212F; in an absorber, water vaporizes cold enough to produce 46F chilled water.)
Most manufacturers now offer units that are either steam or direct fired; earlier units were only steam fired. New units are also called “double effect”, which gives them a much higher efficiency than the older units. The double effect is a second heat exchanger that boosts the efficiency from about 60% to near or just over 100% (100% is achieved when the existing space temperature is high enough to add some “free” heating energy to the process; since vapor compression is not used, it would otherwise be impossible to exceed 100% efficiency with known technology and lithium bromide.) (Third Effect absorbers are under development.)
Operational Issues
An early problem was “crystallization” where something would go wrong in the cycle and the salt and water would permanently separate, and the salt would crystallize on the walls of the absorber. Modern controls pretty much make that impossible to happen now.
Absorbers are large units, with on-site assembly required, especially in the larger tonnage units. However, the direct-fired units with the ability to both heat and cool from the same unit can take up less space overall than a boiler and separate electric chiller. Some units can optionally heat and cool at the same time (for multi-zoned applications that have both a heated and chilled water loop).
Absorbers must have a cooling tower; air cooled units are not an option – even for the smaller units (except for Robur Units).
Absorbers use no CFCs or HCFCs.
All modern double effect absorbers were developed in Japan; only recently, through partnerships, did American names start reappearing on units and very limited US production began.
Chilled water temperature is at its lowest at about 46F. Therefore, absorbers cannot be used in a low-temperature refrigeration application.
General Economics
Absorbers have a COP that is about 1.0, compared to engine driven compressors about 1.5 and electric at about 3.0. However, if CFCs/HCFCs are an issue, or there is an already available source of steam (or “free” steam from a cogen or waste), an absorber could be the system of choice. Units are typically economical at 500 tons and above (on a first cost per ton basis).
Absorbers with a COP of 1.0 burn 12,000 BTUs of gas for each ton-hour of cooling, or at $8.00 per MCF, $0.096/ton-hour. There is an electric load on the absorbers for pumps (in addition to cooling towers and chilled water loops) that must be considered as well.
An absorption chiller can break even with the cost of an electric chiller when the gas cost is below $4.50/MCF and the electric cost is above $0.08/KWH. Then you can deal with the additional first cost of the units, that will be at least 50% higher. Depending on the configuration of a direct-fired system, if a boiler cost is being offset and the tonnage is large enough, first cost may be closer in line with a separate gas boiler and electric chiller plant.
Absorption chillers are typically considered where there is a source of “waste heat” such as from an on-site power generation plant or a high temperature process that can be used as a source of heat recovery. Using “waste heat” requires a detailed analysis to determine if the cost to recover and utilize the heat is less than the value of the work performed by that heat.
Steam-fired units require 50-125 psi steam and about 10 lbs/ton-hour steam usage. The higher the steam pressure, the lower the required pounds per ton usage.
More Information
Go to the Energy Solutions Center’s Gas Air Conditioning Consortium web site at www.GasAirconditioning.org
Manufacturers
Broad
Broad Air Conditioning is a privately owned Chinese company established in 1988 and headquartered in Changsha, the capital of Hunan Province. The company was the first in China to develop their own DFA design and through dedication and quality has become the world’s largest manufacturer of two stage absorption systems. Broad’s primary product is a direct fired lithium bromide absorption chiller/heater called the Spectrum. Double effect or two stage indirect steam and hot water or waste heat driven units are also available.
Direct Fired Double-Effect Chiller/Heater 50 – 2,600 Tons
401 Hackensack Ave, Suite 503
Hackensack, NJ 07601
Telephone: 201-678-3010
Web site www.broadusa.com
Carrier
Carrier currently offers only one line of Steam/Hot Water fired Single-Effect Chiller (Carrier used to have a marketing agreement with a manufacturer of direct-fired equipment. That agreement was terminated; they are currently looking at product options for re-entering the direct-fired market. Per Carrier web site and conversation with Carrier Direct Rep 12/2003 and 1/2004)
Steam/Hot Water Single-Effect
Hermetic Absorption Liquid Chillers
108 to 680 Nominal Tons
(380 to 2392 kW)
Web site: www.carrier.com
McQuay
Former Sanyo-Bohn, next McQuay-Sanyo, now McQuay International
Size Range 100 – 1500 tons direct-fired or steam-fired; (oil fired also available)
Both lines offer heating and cooling from same unit (simultaneously is optional)
Literature claims up to 40% savings in floor space with direct fired chiller/heater over boiler and separate chiller.
Direct Fired COP 1.0; Steam fired COP 1.4 (consider efficiency that steam is produced at)
Ratings for Direct Fired chiller/heaters are 10,000 BTUs heating for each ton of cooling
ie: 500 ton cooling is rated for 5,000,000 BTUs heating; input 6,050,000 BTUs
Steam fired unit requires minimum 57 psi steam; 114 psi max; 9.8 – 10.5 lbs steam/ton-hr (lower steam pressure, higher steam usage)
500 ton unit requires almost 10 KW for auxiliaries
Web site www.mcquay.com
Robur
Robur is the owner of the single still existing US made line of direct fired gas chillers/ air conditioners in small tonnages. The line was extensively marketed as the “Servel” in the 60’s/70’s and was then known as “Dometic” in the 1980’s. Robur is foreign owned, with about 90% of the production going to over-sea’s markets. Manufacturing is still done in Evansville, Indiana.
