Accounting for VRF systems in Ene-1 model
Technical Clarification Number
1) VRF: Outdoor unit energy consumption
The energy consumption of any outdoor unit shall be determined using the ‘interpolated COP data’ as described in item (3) below and the thermal loads as derived from thermal modeling software.
2) VRF: Indoor unit energy consumption
The energy consumption of any indoor unit shall be determined using the ‘specific fan power’ as described in item (4) below and the supply air rates as described in 5) as proposed by the Project Team.
3) Interpolated COP data (outdoor units)
The interpolated COP data for the outdoor VRF units used for the calculation of the annual energy consumption of all the outdoor VRF units included in the project is to be derived from the manufacturer’s product data for –
• All outdoor unit models or types included in the project such that each outdoor unit model or type has a unique interpolated COP data set based on the manufacturer’s product data for that unit;
4) Derived Specific Fan Power (indoor units)
The derived specific fan power for the indoor VRF units used for the calculation of the annual energy consumption of all the indoor VRF units included in the project is to be derived from the manufacturer’s product data for –
• All indoor unit models or types included in the project such that each indoor unit model or type has a unique specific fan power based on the manufacturer’s product data for that unit;
5) Derivation of zone supply air rates
The derivation of zone supply air rates, to which the specific fan power, as outlined in item (4) above, is applied to determine the fan energy consumption of the indoor VRF units, must be determined through modeling the HVAC system as a Constant Volume (CV) system.
6) Treatment of sub-systems
As part-load conditions, thus part-load performance, will vary depending on each sub-system required to serve the different parts of the building that have been connected to that sub-system, it is an unacceptable methodology to aggregate the thermal loads of all zones within the thermal modeling. As each sub-system will have a different installed heating/cooling capacity and the thermal loads within each space will not be equal, each sub-system will have different part load conditions, it is required that each sub-system be post-processed using the methodology approved in item (1) above, individually to account for this. This post-processing method approved in item (1) above must clearly reference the part-load conditions derived from the peak load within the sub-system and the thermal loads of the zones within the sub-system.
Carbon Monoxide (CO) monitoring on basement fans
Technical Clarification Number
Where CO monitoring is used to control the air flow of basement fans, the calculation of the required air flow rates and associated energy savings must be based strictly in accordance with a recognised best practise standard or guideline, e.g. ‘2011 ASHRAE Handbook – HVAC Applications’.
The calculation methodology must at a minimum be based on the following inputs:
• Acceptable level of contaminants in the parking facility
• Number of cars in operation at various times over a 24 hour period
• Length of travel and operation time for cars within the car-park
• CO emission rate for a typical car under various conditions
• Total volume of the parking facility
Within the Energy Modelling Report, the project team must;
• Clearly state the source of the calculation methodology used (recognised best practise standard or guideline).
• Describe the calculation inputs used for each of the items above.
• Provide a description of how the ‘number of cars in operation at various times over a 24 hour period’ and the ‘length of travel and operation time for cars within the car-park’ are a representative or conservative representation of the expected traffic profile for the building.
In addition, the project team must state in the Energy Modelling Report how the following issues have been taken into account within the calculations:
• Accounting for the contaminant level of outside air drawn into the basement;
• Accounting for building form and position of sensors and the effect this may have on operation of the system; and
• Providing efficient, adequate airflow throughout the structure.
The project team must demonstrate with supporting contract documentation (Design rating) or commissioning records (As Built rating) that the CO sensors are set according to the levels used within the calculations.
Note that the project team need not submit the full calculations within the Energy Modelling Report, but simply the confirmations and inputs requested above.
Green Star SA - Multi Unit Residential DTS & Energy Modelling Protocol Guide v1: Page 32
DTS & Energy Modelling Protocol Guide Version 1.0, page 32, Conductance (U-Values), replace ‘total habitable floor area” in the calculation with ‘net floor area”