Dedicated Heat Recovery Chiller System

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UNIVERSITÉ SAINT-JOSEPH Faculté d'ingénierie E.S.I.B. Cursus Génie Electrique et Mécanique Semestre 2

Dedicated Heat Recovery Chiller
Mai 2011

Responsable: Mr. Said CHEHAB

Binȏme: Bassam RASHED Elie HAJJ MOUSSA

Over the past few years, Air Conditioning witnessed immense new changes that are changing the way we see ACs from an addition to necessary. The new trend in construction is green. Greener buildings greener technologies, everything tends to lower the carbon foot print of a building/complex. Mechanical equipments are no different especially since they represent more than 50% of the electrical consumption of a project (residential buildings, Villas, Hotels, Schools etc…) Over the course of this subject we learned the importance of water and air chillers – compared to normal split units – as they tend to give better return on investment as the project grows older and larger. Nevertheless, having numerous AHUs and FCUs in one complex only meant high energy bills, which brought the necessity to join different systems in one. This brings us to the topic of new type of chillers, the dedicated heat recovery chiller (DHRC). Resort/convention hotels, hospitals and nursing homes as well as athletic facilities located in warm climates, demand heat and cool at the same time. Unlike old systems where boilers used to work in parallel to the chiller system to respond to the demand for hot water, DHCR systems include a heat exchanger with allows to heat the water exiting it to the designated water temperature to perform various tasks like: Reheat coils Building heating (low temperature < 130° F) Domestic water heating (washing and showers) Swimming pool heating Laundry water heating Snow melting Process heating Kitchen water for dish washing and clean up

There is only one primary reason to install a Dedicated Heat Recovery Chiller. It is to reduce emission of carbon dioxide released to the atmosphere by the burning of fossil fuel, and to save on the cost of the natural gas, electricity or district steam used to heat water used by the building. Under all circumstances, the building must have a SIMULTANEOUS need for hot water and chilled water (or economizer cycle). The primary application of the DHRC has been during spring, summer and fall, when the building needs chilled water for air conditioning. However, applications where the winter chilled water loads are substantial (e.g. computer rooms) can be easily accommodated by the DHRC™. The chiller control system is designed to operate the chiller based on either condenser water or chilled water demand. The DHRC™ control system will continually poll both the heating and cooling loads in order to meet simultaneous heating and cooling requirements. This ensures that the system will operate the maximum number of available hours in which simultaneous loads exist and therefore will maximize the energy saving potential of the system. The DHRC will not need a separate cooling tower.

So how did the idea emerge? By combining two good ideas: Old Idea #1 A chilled water system based on a primary/secondary piping system. This arrangement, shown in Figure 1, has also been called a “decoupled” system because the primary and secondary pumping duties are hydraulically decoupled.

Figure 1

Old idea #2 The idea of employing heat recovery from water cooled chillers is also an old one.

The combination:
In a typical multiple-chiller plant employing heat recovery, one chiller will be designed for heat recovery. It will usually be the first chiller activated when cooling is required.

The double-bundle condenser of a heat-recovery chiller contains the heating condenser and the tower condenser, as shown in Figure above. The warm refrigerant gas from the compressor flows over both tube bundles. The flow of heat in the double-bundle condenser is controlled by a cooling-tower bypass valve as show in the figure below. The valve receives signals from a temperature...
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