3.8.5 Pumps

Applicability

All pumps

Definition

A unique descriptor for each pump

Units

Text, unique

Input Restrictions

User entry. Where applicable, this should match the tags that are used on the plans.

Baseline Rules

Same as the proposed design. If there is no equivalent in the proposed design, assign a sequential tag to each piece of equipment. The sequential tags should indicate the pump service as part of the descriptor (e.g. CW for condenser water, CHW for chilled water, or HHW for heating hot water).

Applicability

All pumps

Definition

The service for each pump. Choices include:

• Chilled water
• Chilled water (primary)
• Chilled water (secondary)
• Heating water
• Heating water (primary)
• Heating water (secondary)
• Service hot water
• Condenser water
• Loop water (for hydronic heat pumps)

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

As needed by the baseline building system

Applicability

All pumps

Definition

The number of identical pumps in service in a particular loop, e.g. the heating hot water loop, chilled water loop, or condenser water loop

Units

Numeric: integer

Input Restrictions

As designed

Baseline Rules

The number of pumps will be defined as specified below:

• One heating hot water pump for each boiler
• One primary chilled water pump for each chiller and one secondary chilled water pump for the chilled water loop
• One condenser water pump for each chiller
• One district hot water pump for each building served by a district hot water system
• One district chilled water pump for each building served by a district chilled water system

Applicability

All pumps

Definition

The heating and cooling delivery systems can consist of a simple primary loop system, or more complicated primary/secondary loops or primary/secondary/tertiary loops.

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

Heating water systems shall be modeled with primary loops only. Chilled water systems shall be modeled with primary/secondary loops.

Applicability

All pumps

Definition

Software commonly models pumps in one of two ways: The simple method is for the user to enter the electric power per unit of flow (W/gpm). This method is commonly used for smaller systems. A more detailed method requires a specification of the pumping head, impeller efficiency, motor efficiency, and other inputs.

Units

List: Power-Per-Unit-Flow or Detailed

Input Restrictions

Either method may be used, as appropriate.

Baseline Rules

Detailed

Applicability

All baseline building pumps and proposed design pumps that use the Power-Per-Unit-Flow method.

Definition

The electric power of the pump divided by the flow at design conditions.

Units

W/gpm

Input Restrictions

As designed

Baseline Rules

Not applicable

Applicability

All pumps that use the detailed modeling method

Definition

The nameplate motor horspower

Units

Horsepower

Input Restrictions

Constrained to be a value from the following list of standard motor sizes:

A standard motor size table (hp) is defined as: 1/12, 1/8, ¼, ½, ¾, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200

Baseline Rules

Not applicable

Applicability

All baseline building pumps and proposed design pumps that use the detailed modeling method

Definition

The head of the pump at design flow conditions

Units

ft or wg

Input Restrictions

As designed

Baseline Rules

For the baseline building:

• District chilled water: 55 ft
• District hot water: 44 ft
• Chilled water system: baseline system pumppower is 9 W/gpm for the primary loop and 13 W/gpm for the secondary loop and this 31 ft of head for the primary loop and 44 ft of head for the secondary loop
• Condenser water system: 60 ft
• Hot water system: 60 ft

Applicability

All pumps in baseline building and proposed design that use the detailed modeling method

Definition

The full load efficiency of the impeller

Units

Ratio between 0 and 1.0

Input Restrictions

As designed

Baseline Rules

For the baseline building:

• District chilled water system: 72% (assuming motor efficiency of 90% and a total pump efficiency of 65%)
• District hot water system: 66.67% (assuming motor efficiency of 90% and a total pump efficiency of 60%)
• Chilled water system: 72% (assuming motor efficiency of 90% and total pump efficiency of 65%)
• Condenser water system: 66.67% (assuming motor efficiency of 90% and total pump efficiency of 60%)
• Hot water system: 66.67% (assuming motor efficiency of 90% and total pump efficiency of 60%)

Applicability

All pumps in baseline building and proposed design that use the detailed modeling method

Definition

The full load efficiency of the pump motor

Units

Ratio between 0 and 1.0

Input Restrictions

As designed

Baseline Rules

For the baseline building

• District chilled water system: 90%
• District hot water system: 90%
• Chilled water system: 90%
• Condenser water system: Motor efficiency = 90%
• Hot water system: 90%

Applicability

All two-speed or variable-speed pumps

Definition

The minimum pump speed for a two-speed for variable-speed pump.  For two-speed pumps this is typically 0.67 or 0.5.  Note that the pump minimum speed is not necessarily the same as the minimum flow ratio, since the system head may change.

