The bypass factor determines the proportion of air that will pass through the cooling coil and therefore how much air will bypass it altogether. It is commonly used to express the efficiency of a cooling coil. If the contact factor is known then the bypass factor can be calculated using the following relationship: Bypass Factor = 1 - Contact Factor.
If a zone in the actual building is specified as fancoil heating only, mechanical ventilation with or without recirculated air, mixed mode, natural ventilation, or occupied and unheated, then this zone in the notional building will be modelled the same way. Otherwise it will be modelled as fancoil or CAV, depending on which system would use the least fan energy.
For zones where the ventilation system provides heating, cooling, or heating and cooling the notional building's terminal fan SFP will be 0.3 W per l/s and the SFP in the central AHU will be 1.8 W per l/s.
The notional building will have heat recovery with sensible efficiency of 70% for zones with mechanical ventilation providing supply and extract. The heat recovery will be switched off when the air-side system is in cooling mode.
Monitoring for out-of-range values set to True will reduce the heating, cooling, auxiliary, and HWS consumption by 5%.
Exercise and Notes
In this example 90% of the air will come into contact with the cooling coil. You should set the bypass factor to 0.1.
The terminal fan SFP has been specified as 0.3 W per l/s. The notional building will also use a fan SFP of 0.3 W per l/s.
The extract fan has been modelled with an SFP of 0.6 W per l/s and the fresh air fan will produce 1.2 W per l/s. This is equivalent to the notional building which will have an SFP in the central AHU of 1.8 W per l/s.
The associated zones will benefit from demand control ventilation as a function of occupancy density where air flow will be regulated by fan speed as opposed to dampers.
The auxiliary energy will be adjusted accordingly because flow will be regulated by fan speed. If we had selected dampers instead of fan speed then the auxiliary energy would not be affected by the demand control ventilation option.
The fresh air rate will be calculated using Equation 13 of the NCM where the demand control coefficient will be 0.85 per Table 14. In comparison the notional building will use a coefficient of 0.95.
Monitoring for out-of-range values = True.