HVAC tab in model data - Simple HVAC
Check the mechanical ventilation checkbox to indicate that outside air and/or re-circulated air is delivered to the zone. You can use this setting to define mechanical ventilation and air delivered through centrally ducted air conditioning systems or local fresh air systems.
The specification of outside air delivery rates is the same for both options as described in the Outside air section.
The way that mechanical ventilation is modelled in Simple HVAC depends on the Mechanical ventilation method model option:
With the Mechanical ventilation method model option the introduction of outside air through fans is achieved using the EnergyPlus ZoneVentilation:DesignFlowRate data separate from the main HVAC system. Energy consumption and heat pick up from fans is included as described below.
When using Simple HVAC, enter the type of fan. Select from:
Note: In Simple HVAC the Auxiliary energy data accounts for all electric fan and pump distribution EnergyPlus controls and any other electrical energy use associated with HVAC that is not already accounted for elsewhere.
When the Fan type is 1-Supply, enter the pressure rise at full flow and standard conditions. Standard conditions are considered 20°C at sea level, 101325 Pa.
See also Calculating Fan Pressure Rise.
When the Fan type is 1-Supply, enter the product of the fan motor and impeller efficiency of the supply fan. This is the ratio of the power delivered to the air to the electrical input power at maximum flow expressed as a percentage. The motor efficiency is the power delivered to the shaft divided by the electrical power input to the motor. The fan efficiency is power delivered to the air divided by the shaft power. The power delivered to the fluid is the mass flow rate of the air multiplied by the pressure rise divided by the air density. Must be greater than 0 and less than or equal to 100.
The calculations for fan power and airflow temperature pick up are detailed in the EnergyPlus Engineering Document. A summary is shown below:
Total Fan Power = Mass flow rate. DeltaP / (Total fan efficiency . Air density)
Shaft Fan Power = Motor efficiency . Total Fan Power
Heat to air = Shaft Fan Power + (Total Fan Power - Shaft Fan Power) . Motor in air fraction
With the Ideal loads option, Mechanical ventilation is modelled with heating and cooling using the EnergyPlus ZoneHVAC:IdealLoadsAirSystem data. In this case there are options to include the effects of heat recovery, economiser, humidification and dehumidification.
Note: With the Ideal loads option, fan energy and heat pickup are not included in the simulation. In this case you can approximate fan energy using auxiliary energy data but if you need more detailed fan modelling you should use either the Room ventilation option or Detailed HVAC model options.
Economisers are used to provide cooling when the outdoor temperature is lower than the indoor temperature. An economiser is a damper opening that draws up to 100% outside air when the outside air is cooler than the temperature inside the building, thereby providing free cooling. An outdoor air economy cycle can reduce cooling energy requirements by some 20% to 30%, or around 5% of the air conditioning energy use and are often required by energy codes for larger air conditioning units.
Choose from 3 options:
Note: The economiser works together with the cooling system and if cooling is not selected the economiser will not operate.
The upper limit of outside airflow when the economiser is working in ac/h. The default is 15 ac/h.
Note: This value is not used a) when the Cooling limit type is set to 2-Limit capacity and b) when the HVAC Autosize model option is 1-Adequate.
When heat recovery is active you can choose the type of heat recovery. Select from:
With the EnergyPlus Ideal loads system used in Simple HVAC heat recovery heating is only available when a zone is heated, i.e. when the Heated checkbox is checked on the HVAC tab. Likewise cooling heat recovery will only be available if the Cooled checkbox is checked. That is not to say that heat recovery isn't available for zones with heating at times when the heating system is not operating - heat recovery heating is available at any time in this case when the outside air is cooler than zone exhaust air, regardless of whether heating is operating or not. If you need to model heat recovery for systems without heating then you should use Detailed HVAC which is more flexible.
The sensible heat recovery effectiveness, where effectiveness is defined as the change in supply temperature divided by the difference in entering supply and relief air temperatures. The default is 0.70.
The latent heat recovery effectiveness, where effectiveness is defined as the change in supply humidity ratio divided by the difference in entering supply and relief air humidity ratios. The default is 0.65.