CHW Chilled Cooling Water Systems
Being maritime in nature, the UK climate hasn't traditionally been known to require cooling systems to be installed in buildings which are constructed for the purposes of comfort. In specific applications, where heat gain is unavoidable, discrete air-conditioning systems are commonly used. However, when control over temperature is required for process or other reasons then cooling systems, in conjuction with heating systems, are the means to achieve that. Like its heating counterpart, a cooling system consists of a source of cooling, normally referred to as a chiller and a means to distribute the generated cooling to defined loads such as Chilled Beams or coils in Air Handling Units (AHUs).
Common design parameters
The most common design parameters for cooling waters systems are a flow temperature (leaving the chiller) of 6DegC and a return temperature of 12DegC. This results in a Differential Temperature (dT) of 6DegC. These temperatures reflect a compromise of economics, practicality and risks of freezing. Of course, other temperature ranges are available but this range is the most often used. Of course, when chilled water at 6degC is used for cooling air, in an Air Handling Unit for example, condensation is formed on the fins of the coil, reducing the moisture content and hence relative humidity of the air. If the relative humidity requires to remain static, then higher chilled water temperatures are required. Higher flow and return temperatures of 14degC and 17degC respectively could be used to avoid moisture removal since these temperatures are typically above the dewpoint of the air in the space. The selection of the coil operating parameters would need to match the chilled water temperatures for this to work.
An alternative way to avoid condensation at an AHU coil would be to "pump the coil". Tis entails using a pump local to the coil in conjunction with a mixing valve so that the small circuit immediately adjacent to the coil can be operated at different temperatures from the main chilled water system. This configuration avoids having to have more than one chilled water system.
Chilled or Cooling Water Design Service
As consulting engineers, Callidus Design offer a number of services for Chilled or Cooling Water systems including design and specification of entire cooling systems, system modifications and extensions, condition surveys, refurbishment and troubleshooting.
