Liquid Chillers
Chillers provide comfort for people, and a controlled environment for processes and equipment in a variety of facilities and environments. Chiller applications must be able to deliver cooling and heating on demand, consistently, efficiently, and in an environmentally-friendly manner.

Typically, chillers are part of larger system, comprised of control panels, pumping systems, cooling towers, duct work, Variable Air Volume (VAV) boxes, thermostats, and zone sensors, all designed to work seamlessly together to deliver temperature, humidity, and air quality within predetermined limits. Chillers can be found in a number of different applications, including office buildings, data centers, cooling plants, educational facilities, manufacturing, and process applications. They are used on large buildings, as they can take advantage of load diversity and be configured to provide redundancy in cooling capacity.

>1. Typical Chiller Applications
There are many types of chillers to suit a variety of needs; however, space requirements, system requirements, weather conditions and climate zones, and potential ancillary equipment must be considered to determine if a chiller is right for the project.

Like other HVACR equipment, chillers are governed by standards, guidelines, and codes, which have an impact on the technology. Overall, chillers are energy efficient, and use a secondary heat transfer fluid to provide cooling to the occupied space or process.

Contractors consider equipment that provides the best value, as well as easy installation and maintenance, and technical support. The benefits of using a chiller vary depending on the type of chiller used. Units come with different size footprints to fit both large and small mechanical rooms. Performance-based design ensures that energy efficiency and value goals can be met. While all equipment has associated costs, the type of chiller chosen will determine whether or not it will have a low initial cost, or if the cost is spread across the chiller’s life cycle.

Chillers are designed to allow for easier installation and maintenance. Parts that require regular maintenance, such as piping and valves, compressors, and oil sight glass are thoughtfully placed for easy access. Chillers meet performance needs by offering various control methods that are optimized for energy efficiency and value requirements across a wide range of applications.

Technical support, such as a detailed owner’s manual, engineering guide, and a help desk staffed by experienced personnel, is critical for contractor success. Manufacturers conduct classes to teach equipment technicians installation requirements and troubleshoot equipment problems. Technical support also provides help with identifying service or replacement parts.

The commercial building’s heating, ventilating, and air conditioning system maintains the inside environment within a desired range of conditions, independent of the outdoor environment. A well designed system enhances the productivity of the occupants of the building, supports the efficient operation of manufacturing processes and controls, and conserves energy and resources. Chillers are selected because of their high efficiency, ability to operate efficiently over wide operating ranges and capacities, ability to provide redundancy, and ability to take advantage of load diversity in buildings.

Tenant Comfort
HVAC system designers strive to create a building environment that is acceptable to most of the people, most of the time. While a comfortable environment will not always improve productivity, an inadequate environment will certainly reduce it.

In order to design the optimal system for a building, designers will consider and understand the needs of the tenants. Who will be using the building? How will they be using the building? When will they be using the building? Tenants could be workers in office buildings, students in a classroom, patients in a hospital or care facility, or travelers in airport, bus and train terminals. Each type of building application requires different considerations, designs, and HVAC systems.

Improving tenant comfort requires managing the temperature, humidity, air flow, and the indoor air quality.

> 2. Chiller Basics

Types of Chillers
One of the first decisions building developers face is the selection of either a water-cooled or an air-cooled chiller. These names refer to the method that the chiller uses to reject heat to the atmosphere. All chillers are HVAC machines that chill water or other secondary fluids; what distinguishes them is the method by which they reject heat to the ambient.

Water chillers cool secondary fluids (typically water) that are subsequently transported by pumps and pipes. The water passes through the coils in fan coils and air handlers to cool air in an air conditioning system, or it can provide cooling directly to a manufacturing or industrial process. In a water-cooled chiller, condenser water is pumped through a heat rejection heat exchanger while refrigerant vapor is condensed in the heat exchanger. As heat is transferred from hot, high-pressure refrigerant vapor to water, the refrigerant changes from a vapor and condenses to a liquid.

