Ground Heat Exchanger - Pond

The pond heat exchanger model represents a shallow pond with submerged hydronic tubes through which the heat transfer fluid is circulated. The model represents a "shallow" pond in that no attempt is made to model any stratification effects that may be present in deeper ponds.

This type of heat exchanger is intended to be connected to the supply side of a condenser loop, and can be used with any type of plant loop. The pond may be specified as the only heat exchanger on the condenser loop (as shown in top figure below) or it may be connected in parallel with other condenser loop heat exchangers (such as cooling towers, ground surface heat exchangers) as shown in the second figure below.

Pond heat exchanger as only heat exchanger on condenser loop

Pond heat exchanger with other heat exchangers on condenser loop

Technical

 

The pond model uses a ‘lumped parameter’ method where the pond is represented by a single node with thermal mass. The pond surface temperature is the same as the temperature at this node, i.e. the surface temperature is the same as the bulk temperature. A first order differential equation is solved in the model to calculate the pond temperature at each time step. This type of heat rejecter is modelled as several circuits connected in parallel.

 

Heat transfer takes place by surface convection, long-wave radiation to the sky, absorption of solar energy, ground heat transfer and heat exchange with the fluid. A heat exchanger analogy is used to calculate the heat transfer between the heat transfer fluid and the pond.

General

Name

This alpha field contains the editable identifying name for the outside pond heat exchanger.

Ground Heat Exchanger Template

Template

You can use this control to load data to the dialog from a pre-defined Ground heat exchanger template as a starting point for your particular component.

Note: After loading a Ground heat exchanger template it is important to make sure to update the Design heat exchanger flow rates as the sum of connected heat pump rated flow rates.

Ground Heat Exchanger Type

Type

DesignBuilder provides 3 different ground heat exchanger types:

• 1-Vertical (boreholes)
• 2-Pond
• 3-Surface

Note: The Type drop down list is not editable. To select a different type of heat exchanger, you must first select an appropriate template (above).

Ground Heat Exchanger - Pond

Ground thermal conductivity

This numeric field contains the ground thermal conductivity (in W/mK or Btu-in/h-ft2-F).

Pond depth

This numeric field contains the pond depth (in m or ft).

Pond area

This numeric field contains the pond area (in m² or ft²).

Hydronic tubing inside diameter

This numeric field contains the hydronic tubing inside diameter (in m or in).

Hydronic tubing outside diameter

This numeric field contains the hydronic tubing outside diameter (in m or in).

Hydronic tubing thermal conductivity

This numeric field contains the hydronic tubing thermal conductivity (in W/mK or Btu-in/h-ft2-F).

Number of tubing circuits

This numeric field contains the number of hydronic tubing circuits, total in parallel in this pond.

Length of each tubing circuit

This numeric field contains length (in m or ft) of each hydronic tubing circuit.