Robur units are available in 3, 4, and 5 ton models; sizes larger than 5 tons can be modularized and skid mounted (upto 25 tons). The skid mounting and inter-connecting of controls and piping allows for redundancy/ reliability, but not reduce the cost per ton.
Units use ammonia as the refrigerant and water as the working medium; chilled water is produced and circulated to a fan coil unit. They are available as cooling only, or heating and cooling. With the heating option, an auxiliary boiler is attached to the side of the chiller; internal piping diverts the circulating water to the boiler side in the heating mode.
Web site www.robur.com
Trane
Made in the USA
Trane has been manufacturing absorption chillers for more than three decades. The newest line, the Trane Horizon® two-stage steam-fired absorption water chiller is the only line of two-stage absorption products designed, built and supported in the USA.
Steam fired Single Effect 112 – 465 Tons
Steam or hot water fired Single Effect 500-1,350 Tons
Horizon Steam-Fired Double Effect Chillers 380 – 1,650 Tons
ThermaChill Direct Fired 100 – 1,100 Tons
The ThermaChill line is made by Kawasaki, and sold under the Kawasaki label in the rest of the world.
Web site http://www.trane.com/Commercial/Equipment/Refrigeration.aspx
Thermax
Thermax Inc. is part of the Thermax Group, a leading global company specializing in the areas of generation and conservation of energy and preservation of the environment. The company provides integrated services and equipments in Boilers and Heaters, Captive Power, Chemicals, Cooling and Water & Waste Solutions.
Absorption Cooling Division of Thermax which pioneered Vapour Absorption Technology in India, offers global solutions for industrial cooling and air conditioning.
ACD has a technical collaboration with Kawasaki, Japan, world leaders in Absorption Cooling technology and offers cost-effective and “best in class” ecofriendly Vapour Absorption Machines (VAMs). Today the division offers the largest product range in the world to suit every cooling requirement.
Hot Water Driven
Thermax hot water driven machines achieve chilled water temperature up to 40.1F, and are available in 10 to 1400 tons.
Steam Driven
The Thermax Steam Driven Single and Double Effect machines are available in the range of 50-1400 NTR and can produce chilled water up to 40.1ºF. They can operate on an entire range of steam pressures.
Fuel Driven
Thermax Direct Fired Machines are available in models ranging from 40 – 1100 NTR and can achieve chilled water temperature up to 41F.
Thermax-USA
40440 Grand River Avenue,
Novi, MI 48375
Telephone: 248-474-3050
Web site www.thermax-usa.com
Yazaki
A Yazaki absorption chiller-heater, using water as the refrigerant, is today’s best choice in air conditioning for protecting the environment and reducing the cost of energy. Double-effect cycles and advanced technology ensure high performance and long term reliability. With over 100,000 units operating worldwide, Yazaki is a leading supplier of non-CFC based space cooling. Capacities of 30 through 100 RT are available to either cool or heat installations such as schools, offices, hospitals, industrial facilities, and hotels.
Gas fired double effect chiller-heaters 7.5,10,20,30 modular to 150 tons
Gas and/or water fired single & double effect chiller heaters 20 & 30 ton and models to 150 tons.
Solar panel operated for residential 1.3,2,3,5 tons
Yazaki Energy Systems, Inc.
13740 Omega Road,
Dallas, TX 75244-4516
Telephone: 972-385-8725
Web site www.yazakienergy.com
York
Formerly known as Hitachi, the line is now manufactured in United States by York International in Houston, Texas. This is the only large tonnage manufacturing plant in US (since 1992). Before York, the line was represented in US by Gas Energy Inc., subsidiary of Brooklyn Union Gas Co. York now has all marketing activities as well. Units up to 600 tons are completely prepackaged and shipped ready to fire up; larger units require some on-site assembly, but reportedly less than competition.
Optional burner is Nova low NOX with <30 ppm emissions.
IsoFlow line is a single stage absorber. Single stage are the older design (less efficient) but are smaller and cheaper than the two stage. If relatively low cost (or “free”) or low pressure only steam is available, the single stage makes sense. Water at 240F or steam as low as 3 psi can fire the IsoFlow. Single stage units are used in cogen or other waste heat applications. Size range is 120 – 1,377 tons. Chills to 45F.
ParaFlow is a two stage line that can be direct fired or steam fired. Direct fired units can heat and cool at the same time; 140F or optionally, 175F water out. Direct fired sizes 200 – 1,500 tons. Steam fired units are 430 – 1,500 tons (8 sizes). Steam must be 115 to 128 psi.
Direct fired 500 ton unit requires 5,868,000 BTUs ~ COP 1.02; heating capacity 6,000,000 BTUs
Requires 8.5 KW for auxiliaries; Inlet gas pressure 0.5 – 1.0 psi
Web site www.york.com/products/esg/