Benefits:
  • Larger systems
  • Greater energy efficiency at full and large load
  • Ability to operate over a wide range
  • Longer equipment life
  • Allow for redundancy
  • Can take advantage of building load diversity, which results in lower overall equipment capacity
In an air-cooled condenser, propeller type fans are used to draw outdoor air over a heat transfer surface. The hot, high pressure refrigerant vapor flows through the tubes as heat is transferred to the cooler outdoor air. The resulting reduction in the heat content of the refrigerant vapor causes it to condense into liquid. Within the final few lengths of condenser tubing, the condensed liquid refrigerant is sub-cooled.

Benefits:
  • Lower first cost
  • Does not require a machine room
  • Lower maintenance costs (no cooling tower needed)
  • Prepackaged system for easier design and ease of installation
  • Better low ambient operation
  • No makeup water needed for cooling tower
  • Allow for redundancy
  • Can take advantage of building load diversity, which results in lower overall equipment capacity
Equipment and Manufacturing Process
Similar to people, equipment works better in an environment that has fairly narrow range of temperature and humidity. Chillers are an integral part of the system to manage, control, and monitor conditions that support those processes. Whether the application is food processing, drug manufacturing, or petrochemical processes, building owners need a system that is easy to install, operate, and maintain.

HVAC systems can support equipment and process efficiency additionally by:
  • Regulating the building environment to, in some cases, stop equipment if conditions exceed the predetermined safe ranges
  • Performing operational function of starting or stopping equipment in predetermined sequences
Chiller Technology

Scroll compressors
Scroll compressors have emerged as a popular alternative to reciprocating compressors and are generally available in hermetic configurations in capacities up to 30 tons. Multiple scroll compressors are often used in a single chiller to meet larger capacities and can offer as much as 30 stages of capacity. In general, scroll compressors are more efficient than reciprocating compressors and have proven to be very reliable, primarily because they have approximately 60 percent fewer moving parts than reciprocating compressors. Reciprocating and scroll compressors are typically used in smaller water chillers. Scroll compressors also offer stepped or discreet unloading capabilities, while screw and centrifugal compressors have proportional unloading. However, all compressor types are now starting to be offered with variable frequency drive.

Helical-rotary (screw) compressors
Helical-rotary (screw) compressors have been used for many years in air compression and low-temperature-refrigeration applications. They are now widely used in medium-sized water chillers. Helical-rotary compressors have a reliability advantage due to fewer moving parts and a wide operating map; they also operate for comfort cooling, medium temperature solutions, and high condensing temperatures. They have capacity control that use stepped unloading, proportional slide valves, and recently variable frequency electric drives.

Centrifugal compressors
Centrifugal compressors have long been used in larger tonnage water chillers. High efficiency, superior reliability, reduced sound levels, and relatively low-costs have contributed to the popularity of the centrifugal chiller. Centrifugal compressors are generally available in prefabricated chillers from 100 to 3,000 tons [350 to 10,500 kW], and up to 8,500 tons [30,000 kW] as built-up machines. The capacity of a centrifugal chiller can be modulated using inlet guide vanes (IGV) or a combination of IGV and a variable-speed drive. Other common names for variable-speed drive include adjustable-frequency drive (AFD), and variable frequency drive (VFD).

Variable Speed Drives
Variable-speed drives are widely used with fans and pumps, as well as centrifugal, scroll and screw chillers. As a result of the advancement of microprocessor-based controls for chillers, they are now being applied to water chillers. Using an AFD with a chiller can degrade the chiller’s full-load efficiency but can greatly enhance part load efficiency by reducing motor speed at low-load conditions, such as when cooler condenser water or cooler ambient for air cooled is available or a building is not fully occupied. For centrifugal compressors, it is important that the lift decrease with speed reduction to control capacity, which is why both inlet guidevanes and variable speed are required. For screw and scroll compressors, which are positive displacement compressors, speed alone can be used for capacity control.

Certain system characteristics favor the application of an adjustable-frequency drive, including:
  • A substantial number of part-load operating hours
  • The availability of cooler condenser water for centrifugals, but not for positive displacement
  • Chilled-water reset control
  • Low electrical utility demand charges or no peak load control systems

Evaporative chillers

An evaporative chiller is a modified hybrid version of an air-cooled condenser and a cooling tower. In evaporative chillers, the refrigerant is running through tubes and air is drawn or blown over the tubes by a fan; however, in an evaporative chiller, the water is sprayed on the tube surfaces to take advantage of the heat of absorption of water. As the air and water pass over the coil, it causes the water to evaporate, which results in cooler air temperatures and higher efficiency of the condenser. The evaporation process and cooler air absorbs heat from the coil, causing the refrigerant vapor within the tubes to condense. The remaining water then falls to the sump to be recirculated and used again. This application is best suited in dry, hot climates, similar to water cooled chillers using cooling towers.

