Dedicated Waterside Economizers (types)

   Toolbar button for Waterside Economizers (types) list.

 

This facility allows you to define the characteristics of one or more dedicated waterside economizers directly coupled to a single cooling coil. This type of waterside economizer (WSE) can be associated with a backup chiller and is limited to running only when it can meet the load in full.

This dedicated WSE is distinct from and completely independent of the WSE mode available on the Heat rejection tab for water-cooled chillers or chiller sets accessed in the Chilled water loops dialog.

The waterside economizer consists of a chilled water loop serving the cooling coil, and a cooling tower linked to the chilled water loop via a heat exchanger (see diagram in Figure 3-120 in below). There is a pump in the cooling tower water loop and a two-speed fan in the cooling tower. The cooling supplied by the cooling tower is controlled by cycling the fan between the off, low-speed and full-speed settings.

 

The waterside economizer operates when it can meet the coil cooling load in full (the parameter controlling this aspect of operation is currently forced to true). When the waterside economizer is unable to the meet the coil load in full it will redirect the cooling load to the backup chiller, if one is specified. Otherwise, no cooling occurs.

The capacity of the cooling coil will be limited by the capacity of the waterside economizer. A further capacity limitation may be placed on the cooling coil using the cooling coil’s Maximum Duty parameter.

 

The waterside economizers (WSE) entities defined here are types, rather than instances. When a single WSE type is assigned to many cooling coils, an additional instance of the WSE is created for each cooling coil to which the type is assigned. In this respect, waterside economizers differ from chillers.

As of version 6.1, a waterside economizer type can readily be set to duplicate the cooling tower defined in a selected backup water-cooled chiller. When the cooling tower as WSE can no longer meet the entire load presented by the coil, the full load on the coil will be passed to the backup water-cooled chiller, with the chiller then using the same tower model and performance parameters for condenser heat rejection. The WSE performance will be consistent with that of the tower used for chiller heat rejection so long as there is only one coil assigned to that WSE type. If additional coils are assigned to the same WSE type, these can still share a single backup chiller, but the effect will be as though additional copies of the same cooling tower are available (one for each coil) so long as the load on any particular coil can be met by an instance of the WSE.

 

 

 

 

Enter a description of the component. The reference is limited to 100 characters. It is for your use when selecting, organizing, and referencing any component or controllers within other component and controller dialogs and in the component browser tree. These references can be valuable in organizing and navigating the system and when the system model is later re-used on another project or passed on to another modeler. Reference names should thus be informative with respect to differentiating similar equipment, components, and controllers.

The difference between the cooling tower leaving water temperature (T ₂ ) and the outside wet bulb temperature (t _owb ) at the design condition.

The difference between the cooling tower entering water temperature (T ₁ ) and the cooling tower leaving water temperature (T ₂ ) at the design condition.

The outside wet bulb temperature at the design condition.

The load on the cooling tower (and cooling coil) at the design condition. This is used to size the water flow rates in the system. Appropriate sizing is essential for accurate representation of the cooling tower.

The effectiveness of the heat exchanger. This is defined with respect to the water loop with the lower flow.

If the coil loop has the lower flow, the effectiveness is ε _coil , defined by

T_1coil  = T_2coil + ε_coil (T₂ - T_2coil)

If the tower loop has the lower flow, the effectiveness is ε _tower , defined by

T ₁ = T ₂ + ε _tower (T _2coil - T ₂ )

Here

T ₁ is the tower entering water temperature

T ₂ is the tower leaving water temperature

T _1coil is the coil entering water temperature

T _2coil is the coil leaving water temperature

ε _coil and ε _tower are in the ratio of the flows in the coil and tower loops. The heat exchange effectiveness parameter is thus the smaller of these two effectivenesses.

The difference between the cooling coil leaving and entering water temperatures (T _coil2 and T _coil1 ) at the design condition. This, together with the design cooling tower load, is used to size the cooling coil water flow.

The power consumption of the cooling tower fan when running at full speed.

The fraction of the design flow that the cooling tower fan delivers when running at low speed.

The power consumed by the cooling tower fan when running at low speed, expressed as a fraction of the cooling tower design fan power.

The design power consumption of the cooling tower pump. The pump operates when the system delivers cooling.

When this box is ticked the economizer is switched off if it cannot meet the coil load in full. This setting is currently forced to true.

Use this setting to specify a chiller providing backup to the waterside economizer. If the economizer has switched off because it cannot meet the full load, and no backup chiller is specified, no cooling occurs.

An Integrated Waterside Economizer (IWSE) is available as part of the Chilled water loop specification (see Section 2.8.3 ). Both dedicated and integrated waterside economizers can be specified, however, each type will have its own cooling tower.