(Equation 3.8.5-1)

$$Pump \  Speed_{Min} =  Pump \  Speed_{Design} \times \sqrt{\frac{Head_{Min}}{Head_{Design}}}$$

Units

Ratio between 0 and 1.0

Input Restrictions

As designed

Baseline Rules

When the baseline pumps are required to have variable speed drives in accordance with descriptor Pump Control Type, the pump minimum speed shall be 0.10.

Applicability

All pumps

Definition

The flow rate of the pump at design conditions. For the baseline, this is derived from the heating and cooling loads, the appropriate oversizing factors, and the design supply and return temperatures.

Units

gpm or gpm/ton for condenser and primary chilled water pumps

Input Restrictions

Not a user input

Baseline Rules

The temperature change on the evaporator side of the chillers is 12°F (56°F less 44°F) and this equates to a flow of 2 gpm/ton. The temperature change on the condenser side of the chillers is 10 °F, which equates to a flow of 2.4 gpm/ton. The flow for secondary chilled water pumps varies with cooling demand, since there are two-way valves at the coils. The flow for primary only heating varies with demand down to the minimum required for flow through the boiler. A VSD is required for heating pumps when the service area is greater than or equal to 120,000 ft². For hot water pumps servicing boilers, the flow rate in gpm shall be the boiler capacity in Btu/h / 25,000, which corresponds to a loop temperature drop of 50°F.

Applicability

All pumps

Definition

The type of control for the pump. Choices are:

• Fixed speed, fixed flow
• Fixed speed, variable flow (the default, with flow control via a valve)
• Two-speed
• Variable speed, variable flow

Units

None

Input Restrictions

As designed. The default is “Fixed Speed, Variable Flow” which models the action of a constant speed pump riding the curve against two-way control valves.

Baseline Rules

The following rules shall apply:

• Hot water: Hot water loops are primary loops only. For systems serving less than 120,000 ft², the HW pump is modeled as variable flow with a constant speed pump riding the pump curve. For systems serving more than 120,000 ft², the HW pump is modeled as a variable flow with a variable speed pump controlled with a variable speed drive.
• Condenser water pumps: Condenser water loops are primary only. CW pumps are required to be modeled as fixed speed and fixed flow.
• Chilled water pumps:  The CHW pumping for systems 7, 8, 11, 12, and 13 are primary/secondary with variable flow. The chilled water pumps used for the primary loop are fixed speed and fixed flow. For systems with a capacity of less than 300 tons, the secondary system pumps shall ride the pump curve. For systems with a capacity greater than 300 tons, the secondary pumps will be modeled as variable speed.
• District chilled water pump shall follow the same rules for secondary chilled water pumps.

Applicability

All pumps

Definition

The type of pump operation can be either On-Demand, Standby or Scheduled. On-Demand operation means the pumps are only pumping when their associated equipment is cycling, so chiller and condenser pumps are on when the chiller is on and the heating hot water pump operates when its associated boiler is cycling. Standby operation allows hot or chilled water to circulate through the primary loop of a primary/secondary loop system or through a reduced portion of a primary-only system, assuming the system has appropriate 3-way valves. Scheduled operation means that the pumps and their associated equipment are turned completely off according to occupancy schedules, time of year, or outside conditions. Under scheduled operation, when the systems are on they are assumed to be in On-Demand mode.

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

The baseline system pumps are assumed to operate in on-demand mode. The chilled water and condenser pumps are tied to the chiller operation, cycling on and off with the chiller, and the heating hot water pumps are tied to the boiler operation.

Applicability

All pumps

Definition

A part-load power curve for the pump

(Equation 3.8.5-2)

$$CIRC\_PUMP\_FPLR = a + b \cdot PLR + c \cdot PLR^{2} + d \cdot PLR^{3}$$

(Equation 3.8.5-3)

$$P_{Pump} = P_{Design} \times CIRC\_PUMP\_FPLR $$

Where

Units

Data structure

Input Restrictions

As designed. Default is curve above.

Baseline Rules

Use the defaults described above based on pump type. The curve with differential pressure reset isn’t used for the baseline building.