Heating and Cooling Appliances (HVAC)


One of the main appliance categories assessed for NatHERS Whole of Home (WoH) is Heating and Cooling (commonly called 'HVAC' although the "V" for mechanical ventilation is not currently included in NatHERS).

HVAC energy demand in NatHERS WoH is calculated quite differently from the other categories in that it's result are directly determined from the hourly NatHERS Thermal Fabric Heating & Cooling results, albeit under different operating profiles than the Thermal Fabric simulation used in the NatHERS Star Rating.

This means that improving the underlying thermal performance of a home (i.e. reducing it's heating and/or cooling demand) will reduce the required HVAC energy.


WoH Thermal Simulations

NatHERS Whole of Home requires 2 different Chenath simulations to be run to help calculate the HVAC. These profiles have different occupancy profiles (i.e. on/off times and temperatures) to the Star-Rating Thermal-Fabric simulation and are aimed at presenting a more represenative HVAC demand. These two profiles are:

  • WoH Allday profile: a simulation that represents occupants who are generally at home conditioning their dwelling during the day, which is very similar to the Star-Rating profile as well as
  • WoH Workday profile: a simulation that represents occupants who would be away from the home during normal workhours and conditions the home out of office hours.

Whenever the Appliances setting is enabled in Hero, these 2 WoH simulations will be run simultaneously in parallel with the Star Rating simulation (and any optional Thermal Comfort simulation) when you hit the Run simulation button. This means that you only need to run the project once and the Star Rating and Whole of Home results will be updated simultaneously, which improves on other methods where these processes are completely separate process and workflows.

The hourly heating and cooling results calculated by these 2 WoH simulations are the input loads that feed into the hourly HVAC appliance heating and cooling energy calculations that determine the HVAC results. 

The 2 WoH hourly results profiles are blended into a single annual hourly result profile when calculating the HVAC energy usage, on a blended weighting of 60% of the Allday and 40% of the Workday profile results.


Heating and Cooling View

The below section outlines how HVAC is modelled, edited and analysed in the Hero Appliances view.


1 - AC ZERL Climate Zone

The AC Climate Zone is required to determine the correct Energy Rating of air-conditioners that have been approved under GEMS using the new ZERL (Zoned Energy Rating label) which has different Energy Ratings for Heating and Cooling across 


2 - Peak Load

In the information toolbar of the Heating and Cooling, the Peak Thermal Cooling & Heating loads are shown based on the peak hourly values encountered during the WoH Chenath simulations.

These values may assist in sizing HVAC equipment capacity, however it should be noted that Chenath as a calculation engine has an "unlimited" capacity operation, where it will deliver as much heating or cooling as is required to instantly bring a space up to it's required temperature. This means that for simulations where the HVAC has been off, and the temperature of the space is very high (e.g. 35 degrees) then when the HVAC turns on in the simulation it will deliver all the necessary cooling energy to bring that down to the cooling setpoint in one hour (e.g. 35 degrees to 26 or whatever the cooling setpoint is). This is generally not how HVAC is sized, where a warm-up or cool-down period over a period of several hours is usually accounted for to avoid oversizing equipment, and therefore there may be situations where Chenath is overestimating the required capacity. There is also as yet, a lack of research on how will Chenath peak loads relate to real world conditions. The Chenath Peak Loads are therefore more likely a useful ballpark metric in conjunction with other means of HVAC sizing, until further work has been done.


3 - Regulated Load

Heating and Cooling is one of the Regulated Loads that contribute to the NatHERS Whole of Home rating.


4 - Unassigned Zones or Dwellings Warning

When a Conditioned Zone has not been assigned a HVAC system, an alert will be shown to the user alerting them to this fact (see 12 - Zone Selector).

You cannot produce a NatHERS WoH Rating until all conditioned zones of all dwellings have been assigned a HVAC system for both heating and cooling, even if they will not have a HVAC system installed (you should use "Default/None" HVAC type in these instances as per the HVAC Type section below).


5 - Group name label

As per all Appliance categories, when you have created multiple systems of a certain category you can edit the name of the system group by hovering over the group name and editing the label.


6 - Group Sub-Results

As per all Appliances categories, whenever multiple systems have been created, the individual systems energy, running-cost and emissions results will be shown for that system in the Group Sub-Results header.


7 - Remove Group

To remove an unnecessary HVAC system click the delete system group button.


8 - HVAC Types

There are a wide variety of HVAC systems available for user selection, however some types of HVAC systems (such as hydronic and centralised multi-dwelling HVAC systems) are currently missing from the scheme. In these instances, using "None/Unknown" type would be the most appropriate (see details below). Some HVAC types have no ability to vary their efficiency and must use the NatHERS default values.

These options are outlined below:

  • None / Unknown (Default AC): If the HVAC device for a Zone is not known, or there is no expected .All conditioned zones must be assigned a HVAC device.
    Note as per the NatHERS Technical Notes you can assign the HVAC system of an adjacent zone
  • Ducted Air-Conditioner: A reverse cycle air-conditioner that has ductwork to distribute conditioned air to the connected rooms. Ducted air-conditioners 
  • Room Air-Conditioner: This is the common wall mounted split system reverse-cycle air-conditioner. These systems are cost-effective and typically can be very energy efficient (particularly at lower capacities). Most room ACs available in Australia have an Energy Rating
  • Room Electric Resistance:
  • Ducted Gas: 
  • Room Gas: 
  • Wood: 
  • Evaporative: 



9 - Star Rating Type

When a air-conditioner HVAC type is selected, the Star Rating Type row will be shown. This will prompt the user to select the star rating scheme that the HVAC device efficiency values are based on. There are currently two main options in Hero:

Zoned Energy Rating Label (ZERL)



Old Energy Rating Label (ERL) Pre-2019

The old Energy Rating Label (ERL) was used prior to the introduction of the ZERL. In this rating, there is only a single cooling and heating efficiency shown, along with only a single output and input capacity.

For more information on the Air-conditioning Energy Ratings see:







10 - Heating Efficiency



11 - Cooling Efficiency



12 - Zone Selector

For HVAC systems, you can choose the Zones that each HVAC system applies to on a Heating or Cooling basis. This is similar to other appliance categories where for multi-dwelling projects you can select the dwelling the system applies to.

As of Hero v4.0, a Zone can only have one Heating device or Cooling device, and you should follow the NatHERS Technical Guide advice for zones with multiple HVAC devices. You can select the Zones that a HVAC device applies to using the Zone Selector button at the bottom of each HVAC group. If you assign a Zone that is in use on another HVAC system, this will be removed after adding to the current HVAC system. You can however have HVAC devices that only Heat or only Cool a zone, where another device will only Cool or only Heat and vice versa.


13 - Additional Groups

You can create as many HVAC systems as you require to model your project. If you have a Heating only device, and a Cooling only device this will require you to model two different HVAC systems and assign the Heating zones and Cooling zones accordingly as per item 12 above.


14 - HVAC Results

As per all Appliance categories, the individual results of the HVAC category are shown in each section along with the percentage impact of HVAC to the overall Operational Energy, Running-Cost and Operational Emissions of the Project. You can hide this Category Result in the Settings section of the Appliance View.


15 - HVAC Comments

As per all Appliance categories, you can add your own comments, description, recommendations or explanations to the HVAC section to include in your report exports. You can hide this Comments section in the Settings section of the Appliance View.

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