Absorption water chillers
Absorption water chillers differ from vapor-compression chillers in a couple of ways, the first being that they use heat energy as the primary driving force. The heat can be in the form of steam or hot water (indirect-fired), or by oil or natural gas (direct-fired). Secondly, absorption water chillers do not have a compressor; the compressor is replaced by an absorber, a pump, and a generator. In addition to the refrigerant, which in this case is water, the absorption water chiller uses a secondary fluid called an absorbent. The condenser, expansion device, and evaporator sections, however, are similar. Absorption water chillers generally have a higher initial cost than vapor-compression chillers because of the additional heat-transfer tubes required in the absorber and generator(s), the solution heat exchangers, and the cost of the absorbent. This initial cost premium is often justified when there are limited electricity resources and/ or the cost of electricity is high. Because electric demand charges are often highest at the same time as peak cooling requirements, absorption chillers are often selected as peaking or demand-limiting chillers. Backup generator capacity requirements may be lower with absorption chillers than with electrically-driven chillers as the absorption chiller uses only a small amount of electricity. This makes absorption chillers attractive in applications requiring emergency cooling, assuming the alternate energy source is available.

Absorption chillers can also be used in facilities, such as hospitals or factories, where excess steam or hot water result as part of normal operations. Rather than wasting this energy, it is used as fuel, similar to a gas turbine, generate waste steam, or some other waste gas that can be burned. Cogeneration systems often use absorption chillers as a part of their total energy approach to supplying electricity in addition to comfort cooling and heating.

Heat Pump Chiller Packages
Chillers also can be used to produce heat. Water-to-water chillers are used to both cool and heat. The cooled water can be used to cool portions of the building that need cooling and dehumidification while the warm condenser water can be used to heat other areas within the building. They also can be used to cool a process load and provide heat to other requirements or processes, including domestic water. The cooled source can be external to the building and could include river or ground water. Air-to-water reversible heat pumps can be used to cool water during warm seasons, and then reversed to heat water during colder months. In multiple chiller operations they can be used as the first chiller when buildings often operate with cooling and heating loads, and can provide efficiency improvements over separate heating and cooling systems.

Benefits
A variety of factors can influence what type of chiller is needed for a given application. Below is a list of questions that can help narrow the options.
  • What is the load profile? This will help determine if water-cooled or air-cooled is more appropriate.
  • Is there a mechanical room? This will help determine if water-cooled or air-cooled is more appropriate.
  • Is there space outside for an air-cooled chiller? This will help determine if water-cooled or air-cooled is more appropriate.
  • What are the sound requirements of the space/outdoor location? This will help determine if water-cooled or air-cooled is more appropriate. If neighbors are very close, it may be best to locate the chiller inside.
  • What is the load and corresponding condenser water temperature profile? This will help determine if the chiller should be selected with a focus towards full load efficiency or part load efficiency.
  • What is the climate? Dry climates can benefit from evaporative cooled or water cooled chillers. Ice storage and air-cooled chillers also can be a great option here because of the ambient relief at night. This can be a factor in the chiller compressor technology — a humid environment with little ambient relief at night may not need a VFD on a centrifugal compressor.
  • What are the design drybulb and wetbulb temperatures?
  • Is there ambient relief, either web or dry bulb?
  • Is this for process or comfort cooling? Process often needs tighter chilled water control.
  • Is there makeup water for a cooling tower? Some areas have water restrictions and an air-cooled chiller may make more sense.
  • What are the demand charges? High demand charges make the full load efficiency that much more important.
  • Is this a variable primary system? The chiller controls need to be able to handle the change in flow through the evaporator.
  • What is the chilled water setpoint?
  • Is glycol being used in the system?
  • Is the chiller being used for dual conditions, i.e. both comfort cooling and ice storage? Or both comfort cooling and heat recovery?

