Trial / Demo
With the introduction of the Central Plant Heat Pumps (CPHP) in ApacheHVAC, which can serve both the Chilled Water Loop (ChWL) and Hot Water Loop (HWL), users can now model both Air-to-Water Heat Pumps (AWHP) and Water-to-Water Heat Pumps (WWHP). Moreover, this new feature has prompted inquiries about how CPHP can be used to build a custom AWHP or WWHP system. This multi-part article will explore these custom scenarios in detail.
In the first article of this multi-part series, I will explain an approach to modeling a CPHP with a Booster (or Top-off) Heater Boiler. ApacheHVAC allows users to select from a range of heating sources, including Natural Gas Boiler, Electric Boiler, Water-to-Water Heat Pump, or Air-to-Water Heat Pump, as the booster heater source.
Figure 1: Layout of Heat Pump with Booster
Scenario 1 is that a mechanical design engineer might install a new CPHP upstream of an existing (or new) boiler to preheat water to 120°F, with the downstream boiler then heating it to 140°F.
Another scenario is that an AWHP might not supply hot water effectively at low ambient temperatures, so a backup heating source could be installed downstream of the AWHP for such conditions.
These configurations can be set up using the “Auxiliary Heat Source" option in the Hot Water Loop tab of ApacheHVAC, which adds a booster heater downstream of the CPHP to reach the desired temperature. This article explains how to configure this setup in ApacheHVAC.
Step 1: Define the AWHP/WWHP supply water temperature as the “Primary Supply” in the HWL.
This step defines the CPHP leaving water temperature. Referring to Figure 1, we are defining the temperature at “HWL to Booster” section.
Figure 2: Defining AAHP Leaving Water Temperature
Step 2: Add a Secondary Loop and check the “Enable independent secondary loop supply water temperature control" box. Referring back to Figure 1, in this step, we define the temperature of the water leaving the booster heating source, “HWL Supply.”
Step 2a: In the “Secondary Loop,” update the “Design hot water Supply Temperature” to be representative of the booster boiler leaving temperature.
Figure 3: Defining Booster Boiler Leaving Water Temperature
Figure 4: Editing Properties of Booster Boiler
We can verify the implementation of the CPHP with the Booster heater setup in IESVE through the VistaPro application, which provides visualization tools for simulation results.
The screenshot below illustrates the HWL results in VistaPro. It shows that the “Primary Supply Temperature” (HP leaving temperature) in the loop is 120 °F (as defined in Figure 2 above), while the "Auxiliary heat source leaving temperature” (Booster boiler leaving temperature) is 140 °F (as defined in Figure 3).
Figure 5: Result Visualization in VistaPro
Modeling a CPHP with a booster heater in ApacheHVAC offers a simple and effective way to meet hot water temperature requirements under all conditions.
By defining the primary heat pump supply temperature, adding a controlled secondary loop, and enabling the auxiliary heat source, engineers can accurately represent both the heat pump and booster system. VistaPro results confirm how each component contributes to the final supply temperature. This hybrid approach allows the primary heat pump to operate efficiently for most of the year while relying on the booster heater only when needed, offering a cost-effective and reliable solution for buildings in colder climates or requiring higher supply temperatures.
