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  4. 3.8 HVAC Primary Systems

3.8.4 Water-side Economizers

Baseline Building Summary. None of the baseline building systems use a water-side economizer.

Water-Side Economizer Name
Applicability All water-side economizers
Definition The name of a water-side economizer for a cooling system
Units Text, unique
Input Restrictions Descriptive reference to the construction documents. The default is no water-side economizer.
Baseline Rules No water economizer
Water Economizer Type
Applicability All water-side economizers
Definition The type of water-side economizer. Choices include:
  • None
  • Heat exchanger in parallel with chillers. This would be used with an open cooling tower is often referred to as a non-integrated economizer, because the chillers are locked out when the plant is in economizer mode.
  • Heat exchanger in series with chillers. This would be used with an open cooling tower and is often referred to as an integrated, because the chillers can operate simultaneously with water economizer operation.
  • Direct water economizer. This would be used with a closed cooling tower. In this case, a heat exchanger is not needed. This type works only as a non-integrated economizer.
  • Thermo-cycle (also known as refrigerant migration). With thermo-cycle, bypass valves allow for the flow to vapor refrigerant to the condenser and allow gravity flow of liquid refrigerant to the evaporator without use of the compressor.  Only some chillers have this capability and capacity may be limited under this mode.  There is no additional piping; the cooler water from the tower is brought directly to the chiller(s) and the chiller(s) respond by shutting down the compressor and relying on thermal forces to drive the refrigerant. This method is also known as “thermosiphon” since thermal gradients passively move refrigerant between the evaporator and condenser.
Units List (see above)
Input Restrictions As designed
Baseline Rules No water economizer
Water-Side Economizer HX Effectiveness
Applicability Water-side economizers with an open cooling tower

Definition

The effectiveness of a water-side heat exchanger at design conditions. This is defined as:

(6.8.4-1)

$$ W\!SE_{eff} = \frac{t_{ea}-t_{la}}{t_{ea}-t_{ew}}$$where

WSEeff The effectiveness of the water-side economizer coil
tea The entering coil air dry-bulb temperature (°F)
tla The leaving coil air dry-bulb temperature (°F)
tea The entering coil water temperature (°F)
Units Ratio
Input Restrictions As designed. The default is 60 %.
Baseline Rules No water economizer
Water-Side Economizer Maximum Tdb
Applicability All water-side economizers
Definition The control temperature (outside air dry-bulb temperature) above which the water-side economizer is disabled.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 65°F.
Baseline Rules No water economizer
Water-Side Economizer Maximum CWS
Applicability All water-side economizers
Definition The control temperature (condenser water supply temperature) above which the water-side economizer is disabled.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 50°F.
Baseline Rules No water economizer
Water-Side Economizer CWS Setpoint
Applicability All water-side economizers
Definition The design condenser water supply temperature for the cooling tower in economizer mode.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 45°F or 40°F for “Thermo Cycle.”
Baseline Rules No water economizer
Water-Side Economizer Availability Schedule
Applicability All water-side economizers
Definition A schedule which represents the availability of the water-side economizer
Units Data structure: schedule, on/off
Input Restrictions As designed
Baseline Rules No water economizer
Water-Side Economizer Auxiliary kW
Applicability Water-side economizers with an open tower
Definition The electrical input (pumps and auxiliaries) for a dedicated pump for the chilled water side of the heat exchanger. This power is in excess of the condenser water pumps and cooling tower fans for the system during water-side economizer operation.
Units KW or kW/ton
Input Restrictions As designed
Baseline Rules No water economizer

Baseline Building Summary. None of the baseline building systems use a water-side economizer. Additional inputs to those below may be required to simulate actual control sequences.

 

Water-Side Economizer Name

Applicability

All water-side economizers

Definition

The name of a water-side economizer for a cooling system

Units

Text, unique

Input Restrictions

Descriptive reference to the construction documents. The default is no water-side economizer.

Baseline Rules

No water economizer

 

Water Economizer Type

Applicability

All water-side economizers

Definition

The type of water-side economizer. Choices include:

  • None
  • Heat exchanger in parallel with chillers. This would be used with an open cooling tower is often referred to as a non-integrated economizer, because the chillers are locked out when the plant is in economizer mode.
  • Heat exchanger in series with chillers. This would be used with an open cooling tower and is often referred to as an integrated, because the chillers can operate simultaneously with water economizer operation.
  • Direct water economizer. This would be used with a closed cooling tower. In this case, a heat exchanger is not needed. This type works only as a non-integrated economizer.
  • Thermo-cycle (also known as refrigerant migration). With thermo-cycle, bypass valves allow for the flow to vapor refrigerant to the condenser and allow gravity flow of liquid refrigerant to the evaporator without use of the compressor.  Only some chillers have this capability and capacity may be limited under this mode.  There is no additional piping; the cooler water from the tower is brought directly to the chiller(s) and the chiller(s) respond by shutting down the compressor and relying on thermal forces to drive the refrigerant. This method is also known as “thermosiphon” since thermal gradients passively move refrigerant between the evaporator and condenser.