Potential Ancillary Equipment
  • Chilled water pumps, piping, valves, etc., to carry chilled water to load
  • Air-handling units
  • Terminal and air distribution systems (content volume, variable volume, underfloor, and thermal displacement), condenser-water pumps, pipes, and cooling towers (for water-cooled systems)
  • Controls to ensure it all works together


>3. Typical Installation and Maintenance Considerations
Prior to installing a chiller, certain installation requirements need to be considered:

Space — Regardless of chiller type (water-cooled or air-cooled), the minimum space requirements need to account for serviceability as well as local and national building codes. The general accepted clearance for service is three feet to each side and top of a chiller with the following additional considerations; however, it is important to follow installation instructions:

Electrical panel — National Electric Code (NEC) governs the amount of space required in front of electrical panels for safety.

Tube pull — For chillers that can have heat exchanger tubes replaced, the full tube length needs to be available on one end of the unit.

Air flow (for air-cooled chillers) — Additional space may be required next to air-cooled condenser coils to maximize the amount of cooler air flowing across them and to minimize the recirculation of warm air coming from the condenser fans on top of this type of chiller. Installing air-cooled chillers too close to a wall or another unit can reduce the chiller’s performance and overall system efficiency.

System requirements and other equipment needed — It is important to remember that chiller performance can be greatly influenced by maintaining all aspects of the chilled water system, including ancillary components.
  • Pumps and valves
  • Storage tanks and minimum water loop requirements — acts as a buffer in the chilled water system to maintain constant temperatures
  • Flow sensing devices – often tied into the chiller control scheme as a system safety
  • Relief valve piping — according to regulatory codes    
In addition to installation requirements, there are also maintenance requirements to follow. Following the proper maintenance regimen will keep equipment running at peak performance, thus reducing operating and maintenance costs. Most chiller manufacturers include recommended maintenance schedules in their unit installation, operation, and maintenance manuals; however, we briefly cover maintenance requirements below.

Routine service checks include checking the liquid line sight glasses, taking condensing and suction pressure readings, and checking to see that the unit has normal superheat and sub-cooling readings.

Daily operating logs are often kept as a history of unit performance and can offer the most assistance when it becomes necessary to diagnose an issue. Commonly recorded values are for unit refrigerant and oil charges, as well as various temperatures, pressures, and flow rates. Monitoring these values on a regular basis will indicate if further maintenance, such as tube cleaning is beneficial.

Cleaning heat exchanger tubes is necessary when heat transfer becomes less efficient, which reduces the chiller’s overall performance. Tube fouling happens gradually over time and is dependent on the quality of the water in the system. To help eliminate scale, corrosion and biological growth, treat condenser water, especially for water loops using open cooling sources such as cooling towers.

Electrical — For efficient operation of starters and motors, check the safety and sensor calibration on microprocessor unit controllers, according the manufacturer’s recommended guidelines. In addition, check electrical connections, wiring and switchgear related to the chiller for hot spots and worn contacts. For the prevention of insulation faults, test electrical motor windings for insulation resistance to ground and winding to winding.

Sustainability — All things mechanical require maintenance depending on the chosen technology with its specific application. All manufacturers have references manuals to outline specifics for their unique designs all intended to enable operation of the chiller for its design life.

Condenser Maintenance (air-cooled chillers) — The condensers on air-cooled chillers require the routine removal of dirt and debris from the outside surface of the fins and repairing of any fin damage. Check the chiller manufacturer’s recommendations for the use of foaming coil cleaners available at most air conditioning supply outlets.

Cooling Tower and Condenser Maintenance — For water cooled chillers that use cooling towers or evaporative condensers, the water used will contain dissolved particulate material that will concentrate over time and result in fouling of the condenser. It is important to properly treat the condenser water plus control the cycles of concentration of the cooling tower water through blowdown cycles where water is routinely drained to the sewer systems. In addition, routine inspection and cleaning of the condenser tubes may also be required.


