Water to Water Heat Pumps / Ground Source Heat Pumps (GSHP) Beta Only

One single physical water to water heat pump could provide either heating only, cooling only or both heating and cooling. These configurations can be represented in DesignBuilder using Heat pump - heating and heat pump - cooling components connected to hot and chilled water plant loops respectively. Where both heating and cooling are provided by the same physical heat pump both heating and cooling heat pumps must be included in the HVAC layout and the data entry for the heat pumps (especially flow rates), must be coordinated.

The Supply side of the heat pump is usually connected to a Ground Heat Exchanger. The schematic diagram below shows the layout and piping diagram of the water-to-water heat pump.

GSHP Loops

Ground source heat pumps systems are essentially made up of two loops (heating or cooling only cases) or three loops (combined heating and cooling). In this case these 3 loops are required to represent the heat pump system:

• HW loop (for heating applications) - Hot water loop (Water-to-water heat pump heating)
• CHW loop (for cooling applications) - Chilled water loop (Water-to-water heat pump cooling)
• Condenser loop - Ground heat exchanger loop (exchanges heat with ground via either surface, pond or vertical borehole types)

In addition to the above mandatory loops, the system may also require extra loops such as air loops for specific room/block applications.

Tip: You are advised to work through the GSHP Case Study before attempting to model these systems for the first time.

Example layouts

• Heating only
• Cooling only
• Heating and cooling

Component descriptions:

• Water to Water Heat Pump - Heating
• Water to Water Heat Pump - Cooling

Configuring GSHPs in DesignBuilder

Because GSHPs cannot be autosized in EnergyPlus some care is required in setting up these systems. This section describes a process which ensures correct sizing and provides for correct interaction between the various components involved. The process is as follows:

1. Run DesignBuilder Heating design and Cooling design calculations in order to get the maximum heating and cooling loads for the system.
2. Choose/load a correctly sized water-to-water heat pump model from DesignBuilder database by matching the peak heating/cooling loads with heat pump’s ‘Rated heating/cooling capacity’. Or alternatively, creating and applying your own heat pump data if its catalogue data is available (using procedure described in the ).
3. Select ground heat exchanger (vertical) borehole numbers from that quick/simple sizing table; set flow rate equal to the sum of ‘Rated source side flow rate’ of heat pumps connecting to it, or use your own tool to generate (and apply) a vertical ground heat exchanger case for specific conditions or detailed/precise sizing.
4. Condenser loop: set flow rate equal to or greater than the flow rate of ground heat exchanger (vertical) calculated above.

For more detail on these processes see the GSHP Case Study.