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

No water economizer

 

Water-Side Economizer HX Effectiveness

Applicability

Water-side economizers with an open cooling tower

Definition

The effectiveness of a water-side heat exchanger at design conditions. This is defined as:

(Equation 3.8.4-1)

$$WSE_{eff} = \frac{t_{ea} - t_{la}} {t_{ea}-t_{ew}} $$

Where

WSEeff

The effectiveness of the water-side economizer coil

tea

The entering coil air dry-bulb temperature (°F)

tla

The leaving coil air dry-bulb temperature (°F)

tea

The entering coil water temperature (°F)

Units

Ratio

Input Restrictions

As designed. The default is 60 %.

Baseline Rules

No water economizer

 

Water-Side Economizer Maximum Tdb

Applicability

All water-side economizers

Definition

The control temperature (outside air dry-bulb temperature) above which the water-side economizer is disabled.

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. Defaults to 65 °F.

Baseline Rules

No water economizer

 

Water-Side Economizer Maximum CWS

Applicability

All water-side economizers

Definition

The control temperature (condenser water supply temperature) above which the water-side economizer is disabled.

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. Defaults to 50 °F.

Baseline Rules

No water economizer

 

Water-Side Economizer CWS Setpoint

Applicability

All water-side economizers

Definition

The design condenser water supply temperature for the cooling tower in economizer mode.

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. Defaults to 45°F or 40°F for “Thermo Cycle.” If a strainer cycle is specified, changeover temperature from economizer to mechanical cooling shall be set at 50°F.

Baseline Rules

No water economizer

 

Water-Side Economizer Availability Schedule

Applicability

All water-side economizers

Definition

A schedule which represents the availability of the water-side economizer

Units

Data structure: schedule, on/off

Input Restrictions

As designed

Baseline Rules

No water economizer

 

Water-Side Economizer Auxiliary kW

Applicability

Water-side economizers with an open tower

Definition

The electrical input (pumps and auxiliaries) for a dedicated pump for the chilled water side of the heat exchanger. This power is in excess of the condenser water pumps and cooling tower fans for the system during water-side economizer operation.

Units

KW or kW/ton

Input Restrictions

As designed

Baseline Rules

No water economizer

Baseline Building Summary. None of the baseline building systems use a water-side economizer.

Water-Side Economizer Name
Applicability All water-side economizers
Definition The name of a water-side economizer for a cooling system
Units Text, unique
Input Restrictions Descriptive reference to the construction documents. The default is no water-side economizer.
Baseline Rules No water economizer
Water Economizer Type
Applicability All water-side economizers
Definition The type of water-side economizer. Choices include:
  • None
  • Heat exchanger in parallel with chillers. This would be used with an open cooling tower is often referred to as a non-integrated economizer, because the chillers are locked out when the plant is in economizer mode.
  • Heat exchanger in series with chillers. This would be used with an open cooling tower and is often referred to as an integrated, because the chillers can operate simultaneously with water economizer operation.
  • Direct water economizer. This would be used with a closed cooling tower. In this case, a heat exchanger is not needed. This type works only as a non-integrated economizer.
  • Thermo-cycle (also known as refrigerant migration). With thermo-cycle, bypass valves allow for the flow to vapor refrigerant to the condenser and allow gravity flow of liquid refrigerant to the evaporator without use of the compressor.  Only some chillers have this capability and capacity may be limited under this mode.  There is no additional piping; the cooler water from the tower is brought directly to the chiller(s) and the chiller(s) respond by shutting down the compressor and relying on thermal forces to drive the refrigerant. This method is also known as “thermosiphon” since thermal gradients passively move refrigerant between the evaporator and condenser.
Units List (see above)
Input Restrictions As designed
Water-Side Economizer HX Effectiveness
Applicability Water-side economizers with an open cooling tower

Definition

The effectiveness of a water-side heat exchanger at design conditions. This is defined as:

