By Haley Harlow

This article was first published on Phius' website. You can see the original version here.

If you’ve ever modeled a project in WUFI Passive that uses a heat pump for space conditioning, chances are you’re familiar with one of the following versions of the heat pump calculator: 

• Annual Heat Pump Performance Calculator (2012)

• HSPF Derating Calculator (2019)

• HSPF Deration and Multiple Heat Pumps Calculator (2021)

• Heat Pumps in Series (2022)

• Phius Air Source Heat Pump Calculator (2023)

• Phius Heat Pump Calculator (2024)

Historically, these calculators have been used for estimating the performance of air-source heat pumps based on the climate location of the project. The new-and-improved Heat Pump Performance Estimator v25.1 goes a step further with capabilities added to model air-, ground-, and water-source heat pumps. Read on to learn more about how and when to use the new calculator, how to implement the results in WUFI or METr, and a breakdown of the new features.

When do I need to use the Heat Pump Performance Estimator?

All projects that use a heat pump for heating and/or cooling should use the calculator to estimate the performance of the device(s)-in-use.

How do I use it? 

The following instructions can be found directly in the calculator, within the “Inputs for Energy Model” tab. Use the + / - on the left side of the Excel window to expand and collapse sections as needed.

1.  Complete the “Fan and Pump Run-Time Estimator” tab

a.  Data should be retrieved using WUFI Passive (Passive House Verification Report) and entered in the blue cells.

           i. In METr, the report can be downloaded from the ‘Results’ window

2.      Use the “Heat Pumps” tab to define the project climate location:

a.  Typical Climate Data: Use the built-in dropdown options to select the appropriate location

b.  Custom Climate Data: Change the “Type” of climate data to “Custom” and paste the custom climate data set in the “Custom Climate Data” tab. Then, enter the ASHRAE 99% and 1% Design Temperatures in cells C9 and D9 of the “Heat Pumps” tab.

                 i.  Hint: Design temperatures can be found in the custom criteria calculator provided for the custom CD set.

3.      Complete the “System Information” section for each type of system planned (ASHP, GSHP, and/or WSHP). First, enter the fans and pumps associated with each type of system.

a.       This data will be implemented in the final calculated COPs for heating and cooling. The “effective total power” is calculated based on the “Fan & Pump Runtime Estimator” tab, completed in Step 1. Note: Fan coil units (FCUs) and pumps should no longer be modeled as auxiliary energy in WUFI Passive or METr. They should all be accounted for by using this calculator.

b.      Ductless minisplit systems, heat pumps with ducted ratings and heat pumps with energy efficiency data following AHRI Standard 1230 need not fill out this section of the estimator. The fan power associated with space conditioning distribution is already accounted for in the efficiency from the datasheet and does not need to be accounted for separately.

4.      Complete the “Performance Data” section for each heat pump device planned

a.       Important Note: If performance data is provided at temperatures other than 17° F and 47° F, use the “COP - Custom temps” tab to extrapolate the COPs at 17° and 47° for use in this calculator.

5.       Use the “Inputs for Energy Model” tab to enter the calculated system information in WUFI Passive or METr.

How do I implement the results in WUFI/METr?

Combined Cooling System Inputs 

This section represents the performance of all of the heat pump devices as a whole. When multiple cooling systems are needed, the coverage of each cooling system can be defined similarly to the heating system inputs, shown below.

Heating System Inputs

Each heat pump type will require a unique heating device input in WUFI or METr. For example, if both an ASHP and WSHP are planned, one heating system should be modeled for the ASHP, and another should be modeled for the WSHP. The coverage of each heating system is calculated based on the capacities of each system type and is noted in the results section of each respective system.

The coverage of each device should be defined in System 1>General. Only one device should be assigned to “Space cooling”.

Are there any additional new features of the calculator I should know about?

Yes! New testing methods for determining air-source heat pump performance have been released. Instead of EER/SEER & HSPF, the new unit of performance for this equipment is EER2/SEER2 & HSPF2. This new data is more accurate, and generally less conservative than the typical performance data. 

The new estimator allows users the flexibility to model devices with different data types. To do so, the “Heating Data Type” and “Cooling Data Type” can be defined in-line with each device by using the dropdown options.

Experienced users of this calculator will notice there is no longer a “Delivery Method” column for defining whether or not the device is cooling “via Ventilation Air” or “via Recirculation Air”. This is because of the way WUFI prioritizes systems when modeling both delivery methods. In general, all cooling should be delivered “via Recirculation Air” in WUFI unless using a CERV, so we removed this column to ensure the results are implemented correctly for Certification.

All figures courtesy of Phius.