>4. Standards, Guidelines, Codes
ANSI/AHRI Standards 550/590 (I-P)-2011 and 551/591 (SI)-2011 with Addendum 1, Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle
AHRI 550/590 standardizes the method that is utilized to evaluate the performance of a water-chilling package using the vapor compression cycle. It enables customers to efficiently and accurately compare different packages. It standardizes the rating of energy efficiencies, water pressure drops, integrated part load values (IPLV), and non-standard part load values (NPLV), while also determining capacities. This standard is applicable to open drive/hermetic motors, which include centrifugal, rotary screw, reciprocating, and other types of compressors in various types of chiller packages. Download AHRI Standards here.

Need for code
The publication of ASHRAE 90.1-1988 includes an AHRI Full-Load and IPLV rating at standard rating conditions, and is the widely accepted metric used to compare relative chiller efficiencies. This code enables chiller customers to easily compare between chiller equipment since they all use the same rating system. The code enables customers to quickly reference both Full-load and the Part-load (IPLV) of chillers that meet their requirements.

In 2010, a Path B was added to the standard as an alternate compliance option for part load intensive water-cooled chillers. Also, several categories were eliminated, including the separate category for reciprocating water-cooled chillers and the category for condenser-less chillers. The scope was expanded to cover positive displacement chillers with a setpoint about 32°F that are charged with a fluid that protects against freezing.

In 2012, AHRI’s Liquid Chillers Section unanimously approved proposed changes to further improve efficiency that would be added to ASHRAE 90.1 -2013 with an effective date of January 1, 2015. Some of the proposed changes include: adding a Path B for air-cooled chillers; modifying some of the capacity ranges; and moving the efficiency requirements for water-cooled positive displacement and centrifugal chillers closer together.

Impact
This standard ensures the repeatability of energy efficiency in manufactured chilling products. Without this code, manufacturers would not have a reference for publishing claimed efficiencies, including the ability to test to published performance levels.

History
The origins of AHRI Standard, Centrifugal and Rotary Screw Water Chillers, can be traced back to 1963; likewise, AHRI Standard, Reciprocating Water Chillers, began in 1962.

AHRI’s Liquid Chillers Certification Program was launched in 1990 and tested units to AHRI Standard 550-1990, Centrifugal and Rotary Screw Water Chillers. Certification to AHRI Standard 590-1992, Positive Displacement Compressor Water Chillers, began in 1995. In response to work being done by the ASHRAE Standard 90.1 Committee, efforts soon began to update and combine the two ARI standards into one more comprehensive chillers standard, and develop a part load efficiency metric, now known as Integrated Part Load Value (IPLV). The combined standard was first published in 1998 and was quickly updated with addenda.

In 2003, the 1998 version was reaffirmed, the addenda were adopted and the standard was re-released. The next edits began and the standard received significant work, in large part due to the fact that chiller technology had improved and expanded since the last true revisions of the standard.

ANSI/AHRI Standard 560-2000, Absorption Water Chilling and Water Heating Packages
This standard outlines the method used to evaluate an absorption water chiller/water heating packages, allowing customers to properly and efficiently evaluate products. It standardizes the rating of water pressure drops, integrated part load values (IPLV), application part load values (APLV), and determines capacities. This benchmark applies to single/double-effect steam and hot fluid operated water chilling units, double-effect direct-fired (natural gas, oil, LP gas) water chilling/heating units as well as multiple-effect and multi-loop cycle absorption water chilling/heating units.

ASHRAE 90.1, Energy Standard for Buildings except Low-Rise Residential Buildings
The purpose of this standard is to provide minimum U.S. requirements for the energy-efficient design of buildings except low-rise residential buildings. The standard is applied to new constructions, retrofitted older buildings, and new systems. It will be applied towards all major components of building management, such as: power distribution, environmental control, and resource management.

This standard helps engineers select equipment that has low power efficiency and better management systems in a world where bottom lines are becoming tighter by the day.

IECC
The purpose of this standard is to enable the design of energy-efficient building envelopes as well as other systems, such as the power, lighting, and mechanical systems. This standard emphasizes optimal performance and maximum efficiencies, and deters users from wasting finite resources. It is similar to ASHRAE Standard 90.1 and has the same requirements for chillers.

>5. Importance of Certification
AHRI Certified® products demonstrate that manufacturers’ rated performance has been verified by a third-party laboratory. Certified HVAC equipment allows consumers to shop with confidence in an industry where it is hard to evaluate the performance since temperature control varies by individual.

