.Buildings.Templates.Plants.HeatPumps.AirToWater .Buildings.Templates.Plants.HeatPumps.AirToWaterThis template represents an air-to-water heat pump plant with closed-loop controls. While the heat pump plant configuration can be changed through parameters, a typical configuration is shown in the image below.
Only identical heat pumps are currently supported.
The supported plant configurations are enumerated in the table below.
The first option displayed in bold characters corresponds to the default
configuration.
| Configuration parameter | Options | Notes |
|---|---|---|
| Function |
Heating and cooling Heating-only |
The plant always provides heating hot water. Setting the parameter have_chiWat to true (default setting) allows
modeling a plant that provides both heating hot water and chilled water.
|
| Type of distribution | Constant primary-variable secondary centralized |
It is assumed that the HW and the CHW loops have the
same type of distribution, as specified by this parameter. "Centralized secondary pumps" refers to configurations with a single group of secondary pumps that is typically integrated into the plant. Distributed secondary pumps with multiple secondary loops served by dedicated secondary pumps are currently not supported. Options are limited to constant primary distributions because most AWHPs on the market use a reverse cycle for defrosting. This requires maximum primary flow during defrost cycles and hinders variable primary distributions. An option for constant primary-only distributions with ∆p-controlled variable speed pumps will be added in a next release. |
| Type of primary pump arrangement |
Dedicated Headered |
It is assumed that the HW and the CHW loops have the same type of primary pump arrangement, as specified by this parameter. |
| Separate dedicated primary CHW pumps |
False True |
This option is only available for heating and cooling plants with dedicated primary pumps. If this option is not selected (default setting), each AWHP uses a common dedicated primary pump for HW and CHW. Otherwise, each AWHP relies on a separate dedicated HW pump and a separate dedicated CHW pump. |
| Type of primary HW pumps |
Variable speed Constant speed |
For constant primary-variable secondary distributions, the variable speed primary pumps are commanded at fixed speeds, determined during the Testing, Adjusting and Balancing phase to provide design AWHP flow in heating and cooling modes. The same intent is achieved with constant speed primary pumps through the use of balancing valves. |
| Type of primary CHW pumps |
Variable speed Constant speed |
See the note above on primary HW pumps. |
| Controller |
Closed-loop controls with supply temperature and differential pressure reset |
Most parts of the sequence of operation are similar to that
described in ASHRAE, 2021 for chiller plants. See the documentation of Buildings.Templates.Plants.Controls.HeatPumps.AirToWater for more details. An open loop controller is also available for validation purposes. |
The control sequence implemented in this template requires the external input points specified in the documentation of the controller Buildings.Templates.Plants.HeatPumps.Components.Controls.AirToWater.
The pressure drops of the heat pump CHW and HW heat exchangers are calculated
within the isolation valve component valIso based on lumped flow
coefficients for the sake of computational efficiency.