HVAC Natural Gas Chillers Can Help Manage Peak-Demand Electrical Loads Even the shrewdest facility executives wouldn't consider turning off a facility's lights or shutting down a manufacturing line just to save a few bucks during a electric utility's peak-demand period. But what about the HVAC system? Choosing a chiller system Hybrid systems are popular because they offer choices such as gas chiller operation during peak electrical periods and standard electrical chiller usage during off-peak hours. In some instances, standard electrical chillers have not been used because of the efficient operation of the main gas-chiller system. The process of gas absorption uses an evaporator and condenser much like conventional vapor compression units. However, instead of using a standard electrical compressor and motor, a thermal compression system is used. Within a simplified thermal compression system, an absorber and generator are integrated along with a pumping system. An evaporator removes heat from the circulating water system to produce cool water. From the evaporator, refrigerant vapor moves to an absorber where it is compressed and absorbed into a solution, usually lithium bromide. This solution then moves to the generator where heat – either direct-fired gas or steam – is added to remove the refrigerant from the solution. The solution then goes through heat exchangers and is returned to the absorber. The refrigerant returns to the condenser where it is liquefied and sent back to the evaporator. The entire cycle then starts over again. Gas-fired steam absorption chillers work in much the same manner as direct-fired gas chillers. The main difference is that the heat source for the generator is usually an external gas-fired boiler system. These systems are favorable for facilities that have a boiler system already installed on site. In addition to being either gas-fired steam absorption or direct-fired gas, chillers are categorized into two different types: Single-effect and double-effect. There is a triple-effect being developed. Single-effect, or single-stage, absorption chillers usually require low internal pressures around 20 psig to produce chilled water. Double-effect, or two-stage, absorption chillers work at a much higher pressure, around 40 to 140 psig. These chillers also have an extra generator integrated into the absorption system that increases the efficiency by about 30 percent. Double-effect chillers are currently more popular than the single-effect types. Many direct-fired absorption chillers are dual-fuel rated. Natural gas is commonly the primary fuel, however No. 2 fuel oil can be used as an alternate. If for any reason the natural gas supply is interrupted, having the capability to use an emergency fuel may be invaluable. This fuel redundancy may be an important purchasing factor for many facility professionals. Maintenance requirements for gas-absorption chillers are minimal. Pump seals need inspecting periodically if the pumps are not hermetically rated. In addition, scaling and sludge build-up are areas of concern with this equipment. However, automatic chiller and purge controls, along with periodic general maintenance checks, will alleviate most of these potential problems. Equipment size can be a concern for some facilities. Typically, gas absorption chillers are larger than standard electrical chillers of the same Btu rating. Adequate space needs to be allowed for any gas chiller retrofit or new installation. Gas-absorption chillers One of the benefits of using gas-absorption chillers is that it produces enough heat to also activate certain dehumidification systems, which are becoming important components of HVAC systems. Molds, mildews and bacteria flourish in high-humidity conditions. Controlling humidity reduces risks to human health and ensures that sensitive manufacturing processes can be conducted. Dehumidification also increases cooling efficiency. In some instances, installing a dehumidificati

1. HVAC Natural Gas Chillers Can Help
Manage Peak-Demand Electrical Loads
Even the shrewdest facility executives wouldn't consider turning off a facility's lights or shutting down a
manufacturing line just to save a few bucks during a electric utility's peak-demand period. But what
about the HVAC system?
Choosing a chiller system
Hybrid systems are popular because they offer choices such as gas chiller operation during peak
electrical periods and standard electrical chiller usage during off-peak hours. In some instances,
standard electrical chillers have not been used because of the efficient operation of the main gas-
chiller system.
The process of gas absorption uses an evaporator and condenser much like conventional vapor
compression units. However, instead of using a standard electrical compressor and motor, a
thermal compression system is used.
Within a simplified thermal compression system, an absorber and generator are integrated along
with a pumping system. An evaporator removes heat from the circulating water system to
produce cool water. From the evaporator, refrigerant vapor moves to an absorber where it is
compressed and absorbed into a solution, usually lithium bromide. This solution then moves to
the generator where heat – either direct-fired gas or steam – is added to remove the refrigerant
from the solution.
The solution then goes through heat exchangers and is returned to the absorber. The refrigerant
returns to the condenser where it is liquefied and sent back to the evaporator. The entire cycle
then starts over again.
Gas-fired steam absorption chillers work in much the same manner as direct-fired gas chillers.
The main difference is that the heat source for the generator is usually an external gas-fired
boiler system. These systems are favorable for facilities that have a boiler system already
installed on site.

