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Commercial & Industrial

Combined Heating and Power ("CHP")

The air from the heat sink heat exchanger (green arrow) is at a temperature of about 500ºF and can be ducted to any system on the premises that currently uses a gas burner or electric heater to provide hot air for such purposes as space heating, water heating, drying, cooking or other processing.

It may also be used to heat an absorption chiller that provides cooling for central air conditioning or cold storage.

This process is described as "CHP" for Combined Heating and Power or simply "cogeneration".

The great advantage of cogeneration is more efficient use of fuel.

Instead of burning gas to generate heat, the exhaust heat of the turbo generator is substituted.

Under the right circumstances this can increase system efficiency from around 30% to as much as 75%.

In most modern economies utilities in commercial buildings are roof mounted. It is economical to do so and provides easy access for maintenance and servicing to utility equipment such as forced air, ventilation, water heating and air conditioning systems. It is also an ideal location for TMS energy systems, placing them in close proximity to the equipment with which they need to interface to facilitate the utility functions.

Interfaces range from simple duct connections to introduce heat to heat exchangers ordinarily heated with their own separate burners, to more complex heat introduction arrangements such as with absorption coolers.

  • 1. Water enters the evaporator from the condenser.
  • 2. Water droplets fall onto the heat transfer tubes running through the evaporator.
  • 3. The pressure in the evaporator is low enough that the water evaporates at 5ºC thereby cooling the water in the chilled water pipes. The chilled water is passed through the tubes of the air conditioning unit to refrigerate the air.
  • 4 - 5. Lithium Bromide (LiBr) is introduced into the evaporator to absorb the water vapor.
  • 6. The LiBr - water solution is pumped to the generator.
  • 7. The LiBr is heated in the generator by the heat from the turbine heat sink heat exchangers which boils off the water.
  • 8. The boiled off vapor is passed back to the condenser where it returns as water to repeat the cycle.
  • The diagram depicts a single-effect system. To increase thermodynamic efficiency, double-effect systems use high temperature and low temperature generators in series with one another.
  • For sub-freezing refrigeration, liquid refrigerants other than water are used.

Rooftop central air conditioning systems are the common domain of electrically driven vapor cycle systems. However, they can be replaced with heat fired absorption chillers, which are extensively used around the world. The public knows them best as gas refrigerators in campers, boats or rural homes without dependable electric services. Large absorption chillers in excess of 250 kW (60 tons) refrigeration capacity are commonly used in large centrally air conditioned buildings.
 

The coefficient of performance (COP) of compressor driven refrigeration systems is in the order of 4 (for every unit of energy put in 4 units of refrigeration are produced). Absorption chillers seldom achieve COPs of more than 1.5, but they use heat directly. When the inefficiencies of power generation and distribution are included, each unit of electrically driven refrigeration actually costs three units of heat. This effectively reduces the overall COP to about 1.3. The fact that the TMS energy scheme uses exhaust heat to drive the absorption chillers, makes it that much more attractive economically.

 

Several international absorption chiller manufacturers have introduced lines of packaged units in the 5 to 40 ton range, which is what small to medium commercial businesses require. To interface cost effectively with this range of chillers, the generator portion of the system depicted in the diagram could best be integrated into the heat sink system of the turbines to obviate the need for a separate heat transport loop. With grants from the Department of Energy, some of the chiller manufacturers are experimenting with different integration schemes, one of which uses a Capstone Micro Turbine as its cogeneration heat source.

 

As the price of electricity increases relative to the cost of natural gas, packaged absorption chillers are expected to make inroads into the market segment currently dominated by compressor driven vapor cycle packaged units.