Unit ventilators provide a controlled means of introducing conditioned outdoor air during the heating season.
Required Objects
The unit ventilator must have the following property.
- It must be attached to a conditioned zone.
Design Assumptions
If the Draw Ventilation property is selected, the following will occur.
- The unit will provide the design outdoor air flow.
- The fan will run constantly during occupied hours.
If the Draw Ventilation property is not selected, the following will occur.
- The unit will not provide any ventilation.
- The fan will cycle on and off to meet conditioning needs.
| Property | Value | Notes |
|---|---|---|
| System air flow | Constant | |
| Cooling supply air temperature | 12.78°C | |
| Heating supply air temperature | 40°C |
Cooling Coil
The cooling coil has the following assumptions.
- The DX coil is single-speed with aa rated COP of 3.0.
- The sensible-to-latent heat ratio is auto-sized to meet the system needs during sizing.
- The chilled water coil has the following assumptions.
| Property | Value | Notes |
|---|---|---|
| Coil entering air temperature | N/A | Determined by the design day. |
| Coil leaving air temperature | ~11.11°C | Calculated from the air system supply air temperature minus fan heat generated (typically about 1.5°C - 2°C). |
| Chilled water design inlet temperature | N/A | Set by the chilled water loop if chilled water coil is used in the system. |
| Chilled water design outlet temperature | N/A | Set by the chilled water loop if chilled water coil is used in the system. |
Heating Coil
The heating coil has the following assumptions.
- The electric resistence heating coil is 100% efficient.
- The furnace heating coil is 80% efficient.
- The hot water coil has the following properties.
| Property | Value | Notes |
|---|---|---|
| Coil leaving air temperature | 40°C | |
| Hot water design inlet temperature | N/A | Set by the hot water loop. |
| Hot water design outlet temperature | N/A | Set by the hot water loop. |
Supply Fan
The supply fan has the following properties:
| Property | Value | Notes |
|---|---|---|
| Pressure rise | 250 Pa | |
| Total efficiency | 70% | |
| Motor efficiency | 94% |