2. In addition to being either gas-fired steam absorption or direct-fired gas, chillers are categorized
into two different types: Single-effect and double-effect. There is a triple-effect being developed.
Single-effect, or single-stage, absorption chillers usually require low internal pressures around 20
psig to produce chilled water. Double-effect, or two-stage, absorption chillers work at a much
higher pressure, around 40 to 140 psig. These chillers also have an extra generator integrated into
the absorption system that increases the efficiency by about 30 percent. Double-effect chillers are
currently more popular than the single-effect types.
Many direct-fired absorption chillers are dual-fuel rated. Natural gas is commonly the primary
fuel, however No. 2 fuel oil can be used as an alternate. If for any reason the natural gas supply
is interrupted, having the capability to use an emergency fuel may be invaluable. This fuel
redundancy may be an important purchasing factor for many facility professionals.
Maintenance requirements for gas-absorption chillers are minimal. Pump seals need inspecting
periodically if the pumps are not hermetically rated. In addition, scaling and sludge build-up are
areas of concern with this equipment. However, automatic chiller and purge controls, along with
periodic general maintenance checks, will alleviate most of these potential problems.
Equipment size can be a concern for some facilities. Typically, gas absorption chillers are larger
than standard electrical chillers of the same Btu rating. Adequate space needs to be allowed for
any gas chiller retrofit or new installation.
Gas-absorption chillers
One of the benefits of using gas-absorption chillers is that it produces enough heat to also
activate certain dehumidification systems, which are becoming important components of HVAC
systems. Molds, mildews and bacteria flourish in high-humidity conditions. Controlling humidity
reduces risks to human health and ensures that sensitive manufacturing processes can be
conducted. Dehumidification also increases cooling efficiency. In some instances, installing a
dehumidification system can reduce a building’s cooling load by as much as 50 percent.
Solid desiccant dehumidification systems remove moisture from the air by implementing a heat-
activated material. Although a complete system contains many components, the main internal
component is the desiccant wheel. Usually the desiccant wheel is divided into two halves. One
half allows unconditioned air to enter where the air is then dried. When this half becomes
saturated with moisture, it is rotated into a heated area that subsequently regenerates the
desiccant in that half of the wheel. Within this rotating cycle, one half of the wheel regenerates
while the other half absorbs moisture.
Absorption chillers are not the only means in which gas can be adapted to conserve electrical
consumption. Gas-driven chillers are another viable means to reduce peak electrical costs. The
chiller portion of this unit is really just a standard vapor compression system driven by an
externally powered internal combustion engine. Typically, with this type of unit, the engine
couples directly to the input shaft of a rotary-type chiller. The engine can be operated with many
fuels, including natural gas, LP or diesel. Cogeneration systems are a possible addition when an

3. external engine is used in this way. Hot water, steam, dehumidification, cooling and electricity
production all use an internal combustion engine as a power source.
Although most gas chiller systems are not as well-known as the conventional electrically driven
chiller systems, they are becoming more popular because of rising electrical costs. Many facility
executives are experiencing lower electrical consumption since they have made the transition to
gas cooling. When making gas chiller decisions, it may be a good idea to get advice from facility
executives that have already made the transition. Their input and the help of qualified energy
management engineers will help in making a wise energy choice.
Julian Arhire is a Manager with DtiCorp.com – DtiCorp.com carries more than 35,000
HVAC products, including industrial, commercial and residential parts and equipment
from Honeywell, Johnson Contols, Robertshaw, Jandy, Grundfos, Armstrong and more.