Water chilled air conditioning systems are controlled by simple thermostats and often found in residential buildings and hotels
Air conditioning systems for buildings may rely on either a liquid such as water, or air as a distribution medium. Conditioned air is typically distributed by duct and chilled water is distributed by pipe.
Chilled water systems are most commonly used for air conditioning large buildings. The reason for this is it is more efficient and economical to transfer (or remove) heat by water than by air. This is due to the higher heat capacity water has and the fact pipes that carry water are smaller and take up far less space. A third advantage of chilled water is the flexibility for zone control.
The chilled water will cool air locally by convection, through air handling units or fan coil units. Air handling units are typically larger than fan coil units and have more sophisticated zone controls. Air handling units are often found in large office buildings, hospitals, etc. Fan coil units are typically smaller and serve smaller spaces. These units are often controlled by simple thermostats and found in residential buildings, hotels, etc.
Chilled water is typically distributed by pipe from a system that features cooling towers and chillers. A system that is similar to a chilled water system is a water source heat pump system. These would also typically have a cooling tower, but no chiller.
Chilled water distribution systems can use the same pipe system as the hot water heating systems. A water source heat pump system would also provide heat, using the same water loop.
Two-Pipe Chilled Water System
These are reasonably energy efficient. In a two-pipe system, there are only two pipes connected to the air handlers, chiller and boiler.
One pipe is used for the water loop, and the other pipe is used for the condenser loop. In the summer, the two-pipe HVAC system is manually switched to cooling, and in the winter, it is switched to heating. For maintenance personnel, this often means adhering to specific switch-over dates on the calendar.
Four-Pipe HVAC System
Often referred to as water source heat pumps, they are more versatile than their two-pipe counterparts.
This is because four-pipe systems contain a separate pipe system for the heating portion of the unit and a pipe system for the cooling portion of the unit. Since the heating and cooling systems run on two separate piping systems, the HVAC unit has the ability to heat and cool at the same time. The unit does not need to be switched from heating to cooling or cooling to heating prior to seasonal changes.
It also means that if unseasonably warm or cold weather occurs, the HVAC system will be able to maintain the proper indoor temperatures to keep your residents comfortable.
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