Service Water Heating (Domestic Hot Water)

 

Service water heating, also known as domestic hot water, energy can be modeled using ApacheHVAC for any spaces in the model using ApHVAC for HVAC methodology (see Section 1.2.3).  ApacheHVAC offers both an explicit and a simple model for heating domestic hot water (DHW).  The Explicit model couples the DHW tank to any hot water loop via a heat exchanger model and provides for optional pre-heating via an explicit condenser heat recovery heat exchanger model.  The Simple DHW loads model can be used with a hot water loop or generic heat source, but does not include the explicit heat exchanger or the optional condenser heat recovery pre-heating.

Figure 7-1: Explicit DHW System with Condenser Heat Recovery (CHR), Solar Water Heating (SWH), a storage tank, a recirculation loop, and a dedicated DHW pump.

 

Domestic hot water demand is defined using DHW Zones within the model.  For each DHW Zone, domestic hot water demand can be defined as either the sum of the demand from the spaces within that zone, or as a user-entered demand for the DHW Zone.  When the demand is determined by the spaces, the DHW Zone inherits the collective DHW demand from the constituent spaces.  When the demand is set at the DHW Zone level, any DHW settings in the constituent rooms will be overridden.  Instead, a DHW Consumption value and DHW Pattern of Use Profile will be defined in the DHW Zones dialog.

Figure 7-2: Domestic hot water consumption can be defined as a room-level setting for a given space type using a thermal template, as shown above on the Space Conditions tab of the Building Template Manger.

Domestic hot water demand can be defined as a room-level attribute using thermal templates (i.e., a setting that applies to all rooms of a given type) or by editing Space Data for individual rooms.  In the Building Template Manager, DHW consumption is defined on the Space Conditions tab utilizing a peak demand associated with a modulating profile.  The DHW demand schedule may be linked to space occupancy, in which case the profile associated with occupancy for an individual space is used to modulate the peak DHW demand.  Alternatively, users may select and independent profile and use any modulating profile within the model to schedule DHW demand.

A “Room-level setting” check box ensures room-level DHW consumption will be passed to ApacheHVAC whenever the room is placed within a DHW Zone.  This is the default for all rooms with template HVAC Methodology set to ApHVAC.  When the box is unchecked, any Room-level DHW consumption will be ignored, regardless of room placement within a DHW Zone.

 

Domestic hot water demand is defined using DHW Zones within the model.  For each DHW Zone, domestic hot water demand can be defined as either the sum of the demand from the spaces within that zone, or as a user-entered demand for the DHW Zone.

DHW Zones is a protected browser tree grouping scheme set up specifically for organizing Rooms into DHW (Domestic Hot Water) Zones.

Figure 7-3: DHW Zones grouping scheme in the Room Browser

 

By default, one DHW zone is defined in a model and contains all of the rooms.  Rooms appearing in light grey text will not be included in the DHW Zone within ApacheHVAC.  Additional DHW zones can be created by using the ‘Create and edit space groups’ button.

Drag & drop functionality is provided for moving Rooms into and among defined DHW Zones. A right-click menu provides additional tools for moving rooms by cut & paste, renaming zones, accessing the Properties dialog, and re-synchronization of the browser tree when model rooms are added or sub-divided.

 

 

Figure 7-4: DHW Zones accessible from the Apache toolbar

 

The DHW Zones dialog is a tabular, editable view of the DHW zones in a project and can be accessed via the toolbar button in Apache or by right clicking in the DHW Zones grouping scheme and selecting Properties.

For each DHW Zone, domestic hot water demand can be defined as either the sum of the demand from the spaces within that zone, or as a user-entered demand for the DHW Zone.  When the demand is determined by the spaces, the DHW Zone inherits the collective DHW demand from the constituent spaces.  When the demand is set at the DHW Zone level, any DHW settings in the constituent rooms will be overridden.  Instead, a DHW Consumption value and DHW Pattern of Use Profile will be defined in the DHW Zones dialog.

 

Figure 7-5: DHW Zones dialog displaying all DHW Zones present in a model

 

ApacheHVAC offers an explicit model for heating domestic hot water (DHW) cold inlet water using a hot water loop, condenser heat recovery, solar water heating, and/or a hot water loop heat exchanger.

Figure 7-6: Service hot water - DHW Systems dialog for editing domestic hot water parameters and zone assignments within ApacheHVAC.

 

The Service hot water – DHW Systems dialog shown in Figure 7-6 defines DHW Systems and DHW Branches on a tree on the left, with parameters to specify systems on the right.  The tree allows drag-and-drop functionality to assign DHW Zones to DHW Branches.  Multiple DHW Branches may be added to a DHW System using the add button at the bottom.  Assigning DHW Zones to DHW Branches assigns DHW Zones to the associated DHW System.  Multiple DHW Systems may be added to a project using the add button at the bottom.  Only DHW Zones with a setting for demand at the DHW Zone level or containing Rooms with ApacheHVAC DHW demand will be shown in the DHW Systems dialog.

 

DHW systems may have multiple DHW branches associated with them.  Branches are added and removed using the buttons at the bottom of the browser tree.  Each branch may have a unique configuration and will contain unique DHW zones.

Figure 7-13: DHW browser tree showing a DHW System with two DWH branches.

 

Results for Domestic Hot Water modeling can be viewed in VistaPro.  To view all available results, users should ensure outputs for Apache HVAC system results and ApacheHVAC component results are selected by modifying the Output Options for the Apache Simulation (See Figure 7-14).

When there is no heat source available on the DHW System, the tank loss (for both the explicit model and simple model) and recirculation loss (for simple model) are excluded from the simulation and not reported in VistaPro.

 

Figure 7-14: Output options in Apache Simulation illustrating necessary settings for viewing all domestic hot water results available in VistaPro

 

After a simulation is complete, results can be viewed in VistaPro.  To see detailed DHW results, select the HVAC network from the Room Browser to reveal the HVAC Network tree.  Navigating to the DHW systems within the HVAC Network tree displays relevant DHW variables.  See Figure 7-15.

 

Figure 7-15: Domestic hot water results available in VistaPro

 

By plotting variables using the different graphing tools available in VistaPro, users can evaluate DHW system performance and investigate the impact of pre-heating devices.

 

Figure 7-16: Example domestic hot water results in VistaPro illustrating DHW load met by pre-heating devices and total DHW demand load on an XY-plot