Basics of Chilled Water and Piping System
Introduction to Chilled Water System
The use of chilled water to cool a building or process is both efficient and adaptable. A two-inch Schedule 40 chilled water pipe can provide the same amount of comfort cooling as a 42" diameter round air duct. The use of chillers enables the design engineer to produce chilled water in a central building location, or even on the roof, and distribute it economically and without the use of large duct shafts.
The goal of this manual is to go over various piping and control strategies that are commonly used in chilled water systems, such as variable flow pumping systems.
Basics of Chilled water System:
A chiller is a machine that removes heat from a liquid coolant via a vapor-compression, adsorption refrigeration, or absorption refrigeration cycles.
This fluid would then be able to be coursed through a warmth exchanger to cool gear, or another cycle stream, (for example, air or interaction water).
As a necessary by-product, refrigeration creates waste heat that must be exhausted to the ambiance, or for greater efficiency, recovered for heating purposes.
Fume pressure chillers may utilize any of the various kinds of blowers. Most basic today are the airtight parchment, semi-airtight screw, or diffusive blowers.
The gathering side of the chiller can be either air or water-cooled. In any event, when fluid cooled, the chiller is frequently cooled by an actuated or constrained draft cooling tower. Assimilation and absorption chillers require a warmth source to work.
Chilled water is utilized to cool and dehumidify air in mid-to huge size business, modern, and institutional offices. Water or fluid chillers can be fluid cooled, air-cooled, or evaporatively cooled. Water or fluid cooled frameworks can give effectiveness and ecological effect benefits over air-cooled frameworks.
Flow and Capacity Calculations:
The temperature change in the fluid for either the condenser or the evaporator can
be described using the following formula:
Q = W x C x ΔT
Where
Q = Quantity of heat exchanged (Btu/hr)
W = flow rate of fluid (USgpm)
C = specific heat of fluid (Btu/lb· °F)
ΔT = temperature change of fluid (°F )
Energy Efficient:
COP (Coefficient of Performance = kWcooling / kWinput) or
EER (Energy Efficiency Ratio = Tons X 12/ kWinput).
Piping Basics:
Static Pressure
The piping is typically made of steel, copper, or plastic. In most cases, the chilled water piping is a closed-loop. A closed-loop is not exposed to the outside world.
The loop is open when open cooling towers are used in condenser piping. The condenser pump must overcome system friction and "lift" water from the sump to the top of the cooling tower.
The static pressure in high-rise applications can become significant and exceed the pressure rating of the piping and components such as chillers.
The waterside pressure on most chillers is rated at 150 PSI. This should be carefully considered for buildings with more than ten stories.
Expansion Tanks
To allow for thermal expansion of the water, an expansion tank is required in the chilled water loop. Expansion tanks can be open, closed with an air-water interface, or diaphragm. The type will be determined by the tank's location. Open tanks must be placed above the system's highest point.
Tanks with an air-water interface and diaphragms can be placed anywhere in the system.
In general, the smaller the tank, the lower the pressure in the tank. Tank size can be reduced by placing it higher in the system.
Piping Insulation:
Because the water, and thus the piping, is frequently below the dewpoint temperature, chilled water piping is insulated. Condensate would form on it, causing heat loss. The insulation's goal is to minimize heat loss while keeping the outer surface above the dewpoint of the ambient air.
Condenser Water Piping adve:
The condenser water piping is usually an open loop. When the pump is turned off, the level in the supply and return piping will be even with the sump level. When the pump is turned on, it must overcome the system's friction loss and "lift" the water from the sump level to the top of the loop.
Condenser water piping is typically not insulated because there will be minimal heat gain or loss and no sweating. However, if the piping is exposed to cold ambient conditions, it may need to be insulated and heat traced to prevent freezing.
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