Residential cooling and heating load calculations

06 May 2017   #ASHRAE

Residential features

The following unique features distinguish residences from other types of buildings:

• Smaller internal heat gains
• Varied use of spaces
• Fewer zones
• Greater distribution losses
• Partial loads
• Dehumidification issues
• Single-family detached vs. Multifamily

Design conditions

The initial step in the load calculation is selecting indoor and outdoor design conditions.

Indoor Conditions

• Cooling: 24°C db and a maximum of 50 to 65% rh.
• Heating: 20°C db and 30% rh.

Outdoor Conditions

• Cooling: 1% design dry-bulb temperature and mean coincident wet bulb temperature; 3.4 m/s wind speed; hottest-month dry-bulb temperature daily range.
• Heating: 99% design dry-bulb temperature.

Cooling Load

Sensible cooling load:

1. Exterior opaque surfaces
2. Exterior transparent fenestration surfaces
3. Partitions to unconditioned buffer space
4. Ventilation/infiltration
5. Occupants and appliances
6. Distribution

Latent cooling load:

1. Ventilation/infiltration
2. Internal gain (occupants, cooking, laundry, and bathing)

Heating Load

Heating calculations use simple worst-case assumptions, ignoring solar and internal gains, and building heat storage. With these simplifications, the heating problem is reduced to a basic UAΔt calculation.

1. Exterior surfaces above grade
2. Partitions to unconditioned buffer space
3. Walls below grade
4. Floors on grade
5. Floors below grade
6. Ventilation/infiltration