>6. Glossary of Terms

Absorption Water Chilling and Water Heating Package: A factory designed and prefabricated assembly employing water as the refrigerant and consisting of an evaporator, absorber, condenser, generator(s) and solution heat exchangers, with interconnections and accessories used for chilling or heating water. The package utilizes single or multiple reconcentrations of an absorbent solution. The reconcentrations of the absorbent are known as effects. A single effect package employs one step reconcentration of the absorbent in the generator. Water vapor is released after the heat energy is introduced into the generator. The concentrated absorbent is returned to the absorber where it can absorb water vapor flashed off in the evaporator. A double effect package employs a two step reconcentration of the absorbent through the use of an additional high temperature generator.

Application Rating: A rating based on tests performed at application Rating Conditions (other than Standard Rating Conditions).

Bubble Point: Refrigerant liquid saturation temperature at a specified pressure for refrigerant mixtures.

Coefficient of Performance (COP): A ratio of the cooling capacity in watts [W] to the Total Power Input, in watts [W] at any given set of Rating Conditions, expressed in watts/watt [W/W]. For heating COP, supplementary resistance heat shall be excluded.

Compressor Saturated Discharge Temperature:
For single component and azeotrope refrigerants, it is the saturated temperature corresponding to the refrigerant pressure at the compressor discharge. For zeotropic refrigerants, it is the arithmetic average of the Dew Point and Bubble Point temperatures corresponding to refrigerant pressure at the compressor discharge. It is usually taken at or immediately downstream of the compressor discharge service valve (in either case on the downstream side of the valve seat), where discharge valves are used.

Condenser:
A refrigeration system component which condenses refrigerant vapor. Desuperheating and subcooling of the refrigerant may occur as well.
  • Air-Cooled Condenser: A component which condenses refrigerant vapor by rejecting heat to air mechanically circulated over its heat transfer surface causing a rise in the air temperature.
  • Air-Cooled Heat Reclaim Condenser: A component which condenses refrigerant vapor in the process of rejecting the heat of condensation to air causing a rise in the air temperature. This Condenser may be a separate Condenser, the same as, or a portion of the Air-Cooled Condenser.
  • Evaporatively-Cooled Condenser: A component which condenses refrigerant vapor by rejecting heat to a water and air mixture mechanically circulated over its heat transfer surface, causing evaporation of the water and an increase in the enthalpy of the air.
  • Water-Cooled Condenser: A component which utilizes refrigerant-to-water heat transfer means, causing the refrigerant to condense and the water to be heated.
  • Water-Cooled Heat Reclaim Condenser: A component which utilizes refrigerant-to-water heat transfer means, causing the refrigerant to condense and the water to be heated. This Condenser may be a separate condenser, the same as, or a portion of the Water-Cooled Condenser.

Cooling Only Mode:
Operational mode of a Direct-Fired chiller/heater which supplies (only) chilled water.

Dew Point: Refrigerant vapor saturation temperature at a specified pressure.

Direct Fired Package: This type of package reconcentrates the absorbent from heat energy through the combustion of natural gas, LP gas, or oil.

Energy Input: The heat content of the fuel, steam, or hot water, excluding the electrical input.
  • Total Power Input: Power input of all components of the unit.
  • Direct Fired: Energy Input is the gross heating content of the fuel based on the Higher Heating Value in MBH [kW].
  • Indirect Fired: Energy Input is the heat content of the steam or hot water in MBH [kW].

Energy Efficiency Ratio (EER): A ratio of the cooling capacity in Btu/h [W] to the Total Power Input in watts [W] at any given set of Rating Conditions, expressed in Btu/(W·h).

Field Fouling Allowance: Provision for anticipated fouling during use, h•ft2 •F/Btu [m2•°C/W].

Fouling Factor: The thermal resistance due to fouling accumulated on the heat transfer surface.

Heat Reclaim Coefficient of Performance (COPHR): A ratio of the Net Heat Reclaim Capacity (Btu/h) to the Total Power Input to the unit, W converted to Btu/h.

