Requirement Summary
This measure can be claimed if water-cooled chillers are installed for the cooling system, and the fans in the cooling towers of the chillers use only Variable Speed Drive (VSD) motors. These are typically variable frequency drive (VFD) or adjustable-frequency drive motors, although other VSD technologies are available.
Intention
VSD fans offer improved system reliability and process control. By specifying VSD fans for cooling towers, energy consumption is reduced resulting in reduced utility costs. The lifetime of system components is increased because of lesser use at full capacity leading to lesser wear and tear with less maintenance needed.
Approach/Methodologies
Cooling towers need to operate at the maximum (peak) load only at certain times. For most of the hours in a day, they only need to operate at part loads. VSDs on fans control and regulate the fan speeds depending on the load on the cooling towers, as opposed to constant speed fans, thus reducing energy consumption.
To claim this measure, the design team must demonstrate that the project includes Air Conditioning with Water Cooled Chillers, and that the fans on the cooling towers of the HVAC system are VSD fans.
Potential Technologies/Strategies
Water chiller systems include cooling towers which are specialized heat exchangers in which air and water are brought into direct contact with each other to reduce the water's temperature through evaporation. Water carrying heat from the building is pumped through pipes to the cooling tower. There it is sprayed through nozzles onto banks of material that break up the water, exposing a large amount of the water surface to air. The air that is driven across the water to cool it approaches 100% relative humidity and elevated temperatures and is rejected to the atmosphere. A small amount of water evaporates in the process and the rest cools down and is pumped back into the chiller where it again absorbs heat in a continuous cycle.
The air used to cool the water is pulled through the cooling tower by electric motor-driven fans. These fans can be electronically controlled with Variable Speed Drive (VSD) motors. A VSD motor regulates the speed and the rotational force of the fan by varying the motor input frequency and voltage.
Relationship to Other Measures
When VSDs for the fans of the cooling towers is selected as an energy efficiency measure, the cooling system selected must be Air Conditioning with Water Cooled Chiller to show the savings. Reduced fan energy will also reduce the heat loss from fan motors and, therefore, the load on the cooling energy.
Assumptions
The base case for the air conditioning system varies based on ASHRAE 90.1-2007, and is typically a standard Packaged Terminal Air Conditioner (PTAC), as listed in the Key Assumptions for the Base Case in the Design section*. Cooling towers and therefore, VSDs on cooling towers, are not typically part of the baseline. In the Improved Case, this measure will show savings only if ‘Air Conditioning with a Water-Cooled Chiller’ is also selected as a measure because cooling towers are a part of the chiller system. The assumption for the Improved Case is that all fans in the cooling towers will be provided with VSDs.
Compliance Guidance
To demonstrate compliance, the design team must describe the specified system and provide documentation to support the claims.
| Design Stage | Post-Construction Stage |
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At the design stage, the following must be used to demonstrate compliance:
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At the post-construction stage, the following must be used to demonstrate compliance:
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