(6.8.4-1)

$$ W\!SE_{eff} = \frac{t_{ea}-t_{la}}{t_{ea}-t_{ew}}$$where

WSEeff The effectiveness of the water-side economizer coil
tea The entering coil air dry-bulb temperature (°F)
tla The leaving coil air dry-bulb temperature (°F)
tea The entering coil water temperature (°F)
Units Ratio
Input Restrictions As designed. The default is 60 %.
Water-Side Economizer Maximum Tdb
Applicability All water-side economizers
Definition The control temperature (outside air dry-bulb temperature) above which the water-side economizer is disabled.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 65°F.
Water-Side Economizer Maximum CWS
Applicability All water-side economizers
Definition The control temperature (condenser water supply temperature) above which the water-side economizer is disabled.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 50°F.
Water-Side Economizer CWS Setpoint
Applicability All water-side economizers
Definition The design condenser water supply temperature for the cooling tower in economizer mode.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 45°F or 40°F for “Thermo Cycle.”
Water-Side Economizer Availability Schedule
Applicability All water-side economizers
Definition A schedule which represents the availability of the water-side economizer
Units Data structure: schedule, on/off
Input Restrictions As designed
Water-Side Economizer Auxiliary kW
Applicability Water-side economizers with an open tower
Definition The electrical input (pumps and auxiliaries) for a dedicated pump for the chilled water side of the heat exchanger. This power is in excess of the condenser water pumps and cooling tower fans for the system during water-side economizer operation.
Units KW or kW/ton
Input Restrictions As designed

Baseline Building Summary. None of the baseline building systems use a water-side economizer.

Water-Side Economizer Name
Applicability All water-side economizers
Definition The name of a water-side economizer for a cooling system
Units Text, unique
Input Restrictions Descriptive reference to the construction documents. The default is no water-side economizer.
Baseline Rules No water economizer
Water Economizer Type
Applicability All water-side economizers
Definition The type of water-side economizer. Choices include:
  • None
  • Heat exchanger in parallel with chillers. This would be used with an open cooling tower is often referred to as a non-integrated economizer, because the chillers are locked out when the plant is in economizer mode.
  • Heat exchanger in series with chillers. This would be used with an open cooling tower and is often referred to as an integrated, because the chillers can operate simultaneously with water economizer operation.
  • Direct water economizer. This would be used with a closed cooling tower. In this case, a heat exchanger is not needed. This type works only as a non-integrated economizer.
  • Thermo-cycle (also known as refrigerant migration). With thermo-cycle, bypass valves allow for the flow to vapor refrigerant to the condenser and allow gravity flow of liquid refrigerant to the evaporator without use of the compressor.  Only some chillers have this capability and capacity may be limited under this mode.  There is no additional piping; the cooler water from the tower is brought directly to the chiller(s) and the chiller(s) respond by shutting down the compressor and relying on thermal forces to drive the refrigerant. This method is also known as “thermosiphon” since thermal gradients passively move refrigerant between the evaporator and condenser.
Units List (see above)
Input Restrictions As designed
Water-Side Economizer HX Effectiveness
Applicability Water-side economizers with an open cooling tower

Definition

The effectiveness of a water-side heat exchanger at design conditions. This is defined as:

(6.8.4-1)

$$ W\!SE_{eff} = \frac{t_{ea}-t_{la}}{t_{ea}-t_{ew}}$$where

WSEeff The effectiveness of the water-side economizer coil
tea The entering coil air dry-bulb temperature (°F)
tla The leaving coil air dry-bulb temperature (°F)
tea The entering coil water temperature (°F)
Units Ratio
Input Restrictions As designed. The default is 60 %.
Water-Side Economizer Maximum Tdb
Applicability All water-side economizers
Definition The control temperature (outside air dry-bulb temperature) above which the water-side economizer is disabled.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 65°F.
Water-Side Economizer Maximum CWS
Applicability All water-side economizers
Definition The control temperature (condenser water supply temperature) above which the water-side economizer is disabled.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 50°F.
Water-Side Economizer CWS Setpoint
Applicability All water-side economizers
Definition The design condenser water supply temperature for the cooling tower in economizer mode.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 45°F or 40°F for “Thermo Cycle.”
Water-Side Economizer Availability Schedule
Applicability All water-side economizers
Definition A schedule which represents the availability of the water-side economizer
Units Data structure: schedule, on/off
Input Restrictions As designed
Water-Side Economizer Auxiliary kW
Applicability Water-side economizers with an open tower
Definition The electrical input (pumps and auxiliaries) for a dedicated pump for the chilled water side of the heat exchanger. This power is in excess of the condenser water pumps and cooling tower fans for the system during water-side economizer operation.
Units KW or kW/ton
Input Restrictions As designed