Heat Reclaim Water-Chilling Package: A factory-made package, designed for the purpose of chilling water and containing a Condenser for reclaiming heat. Where such equipment is provided in more than one assembly, the separate assemblies are to be designed to be used together, and the requirements of rating outlined in this standard are based upon the use of matched assemblies. It is a package specifically designed to make use of the refrigerant cycle to remove heat from the refrigerant and to reject the heat to another fluid (air or water) for heating use. Any excess heat may be rejected to another medium, usually air or water.

Heating Only Mode: Operational mode of a Direct-Fired chiller/heater which supplies only hot water.

High Pressure Steam: Steam pressures above 15.0 psig [103 kPa], but below 150 psig [1030 kPa].

Higher Heating Value (HHV): The amount of heat produced per unit of fuel when complete combustion takes place at constant pressure, the products of combustion are cooled to the initial temperature of the fuel and air, and the vapor formed during combustion is condensed, Btu/lb or Btu/ft3 [W/m3] for gaseous fuel, or Btu/lb [J/kg] or Btu/gal for liquid fuel.

Hot Water Heating Option: Hot water can be provided from an absorption chiller/heater through either of two circuits:
  • Through the evaporator circuit (2-pipe system); typically applied at temperatures up to 140°F [60.0°C] (standard temperature hot water).
  • Through a separate hot water heat exchanger (4-pipe system); typically applied at temperatures above 140°F [60.0°C] up to and including 175°F [79.4°C] and/or for simultaneous heating/cooling operation (high temperature hot water).

Indirect Fired Package: This type of package reconcentrates the absorbent from heat energy from steam or hot water.

Integrated Part-Load Value (IPLV): A single number part-load efficiency figure of merit calculated per the method described in this standard at Standard Rating Conditions.

Low Pressure Steam:
Steam pressures 15.0 psig [103 kPa] and below.

Net Cooling/Heating Capacity: The net cooling/ heating capacity is considered as the usable capacity to the user's system.

Net Heat Reclaim Capacity: A quantity defined as the mass flow rate of the condenser water multiplied by the difference in enthalpy of water entering and leaving the heat reclaim Condenser, Btu/h [kW].

Net Refrigeration Capacity:
A quantity defined as the mass flow rate of the evaporator water multiplied by the difference in enthalpy of water entering and leaving the evaporator, Btu/h or tons [kW].

Non-Standard Part-Load Value (NPLV): A single number part-load efficiency figure of merit calculated per the method described in this standard referenced to conditions other than IPLV conditions (for units that are not designed to operate at Standard Rating Conditions).

Part-Load Value (PLV): A single number figure of merit expressing part-load efficiency for equipment on the basis of weighted operation at various partial load capacities for the equipment.

Power Input per Capacity:
A ratio of the Total Power Input to the unit, in kW to the Net Refrigerating Capacity at any given set of Rating Conditions, expressed in kW/ton [kW/kW].

Published Ratings: A statement of the assigned values of those performance characteristics, under stated Rating Conditions, by which a unit may be chosen to fit its application. These values apply to all units of like nominal size and type (identification) produced by the same manufacturer. The term Published Rating includes the rating of all performance characteristics shown on the unit or published in specifications, advertising or other literature controlled by the manufacturer, at stated Rating Conditions.

Rating Conditions: Any set of operating conditions under which a single level of performance results and which causes only that level of performance to occur.

Simultaneous Heating/Cooling Mode:
Operational mode of a Direct-Fired absorption chiller/heater whereby chilled water and hot (heating) water are produced at the same time.

Standard Rating: A rating based on tests performed at Standard Rating Conditions.

Standard Rating Conditions: Rating Conditions used as the basis of comparison for performance characteristics.

Water-Chilling Package:
A factory-made and prefabricated assembly (not necessarily shipped as one package) of one or more compressors, Condensers and evaporators, with interconnections and accessories, designed for the purpose of cooling water. It is a machine specifically designed to make use of a vapor compression refrigeration cycle to remove heat from water and reject the heat to a cooling medium, usually air or water. The refrigerant Condenser may or may not be an integral part of the package.


All terms follow the standard industry definitions in the current edition of ASHRAE Terminology of Heating, Ventilation, Air Conditioning and Refrigeration unless otherwise defined in this section.